Migration of radionuclides released from waste solid in engineered barriers was modeled. Mass fluxes of 99Tc, 135Cs and 237Np at the buffer/rock interface were calculated. The model features (1) analysis on groundwater flow around a disposal pit, which shows that in a buffer material of compacted bentonite, the groundwater flow is negligible and the mass transport can be assumed diffusion controlled, (2) analysis on dissolution of waste glass and resulting release of radionuclides from the solid by considering geochemical interactions of groundwater with glass waste form, overpack material and buffer material, (3) analysis on migration of a redox-sensitive element, with the oxidation-reduction reactions incorporated, and (4) analysis on effects of waste geometries by comparing fluxes resulting from a cylindrical waste package and a spherical one.
The study is the first stage for fulfilling our goal to construct a scientifically-sound, integrated performance assessment model for geologic disposal of high-level radioactive waste. The effort presented in this study will help us define future studies to be directed.
by the Atomic Energy Society of Japan