United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-54: Failure of Circuit Breaker following Installation of Amptector Direct Trip Attachment

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C. 20555

                                  July 28, 1988

                                   INSTALLATION OF AMPTECTOR DIRECT TRIP 

All holders of operating licenses or construction permits for nuclear power 


This information notice is being provided to alert addressees to potential 
problems resulting from the installation of Amptector direct trip attachments 
on Westinghouse Electric Corporation (W) and General Electric Company (GE) 
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: 

On December 21, 1987, the "B" train residual heat removal (RHR) pump at the 
R.E. Ginna Nuclear Power Plant failed to start during a required surveillance 
test.  The cause of the failure was attributed to a power supply circuit 
breaker that failed to remain closed on a valid close signal.  The spurious 
opening of this circuit breaker interrupted power to the RHR pump because the 
circuit breaker Amptector direct trip attachment (DTA) was improperly 
installed.  Inadequate clearance existed between the circuit breaker trip bar 
and the DTA's actuating arm.  Therefore, the mechanical vibration that 
generally accompanies the closing of a circuit breaker was sufficient to cause 
the DTA's actuating arm to actuate the circuit breaker trip bar and resulted 
in the reopening of the breaker. 

During the failure, a battery equalizing charge was in progress, which the 
licensee feels also contributed to the opening of the breaker.  The higher 
than normal operating voltage of 140V dc (as opposed to the normal 130V dc) 
applied to the breaker likely increased the vibration generated during the 
closing of the breaker.


As a result of the RHR pump breaker failure, the licensee conducted 
operational tests on all Class 1E circuit breakers that had undergone the 
Amptector modification.  The "B" train safety injection pump breaker failed on
the seventh 

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                                                            July 28, 1988 
                                                            Page 2 of 2 

actuation.  Additional checks of the RHR pump circuit breaker did not result 
in a failure until the 14th actuation.  No other failures were observed and 
the problem was determined to be intermittent.

The licensee, in consultation with W representatives determined that there was 
a direct correlation between the circuit breaker failure and the procedure 
used by the licensee in mounting the Amptector DTA.  The procedures supplied 
by W for installing the trip attachment did not specifically indicate a 
minimum clearance that was to be maintained between the DTA's actuating arm 
and the circuit breaker trip bar.  W representatives orally informed the 
licensee that the clearance should measure between 1/32 and 1/16 of an inch 
which is the gap used by W in establishing the seismic adequacy of the DTA on 
W circuit breakers.  

W representatives stated that this minimum clearance is recommended to ensure 
that there is no contact between the actuating arm and the trip bar during 
pre-trip steady-state operating conditions to reduce the possibility of 
inadvertent actuation.  It is our understanding that W will be issuing a 
technical bulletin addressing the DTA.  

The circuit breakers for which this modification is designed are the W Model 
DB series and the GE Model AK 2A series.  The Amptector DTA is manufactured 
and supplied by W.  The operating plants that are known to have the 
attachments in place are H. B. Robinson, Indian Point 2, Connecticut Yankee, 
Three Mile Island 1, Cooper, Fitzpatrick, Monticello and San Onofre, but this 
list may not be complete.  

No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical con-
tact listed below or the Regional Administrator of the appropriate regional 

                              Charles E. Rossi, Director 
                              Division of Operational Events Assessment 
                              Office of Nuclear Reactor Regulation 

Technical Contact:  N. Fields, NRR 
                    (301) 492-1173 

Attachment: List of Recently Issued NRC Information Notices 
.                                                            Attachment
                                                            IN 88-54 
                                                            July 28, 1988 
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                            NRC INFORMATION NOTICES 
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

88-53          Licensee Violations of NRC    7/28/88        All manufacturers 
               Regulations, Which Led to                    and distributors 
               Medical Diagnostic                           of radio- 
               Misadministrations                           pharmaceuticals 
                                                            for human use, 
                                                            pharmacies, and 
                                                            medical licensees.

88-52          Failure of Intrauterine       7/27/88        Medical licensees.
               Tandem of Fletcher 
               Applicator Brachytherapy 
               Devices During Patient 

88-46,         Licensee Report of            7/26/88        All holders of OLs
Supplement 1   Defective Refurbished                        or CPs for nuclear
               Circuit Breakers                             power reactors. 

88-51          Failures of Main Steam        7/21/88        All holders of OLs
               Isolation Valves                             or CPs for nuclear
                                                            power reactors. 

88-50          Effect of Circuit             7/18/88        All holders of OLs
               Breaker Capacitance                          or CPs for nuclear
               on Availability of                           power reactors. 
               Emergency Power 

88-49          Marking, Handling,            7/18/88        All holders of OLs
               Control, Storage and                         or CPs for nuclear
               Destruction of Safe-                         power reactors and
               guards Information                           all other licensed
                                                            involving a 
                                                            formula quantity 
                                                            of special nuclear

88-48          Licensee Report of            7/12/88        All holders of OLs
               Defective Refurbished                        or CPs for nuclear
               Valves                                       power reactors. 

88-47          Slower-Than-Expected          7/14/88        All holders of OLs
               Rod-Drop Times                               or CPs for PWRs. 

OL = Operating License
CP = Construction Permit 
Page Last Reviewed/Updated Friday, May 22, 2015