United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 75-06: The Westinghouse Electric Corporation



BL75006 

                                                  Inspection and Enforcement
                                                  Bulletin No. 75-06  
                                                  May 30, 1975 

DEFECTIVE WESTINGHOUSE TYPE OT-2 CONTROL SWITCHES 

DESCRIPTION OF CIRCUMSTANCES: 

The Westinghouse Electric Corporation recently reported to the NRC the 
finding of a number of defective Westinghouse type OT-2 electrical switches 
in the main control board of the Sequoyah Station. The defective switches 
were found during installation of the main control board of the Sequoyah 
Station, which is currently under construction. 

The defective switches are of a spring-return-to-neutral type. Manual 
operator action of the switch involves rotating the switch clockwise or 
counterclockwise, and an internal spring force returns it to the central 
neutral position. Westinghouse reported that internal friction caused some 
switches to bind and fail to return to the neutral position, due to an 
adverse tolerance stack-up on internal switch components. 

Corrective action has been taken to replace the defective switches in the 
Sequoyah Station. Westinghouse has issued a Technical Bulletin to utilities 
with Westinghouse NSSS's in operation, advising them of the potential for 
similar defective switches in these facilities. These switches may also be 
installed in other nuclear power facilities. 

In case of uncertainty, licensees are advised to contact the Westinghouse 
Control Products Division regarding test instructions and replacement 
procedures for these switches. 

ACTION TO BE TAKEN BY LICENSEES: 

For all power reactor facilities with operating license or construction 
permit: 

1.   Determine if switches of the type described above are in use, or 
     planned for use, in safety related systems of your power reactor 
     facility(ies). 
.

                                  -2-  

2.   Notify this office in writing, within 30 days for facilities with an 
     operating license and within 60 days for facilities with a construction
     permit, of the results of your findings with regard to item 1, above. 

3.   If switches of the type described are in use or planned for use in 
     Safety related systems, include in your written reply to this Bulletin 
     the extent of their use and the actions you have taken or plan to take 
     to prevent malfunction of the type described above. Your written reply 
     should include the date(s) when your actions in response to this 
     Bulletin were or will be completed. 
Page Last Reviewed/Updated Tuesday, July 23, 2013