Suppressed thermal conductivity in hyperstoichiometric uranium dioxide controlled by phonon lifetimes

Abstract

Thermal transport in nuclear fuels used for nuclear energy applications is directly tied to performance and reliability. Uranium dioxide (UO2), one of the most important nuclear fuels, can accumulate excess oxygen atoms as interstitial defects, which significantly impacts thermal transport properties. In this study, thermal conductivities and inelastic neutron scattering (INS) measurements on UO2+x were performed at low temperatures (2–300 K). The thermal conductivity of UO2+x (x = 0, 0.03, 0.04, and 0.11) is significantly suppressed compared to UO2 except near the Néel temperature TN = 30.8 K, where it is independent of x. INS measurements demonstrate that the heat capacities and phonon group velocities of UO2 and UO2.08 are similar, and the suppressed thermal conductivity results from smaller phonon lifetimes. These perceptions advance our understanding of thermal transport properties in advanced nuclear fuels and guide safe and economic utilization of nuclear energy.