The effect of fission products Xe and Cs on the thermal conductivity of the U 3 Si 2 lattice: a first-principles study

In the past decades, uranium silicide (U 3 Si 2 ) as a promising accident tolerant fuel (ATF) has drawn considerable attention in the field of nuclear physics. In comparison with traditional nuclear fuel (UO 2 ), the U 3 Si 2 has 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 U 3 Si 2 lattice 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 U 3 Si 2 are 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 −1 for 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 U 3 Si 2 has potential as a promising ATF at high temperatures.