United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 90-41: Potential Failure of General Electric Magne-Blast Circuit Breakers and AK Circuit Breakers

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

                                June 12, 1990


Information Notice No. 90-41:  POTENTIAL FAILURE OF GENERAL ELECTRIC
                                   MAGNE-BLAST CIRCUIT BREAKERS AND AK
                                   CIRCUIT BREAKERS


Addressees:

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

Purpose:

This information notice is intended to alert addressees to potential safety 
concerns that may result from failures of GE vertical lift (AM) and 
horizontal draw-out (AMH) Magne-Blast circuit breakers utilizing ML-l3 
operating mechanisms to open or close them and AK circuit breakers.  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. 

Description of Circumstances: 

The particular breaker failures reported herein were caused by operating 
problems with prop springs, snap rings and lubricating grease.  GE Nuclear 
Energy has informed the NRC that it is aware of these problems and that GE 
routinely checks and corrects them if the circuit breakers are serviced at 
one of the four GE nuclear service centers in the United States.  However, 
the NRC is aware that some utilities may have their circuit breakers 
repaired or serviced at facilities other than the four GE nuclear service 
centers. 

I.   Prop Spring

A.   Vertical Lift (AM Type) Magne-Blast Circuit Breakers

     On April 7, 1988, a service water pump at Peach Bottom Atomic Power 
     Station would not auto-start.  The pump circuit breaker (GE AM-4.16-kV) 
     would attempt to close but would trip free due to a broken prop reset 
     spring.  The defective circuit breaker was replaced.  Philadelphia 
     Electric Company authorized an independent analysis of the failed 
     spring.  This analysis revealed that the spring failed as a result of a 
     metal 
     




9006060309
.

                                                            IN 90-41
                                                            June 12, 1990
                                                            Page 2 of 4


     fatigue crack that initiated at a surface lap in the wire.  The 
     licensee authorized the analysis of five additional prop reset springs.  
     Although two of the five springs tested had surface laps similar in 
     depth to those of the original spring, no fatigue- or surface-induced 
     cracks were found on any of these five springs.  The licensee intends 
     to replace the prop reset spring every 2000 cycles.

     On December 2, 1989, a GE AM-4.16-350-1H-type circuit breaker being 
     used to operate a Turkey Point Unit 4 safety injection pump motor 
     failed to remain closed as a result of a broken prop reset spring.  The 
     circuit breaker had operated for approximately 1400 cycles before the 
     failure.  The broken prop reset spring was replaced and the circuit 
     breaker was returned to service on December 3, 1989.  Florida Power and 
     Light Company examined the failed spring metallurgically.  The licensee 
     determined that a fatigue fracture had occurred at the end of the coil, 
     where the wire was bent 90 degrees to form the hook.   
     
B.   Horizontal Draw-Out (AMH Type) Magne-Blast Circuit Breakers

     On August 16, 1989, a GE AMH-4.76-type circuit breaker failed to remain 
     shut at FitzPatrick nuclear power plant as a result of a broken prop 
     reset spring.  This circuit breaker had operated for 1625 cycles.  
     Subsequently, the licensee replaced the prop reset springs on all 
     safety-related circuit breakers with more than 900 cycles of operation.  
     
II.  Snap Ring

A.   Horizontal Draw-Out (AMH Type) Magne-Blast Circuit Breakers

     On November 5, 1988, while FitzPatrick was shut down for refueling, an 
     AMH-4.16-kV residual heat removal (RHR) service water pump motor 
     circuit breaker failed to trip on demand.  Inspection of the 4.16-kV 
     circuit breaker revealed a bent snap ring and two bent spacer washers 
     (shims) in the bottom of the circuit breaker frame.  The snap ring and 
     shims are part of the "prop-pin" assembly.  In an acceptable prop-pin 
     assembly, the prop-pin is aligned with the prop and is secured in that 
     position with shims and a snap ring.  It is believed that the prop-pin 
     and the prop in the failed circuit breaker were not aligned properly.  
     The misalignment permitted the prop to strike the snap ring and the 
     shims instead of the prop-pin.  This resulted in the snap ring and the 
     shims bending and eventually failing.  With the loss of the snap ring 
     and the shims from the prop-pin assembly, the prop-pin was free to 
     shift far enough to hang up in the frame and to prevent the circuit 
     breaker from tripping.  

