To study void swelling behavior for clues regarding the anticipated performance of Type 316 stainless steel in fast reactor environments, two series of electron irradiation experiments were conducted. The first series of experiments were conducted on material which was prototypic of fast test reactor (FTR) steels in composition, but not microstructure. The results indicated that swelling values exceeding 100 percent could easily be obtained in annealed Type 316 and that cold rolling of this material could lead to an increase in the incubation fluence and a reduction in the subsequent swelling rate. The void volume fraction in both the annealed and cold-rolled specimens developed at a constant rate after the incubation period.
In the second series of experiments, specimens were extracted from prototypic cold-drawn FTR tubing, which contained a variable density of deformation twins not found in the cold-rolled specimens. Repetitive experiments showed that each area in the specimen possessed a different incubation fluence but eventually developed the same steady-state swelling rate at a given temperature. This spot-to-spot variation in incubation behavior was strong enough to obscure possible heat-to-heat variations in bulk-integrated behavior. Although the length of the incubation period could not be conclusively related to the deformation twin density, regions containing very high densities exhibited the longest incubation fluences.