NRC Perspectives on Primary Water Stress Corrosion Cracking of High-Chromium, Nickel-Based Alloys

High-chromium, nickel-based alloys, including alloy 690 base material and alloys 52 and 152 weld filler metals, are used in the primary system of new pressurized water reactors (PWRs), as well as for replacement and mitigation of components in existing reactors. These materials are thought to be highly resistant to primary water stress corrosion cracking (PWSCC), which is observed in plant service for components fabricated from the low-chromium alloys 600, 82, and 182. For over 10 years, the U.S. Nuclear Regulatory Commission has sponsored a laboratory testing program to measure the PWSCC growth rates of alloys 690, 52, and 152 in environmental conditions representative of PWRs, with the intent to support technical bases for the determination of appropriate in-service inspection requirements. In many tests, the low crack growth rates are confirmed. For certain cases, however, such as in highly cold worked alloy 690 and at dilution zones between high-chromium weld metals and low-chromium base metals, PWSCC growth rates are reported to be similar to those observed in alloys 600, 82, and 182. Challenges arise in the use of these data for predictive models given the relatively few numbers of tests performed for some material conditions and uncertainties about the correlation between conditions of test materials and those found in the field. This paper will present perspectives on factors that may be considered for the application of these data to the analysis of plant components.