ML20072J749
| ML20072J749 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 12/03/1982 |
| From: | Taylor J BABCOCK & WILCOX CO. |
| To: | Deyoung R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| References | |
| REF-PT21-83-908-000 PT21-83-908, PT21-83-908-000, NUDOCS 8306300220 | |
| Download: ML20072J749 (4) | |
Text
W S/82 M c>.
Babcock & Wilcox soci.ar Power Generation Division
-fs a McDermott company 3315 Old Forest Road P.O. Box 1260 Lynchburg, Virginia 24505 (804) 384 5111 December 3, 1982 Mr. Richard C. DeYoung, Director Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
10 CFR 21 Report
Dear Mr. DeYoung:
Pursuant to the requirements of 10 CFR 21, this report in three copies is submitted concerning loose locking clips that are used to secure terminal boards to the rear terminal panels of safety-related instrumentation cabinets.
Dr. D. H. Roy, acting for Mr. D. E. Guilbert, Vice-President, Utility Power Generation Division, was informed of this reportable concern at 12:00 Noon, December 2, 1982.
A telephone report of this concern was made to Mr. W. R. Mills of the Office of I&E at 4:30 P.M., ~ December 2,1982.
The attachment presents the necessary information relative to this matter.
If you have any questions you may contact Mr. D. Mars of my staff at 804-385-2852.
Yours.very truly, Wl Ta o JHT/fw cc:
-R. B. Borsum, B&W Bethesda Office Attachment f4/9
'f/
B306300220 821203 PDR ADOCK 05000269 8
Report on Loose Terminal Board Locking Clios 1.
Introduction Several loose locking clips (also known as speed nuts) that are used to secure terminal boards to the rear terminal panels of NNI, ESFAS and RPS cabinets were discovered at Oconee Unit 1.
This repcrt concludes that this occurrence and associated generic concern are reportable to the NRC under the requirements of 10 CFR 21.
2.
Description of Concern 2.1 Discovery of Loose Clip t i Loose clips were discovered during a cursory inspection of instrument cabinets at Oconee Unit 1 by Duke personnel.
The clips, which are Tinnerman Push-On Speed Nuts, catalog No. C 7818-014-67,are used to secure the teminal blocks to the rear terminal panels of instrument cabinets.
A speed nut or clip is a thin rectangular strip of spring steel, approximately 1/2*x 5/8",
with a central hole.
The strip has a slight curyature and is perforated to form 2 jaws that grip the post on which the clip is placed in such a aanner as to allow the clip to be pressed on but to resist removal from the post.
The speed nut is pushed on over the insulated post which surrounds each terminal on the system wiring side of the. panel (see attached sketch).
The following discrepancies were discovered at Oconee Unit 1:
1.
One clip was loose on an NNI tarminal board.
The clip was still on the insulated portion of the teminal but was approximately 1/4" away from the cabinet wall, The clip was loose enough to move freely on the teminal.
2.
One clip was found on the floor underneath the rear terminal panel in an l
ESFAS cabinet.
Apparently the clip had come loose from a terminal that did not have a wire soldered to it and slid off the end of the teminal.
3 In another ESFAS cabinet, a clip had come loose, slid off the end of the teminal and was hanging on the wire that was soldered to the terminal.
4.
A clip was found on an RPS teminal board that had apparently shorted from the uninsulated end of the terminal to the cabinet.
2.2 Generic Concern In addition to the specific discrepancies discovered at Oconee 1, there is a general concern with this type of attachment device.
It is possible that some temination panels on NNI, ESFAS and RPS panels in other B&W plants use Tinneman Speed Nuts Cat #C7818-014-67 to fasten the terminal blocks to the panel h
and they maynot adequately grip the outside diameter of the insulated post. It is possible that one or more speed nuts may work loose or completely come off of the insulated posts.
This may result in (a) the terminal block becoming i
loose..(b) a speed nut contacting the uninsuTated portion of a terminal and shorting to adjacent terminals or the cabinet, or -(c) a speed nut falling off of a terminal and into the area below (this is possible where there is no wire on the terminal).
1
~
-l-The safety concern is that loose clips can result in NNI, RPS or
' ESFAS signal paths b2ing shorted to each other or to cabinet ground.
While there are redundant signal paths in these systems, it is cossible that if several-clips were to become loose, a number of circuits could be affected and some safety functions could be defeated.
Suspect clips have been found in safety systems only at Oconee 1.
It is not presently known to what extent other B&W plants have the suspect speed nuts in safety-related systems.
3.
Reportability In consideration of the commen mode failure potential that lodse clips could disable a safety system, it is concluded that the discrepant clips are reportable under the provisions of 10 CFR 21.
e 4.
Corrective Action 4.1 Oconee B&W has advised Duke Power Company (letter No. ONS-82-118 dated August 20, 1982) to locate and remove all speed nuts No. C7818-014-67 (aluminum finish) and replace them with speed nuts No. C185-014-4 (dull, dark finish).
There are significant differences between the two fasteners in inside dimensions, material thickness and material hardness.
The superior properties of No. C185-014-4 have led to its current exclusive use by Bailey Controls Company (BCCo).
-m _ _
4.2 Geseric Bailey Controh Company, supplier of the ICS, NNI, ESFAS and RPS systems, has advised B&W that it is not aware of the exact locations of suspect fasteners.
All B&W plants in operation and under construction, therefore, are being advised that a search be made for defective clips and that they be replaced with the superior clips.
Accordingly, Service Bulletins have been sent to the other B&W operating plants (the Oconee Units were advised as described above), namely, Three Mile Island Units 1 and 2 2f0 Id d Crystal River 3 303 Arkansas Nuclear One Unit 1
?)2 Rancho Seco 3 !.a Davis Besse 1 J t/ b Notification is also being made to the plants under construction, namely Midland Units 1, 2 Bellefonte Units 1, 2 WNP-1 North Anna 3, 4 Pebble Springs
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