Camera traps from inside the Chernobyl exclusion zone reveal how the occupation of Russian forces at the site in February and March 2022 altered the behavior of wildlife living in the area.

After the invasion, which involved significant armed conflict inside the exclusion zone, mammals like deer and horses became less active and spent less time moving around at night, a new study reports.

Researchers discovered the changes by comparing footage from camera traps collected during the early months of Russia's 2022 invasion with recordings from the same period a year earlier, before the conflict began. The findings, published Thursday (June 18) in the journal Science, offer a rare glimpse of how animals respond to the immediate disruption caused by warfare.

"I wish the opportunity to analyze how the unfolding invasion affected wildlife ha[d] never happened," Svitlana Kudrenko, who conducted the study as part of her PhD at the Albert Ludwig University of Freiburg in Germany, told Live Science in an email. "Unlike in preindustrial times, current interstate conflicts are highly detrimental for wildlife because of a long list of warfare, often operated remotely."

The study took place in the Chernobyl exclusion zone, a roughly 1,000-square-mile (2,600 square kilometers) area surrounding the site of the 1986 Chernobyl nuclear disaster. Following the reactor explosion, authorities evacuated the region and restricted most human activity. Over the decades, with little to no human activity, wildlife populations have flourished, turning the zone into a natural laboratory for scientists studying ecosystem recovery and animal behavior.

But in February 2022, Russian forces seized control of the region during the beginning stages of the invasion of Ukraine. Military vehicles, troop movements, weapons being fired and other wartime disturbances suddenly transformed one of Europe's most unusual wildlife refuges into an active war zone.

To investigate the impact, researchers analyzed data from camera traps already operating in the exclusion zone from 2020 to 2022. Studying the ecological effects of armed conflict is difficult because war zones are dangerous and often hard for researchers to access.

By using the existing network of automated cameras, the scientists captured wildlife responses that would have been impossible to record otherwise. In total, the team analyzed almost 2,000 photographs and videos from the exclusion zone to build a picture of behavioral changes in response to the conflict.

The images and footage revealed responses from 11 wild mammal species, ‪showing that some animals changed their behavior during periods of heavier fighting.

Several mammal species — including roe deer (Capreolus capreolus), red deer (Cervus elaphus), moose (Alces alces) and red foxes (Vulpes vulpes) — were less active during the occupation than before the conflict, especially at night, the team reported.

The findings suggest that the impact of conflict can ripple through entire ecosystems. While Russia no longer occupies the Chernobyl exclusion zone, the authors highlighted that this study still shows how animal behavior can adapt to warfare.

Camera traps could become a valuable tool for measuring the environmental costs of conflict and understanding how wildlife copes with sudden human disturbances across the globe, the researchers added.

"Our study highlights the need to develop and implement research and conservation strategies focusing on armed conflict impacts on wildlife and environment in general, especially in areas of conservation importance," Kudrenko said.

What do you know about the animal kingdom? Test your knowledge with our animal quiz!

On April 26, 1986, operators at the Chernobyl Nuclear Power Plant were running a test to see what would happen to its nuclear reactors in a power outage — and they triggered the worst nuclear accident in human history.

The plant generated fission power using several nuclear cores, where uranium atoms were split. The process generates successively more heat and free neutrons as atoms split into progressively lighter ones, eventually turning feedwater into steam that powers turbines. Separate cooling water that circulated around the plant's nuclear cores and a "moderator" material was meant to keep the reaction stable.

Reactor 4 was scheduled to be shut down for regular maintenance, so the operators decided to test whether, during a power outage, the turbines could keep the coolant water circulating long enough for the emergency diesel generators to kick in.

The operators started reducing power to the reactor around 1 a.m. on April 25. However, a Kyiv-based operator that controlled the electricity grid wouldn't allow for a complete shutdown, as the grid needed power. So contrary to the prescribed test protocol, the reactor was kept at half-power levels from 2 p.m. to around 11 p.m. local time. (This decision led to a buildup of xenon that made the reactor unstable.)

By the time the test resumed, a less-experienced night crew was on duty. Ideally, the team should have raised power to a higher level to stabilize the reactor before restarting the shutdown test. Instead of bringing the power back up, the operators accidentally lowered it further.

By about 12:30 a.m. on April 26, they realized the power had dropped too rapidly. They tried to raise it by removing almost all of the control rods, which are designed to slow the atom-splitting reaction by absorbing neutrons. The power levels then fluctuated rapidly, and the operators took multiple measures to control the reaction, including temporarily lowering feedwater levels.

A power surge 100 times larger than normal was detected. The operators then tried to get the reaction under control by lowering all 211 control rods into the core, but they jammed. At 1:23 a.m., two back-to-back steam explosions occurred, blew the roof off the building, and spewed radioactive material high into the atmosphere. The debris triggered a massive fire. The core had partially melted down.

Hundreds of thousands of people were forced to evacuate nearby towns. Two workers died immediately in the disaster, and some of the emergency firefighters and "liquidators" who raced to contain the fire and prevent further melt down ultimately died of radiation sickness or cancer down the line. The cancers were likely caused by the radioactive iodine, strontium and cesium that permeated the area after the explosions.

The former Soviet Union tried to keep the meltdown a secret, but elevated radiation levels were detected across Europe, particularly in Scandinavia, in the weeks following the disaster.

In the years after, children in nearby regions experienced higher levels of thyroid cancer than had been typical in the past. But a United Nations report from 2000 found "no increases in overall cancer incidence or mortality that could be associated with radiation exposure." That said, the report acknowledged that some upticks in cancer rates would be expected to take decades to show up in the data.

Today, the 1,000-square-mile (2,700 square kilometers) Chernobyl exclusion zone around the plant is one of the most radioactive places on the planet and a nature preserve. It is also a natural test bed to see what happens when animals and plants are exposed to high levels of radiation, as well as a direct example of "evolution in action."

Experts have spent decades dissecting the missteps that led to the catastrophe, including the poor training of the nuclear plant operators and their subsequent failure to follow safety protocols. Keeping the reactors at half power for hours didn't help, either.

But at heart of the meltdown was a critical design flaw in the Reaktor Bolshoy Moshchnosti Kanalnyy (RBMK) reactors used at Chernobyl and elsewhere in the Soviet Union. All reactors use a "moderator" material to slow fission-produced neutrons so they can stay in the core and fuel further reactions, while water is used as a coolant to keep the cores from overheating and triggering a runaway reaction.

In the "light water" nuclear reactors typically used in the U.S. and Europe, water is both a moderator and a coolant. This means that, as the reaction gets hotter, more and more water turns to steam, leaving less water to act as a moderator, Live Science previously reported. The reaction has a built-in negative feedback loop in which the more heat and steam is produced, the less efficiently fission occurs.

At Chernobyl, however, graphite served as the moderator. In such a system, as steam forms, the graphite heats up, and the fission reaction speeds up as well. This creates the potential for a runaway positive feedback loop, because steam creates voids where the reaction speeds up, which can quickly boil all the coolant water. This is called a "high positive void coefficient."

It didn't help that the control rods were tipped with graphite, which temporarily sped up the fission reaction just as the operators were trying to slow it down. British officials had warned the Soviets that RBMK reactors had serious defects at least nine years prior to the Chernobyl accident, but most of those issues were not corrected, The New York Times reported at the time.

There are several RBMK reactors still operating in Russia, but most of those have undergone extensive safety retrofitting so that such a runaway reaction is, in theory, much less likely.

Ingrida Domarkienė studies ancient DNA, weaving together fragments of genetic material from modern humans and our long-extinct human relatives to retell their stories.

From a background in molecular biology and medical genetics, Domarkienė now spearheads Lithuania's first ancient DNA lab, headquartered at the Medical Science Centre at Vilnius University. Along with international collaborators, the lab is studying the remains of people in medieval mass graves in Poland to learn about social practices that were prevalent in the region at the time, as well as the migrations of Iron Age individuals in Lithuania.

They're also revealing insights into the aftermath of the 1986 disaster at the Chernobyl nuclear power plant. Looking at the DNA of Lithuanian workers involved in the cleanup after the disaster, the researchers identified genes that help protect against the effects of radiation.

Live Science spoke with Domarkienė, who is also an associate professor at Vilnius, asking about her research, the unique challenges associated with studying ancient DNA, and how delving into our genetic history can lead to medical advances today.

Related: Modern Japanese people arose from 3 ancestral groups, 1 of them unknown, DNA study suggests

Emily Cooke: What is it about ancient DNA that you find interesting?

Ingrida Domarkienė: It's fascinating, how you can reassemble stories from DNA pieces, you know: You just sequence DNA; it's kind of the technological thing.

And for me, coming from molecular biology, it's so fascinating that you read the biochemical fragment, organic molecule, and then you compare it with other samples, and you get a picture of how people moved, where they came from, where they went, how they lived. You can get "admixture signals" — that means that people [from different populations] mixed, and you can get an idea of who met whom and how they went on and on, and you can retell [their] stories.

EC: What are the unique challenges associated with studying ancient DNA?

ID: The most critical challenge is that you have to embrace uncertainty and failure here. Why is that? Because you are never quite sure if you will get the quality and quantity of DNA to work on further.

That's because, when an organism dies, DNA starts to decay, and there's nothing there to repair the DNA as it is in living cells. So it starts to fragment, and changes in composition. What's more, it blends with all other environmental DNA, which, when extracted, appears as contamination. So, in this case, I like an analogy of a confetti — or what is left of it after a huge celebration.

EC: Can you talk a bit about your research on Chernobyl survivors?

ID: Chernobyl survivors — cleanup workers or liquidators, they're also called.

It was our project with colleagues at the Department of Human and Medical Genetics, and in the group, we had the idea to analyze the genomes of Chernobyl liquidators, and we invited them to participate in the study. And when they started coming, we heard their stories, and we understood that — you know, those people went through a lot, but still, there were so many of them who were aging quite healthy, without cancers. You could expect the worst outcomes after what they've been through, but they were quite OK.

And then we got this hypothesis: that maybe there is something in the genomes of those survivors that protects them from all that bad that happened, let's say — also, psychological stress, which was immense back then, when they were taken from where they were at the moment and brought to Chernobyl without saying a word. They were telling stories of how they were woken up, and they were just there on a train going to God knows where.

And then that was a hard time, of course, there, and they had not only to work hard through liquidation work, but also trying to keep sane in that kind of place.

So, we started analyzing their genomes, and we found some potential signals of protective variation. And then we also have this new [as of yet unpublished] paper written by our student, which is on mitochondrial DNA. So, those Chernobyl liquidators might have protective variants also in the mitochondrial genome and nuclear genome [DNA in the nucleus] that supports mitochondrial function. So perhaps that's the idea.

Related: Chernobyl's liquidators didn't pass on radiation damage to their children

EC: How can studying our genetic history help us address medical challenges today?

ID: Studying the past through ancient DNA is fundamental research and takes time to realize what the findings are and how they can be implemented in practice. Perhaps the most important ingredient would be a strong interdisciplinary team that you can trust, and you can't do anything alone, really.

I find Svante Pääbo's work as a benchmarking example: How can you talk about ancient DNA without mentioning Svante's name?

He and his team developed the whole field of paleogenomics and generated the reference genome of Neanderthals. They started to give us explanations of what the differences between human and Neanderthal sequences are and what they mean in a functional way. For example, one of Svante Pääbo's group scientists, Dr. Hugo Zeberg, with colleagues, found that the Neanderthal variant in the progesterone receptor is associated with preterm birth, but also protective against miscarriage, and results in more live births. That knowledge can be translated into real help for women to save their pregnancies.

Or, another love story: metagenomics [the study of genetic material from all organisms in an environment], which is [an] even more challenging field. But it can help with infectious diseases, as we just witnessed one of the pandemics — and with the changing climate, there might be even more. So while reconstructing genomes of pathogens and building phylogenetic trees [diagrams of evolutionary relationships between species], we can understand the ways pathogens evolve and spread.

With those analyses, we can even start new narratives. For example, a long time ago, it was thought that the Spaniards introduced tuberculosis to the New World. But professor Johannes Krause's team [at the Max Planck Institute for Evolutionary Anthropology] showed that the bacteria was there before Columbus was, and apparently it was brought and transferred to humans by seals, which were a nutritious food for the people living there in Peru.

So you can see that, with this field, we can give science and medicine even more.

EC: What do you think the future of ancient DNA research will look like?

ID: From my point of view, I think that with the fast-evolving technologies, we will be able to go deeper in the sequences, wider in the datasets, and more divergent markers that we analyze.

Because now, we usually analyze single nucleotide polymorphisms, or SNPs [pronounced "snips," which are variations in single building blocks of DNA], as we call them. But my dream would be to reconstruct copy number variation, which are the huge chunks of [repeated] DNA, and it's not possible to do that now, but there are initiatives to do that.

We can also go for analysis of epigenomic markers [changes to DNA across the genome that alter the activity of genes without affecting the underlying sequence], which are very good markers for analysis of how the genome is regulated — to understand how it was back then. Those epigenomic markers also would be of great value.

And besides analysis of sociocultural structures of ancient sites, I would say research will definitely be directed towards understanding the functional meaning of the DNA variation that we analyze.

And in the grand finale, we would be integrating the whole data of the holobiome. That means all genomic information from the environment — not only humans, but also bacteria, viruses, plants, animals, everything who lives there. And integrating this data not only from the different disciplines, but also with different methods we have. Because the data comes using different methods, and that would be nice to integrate everything. And maybe then we will have the complete picture.

Editor's note: This interview has been condensed and edited for clarity.

Tiny worms in the Chernobyl Exclusion Zone (CEZ) in Ukraine are thriving despite being in an area marked by high levels of radiation, and scientists think their resilience could provide insights for cancer research in humans.

Researchers traveled to the CEZ and collected microscopic worms of the species Oscheius tipulae. Upon analyzing these worms, which live in the fallout of the Chernobyl (or Chornobyl) nuclear disaster, scientists discovered that their genomes — the complete set of genes that make up an organism — have not been damaged. This is despite generations of the animals being exposed to radiation, according to a study published March 5 in the journal PNAS. 

"Chornobyl was a tragedy of incomprehensible scale, but we still don't have a great grasp on the effects of the disaster on local populations," study lead author Sophia Tintori, a postdoctoral associate in the Department of Biology at New York University, said in a statement. "Did the sudden environmental shift select for species, or even individuals within a species, that are naturally more resistant to ionizing radiation?"

Scientists sequenced the genomes of 15 of the CEZ worms exposed to different levels of radiation, along with five from other parts of the world, and were unable to detect any clear signs of radiation damage in the worms from the CEZ. These results are in stark contrast to other animals, including frogs, which have changed physically after radiation exposure at the site. 

"This doesn't mean that Chornobyl is safe — it more likely means that nematodes are really resilient animals and can withstand extreme conditions," Tintori said. "We also don't know how long each of the worms we collected was in the Zone, so we can't be sure exactly what level of exposure each worm and its ancestors received over the past four decades."

Related: Scientists finally figured out what's making German wild boars radioactive, and it's not just Chernobyl

Researchers wondered if this was simply a case of the worms being particularly adept at repairing their DNA.

To find out, they let the 20 worms breed in the lab, then tested their descendants to see how they responded to exposure to various chemicals that damage DNA. 

The lineages, or strains, differed in how well they could resist DNA mutation in response to the chemicals — but there was no correlation in how well the worms resisted DNA damage and the levels of radiation their ancestors were exposed to.  

This suggested that the Chernobyl worms were not "necessarily more tolerant of radiation and the radioactive landscape has not forced them to evolve," according to the statement.

Instead, some other factors, not yet identified, may explain why some worms are better at resisting DNA damage than others. The study authors now want to investigate what those factors are and whether they could shed light on why some people are more susceptible to cancer than others.

"Now that we know which strains of O. tipulae are more sensitive or more tolerant to DNA damage," Tintori said, "we can use these strains to study why different individuals are more likely than others to suffer the effects of carcinogens."

After puzzling scientists for decades, researchers have finally figured out what's making Bavaria's wild boars radioactive, even as other animals show few signs of contamination. 

Turns out, the animals are still significantly contaminated with radioactive fallout from nuclear weapons detonated over 60 years ago — not just from the Chernobyl disaster, as was previously thought. 

And the boars (Sus scrofa) are likely being contaminated by some of their favorite food — truffles. 

Bavaria, in southeastern Germany, was hit with radioactive contamination following the Chernobyl nuclear accident in April 1986, when a reactor exploded in Ukraine and deposited contaminants across the Soviet Union and Europe.

Some radioactive material can persist in the environment for a very long time. Cesium-137 — which is associated with nuclear reactors like at Chernobyl — takes around 30 years for its levels to be halved (known as its half-life). In comparison, cesium-135, which is associated with nuclear weapon explosions, has a half life of 2.3 million years.

Related: What is the Chernobyl Exclusion Zone?

Boars in Bavaria have continued to have high radioactivity levels since the Chernobyl disaster, even as contaminants in other forest species declined. It was long theorized that Chernobyl was the source of the radioactivity in boars — but something didn't add up. With cesium-137 having a half-life of 30 years, the boars' radioactivity should be declining, yet it is not. 

This is known as the "wild boar paradox."

But now, in a new study published in the journal Environmental Science and Technology on Aug. 30, scientists found that fallout from nuclear weapons testing during the Cold War is behind the wild boar paradox, with radioactive material from both Chernobyl and nuclear weapons tests accumulating in fungi, such as deer truffles, that the boars consume. 

The researchers analyzed the meat of 48 boars in 11 Bavarian districts between 2019 and 2021. They used the ratio of cesium-135 to cesium-137 in the samples to determine the source.

The specific ratios between these two isotopes are specific to each source of radiation, forming a unique fingerprint that researchers can use in analysis — a high ratio of cesium-135 to cesium-137 indicates nuclear weapon explosions, while a low ratio suggests nuclear reactors. 

They compared the isotopic fingerprint of the boar meat samples with soil samples from Fukushima and Chernobyl, as well as from historical human lung tissue collected in Austria. The lung tissue was processed in the 1960s and revealed signs of the isotopic fingerprint left by nuclear weapons testing during the Cold War. While no nuclear weapons were detonated near the study site, fallout from the tests spread in the atmosphere globally.

Findings showed that 88% of samples taken exceeded the German limit for radioactive cesium. Between 10% and 68% of contamination came from nuclear weapons testing. The contaminants from both the weapons test and Chernobyl disaster seeped deep into the earth and were absorbed by underground truffles, explaining the wild boar paradox.

Understanding the ecological persistence of radioactive contamination has been a pressing scientific problem since the first atomic bombs were dropped in 1945 over Japan. Fears over food safety following nuclear strikes or disasters at nuclear power plants are still not well understood in specific regional contexts.

"This study illustrates that strategic decisions to conduct atmospheric nuclear tests 60-80 years ago still impact remote natural environments, wildlife, and a human food source today," the authors wrote.

In the early morning hours of April 26, 1986, the Chernobyl Nuclear Power Plant in Ukraine (formerly part of the Soviet Union) exploded, creating what many consider the worst nuclear disaster the world has ever seen.

Even after many years of scientific research and government investigation, there are still many unanswered questions about the Chernobyl accident — especially regarding the long-term health impacts that the massive radiation leak will have on those who were exposed. 

Related: 5 weird things you didn't know about Chernobyl

Where is Chernobyl?

The Chernobyl Nuclear Power Plant is located about 81 miles (130 kilometers) north of the Ukrainian capital, Kyiv, and about 12 miles (20 km) south of the border with Belarus, according to the World Nuclear Association. It is made up of four reactors that were designed and built during the 1970s and 1980s. A human-made reservoir, roughly 8.5 square miles (22 sq. km) in size and fed by the Pripyat river, was created to provide cooling water for the reactor.

The city of Pripyat, founded in 1970, was the nearest town to the power plant at just under 2 miles (3 km) away and housed almost 50,000 people in 1986. A smaller and older town, Chernobyl, was about 9 miles (15 km) away and home to about 12,000 residents. The remainder of the region was primarily farms and woodland.

Chernobyl nuclear power plant

The Chernobyl plant used four Soviet-designed RBMK-1000 nuclear reactors — a design that's now universally recognized as inherently flawed. RBMK reactors were of a pressure tube design that used an enriched U-235 uranium dioxide fuel to heat water, creating steam that drives the reactors' turbines and generates electricity, according to the World Nuclear Association.

In most nuclear reactors, water is also used as a coolant and to moderate the reactivity of the nuclear core by removing the excess heat and steam, according to the World Nuclear Association. But the RBMK-1000 used graphite to moderate the core's reactivity and to keep a continuous nuclear reaction occurring in the core. As the nuclear core heated and produced more steam bubbles, the core became more reactive, not less, creating a positive-feedback loop that engineers refer to as a "positive-void coefficient."

What happened at Chernobyl?

The explosion occurred on April 26, 1986, during a routine maintenance check, according to the U.N. Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). Operators were planning to test the electrical systems when they turned off vital control systems, going against the safety regulations. This caused the reactor to reach dangerously unstable and low-power levels.

Reactor 4 had been shut down the day before in order to perform the maintenance checks to safety systems during potential power outages, according to the Nuclear Energy Agency (NEA). While there is still some disagreement over the actual cause of the explosion, it is generally believed that the first was caused by an excess of steam and the second was influenced by hydrogen. The excess steam was created by the reduction of the cooling water, which caused steam to build up in the cooling pipes — the positive-void coefficient — which caused an enormous power surge that the operators could not shut down.

The explosions occurred at 1:23 a.m. on April 26, destroying reactor 4 and initiating a booming fire, according to the NEA. Radioactive debris of fuel and reactor components rained over the area while fire spread from the building housing reactor 4 to adjacent buildings. Toxic fumes and dust were carried by the blowing wind, bringing fission products and the noble gas inventory of naturally-occurring odorless and colorless gases with it.

Radioactive fallout

The explosions killed two plant workers — the first of several workers to die within hours of the accident. For the next several days, as emergency crews tried desperately to contain the fires and radiation leaks, the death toll climbed as plant workers succumbed to acute radiation sickness.

The initial fire was stifled by about 5 a.m., but the resulting graphite-fueled fire took 10 days and 250 firefighters to extinguish, according to the NEA. However, toxic emissions continued to be pumped into the atmosphere for an additional 10 days.

Most of the radiation released from the failed nuclear reactor was from fission products iodine-131, cesium-134 and cesium-137. Iodine-131 has a relatively short half-life of eight days, according to UNSCEAR, but it is rapidly ingested through the air and tends to localize in the thyroid gland. Cesium isotopes have longer half-lives (cesium-137 has a half-life of 30 years) and are a concern for years after their release into the environment.

Evacuations of Pripyat commenced on April 27 — about 36 hours after the accident had occurred. By that time, many residents were already complaining about vomiting, headaches and other signs of radiation sickness. Officials closed off an 18-mile (30 km) area around the plant by May 14, evacuating another 116,000 residents. Within the next few years, 220,000 more residents were advised to move to less contaminated areas, according to the World Nuclear Association. 

Related: Images: Chernobyl, frozen in time

Effects of Chernobyl on humans

Twenty-eight of the workers at Chernobyl died in the first four months following the accident, according to the U.S. Nuclear Regulatory Commission (NRC), including some heroic workers who knew they were exposing themselves to deadly levels of radiation in order to secure the facility from further radiation leaks.

