Comparison of microstructural evolution in reactor-irradiated austenitic stainless steels with and without spectrally tailoring

The effects of He-dpa ratio on swelling behavior were examined on three austenitic stainless steels. Materials were solution-annealed JPCA and two low carbon containing alloys (C and K) modified with titanium and niobium. These steels were neutron-irradiated in ORR and HFIR with and without spectrally tailoring, respectively. Achieved damage level was 7.4 dpa in ORR irradiation with average He/dpa of about 21 appm/dpa. In case of HFITR irradiation, they were 33 dpa and 76 appm/dpa, respectively. Alloy to alloy variation and temperature dependence of swelling behavior are far more distinctively detected in ORR irradiation than in HFIR irradiation, in spite of the lower damage level of ORR irradiation. In the case of ORR-irradiation, JPCA exhibited small swelling values of <0.01 and 0.03 % at 603 and 673 K, respectively, while a low carbon alloy K showed relatively larger swelling; 0.2 % at 603 K and 0.6 % at 673 K. Swelling of JPCA and K irradiated in HFIR were almost same values of 0.2% at temperatures of 573 and 673 K. Number densities of cavities in HFIR-irradiated alloys were larger than those observed in ORR by one to two orders. On the other hand, number densities and sizes of dislocation loops produced by ORR irradiation were two to five times as large as those by HFIR irradiation. These facts suggest that in ORR condition with closer He/dpa to that of fusion, mutual annihilation rate of point defects was reduced and then bias driven cavity growth might be enhanced compared with HFIR condition