Survey of operating experience from LERs to identify aging trends. [Licensee event reports

Abstract

The results of a study utilizing the ORNL Nuclear Operations Analysis Center (NOAC) computer files of operating experience reports (licensee event reports (LERs), abnormal occurrences, etc.) are summarized. In this study, specific time-related degradation mechanisms are identified as possible causes of a reportable occurrence. Data collected on domestic commercial nuclear power plants covering 1969 to 1982 yielded over 5800 events attributable to age-related failures. Of these events, 2795 were attributable to instrument drift, which are addressed separately in the report. The remaining events (3098) were reviewed, and data were collected for each event, identifying the specific system, component, and subpart; the information included-age-related failure mechanism, severity of failure, and method of detection of the failure. About two-thirds of the failures were judged to be degraded, with one-third listed as catastrophic failures. No events were found to be incipient failures because an LER is prepared only on degraded or catastrophic failure conditions that place plant operation outside the Technial Specifications. The study found that information desired for evaluation of aging effects (equipment, age, service life, and environment) was seldom available from LERs. This reflects the intent of the LER system as a regulatory instrument, rather than an engineering data collection system.