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
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
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
Addressees:
All nuclear power reactor facilities holding an operating license
(licensees) or a construction permit (CP).
Purpose:
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.
403A947.)
8305110470
.
SSINS No. 6835
IN 83-38
Page 2 of 4
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.
*Sequoyah
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
trip.
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
Page 4 of 4
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
Attachments:
1. Westinghouse Drawing No. 404A605 (superseded)
2. Westinghouse Drawing No. 403A947
3. List of recently issued Information Notices
.
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021