ML20081D674
| ML20081D674 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 10/24/1983 |
| From: | Counsil W NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES |
| To: | Youngblood B Office of Nuclear Reactor Regulation |
| References | |
| A03541, A3541, NUDOCS 8311010294 | |
| Download: ML20081D674 (5) | |
Text
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General Offices
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HARTFORD. CONNECTICUT 06141-0270
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October 24,1983 Docket No. 50-423 A03541 Director of Nuclear Reactor Regulation Mr. B. J. Youngblood, Chief Licensing Branch No. I Division of Licensing U. S. Nuclear Regulatory Commission Washington, D. C. 20555
Reference:
(1)
B. J. Youngblood letter to W. G. Counsil, Docket No. 50-423, dated October 3,1983.
Dear Mr. Youngblood:
Millstone Nuclear Power Station, Unit No. 3 Response to Request for AdditionalInformation Question No. Q 230.6 (SRP 2.5.2.2; 2.5.2.3; 2.5.2.4)
Attached is our response for your request for additional information contained in Reference (1) for Question No. Q 230.6 (SRP 2.5.2.2; 2.5.2.3; 2.5.2.4).
This response is being provided to you ahead of schedule in order to expedite the resolution of this issue.
Based on a telephone conversation with Ms. E. L. Doolittle, NRC Project Manager, our response to Question No. Q 420.6, will be forwarded to you on or before November 30,1983.
If you have any questions related to our response, please contact our licensing representative directly.
Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY, ET AL By NORTHEAST NUCLEAR ENERGY COMPANY, Their Agent
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Then personally appeared before me W. G. Counsil, who being duly sworn, did state that he is Senior Vice President of Northeast Nuclear Energy Company, applicant herein, that he is authorized to execute and file the foregoing information in the name and on behalf of the applicants herein and that the statements contained in said information are true and correct to the best of his
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NRC Letter: October 3,1983 j
REQUEST FOR ADDITIONAL INFORMATION i
MILLSTONE NUCLEAR POWER STATION, UNIT 3 DOCKET NO. 50-423 Question No. Q230.6 (SRP 2.5.2.2, 2.5.2.3, 2.5.2.4)
Your response to question Q230.4 is not_ adequate.
You have not provided extensive geological and seismological information and discussions required to demonstrate that the Millstone site and its surroundings are not similar to the tectonic environment of the New Brunswick earthquake (s) epicentral region. In addition, the staff is not aware of available information or scientific investigations that will support your position. If this extensive new information, supporting bases, and investigations are not provided, then assume that the site 1
is located in the New England-Piedmont Tectonic Province and that the j
mb= 5 3/4 New Brunswick earthquake is the maximum historical earthquake as defined in 10 C.F.R. Part 100, Appendix A for this province. Calculate a site specific spectra using an mb-5 3/4 as the target magnitude.
This can be l
accomplished by collecting a suite of strong motion response spectra recorded on rock sites, within distance of less than about 25 kilometers, for magnitudes (M )
L of 5 3/4 1 50. The 84th percentile of the above spectra should be compared to 0
those assumed for the site.
Provide a discussion regarding the potential for soil amplification for Category I structures located on_ fill or till.
Discuss how much amplification is being-allowed for, and at what frequencies it occurs.
The staff has also noted that you have assumed that the vertical SSE spectrum is 2/3 the horizontal spectrum over all frequencies. This differs from usual staff practice as identified in Regulatory Guide 1.60. Calculate the 84th percentile of l
the vertical components using the same suite of strong motion records as-identified above. Discuss the significance of these results to your assumption-regarding the vertical SSE spectrum.
Response
Through the Applicant's involvement in current informational studies being conducted in New England, a study on the New Bruns _ wick earthquake (s) nd its effect on New England plants will be submitted under separate cover.LI This report concludes that "... the New Brunswick activity can be constrained to its -
tectonic domain and thus has no direct implication'for the New England plants."
