70 MeV-carbon-ion irradiation is used to simulate the radiation swelling induced by neutron irradiation of 3.2×1022 n·cm-2 in domestically-made 316 austenitic stainless steels modified by a 20%-cold-working and Ti-adding from room temperature to 802°C. The created swelling is microscopically examined by the positron annihilation lifetime technique. A radiation swelling peak is observed at 580°C and the corresponding void has an average diameter of 0.7nm which is hardly probed by macroscopic methods.