ML20215N100
| ML20215N100 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Diablo Canyon |
| Issue date: | 01/10/1977 |
| From: | Obrien J Office of Nuclear Reactor Regulation |
| To: | Sihweil I Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20197J003 | List: |
| References | |
| FOIA-86-371 NUDOCS 8611040272 | |
| Download: ML20215N100 (3) | |
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JAN 10 E77 c
g _)N MEf0RANDtX1 FOR:
- 1. Sibwell, Chief, Structural Engineering Branch, DSS FROM:
J. O'Brien, Structural Engineering Branch, DSS TiiRU:
K. Kapur, Section B Leader, Structural Engineering Branch, DSS
SUBJECT:
REVIEW 0F " ANALYSIS OF SOME OF THE MAJOR FARAMETERS INFLUENCING THE RESPONSE SPECTRA FOR THE DIABLO CNiYON SITE" BY DON BERNREUTER AND L. !!. WIGHT DATED OCTOBER 21, 1976 (SEB:1111)
The following remarks are provided at your request with respect to the subject report.
Section I Relation between peak velocity ancL peak acceleration for rock soil sites s
This section tends to confirm work already completed, and moreover reveals some aspects of conservatism embodied in Newmark's approach to Diablo Canyon. Specifically, the Bernreuter report would predict a velocity of about 49 cm/sec for a 19 earthquake on a rock site.
Newmrk' used 32 in/sec. (81 cm/sec) which would produce a higher response spectrum at aid-frequencies.
Iri my memorandum to you of September 9,1976, I indicated that D' Appolonia also obtained velocities lower than those used by Newmark for rock sites and that Newmark was aware of the extra measure of conservatis7. This section of the report tends to dmonstrate the safety of the "Jiablo Canyon Nuclear Power Plant to resist earthquakes.
Section II Effect 'of Lower Velocity Mudstone I.ayer The thrust of this section is that a soft mudstone layer sandwiched between the sandstone and tuff would reduce likely seiscic inputs from an earthquake on the HOSr.RI fault. Ilowever, since the properties of the oudstone are not knoun it woilld be difficult to use these erguments in a licensing proceeding. There is sisply no evidence at this Liue that the nudstone is sof t.
Section III gnan.ic Amplification Factors Y
The suggestion that lomr anplifications for bioh 9 earthquakes is valid is not borne out by other studies. Specifically, NUREG 0003, I
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.u JAN 10 B77 I. Sibweil authored by Newmark, arrives at a contrary conclusion. While this suggestion would be helpful in demonstrating safety, I feel we cannot use it in the light of conflicting reports from other sources.
Section IV Effect of Maanitude This section presents data which shows that spectral shapes depend on the magnitude of the earthquake. The chief conclusion appears to be that increasing the magnitude may not produce a unifom increase in the response spectrum across all frequencies, and that, in fact, higher magnitude earthquakes will have less high frequency content than currently estimated. The evidence presented te support this statement is convincing.and should be studied in greater depth.
I feel this issue, properly developed, may be used to show that additional conservatism may exist because the staff, and its consultants apparently, have not considered the effect of magnitude in constructing design spectra.
Section V Soil-Structure Interaction fT:5 This section concludes that "in spite of the site stiffness there is significant interaction of the structure with the soil". The report also states "The basemat spectral accelerations for frequencies between 2 and 3 llz are less than the free-field sp"ctra by as much a s 50%".
In the Diablo Canyon application no soil-structure interaction computations were included in the anal) sis and therefore this finding could be helpful in supporting the conservatism of the design. However the finding is surprising and must be more closely reviewed before being accepted.
Section VI Effect of Seismic Wave Passage on the Response of Large Basenct Structures This section is the most potentially damaging to the staff since it attenpts to show that the wave passage effect permitted by the staff to reduce response spectra at high frequencies is not supported by observations. The Cernreuter report studies the response of six closely spaced buildings during the San Fernando earthquake of l' 71.
His results indicai.e that buildings with laroe basemats have J
response spectra at high frequencies which sometimes exceed the response spectra of closely spaced buildinn with smaller basemats.
This, of course, is contrary to wave passage theory, which predicts the building with smaller basenat to have the larger rest:onse.
Cernreuter's observations require close scrutiny.
It is known, for example, that the six buildings varied between 7 and 39 stories in height and that sone were of steel construction while others were of m in ivi uud s.u ns i u le s.u ns ti uu li en. One GT the buildings was cEr u >e W mp. alluviumj hile the rema ining five were located on shallow sunwams >
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JAN 101977 I. Sihweil alluvium (30 to 40 feet thick) overlying a layer of shale.
Found-ation types include caissons (2 buildings) spread footings (3 buildings) and friction pilet (1 building). Accelerometers were located anywhere from the ground surface to approximately 60 feet below the ground surface. What is to be gleaned from these remarks is that accelerometers were recording, in addition to wave passage effects, soil-structure interaction effects, and mareover, were recording notions at different depths. It does not appear that Bernreuter considered this in his presentation. We are therefore unable to cccept his findings at this time,although we must acknowledge that his study raises serious questions which deserve answers.
John O'Brien Structural Engineering Branch Division of Systems Safety cc:
D. Allison B"7~'
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