Consistency of the strontium transport parameters in Boom Clay obtained from different types of migration experiments

Performance assessment calculations need accurate values for the transport parameters of radionuclides in Boom Clay. Consistency between the values of the transport parameters, determined from different types of diffusion experiments is studied for strontium. Therefore, a percolation test and two Through-Diffusion tests (on clay cores of different lengths) have been performed. All experiments lead to a robust value for the apparent diffusion coefficient of strontium between 5E-12 m2/s and 10E-12 m2/s. A reliable value for the product R of the diffusion accessible porosity  and the retardation factor R remains problematic. Fitting simultaneously the concentration decrease in the inlet as a function of time with the strontium profile of one of the Through-Diffusion experiments, leads to a value around 400. Estimating in another way R at the inlet/clay interface leads to a similar value. The values obtained from the percolation experiments are in line as well. However, fitting for both Through-Diffusion tests the outlet concentrations versus time leads to much lower values of R (0.15 and 0.5) Also, the strontium profile measured in the other Through-Diffusion test totally deviates from the predicted profile.