Review of Industry Responses to NRC Generic Letter 97-06 on Degradation of Steam Generator Internals (NUREG/CR-6754)
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Manuscript Completed: December 2001
Date Published: December 2001
M. Subudhi, J. C. Higgins, BNL
S. M. Coffin, NRC
Brookhaven National Laboratory
Upton, NY 11973-5000
E. J. Sullivan, NRC Project Manager
Division of Engineering
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
NRC Job Code J2831
This report presents the results of an assessment of the nuclear power industry's responses to NRC Generic Letter (GL) 97-06 on the degradation of steam generator (SG) internals experienced at Electricite de France (EdF) plants in France and at a United States (U.S.) Pressurized Water Reactor (PWR). Before issuing the GL, with the exception of a few licensees, there were no formal inspection programs, nor any industry guidelines for monitoring the secondary side internals of steam generators. Nonetheless, all licensees have been performing some inspection and maintenance on their steam generator internals and have found no significant degradation in them. Most of the steam generators in U.S. plants do not appear susceptible to the degradation found at EdF and in the U.S. PWR.
The Westinghouse (W) Models 44, 51, 5IM, and D3 and the Combustion Engineering Model 67 with carbon steel eggcrates potentially could experience degradation similar to that found at EdF plants and the U.S. PWR. Recent inspections showed that replacement steam generators made by Babcock & Wilcox International of Canada may be vulnerable to tube proximity problems. The owners groups identified possible degradation mechanisms for these models in their assessments and have evaluated their potential causes. Recommendations were made to monitor for these types of degradation.
During this assessment, each owners group identified for its steam generator models all the potential internal components that are vulnerable to degradation while in service. They provided inspection- and monitoring-guidance and recommendations for their particular SG models. The Nuclear Energy Institute (NEI), who has been coordinating the industry's response to this GL, has incorporated in NEI 97-06, "Steam Generator Program Guidelines" a requirement to monitor secondary side SG components if their failure could prevent the SG from fulfilling its intended safety-related function. Licensees plan to implement their owners group recommendations to address the long-term effects of the potential degradation mechanisms associated with the SG internals. Overall, the licensees' submittals have met the intent of the GL and provide reasonable assurance that the SG internals comply with, and conform to, the licensing basis.