A Mixed-Potential Model to Predict Fuel (Uranium Dioxide) Corrosion within a Failed Nuclear Waste Container

A mixed-potential model is described to predict the corrosion behavior of used nuclear fuel inside a steel-lined failed Canadian nuclear waste container under anticipated waste vault (repository) conditions. The model accounts for the effects of the alpha radiolysis of water, the precipitation of corrosion products on both the fuel and the carbon steel (CS), and redox reactions between species produced by either radiolysis or corrosion at the fuel surface and by corrosion on the CS liner. The model is based on a series of ten one-dimensional reaction-diffusion equations, each describing the mass-transport, precipitation/dissolution, adsorption/desorption, and redox processes of the ten chemical species included in the model. These equations are solved using finite-difference techniques. A three-layer spatial grid is used, with the two outer layers (of time-varying thickness) representing porous precipitated corrosion products on the uranium dioxide (UO₂) and CS surfaces. The middle layer represents a layer of groundwater solution in the saturated failed containers. Electrochemical rate expressions are used as boundary conditions for species that participate in interfacial electrochemical reactions.