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.
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