This is the final report on the unsuitable management of Bakelite plates containing radioactive materials on 23 October 2008 to establish the INES ratings.
On 23 October 2008, a person who possessed a large numbers of Bakelite plates emitting radiation (hereafter refer to as “the owner”) arrived the Ministry of Education, Culture, Sports, Science and Technology – Japan (MEXT) with having two sample plates, and the owner asked the MEXT for advice about treatment of them. Measurement of radioactivity in the MEXT indicated few-micro Sv per hour a plate. After the measurement, MEXT immediately sent two staff members of MEXT and specialists of radiation analysis to the place where the Bakelite plates were kept (Bunkyo-city, Tokyo), and carried out further investigation.
Area radiation dose rate around the place was measured and it was evaluated that the received radiation doses from May of this year, when the owner had moved the Bakelite plates to Bunkyo-city at three of neighboring houses were 19mSv, 16mSv and 5.8mSv. Based on the investigation and estimation, the MEXT gave the owner an administrative guidance to ensure the public safety.
Complying with the guidance, the owner accepted to transport the stock of Bakelite plates to the place (Iizuna-machi, Kamiminochi-gun, Nagano-prefecture) where the owner had been keeping the stock until this May, and the owner finished the transportation October 25. The safety at the place is kept enough.
On November 12, MEXT confirmed that the radioactive material contained in the plates was thorium by the information from the owner.
This rating was evaluated and finalized by MEXT with confirmation by the INES Evaluation Working Group under the MEXT held on 27 February 2009.
Event date: Thu, 23-10-2008