Assessment of Age-Related Degradation of Structures and Passive Components for U.S. Nuclear Power Plants (NUREG/CR-6679, BNL-NUREG-52587)

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Publication Information

Manuscript Completed: July 2000
Date Published: August 2000

Prepared by:
J.I. Braverman, C.H. Hofmayer, R.J. Morante, S. Shteyngart, P. Bezler

Nuclear Energy and Infrastructure Systems Division
Brookhaven National Laboratory
P.O. Box 5000, Building 130
Upton, New York 11973-5000

T.Y. Chang, NRC Project Manager

Prepared for:
Division of Engineering Technology
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code W6684

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Abstract

This report describes the results of the first phase of a multi-year research program to assess age-related degradation of structures and passive components for U.S. nuclear power plants. The purpose of this research program is to develop the technical basis for the validation and improvement of analytical methods and acceptance criteria which can be used to make risk-informed decisions and to address technical issues related to degradation of structures and passive components. The approach adopted for this research program consists of three phases. The Phase I effort included collection and evaluation of plant degradation occurrences, an assessment of the available technical information on age-related degradation, and a scoping study to identify which structures and components should be studied in the subsequent phases of the research program. Based on the results of the Phase I effort, selected structures and passive components are evaluated in Phase II to assess the effects of age-related degradation using existing and enhanced analytical methods. Phase III will utilize the results of the analyses to develop recommendations to the NRC staff for making risk-informed decisions related to degradation of structures and passive components. This report presents the results of the Phase I portion of the research program.

The Phase I assessment of age-related degradation of structures and passive components at nuclear power plants has been completed. This assessment consisted of three activities. In the first activity, instances of age-related degradation have been collected and evaluated. The data were collected from Licensee Event Reports, NRC generic communications, NUREG reports, and industry reports. A computerized database was developed to summarize important parameters which describe the applicable cases of degradation. Trending analyses were performed to identify which structures are most susceptible to age-related degradation, what are the most common aging mechanisms and aging effects, whether degradation occurrences are increasing, and other important observations. In the second activity, additional information such as NRC requirements/guidance, NRC programs, industry programs, degradation information from other countries, and other reports/papers on aging degradation were evaluated to identify the significant aging issues for those structures and passive components which would have the greatest impact on plant risk. In the third activity, the collection of degradation occurrences, trending analyses, available technical information, and risk significance of aging effects were utilized in a scoping study to identify those structures and passive components that warrant further detailed evaluation in Phase II of this program.

The scoping study concluded that the structures and passive components that warrant further detailed evaluation are masonry walls, flat bottom tanks, anchorages, concrete structures (other than containments) and buried piping. The focus of further research will be on developing and improving analytical methods to assess the effects of age-related degradation on the structural performance of structures and passive components, including fragility evaluations for probabilistic risk assessment and seismic margins assessment studies. The methodologies that will be developed could then be used to quantify the impact of age-related degradation of structures and passive components on overall plant risk. This would lead to greater confidence in the use of risk assessment as a tool for making risk-informed decisions for age-degraded structures and passive components.