DIFFUSION OF COBALT, CESIUM AND EUROPIUM IN OPALINUS CLAY

This study addresses the diffusion of some representative sorbing elements, as cobalt, caesium and europium into the Opalinus Clay (OPA). The methodology used to determine diffusion coefficients is the "instantaneous planar source" method. In this setup, a paper filter impregnated with the tracer, is introduced between two clay samples, avoiding the contact between the tracer and the experimental vessels. The apparent diffusion coefficients (D a ) perpendicular to the bedding plane, obtained with this method, fitting the experimental results with an analytical solutions, were D a (Co) = (2.4-3.5)·10 -14 m 2 /s, D a (Cs) = (5.9-8.0)·10 -14 m 2 /s, and D a (Eu) = (1.0-2.1)·10 -15 m 2 /s respectively. With cobalt and caesium, classical in-diffusion experiments were also performed and similar D a values were obtained but within a large dispersion. To analyze the possible effects of the paper filter impregnated with the tracer on the determinations of D a , with the analytical solution, one experiment was also analysed using a detailed model of the setup. The good agreement between the two modelling approaches, confirms the validity of this experimental setup and the analytical model fitting procedure.