A Look at the Nuclear Accident Scale

As my colleagues Hiroko Tabuchi, Keith Bradsher and Andrew Pollack report, “Japan has raised its assessment of the accident at the crippled Fukushima Daiichi nuclear power plant to the worst rating on an international scale, putting the disaster on par with the 1986 Chernobyl explosion.”

In technical terms, the decision raised the alert level for the accident from 5 to 7 on the International Nuclear and Radiological Event Scale, which runs from 0 to 7. The increase of two levels is significant because,  according to the International Atomic Energy Agency, “the scale is designed so that the severity of an event is about 10 times greater for each increase in level on the scale.”

Last month, John Large, a nuclear engineer, explained the scale in layman’s terms for Britain’s Channel 4 News: “1 is someone dropping a milk bottle in the control room, and Chernobyl is 7.”

While the decision to raise the alert level was just made by Japanese officials, some scientists in the United States and the head of France’s Nuclear Safety Authority argued almost a month ago that the accident was, at that time, already worse than the 1979 accident at the Three Mile Island plant in Pennsylvania, which was rated a 5.

In a statement on the new rating for the crisis, the atomic energy agency reported:

The nuclear accident at Fukushima Daiichi is now rated as a Level 7 “major accident” on INES. Level 7 is the most serious level on INES and is used to describe an event comprised of “a major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures.”

Although the 1986 Chernobyl explosion is the only other time the maximum rating has been used, an agency official, Denis Flory, told reporters on Tuesday that the Fukushima catastrophe is a “totally different accident.” In a briefing for agency members, Mr. Flory stressed that Japan’s Nuclear and Industrial Safety Agency “estimates that the release of radioactive material to the atmosphere is approximately 10 percent of the Chernobyl accident.”

The atomic energy agency also noted that Japanese health officials had tested 21 food samples — of “various vegetables, spinach and other leafy vegetables, fruit (strawberries), various meats (chicken, beef and pork), seafood and unprocessed raw milk” —   in eight prefectures around the plant in recent days and found that radioactive iodine and cesium “were either not detected or were below the regulation values set by the Japanese authorities.”

This video report from Channel 4 News shows a Japanese cabinet minister eating produce grown in Fukushima, to encourage other citizens to do the same, but also includes video of an employee of the stricken plant’s operator admitting that the total release of radiation “could eventually exceed Chernobyl.”