In this study, the diffusion behavior of cesium and selenium with 10−4M concentration in mudrock was studied by trough-diffusion tests and summarized in order to provide confidence on long-term
performance assessment of nuclear waste repositories. The diffusion process of Cs and Se reached equilibrium after 60 and
500 days, respectively. Besides, it also displays that the distribution coefficients (Kd) of Se in through-diffusion tests is higher than that of Cs in agreement with that obtained from the batch method. The Kd value (15.14±1.99 mL/g) of Cs by diffusion techniques is equivalent to that of batch method (15.10±0.40 mL/g) because sorption
of Cs was assumed to fast sorption step. However, the Kd value of Se (137.58±12.20 mL/g) derived from the diffusion technique is higher than that from batch tests (76.72±2.96) and
showed an obvious variation with Kd of Cs. The difference of Kd between diffusion and batch methods resulted from the fact that 14 days were not long enough to reach equilibrium or stable
state in the batch method.