Stress corrosion cracking is a material degradation mechanism that has proved to be very damaging to the nuclear power generation industry. It has resulted in costly component replacements and ongoing inspections of components at risk. Of particular concern is cracking of the vessels and pipe work that form the primary water pressure boundary. This project will continue with the ongoing global effort of characterising the primary water stress corrosion crack (PWSCC) initiation mechanisms of the pressure boundary structural materials i.e austenitic nickel based materials and stainless steels. Characterising the initiation mechanisms and the defining the environmental conditions in which PWSCC occurs will inform reactor operators of the risk of cracking occurring in their plants and will be used to design mitigation strategies.