United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 96-43: Failures of General Electric Magne-Blast Circuit Breakers

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF NUCLEAR REACTOR REGULATION
                          WASHINGTON, D.C. 20555-0001

                                August 2, 1996


NRC INFORMATION NOTICE 96-43:  FAILURES OF GENERAL ELECTRIC MAGNE-BLAST        
                               CIRCUIT BREAKERS


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 to recent failures of General Electric (GE) 4.16 kV
Magne-Blast circuit breakers at the Dresden Nuclear Power Station, Unit 3
(Dresden 3), caused by hardened grease and failures of Magne-Blast breakers to
latch closed at the Salem Nuclear Generating Station (Salem) and the Maine
Yankee Atomic Power Plant (Maine Yankee).  The NRC staff is preparing a
separate information notice to discuss failures related to refurbishment
practices, including zinc plating of surfaces and recently discovered broken
lock washers at Salem.  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

Failure Due to Hardened Grease

On June 11, 1996, at Dresden 3, a 4.16-kV GE Magne-Blast circuit breaker that
supplies power to a low-pressure coolant injection pump motor failed to open
on demand from the control room following a surveillance run of the pump. 
Examination of the failed breaker showed hardened grease in the breaker
mechanism.
                                  
In subsequent testing of four similar spare breakers, all tripped at required
low voltage conditions.  However, two of the breakers showed the potential for
unreliable operation because their trip latch roller bearings did not freely
rotate.  The cause was hardened grease.  During bench testing of breakers
pulled from the cubicles to date, two additional breakers failed to trip on
required low voltage.  Both breakers exhibited hardened grease conditions in
trip latch roller bearings.

The licensee identified 23 safety-related breakers in Dresden 3 as susceptible
to this failure mechanism.  On June 20, 1996, the licensee initiated a 


9607310096.                                                            IN 96-43
                                                            August 2, 1996
                                                            Page 2 of 4


shutdown of Dresden 3 and contracted with GE Nuclear Energy to completely
overhaul each of these 23 breakers and the similar ones in Dresden 2.

Failure to Latch Closed

On January 5, 1996, at Salem, a 4.16-kV GE Magne-Blast circuit breaker that
supplies power to a service water pump motor failed to latch closed on demand
from the control room.  During the subsequent investigation with the breaker
in test position, the breaker failed to latch closed on the seventh attempt
after successfully latching closed six times.  

On February 15, 1996, a different service water pump breaker at Salem failed
to latch closed.  This breaker had been returned to service after an overhaul
at the GE Apparatus Service Center in Philadelphia.

On September 27, 1993, at Maine Yankee, a 4.16-kV GE Magne-Blast component
cooling water pump breaker failed to latch closed on demand from the control
room.  The licensee enabled this breaker to close reliably by replacing the
upper prop spring with a heavier prop spring (of the gold-colored type used as
a lower prop spring).

Discussion

In 1989, during an NRC maintenance team inspection at Dresden, the team found
a lack of lubrication of these same breakers.  At that time, the licensee
instituted a preventive maintenance program as a corrective measure. 
Subsequent NRC review of that program showed that the licensee had not fully
implemented recommendations of the manufacturer, GE Specialty Breaker Plant.

The GE instruction book applicable to the horizontal-drawout Magne-Blast
circuit breakers used at Dresden (GEI-88771D), a similar book applicable to
vertical-lift breakers used elsewhere (GEK-7320F), and GE Service Advice
Letter (SAL) 354.1, dated August 25, 1995, recommend that these breakers be
lubricated once every 2 years.  The licensee, however, had been using a six-
year maintenance period and had not maintained (cleaned and lubricated) the
failed breaker for six and a half years.  The following factors may have
contributed to the aging and hardening of grease over this protracted
maintenance period:  (1) contamination of grease by an aerosol degreaser
during maintenance in 1989, (2) prevention of the light-weight lubricating oil
applied during the 1989 maintenance from reaching internal bearing surfaces
and refreshing the grease (the licensee had applied a light coating of grease
before applying the oil), (3) premature aging of grease from cubicle heaters,
and (4) presence of fibrous material in the one affected bearing.

In Information Notice 94-54, the NRC staff alerted licensees to failures of
Magne-Blast breakers to latch closed and discussed the recommendation (GE
SAL 352) to add a second prop spring to correct the failure.  The staff
pointed out that breakers that are grossly out of adjustment or badly worn may
fail to latch closed even with the addition of a second prop spring.  

