ML19341C723
| ML19341C723 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 03/02/1981 |
| From: | Keeley G CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19341C724 | List: |
| References | |
| 11590, OC0381-0189A102, NUDOCS 8103040020 | |
| Download: ML19341C723 (8) | |
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f? *OI James W Cook
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- and Construction General o ffices; 1945 West Parnall Fload, Jackson. MI 49201 + (517) 788-0453 March 2, 1981 0
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Mr Harold R Denton, Director g7 I
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US Nuclear Regulatory Commission -
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MIDLAND PROJECT - a v MIDLAND - SITE SPECIFIC RESPONSE SPECTRA -
FINAL REPORT, PARTS I AND III-FILE B2.5.2, 0505.802 UFI 42*05*22*01, 70*01*10*02 SERIAL 11590 The NRC Staff in its letter of October 14, 1980 suggested that Consumers Power Company may use either of two alternate approaches stated in the letter in resolving the FSAR cpen item regarding seismological input parameters. In response to the letter, Consumers Power Company by its letter dated November 28, 1980 submitted a preliminary report entitled, " Site Specific Response Spectra for Safe Shutdown Earthquake," which formed the basis for the meeting with the NRC Staff on December 5, 1980. In this meeting, the contents of the preliminary report were presented in greater detail by Consumers Power Company's consultant, Weston Geophysical Corporation. Also presented was a study on Seismic Hazard Analysis for Midland site. In the ensuing discussion, NRC Staff requested additional information and justification of the positions taken. These requests were documented in NRC's December 22, 1980 summary of the meeting. Furthermore, the NRC Staff requested the applicant to document the December 5, 1980 presentation in more detail for the docket records.
Enclosed are forty (40) copies each of the reports - Site Specific Response Spectra: Part I - Response Spectra-Original Ground Surface, and Part III -
Seismic Hazard Analysis, which partially respond to the above request. As agreed upon during the December 5,1980 meeting, Part II of the report containing proposed site specific reponse spectra for the top of the fill and theoretical studies on possible ground motion amplification through the plant fill under the Diesel Generator Building will be furnished for staff review by April 1981. Subsequent sections of this letter discuss in detail the organization and contents of the report, the proposed site specific response spectra for original ground surface and responds to the concerns raised by the NRC Staff during the December 5,1980 meeting. g d:/
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- 1. Report:
The final report, in three parts, Part I, II and III is the culmination of a study performed by Weston Geophysical Corporation to arrive at suitable site specific response spectra. Part I of the report deals with the
- development of the site specific response spectra for Midland applicable at the original ground surface at the site. This part discusses in detail, Midland site seismicity, site characteristics, selection of accelerograms and presents the resulting response spectra, median, mean and 85th percentile for 5% critical damping. Appendix A of Part I discusses in detail the geological and geophysical descriptions of the strong motion recording sites and justifications as to why they are included in the data set for the determination Midland site specific response spectra. This appendix and Sections 3.3 and 4.1 of Part I of the report respond to the concerns raised by the NRC Staff concerning site selection for the Midland data set in the December 5, 1980 meeting.
As stated earlier, Part II of the report will develop site specific response spectra applicable at the top of the fill. As a part of this effort, theoretical studies on possible ground motion amplification through the fill is being performed and the results will be presented in this part. Similar to Part I, this will have an appendix containing a detailed discussion of applicability of selected accelerometer sites to Midland site original ground surface overlain with the fill material.
Part III of the report describes the results of a seismic hazard assessment of the Midland site. The results include probabilistic seismic ground motion levels and corresponding probabilistic response spectra.
The hazard analysis establishes annual exceedance probabilities for several levels of seismic ground motion. The analysis incorporates alteraate tectonic model definitions and a rather conservative assessment of input seismic parameters. Although the final results show that the probability level of the site specific response spectra for the SSE is comparable to other licensed modern plants, the actual annual probability could be much lower because of the various conservatisms employed. The objective of this study is to provide supportive information pertaining to the relative probabilistic levels of the deterministic site specific response spectra study presented in Parts I and II.
- 2. Proposed Site Specific Response Spectra - Criteria and Results:
In the development of the site specific response spectra all the stipulations made by the NRC Staff in October 14, 1980 letter have been met. Conformance to the magnitude range bounded by 5.3mb + 0.5 and epicentral distances less than 25 kilometers are addressed in detail in Sections 3.3 and 4.1 and Table 2 of Part I of the report. Similar discussions will be presented in Part II of the report for corresponding data set. Though it is quite conservative for'the Midland site which has notably low seismicity, Consumers Power Company will abide by the NRC Staff's position stated in October 14, 1980 letter that the 84th percentile spectra is appropriate for characterizing the SSE.
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Attachment I to this letter shows the 84th percentile site specific l response spectra for 5% critical damping. The Midland SSE design response ;
spectra (modified Housner spectra) is overplotted in the same figure for '
comparison. Details for Midland SSE design response spectra are provided in Sections 2.5.2.6 and 3.7.1.1 and Figure 3.7-2 of Midland FSAR. As stated in Section 3.7.1.1, the spectral acceleration values are increased by 50% in the period range between 0.2 to 0.6 second. This modified spectrum is shown in Attachment 1.
