Swelling of SUS 304 and SUS 316 stainless steels under heavy ion irradiation

To allow more accurate evaluation of the irradiation induced swelling behavior of PWR core internals made of SUS 304 and SUS 316 a heavy ion irradiation study was carried out. In particular, the effects of temperature and damage rate on swelling and the differences in swelling behavior between the two kinds of materials was studied. Microstructural changes in SUS 304 and SUS 316 induced by 4 MeV Ni3+ ion irradiation under variations of damage rate, damage level and temperature were observed by using a transmission electron microscope (TEM). Cavity formation was detected both in SUS 304 and SUS 316 at a temperature of 300degC and an irradiation dose of 2 dpa. It was found that the damage rate dependence of the cavity formation and growth differed between SUS 304 and SUS 316. The primary cause may be the difference in the damage rate dependence of dislocation structures. It was also shown that the swelling of SUS 304, for which the cavity formation was saturated during the initial phase of irradiation, was larger than that of SUS 316 whose cavity formation continued until the exposure dose reached 25 dpa. (author)