TOKAI-MURA, JAPAN IS A NEUTRON SCIENCE RESEARCH FACILITY A criticality accident occurred on September 30, 1999 at the uranium conversion facility of the JCO Company Ltd. in Tokai-mura, Japan. A collaborating scientific investigation team was organized in two groups, the first to carry out research on the environmental impact (the environmental research group) and the second to assess the radiation effects on residents (the biological research group). This report concerns only the activities of the environmental research group. NOTICE NO EFFECTS ON RESIDENTS IS GIVEN! Four investigative teams were sent on different dates to the accident site and its vicinity to collect samples. About 400 samples were collected and subjected to analysis. Some samples containing chlorine such as soil, chemical reagents and table salt have been collected in the JCO criticality accident site and analyzed to detect neutron-induced 36Cl (Clorine) with a half life of 301,000. years. Neutron dose and power released by the JCO criticality accident in Tokai-mura Abstract There was no monitor and no instrumentation to measure neutrons in the JCO facilities when the criticality accident began. Two neutron monitoring posts located at 1.7 and 2.0 km from the JCO site, however, recorded the process of the criticality accident from its beginning. Through the analysis of the monitoring data, neutron doses of 0.096 and 0.014 μSv were evaluated at 1.7 and 2.0 km, respectively. Neutron transport in air-over-ground geometry was calculated to over 2 km from the building where the criticality accident took place, assuming simple models for shielding. The neutron dose calculated at 1 m above ground was fitted to the measured data. The distances corresponding to neutron doses of 1, 0.1, 0.01 and 0.001 mSv were about 450, 700, 1000 and 1300 m, respectively. The neutron dose at 100 m was estimated to have been 81 mSv. The total power released by the accident was estimated to have been about 17 kWh corresponding to 1.9×1018 fissions of .
Posted on: Sun, 06 Oct 2013 09:31:26 +0000
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