United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 83-38: Defective Heat Sink Adhesive and Seismically Induced Chatter in Relays Within Printed Circuit Cards

                                                            SSINS No.: 6835 
                                                            IN 83-38       

                                UNITED STATES
                           WASHINGTON, D.C. 20555
                                June 13, 1983

Information Notice No. 83-38:   DEFECTIVE HEAT SINK ADHESIVE AND 
                                   SEISMICALLY INDUCED CHATTER IN RELAYS 
                                   WITHIN PRINTED CIRCUIT CARDS 


All nuclear power reactor facilities holding an operating license 
(licensees) or a construction permit (CP). 


The purpose of this notice is to inform licensees and holders of CPs of: (1)
potentially defective adhesive used to bond heat sinks on Loop Power Supply 
(NLP) printed circuit cards, and (2) seismic induced chatter in mercury 
relays, used in Temperature Channel Test (NTC) printed circuit cards. These 
cards are a product line of the Industry Electronics Division (IED) of 
Westinghouse. Although these cards are used extensively in Westinghouse's 
7300 Process Protection System, they are also used in balance-of-plant 
systems designed and/or supplied by others. Consequently, the information in
this notice is not limited to the nuclear steam supply system (NSSS) 
portions of plants designed by Westinghouse. In addition, IED supplies this 
type of equipment directly to Architect-Engineers for utility balance of 
plant use and also to other NSSS vendors. 

Description of Circumstances: 

By letter dated June 1, 1983 (NS-EPR 2774, E.P. Rahe to R. C. DeYoung) 
Westinghouse notified the NRC of the above mentioned deficiencies pursuant 
to the requirements of 10 CFR 50.55(e) for plants under construction and 10 
CFR Part 21 for operating plants. The descriptions that follow are based on 
the information contained in the referenced letter. 

1.   Heat Sink Adhesive 

     Several utilities have experienced failures of the adhesive that bonds 
     heat sinks on NLP cards. The adhesive bond is between an insulating 
     washer and a thermal link such that failure of the bond can cause the 
     heat sink plate to separate from the thermal links and fall off the 
     printed circuit board (See Attachment 1, Westinghouse Drawing No. 
     404A605 ). Since the plate is conductive, low level signals could be 
     shorted out if the loose plate were to become wedged between cards in 
     the card frame. Suspect heat sinks can be identified by inspecting the 
     printed circuit card for hex nuts visible on the top side of the 
     assembly. The new style heat sink has screw heads visible from the top 
     side of the assembly. (See Attachment 2, Westinghouse Drawing No. 


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                                                             IN 83-38      
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Corrective actions recommended by Westinghouse include replacing the suspect
heat sinks with those of a new design. To justify continued plant operation 
until the suspect heat sinks are replaced, Westinghouse recommends that 
utilities inspect their 7300 Process Protection System for separated heat 
sinks and to remove any heat sink that has separated. Westinghouse 
recommends that subsequent inspections be conducted during each periodic 
system test until the suspect heat sinks have been replaced. Westinghouse 
also states that NLP cards can-be operated satisfactorily without heat 
sinks, and that if a heat sink becomes dislocated during operation and 
causes a failure, the probability of detecting the failure is high. 

According to Westinghouse, the suspect cards are limited to those shipped  
from IED between August 1, 1980 and September 1, 1982 which are designated 
5NLP Sub-level 18 and above and 6NLP Sub-Level 18 and above. (Previous 
Sub-levels did not contain heat sinks.) Suspect NLP cards are being used in 
both domestic and foreign plants. Domestic plants having potentially 
defective NLP cards within the Westinghouse NSSS scope as well as in systems
outside the Westinghouse NSSS scope are listed below. 

