United States Nuclear Regulatory Commission - Protecting People and the Environment

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. 


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                                                             IN 83-50      
                                                             August 1, 1983 
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(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

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