United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 91-15: Incorrect Configuration of Breaker Operating Springs in General Electric AK-Series Metal-Clad Circuit Breakers

                                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 
.

                                                            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 

.

                                                            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. 
.
Page Last Reviewed/Updated Tuesday, November 12, 2013