Temperature dependence of swelling in type 316 stainless steel irradiated in HFIR

The temperature dependence of swelling was investigated in solution-annealed (SA) and 20% cold-worked (CW) Type 316 stainless steel irradiated to 30 dpa at 300 to 6000C in the High Flux Isotope Reactor (HFIR). At irradiation temperatures ≤4000C, a high concentration (2 to 4x1023 m-3) of small bubbles (1.5 to 4.5 nm diameter) formed uniformly in the matrix. Swelling was low (<0.2%) in both SA and CW materials irradiated to 30 dpa. In SA 316, cavity size increased but the number density decreased with increasing irradiation temperature above 5000C. At 5000C, there was a mixture of bubbles and voids, but at 6000C, most of the cavities were voids. Maximum swelling (≅ 5%) occurred at 5000C. By contrast, cavities in 20% CW specimens were much smaller, with diameters of 6 and 9 nm at 500 and 6000C, respectively, suggesting that they were primarily bubbles. The cavity number density in CW 316 at both 500 and 6000C (≅ 1x1022 m-3) was about one order of magnitude less than at 4000C. Swelling increased slightly as irradiation temperature increased, peaking at 6000C (0.3%). These results indicate that SA 316 swells more than CW 316 at 500 and 6000C, but both SA and CW 316 are resistant to void swelling in HFIR at 4000C and below to 30 dpa. (orig.)