     FitzPatrick reported (Licensee Event Report 88-014-01) that this 
     circuit breaker and other circuit breakers had been refurbished during 
     1986 and 1987 at the GE nuclear service center located in King of 
     Prussia, Pennsylvania.  During the refurbishing process, GE technicians 
     apparently did not specifically verify the alignment.  As a result of 
     this problem, GE has imposed an additional inspection step in their 
     servicing procedures to check the alignment after reassembling the 
     circuit breaker.  GE informed 
     
.

                                                            IN 90-41
                                                            June 12, 1990
                                                            Page 3 of 4


     the NRC that the other three GE nuclear service centers have been 
     alerted to this problem and that similar corrective action has been 
     taken to preclude recurrence of this problem.

B.   AK Circuit Breakers

     On March 12, 1990, a GE model AK-2A-50 480-volt metal clad breaker 
     failed to automatically close during an automatic bus transfer, in 
     preparation for required surveillance testing at Pilgrim.  On March 20, 
     1990, the same GE AK-2A-50 480-volt metal clad breaker failed to trip 
     during an automatic bus transfer to restore the normal lineup.  Both 
     Pilgrim events were attributed to a missing snap ring and shims which 
     held the prop assembly in place.  Boston Edison Co. discovered that the 
     prop which held the breaker closed by latching with the cam of the trip 
     latch roller assembly had slipped out of its support, preventing the 
     breaker from remaining closed.  The bearing on which the prop rotates 
     is held in place in the frame by a snap ring on both sides of the 
     bearing.  Boston Edison Co. found a snap ring on one end of the bearing 
     to be missing.  This permitted the bearing to slip out of the frame and 
     prevented the proper operation of the breaker (failed to latch, failed 
     to trip).  This circuit breaker, as well as other AK 480-volt metal 
     clad breakers were overhauled/refurbished in 1987 by the GE nuclear 
     service center located in King of Prussia, Pennsylvania.

     On March 8, 1989, a GE model AKS-2A-50 480-volt metal clad breaker (a 
     later version of AK-2A-50) failed while Oyster Creek was shutdown and 
     performing a routine check of the control rod drive breaker.  GPU 
     Nuclear Corporation discovered damage to a snap ring, prop bearings, 
     and a breaker clevis pin which had fallen out due to a missing snap 
     ring.  Additionally, the prop shaft assembly was observed to be 
     insecure.  This breaker and others at Oyster Creek were refurbished by 
     GE in 1987 and 1988.

     On June 10, 1986, a GE model AK-2-25 480-volt metal clad breaker would 
     not close at Crystal River 3, while an operator was attempting to reset 
     control rod breakers during shutdown conditions.  Florida Power 
     Corporation discovered the snap ring was out of position which allowed 
     the prop-pin to slip out of its support.

III. Lubricating Grease

A.   Magne-Blast Circuit Breakers

     In January 1990, the NRC conducted an inspection of the GE service 
     center in King of Prussia, Pennsylvania.  During this inspection, the 
     NRC determined that D50H47-type grease (black grease) in the stationary 
     cubicles of the switchgear may not be removed completely prior to the 
     application of the new D6A15A1-type grease (red grease), as GE has 
     recommended.  It is particularly important for licensees who overhaul 
     their circuit breakers at locations other than GE nuclear service 
     centers to ensure that the stationary cubicles and draw-out circuit 
     breakers are properly lubricated and the above recommendations are 
     taken into account when applying the new red grease.  
.

                                                            IN 90-41
                                                            June 12, 1990
                                                            Page 4 of 4


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:  K. Naidu, NRR
                    (301) 492-0980


Attachment:  List of Recently Issued NRC Information Notices
.ENDEND
Page Last Reviewed/Updated Tuesday, November 12, 2013