Management of used nuclear fuel is a major technical challenge faced by nuclear energy producing nations worldwide. In Canada, the Nuclear Waste Management Organization is responsible for the design and implementation of a deep geological repository (DGR), which will be placed ~500 m below ground surface in a stable host rock to safely contain and isolate used fuel. Within a DGR, used nuclear fuel will be placed in used fuel containers (UFCs) that are encased in copper because of copper’s corrosion resistance. The UFCs will be surrounded by highly compacted bentonite to suppress the transport of corrosive agents to the UFC and limit the movement of radionuclides out of a DGR in the unlikely case of a breach. Over the design lifespan of one million years for the DGR, it is possible that sulfate-reducing bacteria near the bentonite-host rock interface can produce bisulfide (HS-) that can be transported to the UFC surface and potentially corrode the outer copper barrier. Therefore, it is crucial to understand HS- transport mechanisms through bentonite to assess the long-term performance of a DGR. This study aims to quantify HS- transport through bentonite using through-diffusion experiments under a range of anticipated DGR and bentonite conditions (e.g., temperature, ionic concentration, bentonite densities). In addition, as geochemical reactions/sorption are expected to affect HS- transport, batch experiments are being conducted to understand these processes independent of transport. The preliminary batch of experimental results show that ~85% of HS- was partitioned from the aqueous to solid phase within first hour and ~97% after 24 hours. However, this partitioning efficiency decreased with increased liquid-to-solid ratio because of the reduction in available reaction/sorption sites on the bentonite. This presentation shows the results from both transport and batch experiments performed on the bentonite under relevant DGR conditions.

Smouldering is a flameless form of combustion driven by exothermic oxidation surface reactions within a porous medium. Smouldering is being harnessed by engineers to remediate liquid hydrocarbon and Per- and Polyfluoroalkyl substances (PFAS) contaminated soils, drive waste-to-energy processes, and to provide off-grid sanitation solutions in the developing world. In all applications, initial heat is supplied to a small ignition region and air is injected to support self-sustaining smouldering. However, engineers and researchers have only a few tools to utilize and study smouldering, and this is a key limitation. This work addresses this limitation via developing a novel multidimensional, thermodynamic-based smouldering model. This model is valuable for both engineers and researchers to gain a deeper understanding into key physical (e.g., temperature, air flow, and oxygen distribution), chemical (e.g., a non-uniform oxidation reaction), and operational processes in smouldering systems (e.g., the effects of radial heat losses on energy efficiency). As smouldering gains popularity as a novel technology, there is a growing need for robust smouldering models. This presentation highlights both the model development and validation from highly instrumented experiments. These results highlight the processes that govern key operational characteristics, such as peak temperature and air flow distributions (critical for PFAS remediation) and overall energy efficiency (critical for waste-to-energy and sanitation purposes). Altogether, this work is anticipated to support investigating, designing, and optimizing the future smouldering systems for a range of applications such as PFAS remediation, waste-to-energy, and improving sanitation in the developing world.