Numerical simulation of coupled thermal-hydro-mechanical processes in geologic nuclear waste disposal with corrosion-induced gas generation

An important challenge in ensuring the long-term effectiveness of geological nuclear waste disposal is predicting the transportation of decay heat and gases released from nuclear waste canisters. In this study, thermo-hydromechanical (THM) coupled simulations were conducted using the TOUGH + FLAC3D simulator to predict the THM behaviors of a generic nuclear waste repository over 100,000 years following closure. The designed engineered barrier system (EBS) consists of the waste canister, backfill, and concrete liner. The objective of this study is to evaluate the long-term performance of the repository in the presence of continued hydrogen (H 2 ) and heat release around the canister. The simulation results show that thermal pressurization and gas accumulation significantly raise the pore pressure within the EBS and surrounding host rock, while the peak pore pressure is not likely to exceed the lithostatic stress so that there is no risk of widespread hydro-fracturing in the host rock. However, tension failure and fracturing can occur at the tunnel scale because of internal gas buildup. Meanwhile, the generated H 2 continuously migrates outward and tends to accumulate in the concrete liner and excavation disturbed zone surrounding the tunnel because of lower capillary pressure. Nevertheless, the fluids that may contain radionuclides will not leach into the confining units over a 100,000-year time frame. Our analysis indicates that for the assumed disposal system in Opalinus Clay, the generated heat and gas can gradually be transported through the host rock without significantly disturbing the isolation characteristics of the repository.