On 6 October a report came out that some test data for the neutron shielding material used in spent fuel transport casks had been altered. The material was used in casks produced for Genden Koji, a subsidiary of the Japan Atomic Power Co, by five cask manufacturers. It is a synthetic resin material containing boron which acts as a moderator and absorber of neutrons. Apparently the density of some of the material was less than the specified value but this fact was covered up by altering the test data. A total of 52 casks wereproduced and they are widely used by the Japanese nuclear industry.
Tokyo Electric reported that it had 6 of the transport casks at Fukushima Daiichi and 2 at Kashiwazaki. The Fukushima casks have been used on 40 occasions for on-site spent fuel movements and the Kashiwazaki casks have been used four times. Whenever they are used TEPCO takes gamma and neutron measurements at the cask surface and at 1 metre around the periphery of the cask. The readings have always been below the permissible limits.
The same type of cask was used for the shipment of spent fuel from the Fukushima Daini plant to Rokkasho Mura on 2 October and on this occasion also, the radiation readings were below the limits. Consequently Tokyo Electric considers this may not be a serious problem from a practical point of view.
However, falsification of data is a very sensitive matter in Japan. False reporting by PNC at the time of the Monju sodium leak and the Tokai bitumen facility fire led to the corporation’s downfall. The Rokkasho Mura reprocessing plant is in Aomori Prefecture, and the prefectural assembly was angered by the news. The governor has said that the prefecture will not discuss further storage of spent fuel at Rokkasho until the problem has been fully investigated. It is therefore unlikely that the second shipment of spent fuel, which had been scheduled for 27 October will take place.