Simulation study of low-temperature irradiation and a LOCA and the resulting microstructural changes in 316 stainless steel

For the first wall of near-term fusion devices, 316-type austenitic stainless steels are the prime candidates. For ITER (International Thermonuclear Engineering Reactor)-type designs, the temperature range of concern for the irradiation response of materials is shifted down to below 673 K. In this study, dual ion irradiation with 4-MeV Ni ions and degraded 1-MeV He ions was carried out to damage levels of 30 dpa at temperatures from 373 to 673 K to simulate both the displacement damage and the transmutant gas effect of fusion neutrons. Materials behavior during a loss-of-coolant accident was also simulated by dual ion irradiation. No cavity formation or irradiation-induced precipitate was detected in the temperature range and displacement damage levels examined. The major microstructural change was in the dislocation structure, which was altered primarily by loop formation. The effect of the dislocation evolution on mechanical behavior is discussed with the results of the postirradiation three-point disk bend test.