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.”
Full text, charts, and videos are available at “A Look at the Nuclear Accident Scale”.