First-principles analysis of intergranular fracture in UN by Σ5(210) grain boundary segregated Xe and vacancy

Segregation of irradiation-generated xenon (Xe) atoms and vacancies to grain boundary (GB) leads to instability and brittleness of uranium mononitride (UN). However, theoretical knowledge about the energetics of its defective interface is lacking, whereas there has been considerable attention on unirradiated UN in experiments. Using first-principles methods, herein we compute the energies of segregation and fracture for typical fission defects. We find that, compared with vacancy, Xe tends more to segregate to Σ5(210) GB, enhancing sensitivity to intergranular fracture. Our predictions clarify the fundamental embrittlement mechanism of irradiated UN GB, which has been discussed so far only on pristine one.