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