Interface Issues Arising in Interim Storage Facilities Using Storage/Transport Dual Purpose Dry Metal Casks in Japan. Annex VIII

The annual amount of spent fuels (SFs) discharged by the operation of commercial reactors nowadays is estimated to be around 10 000 tU level worldwide. While the amount of SFs already reprocessed account about one-third, the rest are currently stored in storage facilities, typically, in wet pools attached to nuclear power plants (NPPs). Cumulative amount of SFs stored is estimated to be about 250 000 tU by 2010 (I. Hanaki, Japan). While wet pool system is dominant in storage facility designs, new design concepts for storage facilities have been continuously developed. One of these new designs is that using dual purpose dry metal casks. "Dual" here means that the casks are not only designed as storage containers, but also designed as transport containers that will satisfy relevant regulatory requirements for transport of radioactive materials such as TS-R-1. Advantage of adopting such "dual" design in storage facilities lies in that this could contribute to reduce the burden associated with handling operations, because, under such designs, SFs once loaded into casks can easily be "transported" to storage facilities, and after storage of several decades, they can again be "transported" to their destinations, regardless they are reprocessing facilities or final disposal sites. Other than these, adopting this kind of design can reduce the amount of radioactive wastes discharged through storage operation, thus can reduce operation costs while maintaining safety level. In Japan, where 53 commercial NPPs are now in operation and with the annual amount of SFs produced sums up to about 1000 tU, keen needs are perceived among SFs producers (namely, utilities) to secure adequate SFs storage capacity. Therefore, a new application for constructing storage facility of 3000 tU scale in Mutsu city, located in northern part of Aomori prefecture, has been submitted in March 2007 by a subsidiary company of utilities named RFS (Recyclable Fuel Storage Company), using 288 large scale dual purpose dry metal casks. The basic concept of this facility is similar to the one already in operation in Germany (BLG at Gorleben), with one important difference that no storage of HLWs containers are planned in Mutsu. Other aspects of the facility designs are similar, including that the both facilities do not equip with hot cells that will enable the casks to be opened for inspections during storage period