Modeling microstructural evolution in fusion reactor environments

Abstract Interactions between dislocation, cavity and precipitate evolution in austentic stainless steels irradiated in fission reactors are analyzed. Cavity evolution is modeled using the critical bubble concept: helium bubbles grow stably with the incremental addition of helium up to a critical size, thereafter they grow rapidly as voids. Dislocations and precipitates are preferred sites for bubbles and influence the critical size, hence, incubation period. The models predict broad trends in the swelling data base, as well as many detailed observations. The calibrated models predict a nonmonotic swelling response to increases in helium, with a peak at intermediate values; this suggests that fusion environments will generally have lower incubation times and higher swelling than found for fission reactor irradiations. The mechanisms controlling swelling in Ti-modified steels are also examined; partitioning of helium to a fine distribution of stable MC phases is found to be the key factor in retarding swelling.