First-principles study of the interaction between helium and the defects in tantalum

As a low power spallation target or target cladding material, tantalum has almost the same defects productions as tungsten under irradiation. In this paper, the detailed analysis of helium behavior in tantalum has been conducted based on density functional theory. The formation energy of tetrahedral interstitial configuration of helium is 0.3 eV lower than that of octahedral interstitial configuration, which means the tetrahedral interstitial configuration of helium is more stable than the octahedral configuration. Tetrahedral helium atoms in tantalum are predicted to have a very low migration, about 0.09 eV. A large binding energy between He and vacancy 2.03 eV indicates that He atom is easily trapped by vacancy, and a tetrahedral interstitial helium atom need overcome about 0.19 eV energy barriers when it directly jumps into the vacancy. Finally, the helium behavior in tantalum is compared with that in tungsten. It is obvious that the binding energy in tantalum is significantly different from those in tungsten. The interaction between two helium atoms in tantalum shows repulsive or weak repulsive other than attractive in tungsten, which suggests that helium atoms are easy to move other than to be a cluster in tantalum.