ML20217B189

Submits Clarification Re Development of Basis for Determining Limiting Internal Pressure Loads Re Review of NRC SE for Cycle 16 Extension Request.Util Intends to Use Guidelines When Evaluating SG Tube Structural Integrity

ML20217B189
Person / Time
Site:	Farley
Issue date:	10/04/1999
From:	Dennis Morey SOUTHERN NUCLEAR OPERATING CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NEL-99-0320, NUDOCS 9910120173
Download: ML20217B189 (3)

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.i" - l D:ve Morey i S:uther2 Nuclear .

.-8 Vice President . Oportting Comp:ny Ferley Project . P.O. Box 1295 l

Birmingham. Alabama 35201 l Tel 205.992.5131

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.0ctober'4, 1999 @MM i; Energy to Serve %ur%rld' Docket Nos.: 50-348 NEL-99-0320 50 364 U. S. Nuclear Regulatory Commission -

ATTN: Document Control Desk -

Washington, DC 20555-0001' Joseph M. Farley Nuclear Plant Review of NRC Safety Evaluation for Cycle 16 Extension Reauest

. Ladies and Gentlemen:

. Southern Nuclear Operating Company (SNC) has reviewed the NRC Safety Evaluation Report (SER) dated August 17,1999 aiid issued for the Cycle 16 extension. SNC would like to make i one clarification co~ncerning the' development of the basis for determining limiting internal

- pressure loads. q The following paragraph was included in the safety evaluation:

SNC indicated that the limiting internal pressure loads applicable to the Farley-1 steam generator tubes occur during normal operation. The differential pressure assumed by SNC for these conditions is 1436 psia. The staff notes that this does not necessarily  :

represent the maximum differential pressure applicable to the Farley-1 steam generator. '!

tubes. The value of 1436 psia was established on the basis of the steady-state pressure on j the secondary side of the steam generators at 100 percent power operation. The assumed  !

differential pressure did not account for transient plant conditions that occur during operation that result in slightly higher differential pressures than those experienced under steady-state conditions. Such transients were not included in SNC's analysis but should i be included in establishing the limiting pressures in accordance with the guidance in the ASME Code and NRC RG 1.121," Bases for Plugging PWR Stan Generator Tubes."

However, the staff concludes that the differential pressures asramed by SNC for the -

Farley-1 are adequate for the licensee's operational assessmera because the results of the staffs risk evaluation are insensitive to this assumption. Applying a safety factor of 3 to the normal operating differential pressure necessitates that the Farley-1 steam generator g

- tubes be capable of withstanding a pressure of 4308 psi. -I Recently at an NRC and industry meeting, this issue was discussed. The resolution reached with b

the NRC staff was the following:

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The safety factors of 3 for normal steady state full power operation and 1.4 for the

. limiting design basis accident concurrent with a safe shutdown carthquake from f ._ OD

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, , , U. S. Nuc! car Regulatory Commission Regulatory Guide 1.121 should be supplemented as necessary to ensure structural l

integrity over the full range of normal operating conditions (including startup, operation in the power range, hot standby, cooldown, and all anticipated transients) and design

basis accidents. Supplemental criieria includes

Primary stress should not exceed yield strength over full range of normal operating conditions (including startup, operation in the power range, hot standby, cooldown, and all anticipated transients).

Loadings contributing to combined primary plus secondary stress should not lead to burst (as consequence of tensile overload or cyclic loading) under the full range of normal operating conditions (including startup, operation in the power range, hot standby, cooldown, and all anticipated transients) and design basis accidents.

Therefore it is SNC's intent to use the above guidelines when evaluating steam generator tube

! structumiintegrity.

This letter contains one NRC commitment as follows; SNC will use the above guidelines when evaluating steam generator tube structural integrity. If there are any questions, please advise.

Respectfully submitted, V 4 )MW' f Dave Morey MJA/maf:SEReycl6. doc k

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I Page 3 7, , U. S. Nuclear Regulatory Commission -

. .cc: Southern Nuclear Oocratine Comoany  !

- Mr. L. M. Stinson, General Manager - Farley U. S. Nuclear Reaul.atory Commission. Washincton. D. C.

Mr. L. M. Padovan, Licensing Project Manager - Farley LL S. Nuclear Regulatory Commission. Reuion 11 Mr. L. A. Reyes, Regional Administrator .

Mr. T. P. Johnson, Senior Resident Inspector - Farley i

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