Investigating the topotactic transformation from UO2 to U3O8

The oxidation of uranium dioxide, 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 performance and safety. Our recent lab-based work has shown that the UO2 (001) surfaces oxidise to form U3O8 (130) in a topotactic transformation. This study aims to investigate this transformation using in-situ x-ray diffraction measurements of a UO2 (001) single crystal thin film as it is oxidised by heating in an oxygen atmosphere. The high flux, and nm beam size at ID11 uniquely enable us to measure single crystal diffraction from such a small sample. These results will provide significant insight into the oxidation mechanism from UO2 to U3O8 and the structures of the intermediate stoichiometries.