ML20069B718

Forwards Response to NRC Request for Further Clarification on Soil Amplification Issue, Per NRC .Info Adequate to Close SER Outstanding Issue 3 in Next SER Suppl

ML20069B718
Person / Time
Site:	Clinton
Issue date:	03/10/1983
From:	Wuller G ILLINOIS POWER CO.
To:	Schwencer A Office of Nuclear Reactor Regulation
References
RTR-NUREG-0853, RTR-NUREG-853 U-0611, U-611, NUDOCS 8303170162
Download: ML20069B718 (17)

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. . U-0611 M1nols Power Company L30-83(03-10)L 500 SOUTH 27TH STREET, P. O. BOX 511, DECATUR. ILLINOIS 62525-1805 Docket No. 50-461 March 10, 1983 Director of Nuclear Reactor Regulation Attention: Mr. A. Schwencer, Chief Licensing Branch No. 2 Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Reference:

NRC letter A. Schwencer to G. Wuller, IP dated January 12, 1983, " Request for Further Clarification on the Soil Amplification Issue".

Subj ect : Clinton Power Station Unit 1 SER Outstanding Issue #3 (NUREG-0853)

Dear Mr. Schwencer:

This is in reply to the referenced letter and the request by Mr. G. Giese-Koch in the telephone conference with NRC, IP and S&L on March 1. Enclosed is the document entitled, " Response to NRC Request for Further Clarification on the Soil Amplification Issue." Figure 4 of our response gives the additional information verbally requested by Mr. Giese-Koch in the March 1 telephone conversation.

We believe that this clarification information is adequate to close SER outstanding issue #3 in the next SER supplement. Your concurrence of issue resolution is kindly requested.

Sincerely, J2%K G. E. Wuller Supervisor-Licensing Nuclear Station Engineering GEW/j mm enclosure cc: Dr. H. Abelson, NRC Clinton Proj ect Manager Mr. G. V. Giese-Koch, NRC GB Mr. B. N. Jagannath, NRC HGEB -

Mr. H. H. Livermore, NRC Resident Inspector g gl Illinois Department of Nuclear Safety 8303170162 830310 PDR ADOCK 05000461 E PDR

{

J' J Illinois Power Company Enclosure to Letter U-0611 l Clinton Power Station Unit 1 March 10, 1983 t

f RESPONSE TO NRC REQUEST FOR FURTHER CLARIFICATION ON j

• THE SOIL AMPLIFICATION ISSUE t

NRC Pageest

In a letter (Reference ~ 1) dated January 12, 1983, the NRC staff f requested IPC to provide further , clarification on the soil ampli-

fication issue. The letter stated:

3 "However, the staff has noted that the " weighted average" 2 amplification peaks are considerably lower than the peaks on

the "mean soil property" amplifications curve (Figure 1) . In

) the case of the amplification factors obtained from the SHAKE

program, the " weighted average" peaks f all outside (below) the r range of peaks . predicted by the range of soil properties (upper / lower bound) assumed for the site (Figure 2). In past safety reviews the NRC has recommended a conservative approach in enveloping the effects of soil amplification if uncer-tainities existed.

i Therefore, we request that you discuss the resulting fluctuations in the theoretical soil design spectrum caused by a assuming a range of soil properties. Subsequently you should i justify, statistically or otherwise, the use of the weighting j procedure referred to earlier in this letter in light of past y NRC positions....."

1 Background i

[

For seismic reevaluation of the Clinton Project a time history consistent with a 0.29 RG 1.60 spectra was used (Reference 2). The response spectrum of this time history is presented in Figure 32 (labeled as Design Basis Time History Spectra) site specific response spectrum report (Reference 3).

To show that this design basis time history is a conservative representation of the expected ground motions for a 5.8 m b earth-quake at the Clinton site, an 84th percentile site specific response spectrum was developed using near field earthquake motion recorded at similar sites for earthquake magnitude of 5.8+0.5 m b.

y

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l ' Figure 32 of Reference 3 compared the 84th percentile site specific

) ,

response spectrum thus developed, to the design basis time history spectrum. It was concluded from this comparison that the design 3 , basis time history is a conservative representation of the expected i ground motion at-the Clinton site for a 5.8 m earthquake.

b

Since the available informaticr. regarding the depth of rock-soil 5 interface at many recording stations used for the Clinton site

! specific spectrum study was limited, the effect of the soil-rock velocity contrast (at 200-feet depth) on the site specific spectrum was further evaluated. Conservative soil amplification curves were obtained using three sets of soil properties presented in Table 220.15-1 of Reference 2 and reproduced here in Table 1 for ready reference. A weighted average of these three amplification curves was obtained by assigning 25%,.50% and 25% weights to upper, mean I and lower bound soil properties respectively. Then the 84th~per-centile 5% damped : response spectra amplification curve corres-ponding to the weighted Fourier amplification curve was computed.

