[en] Reactor vessels of a pressurized water reactor (PWR) are designed for a 40 years usage. Under the consideration of a life extension to 60 years or longer, utilities need to set up a degradation management strategy of the reactor internals like the upper core structure, core baffle/former/barrel, thermal shield, and the lower core support structure. It is required to extend the life of PWRs with a knowledge based degradation management related to the mechanical and corrosion properties of stainless steels in a high dose exposure environment. Degradation mechanisms of the reactor internals are an irradiation embrittlement, void swelling, and an irradiation-assisted SCC(IASCC). These mechanisms need to be understood in order to assure the long term integrity of the internals. This paper aims to review the IASCC experience around the world and in Korea, to introduce a feature of an IASCC of stainless steel mainly used for baffle former bolts in PWR reactor internals