Diffusion and sorption of Cs, I and HTO in samples of the argillaceous Wakkanai Formation from the Horonobe URL, Japan; Clay-based modeling approach

Tachi, Yukio  ; Yotsuji, Kenji; Seida, Yoshimi*; Yui, Mikazu

Diffusion and sorption behaviors of Cs, I and HTO in samples of the Wakkanai Formation from Horonobe URL were investigated as a function of ionic strength (IS) of synthetic groundwater by through-diffusion and batch sorption experiments. The values showed cation excess and anion exclusion effects, which were strongly dependent on IS; for Cs decreased as IS increased, for I showed the opposite dependency and for HTO showed no dependence. The Kd values for Cs determined by through-diffusion and batch experiments were in good agreement and decreased with IS as a result of competitive ion exchange. Diffusion and sorption behaviors were interpreted based on the clay-based modeling approach in assuming the clay components of illite and smectite control diffusion and sorption mechanisms. The model predicted the and Kd trends obtained by the series of experiments reasonably well, implying the key contribution of the clay particle and nano-size pore for ionic migration.