Multiscale modelling of defect kinetics in irradiated iron

Changes in microstructure and mechanical properties of nuclear materials are governed by the kinetics of defects produced by irradiation. The population of vacancies, interstitials and their clusters can however be followed only indirectly, for example by macroscopic resistivity measurements. The information on the mobility, recombination, clustering or dissociation of defects provided by such experiments is both extremely rich and difficult to interpret. By combining ab initio and kinetic Monte Carlo methods, we successfully reproduce the abrupt resistivity changes - so-called recovery stages observed upon annealing at increasing temperatures after electron irradiation in alpha-iron. New features in the mechanisms responsible for these stages are revealed. We show that di-vacancies and tri-interstitials contribute to the stages attributed to mono-vacancy and di-interstitial migration respectively. We also predict the effect of the unexpected low migration barriers found for tri- and quadri-vacancies, and discuss the challenging questions raised by the mobility of larger defect clusters.