An atomistic assessment of helium behavior in iron

High helium generation rates in irradiated materials leads to the formation of small He–vacancy clusters that can evolve into larger bubbles and voids. An equation of state that accurately reproduces their pressure–volume relationship is necessary to understand and predict the behaviour of these He–vacancy defects. Previous research has employed equations of state of varying complexity, including the ideal gas, van der Waals, and hard sphere models. We recently used ab initio calculations to determine the energetics of helium-vacancy clusters and applied the results to develop a new three-body interatomic potential that describes the behaviour of helium in iron. This potential was employed in molecular dynamics simulations to determine the conditions for mechanical equilibrium between small helium-stabilized bubbles and an iron matrix, and to systematically map the pressure–volume relationship for the bubbles at a range of temperatures. These atomistic results are compared to an existing equation of state and a modification is proposed for bubbles with high helium densities.