A multi-scale modeling approach, based upon atomistic simulations, was used to investigate the growth and shrinkage of He-vacancy clusters. A molecular dynamics technique, with empirical interatomic potentials, was first used to determine the energies of formation and dissociation of clusters as a function of their size and He density. The number of He atoms and vacancies in a cluster both ranged from 0 to 20. The dissociation energy of clusters exhibited a strong dependence upon the He density, rather than upon the cluster size. This indicated that the growth and shrinkage of clusters strongly depended upon the He density. These dissociation energies were then used in a kinetic Monte-Carlo simulation in order to explore the long-term cluster-behavior. The kinetic Monte-Carlo simulations indicated that He could stabilize He-vacancy clusters by suppressing thermal vacancy emission, and by promoting thermal self-interstitial Fe atom emission. A preliminary simulation was also made of the migration of He-vacancy clusters.

MD and KMC Modeling of the Growth and Shrinkage Mechanisms of Helium–Vacancy Clusters in Fe. K.Morishita, R.Sugano, B.D.Wirth: Journal of Nuclear Materials, 2003, 323[2-3], 243-50