Cesium sorption and diffusion in Bure mudrock samples

This work deals with cesium diffusion and sorption in rock samples from Bure (Meuse/Haute-Marne, France). Four different samples extracted from the Callovo-Oxfordian layer (between −423 m and −478 m) were investigated to quantify the Cs diffusion parameter range. HTO diffusion properties were also evaluated. The through-diffusion method was used in both cases. The steady-state was reached, allowing a direct access to the values of effective diffusion coefficients (De). Major attention was paid to experimental chemical conditions. Cs and HTO diffusion parameters were quite homogeneous for the different investigated rock samples. De(Cs) was found about one order of magnitude higher than De(HTO). Such observation was already reported in the literature mainly for compacted bentonite. Results presented here show this trend also exists in mudrocks. Batch tests were performed in order to characterize cesium sorption on ground Bure mudrock samples. The isotherms were fitted with a 2-site ion exchange model. This model was extrapolated to intact rock samples and coupled with diffusion equations, using the measured De(Cs) values. This coupled model was tested against experimental data measured in the transient part of Cs diffusion experiments. A fairly good agreement between model and experimental data was found.