The Applicant will undertake an investigation to gather additional evidence to show that the tectonic environment of the Millstone site is' unlike that of the New Brunswick site. This scope of work, an integrated geological, geophysical, and seismological study, will encompass the tectonic setting of the Millstone site. Existing data bases will be assembled, reviewed, and modeled. New field mapping is not anticipated; however, analysis of the prevailing tectonic fabric in the site region (on shore) will be conducted. in order to differentiate _the -
a constituent. elements with-regard to identifying their' spatial and temporal i
development. Extrapolation of surface and near surface geologic conditions to y,
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4 5 m
. depth will be accomplished by modeling the available geophysical data base.
Next, the seismological data base, particularly earthquake epicentral locations and sizes, will be analyzed in the context of possible earthquake tectonic structure correlations. Finally, comparative analyses will be made to define dif ferences and similarities between the regional and local tectonics of the epicentral area of Central Miramichi, New Brunswick, and of the Millstone site area. Results of this investigation will be made available in April 1984.
A probabilistic analysis on se mic hazard has been produced and will be submitted under separate cover. 2) This provides additional evidence to support the validity of the SSE of 0.17g. The probabilistic assessment identifies the frequency of exceedance of various ground acceleration levels and the SSE spectrum at Millstone 3.
Eight alternate configurations of seismogenic zones j
were examined in order to represent the range of different hypothesis on structural and stress mechanisms contributing to the seismicity of the site. The mathematical procedures used to calculate seismic hazards are standard ones for seismic hazard assessment of nuclear power plant safety as outlined in the USNRC Probabilistic Risk Assessment Guide.
Based on this report, the Applicant concludes that the 0.17g SSE for Millstone 3 has an acceptable exceedance frequency determined by acceptable standard methodology.
The results of the two aforementioned studies further support the Applicant's earlier conclusion that a modified Mercalli Intensity VII (mb = 5.3) is the appropriate criteria for the SSE as discussed in Question 230.4, Option B.
In recognition of this and the conservative margin between the SSE spectra and the probabilistic seismic hazard spectra, the Applicant considers that obtaining the vertical design response spectra from the 2/3 value of the horizontal spectra overall frequencies is conservatively adequate. The Applicant considers that further deterministic approaches to justify the 0.17g SSE would be redundant.
However, the Applicant is continuing to consider the value of such approaches.
In response to the concern regarding soil amplification, the Applicant provides the following information.
Soil amplification was considered in the seismic design of the control building and the emergency generator enclosure (EGE). The soil structure interaction analysis is discussed in Sections 2.5.4.7.1 and 3.7B2.4.
Examples of input time history at bedrock and the resulting time history at the base of the EGE are shown on Figures 3.7B-63 and 3.7B-64. The EGE is founded on spread footings overlying 30 feet of basal till. Re till is very dense with a shear modulus of 1.4 x 102 psi. As a result, amplification through the till ;s small. Significantly higher amplification occurs through the structural fill which overlies the basal till. In the free field model, the ground acceleration at the foundation level at the top of the basal till for the Teft 1952 earthquake (S69E component) was calculated from SHAKE as 0.18g. At theground surface, a peak ground acceleration of.35g was calculated. Re mean square frequency for the ground motion at the top of the tillis 3.9 hz and for the ground surface is 5.5 hz.
The control building is also founded on basal till. He structure was modeled with 15 feet of basal till underlying the foundation.
Amplification effects through the till are similar to those determined for the EGE with a peak ground acceleration of.173g calculated at the base of the structure.
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From the above discussion and study results, the Applicant considers the 0.17g SSE to be adequate for developing design response spectra for current plant design. A seismic occurrence with a Modified Mercalli Intensity VII (mb = 5.3) is the maximum seismic event which should be considered in developing criteria for producing the design response spectra.
All deterministic studies and probabilistic assessments conducted to date firmly support this conclusion.
(1)
Weston Geophysical Corporation, " Seismology and Geological Studies for the Miramichi Area, New Brunswick and Central New Hampshire".
(2)
Dames & Moore, " Seismic Hazard and Design Spectra at Millstone Nuclear Power Plant, Unit 3", dated October 1983.
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