ML18114A720

Discusses Position Re Use of Soil Structure Interaction for Seismic Pipestress Analyses Being Performed.Approves Methodology,Provided That Seismic Stresses Calculated Are Increased by Factor of 1.5

ML18114A720
Person / Time
Site:	Surry
Issue date:	05/25/1979
From:	Eisenhut D Office of Nuclear Reactor Regulation
To:	Proffitt W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
References
TAC-11431, NUDOCS 7906250039
Download: ML18114A720 (3)

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DISTRIBUTIO Docket File MAY Docket Nos. 50-280 and 50-281 2 5 1979 a n d ""'l'ail-"'1'.!

NRC PDR (2)

Local PDR _

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V. Stello D. Eiser::ihut R. Vollmer

• B. Grimes W. Russel-1 J. Carter Mr. W. L. Proffttt A. Schwencer Senior Vice President - Power o: N~ighbors Virginia_Electric and Pow~r Compa_ny o. ~Jigginton Post Off1ce Box 26666

• c. Parrish**

Richmond, Virginia 23261 P. Kreutzer OELD I&E (3)

De~r Mr. Proffitt:

TERA J. Buchanan ACRS ( 16)

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The purpose of tnis letter is to state our posit.ion re9ardi119 the "use of,

soil structure'interaction for the seismic pipestress analyses being performed._for *Surry. Power Station, Units l and 2.

Based on the results of the information*you provided by your letter dated May,24, 1979 in response to our May 18, 1979 letter and in other meetings, we confirm that soi 1 structure interaction me tho do 1 ogy may be used for-Surry orovided.that seismic.stresses calculated are increased by a factor of 1.5.

'i°hi s factor applies to the seismic stresses derived from amplified response spectra using 1%.d~mping. *It is further acknowledged that certain individual analyses may require consideration on a ci:1se by case basis.

Th~ earthquake of primary safety concern i's the SSE.

• However, due to the nonlinearities of the soil which are considered in the soil structure interaction analyses, the stiffness of the subgrade is a function of *.the*

earthquake. 1 evel.

Si nee the floor response spectra" are sensitive to the stiffness of the subgrade, they too are dependent on the earthquake l eve 1 *,.Therefore, it is requested that the foll owi.ng two points be addressed;

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Discuss in detail why it can be concluded that the pipjng analyzed for the SSE condition will safely withstand all ea_rthquakes up to and including the SSE.

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For any pi ping systems which meet SSE_ reqtii rements but do not meet the FSAR *osE design requ*irements, provide the level of f { ~?\\t; ~

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~ ~rthquake for~nich _the FSAR OBE design requirements are

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J DOR:S&P DOR:EB iHRussell VN09 an Sincerely, 77(),:;,:;--063 i' 0511,,<!79 0

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e UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 May 25, 1979 Docket Nos. 50-280 and 50-281 Mr. W. L. Proffitt Senior Vice President - Power Virginia Electric and Power Company Post Office Box 26666 Richmond, Virginia 23261

Dear Mr. Proffitt:

The purpose of this letter is to state our position regarding the use of soil structure interaction for the seismic pipestress analyses being performed for Surry Power Station, Units l and 2.

Based on the results of the information you provided by your letter dated May 24, 1979 in response to our May 18, 1979 letter and in other meetings, we confirm that soil structure interaction methodology may be used for Surry provided that seismic stresses calculated are increased by a factor of l.5.

This factor applies to the seismic stresses derived from amplified response spectra using 1% damping.

It is further acknowledged that certain individual analyses may require consideration on a case by case basis.

The earthquake of primary safety concern is the SSE.

However, due to the nonlinearities of the soil which are considered in the soil structure interaction analyses, the stiffness of the subgrade is a function of the earthquake level.

Since the floor response* spectra ~re sensitive to the stiffness of the subgrade, they too are dependent on the earthquake level.

Therefore, it is requested that the following two points be addressed:

1.

Discuss in detail why it can be concluded that the piping analyzed for the SSE condition will safely withstand all earthquakes up to and including the SSE.

2.

For any piping systems which meet SSE requirements but do not meet the FSAR OBE design requirements, provide the level of earthquake for which the FSAR OBE design requirements-are met.

cc:

See next page Sincerely,

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0. G. ::":i senhut, Deputy. Ji rector Division of Operating Reactors.

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Mr. \\./*. L. Proffitt Virginia Electric and Power Company cc:

Mr. Michael w. Maupin Hunton and Wi 11 iams

• Post Office Box 1535 Richmond, Virginia 23213 Swem Library College of Wil 1 iam and Mary Williamsburg, Virginia 23185 Donald J. Burke U. S. t*luclear Regula-:ory Commission Region JI Office of Inspection and Enforcement 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 e