Nuclear Event Rating Scale Revamped
The International Nuclear Event Scale gives a numeric rating to put nuclear events into perspective. Level 0 refers to occurrences with no safety significance.
Credit: IAEA

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.