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
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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
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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.
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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
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