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
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                                                       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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