Thermal-Hydraulic-Mechanical Processes Modeling to Evaluate Salt-based Repositories in the Long-Term

The coupled thermal-hydraulic-mechanical response of a hypothetical high-level nuclear waste repository in a saliniferous rock formation is explored in this study. Although only short-term results are presented in this paper, the ultimate aim of the ongoing research is to evaluate the mechanical and hydraulic barrier integrity of the repository over the long-term. The design adopted involves metallic waste packages horizontally disposed in drifts subsequently backfilled with crushed salt. Some of the THM interactions studied concern porosity and permeability changes within the backfill as consolidation occurs, and also permeability changes within the natural rock salt due to thermomechanically and hydraulically-induced damage processes. The simulations are conducted using an updated version of TOUGH2-FLAC^3D, developed at Lawrence Berkeley National Laboratory. The mechanical behavior of the host rock is modeled using the Lux/Wolters constitutive model, developed at Clausthal University of Technology. Well-adapted relationships are used to couple non-isothermal multiphase flow and geomechanics. In order to ensure the grids consistency, the TOUGH2 mesh is updated as large strains take place. The comparison between TH and THM results shows the relevance of the latter to better simulate the long-term response of structures envisaged for nuclear waste disposal in saliniferous formations.