ML18032A264

Informs of Intention to Utilize Artificial Time History Generated from Plant Design Response Spectra as Input for Seismic Sys Analysis.Fsar Will Be Revised to Reflect Use of Artificial Time History

ML18032A264
Person / Time
Site:	Browns Ferry
Issue date:	05/26/1987
From:	Gridley R TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
TAC-00158, TAC-00159, TAC-00160, TAC-158, TAC-159, TAC-160, TAC-R00158, TAC-R00159, TAC-R00160, TAC-R158, TAC-R159, TAC-R160, NUDOCS 8706030347
Download: ML18032A264 (14)

Text

REGULATORY ORNATION DISTRIBUTION .SY I (RIDS)

ACCESSION NBR: 8706030347 DOC. DATE,: 87/05/26 NOTARI ZED: NO DOCKET 0 FACIL: 50-259 Brains Ferrg Nucleav'ot"er Stationi Unit 1E Tennessee 05000259 50-260 Brogans Fev rg Nucleav Pouer Stationi Unit 2E Tennessee 05000260 50-296 Brains Fev v g Nucleav'ouer Stationi Unit 3E Tennessee 05000296 AUTH. NAKE AUTHOR AFFILIATION GRIDLEYR R. Tennessee Valley Authov itg RECIP. NANE RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Infov'ms of intention to utilize av'tificial time history genevated fv om plant design v esponse spectva as input for seismic sos analgsls. FSAR vill be revised to v ef lect use of av tificial time histov g.

DIBTRIDUTION CODE:

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TENNESSEE VALLEY AUTHORITY CHATTANOOGA. TENNESSEE 87401 5N 157 Lookout Place MAY 26 $ 87 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:

In the Matter of Docket Nos. 50-259 Tennessee Valley Authority 50-260 50-296 BROWNS FERRY NUCLEAR PLANT (BFN) ALTERNATE INPUT FOR SEISMIC SYSTEM ANALYSIS ARTIFICIAL TIME HISTORY By this letter, TVA is informing NRC of its intention to utilize input for BFN seismic system analysis which differs from that. previously used at BFN.

Specifically, TVA will be employing an artificial time history generated from the BFN design response spectra as seismic input, for seismic system analysis in place of the El Centro earthquake record utilized for such analysis up to this time.

This artificial time history reduces some of the excessive margin in the El Centro record over the BFN design basis response spectra and its use in analysis will yield generally lower seismic loads than analysis with the El Centro record. As a result, the number of modifications which will be required for seismic qualification will be reduced.

The use of the artificial time history does not constitute a change in the BFN design basis since the relevant response spectrum obtained from the time history envelopes the corresponding BFN design basis design response spectrum. The Final Safety Analysis Report will be revised to reflect the use of this alternate seismic input in the yearly amendment. The description of the artificial time history and a discussion of how it will be utilized for seismic system analysis are provided in the enclosure.

Please refer any questions on this submittal to Raymond H. Lewis, BFN Site Licensing, (205) 729-3585.

Very truly yours, TENNESSEE VALLEY AUTHORITY 870b030347 87052b . Gridley, Director PDR ADOCK 05000259 Nuclear Safety and Licensing p PDR Enclosure cc: see page 2 ggO An Equal Opportunity Employer

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U.S, Nuclear Regulatory Commission MAY 26 $ 87 cc: Mr. G. G. Zech, Assistant Director Regional Inspections Division of TVA Projects Office of Special Projects U.S. Nuclear Regulatory Commission Region II 101 Marietta St., NW, Suite 2900 Atlanta, Georgia 30323 Browns Ferry Resident Inspector Browns Ferry Nuclear Plant P.O. Box 311 Athens, Alabama 35611 MJM:JDW:RHL'SJL:CEL cc (Enclosure)

RIMS, MR 4N 72A-C C. E. Ayers, MR 5N 25A-C E. S. Christenbury, Ell B33 C-K W. H. Hannum, BR 1N 76B-C T. A. Ippolito, Bethesda Licensing Office N. C. Kazanas, LP 4N 45A-C (2)