The prevailing winds at the time of the accident were from the south and east, so much of the radiation plume traveled northwest toward Belarus. Nonetheless, Soviet authorities were slow to release information about the severity of the disaster to the outside world. But when radiation levels raised concern in Sweden about three days later, scientists there were able to conclude the approximate location of the nuclear disaster based on radiation levels and wind directions, forcing Soviet authorities to reveal the full extent of the crisis, according to the United Nations.

Within three months of the Chernobyl accident, a total of 31 people died from radiation exposure or other direct effects of the disaster, according to the NRC. Between 1991 and 2015, as many as 20,000 cases of thyroid cancer cases were diagnosed in patients who were under the age of 18 in 1986, according to a 2018 UNSCEAR report. While there may still be additional cases of cancer that emergency workers, evacuees and residents may experience throughout their lifetimes, the known overall rate of cancer deaths and other health effects directly related to Chernobyl's radiation leak is lower than was initially feared. "The majority of the five million residents living in contaminated areas … received very small radiation doses comparable to natural background levels (0.1 rem per year)," according to an NRC report. "Today, the available evidence does not strongly connect the accident to radiation-induced increases of leukemia or solid cancer, other than thyroid cancer."

Some experts have claimed that unsubstantiated fear of radiation poisoning led to greater suffering than the actual disaster. For example, many doctors throughout Eastern Europe and the Soviet Union advised pregnant women to undergo abortions to avoid bearing children with birth defects or other disorders, though the actual level of radiation exposure these women experienced was likely too low to cause any problems, according to the World Nuclear Association. In 2000, the United Nations published a report on the effects of the Chernobyl accident that was so "full of unsubstantiated statements that have no support in scientific assessments," according to the chairman of UNSCEAR, that it was eventually dismissed by most authorities.

Chernobyl's effect on the environment

Shortly after the radiation leaks from Chernobyl occurred, the trees in the woodlands surrounding the plant were killed by high levels of radiation. This region came to be known as the "Red Forest" because the dead trees turned a bright ginger color. The trees were eventually bulldozed and buried in trenches, according to the National Science Research Laboratory at Texas Tech University.

The damaged reactor was hastily sealed in a concrete sarcophagus intended to contain the remaining radiation, according to the NRC. However, there is ongoing intense scientific debate over how effective this sarcophagus has been and will continue to be into the future. An enclosure called the New Safe Confinement structure began construction in late 2006 after stabilizing the existing sarcophagus. The new structure, completed in 2017, is 843 feet (257 meters) wide, 531 feet (162 m) long, and 356 feet (108 m) tall and designed to completely enclose reactor 4 and its surrounding sarcophagus for at least the next 100 years, according to World Nuclear News.

Despite the contamination of the site — and the inherent risks in operating a reactor with serious design flaws — the Chernobyl nuclear plant continued operation to meet the power needs of Ukraine until its last reactor, reactor 3, was shut down in December 2000, according to World Nuclear News. Reactors 2 and 1 were shut down in 1991 and 1996, respectively. Complete decommissioning of the site is expected to be completed by 2028.

The plant, the ghost towns of Pripyat and Chernobyl, and the surrounding land make up a 1,000-square-mile (2600 square kilometers) "exclusion zone," which is restricted to nearly everyone except for scientists and government officials.

Despite the dangers, several people returned to their homes shortly after the disaster, with some sharing their stories with news sources such as the BBC, CNN and The Guardian. And in 2011, Ukraine opened up the area to tourists wanting to see the after-effects of the disaster firsthand.

Chernobyl today

Today, the region, including within the Chernobyl exclusion zone, is filled with a variety of wildlife that have thrived without interference from humans, according to National Geographic. Thriving populations of wolves, deer, lynx, beaver, eagles, boar, elk, bears and other animals in Chernobyl have been documented in the dense woodlands that now surround the silent power plant. Nonetheless, a handful of radiation effects, such as stunted trees growing in the zone of highest radiation and animals with high levels of cesium-137 in their bodies, are known to occur. 

Related: Infographic: Chernobyl nuclear disaster 25 years later

The area has recovered to some extent, but is far from returning to normal. But in the areas just outside the exclusion zone, people are beginning to resettle. Tourists continue to visit the site, with visitation rates jumping 30% to 40% thanks to a 2019 HBO series based on the disaster. And the catastrophe that occurred at Chernobyl resulted in a few significant changes for the nuclear industry: concern about reactor safety increased in eastern Europe as well as around the world; the remaining RBMK reactors were modified to reduce the risk in another disaster; and many international programs including the International Atomic Energy Agency (IAEA) and the World Association of Nuclear Operators (WANO) were founded as a direct result of Chernobyl, according to the World Nuclear Association. And around the globe, experts have continued researching ways to prevent future nuclear disasters.

Russian invasion

On Feb. 24, 2022, during a full invasion of Ukraine ordered by Russian president Vladimir Putin, Russian troops captured the Chernobyl Nuclear Power Plant, taking its staff hostage. 

Just a day later (Feb. 25), after heavy fighting between Ukrainian and Russian forces, increased radiation levels were detected at the power plant, according to Ukrainian officials and online data from Chernobyl exclusion zone's automated radiation-monitoring system. Gamma radiation, a high-energy type of electromagnetic radiation, increased 20 times above typical levels at multiple inspection points. This radiation spike was likely due to radioactive dust that was thrown into the air due to nearby disturbances from war equipment and fighting. 

"If it's a resuspension of dust, this is generally stuff that was not that mobile, or it would have blown away," Edwin Lyman, director of nuclear power safety at the Union of Concerned Scientists, previously told Live Science. "So it's probably heavier particles of soil that don't disperse very far."

Even with this radiation spike however, "the dose rates they're finding are not that much greater than the usual dose rates in that area, which, admittedly, are probably about a hundred times the background dose of anywhere else in the world," Lyman said. "But even so, if [the troops] don't spend that much time in the area, it's not going to have a significant impact on their health compared to the threat of dying in war."

The IAEA released a statement on Feb. 24 saying that it was following the situation at the power plant with "grave concern." Rafael Mariano Grossi, IAEA director general, appealed for "maximum restraint to avoid any action that may put the country's nuclear facilities at risk," according to the statement.

At the IAEA General Conference in 2009, the organization's member states (which includes Russia) adopted a decision stating "any armed attack on and threat against nuclear facilities devoted to peaceful purposes constitutes a violation of the principles of the United Nations Charter, international law and the Statute of the Agency," Grossi noted.

On March 9, Ukraine's state energy company announced that Chernobyl's nuclear power plant and all the facilities in the exclusion zone had been completely disconnected and were without electricity. This led Ukrainian officials to express their concern that the spent nuclear material kept in the plant's cooling pools could heat up and evaporate into its immediate surroundings. But nuclear energy experts cautioned that the plant's roughly 20,000 spent nuclear fuel units, which are 22 years old, were fairly cold and that an event of this kind would be highly unlikely.

"The spent fuel rods are at minimum 22 years old. They have very little heat to dissipate," Mark Nelson, the managing director of the Radiant Energy Fund, which advises companies and nonprofits about nuclear energy, wrote on Twitter. "Their heat is low enough that experts I've talked to expect weeks or even months to heat the water enough to dry out the pool. Even then, natural air circulation should be sufficient."

Sometime during the Russian occupation, looters stole radioactive material and isotopes from a radiation monitoring laboratory near the defunct nuclear power plant, according to the Institute for Safety Problems of Nuclear Power Plants (ISPNPP). As it contains no plutonium or uranium, the stolen material cannot be used to make nuclear weapons, but it could possibly make a dirty bomb, although this risk is also low, Live Science previously reported. 

On March 31, Ukraine's state nuclear company Energoatom announced that Russian troops had left the plant, taking a small number of the plant's Ukrainian security officers with them. Russian troops evacuated the area after a failed attempt to capture the nearby Ukrainian capital of Kyiv. The rest of the plant's hostaged workers, who had been forced to maintain the plant under gunpoint, were freed. Energoatom also said that Russian soldiers had dug a number of trenches in the radioactively contaminated soil in the Red Forest, leading to unconfirmed speculation that some of the invaders had contracted radiation sickness. 

Additional resources

Read more about how water cools and moderates nuclear reactors from the International Atomic Energy Agency. Or find the latest news about the Chernobyl Nuclear Power Plant on the power plant's website. To learn about longstanding health effects from the Chernobyl disaster, go to the Canadian Safety Nuclear Commission.

Bibliography

World Nuclear Association. "Chernobyl Accident 1986" Updated May 2021.

World Nuclear Association. "Cooling Power Plants." Updated September 2020.

United Nations Scientific Committee on the Effects of Atomic Radiation. "The Chernobyl accident." Updated April 2021.

Nuclear Energy Agency. "Chapter I The site and accident sequence." Updated 2002.

U.S. Nuclear Regulatory Commission. "Backgrounder on Chernobyl Nuclear Power Plant Accident." Updated/reviewed August 2018.

United Nations. "International Chernobyl Disaster Remembrance Day 26 April." 

United Nations Scientific Committee on the Effects of Atomic Radiation. "Evaluation of Data on Thyroid Cancer in Regions Affected by the Chernobyl Accident." 2018.

Lars-Erik Holm. The Lancet. July 22, 2000.

National Science Research Laboratory. "Chernobyl Research." Copyright January 2020. 

World Nuclear News. "Chernobyl confinement structure systems begin operation." Feb. 8, 2019.

World Nuclear News. "Decommissioning of Chernobyl units approaches." Feb. 19. 2014.

BBC. "The people who refused to leave Chernobyl." April 26, 2016.

CNN. "After Chernobyl, they refused to leave." Nov. 7, 2013.

The Guardian. "Chernobyl now: 'I was not afraid of radiation' – a photo essay." June 7, 2019.

Live Science. "Chernobyl Woos Tourists with Promise of 'Negligible' Risk." Dec. 15, 2010.

Live Science. "Nearly 30 Years After Chernobyl Disaster, Wildlife Returns to the Area." Oct. 13, 2015.

National Geographic. "Animals Rule Chernobyl Three Decades After Nuclear Disaster." April 18, 2016.

Live Science. "Is It Safe to Visit Chernobyl?" June 7, 2019.

BBC. "The people who moved to Chernobyl." Oct. 12, 2018.

Live Science. "Disaster Tourists Are Flocking to Chernobyl, Thanks to HBO Series." June 5, 2019.

Live Science. "Who Will Prevent the Next Chernobyl? (Op-Ed)" April 25, 2016.

Live Science. "Russian troops have taken over Chernobyl power plant, Ukrainian official says." Feb. 24, 2022. 

International Atomic Energy Agency. "IAEA Director General Statement on the Situation in Ukraine." Feb. 24. 2022.

This article was updated on June 20, 2019 by Live Science Contributor Rachel Ross.

Near-black frogs far outnumber their highlighter-yellow fellows in Chernobyl's radiation-blasted ecosystems, in a direct example of "evolution in action," a new study shows. The study, published Aug. 29 in the journal Evolutionary Applications, found that eastern tree frogs (Hyla orientalis) with more skin-darkening melanin pigment were more likely to survive the 1986 nuclear accident in Ukraine than frogs with lighter skin, leading to populations today that are dominated by darker frogs.

"Radiation can damage the genetic material of living organisms and generate undesirable mutations," researchers wrote in a post on The Conversation about their research. "However, one of the most interesting research topics in Chernobyl is trying to detect if some species are actually adapting to live with radiation. As with other pollutants, radiation could be a very strong selective factor, favoring organisms with mechanisms that increase their survival in areas contaminated with radioactive substances."

On April 26, 1986, a reactor at the Chernobyl nuclear power plant in Ukraine exploded, spewing radioactive materials across an 18-mile (30 kilometers) radius. 

"The Chernobyl accident released approximately 100 times the energy released by the nuclear bombs of Hiroshima and Nagasaki," Pablo Burraco, the study's lead author and a biologist with the Doñana Biological Station in Seville, Spain, told Live Science in an email.

Related: Frogs' skulls are more bizarre (and beautiful) than you ever imagined

Officials evacuated residents from the contaminated zone following the disaster and established a 1,040 square-mile (2,700 square kilometers) exclusion zone. In the decades since, the abandoned area has become a wildlife refuge. Burraco and his team wanted to understand how the nuclear meltdown drove evolution in the animals living there.

After studying more than 200 male frogs whose habitats were spread across 12 different breeding ponds throughout the radioactive contamination zone, researchers found that "on average, 44% were darker than those outside of Chernobyl," Burraco said. "We consider the most plausible explanation to [why] frogs within the Chernobyl Exclusion Zone [are changing color] is that the extremely high radiation levels at the moment of the accident selected for frogs with dark skin."

Why dark skin? It turns out that high melanin levels in frogs’ skin shielded them from radiation. 

"Melanin is known to protect against radiation because it can mechanically avoid the production of free radicals caused by the direct impact of the radioactive particles on cells," Burraco said. "Radiation can induce oxidative stress and damage essential structures for life such as the membrane of cells or even DNA."

Cells in the lighter frogs were bombarded with higher levels of damaging radiation, which killed them off at higher rates than their darker counterparts. After the blast, dark frogs had a higher likelihood of surviving, the study concluded. 

Researchers also looked for potential negative effects of excess melanin on the post-Chernobyl dark frogs. They found that like in other species, including certain types of fungi, having darker pigmented skin didn't harm the overall health of the amphibians and actually helped ionize radiation, which prevents ionized molecules from getting into cells and damaging them.

"The production of melanin can be metabolically costly, this has been described, for example, in several bird species," Burraco said. "However, in frogs, the main melanin pigment is called eumelanin and its production seems not to incur in physiological costs."

The United Nations' (UN) atomic watchdog has called for the creation of a demilitarized zone around Ukraine's Zaporizhzhia nuclear power plant, warning that shelling near the facility could cause the "unlimited release" of radioactive materials into the environment.

Russian forces took over the Zaporizhzhia plant, which is the largest nuclear power plant in Europe and produces nearly one-fifth of Ukraine's power, on March 4, the ninth day of their invasion of Ukraine, Live Science previously reported. Since then, Ukrainian nuclear plant workers have been operating the facility under Russian occupation. The site lies on the south bank of the Dnieper River, across from Ukrainian occupied areas, and has been attacked numerous times with both sides accusing the other of shelling the plant. 

Those attacks have produced damage across the plant, according to an International Atomic Energy Agency (IAEA) report produced after a site visit. Observers also experienced active shelling during the team's visit to the plant. Only one of the Zaporizhzhia plant's six reactors is operational, and with all four power lines from Ukraine's electrical grid to the plant disconnected, Zaporizhzhia has just one emergency backup line left: a nearby thermal plant that can pump vital cooling water around the reactor. If the active reactor does not constantly receive this coolant, a meltdown could occur. 

Related: 'Nuclear winter' from a US-Russia conflict would wipe out 63% of the world's population

"We are playing with fire, and something very, very catastrophic could take place," Rafael Mariano Grossi, the IAEA's director general, said Tuesday (Sept. 6) at an emergency session of the U.N. Security Council. "This is why in our report we are proposing the establishment of a nuclear safety and security protection zone limited to the perimeter and the plant itself."

The IAEA said it wants to consult with both Russia and Ukraine "immediately" about the steps needed to establish the security zone. During the Security Council briefing, U.N. Secretary General António Guterres said the first step would be for both sides to cease all military operations around the plant.

"As a second step, an agreement on a demilitarized perimeter should be secured," he said. "Specifically, that will include the commitment by Russian forces to withdraw military personnel and equipment from that perimeter and the commitment by Ukrainian forces not to move in."

The reaction at the heart of all operating nuclear power plants is nuclear fission, in which heavy isotopes of uranium and plutonium absorb incoming neutrons before splitting and releasing energy. This splitting also chucks out more neutrons, which other heavy isotopes absorb before splitting in turn, creating a chain reaction. The thermal energy produced by a chain reaction can be used to heat water, create steam and spin electricity-generating turbines. But if this process isn't carefully managed, a runaway reaction can occur, and a nuclear plant can go into meltdown. 

This is because nuclear reactors run extremely hot — with some parts reaching up to 3,272 degrees Fahrenheit (1,800 degrees Celsius) — and if coolant doesn't constantly circulate around them, the fuel inside can easily melt. This transforms nuclear fuel and its cladding into a radioactive magma-like lump, which sinks through the reactor and then the building, melting everything in its path. The melting of the cladding also generates hydrogen gas — meaning that when the molten goop finally breaks from the reactor and the hydrogen makes contact with the oxygen in the air, it explodes.

Of course, Ukraine has experienced a catastrophe of this kind before. On April 26, 1986, the disastrous meltdown at the Chernobyl nuclear power plant led to two enormous explosions that blew the 2,000-ton (1,800 metric tons) lid from one of the plant's reactors, blanketing the region with reactor debris and radioactive fuel. The explosion released 400 times more radiation into the atmosphere than was produced by the atomic bomb dropped on Hiroshima, and nuclear fallout rained down across Europe, according to a report by the European Parliament.

Despite the frightening surface similarities between the two events, Zaporizhzhia's reactors are safer than the ones at Chernobyl, nuclear scientists say. Unlike Chernobyl, which used RBMK-1000 reactors, Zaporizhzhia has more modern pressurized water reactors, which require significantly less uranium fuel in the reactor core, thus limiting the likelihood of a runaway chain reaction. Two layers of protection — a steel-reinforced concrete outer containment unit and an 8-inch-thick (20 centimeter) steel inner vessel — also surround the reactor. Both layers are designed to withstand earthquakes, explosions and collisions from incoming planes. Pressurized water reactors also shut down automatically in the event of an emergency. 

Nonetheless, a direct shell hit to the outside of a reactor could be dangerous, Robin Grimes, a professor of materials physics at Imperial College London, said in a statement. Be it from a shell outside or a meltdown inside, a puncture to the Zaporizhzhia reactors' twin shells wouldn't lead to an explosion like the one at Chernobyl, but it would still release a lot of dangerous material.

"It is not designed to withstand explosive ordinance, such as artillery shells," Grimes said. "While it seems to me unlikely that such an impact would result in a Chornobyl-like nuclear event, a breach of the pressure vessel would be followed by the release of coolant pressure, scattering nuclear fuel debris across the vicinity of the plant and a cloud of coolant with some entrained particles reaching further."

Zaporizhzhia's reactor cores still contain a decent amount of highly radioactive fuel for an explosion, however, and this is not the only source of concern. Environmentalists and nuclear experts have long warned that the plant's spent nuclear fuel rods, cooling in acres of open water pools and standing in open-air yards behind the site, could produce lethal airborne plumes of radiation if struck by a stray shell or missile.

Two weeks ago, after fire damage to one of the plant's transmission lines temporarily knocked the facility offline, Ukrainian officials began handing out iodine tablets to the residents of the nearby city of Zaporizhzhia. In response to the news, the European Union has donated 5.5 million of these tablets, which help to block the body's absorption of the deadly radioactive byproduct iodine, to Ukraine.

"While the ongoing shelling has not yet triggered a nuclear emergency, it continues to represent a constant threat to nuclear safety and security, with potential impact on critical safety functions that may lead to radiological consequences with great safety significance," the IAEA inspectors wrote in the report.

Originally published on Live Science.

Haunting scenes of the death, destruction and sickness that followed the Chernobyl meltdown 36 years ago — the deadliest nuclear accident of all time — were recorded on film and video but remained hidden for decades. Now, these previously unknown stories are finally coming to light, in a new HBO documentary, "Chernobyl: The Lost Tapes."

A trailer for the film, which HBO shared Friday (June 3) on YouTube, offers a glimpse of what unfolded in Ukraine (then a part of the Soviet Union, or USSR) after the horrific disaster, which took place on April 26, 1986 in the nuclear power plant at Chernobyl, about 81 miles (130 kilometers) north of Kyiv, the Ukrainian capital. 

In the long-lost tapes, testimony from witnesses offer a glimpse of life in Chernobyl before the disaster, and show how it was forever transformed in the accident's aftermath. "Everything was documented," one of the witnesses says in the trailer, but many of the explosion's details and potential dangers were obscured by Soviet officials, who sent in soldiers to "liquidate" the damage and to help cover up the incident, HBO representatives said in a statement. 

Related: 5 weird things you didn't know about Chernobyl

People who lived in Chernobyl and nearby, as well as the workers who were assigned to clean up the damage at the site, were subsequently kept in the dark about the risks posed to their health by exposure to deadly radiation. As more people who had been exposed to Chernobyl's radiation fell sick, their trust in Soviet leadership eroded, contributing to the widespread unrest that ultimately dissolved the Soviet Union, according to the statement.

Chernobyl's reactor explosion killed two plant workers, and 29 more people, many of them firefighters who rushed to battle the blaze, later died from radiation poisoning, according to the International Atomic Energy Agency. Over the years that followed, cancer rates skyrocketed among Ukrainian children, climbing by about 90%, Live Science previously reported. In 2006, a report commissioned by Greenpeace International estimated that over 93,000 people in Ukraine, Belarus and Russia died from illnesses linked to radiation exposure from Chernobyl. 

The report further stated that approximately 270,000 people in those countries who developed cancers, would not have done so had they not been exposed to the high levels of radiation produced by the accident.

"Chernobyl: The Lost Tapes" premieres June 22 on HBO at 9 p.m. ET/PT, and will be available to stream on HBO Max.

Originally published on Live Science.

A Geiger counter, also known as the Geiger-Muller tube, is an inexpensive and useful instrument used to quickly detect and measure radiation. 

There are two types of radiation, non-ionizing and ionizing. Non-ionizing radiation such as microwaves have enough energy to shake atoms around, but not enough to knock electrons off them and change their composition. Ionizing radiation on the other hand can strip atoms of their electrons, in a process called ionization. As a result, an ion pair is formed — a positively charged atom and a negatively charged electron. 

A Geiger counter exploits the natural process of ionization to detect and measure radiation. The device houses a stable gas within its chamber. When exposed to radioactive particles, this gas ionizes. This generates an electrical current that the counter records over a period of 60 seconds. 

When ionization occurs and the current is produced, a speaker clicks and a reading is given — often in millisieverts (mSv). There are several different types of radioactive particles that cause ionization, known as either alpha, beta or gamma radiation. However, Geiger counters cannot differentiate between the different types of radiation. 

Exposure to ionizing radiation can be damaging to human health. When this kind of radiation comes in contact with molecules of DNA in living cells, its energetic nature can disrupt, damage or alter the DNA. Short exposure to some forms of radiation, such as the X-rays for medical examinations, don’t cause immediate health risks. However, prolonged exposure can lead to mutations in DNA and produce cancers. So Geiger counters are an invaluable tool for evaluating a potential source of radioactivity

Types of ionizing radiation

Positively charged Alpha radiation particles contain two protons and two neutrons, such as the nucleus of a helium atom. They are heavy and slow moving, and can be blocked by a piece of paper or a thin layer of skin. This makes them significantly less hazardous than other types of radiation. 

Beta radiation particles are high energy electrons (or sometimes the counterparts of electrons, called positrons). They are relatively light particles, around one thousandth of the mass of a proton. Natural sources of beta radiation are radioactively decaying elements, such as uranium or actinium. 

