Effect of fission defects on tensile strength of U3Si2 Σ5(210) grain boundary from first-principles calculations.

Abstract

U3Si2 is regarded as a promising accident tolerant fuel (ATF) to replace the commercial fuel UO2; however, grain boundary (GB) embrittlement of U3Si2 caused by irradiation-induced defect segregation remains to be clarified. In this work, the U3Si2 Σ5(210) symmetrically tilted GB is taken as a representative to elucidate the individual effect of xenon (Xe) and vacancy on the tensile strength and failure of GBs using first-principles calculations. Compared with the predicted segregation energies of defects at the most energetically favourable positions of GBs, Si vacancy (VSi) has a much stronger preference to segregate to GBs than that of Xe substitution on the Si sublattice (XeSi). Moreover, the strengthening/embrittlement potency of GBs with single vacancy/Xe is evaluated using the first-principles-based uniaxial tensile test. Although both VSi and XeSi yield a weakening effect on the strength of the U3Si2 Σ5(210) GB, such defective GBs exhibit significantly stronger interface strengths compared to the corresponding defects segregated to the UO2 Σ3(111) GB. The underlying mechanism of strength change of U3Si2 GBs is discussed in terms of charge analysis. Our results can provide a fundamental understanding of the mechanical behavior of irradiated GBs from an atomic perspective.