Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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
Attachment:
List of Recently Issued IE Information Notices
.