Gamma radiation, also referred to as gamma rays, is a form of electromagnetic radiation similar to x-rays. It emits the highest energy photons (particles of electromagnetic radiation) in the electromagnetic spectrum. Gamma rays are highly penetrating and can easily pass through the body to cause damage. 

Creating the counter

The Geiger counter was conceptualized and designed by German physicists Hans Wilhelm Gieger and British physicist Ernest Rutherford, in 1908. Their initial creation could only detect alpha particles. 

The pair used their counter to study alpha particles and in 1911, published the findings of several groundbreaking experiments, such as the gold foil experiment, which ultimately revealed the nucleus of atoms to the world. 

Between 1925 and 1928, Geiger and his PhD student Walter Muller improved the sensitivity of the counter to detect all types of ionizing radiation. The design of the Gieger-Muller counter remains relatively unchanged in Gieger counters used today. 

Additional resources

Learn more about radiation on Centers for Disease Control and Prevention, discover how radiation therapy can be used to treat cancer, through Cancer.gov and learn what radiation you might encounter in everyday life.

Bibliography

• H. Friedman: Geiger Counter Tubes
• Richard Doll: Hazards of ionizing radiation: 100 years of observations on man
• Nikola Kržanović, Koviljka Stanković, Miloš Živanović, Miloš Đaletić, Olivera Ciraj-Bjelac: Development and testing of a low cost radiation protection instrument based on an energy compensated Geiger-Müller tube

Sometime during Russia's invasion of Chernobyl in Ukraine, looters stole radioactive material from a radiation monitoring laboratory near the defunct nuclear power plant. There seems to be a low risk that this material would be used in so-called dirty bombs, an expert told Live Science. 

The looters took pieces of radioactive waste, which could theoretically be used to create a dirty bomb, a device that combines radioactive material with a conventional explosive, Anatolii Nosovskyi, director of the Institute for Safety Problems of Nuclear Power Plants (ISPNPP) in Kyiv, told Science. They also swiped radioactive isotopes — radioactive chemical elements with different numbers of neutrons in their nuclei — that are usually used to calibrate instruments in the monitoring lab, Nosovskyi said.

On March 25, Science reported that the radioactive material had been stolen. New Scientist later confirmed these reports with an ISPNPP scientist, who spoke with reporters on the condition of anonymity. The source said that the earlier Science report was "accurate based on the information available." 

The stolen material can't be used to make nuclear weapons, as it doesn't contain any plutonium or uranium, Bruno Merk, a research chair in computational modeling for nuclear engineering at the University of Liverpool, told New Scientist.

Related: What would happen if Russia bombed Chernobyl? 

"There are so many radioactive sources around the world. If someone wants to get their hands on this there's an easier way," Merk said. "These radioactive sources you can steal in every hospital. It would always have been possible for someone to sneak in and steal something. I don't see that the risk is any higher than before the Russians invaded."

Although its not useful for making nuclear weaopns, some of the stolen material could be of very limited use in the construction of a dirty bombs, Merk told New Scientist.

"Calibration sources" — meaning the isotopes — "typically have very small quantities of radioactive materials," Edwin Lyman, a physicist and the Director of Nuclear Power Safety with the Union of Concerned Scientists, told Live Science in an email.

If the stolen waste materials were highly radioactive, they would need to be stored and transported in heavy shielding, to protect the handlers from radiation injury. Because of this, "I suspect the stolen samples are also small quantities," he said.

"I'm skeptical that there would be any strategic purpose for Russia to use these materials in a dirty bomb," Lyman told Live Science. Such a bomb could spew radioactive material over a localized area, but it would be unlikely to cause many immediate severe health effects. That said, the extent and severity of the potential damage would depend on the size and other characteristics of the materials in question, he noted. 

In general, dirty bombs, also known as "radiological dispersal devices" (RDDs), do not release enough radiation to kill people or cause severe illness, according to the U.S. Nuclear Regulatory Commission. Those closest to the bomb when its detonated would be the most likely to be injured by the explosion itself, while the resulting radiation could be dispersed within a few blocks or miles from explosion site. 

"As radioactive material spreads, it becomes less concentrated and less harmful," the Commission notes. "Immediate health effects from exposure to the low radiation levels expected from an RDD would likely be minimal."

"It's unlikely that such a bomb could cause death, destruction and terror anywhere near the scale of Russia's bombardment of civilian areas with conventional weapons," Lyman said. "Although the presence of radioactive contamination could add another element of fear to an already frightful situation."

Originally published on Live Science.

Russian troops have captured the Chernobyl nuclear power plant, which still contains nuclear waste that could pose a threat to the surrounding area. What would happen if the site were to be bombed?

"Our defenders are giving their lives so that the tragedy of 1986 will not be repeated," Ukrainian President Volodymyr Zelenskyy tweeted a few hours before the power plant was seized yesterday. "This is a declaration of war against the whole of Europe."

Chernobyl is the site of four nuclear reactors, three of which have been decommissioned. The fourth was the source of the historic explosion in 1986. That reactor is now protected by an inner concrete sarcophagus and a new, 32,000-ton outer shell. In addition, spent nuclear fuel from the other reactors is still stored at the site, along with radioactive waste from contaminated equipment. 

Even though the reactor is covered, radiation has contaminated the entire site. In fact, dozens of radioactive elements were launched into the air during the meltdown, with a few of them considered the most dangerous to life, including the isotopes iodine 131, strontium 90, cesium 134 and cesium 137; the strontium and cesium isotopes have long enough half-lives that they still linger at the site, according to the International Atomic Energy Agency. 

Now, some public figures have expressed fears that any future shelling of these sites could spread this radioactive material far beyond Chernobyl's exclusion zone — an off-limits area around the disaster — even as far as neighboring countries.

On Thursday morning (Feb. 24), Anton Gerashchenko, an adviser and former deputy minister at the Ukrainian Ministry of Internal Affairs, wrote on Facebook, "If as a result of the occupiers' artillery strikes the nuclear waste storage facility is destroyed, the radioactive dust may cover the territories of Ukraine, Belarus and the EU [European Union] countries!"

Related: 5 interesting facts about Chernobyl

But the reality may not be so dire, according to Edwin Lyman, director of nuclear power safety at the Union of Concerned Scientists. "Even if there were an inadvertent shelling of that confinement structure, I think it would take more than that to mobilize a significant amount of radioactive material," Lyman told Live Science.

"It would be hard for me to imagine that kind of consequence," Lyman added. 

Spent fuel, or the radioactive elements that were used to fuel the power plant, continue to decay into more stable elements and, in doing so, continue to release heat, he said. 

"The most serious concern is the wet storage of spent fuel, because that's probably the most concentrated quantity of radioactive material on-site," Lyman said. "Generally, spent nuclear fuel still has decay heat. And so if it's in wet storage, there has to be some way of removing that heat." 

That fuel has been cooling for at least a couple of decades. "And so that decay heat is not that significant," Lyman said. "But still, if there was disruption to cooling … or if there was a breach of the pool that led to draining water, then that fuel could conceivably heat up to the point where it might burn. That's probably the biggest threat." 

However, such burning could take days or weeks, he added.

A more recent concern involves rising radiation levels around the facility, most likely a result of radioactive dust kicked up by military vehicles. But the type of dust and the radiation doses being measured suggest that this may not be much of a threat, either, according to Lyman.

"If it's a resuspension of dust, this is generally stuff that was not that mobile, or it would have blown away," he said. "So it's probably heavier particles of soil that don't disperse very far." More likely, he added, it might cause a temporary increase in radiation levels, and the data will show whether that's true.

But even such a temporary increase may not be a danger to human health, Lyman said.

"The dose rates they're finding are not that much greater than the usual dose rates in that area, which, admittedly, are probably about a hundred times the background dose of anywhere else in the world," Lyman said. "But even so, if [the troops] don't spend that much time in the area, it's not going to have a significant impact on their health compared to the threat of dying in war."

Nonetheless, Lyman thinks this event shows that plans for nuclear power need to consider the possibility of war. 

"The potential for nuclear power plants to be targets at wartime is something that really needs consideration," Lyman said, "especially when they're talking about expanding nuclear power to parts of the world that currently have more unstable regions." 

Originally published on Live Science.

Editor's note: Originally posted at 12:17 p.m. EST and updated at 2:42 p.m. EST on Feb. 24 to include new key information about the invasion into Ukraine, including that Russian forces have seized the Chernobyl Nuclear Power Plant. 

Russian troops have captured Chernobyl's former nuclear power after heavy fighting near the Chernobyl exclusion zone, according to an advisor to the Ukrainian presidential office.

Ukrainian troops fought with Russian forces, which invaded the region from Belarus and have seized control of the now-defunct power plant, according to Mykhailo Podolyak, an aide to the Ukrainian president Volodymyr Zelensky. 

The attack came as part of a full Russian invasion of Ukraine, the biggest on a European nation since World War II, with Russian forces claiming to have destroyed more than "70 military targets" and 11 airfields as of Thursday (Feb. 24). Advancing Russian forces have reportedly captured Antonov International Airport on the outskirts of Ukraine's capital, Kyiv. 

Related: 5 weird things you didn't know about Chernobyl

"It is impossible to say the Chernobyl nuclear power plant is safe after a totally pointless attack by the Russians," Podolyak said, as reported by Reuters. "This is one of the most serious threats in Europe today."

As one of the most radioactive places in the world, large parts of the Chernobyl exclusion zone have been closed off since the disastrous meltdown of Ukraine’s Chernobyl nuclear power plant in 1986. In that year, two gigantic explosions at the plant blew off the reactor’s 2,000-ton (1,800 metric tons) lid, covering the surrounding 1,000-square-mile (2,600 square kilometers) area with nuclear fallout. The area was later deemed uninhabitable by humans for the next 24,000 years. 

"Russian occupation forces are trying to seize the Chernobyl nuclear power plant. Our defenders are giving their lives so that the tragedy of 1986 will not be repeated," Zelenskyy wrote earlier Thursday on Twitter. "This is a declaration of war against the whole of Europe."

An advisor to the Ukrainian interior ministry also warned that fighting around the power plant could lead to the potential disturbance of nuclear waste and the spreading of dangerous radioactive material across Europe.

"The National Guardsmen, who guard the collectors of unsafe nuclear radioactive waste, are fighting hard," Anton Gerashchenko, an advisor and former deputy minister at the Ukrainian Ministry of Internal Affairs, wrote on Facebook. "If as a result of the occupiers' artillery strikes the nuclear waste storage facility is destroyed, the radioactive dust may cover the territories of Ukraine, Belarus and the EU [European Union] countries!"

About 7,500 more Ukrainian soldiers were stationed in the exclusion zone between December 2021 and February 2022; the site lies close to Ukraine's northern border with Russia's ally Belarus and sits on the most direct route between it and Kyiv. A non-military satellite image posted on Twitter on Tuesday (Feb. 22) appeared to show that a pontoon bridge had been erected at the Pripyat river just 14 miles (22.5 km) north of the Chernobyl plant at the Ukranian-Belarusian border, possibly to facilitate the transport of Russian troops into the zone.

Originally published on Live Science.

Human history is riddled with man-made disasters, from nuclear meltdowns and underwater oil spills to chemical explosions and mine collapses. We find out exactly what happened in some infamous cases – and how humanity played a pivotal role in these events.

The Aberfan Colliery Slip

Big man-made disasters don’t often happen in Britain, which made the Aberfan colliery slip even more shocking. The Welsh Valleys village of Aberfan grew up around the nearby coal mine that was established back in 1869. By 1966, the settlement had grown, and the village was surrounded by seven huge spoil piles – waste material from mining.

That’s not necessarily a problem, but in October 1966 the village of Aberfan was hit by more than six inches of rainfall, and caused the seventh spoil pile to subside. At 09.15 GMT on Oct. 21,1966 a vast quantity of saturated debris broke free from the pile and travelled towards the village at speeds between 11 and 21 miles-per-hour (approximately 17 and 34 kilometers)and in waves up to 30 feet (9meters) high, according to the Smithsonian magazine.

The result was devastating. 144 people lost their lives in the ensuing avalanche – tragically, 116 children were among the dead, according to the Independent. The fast-moving material demolished a primary school (elementary school) and damaged a nearby secondary school (high school), and 18 nearby houses were destroyed.

Thousands of volunteers travelled to Aberfan to aid rescue efforts, and the Prime Minister and Queen Elizabeth both visited in the days following the incident, according to the BBC. The Aberfan disaster remains one of the UK’s worst mining incidents. 

The Seveso disaster

This industrial accident took place at a chemical plant north of Milan, Italy. On Saturday July 10 1976, the factory was producing a chemical called 2,4,5-Trichlorophenol, which has been used as a chemical weapon and in weedkillers, according to the journal Chemosphere.

On that daya chain reaction ruptured the reactor — and that, in turn, caused six tonnes of toxic chemicals to burst into the sky.

The cloud settled over 6 square miles (18 square kilometers) of the surrounding area, including the town of Seveso, according to the journal Environment international. Children were hospitalized with skin inflammations, hundreds of residents suffered from skin conditions, and huge areas of land were evacuated. Thousands of animals died or had to be slaughtered to prevent toxins entering the food chain.

The Seveso disaster has had a long-term impact, too. Since 1976, studies have found that more local residents died from cardiovascular and respiratory diseases, and certain types of cancer increased in frequency in the affected areas. 

Chernobyl meltdown

The explosion at Chernobyl is one of the world’s most infamous man-made disasters — and with good reason. It started innocently enough, with engineers performing a routine experiment that was supposed to find out if the plant’s emergency water cooling would work during a power outage.

The test had been carried out previously, but on this occasion, there was a power surge and engineers couldn’t shut down Chernobyl’s nuclear reactors. Steam built up in one reactor, the roof was blown off, the nuclear core was exposed, and radioactive material was released into the atmosphere.

Workers and firefighters were hospitalised and 28 people quickly passed away from acute radiation exposure. It took nearly two weeks, and military intervention, to extinguish the fires. 

Crucially, it took more than a day for the 50,000 residents of nearby Pripyat to be evacuated. Following this, the government established a 19-mile (30km) "exclusion zone" and built a containment dome over the top of the site.

In the years following the incident, studies estimate that thousands of people have succumbed to cancer because of the radiation. It’s one of the most expensive disasters in history, too, and it’s estimated that containment and clean-up efforts will continue until 2065. 

Montana asbestos clouds

The story of Libby, Montana, began when settlers arrived in the 1800s and the town expanded thanks to mine and railroad construction. In 1919the discovery of a mineral called Vermiculite changed Libby’s fate.

Vermiculite has loads of uses, from gardening to car parts, and the mine in Libby was producing 80% of the world’s supply by 1963. That’s great and lucrative, but some kinds of vermiculite contain asbestos, an exceptionally dangerous substance that can cause a huge range of lung issues.

The vermiculite in Libby, Montana, did contain asbestos, and the mining company knew about its dangerous side effects. But they didn’t tell anyone, and people in Libby used the mine’s waste products for building and landscaping, including in school projects and ice rinks.

As a result, nearly 10% of the town’s population died from asbestos-related illness, and the people who died weren’t always miners – the asbestos fibres that caused health problems are easy to pass to other people, according to the Mesothelioma Hope organization.

The town, effectively, had spent decades operating under a toxic cloud. The mine closed in 1990, but the town’s issues didn’t become well-known until 1999, and in 2009 the US government declared an emergency in Libby to clean up the town, according to the Guardian.

By then it was too late. Hundreds of people have passed away from asbestos-related health issues, thousands more have experienced illness, and new deaths and diseases were still being reported as late as 2018 due to the long-term effects of these poisonous substances.

The Risks of Asbestos

Deadly asbestos fibres can cause serious health problems for decades – including these five issues.

The US government’s Environmental Protection Agency investigated more than 8,000 properties in Libby and had to decontaminate more than 3,000 different sites where asbestos was used in construction. More than one million cubic yards of material was replaced over the course of the clean-up project, and more than half a billion dollars was spent to decontaminate the town. 

Contaminated material is now stored safely at the site of the former mine, and the project has only begun to slow down in the past couple of years – no wonder, as it’s been the biggest asbestos clean-up project in US history.

The Deepwater Horizon oil spill

Oil spills are among the most visible man-made disasters of our times, and 2010’s Deepwater Horizon incident is reputed to be the largest marine oil spill in history.

The name comes from the drilling apparatus at the centre of the incident. The Deepwater Horizon oil rig was a floating platform that was drilling an exploratory oil well around 18,300 feet (5,600 meters) below sea level in the Gulf of Mexico, as Live Science has previously reported. That, in itself, was not a problem, and the rig was operating well within its limits. But on April 20t 2010, methane gas from the underwater well expanded and rose into the drilling rig, where it ignited and exploded.

The explosion quickly engulfed the entire drilling platform, killing eleven workers, and ninety-four crew members were evacuated. Two days later, the rig had sunk.

By that point, though, a vast oil slick had emerged from the underwater well and had begun to spread at the site. BP, the company that had contracted the Deepwater Horizon ship for exploratory drilling, tried to halt the leak with remote-controlled underwater vehicles, a 137-ton (125 metric tonnes) containment dome and by drilling a secondary well, but the oil flowed for 87 days. 

It’s estimated that 210 million gallons (around 954 million liters) of oil were leaked from the underwater well and that the spill directly affected 70,000 square miles (around 181, 000 square kilometers)of ocean in the Gulf of Mexico.

Mopping Up the Spill

The Deepwater Horizon oil spill was an unprecedented disaster. How do you clean it up?

Eventually, the oil was contained and either dispersed or cleaned up using several different methods and thousands of volunteers. By then, though, the environmental impact was being felt on a global scale: the Deepwater Horizon spill killed millions of animals, and the incident affected wildlife and ecosystems across several US states and beyond.

The Bhopal disaster

On December 2, 1984, there was a gas leak at a pesticide plant in Bhopal, India, according to The Atlantic. It was caused by malfunctioning safety systems, and a runaway pressure increase saw 40 tonnes of a chemical called methyl isocyanate leak into the atmosphere. 

That’s a huge amount of toxic material, and the plant was surrounded by densely-packed housing – so more than 600,000 people were exposed to the deadly cloud.

The people living around the plant were not informed quickly, and hospital staff were given conflicting information about the situation. Innocent people suffered from coughing, eye irritation, burns, breathlessness and vomiting, and thousands of people died within hours, as Live Science has previously reported. Thousands of animals passed away, too. 

Longer-term studies since the accident have confirmed that many thousands of people are still affected by eye, lung, and psychological damage – and, even today, it’s hard to say exactly how many people have suffered.

The Sidoarjo mud volcano

Most people think of lava flowing from a volcano, but in Sidoarjo, Indonesia, you’ll find the world’s biggest mud volcano. It was created by an explosion at a gas well drilled by an energy company, although company officials claim that an earthquake around 155 miles (250km) away provoked the problem.

There are more than 1,000 mud volcanoes around the world, but this Indonesian example is probably the only one caused by human activity, according to the journal Mud Volcanoes, Geodynamics and Seismicity It all started on May 28 2006, when a borehole was drilled to nearly 10,000 feet (3,000 meters). This caused water, steam, and gas to erupt from the ground nearby, and by the next day water, steam and mud began to emerge again – and it’s been there ever since. It’s officially called Lumpur Lapindo, and is commonly called the Lusi volcano. 

Initially, the volcano erupted with more than 6.3 million cubic foot (180,000 cubic meters) of mud per day, according to the BBC.

Eleven people were killed during a pipeline explosion, and 30,000 people were evacuated from the area. A dozen villages and more than 10,000 homes were destroyed, and metal from the mud flow has contaminated nearby rivers, according to the news site Boston.com. 

Birth of a Volcano

How the outflow of mud was triggered.

The North Pacific Garbage Patch

There aren’t many man-made disasters that are as large or as visible as the Great Pacific Garbage Patch. There’s nothing particularly complicated about what’s gone on here: a huge amount of rubbish has made its way into the ocean over the past decades because of negligent humans.

The patch stretches from the Californian coast, all the way across the Pacific Ocean to Japan, and it’s actually compromised of two different tracts of trash – one on the western side of the ocean, and another on the east according to National Geographic. Currents combine to suck rubbish into a vortex, and these tiny objects can’t escape.

The Great Pacific Garbage Patch isn’t just made up of crisp packets and drinks bottles. Most of the plastic in the patch has broken down into tiny pieces that simply make the water look cloudy, and ecologists estimate that 70% of ocean debris sinks to the bottom of the sea — so there could be far more below the surface.

The patch’s size varies: estimates range that it sits between around 270,000 and 5.8 million square miles (700,000 and 15,000,000km2) depending on sea movement. Some of the items in the patch are over 50 years old, because plastics just aren’t biodegradable. Scientists reckon that it’s becoming ten times bigger with every passing decade, despite attempts to tackle the problem, according to CBS News.

Unsurprisingly, the patch has a terrible effect on wildlife. Marine animals can get caught in bits of plastic or in abandoned fishing nets, which can quickly lead to death. Animals can die when they mistake plastic items for food.

The patch also has a huge and harmful impact on the ocean’s ecosystems and food chains, because plastic on the surface of the water can block sunlight from algae and plankton and pollutants can leak from different types of plastics.

Californian wildfires

Climate change has seen wildfires become a far more common threat around the world, and 2018 saw huge areas of California affected by some of the worst fires in recent memory,. More than 100 people died in more than 8,500 fires across California, and the fires destroyed more than 24,000 buildings and burned two million acres of land.

Most of the fires in California took place in July and August, and the government declared a national disaster. 

There’s no doubt that the fires were a man-made disaster. The years that preceded the fires saw an increase in temperatures due to climate change, and that killed plenty of trees in California — and those dead, dry trees provide ample fuel for fires to spread. 

Scientists predict that this kind of disaster is only going to become more common because of climate change, so California’s extreme weather may soon feel normal. Sadly, it has significant health effects on people too. 

The Jilin chemical plant explosion

This incident took place in the Chinese city of Jilin in November 2005, and saw a series of explosions at a petrochemical plant. In the immediate aftermath of the blasts more than 10,000 people were evacuated from the local area, according to the New York Times.

That’s bad enough, but it’s not the full story. The explosions released around 110 tons (100 metric tonnes) of pollutants into the Songhua River, and that was a big deal – because several large cities depend on that river for their water supply, according to the Environmental Emergencies Centre. 

Supplies were cut off for several days while the water supplies were cleaned up, and water had to be transported from unaffected cities to help people cope. Some cities dug deep-water wells to ensure that they won’t be totally dependent on rivers for their water supplies.

Toxins from the original explosions didn’t just affect Chinese water supplies, either. Chemicals were detected in Russian cities and in the Sea of Japan.  

Additional resources

For more examples of man-made disasters check out "A Century of Man-Made Disasters" by Nigel Blundell, "World's Worst Historical Disasters: Natural and Man-Made Catastrophes from the Ancient World to the Present Day" by Chris McNab and "Introduction to Natural and Man-made Disasters and Their Effects on Buildings" by Roxanna McDonald. 

Nuclear reactions are smoldering again in an inaccessible basement of the wrecked Chernobyl nuclear power plant in Ukraine, according to news reports.

