ML20126L911

Sser Accepting Seismic Analysis of Soil Structure Interaction for Deeply Embedded Standby Svc Water Cooling Tower Basin

ML20126L911
Person / Time
Site:	Grand Gulf
Issue date:	06/13/1985
From:	NRC
To:
Shared Package
ML20126L898	List: ML20126L894 ML20126L911
References
TAC-49995, NUDOCS 8506200174
Download: ML20126L911 (2)

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l ENCLOSURE 1

I SUPPLEMENT TO SAFETY EVALUATION REPORT l

GRAND GULF NUCLEAR STATION. UNITS 1 AND 2 CONFIRMATORY EVALUATION OF SOIL STRUCTURE INTERACTION i

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INTRODUCTION i

The SSWCTB is the only deeply embedded structure at Grand Gulf and the, j

licensee was requested to compare its seismic responses resulting from the j

finite element method (FEM) reported in the FSAR with the responses j

obtainedusingtheelastichalfspacemethod(ENS). Such a comparison of responses is required by the Section 3.7.2 of the Standard Review Plan

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(SRP)fordeeplyembeddbdstructure. However, the licensee's EMS analysis"was

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considered unacceptable since it incorporated a forty percent reduction factor to account for embedmont effects.

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DISCUSSION I

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In responding to NRC's subsequent request for additional information concerning l

the methodology of the 551 analysis for the $$WCTS, Reference 1 explained that j

the EMS method based on SC-TOP-4 (Ref 3) but without incorporating the 40

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l percent peak reduction has been used. An engineering assessment by the licensee

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was therefore initiated to determine the impact on the $$WCT8 component design l

and equipment qualification using the envelope of the floor response spectra l

(FRS)curvesgeneratedfrom(1)theEMSseismicmodelwithnopeakreduction l

factorand(2)theFEMseismicmodelsemployedearlierbythelicensee.

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In Reference 2 the licensee has further clarified that the proposed FR$ are the envelopesof(1)theFEMwithcontrolmotionatthegroundsurfaceand(2)the 10 percent EMS with control motion input at the foundation level.

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CONCLUSION The Itcensee has complied with the staff position stipulated in Section 3.7.2 of l

the SRP and the FR$ obtained by means of this enveloping procedure are therefore i

acceptable.

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REFERENCES

References:

1.

Letter from L. F. Dale, MP&L to H. R. Denton, NRC, AECM-85/0028, dated January 28, 1985.

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Sumary of April 29, 1985, meeting regarding soil structure interaction for Standby Service Water Basin.

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" Seismic Analyses of Structures and Equipment for Nuclear Power Plants" Bechtel Power Corporation Topical Report BC-TOP-4A, Revision 3 November 1974.

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