J. A. Kirkebo, W12 A12 C-K M. J. May, Browns Ferry G. R. Mullee, 716C EB-C D. R. Nichols, LP 5N 302B-C H. P. Pomrehn, Browns Ferry D. L. Williams, W10 B85 C-K M. B. Whitaker, Jr., LP 5N 303B-C

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ENCLOSURE DESCRIPTION OF ARTIFICIAL TIME HISTORY TO BE UTILIZED AS ALTERNATE INPUT FOR SEISMIC SYSTEM ANALYSIS The Browns Ferry Nuclear Plant (BFN) licensing basis for seismic design is established in the BFN Final Safety Analysis Report (FSAR), Section 2.5.4. As discussed there, the response spectra chosen for BFN as the design basis ground motions are shown in FSAR Figures 2.5-8, the operating basis earthquake (OBE) response spectra, and 2.5-9, the design basis earthquake (DBE) response spectra (figures attached). . The shapes of the spectra were based on the work of G. W. Housner as presented in AEC report TID-7024 (August 1963), normalized to 0.10g maximum ground acceleration for OBE and 0.20g maximum ground

-acceleration for DBE.

At the time BFN was designed and constructed, the analytical techniques were not available for developing artificial time histories which would produce response spectra closely enveloping given smooth design response spectra. In order to generate amplified floor response spectra for seismic system analysis (at the time, a recent advance in design methodology), TVA opted to use for analysis purposes the record of the 1940 El Centro earthquake, N-S component, normalized to 0.10g for OBE and 0.20g for DBE. A comparison of the response spectrum produced by the El Centro record and the design basis response spectrum is shown in FSAR figure 2.5-10 (attached).

Since the time BFN was licensed, the analytical techniques have been developed which allow artificial time histories to be developed which will closely envelope given design response spectra. The current licensi.ng requirements for seismic design parameters, given in NUREG-0800, Standard Review Plan (SRP), section 3.7.1, Rev. 1, provide for the use of an artificial time history in carrying out, a time history analysis of seismic systems.

In 1986, an artificial time history of earthquake ground motion was developed by TVA which produces a five-percent damped response spectrum that closely envelopes the BFN DBE five-percent damped design response spectrum (see attached figure). The five-percent damped ground response spectrum produced by the time history meets the requirements of SRP 3.7.1 in regard to enveloping the five-percent damped design response spectrum when the time history spectrum is calculated using the frequency intervals recommended in SRP table 3.7.1-1.

This artificial time history will be used by TVA in the future as alternate seismic input for seismic system analysis. Specifically, will it will be used to used as input for generate amplified floor response spectra which then be seismic analysis of systems. The use of the time hi.story will be restri.cted to analysis of systems located within "five-percent structures," i.e., those structures, such as the'Reactor Building, which have been analyzed previously as having a damping coefficient equal to five-percent of critical. By restricting the use of the time history to systems within five-percent, structures, TVA is complying with the SRP 3.7.1 requi.rement that the spectra of the time history envelope the design spectra "for all damping values

DESCRIPTION OF ARTIFICIAL TIME HISTORY (Cont'd) actually used in the analysis." (NOTE: TVA interprets "all damping values actually used in the analysis" to mean the damping values for all structures involved in the analysis. Since use of the time history is restricted to analysis of systems in five-percent structures, the design and time hi.story generated ground response spectra need match only for five-percent damping.)

Use of the artificial time history for seismic system analysis in place of the El Centro record does not constitute a change to the BFN design basis since the relevant (five-percent) response spectrum generated by the time history envelopes the corresponding BFN design basis design response spectrum.

Since the artificial time history reduces some of the excessive margin in the El Centro earthquake record over the BFN design basis, use of the artificial time history in analysis will yield generally lower seismi.c loads than analysis with the El Centro record. As a result, the number of modifications which will be required for seismic qualification will be reduced. The initial use of the artificial time history will be in the analysis of piping systems for resolution of Inspection and Enforcement Bulletins 79-02 and 79-14. Other applications of the time history will be determined by TVA on a case-by-case basisi

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