ML19309A216
| ML19309A216 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 12/05/1973 |
| From: | Deyoung R US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Davis E SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| References | |
| NUDOCS 8003260919 | |
| Download: ML19309A216 (2) | |
Text
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f go 5W Docket No. 50- 312 Sacramento Municipal Utility District ATTN: Mr. E. K. Davis General Manager G201 S Street, P. O. Box 15830 Sacramento, California 95813 Gentlemen:
Innpe:. tion of hydraulic shock suppresrors (snubbers) in nuclear power plants has revealed that a large percentage of the seals in units cupplied 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-Pattercon (B-P) cnubbers; a millable gun polyurethane which contains plastici=nra and other additives, and a molded polyurethane known to be free of these additives. Based on limited available infor.ation it is pontu-Inted thst disnolvinn of the plasticizer into the silicone hydraulic fluid has caused seal shrinkage and deterioration. Therefore, millable gum 3
polyurethane should not be used in hydraulic snubbers, except on an emergency nacts.
The performance and reliability of molded polyurethane free of additiven in a reacter environment has not yet been catablished. Test data indicate that an inccmpatibility may also exict between =olded polyurethane and the siliceng fluid which may limit the incervice life of the colded material.
The use of molded polyurethane seals should, therefore, be considered only as an interim meacure until more data is available or an improved raterial is established.
B-P is coordinating a development program to determine a long-term solution to the current snubber proble:n.
Based on the above considerations, we are requiring that the following actions be taken. If 2ancho Seco, Unit 1, has B-P snubbers installed on
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any safety related systems, you vill be required to modify the seals on these snubbers with a material that has been demonstrated to be compatibic j
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 Ef'holded polyurethane seals known to be free of additives will be acceptable as an interim measure. Hovever, 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.
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Sacramento Municipal Utility District 2-Any defective units found during these inspections shall be repaired before returning to power operation. If unavailability of c:sterials 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 compatibla seal material is installed, which should be accomplished at the earliest practical time.
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 inspectioris and any repairs or corrective actions taken to the Directorate of Licensing.
Periodic surveillance of all snubbers installed on safety related systems will be required by the Technical Specifications for Rancho Seco, Unit 1.
If interin seal materials are used, the Technical Specifications must reficct the inspection and reporting requireuents as discussed above.
If coal materiala of demonstrated compatibility with the hydraulic fluid and operating environment are used, the Technical Specifications should reflect inspection requirements that consider the potential degradation gate of the snubber seal raterial used and be consistent with assuring that the anubbers vill perform satisfactorily when needed.
You are harahy cam *a=*ad
- a infer = ::: yithis f 0 days cf youg y1Aui, fus making snubber seal codifications and to subr.it proposed Technical Specifications for a surveillance program for the snubbers in Rancho Seco, Unit 1.
Picace contact us if you have any questions concarning this c:stter.
Sincerely, or'gtnet signed eg
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K. R. Goffer i
R. C. DeYoung, Assistant Director
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f for Pressurised Water Reactors f
Directorate of Licensing-s s
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