Bulletin 77-02: Potential Failure Mechanism in Certain Westinghouse (W) AR Relays With Latch Attachments
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON D. C. 20555
IE Bulletin 77-02
Date: September 12, 1977
Page 1 of 2
POTENTIAL FAILURE MECHANISM IN CERTAIN WESTINGHOUSE (W) AR RELAYS WITH LATCH
ATTACHMENTS
Description of Circumstances:
Westinghouse recently reported that a number of AR Relays, with a latch
attachment to provide a seal-in feature, have failed during the system check
out of the Solid State Protection System (SSPS) at W Nuclear Instrumentation
Control Division in Hunt Valley, Maryland. Westinghouse has determined that
contacts of these AR Relays can reopen after the relay coil is de-energized
even though the latch mechanism is engaged. Normal operation calls for the
contacts to remain closed so that under abnormal conditions Safeguards
actions, once initiated, go to completion.
The failure mechanism has been found to be caused by insufficient
manufacturing tolerances which prevent full travel of the relay contact
assembly which is essential for proper relay operation. This reduction of
contact movement resulted from a design change made in the relay contact
assembly in mid 1973 by the W Control Products Division, Beaver,
Pennsylvania. In addition to the tolerance problem, it was determined that
excessive tightening of the contact cartridge terminal screw may also
contribute to the malfunction of the contacts during relay operation where
tolerances are marginal. AR Relays using latch attachments and produced
prior to mid 1973 are not a matter of concern in this issue.
The enclosed W Technical Bulletin, NSD TB 77-10 W,as sent to all affected
Westinghouse plants notifying them of the problem and of the corrective
actions being taken. The technical bulletin describes in detail the action
developed by W to correct the identified problem. The technical bulletin
also provides specific wiring instructions to assure that design tolerances
are not reduced by excessive tightening of electrical terminals on the
relay.
.
IE Bulletin 77-02
Date: September 12, 1977
Page 2 of 2
Action to Be Taken By Licensees and Permit Holders:
For all power reactor facilities with an operating license or a construction
permit:
(1) Describe what action you have taken to determine whether the relays of
the type and vintage described in the enclosed W Bulletin are in use or
planned for use in safety related systems at your facility.
(2) Describe what action you plan to take regarding replacement of any
relays of the type and vintage described which are in use or planned
for use in safety related systems. Further instruction pertaining to
replacement procedures can be obtained from the W Nuclear Service
Department in Monroeville, Pennsylvania.
(3) Report to this office in writing within 45 days for facilities with an
operating license and within 60 days for facilities with a construction
permit, the results of findings with regard to Item 1 or 2.
Approval of NRC requirements for reports concerning possible generic
problems has been obtained from the U S. General Accounting Office. (GAO
approval B-180225 (R0072) expires 7/31/80).
Enclosures:
1. Extract From W Technical
Bulletin NSD-77-10
Entitled "AR Relays with
Latch Attachment"
2. List of IE Bulletins issued
in 1977
Page Last Reviewed/Updated Tuesday, March 09, 2021