ML20212E748

Requests Approval Per 10CFR50.55a to Use Alternative Method for Determining Qualified Life of Certain BOP Diaphragm Valves than That Specified in Code Case N-31.Proposed Alternative,Encl

ML20212E748
Person / Time
Site:	Vogtle
Issue date:	09/20/1999
From:	Beasley J SOUTHERN NUCLEAR OPERATING CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LCV-1371, NUDOCS 9909270133
Download: ML20212E748 (5)

Text

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. J. Barnie Bea.try Jr., P.E. $1uthrrn Nucint -

Vice Presdent

. Op: rating Ccmpany,Inc.

Vogtle Project . 40 invmess Center Parkway P0. Box 1295 Bummgham, Alabama 35201 Tel 2052923110 Fax 205.992 0403 SOUTHERN COMPANY Energy to Serve hur World" September 20, 1999 LCV-1371 Docket Nos. 50-424 50-425 U. S. Nuclear Regulatory Commission Attn: Document Control Des'k Washington, DC 20555 Ladies and Gentlemen:

VOGTLE ELECTRIC GENERATING PLANT CODE CASE N-31 ELASTOMER DIAPHRAGM VALVES The purpose of this letter is to request approval per 10CFR50.55a to use an attemative method for determining qualified life of certain BOP diaphragm valves than that specified in Code Case N-

. 31. In reviewing the replacement interval of diaphragms associated with ASME Class 2 and 3

' liquid and gaseous diaphragm valves, it was recently discovered that a licensing document change to UFSAR Table 1.9-1 incorrectly interpreted a five-year service life for diaphragms as a manufactumr's . ecommendation, instead of an NRC contingency for use of Code Case N-31. A reference to the " manufacturer's recommendation" had been incorporated into the UFSAR Table 1.9-1 (Footnote b.). Subsequently, a safety evaluation and UFSAR revision were prepared to permit the qualified life of the diaphragms to exceed five years based on a qualified life analysis.

The later revision to UFSAR Table 1.9-1 was prepared using diaphragm test data obtained from

- Wyle Laboratories and Footnote b was revised in UFSAR Revision 2 to allow the service life to exceed five years as long as the qualified life of the diaphragm was not exceeded. The qualified {

life is based on operating conditions seen by the valves and includes an evaluation of thermal, radiation, and mechanical (cycle) aging.

While we incorrectl' ychanged our program based on a misinterpretation of the " manufacturer recommendation vs. NRC contingency for use," we believe that use of the qualified life instead of

, . the five-year service life provides a sound technical methodology, predicated on service conditions, to better predict the service life of the Vogtle elastomer diaphragms. This methodology allows Vogtle to optinaize the replacement of elastomer diaphragms while f recluding diaphragm failure and assuring that an acceptable level of quality and safety is being

- maintained. Therefore, attached is a proposed attemative per 10CFR50.55a(a)(3)(i) for using the qualified life methodology as an altemative to NRC specified conditions for the use of Code Case N-31, g fl ,,

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i Please contact this office if you have any questions.

Sincerely, i

i j . B. Beasle , Jr.

JBB/ Pall

Attachment:

Alternative to Code Case I cc: Southern Nuclear Operatina Company Mr. J. T. Gasser Mr. M. Sheibani SNC Document Management i U. S. Nuclear Reculatory Commission

. Mr. L. A. Reyes, Regional Administrator j Mr. Ramin R. Assa, Vogtle Project Manager, NRR .  ;

' Mr. J. Zeiler, Senior Resident Inspector, Vogtle l

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t ALTERNATIVE TO Tile REQUIREMENTS OF CODE CASE 1540-2 (N-31) AS IMPLEMENTED TIIROUGil Tile PROVISIONS OF REGULATORY GUIDE L84, -

REVISION 20 j

Backcround i Plant Vogtle has elastomer diaphragm valves located in both safety-related Nuclear Steam Supply (NSSS) systems and Balance of Plant (BOP) safety-related systems.

The environmental qualification of the elastomer diaphragms in the NSSS valves (as listed in WCAP-10856) has been addressed, as pan of the environmental qualification of safety-related NSSS mechanical equipment transmitted to the NRC in a Vogtle Project letter dated

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November 13,1986. The transmittal included the results of a thermal and radiation aging analysis. It was concluded in the NRC's Safety Evaluation Report (NUREG-1137, Supplement No. 5 - Subsection 3.11.3.2.2) that the requirements for environmental qualification of safety-related mechanical equipment was adequately addressed.

The BOP diaphragm valves are safety-related, but are manually operated; therefore, they are not listed in the FSAR active valve list (FSAR Table 3.9.B.3-9) and are not included in the IST program. The design criteria used for these BOP supplied diaphragm valves satisfies the requirements outlined in 10 CFR 50 Appendix A (GDC 4),10 CFR 50 Appendix B, and ASME Code Case 1540-2 (N-31). Contingencies for the use of Code Case 1540-2 (N-31) are listed in Regulatory Guide 1.84 and were established to assure that a level of conservatism would be applied to the storage and use of the elastomer diaphragms.

In lieu of these contingencies, Vogtle is proposing the use of technical bases to determine storage and service lifetimes of the BOP elastomer diaphragms. The use of these technical bases will ,

more closely align the methodology used in the evaluation of BOP supplied elastomer .

diaphragms with that for the NSSS valves.