The Salem licensee and GE jointly used high-speed digital video equipment to
learn that the failure mechanism is complex and that the prop-to-prop pin .                                                            IN 96-43
                                                            August 2, 1996
                                                            Page 3 of 4


motion is influenced by the opening and closing spring energy, prop spring
force, and primary contact assembly wipe or rebound.  The timing of the
rebound of the prop pin (if it is present) relative to the prop reset motion
is critical to reliable operation.  If the prop pin impacts the tip of the
prop, it may reverse the prop motion.  The breaker will fail to latch if the
prop does not have sufficient time to recover to a position under the pin
before the pin falls.  The impact also may cause the tips of the prop to
become chipped or flattened.  

In agreement with GE, the Salem licensee believes the prop pin may fail to
achieve the required position because of (1) the age and wear of the breaker,
(2) misalignment of the prop mechanism, (3) errors that may be introduced in
the alignment of the operating mechanism causing the prop and or articulated
mechanism to twist, (4) misalignment of the stationary cubicle in which the
breaker operates, and (5) opening spring adjustment.  The cause of any
particular failure to latch may have to be determined on an individual basis.

This problem affects vertical-lift Magne-Blast circuit breakers with ML-13
mechanisms that have close-latch ratings of 77 kA or above (high momentary
ratings).

The Salem licensee concluded that the following symptoms are indicative of the
conditions present during the high-speed prop reset action that could result
in failure of the breaker to latch closed:

      �   The prop stop pin is not in the fully forward position in the
          inspection window when the breaker is closed.

      �   The tips of the prop are chipped or flattened.  (The prop tips may
          be viewed through both inspection holes.)

      �   The breaker has a history of intermittently failing to latch closed.

      �   If the arcing contacts have overstroked, the tips of the arcing
          contacts will probably be damaged by their impact on the dividers in
          the stationary arcing contacts, and the buffer blocks may be
          cracked. 

      �   Prop wipe is unequal, indicating prop or prop pin twist.

In agreement with GE, the corrective action taken at Salem was to raise the
preload on the opening spring to slow down the closing action, thus allowing
more time for the prop to get into position.  However, this approach is
limited by the minimum speed that must be achieved by the moving contacts to
maintain the high momentary rating.

GE Philadelphia Operations is pursuing an alternative solution:  (1) replacing
the second prop spring with a heavier one, currently under development, (2)
installing a second prop stop to restrict the prop movement on the left-hand
side, and (3) adjusting the wipe on the main contacts.  When testing is
complete, GE plans to issue a SAL on this subject.  
.                                                            IN 96-43
                                                            August 2, 1996
                                                            Page 4 of 4


Related Generic Communications

1.  Bulletin 74-09, "Deficiency in General Electric Model 4KV Magne-Blast      
    Breakers," August 6, 1974.

2.  Information Notice 84-29, "General Electric Magne-Blast Circuit Breaker    
    Problems," April 17, 1984.

3.  Information Notice 90-41, "Potential Failure of General Electric           
    Magne-Blast Circuit Breakers and AK Circuit Breakers," June 12, 1990.

4.  Information Notice 93-26, "Grease Solidification Causes Molded Case        
    Circuit Breaker Failure To Close," April 7, 1993.

5.  Information Notice 93-91, "Misadjustment Between General Electric 4.16-KV  
    Circuit Breakers and Their Associated Cubicles," December 3, 1993.

6.  Information Notice 94-02, "Inoperability of General Electric Magne-Blast   
    Breaker Because of Misalignment of Close-Latch Spring," January 7, 1994.

7.  Information Notice 94-54, "Failures of General Electric Magne-Blast        
    Circuit Breakers To Latch Closed," August 1, 1994.

8.  Information Notice 95-22, "Hardened or Contaminated Lubricants Cause       
    Metal-Clad Circuit Breaker Failure," April 21, 1995.

This information notice requires no specific action or written response.  If
you have any questions about the information herein, please contact one of the
technical contacts listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.


                                          signed by

                                    Brian K. Grimes, Acting Director
                                    Division of Reactor Program Management
                                    Office of Nuclear Reactor Regulation

Technical contacts:  D. Skeen, NRR              K. Naidu, NRR
                     (301) 415-1174             (301) 415-2980
                     E-mail:  dls@nrc.gov       E-mail:  krn@nrc.gov

                     A. Pal, NRR                J. Shannon, Region I
                     (301) 415-2760             (610) 337-5132
                     E-mail:  anp@nrc.gov       E-mail:  jms1@nrc.gov


Page Last Reviewed/Updated Thursday, November 21, 2013