Long-term Sealability of Spent Fuel Casks

In Japan, fuel reprocessing is recognized as one of the policies of the nuclear fuel cycle. But, in the future, the discharge of spent fuel is expected to exceed the fuel reprocessing capacity. Thus, it is necessary to establish methods for intermediate storage of spent fuel before its reprocessing to give flexibility to the nuclear fuel cycle. The spent-fuel cask-storage method is rational and economical. It requires, however, the function of sealing radioactive materials in casks, and the storage duration may sometimes continue for 40 or 50 years, so casks must have long- term sealability. For this purpose, a survey and tests on the long- term sealability of spent fuel casks were started in our institute at 1985 to evaluate the sealability, and we have been striving to accumulate and expand our basic data since that time. This report presents the results of long- term sealability test of full- scale model casks which have been in progress since 1990. (O.Kato and C.Ito 1992) The purpose is to confirm the long-term sealability of the casks.