Plants Using Suspect NLP Cards Within NSSS Process Protection Systems 
Originally Supplied by Westinghouse 

Braidwood Units 1 & 2    Catawba Units 1 & 2        Seabrook Units 1 & 2 
Byron Units 1 & 2        Comanche Peak Units 1 & 2 *Virgil C. Summer Unit 1 
Callaway Units 1 & 2     Millstone Unit 3           Wolf Creek 

Plants or Utilities Using Suspect NLP Cards in Applications Other Than 
Within NSSS Process Protection Systems Originally Supplied by Westinghouse 

*North Anna              *Indian Point 3         Kansas Gas & Electric 1 
*Virgil C. Summer         Duke Power Company    *Joseph H. Farley 
 Commonwealth Edison     *Indian Point 2         Indiana & Michigan Pwr. 

2. Non-Seismically Qualified Relays 

During seismic testing of the Temperature Channel Test (NTC) card, contact 
bounce was experienced in the mercury relay utilized on this card. This 
intermittent contact bounce will result in signal saturation of the 
downstream RTD Amplifier (NRA) card in the Thot and Tcold circuits of the 
7300 Process Protection System. In these systems, filters are adjusted to 
maintain a total time constant of approximately two seconds for the 
RTD/filter combination. Since the filter is downstream of the relay, the 
characteristics of the channel response depends on the time constant of the 
filter. For RTDs specified by Westinghouse, the filter has been set at 
either zero or two seconds depending on the type of RTD used (i.e., slow or 
fast response). 

*Operating Plants 

                                                            SSINS No.: 6835 
                                                            IN 83-38       
                                                            Page 3 of 4    

Saturation of the NRA cards in those applications using filtered signals 
would not prevent plant trips; however, spurious plant trips could result. 
On the other hand, saturation of the NRA card in non-filtered applications 
could delay initiation of Overtemperature-Delta T and Overpower-Delta T 
trips. Such saturation induced delay would only occur as a result of contact
bounce induced by a seismic event coincident with the demand for such a 

NTC cards are not required for plant operation per se, but are needed for 
channel test purposes. Westinghouse is developing and testing a replacement 
relay for the NTC cards and indicates that these relays will be installed 
prior to operation for most plants. In the interim, to justify continued 
operation of the non-filtered plants (i.e., those utilizing a slow response 
RTD) until the replacement relays are available, Westinghouse recommends 
that the existing filters be set for a one second response. (Virgil C. 
Summer is the only domestic non-filtered operating plant.) Although this 
action could result in spurious trips upon a seismic event, it would 
eliminate the potential delay in initiating an Overtemperature or Overpower 
Delta T trip. If the plant does not have sufficient time response margin to 
accommodate the one second response, then Westinghouse states that the 
relays must be bypassed with permanently installed jumpers until the 
replacement relays are installed. A listing of domestic plants having the 
non-seismically qualified relays in their NTC cards, including filtered and 
non-filtered plants, follows. 

Non-Filtered Plants: (Plants utilizing slow response RTDs) 

Comanche Peak Units 1 and 2                         Seabrook Units 1 and 2 
Beaver Valley Unit 2                                Byron Units 1 and 2    
Braidwood Units 1 and 2                             Vogtle Units 1 and 2   
Shearon Harris Units 1 and 2                        Catawba Units 1 and 2  
South Texas Units 1 and 2                           Millstone Unit 3       
Marble Hill Units 1 and 2                          *Virgil C. Summer       
Callaway Unit 1                                     Wolf Creek Unit 1      

Filtered Plants: (Plants utilizing fast response RTDs) 

*Joseph H. Farley Units 1 and 2                  *North Anna Units 1 and 2 
*Wm. B. McGuire Units 1 and 2

*Operating Plants 

                                                            SSINS No.: 6835 
                                                            IN 83-38       
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No response to this notice is required. If you have any questions regarding 
this matter, please contact the Regional Administrator of the appropriate 
Regional Office or the Technical Contact listed in this notice. 

                                   Edward L. Jordan Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  I. Villalva, IE
                    (301) 492-9635

1.   Westinghouse Drawing No. 404A605 (superseded)
2.   Westinghouse Drawing No. 403A947
3.   List of recently issued Information Notices
Page Last Reviewed/Updated Friday, May 22, 2015