4 - Environmentally-assisted cracking of nickel-base alloys in light water reactors

Abstract

Nickel-base alloys, used extensively in light water reactors, are highly susceptible to environmentally- assisted cracking, particularly in primary water of pressurized water reactors. This chapter is aimed at discussing the most relevant aspects of this degradation mode, usually named as primary water stress corrosion cracking (PWSCC). Fundamentals and the role of key parameters such as microstructure, stresses, cold-work level, and hydrogen concentration on the crack propagation and initiation, both in Alloy 600 and 690 and their weld metals Alloy 82/182 and 52/152, are presented. From a more basic approach, surface and intergranular oxidation, including hydrogen effects, are analyzed. Internal oxidation is discussed as a possible PWSCC mechanism. Creep and cavity formation are considered as cracking precursors. Other phenomena such as low-temperature crack propagation as well as thermal aging and ordering are outlined. Finally, crack initiation and propagation models are briefly reviewed and some future perspectives are identified.