Correlating the structure and crystal chemistry of oxidising UO2 nuclear fuel

The oxidation of UO2, is of major concern to the nuclear industry. As UO2 is oxidised to U4O9 and U3O8, either during burn-up or long-term storage, the physical and chemical properties of the fuel are altered, reducing their economic and safety performance. Our previous experiment at ID11 (MA4980) provided the first x-ray diffraction measurements of a single crystal U4O9 and U3O7, giving new insight into their structure, and showed that there are subtle structural changes within each phase, and potentially with varying stoichiometry and therefore uranium valence state. In this proposal, we aim to understand the uranium valence states present as stoichiometric epitaxial UO2 thin film single crystals (001) and (111), are oxidised. Using the unique capabilities available at ROBL, we can systematically correlate structural and chemical changes through the use of in-situ x-ray diffraction and x-ray spectroscopy, giving unparalleled insight into the evolution of valence states.