ML20077G404
| ML20077G404 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek, Callaway, 05000000 |
| Issue date: | 07/21/1983 |
| From: | Seiken S STANDARDIZED NUCLEAR UNIT POWER PLANT SYSTEM |
| To: | Jay Collins, James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III), NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| REF-PT21-83 IEIN-83-38, SDR-83-08, SDR-83-8, SLNRC-0039, SLNRC-39, NUDOCS 8308040214 | |
| Download: ML20077G404 (6) | |
Text
4 Ah SNUPPS Standardized Nuclear Unit Power Plant System SocTmINE.Y20ss0 July 21,1983 (301)8694010 SLNRC 83-0039 FILE: 0491.10.2 SUBJ:
Interim Report: Westinghouse 7300 Process Protection System (SDR 83-08)
Mr. James G. Kepplerc Administrator, Region III U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137 Mr. John T. Collins Administrator, Region IV U.S. Nuclear Regulatory Commission Suite 1000, Parkway Central Plaza Arlington, Texas 76012 Docket Nos. STN 50-482 and STN 50-483 Ref: IE Information Notice 83-38, Defective Heat Sink Adhesive and Seismically Induced Chatter in Relays Within Printed Circuit Cards Gentlemen:
On June 2,1983, NRC Region III and Region IV representatives were informed by SNUPPS Staff (R. White) of deficiencies in Callaway and Wolf Creek 7300 Process Protection Systems manufactured by the Industry Electronics Division (IED) of Lestinghouse.
In the June 2 notifications, it was explained that there were two significant deficiencies within the 7300 Process Protection System. The two deficiencies involve a) the potential failure of the adhesive bond used to bond heat sinks on the Loop Power Supply (NLP) printed circuit cards and b) seismically induced chatter in mercury relays used in Temperature Channel Test (NTC) printed circuit cards. These items were reported by Westinghouse to the NRC pursuant to 10CFR21 and 10CFR50.55(e) requirements, and were subsequently the subject of the referenced IE Information Notice.
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On June 28, 1983, SNUPPS (R. White) contacted NRC Region III and IV (P.
I Pelke and B. Seidle) and obtained an extension from July 2 to July 22, 1983 for providing this report to the NRC. At that time it was antici-l pated that this would be the final report.
However, it has been decided e
to hold this SDR open until after successful completion of Westinghouse l
seismic testing of replacement NTC circuit cards.
JUL 251983 e30804o214 830721 i
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SLNRC 83-0039 Page Two 1
Item a), Heat Sinks on NLP Card Description of Problem Heat sink adhesive failures have been identified at several plants other than Callaway or Wolf Creek and were reported to Westinghouse as field deficiencies. All reported field failures have occurred only on the loop power supply (NLP) cards.
West-inghouse has determined that NLP printed circuit cards shipped from Westinghouse Industry Electronics Division (WIED) between August 1,1980 and September 1,1982, were equipplid with a thermal heat sink assembly on the inverter transistors. The heat sink assemblies are subject to potential failures in the adhesive bond between an insulating washer and the thermal link (see Attachment 1). The affected printed circuit boards are:
5NLP Sub-level 18 and above 6NLP Sub-level 18 and above Note:
Previous Sub-levels did not contain heat sinks. The assembly sub-level identification sticker is attached
-to the solder side of the card near the front edge, and is not the revision identified on the front edge.
The adhesive failure mechanism or expected number of hours of system operation before failure is not defined. All reported problems have occurred under normal system usage or storage.
Consequences of Heat Sink Adhesive Failure If the adhesive bond defect had remained undetected, failure of the bond could cause the heat sink plate to separate from the thermal links and fall off the printed circuit board. The plate is conductive metal and under certain circumstances could cause shorting of low level signals if it were to become wedged between cards in the card frame. These low level signals are associated with various protective functions within a given Pro-tection Set of the 7300 Process Protection System Cabinets.
For example, one such protective function is the Pressurizer Pressure (2 of 4 Logic) Reactor Trip.
Under the unlikely condition of three concurrent adhesive failures in three different cabinets, each resulting in the shorting of one of the four logic signals generating the trip function, it is possible that reactor trip would be delayed, and that fuel temperatures would exceed those presented in certain FSAR analyses.
