United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-44: Mechanical Binding of Spring Release Device in Westinghouse Type DS-416 Circuit Breakers

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

                                  June 24, 1988


Information Notice No. 88-44:  MECHANICAL BINDING OF SPRING RELEASE DEVICE
                                   IN WESTINGHOUSE TYPE DS-416 CIRCUIT 
                                   BREAKERS


Addressees:

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

Purpose:

This information notice is being provided to alert addressees to potential 
problems resulting from the mechanical binding of the spring release device 
(SRD) in Westinghouse type DS-416 metal clad circuit breakers.  It is expected 
that recipients will review the information for applicability to their facili-
ties 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 May 25, 1988, the South Texas Project Unit 1 (STP-1 or licensee) performed 
a loss-of-offsite power test.  During this test, two Class 1E electrical 
circuit breakers failed to reclose as required during load sequencing.  
Subsequent investigation by the licensee identified the failed breakers as 
Westinghouse type DS-416 metal clad breakers.  These DS-416 electrical 
breakers are located in main 480-Vac load centers and are tie and feeder 
breakers for 480-Vac components. 

The breaker has an SRD that initiates the sequence for the breaker closing.  
The SRD is attached to the breaker housing and is comprised of a coil housing 
that is attached to the breaker casing, a closing coil, and a lever that is 
attached to the coil housing.  The lever travels up and down through a window 
(a punched out opening) in the breaker casing.  When the breaker is signaled 
to close, the coil is energized and the lever is designed to move up and make 
contact with the spring release latch that mechanically releases the breaker 
closing springs.  These SRDs also are used in Westinghouse type DS-420 and 
DS-206 circuit breakers.

Discussion:

The licensee's preliminary investigation indicates that the breakers failed to 
reclose because the closing coils had overheated and burned out.  The licensee 




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                                                                 June 24, 1988
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believes that the coils burned out as a result of mechanical binding between 
the lever and the edge of the breaker casing window.  The licensee physically 
inspected and electrically tested 28 other DS-416 breakers installed in Unit 1 
and 18 breakers installed in Unit 2 as of June 16, 1988, and identified 10 ad-
ditional cases where the lever and the edge of the breaker casing window were 
making contact.

Although the root cause of the binding has not been determined, the licensee 
has taken several steps to alleviate the problem.  The licensee has replaced 
the SRD in the STP-1 breakers that indicated signs of possible binding and has 
verified that the clearances between the lever and the casing are sufficient 
to preclude further binding.  In addition, the licensee has extensively 
briefed the STP control room personnel on this binding problem.  It should be 
noted that although the SRD may bind, it is still possible to manually trip 
the breaker closing springs by pushing the "CLOSE" button located at the 
circuit breaker. 

The licensee has contacted Westinghouse for assistance in determining the root 
cause of the binding.  The NRC will remain cognizant of any new developments 
and await the results of the South Texas and Westinghouse investigation.  The 
NRC will issue a further generic communication if warranted by the 
availability of additional information or if additional regulatory action is 
deemed necessary. 

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




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


Technical Contacts:  Kamal Naidu, NRR
                     (301) 492-0980

                     Jaime Guillen, NRR
                     (301) 492-1170


Attachment:  List of Recently Issued NRC Information Notices
.                                                            Attachment
                                                            IN 88-44 
                                                            June 24, 1988 
                                                            Page 1 of 1

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

88-43          Solenoid Valve Problems       6/23/88        All holders of OLs
                                                            or CPs for nuclear
                                                            power reactors. 

88-42          Circuit Breaker Failures      6/23/88        All holders of OLs
               Due to Loose Charging                        or CPs for nuclear
               Spring Motor Mounting Bolts                  power reactors. 

88-41          Physical Protection           6/22/88        All holders of OLs
               Weaknesses Identified                        or CPs for nuclear
               Through Regulatory Ef-                       power reactors. 
               fectiveness Reviews (RERs) 

88-40          Examiners' Handbook for       6/22/88        All holders of OLs
               Developing Operator                          or CPs for nuclear
               Licensing Examinations                       power reactors. 

88-39          LaSalle Unit 2 Loss of        6/15/88        All holders of OLs
               Recirculation Pumps With                     or CPs for BWRs. 
               Power Oscillation Event 

88-38          Failure of Undervoltage       6/15/88        All holders of OLs
               Trip Attachment on General                   or CPs for nuclear
               Electric Circuit Breakers                    power reactors. 

88-37          Flow Blockage of Cooling      6/14/88        All holders of OLs
               Water to Safety System                       or CPs for nuclear
               Components                                   power reactors. 

88-36          Possible Sudden Loss of RCS   6/8/88         All holders of OLs
               Inventory During Low Coolant                 or CPs for PWRs. 
               Level Operation                              

88-35          Inadequate Licensee Performed 6/3/88         All holders of OLs
               Vendor Audits                                or CPs for nuclear
                                                            power reactors. 

88-34          Nuclear Material Control      5/31/88        All holders of OLs
               and Accountability of                        or CPs for nuclear
               Non-Fuel Special Nuclear                     power reactors. 
               Material at Power Reactors 
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit 
Page Last Reviewed/Updated Tuesday, November 12, 2013