Synergistic damage buildup and helium segregation in helium-accumulated copper under overlapping cascades

The accumulation of transmutant helium (He) poses a major challenge to the structural integrity of materials in the nuclear industry. To elucidate the He effects on microstructural evolution, we performed molecular dynamics simulations of overlapping collision cascades in copper containing pre-existing substitutional He, at concentrations up to 10 000 appm and a cumulative dose of ∼0.24 dpa. Based on statistical analysis across multiple independent simulation runs, the results reveal a synergistic evolution between He atoms and radiation-induced defects. In contrast to the large, localized dislocation loops formed in pristine Cu, He-containing samples developed a distinct damage structure characterized by smaller loops and homogeneously distributed defect clusters. This morphology originates from dominant continuous recombination–replacement reactions between self-interstitials and substitutional He, which eject substantial amounts of He into interstitial sites. These He atoms constitute a significant fraction of the interstitial clusters, and their formation into Cu–He complexes severely restricts cluster mobility. Consequently, the agglomeration and growth of dislocation loops are suppressed. Simultaneously, an interstitial-mediated mechanism drives pronounced He segregation and initial bubble nucleation. The atomic-scale insights provided by this study are crucial for understanding He-induced microstructural degradation under prolonged irradiation.