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Information Notice No. 83-50: Failures of Class 1E Safety-related Switchgear Circuit Breakers to Close on Demand
SSINS No.: 6835 IN 83-50 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 August 1, 1983 Information Notice No. 83-50: FAILURES OF CLASS 1E SAFETY-RELATED SWITCHGEAR CIRCUIT BREAKERS TO CLOSE ON DEMAND Addressees: All nuclear power reactor facilities holding an operating license (OL) or a construction permit (CP). Purpose: This notice describes the causes for a number of failures of Class 1E safety-related switchgear circuit breakers to close on demand and provides additional information regarding corrective measures taken to alleviate this recurring problem. Description of Circumstances: There have been a number of occurrences involving the failure of Class 1E safety-related switchgear circuit breakers to close on demand. A study was conducted by the NRC to determine causes of such failures. The data base set for this study consisted of 108 licensee event reports on related circuit breaker failures covering approximately 51/2 years from January 1977 to August 1982. In general, the study concluded that the failure of such circuit breakers to close on demand was attributed to a problem within the malfunctioning circuit breaker's closing control circuitry located inside the circuit breaker cubicle. Typical causes for failures were identified as blown control circuit fuses, intermittent electrical connections, dirty or corroded contacts, malfunctions in the spring charging motor or associated spring position switch contacts. Electrical circuit problems for a given circuit breaker were found to be repetitive, which suggests that initial corrective actions did not correct the cause of the problem. In addition to the general items above, the study also provided the following findings: (1) Nearly 25% of the tabulated events contained in the data base set used for the study involved a diesel generator output breaker. In general, there are more permissive interlocks associated with the closing circuit of these breakers and this may be the reason for the relatively high percentage of occurrences. 8306270418 . IN 83-50 August 1, 1983 Page 2 of 2 (2) Regular local surveillance of the status of the spring charging motor (at the switchgear) could be an effective method of monitoring the readiness of the closing spring to operate on demand. (3) Other factors contributing to circuit breaker failures (such as dirty or corroded contacts, improper return of breakers to operable status following maintenance, or testing) suggest that corrective measures which provide adequate "housekeeping" at the breaker location, regular electrical connection and contact status checkout would improve functional performance of these devices. (4) Operating personnel may require additional training in the control logic and operation of circuit breakers equipped with automatic lockout features that are not indicated in the control room when this inoperable condition exists. This training should include steps that clear such a lockout state to allow reclosure of the tripped breaker. From the results of the above study, it appears that improvements in local surveillance of the circuit breakers, maintenance procedures, training of operations personnel could improve the functional performance of these circuit breakers to close on demand. No written response to this notice is required; however, licensees should review the information contained in this notice for applicability to their facilities, especially if safety-related switchgear circuit breakers continue not to close on demand. If there are any questions regarding this matter, please contact the Regional Administrator of the appropriate NRC Regional Office, or this office. Edward L. Jordan Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Technical Contact: V. D. Thomas (301) 492-4755 M. Chiramal, AEOD (301) 492-4441 Attachment: List of Recently Issued IE Information Notices .
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