Modelling of Uranium Dioxide Corrosion under Flow Conditions

We apply a pore-scale reactive transport model to simulate the corrosion of uranium dioxide (UO₂) under flow conditions during geologic storage of spent nuclear fuel. Simulations are performed directly on the images of UO₂ fuel in a failed clad with different defect orientations. The impact of clad defect orientation on the UO₂ corrosion processes is investigated. The results show that the average corrosion rate of the fuel rod increases with the angle between the flow direction and clad fracture up to 180 degree. A thermal-chemical model is developed to study the effect of temperature on UO₂ corrosion. The results indicate that inclusion of thermal effect leads to faster corrosion rates for UO₂. The pH effect on corrosion rate is also discussed. It is found that higher pH limits the corrosion of UO₂ by reducing the reaction rate. This study can help improve the understanding of uranium dioxide corrosion in geologic repositories for long-term storage of spent nuclear fuels. The numerical method can also be used to predict the corrosion time of nuclear fuel and provide guidance for the safe operations and selection of the appropriate repositories.