Unsaturated flow modeling in high-level nuclear waste repository

In the context of high-level nuclear waste repository safety calculations, the modeling of desaturation and saturation processes in low permeable porous media is of first importance. Indeed these processes are strongly coupled with mechanics, inducing host rock confinement properties changes. They also control corrosion and the other geochemical processes responsible for waste canister failure. Above all, desaturation and saturation time scales of the repository components determine the physicochemical behavior of the repository by trapping or not air in the system. In order to simulate unsaturated flow in the repository host rock media, we developed, in the Cast3m tool, a modified Richard's model with a storage coefficient. This allows to take into account the transient head inside a fully saturated area of the domain. Different spatial schemes are implemented (Mixed Hybrid Finite Elements, Finite Volumes (MPFA)) as well as different non-linear solving algorithms (Picard and Newton). In this paper, we present some classical validation cases of our model. Then we perform a 3D saturation computation of a repository drift seal and a repository gallery backfill. This enables us to evaluate the occurrence of air entrapment and the presence of fully saturated components.