Interstitial hydrogen atoms in W-nitride compounds promoting the formation of atomic vacancies in nuclear fusion reactors

Abstract

Nitrogen gas seeding has been proposed as a feasible strategy to reduce the edge plasma temperature in nuclear fusion reactors, which could cause the W-nitride compounds to form on the surface layer of the tungsten (W) first wall. Many point defects can be generated in the W-nitride compounds under the extreme fusion environment. By performing first-principles calculations, we investigate the interaction of interstitial hydrogen (H) atoms with point defects in W1N1, W2N1 and W2N3, respectively. It is found that the dissolved H atoms can assist the formation of vacancies in W-nitride compounds. And this correlates with the lattice distortion and charge redistribution induced by interstitial H atoms. In addition, studies on the behavior of H migrating to vacancies show that vacancy-containing W-nitride compounds can effectively trap H atoms, thereby reducing the retention of H atoms in the W first wall. Furthermore, calculation results about the interaction of H with interstitial atoms indicate that the predominant interaction between H and interstitial atoms characterizes the feature of repulsion in the concerned systems. Our work not only reveals the details about the interaction between interstitial H atoms and atomic vacancies in W-nitride compounds, but also provides a fundamental insight into understanding the interactions of intersitial H atoms with vacancy in W-nitride compounds.