First-principles calculations to investigate mechanical, thermal, oxidation and hydrogen properties of Y, Zr and Nb alloyed U3Si2

Abstract

Uranium silicide (U3Si2) is considered a potential accident tolerant fuel for next-generation light water reactors, and the reliability of U3Si2 in extreme environments can be further improved by alloying. In this study, the effects of Y, Zr and Nb alloying on the mechanical and thermal properties, oxidation resistance and hydrogen embrittlement resistance of U3Si2 were systematically investigated by first principles. The enthalpy of formation and phonon dispersion curves indicate that the structures are still thermodynamically and dynamically stable after alloying. The addition of Nb improves the mechanical and thermal properties of U3Si2 and its oxidation resistance. However, U2.5Si2Nb0.5(II) exhibited the worst resistance to hydrogen embrittlement. Furthermore, O and H atoms tend to dissolve in the OI(2) and TI sites, respectively. Alloying with elements of smaller atomic radius leads to a reduction in interstitial volume, which facilitates the bonding of O and H atoms with the interstitial atoms and enhances solubility. Moreover, the addition of Nb strengthens the electron bonding and local hybridization between O and H atoms and U atoms, as revealed by the PDOS, charge density and ELF. The findings provide useful information for the improvement and design of novel accident-tolerant fuel materials.