Kinetically evolving irradiation-induced point defect clusters in UO₂ by molecular dynamics simulation

The evolution of irradiation-induced point defects in UO₂ is captured in molecular dynamics simulations. The approach used circumvents their creation during the ballistic phase of a traditional collision-cascade molecular dynamics simulation but rather focuses on their kinetic evolution. The simulations reveal that in the absence of defects on the cation sublattice, the defects initially present on the anion sublattice recombine and annihilate completely during equilibration. However, in the simultaneous presence of defects on both sublattices, Schottky defects are formed, thereby sequestering the oxygen vacancies. The resulting excess oxygen interstitials form cuboctahedral clusters, whose existence has previously been identified experimentally but whose generation mechanism has not been determined. It is concluded that the cation sublattice is primarily responsible for the radiation tolerance or intolerance of the material.