Influence of boundary condition of diffusion test method on migration parameter in compacted bentonite

Seida, Yoshimi; Tachi, Yukio  ; Yoshikawa, Hideki; Yui, Mikazu

The barrier function of engineering barrier in high-level nuclear waste repository is assessed by retardation parameters of radionuclides. To determine effective diffusion coefficient, De, in compacted clay system, outer reservoirs for diffusion source and drain are needed in diffusion test method with porous thin filters. This experimental configulation causes significant disturbances to De measured on the basis of reservoir concentration. In the present study, influence of boundary condition at reservoir-compacted bentonite boundary on effective diffusion coefficient measurement was examined from an electrochemical point of view. Electric potential difference at the boundary was measured to investigate partition of mobile ions (actual boundary concentration) and its influence on De with theoretical basis as a function of salinity of solution and compaction density of clay.