The Staff had expressed concern that the site specific response spectra derived from real time histories, falls off sharply in the long period region. Since there are no well-established means of addressing this concern within the bounds of site specific response spectra methodology and available data set, the 84th percentile response spectra is modified in the long period region by artificially raising the spectra derived from instrumental records as shown in Attachment 2. The proposed response spectra as shown in Attachment 2 is an adequate representation for the SSE at the original ground surface for Midland site.
The SSE spectra shown in Attachment 2 applicable to original ground surface will be conservatively assumed to be applicable to structures founded below the original ground surface at the structural foundation level. These structures are the Reactor Building, the Auxiliary Building and the Service Water Pump Structure. Part II of the report will address the site specific response spectra for structures founded on fill, such as the Diesel Generator Building.
- 3. Lawrence Livermore Laboratory (LLL)/ Tera Corporation Study - Comparison of LLL/ Tera " rock" spectra and Midland site specific response spectra:
NRC raised a question as to why the LLL/ Tera developed spectra for rock sites for the same magnitude range compares favorably in frequencies of interest with Midland site specific response spectra. Attachment 3 responds to this question by examining in detail the sites included in the LLL/ Tera study.
- 4. Discussion with the NRC Staff on Choice of Real Time History Records:
NRC Staff requested Consumers Power Company to discuss the choice of both site stations and specific earthquakes used for real time histories with the Staff. This has been accomplished by direct discussions between Consumers Power Company's consultant, Weston Geophysical Corporation, and the VRC Staff.
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In the December 5,1980 meeting, it was agreed that a follow-up meeting one
! month af ter the receipt 'of the report be appropriate. We urge a quick review of the enclosed submittals and would look forward to setting up a meeting with i the Staff at your earliest convenience.
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l For J W Cook' 1,
JWC/TRT/re CC RJ Cook (NRC Resident Inspector) w/o enc 4
Enclosure Site Specific Response Spectra Part I: Response Spectra-Original Ground Surface Part III: Seismic Hazard Analysis i
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. MIDLAND DESIGN SPECTRUM AND MIDLAND $1TE SPECIFIC RESPONSE SPECTRUM 5% CRITICALLY DAMPED l l
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. PROPOSED SAFE SHUTDOWN EARTHQUAKE SPECTRUM FOR ORIGINAL GROUrlD SURFACE 5% CRITICALLY DAMPED ATTACIC E T NO 2 a
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4 ATTACHMENT NO 3 Comments on Tera Magnitude 5.3 .+. 5 " Rock" Spectra The NRC summary of the December 5,1980 meeting on seismic input parameters cited their concern about the similarity between the 84th percentile spectra developed by Weston for the original ground surface and site conditions of Midland and the 84th percentile real time history spectra for rock sites developed by Tera Corporation. The spectra developed by Weston in the Part I report utilizes records from strong motion accelerograph stations whose site conditions most closely match those of the Midland Site (original ground surface). The selection of appropriate stations is by comparison of the geologic materials as identified by their shear wave velocity; this quantifies the geologic description to eliminate much of what is arbitrary in a qualitative descriation only.
The Tera Corport , 84th percentile " rock" spectra for a magnitude 5.3 + .5 earthquake (Tera Co'rporation Report III, August 1979) is derived from a data set which we believe includes the following eleven (11) accelerograph records (22 components) as indicated in Table 4-3 of that report.
Tera ID No Date-Time Station A15 3/22/1957 Golden Gate Park B37 6/27/1966 Temblor V317 11/14/1941 LA Chamber of Commerce W334 9/12/1970 Wrightwood W335 9/12/1970 Allen Ranch S68/8 8/08/1975-0700 Oroville - Station 6 S89/27 9/27/1975 Oroville - Station 8 S99/27 9/27/1975 Oroville - Station 9 Tol 54 5/09/1976 Tolmezzo Tol 64 5/11/1976 Tolmezzo Roc 132 9/11/1976-1631 S Rocco Temblor, Allen Ranch, Oroville Stations 6, 8 and 9 and San Rocco are
- unquestionably rock stations.
In many locales, the shear wave volocities of the stiffer soils such as at Midland correspond to the shear wave velocities of softer rocks such as those found in California. Some of these soft rock-stiff soils sites have been used by Tera in the development of their " rock" spectra.
The measured shear wave velocities at Golden Gate Park and the shear wave velocities estimated from measured compressional wave velocities at Tolmezzo, are more characteristic of stiff soils than rock even though the sites are described as weathered or broken sedimentary rock. Because of the shear wave velocities, the Golden Gate Park and Tolmezzo sites have been included in the
, response spectra data set for Midland. The Wrightwood site is described by l test borings as a stiff soils site and has been included in the Midland data set. Available data indicate that the L A Chamber of Commerce accelerograph oc0381-0189a102
2 station is located in an area of deep alluvium and is not appropriate for inclusion in either the Midland data set or the Tera " rock" spectra.
In summary, of the eleven (11) records Tera has selected for 5.3 + .5 magnitude " rock" spectra, six (6) are appropriate for a rock site, four (4) are more appropriate for stiff soile sites like Midland and have been included in the Midland data set, and one is representative of deep alluvium.
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