Finally, applying these spectral amplifications to the average of the 84th percentile 5.8 mb rock spectrum generated by LLL/ TERA and TVA, the. theoretical ground response spectrum at the Clinton site was developed. It was shown that the design time history spectrum essentially envelopes this theoretical ground response spectrum (see Figure 37 of Reference 3).

4 Statistical Analysis The Clinton site specific response spectrum was developed at an 84th percentile level consistent with the Regulatory Guide 1.60 o philosophy. In developing the theoretical ground response spectrum l to evaluate the . ef fect of the rock-soil velocity contrast, a heuristic approach (weighting procedure) was taken in the treatment i of the soil. properties without resorting to a detailed statistical l treatment. However, the procedure to develop the theoretical l ground spectrum described in the previous paragraph yielded a l

better than 84th percentile ground response spectrum because the Page 2 of 16 m __ _ __ _ _ _ _ _ . . . _ _ _ _ . _ . _ . . _ . . . , . . . _ _ . _ _ .__ _ , _ ._ . _ _ _ _ _ _ , _ .. _ .,. _ -

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84th percentile rock spectrum was amplified by the 84th percentile

. soil response spectrum amplification curve. The 25%, 50% and.25%

weighting factors for the upper, mean and lower bound soil properties, respectively, was based on the f act that for the design earthquake, the soil properties are more likely to be the mean proprties than upper or lower bound properties. Use of 84th percentile response spectra amplification factors based on- the envelop of the Fourier amplification factor for upper, mean and lower bound soil properties would be overly conservative and would yield ground response spectrum well above the 84th percentile.

level.

In response to the latest request for clarification, we have I

performed a more detailed statistical analysis to show that the I

design time history spectrum essentially envelops the 84th l

percentile ground response spectrum obtained from the theoretical l

soil amplification and the LLL/ TERA and TVA 5.8 m b r ck specua.

The statistical analysis accounts for the effect of variability in soil shear modulus on the surface response spectrum by a more formal statistical treatment, without assigning specific weights to the upper-bound, mean and lower-bound soil properties identified in Table 1. The following steps were undertaken to perform the evaluation:

Step 1 The coefficient of variation of shear modulus at each of the four soil layers shown in Table 1 was calculated using the triaxial test data shown in Figures 220.15-2 through 220.15-5 of Reference 2. .

These calculations used the data for values of shear strain in the range from 2x10 -2 to 2x10 ~1 percent. The shear strain induced by strong earthquakes is expected to be in this range (see Figure 220.15-6 of Reference 2). Table 2 lists the coefficients of variation thus determined for each layer.

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. Step 2 i

2- It-is assumed that the shear modulus in each layer is independent of moduli in other layers and it is a lognormal random variable.

! The values of shear modulus listed for the mean soil property in

Table 1 for four layers were considered to represenc the mean r values:of the shear moduli of the soil profile. Using this inform-g-

ation and the corresponding coefficient of variation from Table 2, i ten sets of shear moduli were: randomly generated to represent the t range of possible soil property variation. Table 3 lists these 10

simulated shear modulus profiles.

Step 3 s The SHAKE Program (Reference 4) was used to compute the response i

spectrum amplification factors for each of the 10 simulated soil profiles by applying 14 different rock motions (shown in Table 4) and computing the resulting ground response spectrum. At each frequency, f, this procedure yielded 10x14=140 realizations of response spectrum amplification factor. The mean value and coefficient variation of the response spectrum amplification factor, A(f) were then calculated from the simulation results and are presented in Table 5. The 14 rock motions listed in Table 4 are all the rock motions available through the California Institute of Technology with maximum ground acceleration between 0.05 and 0.5g.

I For the Clinton site specific spectra report, (Reference 3), the I

response spectrum amplification factors were computed by Dr.

