Annealed Type 316 stainless steel was -8 at 625°C in vacuum (-lxIO Torr) to study maximum fluence used in the investigation, irradiated by 140 keV protons its swelling behavior. The 20 2 2xl0 protons/em, created a peak damage of 590 dpa (displacements per atom) based on 25 eV as the displacement threshold. The swellings integrated along the entire proton range were obtained from the measurements of the step-heights at the junction of the irradiated and unirradiated regions. The swelling-dpa

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... tionship was ascertained from the integrated swellings measured at various doses and the corresponding depth-dpa profiles. There were three stages in the swelling regime. The rate of swelling in stage I (dpa < 200) increased continuously up to 0.8% per dpa. In stage II (425 > dpa > 200) the rate of swelling remained at its highest (0.8% per dpa). Rapid reductions in the rate began to occur beyond 425 dpa and the swelling saturated at about 260% at 500 dpa. The values of swelling at 200 dpa and 425 dpa were 46% and 226% respectively. The entire swelling regime could be explained by assuming reasonable changes in the dislocation density and void density as the void volume increases. To fit the experimental results it was necessary to aSSume that dislocations lying°w ithin a spherical shell of thickness l50A around the voids did not contribute to void growth because of the effects of Pipe Diffusion, and that the dislocation's capture cross-section for interstitials was 4.2% higher than that for vacancies when the assumed displacement threshold (Ed) was 25 eV or alternatively 7.5% higher if Ed was taken as 40 eV. The reduction in the rate of swelling due to Pipe Diffusion amounted to 25% at a dislocation density of 4 x I0 11 /cm 2 and 5% at 5 x IO IO /cm 2 when the inter-void spacing was larger than 20001. 38 demonstrated in the neutron irradiation experiments of Straalsund et al., c CC :'. ,'P.,