ML20147D384

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Forwards Seismic Hazards Assessment, Final Rept Per NRC 830503 Request for Addl Info Re Question 230.6
ML20147D384
Person / Time
Site: Satsop
Issue date: 02/29/1988
From: Sorensen G
WASHINGTON PUBLIC POWER SUPPLY SYSTEM
To:
NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
Shared Package
ML20147D389 List:
References
GO3-88-066, GO3-88-66, NUDOCS 8803040004
Download: ML20147D384 (9)
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Washington Public Power Supply System Box 1223 Elma, Washington 98541 (206)482 4428 February 29, 1988 G03-88-066 Docket No. 50-508 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555

Subject:

NUCLEAR PROJECT NO 3 RESOLUTION OF KEY LICENSING ISSUES RESPONSE TO QUESTION ON SEISMIC HAZARD

References:

a) Letter (G03-88-038), G. C. Sorensen to L. S. Rubenstein, subject "Geosciences Program S:hedule," dated February 10, 1988.

b) HRC letter, R. M. Novak to R.'L. Ferguson, subject "Request for Additional Information on WNP-3 Safety Review", dated May 3,1983.

In accordance with our recent Geosciences Program schedule sent to you via Reference a), we are submitting our response to Question 230.6. That request for additional information was originally included in Reference b). In conformance with 10CFR50.4, we are transmitting one (1) signed original and 38 copies of the question response.

The response references a report prepared for the Supply System by Geomatrix Consultants. This report is quite large and it is not practical to include a copy of the report with each copy of the question response. Therefore, five (5) copies of the referenced report are included for distribution to the NRC Staff.

'bo\4 esoso4ooo4 eso229 I PDR ADOCK 05000508 ,

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..- , c U. S. Nuclear Regulatory Commission G03-88-066 .

Attention: Document Control Desk February 29, 1988  :

Page Two _

i If you have any questions, please cnntact Mr. D. W. Coleman, WNP-3 Project Licensing Manager, phone (206) 482-4428, Ext. 5436.  ;

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G. C. So nsen, Manager Regulatory Programs

.DWC/cae Attachment cc:

  • Mr. J. A. Adams, NESCO '
  • Mr. M. F. Barnoski, Combustion Engineering, Inc.
  • Mr. C. W. Brauer, Pacific Power & Ligh?. Co. '
  • Mr. W. J. Finnegan, Puget Sound Power & Light Co.
  • Mr. C. Goodwin, Portland General Electric Co.
  • Mr. J. B. Martin, Administrator, Region V
    • Mr. L. Reiter, U. S. Nuclear Regulatory Commission
  • Mr. N. S. Reynolds, Bishop. Cook, Purcell & Reynolds
  • Mr. D. Smithpeter, BPA
  • Ms. R. M. Taylor, Ebasco - Elma -
      • Mr. G. Vissing, U. S. Nuclear Regulatory Commission i
        • Document Control Desk - U. S. Nuclear Regulatory Commission -
  • One (1) copy of question response without copy of report l
    • Two (2) copies of report
      • One (1) copy of report
        • Original letter and 37 copies of question response with two (2) copies of report i

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Question No'. ,

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230.6<(SRP Estimate theLannual' exceedance probability for the-SSE,'using as 12.5.2.4,o sources random earthquakes, subduction zone earthquakes,'as :well

.2.5.2.6):  ; as earthquakes on significant, capable ~11 nears. Show the rela-tive contribution 1of _ these sources to the annual. exceedance probability. -If : an integrated assessment ofe exceedance proba-

.bilities is performed, assigning subjective weights to 'different ;

m tectonic models, the exceedance probabilities . for . each . model p .should be presented separately.

- Response:

L '

To resi 'o Question .230.6, a probabilistic ' . seismic ' hazard' analyst been carried out (Geomatrix Consultants. 1988).-

U Importa. .; sues related to the probability of arceeding the SSE:

F. ^ center =;ound the tectonic model in the region, spe.!!itally the

! _' - seismogenic ' potential of the Cascadia ' subduction zone. The

! seismic hazard analysis ' ~ synthesized the present. scientific o understandino of seismic sources 'and particularly subduction zone . sources .tiat may affeet th- 50e. This scientific , under-i standing and the assxiated uncertdnites have been incorporated ,

The present- state- of-

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i- explicitly into the hazard ana'ij. ..

knowledge and uncertainty regarding ground _ motion attenuation for both crustal and subduction zone sources has been included.

Finally, the hazard results have been presented showing the 4

relative contributions and sensitivities of tne results to the

inpuks.

1 To c.arry out the WNP-3 hazard analysis, the current spectrum of I

scientific thinking regarding .the Cascadia subduction zone has' i , , been ' captured using expert opinion. Fourteen experts, con-

[ sisting of geologists, seismologists, and geophysicists having F experience in this region, provided their opinions regarding key

] aspects of the seismic hazard model' including: the potential ~

1 seismic subduction-related sources, .the probability that each j source is seismogenic, the geometry and location of ruptures on

each source, maximum magnitudes, the rate of convergence between j the Juan de Fuca and North American plates, the seismic coupling at the plate interface, and earthquake recurrence models and rates. In developing a methodology for soliciting and utilizing expert opinions, careful consideration has been given to the

! methodologies used in recent major hazard analyses for the

' eastern U. S. (e.g., those by Lawrence Livermore National Laboratory for NRC, and the Electric Power Research Institute).

