Abstract
A critical accident happened at JCO nuclear fuel conversion facility in Tokai-mura on September 30, 1999. After the accident, two workers died due to high dose exposure of gamma-rays and neutrons. Dose estimation for gamma rays was carried out using tooth enamel ESR measurement and the estimated dose was about 12 Gy. And also, the amalgams and gutter-percha which were filled in the teeth of the worker were collected and used to estimated beta- and gamma-ray dose from the induced activities of 64Cu, 108Ag, 110Ag, 110mAg, 197Hg and 203Hg. However, neutron dose estimations was not carried out using the induced activities in these samples. We determined specific activity of 110mAg and 65Zn in the samples measureing gamma rays with Ge detector at the Ogoya under ground laboratory, Kanazawa University. From the result of the measurement, specific activity of 110mAg/Ag:51(+/-)0.7Bq/g, and specific activity of 65Zn/Zn:38(+/-)11Bq/g was obtained Neutron dose was evaluated based on the neutron spectrum which was previously obtained simulating neutron released from a conversion tank at the time of the criticality accident as well as a Monte Carlo technique using a mathematical head phantom and MCNP code. The neutron dose was estimated to be 3(+/-)0.2Gy from Ag sample measurements, while Zn-samples gave a larger value of result as 21(+/-)7Gy with large uncertainty.
