United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 94-02: Inoperability of General Electric Magne-Blast Breaker because of Misalignment of Close-Latch Spring

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF NUCLEAR REACTOR REGULATION
                            WASHINGTON, D.C. 20555

                                January 7, 1994


NRC INFORMATION NOTICE 94-02:  INOPERABILITY OF GENERAL ELECTRIC MAGNE-BLAST
                               BREAKER BECAUSE OF MISALIGNMENT OF CLOSE-LATCH
                               SPRING


Addressees

All holders of operating licenses or construction permits for nuclear power
reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees that a misalignment of the close-latch reset spring
(tension style) in 4.16 kV General Electric (GE) Magne-Blast circuit breakers
could prevent the breaker from closing on demand.  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 are not NRC requirements;
therefore, no specific action or written response is required.

Description of Circumstances

On April 7, 1993, the Arizona Public Service Company, licensee for the
Palo Verde Nuclear Generating Station, notified the NRC that a safety-related
4.16 kV GE Magne-Blast breaker (Model AM-4.16-250-9H, 1200 ampere breaker with
ML-13 mechanism) was found inoperable with the closing springs discharged.
The inoperability was caused by misalignment of the close-latch reset spring.
This misalignment resulted in the coils of the spring catching on the close-
latch monitoring switch mounting plate.  This prevented the close-latch
monitoring switch from closing and prevented the charging motor from
recharging the closing springs, which rendered the breaker inoperable.  The
condition was identified by an auxiliary operator who noticed that the clear
control power/closing springs charged lamp was not illuminated on the front of
the breaker cubicle.  There was no indication of this problem in the control
room.

Further details can be found in NRC Inspection Report 50-528; 50-529; and
50-530/93-11.






9401030245.

                                                            IN 94-02
                                                            January 7, 1994
                                                            Page 2 of 2


DISCUSSION

GE Magne-Blast breakers are used in many safety-related circuits throughout
the nuclear industry.  At Palo Verde, these breakers are used for numerous
safety-related pumps (e.g., high-pressure safety injection, low-pressure
safety injection, and containment spray) and in safety-related load centers.
While this condition occurred in a 4.16 kV breaker, all GE Magne-Blast
breakers equipped with the ML-13 mechanism having the tension style close-
latch spring may be susceptible to this problem.

There are two different designs for the close-latch spring in the GE Magne-
Blast breakers.  The design that caused the problem was the tension-style
spring that is positioned beside the close-latch monitoring switch.  GE
subsequently replaced this spring with a torsion-style spring, which surrounds
the close-latch shaft and prevents the spring from catching on the mounting
plate.  GE considers this modification to be a design enhancement and has not
issued a service advisory letter or instruction on this subject.

The failed condition described above may not be evident if a breaker racking
operation is performed before the close-latch spring is inspected.  The
vibration associated with the racking operation may be sufficient to free the
spring from the close-latch monitoring switch mounting plate.  However, during
subsequent breaker operation, the spring coils may catch and render the
breaker inoperable.  Although there would likely be local indication that the
spring was not fully charged, there would be no control room indication of the
inoperability of the breaker.

No specific action or written response is required by this information notice.
If you have any questions regarding this matter, please contact one of the
technical contacts listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.


                                    ORIGINAL SIGNED BY


                                    Brian K. Grimes, Director
                                    Division of Operating Reactor Support
                                    Office of Nuclear Reactor Regulation

Technical contacts:  J. Frederick Ringwald, RIV
                     (316) 364-8653

                     Kamalakar R. Naidu, NRR
                     (301) 504-2980

Attachment:
List of Recently Issued NRC Information Notices

Page Last Reviewed/Updated Friday, November 15, 2013