1 Vanmarcke using a random vibration approach. For the present I

I statistical evaluation the services of Dr. Vanmarcke were not available in a timely manner and the alternate SHAKE program procedure was used. To establish the validity of the SHAKE procedure a mean plus one standard deviation amplification curve was generated for upper bound, mean and lower bound soil property (Table 1) using the fourteen different rock motions (Table 4) and Page 4 of 16

L ~ computing the ground surface spectra resulting from these rock I

motions. The mean plus one' standard deviation amplification curve l

• was generated for each soil property using the fourteen sets of amplification factors. The. weighted average of the mean plus one sigma response spectrum amplification was obtained by assigning 25%, 50% and 25% weights to upper, mean and lower bound soil pro 1Qrties. Figure 1 compares the 84th percentile response spectrum amplification factors.obtained from the SHAKE procedure to l

the corresponding amplification factors obtained by Dr. Vanmarcke L

using random vibration method. It can be observed that the two procedures yield very similar results with the SHAKE procedure l

i giving slightly more conservative results at higher frequencies.

Figure .2 compares the 84th percentile response spectrum ampli-fication curve obtained by the use of the weighting procedure and' the 84th percentile response spectrum amplification curve obtained from a more detailed statistical analysis. It can be observed that the two curves are in good agreement, thus justifying the weighting procedure used in Reference 3.

Step 4 The mean and the coefficient of variation of - the LLL/ TERA and TVA 5.8 magnitude rock site spectra were obtained from the mean and the

! 84th percentile spectra presented in References 5 and 6.

I l

Step 5

]

Using response spectra and amplification statistics from Step 3 and the rock response spectra statistics from Step 4, the 84th per-centile value of the ground response spectrum was determined using both LLL/ TERA and TVA rock spectra. Figure 3 shows the average of the 84th percentile surface spectra thus determined. This spectrum is compared to the design basis time history spectrum. This

- comparison shows that with very minor exceptions at very limited range of periods the 84th percentile surface spectra are less than Page 5 of 16

2 those used for design. Therefore an explicit and formal consider-

ation of reasonable variation in soil properties leads to surface

spectra at the Clinton site which are less than the spectra used in design.

3 Note also, that the spectrum of the present analysis is in close

agreement with the ground surface spectrum obtained by Weston af ter

considering soil amplification (Reference 3, Figure 37).

Figure 4 presents the comparison of the Clinton design time history

spectrum to the theoretical surf ace spectrum obtained by multi-

plying the average of the 84th percentile 5.8 magnitude rock site r spectrum developed by - TVA and LLL by the 84th percentile soil 9 response spectrum amplification factors obtained in Step 3 above.

It can be observed from the figure that the design spectrum z

envelopes the theoretical surf ace spectrum at all frequencies signi-t ficant to the systems and structure design.

I h

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j References i

l. Letter from A. Schwencer of the NRC Staff to George Wuller of i IPC, dated January 12, 1983,

Subject:

Request for Furthpr 3 , Clarification on the Soil Amplification Issue - Clinton Power j Station, Units 1 and 2.

2. Illinois Power Company Letter No. U-0374 from J. Geier to j 7. R. Miller; Nuclear Regulatory Commission dated December 3, 1981.

g 3. " Site Specific Response Spectra Clinton Power Station -Unit 1 4

of Illinois Power Company", Revision 1, May 1982, prepared for

Sargent & Lundy by Weston Geophysical Corporation.

s 4. SHAKE, Soil Layer Properties and Response for Earthquake i Motions (09.7.119-3.3). S&L modified program written by

• J. Lysmer and P. B. Schnabel of the University of California, 2

- Berkeley which computes response in a horizontally layered 5

semi-infinite system subjected to vertically traveling shear t

waves equation.

based on the continuous solution of the shear wave 5 5. TERA Corporation, " Seismic Hazard Analysis", Report NUREG/

2 CR-1582, August 1980.

i 6. Tennessee Valley Authority, Division of Engineering Design,

" Justification of the Seismic Design Criteria Used for the i Sequoyah, Watts Bar and Bellefonte Nuclear Power Plants -

I Phase II,", August 1978.

I i

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s Table 1 Dynamic soil Properties Used for the Soil Amplificaton Study

• Soil Layer Weight Layer Depth SOIL SHEAR MODULUS (KSF)

Poisson's Damping Number (ft) Density)

(k/ft Ratio Ratio Upper Bound Mean Lower Bound 1 20. 0.132 0.4o 0.o84 6063.

4547. 3032.

2 105. 0.150 0.35 0.101 70o0. 5250. 3500.

3 10. 0.134 o.35 o.oS9 550o. 4125. 2750.

, .4 -

75. 0.145 0.40 0.089 5500. 4125.

w 2750. >

5 ";,1, o.15, 0.2, o.ooo 3ooo0o. 3o0ooo. 3ooooo.

