Determination of diffusion coefficients of dissolved gases in Boom Clay and Opalinus Clay

Diffusion coefficients of gases in Boom Clay and Opalinus Clay are investigated in the framework of characterisation of the formations and performance assessment of potential geological disposal of radioactive waste in these formations. The diffusion coefficients of Ne and Ar in Boom Clay were measured in a cross through diffusion experiment to verify if a relation exists between the diffusion coefficient and the size of the diffusing gas. This relation could then be used to determine the diffusion coefficient of H2, which has proven difficult to measure experimentally. Apparent diffusion coefficients of 5.1 * 10-10 m²/s for Ne and 2.0 * 10-10 m2/s for Ar were obtained. In a 2nd experiment, the diffusion coefficient of He in Opalinus Clay was measured. Profiles of natural tracers, like He, are used to characterise transport properties of argillaceous rock formations on a large spatial and temporal scale. An apparent diffusion coefficient of 4.0 * 10-10 m²/s was obtained for He.