Researchers monitoring the plant — which infamously exploded in a deadly 1986 meltdown — have detected a steady spike in the number of neutrons in an underground room called 305/2. The room is full of heavy rubble, concealing a radioactive mush of uranium, zirconium, graphite and sand that oozed into the plant's basement like lava, before hardening into formations called fuel-containing materials (FCMs).

Rising neutron levels indicate that these FCMs are undergoing new fission reactions, as neutrons strike and split the nuclei of uranium atoms, creating energy.

Related: 5 Weird things you didn't know about Chernobyl

For now, this radioactive waste is smoldering "like the embers in a barbecue pit," Neil Hyatt, a nuclear materials chemist at the University of Sheffield in the U.K., told Science magazine. However, it's possible that those embers could fully ignite if left undisturbed for too long, resulting in another explosion.

This potential explosion wouldn't be anywhere near as devastating as the one that shattered the plant in 1986, which resulted in thousands of deaths and spewed a radioactive cloud over Europe, Maxim Saveliev, a senior researcher with the Institute for Safety Problems of Nuclear Power Plants (ISPNPP) in Kyiv, Ukraine, told Science. If the nuclear material ignites again, the blast will be largely contained within the steel and concrete cage known as the Shelter, which officials built around the plant's ruined Unit Four reactor one year after the accident.

Still, even a contained explosion would make the long-term mission of removing the plant's FCMs much harder, Saveliev said. The Shelter is old and could easily crumble from the force of an explosion, filling the area with heavy debris and radioactive dust. (The Shelter itself is contained in a larger steel structure called the New Safe Confinement, which was completed in 2018.)

Neutron levels have been steadily rising in room 305/2 for four years, Saveliev said, and could continue rising for several more years without incident. It's possible these nuclear nuggets will fizzle out on their own in that time. But if neutron levels keep rising, scientists will have to intervene.

That is more easily said than done, of course; plant managers have yet to figure out how to access the tons of radioactive material buried below the room's thick layers of concrete debris. Radiation levels are too high for humans to endure, but radiation-resistant robots might be able to drill through the rubble and install neutron-absorbing control rods into the room, according to the ISPNPP.

Ukraine hopes to present a detailed plan for the removal of Chernobyl's still-smoldering FCMs by September, Science reported.

Originally published on Live Science.

In 2019, a group of scientists and distillers decided to create a bold new type of booze: Atomik, an artisanal alcoholic spirit made from ingredients grown in the Chernobyl nuclear power plant's still-radioactive exclusion zone. (The booze itself was not radioactive after the distilling process, Live Science previously reported).

Now, the first batch of Atomik is finally complete — and all 1,500 bottles of it have been seized by Ukrainian Secret Services agents for unknown reasons, according to a statement from Atomik's manufacturer, The Chernobyl Spirit Company.

"It seems that they are accusing us of using forged Ukrainian excise stamps, but this doesn't make sense since the bottles are for the U.K. market and are clearly labelled with valid U.K. excise stamps," Jim Smith, founder of the company and a professor at the University of Portsmouth in the U.K., said in the statement.

Related: 5 weird things you didn't know about Chernobyl

Elina Smirnova, a lawyer representing the company, added that the seizure was a "clear violation" of Ukrainian law. If Atomik does make its way onto shelves, it will be the first consumer product from the Chernobyl region since the infamous 1986 meltdown, the company said.

Soon after the nuclear disaster, officials deemed the Chernobyl exclusion zone — the 1,000-square-mile (2,600 square kilometers) area surrounding the damaged power plant — uninhabitable by humans for 24,000 years. However, plants and animals are now thriving in the region — and so is tourism. According to local tourism officials, Chernobyl sees upwards of 60,000 visitors a year, with visits spiking after the May 2019 debut of HBO's "Chernobyl" miniseries.

Atomik is made from apples grown in Ukraine's Narodychi District, which sits on the edge of the exclusion zone and was heavily polluted by fallout from the meltdown. This region still has a population of nearly 10,000 people, according to Ukraine's State Statistics Service, and must abide by stringent agricultural restrictions.

With Atomik, Smith and his colleagues hope to prove that some products made near  the exclusion zone can be safe for consumption, according to the company's website. Several years ago, the Atomik team tested rye crops from the exclusion zone for radiation, and found that the grains were indeed contaminated. However, Smith said, all traces of radiation were removed during the distillation process, making Atomik no more dangerous than other commercially available spirits.

Since then, the founders have changed their recipe from a rye-based booze to an apple-based one — but, according to Smith, the distillation process still renders the final product completely radiation-free. If Atomik makes it to liquor shops, 75% of the company's profits will be used "to help bring jobs and investment to the Chernobyl affected areas of Ukraine and to further support the community," according to the company's statement.

In the meantime, would you care to try a bottle of wine exposed to cosmic radiation aboard a space station for 14 months? It'll only cost you $1 million.

Originally published on Live Science.

Chernobyl, the site of the deadliest nuclear accident of all time, should become a World Heritage site, Ukranian officials say. If their efforts succeed, the site of one of humanity's darkest chapters could join the ranks of the most iconic monuments to human culture and civilizations, such as Jordan's ancient city of Petra, the immense pillars of Stonehenge, Beijing's Forbidden City and the towering Easter Island statues in Rapa Nui. 

On April 26, 1986, 35 years ago today, a reactor explosion rocked the Chernobyl Nuclear Power Plant, located about 81 miles (130 kilometers) north of Kiev. Two workers died almost immediately, dozens died soon after and thousands more later died or were sickened by radiation exposure, as fallout from the disaster dispersed across Ukraine, Russia and Belarus. 

Soviet officials evacuated a 19-mile (30-km) area around the plant, now known as the Chernobyl exclusion zone. The Ukraine government seeks to add the plant — and the zone around it — to the global list of World Heritage Sites maintained by the United Nations Educational, Scientific and Cultural Organization (UNESCO), Reuters recently reported.

Related: 5 weird things you didn't know about Chernobyl

To be considered for the World Heritage List, a site "must be of outstanding universal value," and should display at least one quality that matches the agency's selection criteria, according to the UNESCO website. Some locations on the list represent breathtaking and unique examples of grandeur in the natural world, such as Yosemite and Yellowstone National Parks in the United States; Vietnam's Hạ Long Bay; Australia's Great Barrier Reef; and the primeval Białowieża Forest straddling Russia and Belarus.

Other locations, such as the Great Wall of China, Mexico's Chichén Itzá ruins and the city of Venice, Italy, earned a spot on the list for their importance in human history as well as their rare beauty. Sites on the list obtain certain legal protections and can receive financial assistance from the World Heritage Fund to help with preservation, according to UNESCO.

In order for a site to be eligible for UNESCO's list, it must first be added to a cultural and historic heritage list in its country of origin, Reuters reported. Oleksandr Tkachenko, Ukraine's Minister of Culture and Information Policy, told Reuters that the ministry initially sought to add the abandoned Chernobyl Nuclear Power Plant and nearby buildings to a list in Ukraine, and officials are now considering expanding that proposal to encompass the entire exclusion zone.

"We believe that putting Chernobyl on the UNESCO heritage list is a first and important step towards having this great place as a unique destination of interest for the whole of mankind," Tkachenko told Reuters.

"The importance of the Chernobyl zone lays far beyond Ukraine's borders," Tkachenko said. "It is not only about commemoration, but also history and people's rights."

In fact, tourism is already booming in the exclusion zone. One of the cities in the zone — Pripyat, home to about 49,000 people in 1986 — is today a post-apocalyptic ghost town, its homes, schools and hospitals uninhabited and reclaimed by plants and wildlife. The exclusion zone was initially opened to visitors in 2010, and Pripyat's eerie, overgrown buildings quickly became a popular destination for photographers and so-called disaster tourists. 

But Chernobyl tourism really took off after the success of HBO's 2019 dramatic series, "Chernobyl," with guides in the Ukraine reporting a 30% rise in 2019 bookings compared to the year before, Live Science previously reported. Approximately 124,000 tourists visited Chernobyl last year, and about 100,000 of them came from outside Ukraine, Agence France-Presse (AFP) reported in 2020.

Scientists are also keeping an eye on Chernobyl, to track how wildlife in the exclusion zone is adapting to levels of radiation exposure that make the zone unsafe for human habitation — and some of their findings are surprisingly positive. 

For example, recent surveys show that gray wolves (Canis lupus) are thriving near Chernobyl, likely in part because they have lots of prey and plenty of territory that's untouched by humans. And a rare species of Asian wild equine known as Przewalski's horse (Equus ferus przewalskii) is also flourishing in the exclusion zone, AFP reported. 

Originally published on Live Science.

Crops grown near the Chernobyl nuclear site in Ukraine are still contaminated with radiation from the explosive 1986 disaster. 

In a new study, researchers found that wheat, rye, oats and barley grown in this area contained two radioactive isotopes — strontium 90 and cesium 137 — that were above safe consumption limits. Radioactive isotopes are elements that have increased masses and release excess energy as a result.

"Our findings point to ongoing contamination and human exposure, compounded by lack of official routine monitoring,” study author David Santillo, an environmental forensic scientist at Greenpeace Research Laboratories at the University of Exeter, said in a statement, referring to the fact that the government suspended its radioactive goods monitoring program in 2013. 

Related: 5 weird things you didn't know about Chernobyl

Santillo and his colleagues, in collaboration with researchers from the Ukrainian Institute of Agricultural Radiology, analyzed 116 grain samples, collected between 2011 and 2019, from the Ivankiv district of Ukraine — about 31 miles (50 kilometers) south of the nuclear plant. 

This area is outside of Chernobyl's "exclusion zone," which is a 30 mile (48 km) radius around the plant that was evacuated in 1986 and has remained unoccupied. They found radioactive isotopes, predominantly strontium 90, were above safe consumption level in 48% of samples. They also found that wood samples collected from the same region between 2015 and 2019, had strontium 90 levels above the safe limit for firewood.

The researchers believe that the lingering radiation in the wood, in particular, may be the reason for the continued contamination of crops, almost 35 years after the disaster. When analyzing the wood ash from domestic wood-burning ovens, they found strontium 90 levels that were 25 times higher than the safe limit. Locals use this ash, as well as ash from the local thermal power plant (TPP), to fertilize their crops, which continues to cycle the radiation through their soil. 

However, computer simulations suggest that it could be possible to grow crops in the region at "safe" levels if this process of repeated contamination ceased. The researchers are now calling for the Ukrainian government to reinstate its monitoring program and create a system for properly disposing of radioactive ash. 

"Contamination of grain and wood grown in the Ivankiv district remains of major concern and deserves further urgent investigation,” study author Valery Kashparov, director of the Ukrainian Institute of Agricultural Radiology, said in the statement. "Similarly, further research is urgently needed to assess the effects of the Ivankiv TPP on the environment and local residents, which still remain mostly unknown."

The findings were published on Dec. 17 in the journal Environment International.

Originally published on Live Science.

Radioactivity levels have spiked in the atmosphere over northern Europe, and that could indicate damage at a nuclear power plant in western Russia, according to a Dutch health agency that has analyzed the data. The radioactive spike suggests damage to a nuclear fuel element, the Associated Press reported.

However, the Russian nuclear power operator Rosenergoatom has denied problems related to facilities in Kola and Leningrad, the two nuclear plants operating in the region, according to TASS, a Russian news agency, as reported by the AP.

Related: 5 weird things you didn't know about Chernobyl

Several Scandinavian watchdog agencies detected the elevated levels of the radionuclides (or radioactive isotopes). Radionuclides are atoms whose nuclei are unstable; the excess energy inside the nucleus gets released through radioactive decay. In particular, concentrations of the radionuclides cesium-134, cesium-137 and ruthenium-103 rose in parts of Finland, southern Scandinavia and the Arctic, Lassina Zerbo, the Executive Secretary of the Comprehensive Nuclear-Test-Ban Treaty Organization, wrote on Twitter. Though these pose no harm to humans, they are byproducts of nuclear fission, Zerbo wrote. 

"The radionuclides are artificial, that is to say they are man-made. The composition of the nuclides may indicate damage to a fuel element in a nuclear power plant," an official with the National Institute for Public Health and the Environment in the Netherlands, which analyzed the isotope data, said on Friday (June 26).

Because so few measurements have been taken, monitoring agencies weren't able to identify a specific source, NIPHE officials said.

The sudden radioactivity spike echoes the events following the Chernobyl nuclear meltdown, the biggest nuclear disaster in history. Within a few days of the 1986 disaster, a Swedish nuclear power plant detected elevated radioactivity levels, according to an account from the European parliament.

In recent years, another radioactive mystery cloud wafting over Europe was tied to Russia. In 2017, a plume holding 1,000 times the normal levels of ruthenium-106 was detected over Europe, The Washington Post reported. Russia denied any involvement, though a nuclear reprocessing plant in Russia was a strong suspect, according to a 2019 study in the journal Proceedings of the National Academy of Sciences.

• 5 everyday things that are radioactive
• Images: Chernobyl, frozen in time
• Stunning images of Russia from above

Originally published on Live Science.

Part of the Chernobyl Exclusion Zone where the infamous power plant explosion occurred in 1986 is on fire, and radiation in the area is spiking.

The fire covers about 50 acres (20 hectares) near the abandoned village of Vladimirovka in Ukraine's Chernobyl Exclusion Zone, according to CNN. In a Facebook post, Yegor Firsov, head of Ukraine's ecological inspection service, showed a Geiger counter near the fire reading 2.3 microsievert per hour, a measurement of ambient radiation. The normal reading in the area is 0.14 μSv/h, which is significantly higher than typical radiation levels in other places.

The environmental conditions around Chernobyl are not fully understood, but a 1996 paper in the journal Science of the Total Environment showed that key radiation-carrying elements — cesium, iodine and chlorine — can get picked up by plants and animals in the region and end up in ash when they burn.

"But this is only within the area of the fire outbreak," Firsov wrote.

Related: 5 Weird Things You Didn't Know About Chernobyl

In the city of Chernobyl itself, and in more distant Kiev, radiation levels remain normal, according to CNN. 

Fires in the exclusion zone aren't uncommon, according to Firsov's post. The 1,000-square-mile (2,500 square kilometers) area around the power plant has been largely abandoned since the 1986 meltdown of the Chernobyl Nuclear Power Plant. And in that time, trees and other plants have colonized the area. 

Firsov blamed humans for the periodic fires in the zone.

"The problem of setting fires to grass by careless citizens in spring and autumn has long been a very acute problem for us," he wrote. "Every year we see the same picture — fields, reeds, forests burn in all regions."

He called for a crackdown on starting fires in the exclusion zone.

Ukraine has met this fire with  water drops from aircraft above and a 124-person firefighting force, according to CNN. Another 14 firefighters are also in the area, fighting a smaller fire. These fires are far from the site of the reactor, which is buried under a thick "sarcophagus" of steel and concrete. 

• Images: Chernobyl, Frozen in Time
• Chernobyl Nuclear Disaster 25 Years Later (Infographic)
• 5 Everyday Things That Are Radioactive

Originally published on Live Science.

Tourists can now visit the control room of Chernobyl's Reactor 4, the scene of the world's worst nuclear disaster. But the control room is still highly radioactive, and people are required to wear protective gear when inside, according to recent news reports. 

Ukranian President Volodymyr Zelensky declared Chernobyl an official tourist attraction in June at the inauguration of a gigantic dome built to contain radioactive material. But Chernobyl has been a tourist destination for far longer — parts of it having been open to the public for nearly a decade. In May, bookings to Chernobyl increased by about 30% following the release of the popular HBO series of the same name, according to a previous Live Science report.

But Reactor 4 had remained closed off to most of the public, save for a few researchers and cleanup workers. Now, Chernobyl tour companies have confirmed that the control room is open to the brave souls who wish to be closer to the scene of the disaster, according to CNN.

The control room, which was highly damaged from the explosion, was where the reactor was operated from and where many of the decisions the day the reactor exploded, were made. It sits under the new containment arch but outside of the original sarcophagus that contained the radiation of the reactor itself, according to the Telegraph.

Related: 5 Weird Things You Didn't Know About Chernobyl

The radiation in the room is 40,000 times higher than normal levels, according to Ruptly, a German news agency. Anyone who wishes to visit the site must wear a protective suit, a helmet and a mask, and limit their visit to 5 minutes. Afterward, visitors are required to undergo two radiology tests to measure the amount of radiation they were exposed to, according to CNN. 

That's typical of most tours in Chernobyl; people must go through radiation checkpoints at the beginning, middle and end of one-day tours, according to a previous Live Science report. Tourists are not permitted to wander on their own; they must stay with the tours because of ongoing radiation concerns.

Other parts of Chernobyl remain off-limits, including the "machine cemetery" in the Rossokha village, which is where the contaminated machines used during the Chernobyl cleanup were dumped, according to CNN. Exposure to large amounts of radiation can cause tissue damage and acute sickness, as well as increase the risk of cancer. However, Ukranian officials have deemed the areas that are open to tourists to be safe, as long as they follow the rules.

• 10 Times HBO's 'Chernobyl' Got the Science Wrong
• Images: Chernobyl, Frozen in Time
• 5 Everyday Things That Are Radioactive

Originally published on Live Science.

Thrill seekers visiting the ruins of the Chernobyl Nuclear Power Plant in Ukraine may soon be able to take a piece of the site's radioactive history home with them — in their livers.

A team of scientists from the U.K. and Ukraine have just produced the first bottle of what they're calling Atomik vodka: artisanal spirits made from water and grain harvested in the reactor's once-forbidden exclusion zone. 

Though the 1,000-square-mile (2,600 square kilometers) zone surrounding the plant was initially declared uninhabitable by humans for 24,000 years following the 1986 meltdown, the makers of Atomik assured BBC News that their product is no more radioactive than any other liquor on the market.

Related: 5 Weird Things You Didn't Know About Chernobyl

Part of that is because much of the exclusion zone is not nearly as dangerous as it was feared to be 33 years ago. Some radiation hotspots — such as the Red Forest, where much of the radioactive material from the reactor spilled — remain off-limits to visitors. However, for the most part, the risk of radiation contamination throughout much of the exclusion zone is now considered "negligible" by the Ukrainian government, which reopened the zone to tourism nearly a decade ago. 

Today, Chernobyl is the No. 1 tourist destination in Ukraine, hosting more than 60,000 visitors in 2018, local tourism officials reported. Visits spiked by about 30% in May 2019, following the debut of HBO's "Chernobyl" miniseries.

Still, trips to the zone are highly controlled, with tour groups often forbidden from touching local plants or eating local produce. According to Anders Moller, a biologist who's spent several weeks a year studying the exclusion zone for the past few decades, local crops are often contaminated with radiation and can cause "serious problems" if ingested, Moller previously told Live Science.

Sure enough, the rye that the Atomik founders grew in the exclusion zone for their vodka tested positive for radiation. However, according to Atomik co-founder and University of Portsmouth professor Jim Smith, all traces of contamination disappear in the distillation process, during which the fermented liquid gets purified and water and other diluting substances are removed.

"Any chemist will tell you, when you distill something, impurities stay in the waste product," Smith told the BBC. (Radiation tests conducted by Smith's colleagues at the University of Southampton confirmed the product to be as safe as any other hard liquor.)

Just one bottle of Atomik vodka exists at the moment, but the founders hope to cap at least 500 others by year's end and sell them to thirsty Chernobyl tourists. According to Smith, 75% of the vodka's profits will go back to locals living in exclusion zone villages, which have seen scant economic development since the nuclear disaster 33 years ago. 

"After 30 years, I think the most important thing in the area is actually economic development, not the radioactivity," Smith told the BBC.

Atomik vodka is the first consumer product to come from the exclusion zone since the meltdown, the BBC reported. Apparently, it tastes like rye whiskey with "fruity notes."

• Images: Chernobyl, Frozen in Time
• 10 Times HBO's 'Chernobyl' Got the Science Wrong
• Chernobyl Nuclear Disaster 25 Years Later (Infographic)

Originally published on Live Science.

The giant structure originally constructed around the Chernobyl nuclear power plant in 1986 to contain the radioactive material released in one of history's worst nuclear disasters is crumbling. Soon, it will be torn down.

The Ukranian company managing the nuclear power plant, SSE Chernobyl NPP, recently signed a contract with a construction company to take the structure apart by 2023, according to a statement. That's when the sarcophagus will reach the end of its stable life and "expire," so to speak.

But that doesn't mean radioactive material will just slip out into the world. In 2016, a large steel structure called the "New Safe Confinement" was crafted to blanket the sarcophagus and the radiation underneath it. This confinement structure, 354 feet (108 meters) high, was built a distance from the radioactive site and slid into place with 224 hydraulic jacks, according to a previous Live Science report.

The New Safe Confinement is expected to last at least 100 years and is strong enough to withstand a tornado, according to the report. On the other hand, the crumbling sarcophagus underneath it wasn't built to last long, and was a kind of Band-Aid approach to quickly contain the radiation during the time of the accident. [10 Times HBO's 'Chernobyl' Got the Science Wrong]

The sarcophagus is massive, made up of over 7,700 tons (7,000 metric tons) of metal and 14.1 million cubic feet (400,000 cubic meters) of concrete. But it's flimsy — it doesn't have any welded or bolted joints — and could be easily knocked down by an earthquake, according to the report.

It stays upright, not through sturdy engineering but through the force of gravity, according to the statement. Dismantling it will be "extremely complicated" and will happen under conditions of "high nuclear and radiation risk," the statement said.

But the plan is to take apart the sarcophagus piece by piece — all the while reinforcing the pieces that are left so that they won't collapse. If they do collapse, radioactive material could be released within the new safe confinement, according to the statement.

The disassembled parts will then be cut into smaller pieces, decontaminated and transported in shipping casks to be processed or thrown away — marking the end of a giant project that will cost around $78 million.

Editor's note: This article was updated to clarify that it's not the new dome-shaped structure that's being dismantled, it's the sarcophagus underneath.

• 5 Weird Things You Didn't Know About Chernobyl
• Images: Chernobyl, Frozen in Time
• In Photos: World's 10 Most Polluted Places

Chernobyl has become a byword for catastrophe. The 1986 nuclear disaster, recently brought back into the public eye by the hugely popular TV show of the same name, caused thousands of cancers, turned a once populous area into a ghost city, and resulted in the setting up of an exclusion zone 2600km² in size.

But Chernobyl's exclusion zone isn't devoid of life. Wolves, boars and bears have returned to the lush forests surrounding the old nuclear plant. And when it comes to vegetation, all but the most vulnerable and exposed plant life never died in the first place, and even in the most radioactive areas of the zone, vegetation was recovering within three years.

Humans and other mammals and birds would have been killed many times over by the radiation that plants in the most contaminated areas received. So why is plant life so resilient to radiation and nuclear disaster?

Related: Chernobyl - Facts About the Nuclear Disaster

To answer this question, we first need to understand how radiation from nuclear reactors affects living cells. Chernobyl's radioactive material is "unstable" because it is constantly firing out high energy particles and waves that smash cellular structures or produce reactive chemicals which attack the cells' machinery.

