Migration of rhenium and osmium interstitials in tungsten

Tungsten is expected to be a promising plasma-facing material for future fusion devices, but radiation-induced precipitation (RIP), which leads the material to hardening, is a concern at their practical use. One of the keys to accurate prediction of the emergence of RIP is migration of solute atoms, rhenium and osmium, that are produced by nuclear transmutation through irradiation. We conduct a series of numerical simulations using an atomic kinetic Monte Carlo method and investigate the migration of these solute atoms in the form of tungsten–rhenium and tungsten–osmium mixed dumbbells, considered to be the most efficient "carriers" of the solute atoms. We find that the low rotation energy barrier of these mixed dumbbells leading to three-dimensional migration greatly influences their diffusivities. The result also suggests that, although these dumbbells have three-dimensional motion, one cannot simply reduce their migration behavior to that of vacancy-like spherical objects. - Highlights: • We investigate the migration of rhenium and osmium in tungsten. • The low rotation barrier of mixed dumbbells greatly influences their diffusivities. • One cannot reduce their migration behavior to that of spherical objects.