Radioactive Water Leaks from Fukushima: What We Know

The Fukushima Daiichi Nuclear Power Plant in Japan.

(Image credit: TEPCO)

Here is what you need to know about the radioactive water leaking from Japan’s Fukushima nuclear plant into the Pacific Ocean.

Scientists on both sides of the Pacific have measured changing levels of radioactivity in fish and other ocean life since the March 2011 earthquake and tsunami triggered a nuclear meltdown at Japan’s Fukushima Daiichi nuclear plant. On Aug. 2, 2013, when Japan’s Tokyo Electric Power Co. (TEPCO) gave its first estimate of how much radioactive water from the nuclear plant has flowed into the ocean since the disaster, the company was finally facing up to what scientists have recognized for years.

Latest Videos From

Watch full video here:

TEPCO estimated that between 20 trillion and 40 trillion becquerels (units of radioactivity representing decay per second) of radioactive tritium have leaked into the ocean since the disaster, according to the Japanese newspaper Asahi Shimbun. The Fukushima plant is still leaking about 300 tons of radioactive water into the ocean every day, according to Japanese government officials. [Infographic: Inside Japan's Nuclear Reactors]

The Fukushima plant is leaking much less contaminated water today compared with the immediate aftermath of the nuclear meltdown in June 2011 — a period when scientists measured 5,000 to 15,000 trillion becquerels of radioactive substances reaching the ocean. Even if radioactivity levels in the groundwater have spiked recently, as reported by Japanese news sources, Buesseler expects the overall amount to remain lower than during the June 2011 period.

The biggest threat in the contaminated water that flowed directly from Fukushima's reactors into the sea in June 2011 was huge quantities of the radionuclide called cesium. But the danger has changed over time as groundwater became the main source for leaks into the ocean. Soil can naturally absorb the cesium in groundwater, but other radionuclides, such as strontium and tritium, flow more freely through the soil into the ocean. (TEPCO is still coming up with estimates for how much strontium has reached the ocean.)

A number of fish species caught off the coast of the Fukushima Prefecture in 2011 and 2012 had levels of cesium contamination greater than Japan's regulatory limit for seafood (100 becquerels per kilogram), but both U.S. and Japanese scientists have also reported a significant drop in overall cesium contamination of ocean life since the fall of 2011. The biggest contamination risks came from bottom-dwelling fish near the Fukushima site. [In Photos: Fukushima Butterflies Plagued With Defects]

TEPCO is facing two huge issues in stopping the radioactive water leaks. First, groundwater from nearby mountains is becoming contaminated as it flows through the flooded basements of the Fukushima plant's reactor buildings. The water empties into the nuclear plant's man-made harbor at a rate of about 400 tons per day — and TEPCO has struggled to keep the water from leaking beyond existing barriers into the ocean.

Second, TEPCO must also deal with contaminated water from underground tunnels and pits that hold cables and pipes for the Fukushima nuclear plant’s emergency systems. The underground areas became flooded with highly radioactive water during the initial meltdown of the Fukushima plant’s reactors, and have since leaked water into the ocean despite TEPCO’s efforts to seal off the tunnels and pits.

TEPCO has also been racing to deal with the problem of storing hundreds of thousands of tons of radioactive water from the Fukushima plant, said Hiroaki Koide, a nuclear engineer at Kyoto University in Japan. The Japanese utility is testing a water decontamination system called ALPS that can remove almost all radioactive substances except for tritium, but has put much of the contaminated water in storage tanks in the meantime.

Jeremy has written for publications such as Popular Science, Scientific American Mind and Reader's Digest Asia. He obtained his masters degree in science journalism from New York University, and completed his undergraduate education in the history and sociology of science at the University of Pennsylvania.