[SY-B1] Defect production in cascade overlap with defect clusters in iron and tungsten
During the lifetime of a typical reactor, the radiation damage in the wall materials will reach high damage doses. Collision cascades initiated by subsequent irradiation will therefore become increasingly likely to overlap with pre-existing atomistic damage, such as dislocation loops, voids, and other defect structures. We have therefore carried out a large number of molecular dynamics simulations using well-established interatomic potentials, to build a database for the defect production in collision cascades overlapping with pre-existing defect clusters in both iron and tungsten. We primarily study cascades overlapping with dislocation loops of different size. Cascade overlap on other defect clusters leads to similar results. We find that cascades overlapping with pre-existing interstitial clusters result in a significant reduction in the number of new point defects. The overlap effect on vacancy clusters is weaker. By running cascades on different-sized clusters, with different cascade energies and at different temperatures, we obtain a database that can be used to fit a simple analytical model for the defect production bias due to the overlap effects. The data and the fitted analytical model can be transferred to larger-scale simulation methods, such as Monte Carlo techniques, to model the radiation damage accumulation at longer length and time scales.