Mechanical properties, structural changes and hydrogen interactions with stainless steel 12Cr18Ni10Ti subjected to accelerated radiogenic 3He buildup by means of “tritium trick” technique were studied. After saturation with tritium up to equilibrium concentration at a pressure 50 MPa and T=773 K the samples were rapidly cooled to room temperature and aged at this temperature up to the buildup of a predetermined 3He concentration. Kinetics of helium thermal release, hydrogen transport, trapping and accumulation in steel containing various concentration of 3He, synergistic influence of 3He and hydrogen on mechanical properties of steel containing up to 500 appm 3He and structural changes at various 3He concentrations are discussed.