ICONE23-1677 THE LONG-TERM SAFETY ASSESSMENT OF THE PEM METHOD

Abstract

The PEM (Prefabricated engineering barrier system module) concept is one of the promising methods of the emplacement of EBS (engineered barrier system) for high level radioactive waste in Japan. To chose this method as a most potential one, the engineering feasibility and the long-term stability must be evaluated. The key technology of assemblage and emplacement of PEM has been partly demonstrated in the laboratory. While the long-term issues such as chemical interactions between buffer materials and residual materials such as the metal shell and concrete supports by using the numerical analysis coupling the mass-transport and chemical reaction are focused in this study, because it could degrade the performance of buffer material by chemical interaction and degrade the confinement performance of overpack by passivation. In this study, The mass-transport-chemical reaction coupling analysis is performed in consideration of iron corrosion and layer formation of corrosion product on the surface of overpack/metal shell, diffusion of ferrous ions in buffer material, backfill material and concrete support, dissolution of buffer material, backfill material and concrete support, and precipitation of secondary minerals. The analytical results show that there was a little amount of the alteration of buffer material, because much of ferrous ion was precipitated as magnetite mainly on the surface of overpack/metal shell, while other ferrous ions contributes the alteration of bentonite, such as chamosite and greenalite. Because the alteration of bentonite is limited to the vicinity of the interface between the bentonite buffer and the overpack/metal shell, it was suggested that the durability of buffer material is maintained at the view point of low water permeability. Then, it was suggested that the change of EBS is not effect on confinement performance of overpack at the view point of pH.