Effect of High helium Content on Stainless-Steel Swelling

Type 316 stainless-steel specimens have been irradiated in the High Flux Isotope Reactor at temperatures between 380 and 680°C to displacement damage levels up to 120 displacements per atom and transmutation produced helium contents up to 6090 ppm. Swelling in solution annealed samples was found to be smaller than predicted by the helium swelling models but larger than predicted by fast reactor irradiation results, and the temperature dependence of swelling was also not in agreement with either prediction. Cold work reduced swelling for irradiation temperature up to 600°C but was ineffective at 680°C. For both annealed and cold-worked materials, the swelling was nearly temperature independent between 380 and 600°C but increased markedly at 680°C. Present models are inadequate to explain the swelling results in the presence of these high helium concentrations.