What’s the News: Japan raised its assessment of the severely damaged Fukushima Daiichi nuclear power plant to Level 7, “Major Accident,” the highest ranking on the International Atomic Energy Agency’s International Nuclear and Radiological Event Scale. The explosion at Chernobyl in 1986 is the only other nuclear accident to be ranked at Level 7. Both accidents were extremely severe, the two largest nuclear power accidents ever—but there are some big, important differences between them.
Reactor 3 at the Fukushima Daiichi plant, on March 24
What’s the News: A non-peer-reviewed study (pdf) publicized last week by radioactivity-detection expert Ferenc Dalnoki-Veress suggests that nuclear fission reactions continued at Japan’s Fukushima nuclear power station well after the plant’s operators had allegedly shut down the reactors there. The paper says there may be what are called “localized criticalities” have occurred in the plutonium and uranium left in the reactors—little pockets of fuel that have gone critical, propagating the nuclear chain reaction and generating potentially harmful radiation. The existence of criticalities is controversial: some researchers say there are certainly none; Dalnoki-Veress himself says it’s only a possibility.