In addition to those aspects of the seismic hazard model defined by the experts, other aspects of the model were parameterized on the basis of recent studies carried out for the Supply System.

. The shallow crustal seismic sources (including faults, linea-i- ments, and random sources) were characterized by the geologic L and seismicity data gathered for the WNP-3 FSAR and responses to Q231.1 - Q231.4. Also, ground motion attenuation relationships i

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Question No.

230.6 were developed .specifically for this study to include strong ,

Response: motion data for rock sites from ~ the recent Chile and Mexico (Cont'd) earthquakes, as well as the results of numerical modeling of ground motions from large interplate earthquakes.

The results of the uncertainty analysis of hazard are distri-

.butions for the annual frequency of exceeding specific levels of ground motion. These dist,ibutions are presented in Geomatrix Consultants - (1988) in terms of 15th,' 50th, and 85th fractile hazard curves for peak ground acceleration and 5% damped spectral accelerations at periods of 0.15, 0.8, and 2 seconds.

The periods of 0.15 and 0.8 seconds are the points of maximum amplification of spectral acceleration and spectral velocity, raspectively, in the response. :pectra developed for subduction zone earthquakes. Utilizing those results,- the following fre-quencies of exceeding the horizontal SSE spectrum were obtained; SSE Spectral Period Acceleration Annual Frequency of Exceedance (x 10-3)

(sec.) (g) 15th percentile 50th percentile 85th rarcentile 0 0.32* 0.62 1.2 2.1 0.15 0.871 0.21 0.46 1.1 0.8 0.566 0.020 0.10 0.66 2.0 0.266 0.002 0.01 4 0.22

  • Peak ground acceleration The range in annual frequency of exceedance from the 15th to 85th is about one-half to two orders of magnitude, depending on the period. This range incorporates all of the uncertainties in the tectonic understanding of the seismic environment as well as

[ the statistical variability in ground motion estimates. This l range of 15th to 85th percentile in hazard is comparable to that

! obtained at other plant sites (e.g., Bernreuter et al.,1985).

Extensive sensitivity analyses were conducted (Geomatrix l Consultants,1988, Section 4) to identify the relative contri-l butions to the uncertainty in the hazard from expert-to-expert

! differences, "within expert" uncertainties, and attenuation relationships. The "within expert" uncertainties include slab 1 geometry, source activity, segmentation, extent of rupture, maximum magnitude, recurrence methodology, convergence rate,

! seismic coupling, and magnitude distribution model s. These analyses indicated that primary contributors to the total l

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-Question No. l 230.6 uncertainty in the hazard at the site were expert-to-expert Response: variability in source interpretation and the assessment of the (Cont'd) probability that the plate interface is active.

.To specifically respond to the' question, the relative contri-bution of various seismic sources to the annual probability of exceeding various levels of peak accelaration is given in Figure 230.6-1. It is cl2ar from these resuics that 'the subduction-related seismic sources (plate interface and intraslab) con-tribute about 10 times more to the hazard than the shallow crustal sources (capable faults and random shallow crustal sources). Further characterization of the source contribution is given in Figure 230.6-T., which shows the average contri-butions to the total hazard from earthquakes in various magni-tuae increments and from various sources for peak accelerations of 0.1, 0.3, and 0.5g. As the acceleration level increases, the larger magnitude events increasingly dominate the hazard. At the SSE peak acceleration (0.32g), the hazard is due to earth-cuakes in the magnitude 6 to 7.5 range on the intraslab source and from large earthquakes (greater than 7.5) on the plate interface.

The principal tectonic issue affecting seismic hazard at the site is whether or not the plate interface is active (seismo-genic). Therefore, sensitivity to "tectonic models" is best seen by- examining the variation in the results assuming that the plate interface is active or is not active. Figure 230.6-3 compares the median hazard curves obtained assuming the inter-face is active with certainty (probability of activity = 1.0) and obtained assuming the interface is inactive with certainty (probability of activity = 0.0) with the 15th, 50th, and 85th hazard curves for subduction zone sources. It is clear that the hazard results are sensitive to the assessment of source activity. Each expert was asked to assess the probability that the interface is active and the distribution of probabilities for all experts is given in Geomatrix Consultants (1988, Figure 3-3).

In sumary, we believe that the seismic hazard analysis has l incorporated the present scientific and tectonic understanding i of the seismic envi ronment in the Satsop site region. The l results provide a complete expression of the hazard at the site l

and the associated uncertainties, and as such, provide a solid basis for evaluating the SSE spectrum. The results indicate that the probability of exceeding the SSE ground motions at the WNP-3 ple.nt site is within the range of values determined for other piant sites. Within that context, the seismic design values utilized at WNP-3 are consistent with established I

licensing practice, l

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Question No.

230.6.

Response

(Cont'd)

References:

Bernreuter', ' D. L. , Savy, J. B. , Mensing, R. W. , Chen, J. C.~,' and Davis, ~B. C., 1985, - Seismic hazard characterization of the eastern United States, Volume I: Methodology and results for ten sites: Lawrence Livemore National Laboratory, UCID-20421, Vol . 1.

.Geomatrix Consultants, 1988, Seismic hazard assessment for WNP-3, Satsop Washington, Contract No. C-20453: Report for Washington Public Power Supply System,~ February,1988.

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