Austenitic stainless steels are used for the core internal structures (bolts, baffles, formers) in Pressurized Water Reactors (PWR). During operational service, baffle to former bolts have been observed to undergo Irradiation-Assisted Stress Corrosion Cracking (IASCC), which is characterized by intergranular cracking. IASCC results from the material corrosion susceptibility, the microstructural changes induced by irradiation, the corrosive media and the mechanical loading. Numerous studies have been conducted to evaluate the complex interplay between the different factors, mostly focusing on InterGranular Stress Corrosion Cracking (IGSCC) of pre-irradiated samples in PWR environment. In particular, the oxidation behavior of grain boundaries and the mechanical loading of grain boundaries have been assessed in details. Depending on the oxidation time and the GB nature, oxide penetration along GB has been observed. The intergranular oxide is composed of (Nix,Fe1-x)Cr2O4 spinels. However, all grain boundaries (GBs) do not have the same oxidation behavior, and it has been reported that high angle grain boundaries show higher oxidation susceptibility than special grain boundaries. Radiation induced segregation at grain boundaries might also lead to higher susceptibility to intergranular oxidation. Irradiation also modifies the deformation mechanisms in austenitic steels resulting in strain localization which is believed to be an important factor in IASCC initiation as it can lead to local increase of the stress due to dislocation pile-ups at GB.