ML19210B382
| ML19210B382 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 12/03/1973 |
| From: | Deyoung R US ATOMIC ENERGY COMMISSION (AEC) |
| To: | John Miller METROPOLITAN EDISON CO. |
| References | |
| NUDOCS 7911070704 | |
| Download: ML19210B382 (2) | |
Text
e Docket No. 50-2396 5EE J '4?)
!!etropolitan Edison Company ATTN: !ir. John G. Miller Vice President P. O. Box 542 Reading, Pennsylvania 19603 Gentlemen:
Inspection of hydraulic shock suppressors (snubbers) in nuclear power plants has revealed that a large percentage of the seals in units supplied by the Bergen-Patterson Company were defective and that defects can recur in six weeks time or less. Two different seal materials have been used in Bergen-Patterson (B-P) snubbers; a millable gum polyurethane which contains plasticizers and other additives, and a molded polyurethane known to be free of these additives. Baaed on limited available information it is postu-lated 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 anubbers, except on an emergency basis.
The performance and reliability of molded polyurethane free of additives in a reactor environment has not yet been established. Test data indicate that an incompatibility may also exist between molded polyurethane and the silicone fluid which may limit the inservice life of the molded material.
The use of molded polyurethane seals should, therefore, be considered only as an interim measure until more data is available or an improved =sterial is established.
B-P is coordinating a development program to determine a long-term solution to the current snubber problem.
Based on the above considerations, we are requiring that the following actions be taken. If Three Mile Island, Unit 1, has B-P snubbers installed on any safety related systems, you will be required to modify the seals on these snubbers with a material that has been demonstrated to be compatible with the hydraulic fluid in the operating environment. If such a material is not available on a schedule compatible with your fuel loading date, the use of molded polyurethane seals known to be free of additives will be acceptable as an interim neasure. However, you will be required to reinspect these interim seals 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 these snubbers have not been inspected for 30 days, but in no event shall the interval between inspections exceed 120 days.
1584 324 791107070 4
- Ietropolitan Edison Company Any defective units found during these inspections shall be repaired before returning to power operation. If unavailability of materials dictates the use of millable gum seals, only defective units need be repaired. Under these conditions, you will be required to reinspect every 30 days until compatible seal material is installed, which should be accomplished at the earliest practical ti=e.
During the required inspections of B-P snubbers, you will also be required to inspect all snubbers supplied by manufacturers other than B-P.
You will also be required to report the results of all inspections and any repairs or corrective actions taken to the Directorate of Licensing.
Periodic surveilla'5te of all snubbers installed on safety related systems will be required by the Technical Specifications for Three :lile Island, Unit 1.
If interim seal materials are used, the Technical Specifications nust reflect the inspection and reporting require =ents as discussed above.
If seal materials of demonstrated compatibility with the hydraulic fluid and operating environment are used, the Technical Specifications should reflect inspection requirements that consider the potential degradation rate of the snubber seal material used and be consistent with assuring that the snubbers will perform satisfactorily when needed.
You are hereby requested to inform us within 60 days of your plans for making snubber seal modifications and to submit proposed Technical Specifications for a surveillance program for the snubbers in Three !!ile Island, Unit 1.
Please contact us if you have any questions concerning this matter.
Sincerely, r+. x ;,
4
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'yR.C.DeYoung,AssistantDirector for Pressurized Water Reactors Directorate of Licensing cc:,:fr. George F. Trowbridge, Esquire DISTRIBUTION:
Shaw, Pittman, Potts &
AEC PDR ASchwencer Trowbridge Legal PDR EGoulbourne 910 17th Street, N. W.
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