Thermal and mechanical properties of U3Si2: A combined ab-initio and molecular dynamics study

Abstract

Triuranium disilicide (U3Si2) has been identified as an accident resistant alternative to uranium dioxide (UO2) based fuels. While experimental studies of U3Si2 are not new, only few studies on the thermal conductivity has been reported. Moreover, theoretical studies of the thermal properties of U3Si2 are scarce. We found that inaccuracies in experimental data were a source of discrepancies in recently reported theoretical results, as such need to be addressed. In this work, the structural, thermal, and mechanical properties of, the non-magnetic and magnetic phases, of U3Si2 were investigated using Hubbard corrected density functional theory (DFT+U) and molecular dynamics (MD) simulations. The lattice and electronic thermal properties were determined based on Boltzmann transport equation (BTE) approaches. A considerable anisotropy was determined the lattice and electronic contributions to the thermal conductivity from DFT+U/BTE results, in which the electronic contribution is predominant. A relative good agreement between the lattice contributions to the thermal conductivity, predicted from DFT+U and MD computations, was associated to similarities in the acoustic phonon modes. The present computational results significantly enhance the understanding of the thermal properties of U3Si2. The good agreement between DFT+U/BTE results with experimental data confirm the accident tolerant characteristic of U3Si2, but also further demonstrating the accuracy of the DFT(+U)/BTE approach for the investigation of thermal properties of advanced nuclear fuels.