The accident began when workers were converting enriched uranium into oxide powder for use in preparing fuel for the Joyo experimental fast breeder reactor...
An inadvertent nuclear chain reaction, or so-called “criticality accident,” began at 10:35 AM local time on Thursday, September 30 at the JCO Co. Ltd. Conversion Test Building at Tokai-mura, Japan, about 75 miles northeast of Tokyo. The chain reaction, which gave off intense heat and radiation, could not be stopped until 18 hours later....
It appears that workers deliberately circumvented safety measures to save time. A solution of uranyl nitrate was transferred into a large-volume precipitation tank, rather than the smaller, cylindrical container required by regulations. According to JCO Inc. official Yutaka Tatsuta, one of the injured workers reported that some 16 kilograms of uranium solution had been poured into the precipitation tank, nearly eight times more than its criticality safety limit of 2.4 kilograms.
Workers reported seeing a blue flash and then started to feel ill. According to one report, “the area was wrapped in a haze of blue smoke.” Workers told plant staff that “they saw a blue flame rising from the fuel.” Kenji Sumida, a member of Japanese government’s Nuclear Safety Commission, concluded, “I know this is difficult to believe, but I think that we have no choice but to recognize this accident as having been critical.” The criticality continued for about 18 hours until the water that was moderating the flow of neutrons and allowing the chain reaction to continue was drained and the tank was flooded with boron, a neutron absorber.
Tokyo Electric Power, Japan's largest utility, made people even more nervous when it was found to have falsified its nuclear plant repair reports for 15 years.
Maybe the anti-nuclear power sentiment is fading though, as 8 new nuclear plants opened last year from Hokkaido to Kyushu.
I still don't think I'd be comfortable living next to a nuclear power plant, even if it gave off less greenhouse gases than a fossil fuel plant. Then again there are 18 nuclear-powered submarines at Pearl Harbor just a few miles from Honolulu. Each has a mini nuclear power plant on board.
