Conceptual and numerical models of solute diffusion around a HLW repository in clay

Reactive transport models have been utilized to simulate solute diffusion, canister corrosion, interactions of the corrosion products with bentonite, and the long-term hydrochemical evolution of porewater composition around radioactive waste repositories. These models often depend on simplifications regarding the geometry and dimensionality of the problem. In contrast, detailed three-dimensional flow and transport models are employed, which frequently oversimplify the geochemical reactions involved. Therefore, it is crucial to ascertain which simplifications and assumptions are acceptable. This study presents both conceptual and numerical models of radionuclide diffusion and sorption surrounding a high-level waste (HLW) repository in clay, following the French reference concept. Models of increasing dimensionality have been executed, including: (1) one-dimensional transport perpendicular to the axes of disposal cells; (2) one-dimensional axisymmetric transport for bounded and unbounded domains; (3) two-dimensional transport through vertical planes; and (4) one-dimensional vertical transport from the disposal cells into the overlying Oxfordian formation. The model results were compared to assess the effectiveness of each approach.