Thermal conductivity and diffusion mechanisms of noble gases in uranium dioxide: A DFT+U study

The bulk properties of uranium dioxide (UO₂) have been investigated using Hubbard corrected density functional theory (DFT + U) calculations. Monitoring of the occupation matrix for $5f$ electrons of the uranium atoms is found to be crucial to avoid metastable state solutions and consequently to obtain the true ground state properties of bulk UO₂. The lattice contribution to the thermal conductivity was obtained by the solution of the Boltzmann transport equation for phonons based on the interatomic force constants obtained from DFT + U calculations. Furthermore, the relative stabilities of noble gases (He, Ne, Ar, Kr, and Xe) in the octahedral interstitial site of bulk UO₂ and their migration are revisited. The effect of the supercell approach for point defects is taken into account by considering the long-range elastic interactions. The computed incorporation energies and energy barriers indicate a size-dependent mechanism for the interstitial migration of noble gases.