Effects of H and He on the clustering behavior of transmutation elements in tungsten

Nuclear fusion energy is widely considered as the ultimate solution to the energy shortage in the future. Plasma facing material (PFM) is one of the key problems which determine the success of fusion device. Tungsten (W) is considered as the most potential candidate material for the PFM, however, transmutation elements (TE) tantalum (Ta), rhenium (Re), and osmium (Os) are produced in W-based PFM due to the (n,γ), (n,2n), and (n,β⁺) transmutation reactions caused by the fusion neutron irradiation. The clustering behavior of the TE atoms in W is very important for the integrated performance of the W-based PFM during the fusion device operation. In this paper, the effects of H/He on the clustering behavior of the TE atoms in W were investigated through the first principles calculation method. The results show that, the formation of H defects in the bulk Ta, W, Re, and Os is an exothermic process with a negative formation energy, while the formation of He defects is an endothermic process with a positive formation energy. An attractive interaction exists between H and TE atoms, conversely, a repulsive interaction exists between He and TE atoms in W. The binding energy demonstrates that H/He can facilitate the formation of the TE clusters in W, which caused by the synergistic effect of charge and local stress.