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 (V_Si) has a much stronger preference to segregate to GBs than that of Xe substitution on the Si sublattice (Xe_Si). Moreover, the strengthening/embrittlement potency of GBs with single vacancy/Xe is evaluated using the first-principles-based uniaxial tensile test. Although both V_Si and Xe_Si 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.