EFFECT OF HELIUM ON DEFECT CLUSTER FORMATION IN MODIFIED 316 STAINLESS-STEEL IRRADIATED BY ELECTRON-ION DUAL BEAMS

To investigate the effect of helium with different concentration on defect cluster formation, such as dislocation loops and voids, an in situ observation with the dual beam irradiation of electrons and ions has been carried out for commercial and Ti-modified 316 stainless steels, and the results have compared with neutron-irradiated data. In both steels the void nucleation was strongly enhanced by the dual beam irradiation up to high doses, and the bimodal distribution in void size was developed at higher He concentration, more than 20 at.ppm He/dpa. The He concentration dependence of void swelling showed a maximum value at 20 at.ppm He/dpa, which is corresponding to the condition in fusion reactor. These results indicate that the formation of small sized cavities with high number density can suppress the swelling, because they act as neutral sinks for point defects.