The effect of fission products Xe and Cs on the thermal conductivity of the U3Si2lattice: a first-principles study

Abstract

In the past decades, uranium silicide (U₃Si₂) as a promising accident tolerant fuel (ATF) has drawn considerable attention in the field of nuclear physics. In comparison with traditional nuclear fuel (UO₂), the U₃Si₂has higher thermal conductivity and uranium density, thereby resulting in lower centerline temperatures and better fuel economy. However, during the nuclear fission reaction, some unexpected fission products, such as Xe and Cs, are released and form the defective states. In this study, we explore the influence of Xe and Cs on the thermal conductivity of the U₃Si₂lattice from 200 to 1500 K using density functional theory calculations combined with Boltzmann transport equation. Our results reveal that the lattice and electronic thermal conductivities of defective U₃Si₂are reduced at a constant temperature, as compared with that of ideal system, thus resulting in a decrease of the total thermal conductivity. In the case of Cs occupation at U1 site, the total thermal conductivity (4.42 W mK^-1) is decreased by ∼56% at 300 K, as compared with the value of 9.99 W mK^-1for ideal system. With U1 and Si sites being occupied by Xe, the total thermal conductivities (4.45 and 6.52 W mK^-1) are decreased by ∼55% and 35% at 300 K, respectively. The presented results suggest that the U₃Si₂has potential as a promising ATF at high temperatures.

Keywords: first-principles calculations; fission products; nuclear fuel; thermal conductivity; uranium sesquisilicide.