Quantitative assessment of submodes of stress corrosion cracking on the secondary side of steam generator tubing in pressurized water reactors: Part 1

The work in this article is part of a project to develop a quantitative description of stress corrosion cracking (SCC) on the secondary side of pressurized water reactor (PWR) steam generator tubing based on existing information from operating plants and from laboratory experiments. This work is the second step in developing a predictive model for SCC on the secondary side. The first step involved developing a statistical framework into which dependencies of the various submodes of SCC can be inserted. The results of the present work will lead to quantitative descriptions of corrosion processes that, in turn, will be incorporated into the statistical framework. The chemistry of heat-transfer crevices will then be assessed to determine the proper inputs to the dependencies of the various submodes of SCC, and these will be connected to bulk environments. The modeling here is directed toward predicting the early occurrence of SCC that is too shallow to be detected by nondestructive examination (NDE). The various submodes of SCC considered in this article include: alkaline stress corrosion cracking (AkSCC), low-potential stress corrosion cracking (LPSCC), acidic stress corrosion cracking (AcSCC), high-potential stress corrosion cracking (HPSCC), lead stress corrosion cracking (PbSCC), low-valence stress corrosion cracking (S^y-SCC), organic stress corrosion cracking (OgSCC), doped steam stress corrosion cracking (DSSCC), and low-temperature stress corrosion cracking (LTSCC). To develop a model for each of these submodes, their dependencies on the seven primary variables are evaluated in this article; these variables are: pH, potential, species, alloy composition, alloy structure, temperature, and stress. For some of these submodes, there is broad agreement in the literature on dependencies. In other cases there is some disagreement, but these are mostly related to lack of information or to inconsistencies among experiments that have been conducted under different conditons. To develop a framework for this discussion of submodes, supporting sections are included on designs of steam generators as they affect corrosion, bulk water chemistry as it relates to chemistry in heat-transfer crevices, and the chemistry of heat-transfer crevices. At the end of each section, the state of present knowledge is summarized including the lessons learned from service and laboratory experience. In addition, possible problems for future reliable performance as affected by corrosion are identified.