Information Notice No. 89-86: Type HK Circuit Breakers Missing Close Latch Anti-Shock Springs
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
December 15, 1989
Information Notice No. 89-86: TYPE HK CIRCUIT BREAKERS MISSING
CLOSE LATCH ANTI-SHOCK SPRINGS
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
Information Notice No. 87-41, "Failures of Certain Brown Boveri Electric
Circuit Breakers" (IN 87-41) was issued August 31, 1987. This information
notice is intended to alert addressees of additional information regarding
Type HK circuit breakers that may have been manufactured without a close
latch anti-shock spring. It is expected that recipients will review the
information for applicability to their facilities and consider actions, as
appropriate, to avoid similar problems. However, suggestions contained in
this information notice do not constitute NRC requirements; therefore, no
specific action or written response is required.
Background:
Type HK circuit breakers utilize a charging spring motor to charge
(compress) the charging springs. At the end of the charging cycle, a close
latch is engaged to hold the charging springs in the charged (compressed)
position. The circuit breaker can then be closed (by spring force) on
demand.
IN 87-41 highlighted instances at Limerick Unit 1 and Beaver Valley Unit 2
where Type HK circuit breakers inadvertently closed following completion of
the charging cycle. Subsequent to the occurrence at Limerick Unit 1, the
manufacturer indicated that this condition can be corrected by adding an
anti-shock spring to the close latch. The manufacturer also indicated that
this anti-shock spring was not included in Type HK circuit breakers
manufactured prior to 1973 and from June 1975 to June 1977.
Description of Circumstances:
During the recent refueling outage at Fermi Unit 2, the licensee inspected
both safety-related and non-safety-related Type HK circuit breakers. The
close latch anti-shock springs were observed to be missing in approximately
40 safety-related Type HK circuit breakers that had been manufactured
outside of the previously identified timeframes. (The identified circuit
breakers
8912110174
.
IN 89-86
December 15, 1989
Page 2 of 2
were manufactured in 1974.) Thus, the timeframes previously identified by
the manufacturer (prior to 1973 and from June 1975 to June 1977) may not be
totally inclusive. In addition, because of changes in corporate name,
mergers, etc., Type HK circuit breakers may indicate manufacture by ITE, ITE
Imperial, Gould, Brown Boveri, or a combination thereof. The current name
of the manufacturer is ASEA Brown Boveri. Recipients may need to be
cognizant of this when determining whether they utilize potentially affected
equipment.
Discussion of Safety Significance:
Failure to close on demand or inadvertent closure of a Type HK circuit
breaker could result in a circuit breaker not performing its intended
function. This, in turn, could result in the loss of a power supply. For
example, inadvertent closure of a Type HK circuit breaker onto a vital bus
supplied by an emergency diesel generator, such as during load sequencing,
could result in overloading the emergency diesel generator. This could
occur at the end of a spring charging cycle on a Type HK circuit breaker
which was tripped by a loss-of-offsite power signal, as typically happens
just prior to load sequencing.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate NRR project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: Jack Ramsey, NRR
(301) 492-1167
Attachment: List of Recently Issued NRC Information Notices
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