  Tungsten (W) is widely considered as the most promising plasma facing
material (PFM), which will be used in nuclear fusion devices. Due to the
transmutation reaction caused by the fusion neutron irradiation, transmutation
elements (such as Re, Os, and Ta) are generated in the W-based PFM during the
operation of nuclear fusion devices. In this paper, transmutation elements
effects on mechanical properties of the W and the behavior of hydrogen/helium
(H/He) atom in the W were investigated by using the first-principles
calculation method. The results show that the ductility of the W is enhanced by
transmutation elements if dislocation and other defects were ignored, while
mechanical properties of the W incompletely depend on transmutation elements
content. Compared with the pure W, the formation energy of the H/He in the W is
reduced by transmutation elements, but the most favorable sites of the H/He in
the W is not changed. Except for a repulsion between Ta and He in the W, the
H/He in the W is attracted by transmutation elements. In addition,
transmutation elements can change the best diffusion path of the H/He in the W
and increase the diffusion rate of the H/He in W. This study provides a
theoretical basis for the Tungsten (W) application, and further study on the
effects of transmutation elements in the W will be needed.