Most parts of the cell are replaceable if damaged, but DNA is a crucial exception. At higher radiation doses, DNA becomes garbled and cells die quickly. Lower doses can cause subtler damage in the form of mutations altering the way that the cell functions — for example, causing it to become cancerous, multiply uncontrollably, and spread to other parts of the body.

In animals this is often fatal, because their cells and systems are highly specialised and inflexible. Think of animal biology as an intricate machine in which each cell and organ has a place and purpose, and all parts must work and cooperate for the individual to survive. A human cannot manage without a brain, heart or lungs.

Plants, however, develop in a much more flexible and organic way. Because they can't move, they have no choice but to adapt to the circumstances in which they find themselves. Rather than having a defined structure as an animal does, plants make it up as they go along. Whether they grow deeper roots or a taller stem depends on the balance of chemical signals from other parts of the plant and the "wood wide web", as well as light, temperature, water and nutrient conditions.

Related: 5 Weird Things You Didn't Know About Chernobyl

Critically, unlike animal cells, almost all plant cells are able to create new cells of whatever type the plant needs. This is why a gardener can grow new plants from cuttings, with roots sprouting from what was once a stem or leaf.

All of this means that plants can replace dead cells or tissues much more easily than animals, whether the damage is due to being attacked by an animal or to radiation.

And while radiation and other types of DNA damage can cause tumours in plants, mutated cells are generally not able to spread from one part of the plant to another as cancers do, thanks to the rigid, interconnecting walls surrounding plant cells. Nor are such tumours fatal in the vast majority of cases, because the plant can find ways to work around the malfunctioning tissue.

Interestingly, in addition to this innate resilience to radiation, some plants in the Chernobyl exclusion zone seem to be using extra mechanisms to protect their DNA, changing its chemistry to make it more resistant to damage, and turning on systems to repair it if this doesn't work. Levels of natural radiation on the Earth's surface were much higher in the distant past when early plants were evolving, so plants in the exclusion zone may be drawing upon adaptations dating back to this time in order to survive.

A new lease of life

Life is now thriving around Chernobyl. Populations of many plant and animal species are actually greater than they were before the disaster.

Related: Is It Safe to Visit Chernobyl?

Given the tragic loss and shortening of human lives associated with Chernobyl, this resurgence of nature may surprise you. Radiation does have demonstrably harmful effects on plant life, and may shorten the lives of individual plants and animals. But if life-sustaining resources are in abundant enough supply and burdens are not fatal, then life will flourish.

Crucially, the burden brought by radiation at Chernobyl is less severe than the benefits reaped from humans leaving the area. Now essentially one of Europe's largest nature preserves, the ecosystem supports more life than before, even if each individual cycle of that life lasts a little less.

In a way, the Chernobyl disaster reveals the true extent of our environmental impact on the planet. Harmful as it was, the nuclear accident was far less destructive to the local ecosystem than we were. In driving ourselves away from the area, we have created space for nature to return.

Stuart Thompson, Senior Lecturer in Plant Biochemistry, University of Westminster

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Audiences have been gripped by Chernobyl, the HBO/Sky series that charts the events and aftermath of the Chernobyl nuclear power plant disaster of April 1986.

I have coordinated a number of international research projects on the impacts of the Chernobyl accident, and made dozens of visits to the Exclusion Zone around Chernobyl. There has been considerable praise for the attention to detail in the sets, props and clothes that helped immerse viewers in a sense of being in late-period Soviet society — including from those that remember it first hand. But there are also errors, or aspects of how the story plays out that have been invented to add drama to the story.

Related: 5 Weird Things You Didn't Know About Chernobyl

1. The helicopter crash

The dramatic scene early on in which a helicopter crashes while attempting to fly over the reactor — apparently due to the intense radiation — never happened. But helicopter video footage taken at the time shows static and distortions generated by the intense radiation field above the reactor core, and there were reports of pilots getting radiation sickness from their sorties.

2. The 'Bridge of Death'

The unforgivably late response of the authorities meant that citizens of Pripyat were out in the open after the accident — and some did go to the so-called "bridge of death" nearer the plant to watch the fire. But I've seen no evidence that all the people on the bridge died, and no evidence that radiation doses there were so dangerously high.

3. Radiation sickness in Pripyat

In fact, on average, residents of Pripyat received an average dose of around 30 millisieverts (mSv) — about the same as three whole-body CT scans - due to the late warning about the danger. There is a scene in the local hospital that appears to show children suffering from radiation sickness: Experts confirmed 134 cases of radiation sickness among the firemen and plant operators, but none among the population of Pripyat.

Related: Why did people take iodine pills after Chernobyl exploded?

4. 'You're sitting next to a nuclear reactor'

In highly emotional scenes we see the pregnant wife of a firefighter visiting her husband suffering from acute radiation syndrome in Moscow Hospital Number Six. This happened, and is one of numerous first-hand accounts the series draws from Voices from Chernobyl by the Belarussian journalist and Nobel laureate Svetlana Alexievich. But the drama implies that the baby absorbed such high doses of radiation from the husband that it subsequently died. A US doctor who helped treat the plant workers and firefighters says that the patients didn't present a significant radiation risk to staff and visitors. Studies after Chernobyl have found no convincing evidence that pregnancy outcomes were affected by radiation exposures.

5. Reactors aren't nuclear bombs

The fears of a nuclear explosion in the two to four-megatonne range due to reactor core meltdown, which, it was claimed, would destroy the nearby city of Kiev and make large areas of Europe uninhabitable, turned out to be wrong. Nuclear power stations don't explode like nuclear bombs — and certainly not thermonuclear ones in the megatonne range. In any case, such an explosion wouldn't have destroyed Minsk, nor would it have made Europe uninhabitable.

Related: 10 Chernobyl-Style Reactors Still Operate Across Russia

6. The divers

The three heroic men who worked to drain the tanks of water below the primary containment chamber to prevent nuclear fuel coming into contact with water which was believed would cause an explosion did so in vain. Subsequent analysis found that the tanks were already mostly empty, and the interaction of the melting fuel with the water might even have helped cool it.

7. The helicopter pilots

The incredibly brave attempts by helicopter pilots to drop boron, sand and lead onto the melting fuel rods likely helped to put out the fire burning in the graphite moderator, but it largely missed the nuclear fuel and the melted core which, after burning through the primary containment, cooled down by itself.

Related: Is It Safe to Visit Chernobyl?

8. The miners

The brave miners who made huge efforts to dig a tunnel under the reactor building to install a heat exchanger to remove heat from under the core also did so in vain: the heat exchanger was never used as the core cooled before it was installed. The risk of radioactivity entering the water table under the reactor (sited near a lake and river system) was found to be elevated, but still low.

9. The liquidators

At the end of the series, claims about the aftermath shown onscreen imply that no studies were made of the hundreds of thousands of liquidators who cleaned up after the accident. In fact there were many studies of this group, and they have proved inconclusive on whether there was an increase in cancer. It is likely they did experience an increased cancer risk, but this was very small compared to the many other health risks they faced and continue to face, including cardiovascular disease, smoking and — a general problem across former Soviet countries — excess alcohol consumption.

Related: How Did Radiation Affect the 'Liquidators' of the Chernobyl Nuclear Meltdown?

10. Failings

Scientists come out as heroes from the show. While there were countless heroes, including scientists, in the aftermath of Chernobyl, ultimately the Soviet scientific community as well as its political system was responsible for the design flaws of the RBMK reactor, the lack of safety culture, and unforgivable lack of preparedness for such an accident.

A cautionary tale

It is important not to underestimate the consequences of the Chernobyl disaster. Studies have found an increase in thyroid cancer, mainly due to the failure of the Soviet authorities to prevent consumption of products contaminated with short-lived radioactive iodine-131 in the weeks after the accident.

Recent analyses of affected populations up to 2015 found 5,000 out of a total of 20,000 thyroid cancer cases to be due to radiation. Fortunately, though serious, thyroid cancer is treatable in 99% of cases. Some reports suggest that the consequences of relocating hundreds of thousands of people, the economic consequences of abandonment of land and the understandable fear of radiation have had greater negative effects than the direct health consequences of radiation.

Chernobyl the series is amazing to watch, and the reconstruction of events before and during the accident was remarkable. But we should remember that it is a drama, not a documentary. In the years since 1986, many myths have been perpetuated about the accident, and these myths have unquestionably hindered the recovery of the affected populations.

More than 30 years on, this recovery continues. If it is to have any chance of success it must be based not on the emotion and the drama, but on the best available scientific evidence. Evidence which shows that, except at the extreme doses which plant operators, firemen and helicopter pilots received during the Chernobyl disaster, the risks of radiation are tiny compared to other health risks we all face in our lives.

Jim Smith, Professor of Environmental Science, University of Portsmouth

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Chernobyl, site of the world's deadliest nuclear accident, is now a surprisingly popular tourist destination. But lethal radiation still permeates the landscape around the site, so why is it safe to visit at all?

Ukrainian officials opened the area to tourists nearly a decade ago, declaring that visits were safe, though tours would be strictly regulated. Since then, thousands of people have flocked to the Chernobyl exclusion zone. [5 Everyday Things That Are Radioactive]

It's true that radiation in large doses can cause tissue damage and acute sickness and increase the risk of cancer, according to the American Cancer Society.

However, people everywhere on Earth are bathed every day in radiation that's a natural part of the environment. This includes terrestrial radiation emanating from Earth itself, internal radiation generated by living organisms, and cosmic radiation from the sun and stars, according to the U.S. Nuclear Regulatory Commission (NRC).

Calculating exposure

On average, a person in the U.S. is exposed to about 3 millisieverts (mSv) of radiation per year, which is considered to be well within safe exposure levels. Radiation from medical imaging technology ranges from less than 1 mSv to about 20 mSv for certain computed tomography (CT) scans, the American College of Radiology reported.

Radiation doses of 50 to 200 mSv can lead to chromosomal damage, while doses of 200 to 1,000 mSv can cause a temporary drop in white blood cell count; serious radiation sickness sets in at about 2,000 mSv, and death follows within days of exposure to 10,000 mSv, according to the Atomic Archive.

Soon after the nuclear meltdown at Chernobyl, dozens of cleanup workers at the plant were exposed to radiation levels as high as 8,000 to 16,000 mSv, the equivalent of 80,000 to 160,000 chest X-rays. This led to at least 134 workers developing serious radiation sickness and caused 28 deaths.

When the Chernobyl reactor exploded, it released deadly levels of radiation, but radioactive fallout wasn't distributed evenly across the surrounding area, due to weather conditions and changing winds. Locations that were farther away from the reactor became radioactive hotspots, "and there were villages that were reasonably close to the plant that didn't get much contamination," said Fred Mettler, a professor emeritus and clinical professor with the Department of Radiology at the University of New Mexico School of Medicine.

Even within villages, radiation was unequally distributed and could vary from street to street, as Mettler learned when he visited the region from 1989 to 1990 with the U.N. Scientific Committee on the Effects of Atomic Radiation (UNSCEAR).

Gauging the risk

The ruins of the Chernobyl reactor, now contained under a metal shell, are still highly radioactive and will likely remain so for up to 20,000 years. However, the zones in Chernobyl that are now open to the public may have initially received lower doses of radiation, despite their proximity to the damaged reactor, Mettler told Live Science.

Background levels of radiation around Chernobyl overall were also lower than the global average before the accident, which may have helped to mitigate the radiation boost from the accident, Mettler added.

Nevertheless, ongoing radiation-safety concerns dictate that tourists are restricted to certain areas and are not permitted to wander on their own, tour leaders with Chernobyl Tour wrote on the Ukrainian company's website.

An average one-day visit to Chernobyl begins and ends with passage through an official checkpoint for dosimetry control, or radiation measurement, and there is an additional radiation checkpoint midway through the tour, according to the State Agency of Ukraine on Exclusion Zone Management.

Visitors may not touch any structures or plants or remove anything from the zone, and they are prohibited from sitting or placing any camera equipment on the ground, Chernobyl Tour representatives said.

An estimated 60,000 tourists visited Chernobyl in 2018, Anton Taranenko, the chief of the Tourism and Promotion Department of the Kiev City State Administration, recently said at a news briefing; of all the most popular tourist destinations in Ukraine, "Chernobyl zone is the leader," said Taranenko, according to the National News Agency of Ukraine.

Ukrainian tourism agency representatives claimed that bookings to Chernobyl rose by about 30% in May and will likely be even higher during the summer months due to the popularity of the recent HBO series "Chernobyl," Live Science previously reported.

• 5 Weird Things You Didn't Know About Chernobyl
• Images: Chernobyl, Frozen in Time
• Chernobyl Nuclear Disaster 25 Years Later (Infographic)

Originally published on Live Science.

The success of HBO's dramatic series "Chernobyl" seems to have boosted the region's tourism industry, with leaders of guided tours to Chernobyl claiming that bookings have increased by about 40% compared to last year, Reuters recently reported.

HBO debuted the first episode of "Chernobyl" on May 6. By the end of the month, Ukrainian tour company SoloEast saw a 30% rise in tourists compared to May 2018, and bookings for June, July and August are up by about 40%, company director Sergiy Ivanchuk told Reuters. [5 Weird Things You Didn't Know About Chernobyl]

After the Chernobyl reactor exploded in 1986, radioactive particles quickly dispersed into the surrounding area and approximately 200,000 people were evacuated and relocated. Authorities declared a so-called exclusion zone covering 18 miles (30 kilometers) around the site of the explosion, and the abandoned towns remain uninhabited to this day.

But in 2010, the exclusion zone was opened to tourists and Ukrainian officials declared that any lingering radiation was "negligible." Since then, Chernobyl tourism has grown in popularity, and the HBO series may have sparked even greater interest in the blighted destination, tour guide Viktoria Brozhko told Reuters.

"Radiation makes the zone particularly interesting," Ukrainian tour company Chernobyl Tour says on its website in a description of their company's one-day tour package. The company's tours now include visits to landmarks featured in the HBO series, such as the bunker where local officials initially decided to delay evacuation, according to Reuters.

During Chernobyl Tour's day trips to the site, visitors typically see monuments to victims; vacant and overgrown homes; an eerie, abandoned amusement park; and the reactor that exploded, which is now entirely covered by a metal dome measuring 344 feet (105 meters) high, Reuters reported.

Chernobyl Tour's website describes the exclusion zone as "safe for visitors," though the company acknowledges that some places in the exclusion zone still have elevated radiation, which could pose some risk.

"We definitely would NOT recommend you staying at them for a long time," representatives wrote on the website.

• Images: Chernobyl, Frozen in Time
• Chernobyl Nuclear Disaster 25 Years Later (Infographic)
• In Photos: World's 10 Most Polluted Places

Originally published on Live Science.

In the HBO miniseries "Chernobyl," the Soviet nuclear physicist Ulana Khomyuk (a composite character played by Emily Watson) realizes that there's been a massive release of radioactive material somewhere nearby and immediately pops an iodine pill. She then encourages others she encounters to do the same. So, why that pill? How does a simple element like iodine protect against radiation?

The short answer is that it doesn't have any direct anti-radiation effects, but might offer some indirect protection. Iodine doesn't ward off free-flying neutrons or remove radioactive dust from drinking water. It does however change how your body behaves, in ways that can reduce the risk radioactive materials pose. Here's how:

Under normal circumstances, your body is fairly iodine-greedy. Your thyroid needs the chemical, and without iodine, the thyroid can't produce the hormones it usually does. People with severe iodine deficiencies develop enlarged thyroid glands, or goiters. Very young children with iodine deficiencies can even develop intellectual disabilities, according to the American Thyroid Association. In the U.S. and other parts of the world, iodine gets added to table salt to prevent these issues. [5 Weird Things You Didn't Know About Chernobyl]

But iodine, like all basic elements, comes in different "isotopes," or versions of the element. Every isotope of iodine has the same number of protons (53), but the number of neutrons varies. In its natural state, Earth has only one isotope of iodine: iodine-127, which has 53 protons, 74 neutrons and negligible radioactivity. But as uranium atoms shatter in the core of a nuclear reactor, they split into smaller atoms, most notably iodine-131.

The difference between iodine-127 and iodine-131 is small, just four neutrons. But iodine-131 is radioactive, firing off neutrons and rapidly decaying, with a half-life of just eight days, meaning half of it will remain after that time. Your body can't tell the difference between these two isotopes, though, and your thyroid gland will hungrily absorb as much iodine-131 as it does iodine-127. And once absorbed, that iodine will sit in your body, spewing radiation into the surrounding tissue and damaging DNA. Taking a large dose of iodine, in theory, will sate your body's hunger for the substance and prevent you from absorbing the iodine-131 once it arrives.

It's best to act quickly though. Iodine-131 is "highly mobile" in its environment, Kathryn Huff, a nuclear reactor engineer and University of Illinois at Urbana-Champaign professor, told Live Science for a previous article. The substance enters the water, where plants pick it up and pass it on to animals. Once the radioactive iodine has been released, it's very difficult to get rid of until it decays away. [Infographic: Chernobyl Nuclear Disaster 25 Years Later]

Nuclear accidents are still (fortunately) rare enough that there haven't been very conclusive studies on the results of radioactive iodine exposures. But after Chernobyl, the most significant release of radioactive iodine ever, there was a spike in thyroid cancer in children in the affected area.

According to a paper published in April 2000 in the journal Reviews in Endocrine and Metabolic Disorders, thyroid cancer rates across Ukraine in children under age 15 spiked from less than 1 in 1 million to 3 per 1 million. In Belarus, they spiked to 30 per 1 million. And in Gomel Oblast in Belarus, one of the worst-hit regions, thyroid cancer rates in children spiked to 100 per 1 million. (Chernobyl was just 12 miles from the Belarus border.) Elevated cancer rates appeared just four years after the accident, and children born after the explosion developed thyroid cancer at normal rates.

It's unclear, the authors wrote, to what degree iodine pills saved lives. Potassium iodide was distributed after the accident, the authors noted, but that effort "was not begun until several days after the accident, and its use was very erratic."

People living in the area may have also been unusually susceptible to poisoning via radioactive iodine, the researchers wrote.

"The mild iodine deficiency in the region surrounding Chernobyl could ... have affected the radiation dose," they wrote, "by increasing the amount of iodine accumulated and increasing the size of the gland in which it was deposited, and it might also alter the radiation effect itself."

While it may remain unclear just how many lives iodine pills can save after a nuclear disaster, it's still standard practice in the U.S. to distribute the pills to people living near a nuclear plant. In the event of an emergency, according to handbooks distributed by the U.S. Nuclear Regulatory Commission, safety officials will instruct people in the affected area to take the pills.

• 5 Everyday Things That Are Radioactive
• Images: Chernobyl, Frozen in Time
• Top 10 Greatest Explosions Ever

Originally published on Live Science.

Editor's Note: This story was updated on Monday, June 10 at 4:45 p.m. E.D.T.

In the new HBO miniseries "Chernobyl," Russian scientists uncover the reason for an explosion in Reactor 4 at the Chernobyl Nuclear Power Plant, which spewed radioactive material across northern Europe.

That reactor, a design called the RBMK-1000, was discovered to be fundamentally flawed after the Chernobyl accident. And yet there are still 10 of the same type of reactor in operation in Russia. How do we know if they're safe?

The short answer is, we don't. These reactors have been modified to lessen the risk of another Chernobyl-style disaster, experts say, but they still aren't as safe as most Western-style reactors. And there are no international safeguards that would prevent the construction of new plants with similar flaws. [Images: Chernobyl, Frozen in Time]

"There are a whole number of different types of reactors that are being considered now in various countries that are significantly different from the standard light-water reactor, and many of them have safety flaws that the designers are downplaying," said Edwin Lyman, a senior scientist and the acting director of the Nuclear Safety Project at the Union of Concerned Scientists.

"The more things change," Lyman told Live Science, "the more they stay the same."

Reactor 4

At the center of the Chernobyl disaster was the RBMK-1000 reactor, a design used only in the Soviet Union. The reactor was different from most light-water nuclear reactors, the standard design used in most Western nations. (Some early U.S. reactors at the Hanford Site in Washington state were a similar design with similar flaws, but were fixed in the mid-1960s.)

Light-water reactors consist of a large pressure vessel containing nuclear material (the core), which is cooled by a circulating supply of water. In nuclear fission, an atom (uranium, in this case), splits, creating heat and free neutrons, which zing into other atoms, causing them to split and release heat and more neutrons. The heat turns the circulating water to steam, which then turns a turbine, generating electricity.

In light-water reactors, the water also acts as a moderator to help control the ongoing nuclear fission within the core. A moderator slows down free neurons so that they're more likely to continue the fission reaction, making the reaction more efficient. When the reactor heats up, more water turns to steam, and less is available to play this moderator role. As a result, the fission reaction slows. That negative feedback loop is a key safety feature that helps keep the reactors from overheating.

The RBMK-1000 is different. It also used water as a coolant, but with graphite blocks as the moderator. The variations in the reactor design allowed it to use less-enriched fuel than usual and to be refueled while running. But with the coolant and moderator roles separated, the negative feedback loop of "more steam, less reactivity," was broken. Instead, RBMK reactors have what's called a "positive void coefficient."

When a reactor has a positive void coefficient, the fission reaction speeds up as the coolant water turns to steam, rather than slowing down. That's because boiling opens up bubbles, or voids, in the water, making it easier for neutrons to travel right to the fission-enhancing graphite moderator, said Lars-Erik De Geer, a nuclear physicist who is retired from the Swedish Defence Research Agency.

From there, he told Live Science, the problem builds: The fission becomes more efficient, the reactor gets hotter, the water gets steamier, the fission becomes more efficient still, and the process continues.

Run-up to disaster

When the Chernobyl plant was running at full power, this wasn't a big problem, Lyman said. At high temperatures, the uranium fuel that powers the fission reaction tends to absorb more neutrons, making it less reactive.

At low power, though, RBMK-1000 reactors become very unstable. In the run-up to the Chernobyl accident on April 26, 1986, operators were doing a test to see if the plant's turbine could run emergency equipment during a power outage. This test required running the plant at reduced power. While the power was lowered, the operators were ordered by Kiev's power authorities to pause the process. A conventional plant had gone offline, and Chernobyl's power generation was needed.

"That was very much the main reason why it all happened in the end," De Geer said.

The plant ran at partial power for 9 hours. When the operators got the go-ahead to power most of the rest of the way down, there had been a buildup of neutron-absorbing xenon in the reactor, and they couldn't maintain the appropriate level of fission. The power fell to nearly nothing. Trying to boost it, the operators removed most of the control rods, which are made of neutron-absorbing boron carbide and are used to slow the fission reaction. Operators also reduced the flow of water through the reactor. This exacerbated the positive void coefficient problem, according to the Nuclear Energy Agency. Suddenly, the reaction became very intense indeed. Within seconds, the power surged to 100 times what the reactor was designed to withstand. [Chernobyl Nuclear Disaster 25 Years Later (Infographic)]

There were other design flaws that made it difficult to get the situation back under control once it started. For example, the control rods were tipped with graphite, De Geer says. When the operators saw that the reactor was starting to go haywire and tried to lower the control rods, they got stuck. The immediate effect was not to slow the fission, but to enhance it locally, because the additional graphite at the tips initially boosted the fission reaction's efficiency nearby. Two explosions rapidly followed. Scientists still debate exactly what caused each explosion. They both may have been steam explosions from the rapid increase in pressure in the circulation system, or one may have been steam and the second a hydrogen explosion caused by chemical reactions in the failing reactor. Based on the detection of xenon isotopes at Cherepovets, 230 miles (370 kilometers) north of Moscow after the explosion, De Geer believes that the first explosion was actually a jet of nuclear gas that shot several kilometers into the atmosphere.

