Simultaneous effects of radiation induced defects and gas atoms of various types in the near surface layers of the first wall material of a fusion reactor produced rather intricate pictures of their interaction and diffusion. This work describes our attempt, by using computer simulation methods, to look into He and H interaction reactions with radiation - induced vacancies and interstitial atoms, to determine the more movable defect formations that are responsible for gas migration. More movable mixed helium-vacancy cluster is discovered (H+2V). Reactions of pushing out helium from substitutional position by self - interstitial atom as well as hydrogen by helium atom which has come to it have been discovered. It is shown that the latter reaction pointing out the possible competition between He and H, while occupying vacancy trap, can cause He permeability reduction compared to hydrogen permeability, that is to supposed affect gas porosity formation.