ML19319C200
| ML19319C200 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 03/08/1977 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19319C198 | List: |
| References | |
| NUDOCS 8002050789 | |
| Download: ML19319C200 (3) | |
Text
.
e
~
gq 3 BII SAFETY EVALUATION REPORT SUPPLEMENT DAVIS-BESSE UNITS 1 GEOLOGY DOCKET NO. 50-500/501 The vibratory motion for seismic design at the Davis-Besse 1 site is assumed to result frem a Modified Mercalli intensity VII-VIII.
This corresponds to the Anna, Ohio event of March 8, 1937, the highest intensity earthquake in the central stable region that has not been definitely associated with utructure.
It had a felt area of 150,000 sq. miles and an estimated magnitude of 5.5 (5 to 6) based upon l
limited instrumental data, felt area and intensity-magnitude correlations.
The extent of the felt area indicates that it could not have been a very shallow (less than 5 km deep) event.
The foundation conditions at the Davis-Besse 1 site 100 miles north of Anna consist of 15 feet of glacial y
till overlying bedrock (dolomite and shale). The Category I structures are either on or near the bedrock surface. Vibratory ground motion estimates that best approximate the safe shutdown earthquake would then be that derived from accelerograms recorded on rock near magnitude 5 to 6 earthquakes that had maximum intensities of VII-VIII.
The applicant designed the Davis-Besse 1 power plant prior to the issuance of Appendix A to 10 CFR Part 100 and Regulatory Guide 1.60.
The design response spectrum was based on a modification of the E-W accelerogram recorded during the Helena, Montana earthquake of October 31, 1935. This earthquake had an instrumentally determined magnitude of 6.0, a maximum epicentral 8 0 02 oso77cq
2 -
y;; 3 7377 intensity of VIII, and a felt area of 140,000 square miles. Due to regional variations in seismic wave attenuation, western earthquakes have smaller felt areas H.an eastern earthquakes of similar magnitude.
The accelerogram which had a peak acceleration of 0.16g was recorded on a rock site approximately 5 miles from the epicenter. Considering the parameters of the safe shutd wn earthquake required for the Davis-Besse site this accelerogram may be considered a good choice for design basis with respect to expected earthquake magnitude, intensity, epicentral dis tance and foundation conditions.
The seismic design basis for the Davis Besse Unit 1 is the modified Helena F-V response spectrum scaled to 0.15;,.
This motion was appited at the foundation let:al of structures. In our review of Davis Besse Units 2 and 3 6
we have concluded that the Units should be designed for a level 6f ground motion represented by Regulatory Guide 1.60 scaled to an acceleration for seismic design of 0.2g.
This design is based on an assumed MM intensity VII-VIII at the site and, consistant with recent staff practice the use of the Trifunac and Brady empirical relation between MM intensity and acceleration rather than the Gutenberg and Richter relationship used for Unit 1.
~
MAR 8 1977 References 1.
Trifunac, M. D. and A. G. Brady, "On the Correlation of Seismic Intensity Scales with Peaks of Recorded Strong Ground Motion."
Bulletin of the Seismological Society of America, Volume 65, pages 139 -162,1975.
i T
t
?
I r
i r
i
.