Molecular dynamics simulations of point defects in plutonium grain boundaries

A modified analytic embedded atom method （MAEAM） potential is constructed for fcc 5-Pu. Molecular dynamics （MD） simulations with the potential are performed to investigate the interactions between two symmetrical tilt grain boundaries （GBs） and point defects such as He atom, vacancy and self-interstitial atom （SIA） in Pu. The calculated results show that point defect formation energies are on average lower than those in the lattice but variations from site to site along the GBs are very remarkable. Both substitutional and interstitial He atoms are trapped at GBs. Interstitial He atom is more strongly bound at the GB core than the substitutional He atom. The binding energy of SIA at GB core is higher than those of He atom and vacancy. GB core can bind many He atoms and SIAs due mainly to the fact that it contains many vacancies. Compared with He atom and SIA, the vacancy far from GB core is difficult to diffuse into the core. The GBs can act as sinks and sources of He atoms and SIAs, which may be a reason for the swelling of Pu after a period of self-irradiation because of the higher concentration of vacancy in the bulk.