Chemistry Control During Long-Term Storage of SMR Used Fuel

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Small modular reactors (SMRs) have been identified as having great potential to meet society's needs for carbon-free, safe, and cost-effective energy. The proposed, long-term disposal of Canada's current used nuclear fuel is in a deep geological repository (DGR), with waste forms from new nuclear technologies currently planned to be stored likewise. As DGR storage is expected to last centuries, scenarios such as water infiltration into storage containers, seeping through the outer defense barriers, require consideration. With a variety of proposed SMR fuel types, sizes, and compositions, some fuel waste forms may require further processing to meet the waste acceptance criteria for Canada's future DGR. This is particularly important for SMRs proposing to use sodium metal as a layer between the fuel and the fuel cladding to improve heat transfer, as sodium is highly reactive with water. Experiments on water ingress through storage canisters and fuel cladding have not yet been adapted to SMR spent fuels. In partnership with the CanmetMATERIALS laboratory in Hamilton, Ontario, a custom test cell, representative of the current defence in depth approach to DGR storage, will be designed and commissioned to conduct leak testing. Experiments will simulate groundwater ingress into the used fuel storage container along with some initial cladding damage. Changes to the local environment (pH, temperature, hydrogen gas evolution) due to the resulting water-sodium bond interactions will be monitored, including the subsequent degradation rate of the cladding and storage container materials. This program supports the pathway to commercialization of SMRs in Canada, ensuring that several knowledge gaps in the safe, long-term storage of SMR fuel in a DGR environment are addressed.