Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
March 6, 1991
Information Notice No. 91-15: INCORRECT CONFIGURATION OF BREAKER
OPERATING SPRINGS IN GENERAL ELECTRIC
AK-SERIES METAL-CLAD 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 a potential
problem caused by the incorrect configuration of the breaker operating
springs in the AK-series metal-clad circuit breakers manufactured by the
General Electric Company (GE). 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:
On October 28, 1990, the Florida Power and Light Company, the licensee for
the St. Lucie Nuclear Power Plant (St. Lucie), Units 1 and 2, reported that
a reactor trip circuit breaker failed to close at St. Lucie, Unit 1, during
prep-aration for control element assembly testing. The St. Lucie reactor
trip breakers are AK-series, metal-clad circuit breakers manufactured by the
General Electric Company (GE). The licensee determined that the breaker
failed to close because the configuration of an operating spring was
incorrect. During a subsequent inspection of the remaining reactor trip
breakers in Unit 1, the licensee determined that the configuration of the
operating springs was incorrect on three of the breakers; however the
breakers were functioning properly. St. Lucie personnel stated that the GE
service shop in Atlanta, Georgia, had last serviced all of their reactor
trip breakers.
On November 11, 1990, the Maine Yankee Atomic Power Company, the licensee
for the Maine Yankee Atomic Power Station (Maine Yankee), reported that a
reactor trip breaker failed to close during the performance of a
surveillance test. The licensee determined that the two operating springs
were disengaged. The licensee personnel, with the assistance of field
service personnel from GE Nuclear Energy (GENE), inspected the remaining
eight breakers and observed that the configuration of the springs was
incorrect in one of these reactor trip breakers.
9102280098
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IN 91-15
March 6, 1991
Page 2 of 2
Discussion:
In a GE AK-series (AK-, AKF-, or AKR-) metal-clad circuit breaker, two
operating springs are attached to the circuit breaker mechanism, which
closes and latches the circuit breaker contacts. After the contacts close,
the tension of the springs maintains latch engagement to keep the breaker in
the closed position and supplies the motive force to open the contacts upon
demand. If the two operating springs become disengaged from the mechanism,
the circuit breaker contacts will not remain closed. On December 28, 1990,
Maine Yankee reported to the NRC that, although an AK-2 breaker could close
properly with one spring available, the disengaged spring could jam the
operating mechanism and prevent the breaker from tripping.
GENE inspected the failed reactor trip breaker from St. Lucie at the GE
service facility in Atlanta, Georgia, and confirmed that the failure was
caused by the incorrect configuration of the operating springs in the
breaker. GENE conducted tests to determine if the circuit breaker would
fail to close with the operating springs installed incorrectly, and
determined that the operating springs are less likely to disengage from the
circuit breaker mechanism if the first curve between the spring hook and the
first coil of the operating spring turns away from the centerline of the
circuit breaker.
GENE informed the NRC that it has notified its four service centers, which
periodically refurbish safety-related circuit breakers, to verify the
correct configuration of the operating springs. The GE maintenance
instructions provide neither instructions nor sufficient information to
verify if the operating springs are correctly oriented.
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 contacts listed below or the appropriate NRC project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: Kamal R. Naidu, NRR
(301) 492-0980
Stephen D. Alexander, NRR
(301) 492-0995
Attachments:
1. List of Additional Failures in GE AK-series Circuit Breakers
2. List of Recently Issued NRC Information Notices
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Attachment 1
IN 91-15
March 6, 1991
Page 1 of 1
List of Additional Failures in GE AK-Series Circuit Breakers
On April 16, 1989, plant personnel at the St. Lucie plant observed that
fuses were blowing when they attempted to close a reactor trip breaker.
During an inspection, plant personnel determined that the operating springs
had become disconnected from the mechanism. Plant personnel reconnected the
operating springs, tested the breaker successfully, and returned it to
service.
On January 1, 1989, while plant personnel performed surveillance tests on
the reactor trip breakers at the Calvert Cliffs Nuclear Power Plant (Calvert
Cliffs), Unit 2, a breaker failed to close. Plant personnel performed an
inspection and determined that the left operating spring had become
disconnected from the mechanism. Plant personnel reconnected the operating
spring, tested the breaker for reclosing successfully, and returned it to
service.
On March 21, 1988, while performing surveillance tests on a reactor trip
breaker at Calvert Cliffs, Unit 2, plant personnel determined that the
operating springs had become disconnected from the mechanism. After
replacing the front frame assembly, plant personnel completed the
appropriate portions of the surveillance tests and returned the breaker to
service.
On March 12, 1988, while performing surveillance tests on reactor trip
breakers at Calvert Cliffs, Unit 2, plant personnel observed that a breaker
had failed to close. Plant personnel inspected the breaker and determined
that the operating springs had become disconnected from the mechanism.
Plant personnel reconnected the operating springs, functionally tested the
breaker for operability, and returned it to service.
On January 8, 1987, during normal operations at Calvert Cliffs, Unit 2, a
reactor trip breaker failed to close after plant personnel had opened it
from the control room panel. Plant personnel inspected the breaker and
determined that the operating springs had become disconnected from the
mechanism. Plant personnel reconnected the operating springs and returned
the breaker to service.
On December 15, 1986, during normal operations at Calvert Cliffs, Unit 2, a
reactor trip breaker failed to close after an operator had opened it from
the control room panel. Plant personnel inspected the breaker and
determined that the operating springs had become disconnected from the
mechanism. Plant personnel reconnected the operating springs and returned
the breaker to service.
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