T2GGM: A Coupled Gas Generation Model for Deep Geologic Disposal of Radioactive Waste

Deep geologic disposal of radioactive waste is being planned in a number of international programs. Within a deep geologic repository (DGR), gases can be generated by corrosion of metals and degradation of organics. Reactions, and thus gas generation rates, are dependent upon pressures, temperature, and the availability of water or water vapor within the repository. Furthermore, many reactions consume water. Consumption rates and repository state are not known a priori and are in general coupled processes. A numeric model of coupled gas generation and transport has been developed and implemented in the T2GGM code. T2GGM consists of a gas generation model (GGM), which calculates rates of gas generation and water consumption within the DGR due to corrosion and microbial degradation of the waste packages, integrated with the widely used two-phase-flow code TOUGH2, which models the subsequent two-phase transport of the water and gas through the repository and into the DGR shafts and geosphere. T2GGM has been applied to assess gas transport from a proposed low- and intermediate-level radioactive waste DGR and to study the impact of container corrosion in a hypothetical used fuel DGR.