Detailed Gas Generation and Transport Modelling at the Room and Repository Scale

摘要

The NWMO has undertaken a postclosure safety assessment of a conceptual deep geological repository for used nuclear fuel at a hypothetical sedimentary rock site in the Michigan Basin in Ontario. The assessment includes a Disruptive Scenario where container failure 10,000 years post-closure exposes steel components of the containers to groundwater. The migration of gas generated by steel corrosion processes is assessed through simulations conducted with the T2GGM code at the placement-room and repository scales. The model results indicate: 1) that room resaturation (in the absence of gas generation) is 90 percent complete by 10,000 years, 2) pore pressure in the host rock never exceeds 80 percent of the lithostatic stress, and 3) gas transport is primarily in gaseous (as opposed to dissolved) form and is substantially confined to the engineered sealing materials and excavation-damaged zone. The different scale models were linked through a manual iterative process, where gas flows calculated using the Room-Scale Model were provided to the Repository-Scale Model. End-of-room boundary conditions on the Room-Scale Model were adjusted based on Repository-Scale Model results and the process repeated until sufficient congruence was attained. Recent T2GGM code developments have included the capability to link different scale models explicitly. Preliminary results are presented that illustrate the advantages of this approach.