Data investigation on effects of neutron irradiation on material properties of the heat-affected zone near weld fusion line of austenitic stainless steel with low carbon for core internals of boiling water reactors (Contract Research)

Kasahara, Shigeki; Hata, Kuniki ; Iwata, Keiko ; Chimi, Yasuhiro

It has been reported that intergranular stress corrosion cracking (IGSCC) has occurred near weld fusion lines of low-carbon, namely unsensitized austenitic stainless steel for pipings and reactor internals used under the primary coolant environment of boiling water reactors in Japan since the early 2000s. It becomes one of the critical technical issues clarification of the mechanism and development of countermeasure techniques for IGSCC of low-carbon-containing stainless steel. From previous research, the hardness of stainless steel is increased due to the accumulation of local strain, after expansion and contraction during welding heat input, and the increment of hardness in such heat-affected zone is recognized one of the possible material factors caused by IGSCC. In particular, for boiling water reactor internal structures, it is essential to evaluate IGSCC taking into account neutron irradiation as well as strain accumulation for hardness increase, and it is desirable to accumulate multifaceted and systematic data that can be dedicated to evaluating the irradiation effect of weld heat-affected and hardened zones. In this study, we investigated and collected irradiation data on the crack growth rates and other material properties evaluated under simulated primary water conditions of boiling water reactor environments for neutron-irradiated low-carbon stainless steel weld heat-affected zones. Those were obtained through the ENI project of the Japan Nuclear Energy Safety Organization, including data that had not been made public until now.