ML20212L117

Comments on 770621-23 Facility Subcommittee Meeting in Los Angeles,Ca Re Seismic Design.Considerable Discussion of Various Statistical Approaches Did Not Lead to Resolution of Differing Conclusions

ML20212L117
Person / Time
Site:	05000000, Diablo Canyon
Issue date:	06/28/1977
From:	AFFILIATION NOT ASSIGNED
To:	Mckinley J Advisory Committee on Reactor Safeguards
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References
FOIA-86-391 ACRS-CT-0814, ACRS-CT-814, NUDOCS 8608250210
Download: ML20212L117 (1)

Text

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2200'Donisteel Boulevard Ann Arbor, Michigan 48109 r.di. i June 28,.1977

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,:. a a Mr. John C. McKinley - ACRS Nuclear Regulatory Commission-b.'..

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Wa^hington, DC 20555 h

D2ar Mr. McKir. ley:

I am writi ig to give you my impressions of the Diablo sub-committee meeting held in Los Angeles on June 21-23, 1977 The considerable discussion of the various statistical npproaches did not lea _* to a resolution of the differing conclu-Dions although I think they are related to the different choices of ceismicity and spectral attenuation.

In any case, it became clear that probabilistic approaches would not fully answer our questions for this site.

Increasi ngly, I think evidence is accumulating that a mag-nitude 7'} or. the Hosgri fault may be too large.

This is, of cc.itrs e, scmewhat moot as the expected accelerations may well top cut at magnitude 6 3/4 or.less.

I still think the nature of the Hosgri fault -- its expected atrsss drop and type of s.l.ip.-

'is controlling for the maximum cccoleration and that its expected seismicity -- less than'the San Andrc-as ? -- controls the. probability.

Evidence is accumulating fog C 75 g as an appropriato anchor point for the Diablo spectrum.

particularAy, with regard to the $$gwever, questions still remain, plicant's use of 7% damping and

'D factor for the larger structbr,es.

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Professor Brune raised valid questions regarding focussing near the f.. ult; however, these effects will be minimized at high frequencies (greater than 2 Hz) and in my opinion, argue more for the choice of a truly conservative anchor point from existing data than for markedly increasing such an anchor point.

Very truly yours, s

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