First-Principles Study of UO ₂ Lattice Thermal-Conductivity: A Simple Description

Abstract

Modeling the high-T paramagnetic state of bulk UO2 by a non-spin-polarized calculation and neglecting the Hubbard-U correction for the f electrons in U atoms, the lattice thermal conductivity of bulk UO 2 is investigated by the exact solution of the Boltzmann transport equation for the steady-state phonon distribution function. The results show that TA branches corresponding to U-atoms vibrations have the largest lifetimes and therefore have dominant role in thermal conductivity, while the optical branches corresponding mainly to O-atoms vibrations have the shortest lifetimes. Our results show a very good agreement with the experiments. The calculations are repeated for bulk UO 2 with different U-235 concentrations of 3%, 5%, 7%, and 20%, and the results show a small decrease of thermal conductivity which arise from scattering of phonons by impurities.