Investigating the structural and chemical properties in the oxidation of U-Th MOx

The long-term stability of uranium dioxide spent nuclear fuel is of significant concern to the UK nuclear industry. UO2 oxidises to U3O8 during long-term waste storage, altering the structural and chemical properties and adding complexity to its safety performance as a waste form. Spent nuclear fuel can be combined in a solid solution with ThO2 to provide non-proliferation benefits and improved long-term stability. Previous investigation into the oxidation of U-Th MOx indicate oxidation is fully inhibited by a very small quantity of doped thorium. Where oxidation did occur, the structural transformation has significant differences to pure UO2, with one expected stable phase being entirely missing. In this proposal, we aim to correlate the structural and chemical changes occurring in the oxidation of U-Th MOx, utilising both in-situ diffraction and spectroscopy measurements to determine the overall inhibition mechanism.