ML20053B029
| ML20053B029 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 05/19/1982 |
| From: | Emch R Office of Nuclear Reactor Regulation |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8205270641 | |
| Download: ML20053B029 (3) | |
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May 19, 1982 s'S M '/ /S s
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Docket tio. 50-155 3
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Luw w.cax u 2C MEliORAt!DlP1 FOR: Dennis M. Crutchfield, Chief p'
Operating Reactors Branch #5, DL s
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Richard Ench, Project Manager Operating Reactors Branch #5, DL
SUBJECT:
!!EETIrlG WITil CONSUL!ERS POWER COMPANY Ott BIG ROCK POIllT Date & Time:
Tuesday May 25, 1982 10:00 Mi Location:
Room 6110 t-taryland fiational Bank Building Bethesda,!!aryland
Purpose:
To discuss the site specific seismic spectra of Big Rock Point Plant. (Topic of discussion attached)
Participants:
NRC R. Emch T. Cheng L. Reiter J. Kinball B. Jagannath R. Itermann.
Representatives from Lawrence Livermore National Laboratory j
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R. V1.1 cent Representatives from Weston Geophysical Original signed by Richard Each, Project Manager Operating Reactors Branch #5 Division of Licensing 820 5 27 0[f y/
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l TOPICS OF DISCUSSION FOR 5/25/82 MEETING i
POSSIBLE GROUND MOTION AMPLIFICATION AT BIG ROCK POINT AND ON SITE SPECIFIC RESPONSE SPECTRUM FOR BIG ROCK POINT
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In reviewing the site conditions that exist at Big Rock Point'(40 feet of till over bedrock) discussions have been initiated regarding possible ground motion I
amplification which might exceed the recommended spectrum developed as part of the Systematic Evaluation Program (SEP).
It is important to initially clarify l
the issue which must be addressed in this review. This issue is: Are the site conditions at Big Rock Point (BRP) significantly different than the gound motion recording sites used to develop the response spectrum as part of the SEP?
l Two different ground motion data sets were used by LLNL/ TERA in their analysis.
..ay were (1) the Trifunac Brady (1975) data base used to develop the ground motionattenuation relationships as part of the Uniform Hazard Spectrum and
. (2) the real time histories used to develop the 50th and 84th percentiles of the M = 5.3 near source earthquake. The site conditions at BRP should thus be compared to #'s 1 and 2 above.
In reviewing the Weston report on the BRP site specific spectrum, the staff has identified various concerns.
In general these are the sparse data available which match the site conditions at BRP and given this, the sensitivity of this data set to additional data.
In addition, the staff suggests that if possible multiple approaches be investigated in order to make a better judgement regarding the BRP site conditions. Each of these topics are discussed below.
(1)
In reviewing figures 2-9 of the Weston report, the staff has observed that the following sites do not appear to match the BRP shear velocity profile-particularly the sharp shear velocity increasein the upper 40 to 60 feet.
These stations are Cedar Springs, Golden Gate Park, Tarcento and Tolmezzo.
If these stations were removed, would there be enough data available for the site specific spectrum?
(2) Cholame station #8 from the 1966 Parkfield earthquake seems to qualitatively match the BRP site conditions as well as those listed in #1 above. Although the softer material goes to a depth of about 80 feet the shear velocity profile shows a sharp increase at 80 feet. What is the effect of adding this site to the entire data set?
In answering #'s 1 and 2, the staff requests a copy of the individual station's response spectrum for the entire data set along with plots of original data composed to the LLNL M = 5.3 soil real time histories spectrum.
(3) The 50th and 84th percentiles of the BRP site specific spectrum are less than or equal to the Midland Nuclear Plant site specific spectrum although the shear velocity profile is quite different between the two sites.
Justify (other than the site specific spectrum) that the free field response at Midland would be the same as BRP.
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f-(4) The staff suggests that if possible ratios of response spectra be provided comparing sites similar to BRP and those used in the SEP program. An example might be Johnson's Ranch and the Medical Center compared to deeper soil sitesin the Oroville area. Other examples '(which may need verification) might be strong motior, stations from Friuli, Italy; Ancona, Italy; )
Matsushiro, Japan; Magnoth Lakes, California; or other examples that you-feel are appropriate.
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(5) Geotechnical. data developed for the BRP site indicates that the bedrock is highly fractured between elevations 462.0 feet to %.13.0 feet. The shear modulus of this soft zone is nearly 50% 'of that for the competent rock above, between elevations 538.0 feet to 462.0 feet.. How does thic anomalous condition effect the results of your study?
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