United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 87-61: Failure of Westinghouse W-2-Type Circuit Breaker Cell Switches

                                                      IN 87-61

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

                                December 7, 1987


Information Notice No. 87-61:  FAILURE OF WESTINGHOUSE W-2-TYPE 
                                   CIRCUIT BREAKER CELL SWITCHES


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 failure of Westinghouse W-2-type circuit breaker 
cell switches.  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 16, 1987, Westinghouse Electric Corporation notified the Nuclear 
Regulatory Commission (NRC) staff, pursuant to the requirements of 10 CFR 
Part 21, of the failure of a modified Westinghouse W-2-type switch that was 
being utilized as a circuit breaker cell switch.  The failure was identified 
at Indian Point Station, Unit 3, on May 15, 1987, while the reactor was at 
cold shutdown for a scheduled refueling outage.  The output breaker for 
emergency diesel generator (EDG) No. 31 was prevented from re-energizing the 
480-volt bus 2A after plant personnel had inadvertently de-energized 480-volt 
buses 2A and 5A.  Subsequent investigation by the licensee determined that an 
erroneous input to the EDG logic system had prevented the EDG output breaker 
from closing.  The licensee identified deformation of the spring retainer in 
the spring-return mechanism of the cell switch in the 52/2A breaker cell as 
the root cause of the erroneous input.

The spring retainer is continuously under stress whenever the breaker is 
racked in (which it is, except when the breaker is racked out for testing or 
maintenance) and releases whenever the breaker is racked out.  Its deformation 
allowed a loss of spring tension that rendered the cell switch unable to 
spring-return to the racked out position when normal supply breaker 52/2A was 
racked out for maintenance.  Thus, the EDG logic system received an erroneous 
input indicating that breaker 52/2A was racked in and the main contacts were 
still closed.  This erroneous input prevented the EDG No. 31 output breaker 
from closing automatically in response to a loss of power.  During 


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subsequent inspections by Indian Point personnel, 35 of a total of 37 similar 
W-2-type switch spring retainers in the 480-volt system breakers exhibited 
some sign of deformation.  

All the cell switches had been shipped to Indian Point in 1971-1972 and all 
had been in service for close to 15 years.  The licensee reported the results 
of its investigation to the NRC in Licensee Event Report 87-009-00 on October 
2, 1987.  

Discussion:

Westinghouse has determined (1) that the deformation of the spring retainer in 
the spring-return mechanism of the cell switches was related to the aging of 
the component and (2) that the failure mechanism was the continuous stress it 
experiences while the breaker is racked in.  The W-2-type cell switches are 
available as optional equipment for all Westinghouse DS switchgear cabinets.  
Westinghouse has indicated that inspection or testing performed when the 
breaker is racked out would determine if a failure has occurred.  Where 
inspections and/or testing have not been performed, the potential exists that 
if the breaker is not racked in, a cell switch malfunction may prevent the 
completion of safety-related functions dependent on cell switch indication of 
the breaker being racked out or in the test position.  

In the 10 CFR Part 21 notification submitted to the NRC, Westinghouse 
recommends that proper cell switch operation be verified through periodic 
inspections or testing, or whenever the breaker is racked out.  Proper 
operation of the spring retainer is only verifiable when the breaker is moved 
from its racked in position.  Visible inspection may be used to verify cell 
switch operation.  However, it will be necessary to move the breaker out on 
the rails to observe whether the switch operating lever is in its proper 
position (30 degrees off vertical for the W-2 cell switch).  Any uncertainty 
in this observation may be resolved by manually ensuring that the switch has 
returned to the proper position.  Persons performing this inspection should 
use caution not to contact any energized terminals.  

No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical 
contact 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:  K. R. Naidu, NRR
                     (301) 492-9656

                     Jaime Guillen, NRR
                     (301) 492-8933

Attachment:  List of Recently Issued NRC Information Notices
Page Last Reviewed/Updated Tuesday, November 12, 2013