Overview and consistency of migration experiments in clay

An overview is given about the types of migration experiments in clay and their corresponding mathematical models aimed to determine the product R of the diffusion accessible porosity  and the retardation factor R, and the apparent dispersion coefficient D. An important concern is consistency. Consistency requires a good correlation between the diffusion accessible porosity  of tritiated water and the independently measured water content. Migration experiments confirm this correlation and lead to the expected value of the grain density, showing that nearly the entire porosity is accessible for water diffusion. Another requirement for consistency is that different experimental set-ups lead to the same value for the migration parameters. The average values of the apparent diffusion coefficient of dissolved silica obtained with different types of tests in Boom Clay are respectively 6 10-13m2/s (In-Diffusion), 2 10-13m2/s (Percolation) and 9 10-13m2/s (combined glass-dissolution/diffusion). The values of R are around 60 to 70 (In-Diffusion) and between 100 and 150 (Percolation). Using fit results from the combined glass-dissolution/diffusion experiments with other results, leads to R values ranging from 40 to 90. The values of the migration parameters obtained from different types of experiments and the corresponding models are consistent.