Defect evolution mechanism in U3Si2 from molecular dynamics simulations

Abstract

U3Si2 is proposed as a promising candidate for accident tolerant fuel (ATF) in recent years. Compared to previous extensively-used UO2 fuel, U3Si2 has the advantage of a higher fissile density and thermal conductivity, which allows for extra coping time in case of accidents. The phase stability and thermophysical properties of U3Si2 have been studied previously with the purpose of evaluating its fuel performance. Nevertheless, the critical issue of irradiation damage in the U3Si2 fuel is still an underexplored area, and the evolution mechanism of irradiation-induced defects remains unclear. In this work, we perform molecular dynamics (MD) simulations to study defect evolution and defect properties in U3Si2. We simulate defect evolution by creating Frenkel defects directly in the system. We find that defects in U3Si2 prefer to form single or small defect clusters. With increasing defect concentration, amorphization is observed. To reveal the mechanism governing the observed defect evolution, we have carried out a systematic analysis of defect energetics and defect migration pathways in U3Si2. Our results indicate that VSi and Ui are stable defects after evolution, consistent with their low formation energies. Defect diffusion exhibits an anisotropic nature in U3Si2, with the fastest diffusion along the c direction instead of in the a-b plane for both vacancy and interstitial-mediated diffusion. These results are helpful in the understanding of irradiation behavior of U3Si2.