It was noted that studies of He clustering kinetics in body-centred cubic Fe had revealed a noticeable mobility of small He-vacancy complexes; which were usually thought of as being immobile. Here, the lifetimes and diffusion coefficients of small He-vacancy clusters were quantified. These kinetic parameters were estimated, for clusters of various sizes and compositions, by using lattice kinetic Monte-Carlo methods and ab initio data for He and vacancy interaction-energies. It was shown that nanosized He-vacancy clusters had high thermal stability. It was also found that the diffusion coefficients of some small clusters were indeed very high, being (at 573K) only 1 to 2 orders of magnitude lower than the diffusion coefficient of a monovacancy. It was demonstrated how the coupling of Monte-Carlo numerical experiments with rate theory approaches could be used to estimate the rate theory parameters, such as the defect and cluster agglomeration rates.

Diffusion Coefficients and Thermal Stability of Small Helium-Vacancy Clusters in Iron. V.A.Borodin, P.V.Vladimirov: Journal of Nuclear Materials, 2007, 362[2-3], 161-6