Stress Corrosion Cracking Behavior of Alloys in Aggressive Nuclear Reactor Core Environments

The effects of irradiation on stress corrosion cracking occur through changes in the water chemistry and in the alloy microstructure. Considerable reactor experience has shown that a high-temperature water environment and a radiation field combine to produce irradiation-assisted stress corrosion cracking (IASCC) in core components of light water reactors. The principal effect of irradiation on water chemistry is through radiolysis, which results in an increase in the corrosion potential through the formation of radiolytic species consisting of radicals and molecules that can be oxidizing or reducing. In addition, profound effects of irradiation on the microchemistry and alloy microstructure create numerous pathways for IGSCC to occur. Radiation-induced segregation, the formation of a dislocation loop microstructure, irradiation hardening, and irradiation creep all occur simultaneously in space and time. Unfolding these various effects to determine the primary factors governing the observed effects of irradiation on stress corrosion cracking is an enormous challenge. This paper describes the state of our understanding of the role of irradiation on stress corrosion cracking in the highly aggressive nuclear reactor core environment. Documentation of service failures due to IASCC are provided, followed by a comprehensive examination of the effect of irradiation on water chemistry and alloy microchemistry, microstructure, hardening, deformation, and creep. The current understanding of the mechanism(s) of IASCC and the research challenges that remain are described.