' S, g *Same as Table 220.15-1 of Reference 2.

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'1 TABLE 2 COEFFICIENT OF VARIATION OF SOIL SHEAR MODULUS

' Coefficient of Layer Variation

. 1. Structural Fill 0.36 1 2. Illinoian Till ~ 0.98 5 3. Lacustrine Deposit 0.25 1 4. Pre-Ill.inoian Deposit 0.57 9

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i j TABLE 1: Values of Simulated G for Different Soil Layers Soil Shear Modulus (KSF)

Simulation # Layer #1 Layer #2 Layer #3 Layer #4 1 5559 4565 4710 3737 2 6816 1195 3512 2508 3 3319 8749 4286 6502 4 3220 9160 3927 3955 5 5417 8341 4015 1824 .

6 2488 10368 3516 , 4548 7 5711 716 4150 3760 8 4437 2951 4295 5259 9 -7929 5429 5213 3221 10 4142 1968 5260 7880 l

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TABLE 4 Earthquakes Used to Determine Spectral Amplification Factors Epicentral Maximum Recording Distance Instrument Acceleration Earthquake Date/ Time Station Magnitude (km) Orientation (g)

Helena, Montana 10-31-35/1138 MST Caroll College 6.0 7 S00W .146 S90W .145 Eureka, California 12-21-54/1156 PST Eureka Federal 6.Q 25 N11W .168 Building N79E .258 San Francisco, 3-22/57/1144 PST Golden Gate Park 5.3 13 N10E .084 y California S80E .105 m

• Parkfield, 6-27-66/2026 PST Temblor 5.5 7 N65W .270 p California S25W .348 R Parkfield, 6-27-66/2026 PST Ch alame-S andron , 5.5 6 N05W .355 California Array No. 5 N85E .434 San Fernando, 2-9-71/0600 PST Castiac Old Ridge 6.6 30 N21E .316 California Rou te . N69W .271 San Fernando, 2-9-71/0600 PST Pacoima Dam, 3.0-5.0 9 574W .112 California After S ock at 516E .115 104.6 sec O

w--_-_-- _ - - - - - - - - -

s 2 Table 5 Response Spectra Amplification Factors:

Mean and Standard Deviation J Frequency Mean SD Frequency Mean SD

.20 1.23 .18 4.20 1.11 .22

.30 1.35 .30 4.41 1.09 .22

, .40 1.46 .34 4.61 1.03 .23

, .50 1.69 .40 4.81 1.09 .24

. .60 1.81 .52 5.00 1.07 .25

.70 2.15 .68 5.24 1.05 .22

.80 2.29 .63 5.49 1.05 .24

.90 2.38 .47 5.75 1.01 .21 1.00 2.31 .46 5.99 1.00 .21 1.10 2.31 .54 6.25 1.00 .22 1.20 2.29 .56 6.49 .98 .24 1.30 2.16 .58 6.76 .94 .23 1.40 2.01 .55 6.99 .92 .25 1.50 1.82 .45 7.25 .91 .27 4 1.60 1.64 .38 7.52 .90 .27 1.70 1.50 .36 7.75 .92 .28

. 1.80 1.36 .36 8.00 .93 .29 1.90 1.30 .36 8.47 .96 .28 2.00 1.28 .36 9.01 .92 .25 2.10 1.25 .36 9.52 .86 .23 2.20 1.23 .35 10.00 .86 .23 2.30 1.21 .34 10.53 .87 .23 2.40 1.16 .31 10.99 .91 .26 2.50 1.13 .30 11.49 -

.91 .26 2.60 1.11 .29 12.05 .93 .27 2.70 1.10 .29 12.50 .94 .29

2.80 1.10 .29 12.99 .94 .28 2.90 1.12 .30 13.51 .95 .29 3.00 1.13 .30 14.08 .97 .30 3.15 1.14 .30 14.49 .96 .31 3.30 1.14 .29 14.93 .95 .32 3.45 1.15 .28 15.87 .96 .32 3.60 1.14 .25 16.95 .96 .34 3.80 1.14 .22 18.18 .98 .36 4.00 1.14 .23 20.00 .96 .34

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Figure 3: Comparison of Design Basis Time History Spectrun to Theoretical Spectra Considering Soil Amplification Page 15 of 16

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Figure 4: Comparison of Design Basis Time History Spectrum to Theoretical Spectra Considering Soil Amplification Page 16 of 16

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