Changes made

The immediate aftermath of the accident was "a very unnerving time" in the Soviet Union, said Jonathan Coopersmith, a historian of technology at Texas A&M University who was in Moscow in 1986. At first, the Soviet authorities kept information close; the state-run press buried the story, and the rumor mill took over. But far away in Sweden, De Geer and his fellow scientists were already detecting unusual radioactive isotopes. The international community would soon know the truth.

On May 14, Soviet leader Mikhail Gorbachev gave a televised speech in which he opened up about what had happened. It was a turning point in Soviet history, Coopersmith told Live Science.

"It made glasnost real," Coopersmith said, referring to the nascent policy of transparency in the Soviet Union.

It also opened a new era in cooperation for nuclear safety. In August 1986, the International Atomic Energy Agency held a post-accident summit in Vienna, and Soviet scientists approached it with an unprecedented sense of openness, said De Geer, who attended.

"It was amazing how much they told us," he said.

Among the changes in response to Chernobyl were modifications to the other RBMK-1000 reactors in operation, 17 at the time. According to the World Nuclear Association, which promotes nuclear power, these changes included the addition of inhibitors to the core to prevent runaway reactions at low power, an increase in the number of control rods used in operation and an increase in fuel enrichment. The control rods were also retrofitted so that the graphite would not move into a position that would increase reactivity.

Chernobyl's other three reactors operated till 2000 but have since closed, as have two more RBMKs in Lithuania, which were shut down as a requirement of that country entering the European Union. There are four RBMK reactors operating in Kursk, three in Smolensk and three in St. Petersburg (a fourth was retired in December 2018).

These reactors "aren't as good as ours," De Geer said, "but they are better than they used to be."

"There were fundamental aspects of the design that couldn't be fixed no matter what they did," Lyman said. "I would not say they were able to increase the safety of the RBMK overall to the standard you'd expect from a Western-style light water reactor."

In addition, De Geer pointed out, the reactors weren't built with full containment systems as seen in Western-style reactors. Containment systems are shields made of lead or steel meant to contain radioactive gas or steam from escaping into the atmosphere in the event of an accident.

Oversight overlooked?

Despite the potentially international effects of a nuclear plant accident, there is no binding international agreement on what constitutes a "safe" plant, Lyman said.

The Convention on Nuclear Safety requires countries to be transparent about their safety measures and allows for peer review of plants, he said, but there are no enforcement mechanisms or sanctions. Individual countries have their own regulatory agencies, which are only as independent as local governments enable them to be, Lyman said.

"In countries where there is rampant corruption and lack of good governance, how can you expect that any independent regulatory agency is going to be able to function?" Lyman said.

Though no one besides the Soviet Union made RBMK-1000 reactors, some proposed new reactor designs do involve a positive void coefficient, Lyman said. For example, fast-breeder reactors, which are reactors that generate more fissile material as they generate power, have a positive void coefficient. Russia, China, India and Japan have all built such reactors, though Japan’s is not operational and is planned for decommission and India’s is 10 years behind schedule for opening. (There are also reactors with small positive void coefficients operating in Canada.)

"The designers are arguing that if you take everything into account, overall they're safe, so that doesn't matter that much," Lyman said. But designers shouldn't be overconfident in their systems, he said.

"That kind of thinking is what got the Soviets into trouble," he said. "And it's what can get us into trouble, by not respecting what we don't know."

Editor's Note: This story was updated to note that most, but not all, of the control rods were removed from the reactor, and to note that some early reactors in the United States also had a positive void coefficient, though their design flaws were fixed.

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• In Photos: World's 10 Most Polluted Places

Originally published on Live Science.

The 1986 nuclear power plant explosion in Chernobyl hurled huge amounts of radioactive material into the air. In the minutes to years that followed, around 530,000 recovery operation workers, such as firefighters, called "liquidators," went in to put out the fires and clean up the toxic mess.

These liquidators, who worked between 1987 and 1990, were exposed to high levels of radiation, on average around 120 millisievert (mSv), according to the World Health Organization. That's over a thousand times more powerful than a typical chest X-ray, which delivers 0.1 mSv of radiation. And some of the very first responders were exposed to levels astronomically higher than that.

So, what happens to the human body when exposed to such high levels of radiation? [5 Weird Things You Didn't Know About Chernobyl]

It's like walking into a giant, powerful X-ray machine shooting radiation everywhere, said Dr. Lewis Nelson, chairman of emergency medicine at Rutgers New Jersey Medical School. Except, in this case, most of the radiation consisted of an even more damaging type of radiation than X-rays, called gamma-rays. This radiation, as it passes through the body, is ionizing.

This means that it removes electrons from atoms in the body's molecules, breaking chemical bonds and damaging tissues. Very high levels of ionizing radiation cause "radiation sickness."

At Chernobyl, 134 liquidators quickly developed radiation sickness, and 28 of them died from it. These people were exposed to radiation levels as high as 8,000 to 16,000 mSv, or the equivalent of 80,000 to 160,000 chest X-rays, according to the World Health Organization.

Radiation sickness mostly manifests in the gastrointestinal tract and the bone marrow, Nelson said. Those areas have rapidly dividing cells, which means that instead of being tightly coiled and a little more protected, the DNA is unraveled so that it can be copied. That makes it more susceptible to the radiation (this is also why radiation therapy works to target cancer cells, which also rapidly divide).

Within a couple of hours of the exposure, people with radiation sickness develop symptoms such as diarrhea and vomiting, Nelson said. When cells cannot properly divide, the mucosa or tissue lining of the GI tract also break downs, releasing cells and the bacteria that live in the gut (including in the stool) into the bloodstream.

This would make even a healthy person sick, Nelson said. But because the radiation is also stopping the bone marrow from producing infection-fighting white blood cells, the body can't fight those infections. People who have radiation sickness therefore have a weakened immune system and frequently die of blood poisoning, or sepsis, within a couple of days, he said.

High levels of radiation can also cause burns and blisters on the skin, which show up minutes to a few hours after the exposure and look just like a sunburn, Nelson said.

While the GI-tract symptoms and burns happen almost immediately to a couple of hours after exposure to the radiation, the bone marrow survives for a couple of days. This means there is a latency period, when the person might even seem to improve, before showing symptoms of sepsis.

The people who survived radiation sickness from Chernobyl took years to recover, and many of them developed cataracts because the radiation damaged the eye lenses, according to the World Health Organization.

Lower exposures

But much of the health focus around Chernobyl survivors has focused on the long-term consequences of the radiation exposure in these areas. The main consequence, for them, is an elevated risk of cancer.

"But remember, the cancer risk is something you see 10 years down the road, so you have to live for 10 more years in order to see [that]," Nelson said. So the cancer risk is generally more of a concern for those who survived Chernobyl but were exposed to lower levels of radiation.

The data on this risk is murky, with very approximate numbers, but it is estimated that 270,000 people in the Ukraine, Russia and Belarus who wouldn't have otherwise developed cancers did develop these illnesses. This mainly manifested as thyroid cancer, directly caused by radioactive particles of iodine-131 released by the explosion.

The thyroid needs iodine in order to produce hormones that regulate our metabolism. But if it doesn't have enough of the healthy, nonradioactive iodine found in many foods, it absorbs the radioactive iodine, and this can eventually lead to thyroid cancer.

This is why in the HBO series "Chernobyl," people take iodine pills; filling those stores of iodine in the thyroid prevents it from absorbing the radioactive iodine. These radioactive particles, which also include others such as cesium-137 enter the body through contact with the skin or through the mouth and nose. In Chernobyl, these particles were thrown into the air, carried by winds and later fell back down in surrounding areas, contaminated crops and water, and the people who ate them.

• Images: Chernobyl, Frozen in Time
• Chernobyl Nuclear Disaster 25 Years Later (Infographic)
• 5 Everyday Things That Are Radioactive

Originally published on Live Science.

The new HBO series "Chernobyl" dramatizes the accident and horrific aftermath of a nuclear meltdown that rocked the Ukraine in 1986. Twenty-five years later, another nuclear catastrophe would unfold in Japan, after the magnitude 9.0 Tohoku earthquake and subsequent tsunami triggered a disastrous system failure at Fukushima Daiichi Nuclear Power Plant.

Both of these accidents released radiation; their impacts were far-reaching and long-lasting.

But how do the circumstances of Chernobyl and Fukushima compare to each other, and which event caused more damage? [5 Weird Things You Didn't Know About Chernobyl]

Only one reactor exploded at Chernobyl, while three reactors experienced meltdowns at Fukushima. Yet the accident at Chernobyl was far more dangerous, as damage to the reactor core unspooled very rapidly and violently, said Edwin Lyman, a senior scientist and acting director for the Union of Concerned Scientists Nuclear Safety Project.

"As a result, more fission products were released from the single Chernobyl core," Lyman told Live Science. "At Fukushima the cores overheated and melted but did not experience violent dispersal, so a much smaller amount of plutonium was released."

In both accidents, radioactive iodine-131 posed the most immediate threat, but with a half-life of eight days, meaning half of the radioactive material decayed within that time, its effects soon dissipated. In both meltdowns, the long-term hazards arose primarily from strontium-90 and cesium-137, radioactive isotopes with half-lives of 30 years.

And Chernobyl released far more cesium-137 than Fukushima did, according to Lyman.

"About 25 petabecquerels (PBq) of cesium-137 was released to the environment from the three damaged Fukushima reactors, compared to an estimate of 85 PBq for Chernobyl," he said (PBq is a unit for measuring radioactivity that shows the decay of nuclei per second).

What's more, Chernobyl's raging inferno created a towering plume of radioactivity that dispersed more widely than the radioactivity released by Fukushima, Lyman added.

Sickness, cancer and death

At Chernobyl, two plant workers were killed by the initial explosion and 29 more workers died from radiation poisoning over the next three months, Time reported in 2018. Many of those who died had knowingly exposed themselves to deadly radiation as they worked to secure the plant and prevent further leaks. Government officials relocated an estimated 200,000 people from the region, according to the International Atomic Energy Agency.

In the years that followed, cancers in children skyrocketed in the Ukraine, up by more than 90%, according to Time. A report issued by United Nations agencies in 2005 approximated that 4,000 people could eventually die of radiation exposure from Chernobyl. Greenpeace International estimated, in 2006, that the number of fatalities in the Ukraine, Russia and Belarus could be as high as 93,000 people, with 270,000 people in those countries developing cancers who otherwise would not have done so.

At Fukushima, there were no deaths or cases of radiation sickness directly associated with the accident — neither workers nor members of the public, according to the World Health Organization (WHO).

However, Japan's aggressive disaster response, which relocated 100,000 people from their homes near Fukushima, is thought to have indirectly caused around 1,000 deaths, most of which were people age 66 years or more, the World Nuclear Association reported.

No-go zones

Japanese authorities created a no-go zone around Fukushima that extended for 12 miles (20 kilometers); the damaged reactors were permanently closed, while cleanup efforts continued.

The extent of Fukushima's environmental impact is still unknown, though there is already some evidence that genetic mutations are on the rise in butterflies from the Fukushima area, producing deformations in their wings, legs and eyes. [See Photos of Fukushima's Deformed Butterflies]

Radiation from contaminated water that escaped Fukushima reached North America's western coast in 2014, but experts said that contamination was too low to pose a threat to human health. And in 2018, researchers reported that wines produced in California after the Fukushima accident had elevated levels of radioactive cesium-137, but the California Department of Public Health declared that the wines were not dangerous to consume.

Chernobyl's exclusion zone encompassed an area 18 miles (30 km) around the ruins of the plant, and the towns within its boundaries remain abandoned to this day. Trees in nearby forests turned red and died soon after the explosion. But decades later, diverse wildlife communities appear to be thriving in the zone, in the absence of human inhabitants.

By 2010, the Ukrainian government determined that danger from radiation exposure in the area around Chernobyl was "negligible," and the exclusion zone would be widely opened to tourists by the following year (though living in the area is still prohibited). But people who visit certain locations more than once will be supplied with handheld dosimeters to check their radiation exposure, so the visits are not without risk, Live Science previously reported.

What's more, radiation levels around Chernobyl can vary widely. Aerial drone surveys revealed in May that radiation in Ukraine's Red Forest was concentrated in previously unknown "hotspots," which scientists outlined in the region's most accurate radiation maps to date.

The Fukushima nuclear power plant is closed; nonetheless, ongoing concerns about safety during decommisioning and cleanup work still linger. The Tokyo Electric Power Company (TEPCO) recently announced that it would not hire foreign workers coming to Japan under newly relaxed immigration rules; TEPCO representatives cited concerns about the ability of non-native Japanese speakers to follow the plant's highly detailed safety instructions, The Japan Times reported yesterday (May 23).

In the end, both disasters provided important lessons for the world on the inherent risks of using nuclear energy, Lyman told Live Science.

"No one should underestimate the challenges needed to ensure nuclear power is safe enough for it to play a major role in the world's energy future," he said. "The key for regulators and operators is to always prepare for the unexpected."

• See Images of Chernobyl, Frozen in Time
• Fukushima Radiation Leak: 5 Things You Should Know
• Fire and Fury: How to Survive a Nuclear Attack

Editor's note: This story was updated on May 28 to indicate that the Fukushima power plant is no longer operating.

Originally published on Live Science.

In the second episode of "Chernobyl," the HBO miniseries about the 1986 accident that became the worst nuclear power disaster in human history, the situation is pretty bad. A large fire rages in the ruins of the No. 4 reactor of the Chernobyl Nuclear Power Plant. A hospital in the nearby town of Pripyat is overrun with radiation victims. Deadly radioactive dust has drifted all the way out of the Soviet Union and into Sweden. The air above the reactor literally glows where the uranium core has become exposed. And the people leading the disaster response decide to dump thousands of tons of sand and boron on the core.

This is more less what happened during the actual disaster in April 1986. But why did first responders use sand and boron? And if a similar nuclear disaster were to occur in 2019, is this what firefighters would still do?

You really don't want an open-air fire on an exposed nuclear core

Exposing a burning nuclear core to the air is a problem on at least two levels, as nuclear reactor engineer and University of Illinois at Urbana-Champaign professor Kathryn Huff told Live Science. [5 Everyday Things that Are Radioactive]

Your first problem is that you've got an ongoing nuclear-fission reaction. Uranium is firing off neutrons, which are slamming into other uranium atoms and splitting them. Those uranium atoms are releasing yet more energy and feeding the whole hot mess. This reaction, no longer contained, is also spewing incredible levels of direct radiation, posing a mortal danger to anyone who tries to get near it.

Your second, related — and much more serious — problem is that the fire is releasing lots of smoke and dust and debris into the air. All that gunk is coming right out of a nuclear reactor, and some of it is in fact matter straight from the nuclear core. That includes an assortment of types (or isotopes) of relatively lightweight elements that form when uranium atoms split.

"This is the dangerous part of an accident like this," Huff said. "Those isotopes, some of them, are toxic to humans. And some of them are more radioactive than what you would encounter in your day-to-day life. And some of them, in addition to being quite toxic and radioactive, are very mobile in the environment."

Mobile, in this case, means that those isotopes can enter the bodies of living things to cause problems. Take, for example, iodine-131, a radioactive isotope of iodine that living cells treat just like regular iodine.

A smoke plume like Chernobyl's contains lots of iodine-131, which can drift hundreds of miles. It can end up in rivers and make its way into plants, animals and humans. Our thyroid glands rely on iodine and will absorb iodine-131 just like ordinary iodine, creating a long-term source of serious radiation inside our bodies.

(This is why, in the immediate aftermath of nuclear disasters, people in the impacted area are supposed to take iodine pills, to fill up their body's reserves and prevent their thyroids from absorbing any of the radioactive isotopes.)

Sand and boron

Dumping sand and boron (the actual Chernobyl mixture also included clay and lead) is an attempt to solve both the first and second problems.

The sand smothers the exposed reactor, squelching that deadly smoke plume. And the boron, in theory, could squelch the nuclear reaction.

"In a nuclear reactor, there are isotopes that make the reaction go and isotopes that make the reaction slow," Huff said.

To get a nuclear chain reaction going, she explained, you need to get enough radioactive isotopes close together that their neutrons, firing wildly into space, tend to slam into other atomic nuclei, splitting them. [Infographic: Chernobyl Nuclear Disaster 25 Years Later]

"When a neutron interacts with an isotope, there's a certain probability, due to the structure of its nucleus, that it will absorb the neutron," she said. "Uranium, specifically uranium-235, has a tendency to absorb the neutron and then immediately split apart. But boron tends to just absorb the neutron. Due to its nuclear structure, it's sort of neutron-thirsty."

So, dump enough boron onto the exposed reactor No. 4 core, the theory went, and it would absorb so many of those wildly firing neutrons that the reaction would stop.

In Chernobyl's case, however, dumping the boron and other neutron absorbers onto the reactor turned out not to work, in part due to the ad hoc helicopter-dumping approach that the plant's design necessitated.

"The intense radiation killed several pilots," the BBC reported in 1997, adding, "It is now known that, despite those sacrifices, almost no neutron absorbers reached the core." [5 Weird Things You Didn't Know About Chernobyl]

Still, Huff said, the principle the Soviets used — neutron absorbers to stop the reaction, coupled with materials to knock the radioactive isotopes out of the air — was sound. And in the event of a similar disaster today, response teams would take an approach based on the same underlying theory.

The big difference, she said, is that modern nuclear plants (at least in the United States) are designed to do a lot of that work themselves.

Modern reactors are way more safe and much more prepared for problems — but they still use boron in their emergency handbooks

Huff pointed out at length that U.S. (and other properly advanced) nuclear reactors are much less likely than Chernobyl to encounter any sort of disaster — never running as hot and operating in sturdier vessels. And the buildings themselves are designed to do much of the work to squelch a nuclear reactor fire and a radioactive plume, she added.

Modern reactors are outfitted with chemical sprays that can flood a reactor building, knocking radioactive isotopes out of the air before they can escape. And unlike Chernobyl, nuclear facilities in the U.S. are entirely contained in sealed structures of cement and rebar (a mesh of reinforced steel bars). These sealed shells are over-engineered to the point that, in theory at least, even a significant explosion wouldn't breach them. You could crash a small jet into the side of one of these buildings, and it wouldn't expose the core. In fact, as part of a test, the U.S. government did just that to an empty containment vessel in 1988. The NRC states that studies regarding large jet impacts are still ongoing.

All that makes a Chernobyl-scale disaster unlikely, though the Union of Concerned Scientists writes that smaller (but still-dangerous) radiation leaks are a real threat for which the United States is not adequately prepared.

That said, the U.S. Nuclear Regulatory Commission (NRC) has, for every one of the 98 nuclear power reactors operating in the country, drafted emergency handbooks hundreds of pages long. These lay out instructions for what responders should do in the event of all sorts of somewhat-plausible to highly unlikely emergencies).

Those handbooks are available in plain English on the NRC's website. Here's the one for Palo Verde, a large plant in western Arizona. You can find instructions for when to shove lots of boron into the core (as soon as the reactor fails to shut down normally). It saw what to do if hostile forces attack the plant (among other things, start preparing a regional evacuation the moment it becomes clear that the forces might cause a significant radiation leak). And, in the event of significant amounts of radioactive material escaping into the atmosphere, it says who declares an evacuation (Arizona's governor, based on recommendations from site supervisors).

Those plans don't go into great detail about Chernobyl style events, though since 9/11 the NRC has developed guidelines for more extreme disasters. However, Huff said, fighting a fire on an exposed uranium core will always come down to more or less fancy versions of dumping boron and sand.

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Originally published on Live Science.

The Chernobyl nuclear power plant exploded more than three decades ago, in 1986, but you can watch it unfold on HBO's TV miniseries "Chernobyl," which premiered earlier this week.

While most people know the general story — that due to human error, the nuclear reactor exploded and unleashed radioactive material across Europe — few know the nitty-gritty details. Here are five weird facts you probably didn't know about Chernobyl. [Images: Chernobyl, Frozen in Time]

1. Similar to Hiroshima

About 30,000 people were near Chernobyl's reactor when it exploded on April 26, 1986. Those exposed to the radiation are thought to have received about 45 rem (rem is a unit of radiation dosage), on average, which is similar to the average dose received by survivors after the atomic bomb was dropped on Hiroshima in 1945, according to the book "Physics for Future Presidents: The Science Behind the Headlines" (W. W. Norton & Company, 2008) by Richard Muller, a professor emeritus of physics at the University of California, Berkeley. 

While 45 rem is not enough to cause radiation sickness (which usually occurs at about 200 rem), it still increases the risk of cancer by 1.8%, Muller wrote. "That risk should lead to about 500 cancer deaths in addition to the 6,000 normal cancers from natural causes."

However, a 2006 estimate from the International Atomic Energy Agency (IAEA), which is associated with the United Nations, calculated much higher cancer fatalities. The IAEA looked at the total distribution of the radiation, which reached across Europe and even to the United States, and estimated that the cumulative radiation dose from Chernobyl was about 10 million rem, which would have led to an additional 4,000 cancer deaths from the accident, Muller wrote.

2. Greatest harm ended within weeks

The initial blast was enormous, but the greatest harm from the radiation happened within the first few weeks. You can think of radiation as fragments that fly outward as a nucleus explodes, like shrapnel from a bomb, Muller wrote.

Just like popped bubble wrap, each nucleus can explode and release radiation only once. Just 15 minutes after the Chernobyl explosion "the radioactivity had dropped to one-quarter of its initial value; after 1 day, to one-fifteenth; after 3 months, to less than 1%," Muller wrote.

"But there is still some left, even today," he noted. "Much of the radiation literally went up in smoke, and only the radiation near the ground affected the population."

3. Dozens of firefighters died

The Chernobyl explosion not only released a lot of radiation; it also started a fire at the power plant. The firefighters who rushed in to stop the flames were exposed to high levels of radiation, and dozens died from radiation poisoning, Muller wrote.

These firefighters were exposed to over 1 quadrillion gammas each. But what does that mean?

Gamma rays — a penetrating kind of radiation that is released from nuclear weapons, dirty bombs and reactor explosions — is like an extremely energetic X-ray. There are about 10 trillion gamma rays in every 1 rem of radiation, Muller wrote.

A person who gets a whole-body dose of 100 rem probably won't notice, as our systems can repair most of this damage without making a person sick. At 200 rem, a person can develop radiation poisoning. Patients who received chemotherapy sometimes experience this type of sickness, leading to side-effects such as hair loss and feeling nauseated and listless. (This nausea is caused, in part, by the body feverishly working to fix the damage caused by the radiation, so it cuts back on other activities, such as digestion, Muller wrote.)

People hit with 300 rem have a good chance of dying unless they get immediate treatment, like a blood transfusion, Muller wrote.

4. There was no containment building

Chernobyl didn't have an important safety measure in place: a containment building.

