ML20058K797
| ML20058K797 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 10/01/1973 |
| From: | Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Mayer L NORTHERN STATES POWER CO. |
| References | |
| IEB-73-03, IEB-73-04, IEB-73-3, IEB-73-4, NUDOCS 9102140413 | |
| Download: ML20058K797 (3) | |
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ATOMIC ENERGY COMMISSION
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Docket No. 50-263 l
1 Northern States Power Company ATTN:
Mr. L. O. Mayer Director of Nuclear Support-i Services 414 Nic.ollet Mall Minneapolis, Minnesota 55401 j
Gentlemen:
i l
Inspections of hydraulic shock suppressors (snubbers) as required by RO Bulletin 73-3 revealed that a large percentage of the seals in i
Bergen-Patterson units were defective. Reinspections in compliance with R0 Bulletin 73-4 indicated that defects can recur 'in six weeks' time or less.
t Two different seal materials have been used in Bergen-Patterson i
snubbers; a millable gum polyurethane which contains plasticizers and
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other additives and a molded polyurethane known to be free of these additives. It has been postulated that dissolving of the plasticizer into the silicone hydraulic fluid has caused seal shrinkage and deterioration. Therefore, millable gum polyurethane should not be used in hydraulic snubbers, except on an emergency basis.
The performance and reliability of unadulterated molded polyurethane in a reactor environment ht.s not yet been established. Test data-indicate that an incompatibility exists between molded polyurethane and the silicone fluid which may limit the inservice life of the molded material.
The use of =cided polyurethane seals should, there-fore, be considered an interim repair until more data is available or an improved material is established.
Based on the above considerations, we require the following action be taken on all Bergen-Patterson snubbers installed on safety related systems af ter the shutdown required by RO Bulletin 73-4.
1.
Snubbers Inaccessible During Reactor Operation j
l During the shutdown required by RO Bulletin 73-4, replace seal material in all snubbers inaccessible during reactor operation with material demonstrated to be compatible with the hydraulic I
9102140413 731001 CF ADOCK 05000263 CF l
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g 1 1973 fluid at 'the operating environment.
(If such material is unavailable, the use of molded polyurethane known to be free of additives will be acceptable as an interim repair.) Reinspect these snubbers whenever the reactor is shutdown for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or longer and snubbers have not been inspected for 30 days, but in no event should the interval between inspections exceed 120 days. Repair defective units before returning to power operation.
If unavailability of materials prevents the changeout of all inaccessible snubbers or dictates repairs with millable gum seals, only, defective units need be repaired.
Under these conditions, reinspect 'every 30 days until improved seal material is installed which should be accomplished at the earliest practical time.
2.
Snubbers Accessible During Reactor Operation Repair defective snubbers accessible during reactor operation as outlined in 1. above. Reinspect accessible snubbers every 30 days or less and repair defective units as needed.
During the required surveillance, inspect snubbers supplied by manufacturers other than Bergen-Patterson. Report the results of the inspections and corrective action taken to the Directorate of Licensing within 15 days af ter the inspection. This report should include for each manuf acturer the number of snubbers inspected, identification of defective units, and corrective action taken, including specific description of materials used in your repair.
Bergen-Patterson is coordinating a development program to determine a long-term solution to the current snubber problem. Based on the results of this program, the results of your reinspections, and any other pertinent information available, submit to the Directorate of Licensing at an appropriate time, but within one year, your proposed program to improve snubber service life and reliability and proposed changes to your Technical Specifications describing a snubber surveil-lance program with basis.
We also request that you submit to us within 60 days af ter your next shutdown information describing snubber temperature and radiation environment at f ull power.
Sincerely,
,/h:.
b Y
Donald J,.CS.ovholt Assistant Director for Operating Reactors Directorate of Licensing cc: See next page
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cc: Donald E. Nelson, Esquire VP and GC i
Northern States Power Company 414 Nicollet Mall Minneapolis, Minnesota 55401 Gerald Charnoff f
Shaw, Pittman, Potts, Trowbridge & Madden 910 - 17th Street, N. W.
Washington, D. C.
20006 i
Howard J. Vogel, Esquire Knittle & Vogel j
814 Flour Exchange Building Minneapolis, Minnesota 55415 i
Steve Gadler, P. E.
2120 Carter Avenue St. Paul, Minnesota 55108 Harriett Lansing, Esquire Assistant City Attorney City of St. Paul 6
638 City Hall St. Paul, Minnesota 55102 Ken Dzugan Minnesota Pollution Control Agency 717 Delaware Street, S. E.
Minneapolis, Minnesota 55440 i
Warren R. Lawson,,M.D.
1 Secretary & Executive Officer State Department of Health 717 Delaware Street, S. E.
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Minneapolis, Minnesota 55440 Environmental Library of Minnesota 1222 S. E. 4th Street Minneapolis, Minnesota 55414
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