Lawrence Berkeley National Laboratory

Coupled thermal-hydro-mechanical (THM) numerical modeling is conducted to study thermal management associated with geologic disposal of spent nuclear fuel (SNF) in large dual-purpose canisters (DPCs). DPCs, are containers designed for SNF storage and transportation and if determined to be feasible for permanent geological disposal could provide a cost effective disposal solution. However, one of the challenges to direct disposal of DPCs is thermal management to avoid overheating of the Engineered Barrier System (EBS), including bentonite-backfill used as a protective buffer. The model simulations show that the use of a backfill that is thermally engineered for high heat conduction can reduce the EBS temperature to acceptable levels for disposal of large waste canisters in backfilled tunnels. On the other hand, the use of high heat conduction backfill will not reduce the far field rock peak temperature that can occur several thousand years after closure of the repository. This longer term host rock peak temperature generates thermal-poro-elastic stress and geomechanical changes that must be considered in the thermal management and design of a repository.