Migration Behavior of Technetium-99 in Granite, Clay Rock, and Shale: Insights into Anionic Exclusion Effects

One of the key tasks in the geological disposal of radioactive waste is to investigate the blocking ability of different host rocks on nuclide migration in the disposal site. This study conducted experimental and numerical methods to the adsorption, diffusion, and advection-dispersion behavior of ⁹⁹Tc in three types of rocks: granite, clay rock, and mudstone shale, with a focus on the influence of anion exclusion during migration. The research results found that the three types of rocks have no significant adsorption effect on ⁹⁹Tc, and the anion exclusion during diffusion and advection-dispersion processes can block small "channels", causing some nuclide migration to lag, and accelerate the nuclide migration rate in larger "channels". In addition, parameters characterizing the size of anion exclusion in different migration behaviors, such as effective diffusion coefficient (De) and immobile liquid region porosity (θim), were fitted and obtained.