Helium bubble nucleation in bcc iron studied by kinetic Monte Carlo simulations

Fast reactors and other advanced nuclear systems are increasingly considering the use of ferritic and ferritic-martensitic steels for cladding and structural applications. For these materials applications, radiation damage and relatively large amounts of helium generated during the irradiation damage process are recognized to be major issues with materials durability and performance. In these cases, irradiation damage alone is significant; however the added effect of helium on the accumulation of defects and defect clusters can dramatically imact the effect of the resulting microstructure on physical and mechanical properties. Using a kinetic Monte Carlo method we study embryonic bubble nucleation under irradiation damage conditions and helium generation. Migration of helium, vacancies, self interstitial atoms and their clusters is included in the kinetic Monte Carlo model. We estimate embryonic bubble density, interstitial cluster density and embryonic bubble size as a function of the helium content and displacements per atom. Bubble density and size increases with increasing helium content; there is a slight increase in interstitial cluster density as well.