A containment structure is a gas-tight shell that surrounds a nuclear reactor. This shell, which is usually dome-shaped and made of steel-reinforced concrete, is designed to confine fission products that may be released into the atmosphere during an accident, according to the U.S. Nuclear Regulatory Commission.

If there had been a containment building at Chernobyl, according to Muller's book, "the accident may very well have caused virtually no deaths."

5. There's wildlife there now

The Chernobyl area was evacuated following the explosion; once humans left, wildlife moved in.

The numbers of moose, roe deer, red deer and wild boar living in the exclusion zone are similar to population numbers in nearby uncontaminated nature reserves, a 2015 study found. Wolves are doing especially well, with a population that is seven times the size of wolf populations in neighboring reserves, the study researchers found.

"This doesn't mean radiation is good for wildlife, just that the effects of human habitation — including hunting, farming and forestry — are a lot worse," Jim Smith, the study's observation team coordinator and a professor of environmental science at the University of Portsmouth in the United Kingdom, said in a statement.

However, other scientists pointed out that wildlife levels at Chernobyl are lower than those at other protected regions in Europe, indicating that the radiation is still affecting the area.

• 15 Secretive Places You Can Now See on Google Earth (And 3 You Can't)
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Originally published on Live Science.

Near ground zero of the catastrophic 1986 explosion at the Chernobyl Nuclear Power Plant, aerial drones recently revealed radioactive hotspots that aren't on official maps.

An interdisciplinary team flew special drones over Ukraine's Red Forest, one of the most radioactive spots in the world, which is located 0.3 miles (500 meters) from the Chernobyl complex, University of Bristol (UB) representatives announced in a statement.

Using data from the drone observations, the UB scientists, who are part of the National Centre for Nuclear Robotics (NCNR), created the most detailed map to date of radiation in the forest. They also pinpointed previously unsuspected locations where contamination was unusually intense, according to the statement. [See Images of Chernobyl, Frozen in Time]

The researchers deployed fixed-wing drones, flying 50 missions over the forest over 10 days and mapping a grid over an area measuring about 6 square miles (15 square kilometers). First, drones used a remote-sensing method called lidar — light detection and ranging — to create 3D maps of the terrain. Then, lightweight gamma spectrometers scanned for signatures of radioactive decay.

Radiation contamination in the Red Forest was already known to be higher overall than in any other natural site on Earth. Nevertheless, the scientists found that radioactivity there was unevenly distributed. While radiation had subsided in some areas, others maintained contamination levels that were dangerously high, project leader Tom Scott, a professor at the UB School of Physics, told British television network ITV.

They detected one unexpected hotspot in the ruins of a facility that performed soil separation during cleanup efforts after the accident, the BBC reported. Spent nuclear fuel in the abandoned building was emitting so much radiation that exposure for just a few hours would dose a person with as much radiation as is normally absorbed over an entire year, Scott told the BBC.

And certain radioisotopes that were identified in the Red Forest have very long half lives (the time required for half of their atomic nuclei to decay), "so they're going to be around for a long time," Scott told ITV.

For decades after the accident, the Chernobyl exclusion zone — an area about 1,660 square miles (4,300 square km) around the nuclear complex — was so toxic that nearly all of it was strictly off-limits to people (though wildlife continued to thrive there). But as the radioactivity dissipated, parts of the zone have been opened to tourists, ITV reported.

The recent expedition to the Red Forest was the first in a series of surveys that NCNR will conduct in Ukraine over the next year, and the new maps it is making will help officials to prevent risks to visitors, according to the statement.

• Chernobyl Nuclear Disaster 25 Years Later (Infographic)
• The Top 10 Ways to Destroy Planet Earth
• Fire and Fury: How to Survive a Nuclear Attack

Originally published on Live Science.

Gray wolves from the radioactive forbidden zone around the nuclear disaster site of Chernobyl are now roaming out into the rest of the world, raising the possibility they'll spread mutant genes that they may carry far and wide, a new study finds.

The wolves are prospering not due to any mutant superpower, but because the radioactive zone now acts like a wildlife preserve, researchers added.

In 1986, explosions destroyed a reactor at the Chernobyl nuclear power plant in Ukraine, releasing about 400 times more radioactive fallout than the atomic bomb dropped on Hiroshima, according to the International Atomic Energy Agency. [See Images of Chernobyl, Frozen in Time]

Afterward, it was unclear how contaminated Chernobyl's surroundings were, so the authorities declared an arbitrary 18.6-mile (30 kilometers) diameter around the reactor off-limits. People are still prohibited from living in this "exclusion zone," although it is now open to tourism.

Numerous investigations into the effects of Chernobyl's radioactive fallout on its surroundings have returned conflicting results. While some studies have found that local wildlife suffered, others have discovered evidence that wildlife has prospered, likely because the exclusion zone — devoid of people — has "become a de facto nature reserve," study lead author Michael Byrne, a wildlife ecologist at the University of Missouri at Columbia, told Live Science.

Gray wolves have especially flourished in the exclusion zone, "with their population density within the zone estimated at up to seven times greater than in surrounding reserves," Byrne said. Given this high population density, the researchers expected that some wolves born within the zone would disperse into the surrounding landscapes, "since one area can hold only so many large predators," Byrne said.

Now, for the first time, "we have tracked a young wolf that has definitely left the exclusion zone," Byrne said.

The scientists tracked 14 gray wolves in the Belarusian region of the exclusion zone — 13 adults over 2 years old and one male juvenile 1 to 2 years old — by fitting them with GPS collars. "No wolves there were glowing — they all have four legs, two eyes and one tail," Byrne said.

The researchers found that while the adult wolves stayed within the zone, the juvenile roamed far beyond its boundaries. The young wolf began to consistently move away from its home range about three months after scientists began tracking its movements. Over the course of 21 days, the animal ended up about 186 miles (300 km) outside the exclusion zone.

Due to a malfunction in the young wolf's GPS collar, the researchers couldn't determine if the animal eventually returned to the exclusion zone or remained outside permanently. Still, "it's just cool to see a wolf went that far," Byrne said.

These findings are "the first proof of a wolf dispersing beyond the exclusion zone," Byrne said. "Instead of being an ecological black hole, the Chernobyl exclusion zone might actually act as a source of wildlife to help other populations in the region. And these findings might not just apply to wolves — it's reasonable to assume similar things are happening with other animals as well."

A question these findings raise "is whether animals born in the exclusion zone are bringing mutations with them as they go out into the landscape, because with Chernobyl, the first thing people think about are mutations," Byrne said. However, "we have no evidence to support that this is happening. It is an interesting area of future research, but it is not something I would worry about."

The scientists detailed their findings online June 15 in the European Journal of Wildlife Research.

Original article on Live Science.

WASHINGTON — When 10 people in New York City developed a very rare form of eye cancer over just a four-year period, doctors were puzzled. The cancer, called vitreoretinal lymphoma, had been diagnosed in the U.S. only a handful of times over the previous 20 years. 

The doctors tried to figure out what might have caused this rare cancer in these 10 patients, all of whom were diagnosed between 2010 and 2013, and they discovered that six of the patients had an interesting connection: They all had lived near the Chernobyl Nuclear Power Plant.

The Chernobyl disaster is considered the worst nuclear power plant accident in history: On April 26, 1986, an explosion occurred at the plant in Ukraine, leaking massive amounts of cancer-causing radiation into the atmosphere. [Cancer-Fighting Diet: 6 Tips to Reduce Your Risk]

Vitreoretinal lymphoma is a type of eye cancer that affects white blood cells in the retina, the optic nerve or the vitreous humor (the gel-like substance found inside the eye), said Roxana Moslehi, a genetic epidemiologist at the University at Albany, State University of New York, and the senior author of the study on the New York cases. The doctors who diagnosed the cancers had reached out to Moslehi when they realized they were seeing something strange happening with the rates of this cancer, she said.

Moslehi set out to determine if the cases of vitreoretinal cancer represented a "cluster" — in other words, a group of cases that are close together in time and location and occur at higher rates than expected. She presented her findings here today (April 2) at the American Association for Cancer Research's annual meeting. The findings have not been published in a peer-reviewed journal.

Based on data from the New York State Cancer Registry, Moslehi found that statistically, there should be only one case of vitreoretinal lymphoma in New York state in a four-year period. So to find 10 cases in New York City alone in that same time period was certainly "unanticipated," and represented a cluster, she said. Moslehi also looked at national rates of the disease, and also found incredibly low rates.

To figure out what could be causing this cluster, the researchers looked for commonalities among the patients, Moslehi said. They noted that eight of the 10 were of Ashkenazi Jewish descent, she said.

But even more interesting to the researchers was that six of the 10 patients had lived near Chernobyl at the time of the disaster, Moslehi said. Four of the patients had lived in Ukraine, one patient had lived in Poland and one patient had lived in Moldova, according to the case report.

"It was very surprising to discover this," Moslehi told Live Science. The cause of vitreoretinal lymphoma is unknown, "so any clues that you get as to possible causes make you very excited," she said. [10 Do's and Don'ts to Reduce Your Risk of Cancer]

Indeed, in looking through the literature, the researchers found several studies linking other types of lymphoma to exposure to radiation, Moslehi said. For example, clean-up workers at Chernobyl have been shown to have higher rates of a type of cancer called chronic lymphocytic leukemia, she said. In addition, rates of leukemia in children and adults are increased in people who were exposed to either Chernobyl or the atomic bombs that the U.S. dropped on Japan during World War II, she said. (Both leukemia and lymphoma affect white blood cells.)

The New York City patients who had lived near Chernobyl ranged in age from 62 to 85 at the time of their diagnosis, according to the case report. The diagnoses took place between 24 and 27 years after the nuclear disaster, meaning that a number of the patients were in their late 30s when the disaster took place. Moslehi is still looking at the cases in the other four patients, who did not live near Chernobyl, for clues in those cases, she said.

There was also another cluster of cases that involved related conditions, called myeloproliferative disorders, that was found in Israel, Moslehi said. Myeloproliferative disorders cause blood cells proliferative abnormally. Similar to the group in New York City, the patients in Israel were of Ashkenazi Jewish ethnicity and lived near Chernobyl at the time of the disaster.

Moslehi noted that they "still cannot link this disease or lymphoma to radiation per se" — more studies are needed to fully understand the cause. For example, it may be that Ashkenazi Jews are more susceptible to the effects of radiation, she said.

Editor's note: This story was corrected from the original version. The Israeli cluster had myeloproliferative disorders, not vitreoretinal lymphoma.

Originally published on Live Science.

To safely entomb the radioactive wreckage of Chernobyl, the site of the infamous 1986 nuclear accident, a mobile metal arch is now on the move that is taller than the Statue of Liberty. The giant arch, the largest man-made object ever to move on land, is now sliding over the ruins in Ukraine.

When nuclear reactor No. 4 exploded at the Chernobyl power plant in 1986 due to errors in both operation and design, it sent plumes of radioactive dust as far away as the United States and Japan, previous research found. To contain the fallout, the Soviet Union enclosed the ruins in a structure that is technically known as the Shelter Object but more commonly called the sarcophagus.

Although the sarcophagus is massive — consisting of more than 7,700 tons (7,000 metric tons) of metal and 14.1 million cubic feet (400,000 cubic meters) of concrete — this makeshift structure was never meant to last forever, according to the World Information Service on Energy (WISE). Instead, the structure was raised as quickly as possible to limit workers' exposure to radiation. Now, after standing for decades, the sarcophagus is in danger of collapse, according to the European Bank for Reconstruction and Development. [In Photos: Chernobyl, Frozen in Time]

For example, the hastily built sarcophagus has no welded or bolted joints, so it would not take much of a seismic event to knock it down, researchers have found. Moreover, there are many openings in its roof that allowed water in, resulting in corrosion that is hastening its demise, according to the European Bank for Reconstruction and Development.

To safely entomb the failing sarcophagus and its deadly contents, the French consortium Novarka started building a gargantuan replacement in 2012 — the New Safe Confinement, a steel structure 354 feet (108 meters) high at its tallest point, 531 feet (162 m) wide and 843 feet (257 m) long, and weighing more than 39,000 tons (36,000 metric tons). For comparison, the Statue of Liberty, from the ground to the tip of its torch, is about 305 feet (93 m) high.

Because the ruins of the reactor are still highly radioactive, to protect the workers building the New Safe Confinement, the titanic arch was not built over the sarcophagus. Instead, it was assembled a distance away from the reactor building, and 224 hydraulic jacks are now sliding it the total distance of about 1,070 feet (327 m) into place.

"The start of the sliding of the Arch over reactor 4 at the Chernobyl NPP [Nuclear Power Plant] is the beginning of the end of a 30-year-long fight with the consequences of the 1986 accident," Ostap Semerak, Ukraine's minister of ecology and natural resources, said in a statement. 

The arch is designed to last at least 100 years and is strong enough to withstand a tornado, according to the European Bank for Reconstruction and Development, which led the $1.6 billion project. Inside, robotic cranes will help dismantle the sarcophagus, while vacuum cleaners will suck up radioactive dust. Cameras will help workers remotely operate the tools, and the arch's ventilation system is designed to eliminate the risk of corrosion.

The arch began its slide on Nov. 14, and the entire operation is expected to take five days.

Follow Charles Q. Choi on Twitter @cqchoi. Follow us @livescience, Facebook & Google+. Original article on Live Science.

Almost 30 years after a horrific accident at the Chernobyl Nuclear Power Plant released massive amounts of radiation and became one of the world's worst nuclear catastrophes, the long-abandoned site has some new inhabitants: New research finds that many native wildlife species are once again finding refuge in the human-free Chernobyl Exclusion Zone in Ukraine.

Scientists found that the numbers of moose, roe deer, red deer and wild boar living in the Chernobyl Exclusion Zone — a roughly 1,000-square-mile (2,600 square kilometers) designated area of contamination around the disaster site — are similar to the animals' population numbers in nearby uncontaminated nature reserves. In fact, they noted that wolf census data in the area has a population seven times greater than populations in nearby reserves.

The researchers examined long-term census data compiled from helicopter surveys (from 1987 to 1997) and animal track surveys, in which scientists recorded animal tracks in the region over several years. [Images: Chernobyl, Frozen in Time]

In 1986, a reactor at the Chernobyl Nuclear Power Plant exploded, triggering a fire and unleashing clouds of radioactive particles that contaminated the area surrounding the power plant for at least an 18-mile (29 km) radius, according to the World Nuclear Association, an international organization that supports the nuclear energy industry.

Residual radiation from the nuclear meltdown forced a massive human evacuation from the area, but the new findings suggest that some wildlife species have started to call the area home over the past decade.  

The researchers suspect that wildlife initially returned to the area because it has been largely undisturbed by humans, which has allowed many species — larger mammals, in particular — to thrive, according to Jim Smith, the study's observation team coordinator and a professor of environmental science at the University of Portsmouth in the United Kingdom.

"This doesn't mean radiation is good for wildlife, just that the effects of human habitation — including hunting, farming and forestry — are a lot worse," Smith said in a statement.

However, some scientists think the scope of this study was too limited. Timothy Mousseau, a professor of biological sciences at the University of South Carolina who was not involved in the new study, told NBC News that he thought the study did not address the effect that radiation has on animal populations and didn't have a control group (a group in an experiment or study that does not receive treatment or, in this case, exposure to radiation) to compare the results to those of typical populations.

Overall, the wildlife population around Chernobyl is much lower compared to that in other protected regions in Europe, which seems to indicate that radiation is having an observable effect on the wildlife, he added.

After the March 2011 nuclear leak at the Fukushima Daiichi Nuclear Power Plant in Japan, researchers closely examined animals that were exposed to radioactive particles from the disaster. Scientists reported radiation-related mutations in local butterfly populations, notably pale grass blue butterflies. A 2014 study published in the journal Scientific Reports also showed signs of radiation exposure in the blood of Japanese monkey species, and scientists think it's likely this exposure will make the monkeys more susceptible to infectious disease.

The new study did not include information about the health or reproductive success of different animal species, although the researchers did note that the population numbers didn't seem to be influenced much by animal migration. Moreover, Smith and his colleagues didn't closely observe lifestyle habits that may explain how residual radiation affects wildlife that has come back to Chernobyl.

The new study was published online Oct. 5 in the journal Current Biology. 

Follow Elizabeth Newbern @liznewbern. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.

A massive 32,000-ton, stainless steel arch — so large it could conceal the Statue of Liberty — is being constructed to cover what's left of a nuclear reactor in Chernobyl that exploded in 1986, which triggered a massive radiation leak that has been described as the world's worst nuclear accident to date.

The sarcophagus-type structure, which is scheduled to be ready by 2017, is designed to trap any radioactive dust that may escape into the atmosphere from the former Chernobyl Nuclear Power Plant in Ukraine, reported The New York Times. The enormous cap will also enable workers to complete cleanup operations in the area, which includes safely moving radioactive debris into permanent storage facilities.

"It's an amazing structure," said Nicolas Caille, project director for Novarka, the French company in charge of building the arch, according to the New York Times. "You can't compare it to anything else."

The steel covering is designed to stand for 100 years, and is expected to cost roughly $1.5 billion — a sum that is being financed, in part, by the United States and some 30 other nations, according to The New York Times.

The explosion at the Chernobyl Nuclear Power Plant occurred in the early morning hours of April 26, 1986. Emergency crews battled fires and radiation leaks in the aftermath of the explosion, and residents of the nearby city of Pripyat were evacuated. A total of 31 people died from radiation exposure within three months of the accident, and more than 6,000 cases of thyroid cancer may be linked to the fallout, though direct connections may be impossible to prove.

Follow Denise Chow on Twitter @denisechow. Follow Live Science @livescience, Facebook & Google+.

The explosion at the Chernobyl Nuclear Power Plant is among the worst nuclear accidents the world has ever witnessed.

Where is Chernobyl?

Chernobyl is located north of Kiev, Ukraine, near the border with Belarus. The nuclear plant was close to the newly built city of Pripyat, the small town of Chornobyl and was surrounded primarily by farms and woodland.

The Chernobyl plant

Chernobyl used four Soviet-designed RBMK-1000 nuclear reactors, a design that's now recognized as inherently flawed. This system uses enriched U-235 uranium fuel to heat water, creating steam that drives the reactors' turbines and generates electricity. The nuclear core in the RBMK-1000 actually became more reactive as it produced steam, creating a positive-feedback loop known as a "positive-void coefficient."

What happened at Chernobyl?

Plant operators were preparing for routine maintenance on reactor number 4 on April 25, 1986, and, against safety regulations, disabled the automatic shutdown mechanisms and other plant equipment. The incident began at 1:23 a.m. on April 26, when hot nuclear fuel rods were lowered into cooling water, releasing an immense amount of steam and creating more reactivity because of the RBMK reactor's design flaws. This started a series of explosions and fires that damaged reactors number three and four.

The official reaction

While Soviet authorities were slow to release details of the incident, the nearest city of Pripyat was evacuated about 36 hours after the accident. Many residents were already exhibiting symptoms of radiation sickness.

Soviet authorities come clean

The prevailing winds at the time of the accident were from the south and east, so much of the radiation traveled northwest toward Belarus. When radiation alarms began to go off at a nuclear plant in Sweden, Soviet authorities were forced to reveal the full extent of the crisis.

An imminent return

Residents were told they would be returning in a few days, so many left valuables and personal belongings behind.

Modern-day ruins

Abandoned ruins are all that remains from the once bustling cities around Chernobyl. Within three months of the accident, 31 people died from radiation exposure or other direct effects of the disaster, according to the NRC, UNSCEAR and other sources. More than 6,000 cases of thyroid cancer may eventually be linked to radiation exposure, but the precise number of illnesses related to the Chernobyl accident is difficult, if not impossible, to ascertain.

Long-lasting effects

The forests around Chernobyl are still heavily contaminated with radiation from the 1986 Chernobyl nuclear disaster.

A ghost town

Hotel Polesie in Pripyat stands empty as if awaiting the return of staff and guests. The overall rate of cancer deaths and other health effects related to Chernobyl's radiation is lower than what was initially feared.

The emergency reponse

The damaged reactor was hastily sealed in a concrete sarcophagus, but the effectiveness of this is the subject of intense scientifi debate. The plant itself continuted in operation for several years, and was finally shut down entirely in December 2000. The plant, the ghost towns of Pripyat and Chornobyl, and a large area surronding the plant now known as the "zone of alientation" are largely off-limits to humans.

Chernobyl today

Because of the long-lived radiation in the region surrounding the former Chernobyl Nuclear Power Plant, the area won't be safe for human habitation for at least 20,000 years.

Almost 30 years ago, the world's attention was fixed on Chernobyl, the nuclear power plant in Ukraine that exploded in one of the world's worst nuclear disasters.

The world has moved on since that 1986 catastrophe, but at Chernobyl, one thing hasn't changed very much: The dead trees, plants and leaves at the contaminated site don't decay at nearly the same rate as plants elsewhere, researchers have found.

"We were stepping over all these dead trees on the ground that had been killed by the initial blast," Tim Mousseau, a professor of biology at the University of South Carolina, said in a statement. "Years later, these tree trunks were in pretty good shape. If a tree had fallen in my backyard, it would be sawdust in 10 years or so." [Images: Chernobyl, Frozen in Time]

Mousseau and Anders Møller of the Université Paris-Sud have made ongoing investigations into the biology of radioactive areas like Chernobyl and Fukushima, Japan.

Much of their work has taken them into the Red Forest, the infamous wooded region surrounding Chernobyl where the trees turned an ominous reddish-brown color before dying. The pair noticed that the tree trunks seemed largely unchanged, even after a few decades.

"Apart from a few ants, the dead tree trunks were largely unscathed when we first encountered them," Mousseau, who is also co-director of the Chernobyl and Fukushima Research Initiatives at the University of South Carolina, told Smithsonian.

To find out what was happening — or, more accurately, what wasn't happening — the research team collected hundreds of samples of leaf litter from forest floors that were not contaminated by radiation and stuffed the leaves into bags lined with panty hose (to keep out insects). They then distributed these bags around the Chernobyl area and waited nine months.

The results were striking: Samples of leaf litter that were placed in highly contaminated areas showed 40 percent less decomposition than samples that were placed in uncontaminated sites. The degree of decay was proportional to the degree of radioactive contamination at each site, according to the study, published in the journal Oecologia.

Radiation is known to have harmful effects on microorganisms such as bacteria and fungi. Recent research has found that radiation therapy can cause severe complications in cancer patients by reducing the populations of helpful bacteria in the intestines. [Infographic: How Radiation Affects the Human Body]

Mousseau and other researchers are concerned that the buildup of leaf litter on the forest floor presents a real danger. "There is growing concern that there could be a catastrophic fire in the coming years," Mousseau said.

In the event of a forest fire, 28 years' worth of undecayed leaves would provide an ideal fuel for the fire, which could then spread radiation throughout the region. "That would end up moving radiocesium and other contaminants via smoke into populated areas," Mousseau said.

"This litter accumulation that we measured, which is likely a direct consequence of reduced microbial decomposing activity, is like kindling," Mousseau added. "It's dry, light and burns quite readily. It adds to the fuel, as well as makes it more likely that catastrophically sized forest fires might start."

