Due to the widespread use of thick-wall Alloy 690 and its corresponding weld metals Alloys 52 and 152 in various replacement, repair, mitigation, and new plant pressurized water reactor (PWR) applications, there is a need in the industry for an equation or methodology for predicting crack growth rates (CGRs) for primary water stress corrosion cracking (PWSCC) of these materials. Although there have been no indications of PWSCC reported in these materials in PWRs to date, there is the possibility that such an indication could be reported in the future or the possibility that a manufacturing defect could be conservatively interpreted as PWSCC. Crack growth rates are thus needed to support leaving such an indication in service for a justified period of time. In addition, safety assessments of hypothetical PWSCC flaws require prediction of PWSCC crack growth rates for these materials, so as to set appropriate inspection intervals. Current inspection intervals were selected to be conservative pending a consensus CGR model.

Example applications for which PWSCC CGRs are needed to determine appropriate reexamination intervals include Alloy 690 penetration nozzles attached to the inside of the reactor pressure vessel top head with Alloy 52/152/variant welds, and Alloy 52/152/variant weld inlays and onlays used to mitigate Alloy 82/182 piping butt welds.

An international PWSCC CGR Expert Panel was organized by EPRI, with the participation of national laboratories sponsored by the US Nuclear Regulatory Commission (NRC),1 to support the development of such PWSCC CGR equations. A database of over 500 Alloy 690 CGR data points and over 130 Alloy 52/152 CGR data points using thick-wall compact tension specimens from seven research laboratories was compiled, scored for data quality, and assessed to determine the effects of numerous parameters such as temperature, crack-tip stress intensity factor, yield strength, and crack orientation. The methodology and results of these statistical analyses are presented in this paper. It should be noted that this paper provides a status of the ongoing work, which is planned for completion in late 2017.

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