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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 .
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