Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 87-41
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
August 31, 1987
Information Notice No. 87-41: FAILURES OF CERTAIN BROWN BOVERI
ELECTRIC CIRCUIT BREAKERS
Addressees:
All nuclear power reactor facilities holding an operating license or a con-
struction permit.
Purpose:
This information notice is provided to inform recipients of failures of
certain Brown Boveri Electric (BBE) circuit breakers. It is expected that
recipients will review the information for applicability and consider actions,
if appropriate, to preclude similar problems from occurring at their
facilities. Suggestions contained in this notice do not constitute NRC
requirements; therefore, no specific action or written response is required.
Description of Circumstances:
Concerns regarding BBE circuit breakers have been recently reported to the
NRC. On April 20, 1987, Duquesne Light Company, the Beaver Valley Unit 2
licensee, notified the NRC in accordance with the reporting requirements of 10
CFR 50.55(e) of the failure of a BBE Type 5HK Class IE 4-KV circuit breaker.
When the circuit breaker was racked onto the bus and 125-V DC control power
was applied to the breaker's control circuit, the closing spring charged and
the circuit breaker immediately closed and opened several times before the
control power could be turned off. The licensee determined by field testing
that the closing coil was not being energized.
Another problem with BBE circuit breakers occurred at River Bend and was
reported in Licensee Event Report (LER) 87-004, dated March 6, 1987. On
February 6, 1987, with the unit at full power, the Division I diesel generator
4.16-KV output circuit breaker (Gould-Brown Boveri Type 5HK) failed to close
during a weekly surveillance test. The licensee's inspection of the output
circuit breaker revealed that a mounting bolt had fallen out of the closing
spring charging motor, rendering the motor inoperable. Further investigation
revealed several other circuit breakers that contained loose or missing charg-
ing motor mounting bolts. The licensee also stated that the River Bend
circuit breaker preventive maintenance program, which the licensee believes to
be in accordance with the vendor's recommendations, did not detect this
problem. The licensee believes the root cause of the problem to be
insufficient torquing of the charging motor mounting bolts by the vendor.
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. IN 87-41
August 31, 1987
Page 2 of 2
Discussion:
With regard to the repeated closing and opening of the breaker, this problem
was also reported to the NRC in accordance with the reporting requirements of
10 CFR 50.55(e) by Philadelphia Electric Company, for Limerick Unit 1, in
1983. The circuit breakers involved were returned to BBE for analysis, and
BBE transmitted its findings to the NRC in a letter dated April 20, 1983. BBE
stated that the repeated closing and opening of the circuit breaker can be
corrected by the addition of a light spring to the close latch in the circuit
breaker operating mechanism. BBE also stated that, depending upon the year of
manufacture, circuit breakers may or may not have been originally supplied
with this spring. BBE recommended that these springs be installed in circuit
breakers that were not originally supplied with one. This problem may also
affect BBE Type 7.5HK, 15HK, and 38HK circuit breakers. Although information
regarding this problem has been distributed by BBE and the Institute for
Nuclear Power Operations (INPO), the Beaver Valley event indicates that this
problem still exists. Licensees and applicants may wish to contact BBE to
obtain additional information regarding this problem and appropriate
corrective actions.
Failure of a circuit breaker to fully close on demand, inadvertent closure of
a circuit breaker, or loose or missing closing spring charging motor mounting
bolts could result in a circuit breaker not performing its intended function.
This, in turn, could result in the loss of a power supply (such as a vital bus
or a diesel generator).
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the Regional
Administrator of the appropriate regional office or this office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: Jack Ramsey, NRR
(301) 492-9081
Attachment: List of Recently Issued NRC Information Notices