Modeling oxygen diffusion in UO₂±x, PuO₂±x, and (U,Pu) O₂±x systems

This paper combines molecular dynamics, kinetic Monte Carlo, and density functional theory (DFT) methods to calculate the diffusion coefficients of oxygen vacancies and interstitials based on the migration of point defects on the lattice in UO₂±x,PuO₂±x, and (U, Pu) O₂±x systems. The valence and electronic structures of oxygen defects in the MO₂±x system are considered, the configurations of oxygen vacancies and interstitials were identified using the DFT and lattice dynamics methods, and the influence of cation valence change on oxygen diffusion were analyzed quantitatively. The chemical and self-diffusion coefficients in the different stoichiometric MO₂±x systems were obtained on the basis of the defect chemistry theory. In addition, the oxygen diffusion model of the MO₂±x system, considering the effects of cation valence change due to local charge conservation effect, is constructed at the mechanistic level, and the relationships between the diffusion coefficients and the O/M ratio, temperature, Pu concentration, and oxygen partial pressure were analyzed. The findings of this paper provide reference parameters for macrobehavioral analyses of mixed-oxide and UO₂ fuels, such as constituent redistribution and fuel restructuring. The method in this paper also provides a fresh perspective for the simulation and calculation of oxygen point defect behavior in oxide systems with variable valence cations.