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.

英国核工业界高度关注二氧化铀（UO2）乏核燃料的长期稳定性。在长期废物储存过程中，二氧化铀（UO2）会氧化为八氧化三铀（U3O8），改变其结构与化学性质，进而增加该乏燃料作为放射性废物形式的安全性能评估复杂度。将乏核燃料与二氧化钍（ThO2）制备为固溶体，可获得防扩散效益并提升其长期稳定性。此前针对铀-钍金属氧化物（U-Th MOx）氧化行为的研究显示，仅需极少量掺杂钍即可完全抑制氧化反应。即便发生氧化，其结构转变过程与纯二氧化铀（UO2）存在显著差异，甚至缺失了一种预期的稳定物相。在本研究提案中，我们旨在结合原位衍射（in-situ diffraction）与光谱测量（spectroscopy measurements）手段，厘清铀-钍金属氧化物（U-Th MOx）氧化过程中发生的结构与化学变化，进而明确其整体抑制机制。