Modeling Defect-Mediated Diffusion in Cr-Doped UO 2 using a Variable-Charge Interatomic Potential
Résumé
Chromium doping of uranium dioxide is one of the different strategies for the development of Accident Tolerant Fuels (ATFs), promoting a large-grained microstructure that is anticipated to enhance fission gas retention. However, the underlying atomic-scale mechanisms governing this behavior remain incompletely elucidated. This study aims to clarify these mechanisms by systematically investigating defect energetics and diffusion dynamics in Crdoped UO 2 using a semi-empirical tight-binding (SMTB-QB) potential, benchmarked against Density Functional Theory (DFT) calculations. Our approach combines static calculations for defect incorporation and migration energies with high-temperature molecular dynamics simulations to compute atomic diffusion coefficients. Results show that the SMTB-QB model reproduces the stability hierarchy of defects, identifying uranium substitutional sites as energetically favorable. Notably, our calculations reveal that the presence of chromium lowers the uranium migration barrier by approximately 1 eV, resulting in a 1.5-to 2-fold increase in the uranium diffusion coefficient. These findings provide a direct atomistic explanation for the enhanced uranium diffusion that promotes accelerated grain growth, a mechanism acting in concert with proposed liquid phase effects, thereby validating the SMTB-QB potential as a tool to refine multi-faceted fuel performance models.
