DFT+ U Study of the Thermal Conductivity and Noble Gas Impurities in Uranium Dioxide

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 energy and energy barriers indicate a size-dependent mechanism for the interstitial migration of noble gases.