ML20091A170

Responds to NRC 831118 Ltr Re Violations Noted in IE Insp Rept 50-237/83-17.Corrective Actions:Valve mock-up Constructed to Facilitate Exposure of Design Samples to Anticipated DBA Environ Conditions

ML20091A170
Person / Time
Site:	Dresden
Issue date:	04/30/1984
From:	Rybak B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20091A159	List: ML20091A170
References
8537N, NUDOCS 8405290291
Download: ML20091A170 (3)

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/ Commonwealth Edison h - @Cp ]/Reply h Address one First to. Post OfficeNationti Box 767 PL:n. Chic'go, lihnois g y / Chicago. Illinois 60690 April'30, 1984-Mr. James C. Keppler

. Regional-Administrator U.S. Nuclear Regulatory Commission Region III 799 Roosevelt Road Glen Ellyn, IL 60137

Subject:

Dresden Station Units 2 and 3 Drywell/ Torus Vacuum Breaker Seal Qualification NRC Docket Nos. 50-237 and 50-249 Reference (a): J. G. Keppler letter to J. J. O'Connor dated November 18, 1983.

Dear Mr. Keppler:

This letter and its attachments is Commonwealth Edison's (CECO's) response to Item 2.4. (iv).(1) of the referenced report. This item identified CECO's commitment to determine and assess the environmental qualification status of the subject vacuum breaker seals and lubricants used with them. An abstract of the program implemented for this purpose and a technical status report on the seals and lubricants relative to Dresden's vacuum breakers is provided here. The attachments are informational copies of the program specifications and the program final analysis report. We believe that this material will provide the information necessary for an NRC review.

Program Abstract Commonwealth Edison's plan to address this concern was to design and perform an operability and external' leakage control functional test program. The tests covered the static and dynamic seals (and corresponding lubricants), either in use then or proposed for future use. - A valve mock-up was constructed to facilitate exposure of design

-samples to the anticipated DBA environmental conditions and perform the functional tests.

The mock-up (sample). exposures were performed by Argonne National Laboratories, under the requirements and direction of Station Nuclear Engineering Department (SNED). The tests themselves were performed exclusively by CECO personnel, with the use of the same procedures and apparatus employed by Dresden to assess the operability and leakage control performance of the actual vacuum breaker seals. These procedures were reviewed and regarded as suitably conservative, given the fact that conservative environmental conditions for sample exposures were also used.

7 8405290291 840522 PDR ADOCK 05000237 s a PDR g ,

a J. G..Keppler April 30, 1984

. Fundamental to test program design was development of a specification document (Attachment A). In detail, this effort provided requirements for such items as; 1) environmental exposure criteria, 2) sample selec-tion and mock-up construction, and 3) the specifics of the functional tests and their attendant seal performance acceptance criteria. The express objective of these requirements was to provide the means to qualify the designs involved for the environmental conditions commensurate with a period of four fuel cycles (Approximately six years, which equates to the vacuum breaker refurbishment cycle), plus 28-30 days after a DBA event, which was determined to be adequate for the plant safety functions of the valve external seals. In this regard, the environmental cunditions of greatest importance were cumulative gamma radiation to 3.2x107 Rads (+10%) with peak temperatures of up to 3340 F (+50F).

The subsequent test results are discussed in depth in the final analysis report (Attachment B). In summary, all of the designs involved met the specified performance acceptance criteria without difficulty.

Consequently, it is our position that the designs tested, both now in use 4 or planned for future use, are in fact environmentally qualified to the extent necessary to support the vacuum breaker external seal operability and leakage control safety related functions.

One particular dynamic seal design, a bronze bushing /EPR 0-ring prototype, was obviously superior. Although it had distinctively excellent performance, clearly its best advantages were related to its maintainability. In fact, we believe the comparison of test results for this design to those for the other designs shows that the maintainability aspect was much more directly related to Dresden's past vacuum breaker seal problems than the design qualification aspect itself.

Status In recognition of the test findings, Dresden has initiated modifications for both Units 2 and 3 to employ the bushing /O-ring dynamic seal and EPR 0-ring static seal designs. SNED has performed the necessary design review actions, per the applicable CECO Q.A. Program requirements. The modifications have now been fully implemented on Dresden Unit 3 (with excellent confirmatory in-plant test results), and will be fully implemented on Unit 2 during the next available off critical path outage opportunity. With the decision to employ the bronze bushing design, we will discontinue the use of the 75 psi proof test during future local leak rate testing of the vacuum breaker seals.

The dynamic 0-rings will'be procured safety-related commercial grade. That is, the material will be purchased from an approved vendor, ordered to certain specifications (I.D. cross section and compound i . number) and requiring a -Certificate of- Conformance with each shipment.

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. i J. G.-Keppler April 30, 1984 If.there.are any further questions regarding this matter, please

.. contact this office.

Very truly yours, B. Ry

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Nuclear Licensi Administrator 3 1m Attachment cc: Region III Inspector - Dresden w/o Att._ .

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