Structural Changes in Uranium Dioxide Induced by Chromia Doping—Insights from U-L3 EXAFS Under Varying Sintering Conditions and Dopant Level

Chromia (CrO_x) doping has become a key method for promoting grain growth and enhancing fission gas retention in uranium dioxide (UO₂), leading to the commercial development of products like 'ADOPT' and 'PROtect.' While much of the research is focused on the local structure and valence of chromium, less attention has been given to the U environment in Cr-doped UO₂, which was assumed to have minimal changes after being introduced with dopant levels of Cr. In this work, we observed non-trivial changes in the U local structure of Cr-doped UO₂ using extended x-ray absorption fine structure (EXAFS) when the material was sintered under varying oxygen partial pressures at high temperatures. These changes are driven by the valence states of Cr susceptible to oxygen partial pressures and temperatures during the sintering. The structural change by the Cr dopant level was also systematically investigated. These findings offer new insights into the fundamental behavior governing the diffusion of species, which influences the grain growth of the Cr-doped UO₂. In the context of fuel performance, this understanding will contribute to the development of enhanced nuclear fuels.