Nuclear Emergency Is Worst in Decades





The earthquake and tsunami that battered northern Japan on Friday set in motion one of the worst nuclear accidents in over two decades.

The International Atomic Energy Agency rates the severity of radiological events, with a scale starting at one, an “anomaly,” and rising to seven, a “major” accident. Six and seven designate full meltdown, where the nuclear fuel or core of a reactor overheats and melts. The scale of the ensuing uncontrolled release of radiation that follows differentiates the two. Partial meltdowns, in which the fuel is damaged, are rated a four or a five.

The accident at Chernobyl in the former Soviet Union in 1986 — which killed 56 people directly and thousands of others through cancer and other diseases — was the only nuclear accident so far to have been designated a seven. Just one other accident has surpassed five on the scale: an explosion of dried radioactive waste at the Mayak Nuclear Power Plant near the Soviet city of Kyshtym in 1957. The blast produced a radioactive cloud that spread for hundreds of miles over what is now Russia, forcing the evacuation of 10,000 people and causing the deaths of at least 200.

The Mayak blast was rated a six on the atomic agency’s scale....

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