Formation of he bubbles by repair-welding in neutron-irradiated stainless steels containing surface cold-worked layer

Abstract

Stress corrosion cracking (SCC) has been found on surfaces of reactor internals which are heavily cold-worked by machining. When repair welding is applied to the cracked region, the cold-worked surface will be included in the welding region. Therefore, the effect of the cold-worked layer on the weldability of irradiated stainless steels (SSs) needs to be clarified. In this study, helium bubbles formed by welding on irradiated SSs were investigated by measurements and comparisons to published results. TIG welding was performed on an irradiated SS plate with a cold-worked layer generated by wire peening. Re-crystallization was confirmed in the weld after peening at the surface near the weld heat affected zone (HAZ). The helium bubble number density along the grain boundary in the re-crystallized region was the same as in the non-re-crystallized region, whereas the bubble diameter was smaller. Helium bubble growth was suppressed by the re-crystallization behavior.