Publication Laka-library:
JCO Criticality Accidents and Local Residents: Damages, Symptons and Changing Attitudes (2001)
| Author | Hasegawa, Takubo, CNIC |
| Date | June 2001 |
| Classification | 4.21.8.20/03 (JAPAN - TOKAI MURA) |
| Front | 
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From the publication:
Foreword A criticality accident was triggered at 10:35 a.m. on 30 September 1999 at the conversion building of JCO CO. in Tokai Village, Ibaraki Prefecture - a village which has been the center of nuclear energy development in Japan. This criticality accident was the first of its kind in Japan, and it was the first example where people died of acute radiation injury in the course of carrying out tasks as part of Japan's "peaceful use of nuclear energy." It was also rare even in the international realm in that citizens were exposed to neutrons due to a nuclear accident, and thus the accident was widely reported in magazines and newspapers overseas. The accident occurred during the final process of preparing a solution needed for manufacturing fuel for the Joyo Experimental Fast Breeder Reactor. The solution instantaneously reached criticality because a large amount of this dangerous highly enriched uranium solution, containing 18.8% of uranium 235, was poured into a "precipitation tank" where criticality can easily be reached. Criticality, a nuclear chain reaction, continued for about 20 hours. Criticality was contained early in the morning of the next day, when the cooling water surrounding the precipitation tank was removed and borate solution was poured into the tank. Until that time, neutrons and gamma-rays were continuously emitted and radioactivity kept being produced. Local residents were either evacuated or advised to stay indoors. Transportation was greatly affected as trains went out of service and roads were sealed off. Among the three JCO employees who were exposed to lethal or nearly-lethal doses of radiation, Mr. Ouchi who was exposed to the highest dose died on 21 December 1999, and Mr. Shinohara, who was exposed to a lesser dose, also died on 27 April 2000. Mr. Yokokawa, who was exposed to the least dose among the three, was able to leave the hospital in mid-December 1999, but has not yet fully recovered. (1) The government recognized the seriousness of the accident and has been reforming laws and nuclear regulatory bodies to improve the administration of nuclear matters. However, the effectiveness of such reforms can only be evaluated after observing changes over a long period of time. While such reforms can not have worsened the conditions at nuclear facility sites, citizens must keep a watchful eye on whether the countermeasures implemented by the central government are adequate or not.
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