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Background
Usually, the JCO fuel production plant at the Tokaimura plant processed uranium oxide for commercial reactors, which usually contains less than 5 percent uranium 235. However, the JOYO experimental fast reactor required uranium-enriched to 18.8 percent uranium 235. Workers were working with this material in the test facility. This facility was used only a couple of months a year, and two of the workers hadn't worked there before. -
When and Where
A private-sector nuclear fuel-processing facility in Tokaimura, Japan
September 30, 1999
10:35 am -
Chain Reaction
To make the rods, a precipitation tank was encased in a jacket that circulated cooling water. This jacket both reflected neutrons back and allowed easy heat removal. Ouchi and Shinohara were turning the precipitation tank into a low-power nuclear reactor. The chain reaction began when the total amount of uranium in the tank reached 16.1 kilograms-nearly seven times the authorized amount. At 10:35 an intense burst of neutrons and gamma rays were emitted for almost 20 hours. -
The Beginning
Two workers, Ouchi and Shinohara were working with their supervisor, Yokokawa. The production plant processed uranium oxide to make fuel rods. -
The Accident
Ouchi and Shinohara, who were working next to the tank, saw the blue flash of radiation. They immediately fell ill due to radiation poisoning. Yokokawa, in an adjacent room, was less severely affected. Gamma radiation alarms sounded and the evacuation of the site began. -
Workers
Ages when accident occurred:
Hisashi Ouchi, age 35, died 83 days later
Masato Shinohara, age 29, died 7 months later
Yutaka Yokokawa, aged 54, death unknown -
Hospital
After arriving to the hospital, Yokokawa received 3 sieverts, Ouchi 10, and Shinohara 17. They were all treated for radiation poisoning, each awake during the treatment. They had symptoms of nausea, diarrhea, and dehydration. They were all severally wounded and the two workers died. -
Before Testing for Radiation Poising
JCO took more than an hour to inform the local authorities about the accident, and the central government waited 12 hours before warning 310,000 residents within a 10 km radius of the site that they should stay indoors and close their windows. Roads were closed, schools shut, and rail services suspended. The authorities advised residents not to drink water from wells or harvest their crops. The all clear came 27 hours after the accident. More than 10,000 residents have requested medical checks. -
Aftermath
A farmer continues to work in the shadow of the JCO Uranium Processing Plant. -
The End (ish)
The last worker apart of the accident died.
But the radiation levels are still high.
