The final report on the accident said that the maximum measured dose to the general public (including local residents) was 16 mSv, and the maximum estimated dose 21 mSv.While 160 TBq of noble gases and 2 TBq of gaseous iodine were apparently released, little escaped from the building itself. At the time, Japan limited workers’ exposure to radiation to 50 millisieverts a year. They are correspondingly less regulated in some countries, such as Japan.The 1999 Tokai-mura accident was in a very small fuel preparation plant operated by Japan Nuclear Fuel Conversion Co. (JCO), a subsidiary of Sumitomo Metal Mining Co. Neutron radiation had ceased.The radiation (neutron and gamma) emanated almost entirely from the tank, not from any dispersed materials. The installation consists of three auxiliary uranium conversion buildings:. No major civil reactor uses uranium enriched beyond 5% U-235.While this was Japan's first such accident, similar criticality incidents have occurred, especially in US and Russian military plants and laboratories. However, owing to the detection of low levels of iodine-131 being released to the environment through the exhaust, it was later decided to stop ventilation and to rely on the passive confinement provided by the building.Five hours after the start of the criticality, evacuation commenced of some 161 people from 39 households within a 350 metre radius from the conversion building. The three had apparently received full-body radiation doses of 16-20,000, 6-10,000 and 1-5000 millisieverts (about 8000 mSv is normally a fatal dose), mainly from neutrons.

The accident happened on September 30, 1999.

* on basis of IPSN report quoting fissions ranging from 10The fuel preparation accidents were all in wet processes, due to putting too much uranium-bearing solution in one tank. Akashi, M., Aoki, H., Endo, A., Fujimoto, K., Homma, T., Kukita, Y., … Zombori, P. (2000). This incident led Japanese … Over twenty people were exposed to radiation.The second incident on 30 September 1999 happened at the JCO plant. None of the previous accidents resulted in significant release of radioactivity outside the plants. The mixing designed to occur in the storage column was instead undertaken by mechanical stirring in the precipitation tank, thus bypassing the criticality controls. One died 12 weeks later, another 7 months later. )The criticality continued intermittently for about 20 hours. The Tokaimura nuclear accident was a serious nuclear radiation accident in Japan. It was essentially an 'irradiation' accident, not a 'contamination' accident, as it did not result in any significant release of radioactive materials. Dutch radio news broadcast higher numbers of workers that inhaled the contaminants.PNC management mandated workers to falsely report the chronological events leading to the fire in order to cover up lack of proper supervision.Later Prime Minister Ryutaro Hashimoto criticized the delay that allowed radiation to continue to impact local areas.The second, more serious Tokaimura nuclear accident (The JCO facility started to dissolve and mix high-purity enriched uranium oxide with nitric acid to produce uranyl nitrate for shipping on 28 September 1999.

This surprising accident of "criticality"came about in October 1999 in Japan. The water served as a By mid-afternoon the plant workers and surrounding residents were asked to evacuate. Tokaimura's location and available land space made it an ideal investment for nuclear power production.

Nuclear power has become an important energy alternative for natural-resource poor Japan to limit dependence on imported energy. Seven workers immediately outside the plant received doses estimated at 6 - 15 mSv (combined neutron and gamma effects).