ML20137D924

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Forwards Background Info on Request for Interpretation of ACRS OL Ltr Re Facility Seismic Design Margin
ML20137D924
Person / Time
Site: Davis Besse, 05000000
Issue date: 01/04/1979
From: Wright R
Advisory Committee on Reactor Safeguards
To:
Advisory Committee on Reactor Safeguards
Shared Package
ML20136A555 List: ... further results
References
FOIA-85-363 NUDOCS 8508230089
Download: ML20137D924 (3)
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n January 4, 1979 ,,

ACDS MPGERS DAVIS-BPSSE 1 SEISMIC MARGItG

'Ihe attached write up was prepared in February 1977 at the time of Mr. Froley's letter of clarification on ACRS Davis Besse 1 report.

' It has been brotryht up to date and should provide the background information on Davis Fesse that you requested.

R. L. Wright Staff Enginaer

Attachment:

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2 BACEROLMD INFORMATION REGARDIC 1HE RE0thEST FOR INTERPRETATION -

.OP THE COMMITTEE'S OL LE' ITER 09 DAVIS BESSE UNIT 1 REIATING 1D SEISMIC DESIGN MARGIN Using procedures in effect at the time of the CP application (1969) the Toledo Edison Company established an SSE value of 0.15g at the i foundation level and an OBE of 0.08g. % e 0.15g was applied at the

! foundation with spectra modified from the Helena earthquake of 1935.

I Wis spectra is less conservative than used now, but danping factors

are about 1/2 of those used now. At the CP stage the NRC Staff accepted these values and also the selection of the naximum possible earthquake (medim MM VII) . In October 1974, the NRC Staff changed their procedures for establishing the SSE value. % is procedure involves the tectonic approach to arrive at an intensity value at the site.
Trifunac-Brady curves (best fit) are then used to relate-intensity to acceleration. %e acceleration value is then used for the Reg. Guide I

1.60 Spectrun and is applied at finished grade in the free field. Wis j is then deconvoluted to foundation level for deep and sometimes meditra

depth soil sites. (Tr 46 201st Meetirvj) . Fb11owing the procedures now in effect would yield an SSE of 0.20g at the ground surface in free l field as the scismic criteria for the Davis Besse Site. Deconvolution i would not be applied to Davis Besse. i At the Subcommittee meeting (December 21, 1976) the only mention of seismic i design was a statenont by the NRC Project Manager (Leon Engle) that the  ;

i seismicity of the Davis Besse Site is being evaluated by the EC Staff I and there nay be a Staff difference in opinion in the final Staff position..

l %is apparently related to Mr. Rider's opinion that a 0.25g SSE value l' should be used at a site such as Davis Besse in the central stable region.',

Mr.' Rider nade a presentation on this to the Committee at the January 1977 meeting (Tr 51, 201st Meeting).

1 l On December 15, 1976, the NRC Staff infomed Toledo Edison that they might i' j impose 0.29 at the ground surface in the free field. About a day or two before the January 1977 full Co9mittee neeting, the NRC Staff decided not , %;

to impose this 0.29 value on Davis Eesse 1; they were satisfied with the ' dN I 0.15g at the foundation level. W e NRC Staff reported this to the full Committee during- the Davis Besse 1 review at the January 1977 Committee

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meeting. Se NRC Staff did, however, inform the Applicant that they

, would impose the 0.29 free field value as the seismic criteria for Davis j Besse 2 arri 3. At the January 1977 meeting, Harold Denton said that since q l the Sumer of 1976, the NRC Staff has consistently applied acceleration j at the ground surface in free field, and that the computer code SimKE is used to derive data for the foundation of each building. He said that  :

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. V during'the preceeding two years (1974-76) the deconvolution was not used except on a few plants.

I At the full Connittee neeting in Jantary 1977, the Applicant stated that there is about 25 to 35 feet of compacted soil material to which

a deconvolution process can be applied. We Applicant stated that pre-lininary calculations deconvoluting a . 0.29 through the 25-35 feet of soil to the foundation results in a g- value of about 0.16. We Connit-i tee (Dr. Siess and Dr. Okrent in particUlar) does not seen to be con-fident as to the justification and procedure for the deconvolution pro-l cess. %c NRC Staff stated that reevaluation of the selsnic design of

. the plant had not been done, and they implied that a process of exper-ience and judgment went into their decision not to impose the 0.29 free field value. Dr. Okrent pinted out that the North Anna Subconnittee f had asked for an analysis of the safety margins of all safety-related systens under SSE conditions. At the ! brth Anna Subcommittee meeting

. the Applicant gave sone examples, but apparently did not know values for all safety-related syntems. We Comittee put the same reconnendation in the North Anna and Davis.Besse letters regarding an NRC staff review of the SSE design and prestnably for the sane reasons. bledo Edison Muhaitted a preliminary reyrt on January 27, 1977 on their seisnic design l review.

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