Follow Marc Lallanilla on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on Live Science.

Remote industrial towns, e-waste processing centers and the site of an infamous nuclear disaster top 2013's worst polluted places, according to a new list from the New York-based nonprofit Blacksmith Institute.

The toxic locations are not ranked, but they include Chernobyl, Ukraine, which is still suffering the consequences of a radioactive meltdown that occurred in 1986; the Niger River Delta in Nigeria, where each year 240,000 barrels of crude oil are spilled; and Hazaribagh, Bangladesh, where carcinogens enter the water supply from more than 200 tanneries concentrated in a small area of the city.

"In this year's report, we cite some of the most polluted places we've encountered. But it is important to point out that the problem is really much larger than these 10 sites," Richard Fuller, president of the Blacksmith Institute, dedicated to eliminating life-threatening polluting in developing countries, said in a statement. "We estimate that the health of more than 200 million people is at risk from pollution in the developing world." [See Images of the Most Polluted Places] 

According to the report, the World Health Organization (the public health arm of the United Nations) has estimated that 23 percent of deaths in the developing world can be attributed to environmental factors like pollution. Besides cancer, exposure to toxic chemicals can cause acute and chronic poisoning, cognitive impairment, organ damage and respiratory problems, the report said, adding that children are most vulnerable to these impacts.

Researchers said the 10 sites were chosen based on the severity of their health risk and prioritized by their value as examples of different kinds of pollution threats around world.

Here are the 10 sites listed in the report, in alphabetical order:

Agbogbloshie, Ghana: This dumpsite in the Ghanaian capital Accra is the second largest e-waste processing area in West Africa. When sheathed cables from electronics like microwaves and computers are burned to recover the copper material inside, metals can particulate in the smoke and get left behind in the soil. An estimated 40,000 people are affected by the pollution threat.

Chernobyl, Ukraine: The world's worst nuclear disaster at Chernobyl in 1986 released 100 times more radiation than the atom bombs dropped over Hiroshima and Nagasaki. Skin lesions, respiratory ailments, infertility and birth defects affected people in contaminated areas in Belarus, Russia and Ukraine for years and the accident has been linked to more than 4,000 cases of thyroid cancer. Pollution from Chernobyl is estimated to have affected some 10 million people.

Citarum River, Indonesia: More than 500,000 people are directly affected, and up to 5 million people are indirectly impacted, by chemical pollution in the Citarum River Basin in West Java. Lead, aluminum, manganese and iron concentrations in the river are several times higher than world averages because of pollution from industrial and domestic sources.

Dzershinsk, Russia: A major site of chemical manufacturing in Russia, Dzershinsk has high levels of pollutants like dioxins and phenol in the groundwater. Residents suffer from diseases and cancers of the eyes, lungs and kidneys and life expectancy in the city is just 47 for women and just 42 for men.

Hazaribagh, Bangladesh: Tanneries using old, outdated and inefficient processing methods to make leather dump 22,000 cubic liters of toxic waste each day into the city's main river, impacting more than 160,000 people. This waste includes the cancer-causing chemical hexavalent chromium.

Kabwe, Zambia: Decades of unregulated lead mining in this African city have caused serious health problems for residents of Kabwe, where more than 300,000 people are thought to be affected by pollution. In 2006, children's blood lead levels in Kabwe were found to exceed the recommended levels by five to 10 times.

Kalimantan, Indonesia: On the island of Borneo, Kalimantan and the surrounding areas have become contaminated with mercury because of small-scale gold mining, impacting some 225,000 people. Miners in the region use mercury in the gold extraction process, resulting in mercury emissions during the amalgamation and smelting processes.

Matanza Riachuelo, Argentina: More than 15,000 industries are thought to be releasing a variety of pollutants into the Matanza River, which passes through Buenos Aires and empties into the Rio de la Plata. Contaminants include zinc, lead, copper, nickel and total chromium (a term that includes two forms of chromium), making the drinking water near the Matanza-Riachuelo river basin seriously unsafe, threating more than 20,000 people who live in the area.

Niger River Delta, Nigeria: An unknown number of people are impacted by the voracious petroleum industry in this densely populated part of Africa, where there were nearly 7,000 incidents involving oil spills between 1976 and 2001. The report said that about 2 million barrels of oil were being extracted from the delta every day as of last year.

Norilsk, Russia: Norilsk is an industrial city in Siberian Russia, where each year, nearly 500 tons each of copper and nickel oxides and 2 million tons of sulfur dioxide are released into the air. Life expectancy for factory workers in Norilsk is 10 years below the Russian average.\

Editor's note: An earlier version of this article incorrectly stated that Kabwe was in Zimbabwe. It is in Zambia.

Follow Megan Gannon on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on LiveScience.

The amount of radioactive material being released from the damaged nuclear reactors in Japan, and the eventual impact it will have on human health, are still being determined.

How does nuclear radiation harm the body, and what are the risks from long-term exposure to low levels after an accident? MyHealthNewsDaily spoke with experts about these questions.

How does radiation harm the body?

There's been some reported evidence that radioactive iodine and cesium are being released into the environment from the malfunctioning nuclear reactors in Japan, said Kathryn Higley, director of the Oregon State University department of nuclear engineering and radiation health physics.

As radioactive material decays, or breaks down, the energy released into the environment has two ways of harming a body that is exposed to it, Higley said. It can directly kill cells, or it can cause mutations to DNA. If those mutations are not repaired, the cell may turn cancerous.

Radioactive iodine tends to be absorbed by the thyroid gland and can cause thyroid cancer, said Dr. Lydia Zablotska, an assistant professor in the department of epidemiology and biostatistics at the University of California, San Francisco.

But radioactive iodine is short-lived and will be around for only about two months after an accident, said Andre Bouville of the National Cancer Institute,  who has studied radiation doses from the fallout of the 1986 Chernobyl explosion in Ukraine. So, if the exposure to the air comes after that time,  radioactive iodine does not pose a health risk, Bouville said.

Children are most at risk for thyroid cancer, since their thyroid glands are 10 times smaller than those of adults, he said. The radioactive iodine would be more concentrated in them.

Radioactive cesium, on the other hand, can stay in the environment for more than a century. But it does not concentrate in one part of the body the way radioactive iodine does.

The Chernobyl accident released a plume of radioactive materials into the atmosphere in a fraction of a second. In the following years, the incidence of thyroid cancer among those exposed as children increased in Ukraine and nearby countries, Zablotska said. The cancer showed up between four and 10 years after the accident, Bouville said.

Children were exposed to radioactive material mainly from eating contaminated leafy vegetables and dairy. There have been no detectable health effects from exposure to radioactive cesium after the accident.

In general, it takes a pretty high dose of radiation to increase cancer risk, Higley said. For instance, there were reports that one Japanese worker was exposed to 10 rem (100 millisievert, mSV), a measurement of radiation dose. From that exposure, his lifetime cancer risk would go up about half a percent, Higley said. According to Higley, the dose is the equivalent of about five CT scans. Americans are exposed to about 0.3 rem (3 mSv) each year from natural sources, such as the sun.

Potentially, exposure to any type of radiation can increase cancer risk, with higher exposure increasing the risk, Bouville said.

No increases in cancer rates were observed after the release of radioactive from a power plant on Three Mile Island, Pa., in 1979, Zablotska said.

Radiation sickness

A person's risk of getting sick depends on how much radiation the body absorbs. Those exposed to high levels of radiation, about 200 rem, (2000 millisievert ) could develop radiation sickness, Bouville said. A chest X-ray is about 0.02 rem, (0.2 millisieverts mSv),  according to the Interational Atomic Energy Agency.

People are exposed to about 0.24 rem (2.4 mSv) per year from natural background radiation in the environment, the IAEA says.

Radiation sickness is often fatal and can produce such symptoms as bleeding and shedding of the lining on the gastrointestinal tract, Zablotska said. About 140 people suffered from it as a result of the Chernobyl accident, Zablotska said.

A radiation dose of 40 rem, (400 mSv) per hour was reported at one of the Japanese power plants at one point following the March 11 earthquakes and tsunami that damaged their cooling systems, according to the IAEA. This is a high dose but was isolated to a single location, the IAEA says.

"That is definitely an area where you do not want to stay for prolonged period," Higley said. She notes  that a total dose of 400 to 600 rem can be lethal. But the radiation levels have been decreasing after the observed spike, she said. She speculates the spike may have been due to the release of a puff of radioactive material when pressure dropped at the facility.

Follow MyHealthNewsDaily staff writer Rachael Rettner on Twitter @RachaelRettner.

This story was provided by MyHealthNewsDaily, a sister site to LiveScience.

Explosions, both natural and man-made, have caused awe and terror for centuries. From tragic munitions accidents, to intentional acts of wartime destruction, to spontaneous cosmic cataclysms, here are 10 of the most powerful explosions in recorded history... with a surprise honorable mention at the end.

Trinity blast - the first atom bomb in history

The first atom bomb in history, dubbed "the gadget," was detonated at the Trinity Site near Alamogordo, N.M., in 1945, exploding with a force of roughly 20 kilotons of TNT. Project leader J. Robert Oppenheimer later said that while he watched the test, he thought of a line from the Hindu scripture the Bhagavad Gita: "I am become Death, the destroyer of worlds." Nuclear weapons later ended World War II and ushered in decades of fear of nuclear annihilation. Scientists recently found that civilians in New Mexico may have been exposed to thousands of times the recommended level of public radiation.

Jack Aeby took the only known well-exposed color photograph of the detonation (shown here).

Related: 'The night turned into day': How Manhattan Project scientists reacted to the world's first atomic bomb test

The Chernobyl nuclear disaster

In 1986, a nuclear reactor exploded at Chernobyl in Ukraine, then part of the Soviet Union. It was the worst nuclear accident in history. The blast, which blew the 2,000-ton lid off the reactor, sent out 400 times more radioactive fallout than the Hiroshima bomb, contaminating more than 77,000 square miles (200,000 square km) of Europe. Roughly 600,000 people were exposed to high doses of radiation, and more than 350,000 people had to be evacuated from contaminated areas.

Following the accident, authorities established the 1,040 square mile (2,700 square kilometer) Chernobyl Exclusion Zone around the radius of the plant, which remains off-limits to people today (though some individuals have returned to settle there illegally). It is still considered one of the world's most radioactive places.

Texas City Disaster

A fire onboard the cargo ship SS Grandcamp docked at Texas City in 1947 detonated 2,300 tons of ammonium nitrate, a compound used in fertilizers and high explosives. The explosion blew two planes out of the sky and triggered a chain reaction that detonated nearby refineries as well as a neighboring cargo ship carrying another 1,000 tons of ammonium nitrate. The disaster killed roughly 600 people and injured roughly 3,500, and is generally considered the worst industrial accident in U.S. history.

Halifax Explosion

In 1917, a French cargo ship fully loaded with explosives for World War I accidentally collided with a Belgian vessel in the harbor of Halifax, Canada. It exploded with more force than any man-made explosion before it, equivalent to roughly 3 kilotons of TNT. The blast sent a white plume billowing 20,000 feet (6,100 meters) above the city and provoked a tsunami that washed up as high as 60 feet (18 meters). For nearly 1.2 miles (2 km) surrounding the blast center, there was total devastation, and roughly 2,000 people were killed and 9,000 injured. It remains the world's largest artificial accidental explosion.

Tunguska Explosion

The mysterious explosion near the Podkamennaya Tunguska River in 1908 flattened some 500,000 acres (2,000 square kilometers) of Siberian forest, an area nearly the size of Tokyo. Scientists think the blast was caused by a cosmic impact from an asteroid or comet perhaps 65 feet (20 meters) in diameter and 185,000 metric tons in mass — more than seven times that of the Titanic. The resulting explosion could have been roughly as strong as four megatons of TNT — 250 times more powerful than the atom bomb dropped on Hiroshima.

Mount Tambora

In 1815, Mount Tambora in Indonesia exploded with the force of roughly 1,000 megatons of TNT, the largest volcanic eruption in recorded history. The blast hurled out roughly 140 billion tons of magma and not only killed more than 71,000 people on the island of Sumbawa and nearby Lombok, but the ash it released created global climate anomalies. The following year, 1816, became known as the Year Without a Summer, with snow falling in June in Albany, N.Y., river ice seen in July in Pennsylvania, and hundreds of thousands of people dying of famine worldwide.

K-T Extinction Impact Event

The Age of Dinosaurs ended in a cataclysm roughly 65 million years ago that killed off roughly half of all species on the planet. Although research suggests the planet was on the verge of an environmental crisis before the Cretaceous-Tertiary or K-T extinction, the straw that broke the dinosaur's back is widely thought to have been a cosmic impact with an asteroid or comet some six miles (10 km) wide, exploding with the force of roughly 10,000 gigatons of TNT, or some 1,000 times the size of the world's nuclear arsenal. The collision would have blanketed the world with dust, ignited global firestorms and triggered tsunamis thousands of feet high. A vast crater roughly 110 miles (180 km) wide at Chicxulub on the coast of Mexico may be the blast site.

Comet Shoemaker-Levy 9

The comet Shoemaker-Levy 9 collided spectacularly with Jupiter in 1994. The giant planet's gravitational pull ripped the comet apart into fragments up to 1.8 miles (3 km) wide, and they struck at 37 miles (60 km) per second, resulting in 21 visible impacts. The largest collision created a fireball that rose about 1,800 miles (3,000 km) above the Jovian cloudtops as well as a giant dark spot more than 7,460 miles (12,000 km) across — about the size of the Earth — and was estimated to have exploded with the force of 6,000 gigatons of TNT.

Shadow-casting Supernova

Supernovas are exploding stars that often briefly outshine entire galaxies. The brightest recorded supernova in history was sighted in the constellation Lupus (Latin for wolf) in the spring of 1006. The extraordinary golden explosion now known as SN 1006 took place roughly 7,100 light years away in a fairly nearby part of the galaxy, and was bright enough to cast shadows and read by at night, remaining visible for months in the daytime.

This blast has some recent competition. In 2016, astronomers detected another ultrabright supernova, named SN2016aps, which emitted more light than any supernova ever recorded. However, because this blast occurred 3.6 billion light-years from Earth, only the best scientific telescopes observed it.

The biggest explosion since the Big Bang

Gamma-ray bursts (GRBs) are the most powerful explosions known in the universe. On October 9, 2022, astronomers spotted the brightest GRB ever recorded, launched across space when a massive star located around 2.4 billion light-years from Earth collapsed, birthing a black hole. The GRB, officially designated GRB 221009A but nicknamed the BOAT, or the brightest of all time, is thought to be brighter than other highly energetic GRBs by a factor of at least 10. Scientists have dubbed it the biggest explosion in the universe since the Big Bang.

Oh, and speaking of which ...

Honorable mention: The Big Bang

The universe was born in the Big Bang, theorists say. Although it is often thought of as an explosion — perhaps because of its very name — it actually wasn't. In the very beginning, the universe was super-hot and extraordinarily dense. The common misconception is that the universe then exploded out from a single, central point into space. The reality appears to be much stranger — instead, the fabric of space itself seems to have stretched, and as it expanded it carried galaxies along with it like raisins in a rising loaf of bread.

The site of the worst nuclear accident in history will be a new tourist attraction, the Ukranian government announced Monday (Dec. 13). The area around Chernobyl is scheduled to open to visitors next year.

Where tourists are allowed to go, how long they may stay, and what they eat will be carefully controlled, government officials say, so the radiation risks are "negligible."

"They will be properly channeled at all times," said Vadim Chumak at the Research Center for Radiation Medicine of Ukraine.

Scientists researching the effects of Chernobyl at the U.S. National Cancer Institute declined comment, deferring to Chumak, but an unaffiliated biologist pointed out that many other adventurous vacations (think a steep mountain climb) are not risk-free, either.

The fallout

A nuclear reactor exploded at Chernobyl in Ukraine in 1986. The blast knocked the 2,000-ton lid off the reactor and spewed out 400 times more radioactive fallout than the Hiroshima bomb, contaminating more than 77,000 square miles (200,000 square kilometers) of Europe. Roughly 600,000 people were exposed to high doses of radiation. [Top 10 Greatest Explosions Ever]

The exclusion zone around Chernobyl — the highly contaminated area covering a radius of 19 miles (30 km) around the doomed reactor — will be open to visitors next year.

"The visits of tourists would be strictly controlled, so that the radiation risks would be negligible," Chumak, who heads the Ukraine research center’s laboratory of external exposure dosimetry, told LiveScience.

After the disaster, it was uncertain how contaminated the surroundings were, and in a hurry, the authorities declared an arbitrary distance from the reactor off-limits. Researchers later found that some areas within the exclusion zone contained only low levels of radiation. Also, radioactive material decays over time, and some of it disappeared soon after the explosion.

Still, other areas of the exclusion zone, such as the radioactive-waste disposal sites, the sarcophagus entombing the remains of the damaged reactor, and the Red Forest where much of the radioactive material from the reactor spewed, are still hazards. Radioactive cesium, strontium and plutonium are also still around. Plutonium in particular is expected to linger; it takes thousands of years to decay.

"However, the visits of the tourists would be strictly monitored so that they would not have access to locations with relatively high radiation levels," Chumak said. "The visitors would be safe from the radiation point of view, as they would not be free to go wherever they want.”

Don't eat the fruit

Ecologist and evolutionary biologist Anders Moller at the University of Paris-Sud in France said he has spent one to three weeks in the exclusion zone every year for the last two decades, to assess the effects of radiation on animals, plants and people there.

"The level of background radiation I experience during such visits amounts to something like that from an X-ray at a doctor's office," Moller said. "But there is extreme variation in how 'hot' different spots are. There is a more than a factor-of-10,000 difference between the cleanest and the hottest areas in the exclusion zone."

The biggest danger for all life in that area, Moller said, would come from consuming anything that contained radioactive material. "It might end up in your gut and cause serious problems," he explained.

"I don't eat the local produce. The people that live in this contaminated area don't have this luxury, and live from what they grow in their gardens. I've seen with my own eyes with a Geiger counter that locally grown potatoes and onions and so on are often contaminated."

Tourists will not be given any food from the area, "and no airborne radioactivity — dust or aerosols — will be present in the areas visited by tourists," Chumak said. (People who work at Chernobyl must wear respirators where there is a risk of radioactive particles in the air, and they change into and out of special clothing. They are sometimes also given more-protective suits and masks.)

A limited amount of tourism to Chernobyl is already being tolerated, and given the new Ukrainian administration's increased emphasis on economic development, opening Chernobyl for tourism could pay off. For instance, Chumak said, soccer fans attending the European Cup in 2012, to be held in Ukraine and Poland, might be interested in making side trips to Chernobyl.

So what is there for visitors to see? Stopovers would include Chernobyl town, "where the level of man-made radiation is small in comparison to the natural radiation background," Chumak said. (The world is normally bathed in a low level of radiation.)

There is also a special viewing terrace that looks upon the sarcophagus. "The closer you get to the sarcophagus, the higher the external radiation, thus justifying the use of a location far enough from the sarcophagus to limit the exposure to a level about two to three times the natural background," Chumak said.

Tourists also could go close to the power plant and "see and feed large catfishes from the nuclear power plant cooling pond."

One could also visit the town of Pripyat, "which had been evacuated the day following the accident," Chumak added. "The radiation levels there are relatively high, but due to limited stay time, cumulative doses are kept very low." If they made return trips, tourists would be given personal dosimeters to measure their radiation levels, Chumak said.

Moller called the exclusion zone "a ghostly place. It is peculiar in many ways. There are all these villages that have been permanently evacuated, and you can see and hear many fewer birds and other signs of nature."

"It's a kind of reverse ecotourism," said biologist Tim Mousseau at the University of South Carolina at Columbia. "It could prove useful for educating people about the potential consequences of accidents related to nuclear energy, and I think any kind of increased awareness there is good.

"As long as people are informed that it's not completely risk-free, I don't see any problem with it. When people try and climb Mount Everest, they know hundreds of people have died trying, and they still do it."

However, Moller added, "I'm not sure this is where I would go for my honeymoon."

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The brighter the bird, the less likely it is to survive the devastating effects of radiation exposure, according to a new study that examined avian populations around the 1986 nuclear disaster site at Chernobyl, Ukraine.

The same chemicals that some birds use to color their feathers are also used to mop up the cancer-causing free radicals that bombard them upon exposure to radiation, so when birds hijack these chemicals for their plumage, they have less left over for protection, the scientists said.

Previous research has suggested that animals deficient in chemicals called antioxidants are more likely to suffer DNA damage in the presence of radiation than other animals, because antioxidants soak up the damaging free radicals that radiation creates in the body.

Anders Møller, an ecologist at the Université Pierre et Marie Curie in Paris, and Timothy Mousseau, a biologist at the University of South Carolina, took their research one step further: They wanted to know whether birds that use more antioxidants in their everyday lives are, by extension, less likely to survive in radioactive environments.

The researchers counted the numbers and types of birds seen in 257 locations around Chernobyl and compared these to radiation levels measured in these areas.

The populations of birds with yellow, orange and red feathers—colors thought to be made using a class of antioxidants called carotenoids —were much smaller in the radioactive areas, when compared to other areas, than the populations of birds with plumage colors that did not require the use of antioxidants.

The findings confirm that antioxidants play a crucial role in protecting animals against the effects of radiation. Birds that used up their available antioxidants for plumage were less likely to survive the aftermath of the accident.

“We found that bird species differed in their response to radiation from Chernobyl,” the researchers said in a prepared statement. “Although all species must cope with the potentially detrimental effects of free radicals, because of their use of antioxidants, certain species are predisposed to suffer most from these negative effects.”

Møller and Mousseau, whose study is published this week in the Journal of Applied Ecology, also found that the birds that migrate and disperse over long distances, as well as those that lay large eggs, suffer more of a population decline in radioactive areas compared to other species.

This is thought to be because strenuous physical activity—such as flying—and egg formation use up antioxidants too, they said.

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A scale used to classify the severity of a nuclear accident is being expanded to include incidents related to the transport of radioactive materials.

The International Nuclear Event Scale (INES) works like the Richter scale for earthquakes. Government officials use a numeric scale to classify and report the severity of nuclear events to the world at large. The nuclear ratings are communicated to officials and others by the International Atomic Energy Agency.

More than 60 countries have agreed to report nuclear events and their ratings to the Atomic Energy Agency, most within 48 hours.

The INES is not yet well-known to experts, let alone the public. Cynthia Jones, a U.S. representative to the INES Advisory Committee and a senior technical advisor at the Nuclear Regulatory Commission, will illustrate how the scale is used and recent additions to it this week at an annual meeting of the Health Physics Society in Oregon.

The scale ranges from 1 to 7, as follows:

Rating 1—an anomaly Rating 2—an incident, such as when the regulatory limit for a radiation worker has been exceeded Rating 3—a serious incident Rating 4—an accident with mostly local consequences Rating 5—an accident with wider consequences Rating 6—a serious accident Rating 7—a major accident

The accident at Three Mile Island nuclear power plant in Pennsylvania in 1979 would be classified as a 6 on this scale, while the Chernobyl disaster of 1986 would rank as a 7,  the highest rating.

The additions will cover any radiation sources and transport incidents, including those in which radioactive packages are lost or stolen.

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