Simulation of first wall damage: effects of the method of gas implantation

Cavity formation in an austenitic alloy of similar composition to Type 316 stainless steel has been explored with regard to various methods of gas implantation. Irradiations were conducted at 900 K to doses of 1, 10, and 70 dpa with helium injection levels of 20 appm/dpa. Highest swelling (18%) was exhibited by the unimplanted reference material; a lesser amount by simultaneous helium injection (11%). Greatly reduced swelling due to profuse cavity nucleation was the results of the preinjection of 1400 appm He, either at room temperature (S = 1%) or at 900 K (4%). The dislocation density was not sensitive to helium injection technique. Simultaneous injection of 50 appm H/dpa, along with the He, may have caused a modest increase in the cavity and dislocation concentrations at higher doses. The observations are compared with a theory of void growth kinetics to estimate the relative influence of voids and dislocations as point defect sinks