Regulatory Reauirements i

Code Case 1540-2 (N-31) was implemented through the provisions of Regulatory Guide 1.84, j Revision 20 (which is referenced in FSAR Section 1.9.84), which required: I i

1. Each applicant who applies the Code Case should indicate in the referencing Safety Analysis Report that the service life of the elastomer diaphragm should not exceed the manufacturer's l

recommended service life. Note: For Vogtle, the manufacturer provided a " minimum cycle i life" as the " recommended service life".

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2. The recommended service life should not exceed one-third of the minimum cycle life as )

established by the requirements of paragraph 3 of the Code Case. In addition, the service life of the elastomer diaphragm should not exceed five years and the combined service and storage life of the elastomer diaphragm should not exceed ten years.

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Pronosed Alternative to the Regulatory Requirements with Bases In lieu of the above listed Regulatory Requirements, Vogtle proposes using the following technical methodology:

Shelf Life The methodology for determining the shelflife of diaphragms at Vogtle is based on EPRI Report NP-6408 (NSIG-13), entitled Guidelines for Establishing, Maintaining, and Extending the Shelf Life Capability of Limited Life items. The use of this report to detemiine the shelflife, in lieu of the existing requirements, will assure that high quality, non-degraded elastomer materials will be installed in the diaphragm valves, thus maintaining an acceptable level of quality and safety.

Appendix B of the report provides shelflife determination for 70 different materials. Appendix B also identifies the specific method used for each shelflife detennination as the manufacturer's recommendation, natural aging, or Arrhenius methodology and further delineates the function, aging data, activation energy, mechanical properties, and shelflife of various elastomer materials including diaphragm materials.

When using Arrhenius methodology and aging data, Vogtle applies two-thirds of the determined life for maximum shelflife. When using manufacturer's recommendations, the shelf! u is applied without change. The methodology used in shelflife evaluations is consistent with the requirements for enviromnental qualification of equipment in harsh environments and satisfies the intent of 10 CFR 50.49. Under storage conditions, there is no significant degradation that would affect the service life of the elastomer.

j Qualified Life Elastomer diaphragms at Vogtle will be replaced based on the qualified life. The qualified life methodology considers process fluid and location effects on valve materials and is defined as the minimum life determined from thermal aging ef fects, radiation aging effects, and mechanical aging effects, .

To detennine the qualified life, a review of drawings and associated Bill of Materials was 1 performed to identify non-metallic parts and material types. After identification of materials, the j environmental conditions were identified and a functional review was performed to determine process fluid conditions. Based on the overall review of diaphragm valve materials, the minimum life from (1) thermal aging, (2) radiation aging. and (3) mechanical aging was established as the service life for the materials. The Maintenance and Surveillance (M/S) Program schedules equipment maintenance activities to maintain eqaipment in a condition that is safe for operation.

Each of these are discussed below:

1. Thermal Service I.ife - The thermal aging analysis was performed using the nonnal operating temperature from FSAR Table 3.11.B.1-1 or the process fluid temperature, whichever was higher, to determine the thermal service life. The analysis included an evaluation of aging i data from the Wyle Aging Database and Arrhenius methodology. The Wyle Aging Database, i l which has been audited by the NRC, contains material aging data for over 700 generic i l materials. The database also contains computation routines with Arrhenius equations. The Arrhenius equations, which are a function of the material's aging data, were used to calculate f

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the expected thermal life for the diaphragm materials. The Arrhenius methodology has been endorsed through IEEE 101-1972 and NUREG-0588 as an acceptable method to address time / temperature aging.

2. Radiation Service Life - An evaluation was performed using internal radiation doses, as well as external radiation doses, for specific areas in which the valves are located. Normal and post-accident doses were applied as appropriate. The radiation doses were then compared with radiation threshold data to establish a radiation life. The radiation threshold data, which is a function of elongation properties and tensile strength for specific materials, is documented in EPRI Report NP-2129. Based on the evaluation of radiation threshold data, the radiation service life was established for each valve.

3. Mechanical Senice Life - The mechanical service life was established using cycle aging data from the manufacturer. However, it is recommended that the service life not exceed one-third of the manufacturer's minimum cycle life. This recommendation is based on the guidance in Regulatory Guide 1.84 and licensing commitments in FSAR section 1.9.84.2.

Therefore, the mechanical service life was established to be one-third of the manufacturer's cycle aging data.

The results of the senice life evaluations for BOP supplied valves have been incorporated into the Vogtle EQ Program and (M/S) Program. The M/S Program schedules equipment maintenance activities to maintain equipment in a condition that is safe for operation. The use of qualified life for replacement scheduling will preclude diaphragm failure and assure that an acceptable level of quality and safety is being maintained, while optimizing the replacement of elastomer diaphragms.

Justification The subject manually operated elastomer diaphragm valves are located in the various systems, including the Chemical Volume and Control System and waste gas systems. Valve bodies,  !

bonnets, and bolting are constructed as pressure retaining items in accordance with Code Case 1540-1 (N-31) and in the unlikely case the diaphragm fails, the primary issue would be leaking process fluid. Application of the " Proposed Alternative to the Regulatory Requirements" will provide sufficient conservatism to reduce the possibility of a diaphragm failure and ensures that the valves will perform their intended function. This overall approach will ensure that an acceptable level of quality and safety is being maintained; therefore, the proposed alternative should be granted pursuant to 10 CFR 50.55a(a)(3)(i).

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