Matrix diffusion and sorption of Cs, Na, I and HTO in granodiorite; Laboratory results and their extrapolation to the in-situ condition

Tachi, Yukio  ; Ebina, Takanori*; Takahashi, Hiroaki; Nemoto, Kazuaki; Suyama, Tadahiro*; Martin, A.*

Matrix diffusion and sorption of radionuclides in crystalline host rocks are key processes controlling safe geological disposal of radioactive waste. Diffusion and sorption parameters for Cs, Na, I and HTO were determined by laboratory experiments using granodiorite samples from the Grimsel Test Site, Switzerland. The De values derived were in the order Cs Na HTO I. The capacity factor and Kd values show the same trends. Depth profiles of Cs and Na obtained by abrasing samples after a diffusion period showed typical dual profiles. The results of in-situ long-term diffusion tests at GTS were interpreted by using GoldSim code and transport parameters based on laboratory results and their extrapolations to in-situ conditions. These model calculations could the in-situ LTD results of Cs and Na reasonably well, although it was difficult to interpret HTO results. Key findings from these comparative studies between laboratory experiments and in-situ LTD tests were discussed.