Safety Function of Cementitious Materials and the Analytical Assessment of Long-Term Evolution of Cement-Bentonite Interface for Geological Disposal in Japan

Cementitious materials used in geological disposal repositories are expected to have various functions for construction, operation and closure of the high-level radioactive waste (HLW)/TRans-Uranic (TRU) waste repositories and they also have functions for safety. In the long term after closure of the repositories, cementitious materials are expected to reduce the release of radionuclides from the waste. However, the expected performance of cementitious materials may decrease in the long term because of their gradual dissolution/alteration. In addition, there is a concern that the high pH groundwater due to alkaline ions leached from cementitious materials may degrade the safety functions of other components (buffer, backfill, host rock) of the repositories. Therefore, in order to understand how the expected safety functions of the cementitious materials and other components can be achieved in the post-closure period, NUMO carried out the analytical evaluation of the evolution of each component. The results showed that most of the cementitious materials and other components will remain during a long-term post-closure period. At present, we are aiming to improve the reliability of the analytical model and to develop a more realistic nuclide migration model that reflects the effect of cementitious materials on reducing mass transfer.