Time: About 10:35 a.m., Thursday, September 30, 1999. Place: Conversion Test Building, JCO, Ltd.
An area radiation monitor was activated at the Conversion Test Building of the JCO Co., Ltd. Three workers were exposed to radiation and were taken to National Institute of Radiological Science. Two of them seriously. Details are being investigated.
The cause is now under investigation. It is fact that it occurred during transfer of low enriched uranium in nitric acid. A maximum dose of 084 mSv/h was recognised at the boundary of the site. A maximum dose rate (neutron) of 4.0 mSv/hr was recognised at the boundary of the site. STA's Action & Strategy: the evacuation was to 350 m. Most of the cooling water has been drained from the jacket. After that the dose rate of neutron decreased at the boundary of the site. Boron injection into the container is being considered now.
Justification of Rating:
Provisionally rated at INES level 4 based on on-site and off-site impact.
Event date: Thu, 30-09-1999