First-principles study of the impact of rhenium and osmium on the energetics of helium clusters in tungsten

Abstract Understanding interaction between transmutation elements and helium is critically important for precisely predicting the performance of tungsten plasma facing materials in fusion reactors. The energetics of He interstitial clusters (He n ), He interstitial- rhenium (Re)/osmium (Os) substitutional clusters (He n Re sub /He n Os sub ), He interstitial-tungsten(W)/Re/Os interstitial clusters (He n I W/Re/Os ), He-vacancy-Re/Os substitutional clusters (He n V 1/2 Re sub /He n V 1/2 Os sub ) and He-vacancy-W/Re/Os interstitial clusters (He n V 1/2 I W/Re/Os ) in bulk body-centered cubic tungsten were investigated by using first-principles calculations. The critical numbers of He required for the self-trapping and trap mutation reactions were calculated with/without a neighboring Re/Os substitutional as well as for the case of a neighboring W/Re/Os interstitial present, based on both dissociation and transformation mechanisms. The trapping effects of Re/Os substitutional or W/Re/Os interstitial on the mobile small He n clusters were discussed.