Managing PWSCC in Butt Welds by Mitigation and Inspection(NUREG/CR-7187)
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Publication Information
Manuscript Completed: September 2014
Date Published: November 2014
Prepared by:
E. J. Sullivan and M. T. Anderson
Pacific Northwest National Laboratory
P.O. Box 999
Richland, WA 99352
W. E. Norris, NRC Project Manager
NRC Job Codes V6085/V6411
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001
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Abstract
Operating experience has shown that Alloy 82/182/600 materials exposed to primary coolant water (or steam) under the normal operating conditions of pressurized water reactors (PWRs) are susceptible to primary water stress corrosion cracking (PWSCC). These materials were widely used in the original construction of domestic PWR reactor coolant systems (RCS). Cracking typically initiates at the inside surface of these materials when exposed to reactor coolant and in the presence of high tensile residual stresses introduced by welding. The locations in which PWSCC has been identified include partial penetration nozzles, nozzle welds, and piping butt welds. PWSCC increases the probability of a loss-of-coolant accident. This NUREG/CR pertains to managing PWSCC in Alloy 82/182 butt welds.
In response to this degradation mechanism, the nuclear industry and the U.S. Nuclear Regulatory Commission (NRC) undertook a variety of actions. These actions included conducting crack growth rate studies for Alloy 82/182/600 materials, developing augmented inspection programs for varied component configurations, and establishing an improved regulatory environment for addressing PWSCC. In Alloy 82/182 butt welds, the nuclear industry began implementing mitigation strategies for the most susceptible of these welds.
This report provides a summary of the operating experience with PWSCC in Alloy 82/182 butt welds and an overview of industry and regulatory activities to address the safety concern. This report describes the strategies being used to manage potential PWSCC in butt welds, the basic design and regulatory requirements of each strategy/mitigation technique, and an assessment of the issues that may impact the effectiveness of each management strategy. This report also summarizes the NRC regulatory requirements, ASME Code Cases, and the regulatory status of ASME Code Cases related to management of PWSCC in Alloy 82/182 butt welds. A historical summary and timeline of the major events, activities, and decision processes is provided in an appendix.
The effectiveness of the mitigation and inspection strategies being used is evaluated and issues that could affect the reliability of inspections that are required to be performed are also discussed.
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