Accumulation of beryllium and its effects on hydrogen retention in tungsten divertor

Tungsten (W) and beryllium (Be), as superiorly structural materials, may mutually permeate into each other when used as the plasma-facing materials in a fusion reactor, and interact with hydrogen (H) which commonly exists in the fusion environment. By performing first-principles calculations, we investigate the interactions among W, Be and H in W materials. We find that multiple (up to 10) Be atoms can dissolve in W monovacancy to form nBe-V W complexes, and these complexes can decrease the formation energy of a vacancy nearby, which in turn promotes the growth of nBe-V W complexes. The presence of the nBe-V W complexes reduces the retention of H in vacancy. However, we also find that a small amount of Be dissolved in the small-angle tilt grain boundary (GB) has no obvious influence on H retention, while a large amount of Be will promote the growth of cavities in the GB regions. In addition, the adsorbed Be atoms on W (0 0 1) surface are energetically favorable to aggregate together and form a monolayer structure. The presence of Be atomic layer can weaken the adsorption of H on W surface. This work provides a fundamental insight for understanding the accumulation of Be in W, as well as its effects on H retention. This work did not deal with the case relevant to the Be–W alloying phase, which requires further study.