The void nucleation behavior of an alloy is related to the development of the initial microstructure during irradiation. There is some concern that the void nucleation and swelling behavior of fast reactor steels may be controlled by the presence of microstructures that can develop only in-reactor. It is, therefore, proposed that charged particle simulation experiments might be improved by using specimens which were preconditioned in a neutron environment. The void incubation period would be bypassed, and the swelling behavior observed in the simulation would be related at least initially to a reactor-representative microstructure.
The results of three exploratory experiments are reported which involve the electron irradiation of Types 304 and 316 stainless steels, preconditioned by reactor exposure. The analysis of such experiments must include consideration of the time-dependent influence of the specimen surfaces on the stability of voids produced by neutron irradiation. In the central regions of the thin foil, the surface influence is negligible and voids nucleated in-reactor are stable and continue to grow. Nucleation processes that were not yet complete in-reactor also continue in the simulation experiment. It is proposed that charged particle irradiations proceed at a temperature approximately 120°C higher than the reactor irradiation temperature in order to compensate for the increase in displacement rate.