Herewith, a report of an accidental NUCLEAR
criticality and consequent radiation release. Note
that Japan is non-Communist. Note also the level of
blinding stupidity. As Edward Teller once remarked,
Nothing is foolproof. Fools are so ingenious...
Japan’s Nuclear Criticality Accident
Steven Dolley Research Director Nuclear Control Institute
October 4, 1999
When and where did the accident take place?
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.
The accident began when workers were converting enriched uranium into oxide powder for use in preparing fuel for the Joyo experimental fast breeder reactor. This reactor is part of Japan’s plutonium-production program. The uranium was enriched to 18.8% U-235, far higher than the 3 to 5% enriched uranium used as fuel in Japan’s conventional nuclear power reactors. Breeder fuel, whether enriched uranium or plutonium, is far more susceptible to criticality accidents than power-reactor fuel.
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.
How much radiation was released?
At one point, radiation levels near the plant were 15,000 times above normal background. A total of at least 49 people were contaminated with radiation, including 39 JCO staff, seven residents, and three firefighters who transported the injured workers. Two of the workers received such high doses of radiation that they are not expected to survive.
--- Michael M. Butler wrote:
--One historical quibble on your otherwise quite worthwhile post: The way I heard it, the "going critical" of the radwaste was a _chemical_ criticality, not a nuclear one. You didn't specify, but I like to get that information out.
For those who don't know:
At least as I heard it, there was something like a mineshaft full of contaminated stuff that was largely ammonium nitrate. That substance is one which in crystalline form can achieve a chemical "critical mass" ("critical configuration" is probably a better term)--if you pile up enough, the physical pressure on the bottom crystals causes detonation. I'm not sure how far the detonation wave spreads. I believe they delivered the waste as liquid or sludge, and it didn't stay liquid. Oopski.
And yes, the end result was a large nuclear waste contaminated area. So it doesn't blunt John's point, necessarily.
John Marlow wrote:
> As to Mikle Lorrey's comment on "failing" to prove a > catastrophe resulting from nuclear mishaps--anyone > recall a certain Russian radwaste storage facility > going critical and devastating the surrounding > countryside?
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