Diffusion of Gases in Unsaturated Clay Based Materials

In many countries in Europe, clay-based materials are considered for safe disposal of high and intermediate level radioactive waste, either as an important component in the engineered barrier system, or as geological formation to host the repository. Furthermore clays under consideration all have high sorption capacity for many radionuclides. As these clay-based materials have a low water permeability, diffusion is the main transport mechanism. Hence, a good knowledge of relevant diffusion coefficients is important to assess the safety function of these clay materials. In literature, mainly diffusion coefficients for radionuclides have been reported as part of the inventory. However, next to the radionuclide inventory also gases are released (mainly generated by anaerobic metal corrosion) and knowledge of the diffusion coefficients of dissolved gases are also important because they are an essential parameter for evaluating the balance between gas generation and gas dissipation by diffusion. The diffusion of gases in fully saturated clays has been study and the characteristics have been determined. Hence, this study seeks to determine the diffusion coefficients of gases in partly saturated clays.