Studies of helium clustering kinetics in bcc iron had revealed noticeable mobility of small He-vacancy complexes, which were commonly thought of as immobile. Here, the lifetimes and diffusion coefficients of small He-vacancy clusters were quantified. These kinetic parameters were estimated for clusters of different sizes and compositions by lattice kinetic Monte Carlo using ab initio data for helium and vacancy interactions 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. Finally, it was demonstrated how the coupling of Monte Carlo numeric experiments with the rate theory approach could be used for the estimation of 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