  Transmutation elements are the essential products in plasma facing materials
tungsten, and have further effects on point defects evolution resulted by
radiation. Here, transmutation elements Re and Ta atoms have been selected to
assess the effects on property of vacancy and vacancy cluster in W material via
first-principles calculations. The formation energy indicates mono-vacancy is
more likely to form in W-Re system than pure W and W-Ta system. Both Re and Ta
have reduced the diffusion barrier energy in the mono-vacancy migration. The
calculation presents that vacancy cluster prefers to grow up by combining
another vacancy cluster relative to a single mono-vacancy. Re is favorable to
the nucleation and growth of vacancies clusters, while Ta has a suppressive
effect on the aggregation of small vacancy cluster. The emphasis analysis is
obtained according the volumetric dependent strain. Vacancy dissociation
calculations show that the dissociation of vacancy clusters is easier to begin
with a single vacancy dissociation process.