To date, Westinghouse reports that adhesive failures have not resulted in any damage to the affected 7300 Process Protection Systems nor have these failures resulted in any_ loss of system safety function.
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SLNRC 83 0039 Page Three Corrective Action, NSSS Equipment Heat sinks that are subject to this potential adhesive failure mechanism will be identified by Westinghouse and replaced.
These heat sinks will be identified by inspection of the printed circuit card for hex nuts visible on the top side of the assembly.
See attached, superseded drawing 404A605 (Attachment 1).
The replacement heat sinks have screw heads visible from the top side of the assembly (see Drawing 403A947, Attachment 2). The new style replacement heat sink cards feature screws that penetrate the heat sink material and hold the material securely in place.
Replacement heat sinks for NSSS equipment will be installed at Callaway and Wolf Cred. prior to fuel load. The installation will be in accordance with standard practices and procedures governing site rework and repair.
Corrective Action, B0P Equipment Westinghouse reports that WIED supplies this type of equipment directly to Architect /Engilieers for utility balance of plant (B0P) use and also to other NSSS vendors.
Preliminary indications are that it is unlikely that NLP cards with heat sinks have been used at Callaway, but that one or more NLP cards may have been used at Wolf Creek (other than in the Westinghouse 7300 Process Protection System). An investigation is being made to verify that no other NLP cards have been used at Callaway and to con-firm the preliminary indications of defective NLP card (s) at Wolf Creek. Should the investigation confirm receipt or installation of these NLP cards at either Callaway or Wolf Creek, the defective cards will be replaced prior to fuel load.
The results of this investi : tion will be available on site for NRC review.
9 Item b), NTC Card Relay Description of Problem During 3-axis seismic testing of the Temperature Channel Test (NTC) card, contact bounce was experienced in the mercury relay utilized on this card. These cards had previously undergone single-axis seismic testing, and had been released based on successful completion of that testing. The intermittent contact bounce exhibited in the 3-axis testing could result in signal saturation of the downstream RTD Amplifier (NRA) card in the Tcold and T ot circuits of the Westinghouse 7300 Process Pro-h tection System.
In these systems, filters are adjusted to main-tain 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 RTD's specified by West-inghouse, the filter has been set at either zero or two seconds, depending on the type of RTD (fast or slow response) utilized.
Callaway and Wolf Creek applications utilize unfiltered signals.
SLNRC 83- 0039 Page Four Consequences of Seismic Relay Chatter For unfiltered signals, saturation of the NRA card could delay initiation of the Overtemperature - Delta T and Overpower -
Delta T trips.
Had this problem gone undetected, and tiad the problem occurred during plant operation, the delay in reactor trip could have resulted in fuel temperatures in excess of those presented in certain FSAR analyses. This problem would only occur as a result of contact bounce induced by a seismic event.
Corrective Action Two candidate replacement relays have been identified, and are being tested by the Westinghouse Advanced Energy Systems Division.
The current testing is scheduled for completion in October, 1983.
Each of the two replacement relay candidates are solenoid activated electromechanical relays, and should eliminate the chatter exhibited by the mercury relay being replaced. The SNUPPS project will review and confirm that the results of the Westinghouse test program are satisfactory prior to release of the replacement cards for installation. Replacement relays for NSSS equipment will be installed prior to fuel load for Callaway and Wolf Creek.
This report should be considered an interim report concerning the NLP and NTC circuit card deficiencies.
It is anticipated that the final report will be issued by the end of the year, after the completion of seismic testing of the replacement NTC cards. The NRC will be informed should there be any significant developments concerning this issue in the interim.
Very truly yours, YE S. J.
eiken Manager, Quality Assurance RPW/dckl0al2&l0bl-3 Attachments:
1.
Superseded Drawing 404A605 2.
Drawing 403A947 cc:
D. T. McPhee KCPL H. W. Roberds USNRC/ CAL G. L. Koester KGE J. H. Neisler USNRC/WC D. F. Schnell UE H. M. Wescott USNRC Region III Record Richard DeYoung Director I&E
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