DCL-10-059, Calculation Number GEO.DCPP.10.02, Evaluation of Shear-Wave Velocity at the DCPP Isfsi.

Calculation Number GEO.DCPP.10.02, Evaluation of Shear-Wave Velocity at the DCPP Isfsi.

ML101660531
Person / Time
Site:	Diablo Canyon
Issue date:	04/29/2010
From:	Abrahamson N Pacific Gas & Electric Co
To:	Office of Nuclear Material Safety and Safeguards, Office of Nuclear Reactor Regulation
References
DCL-10-059 GEO.DCPP.10.02, Rev 0
Download: ML101660531 (11)

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Page 1 of 11 GEO.DCPP.10.02, Rev 0 PACIFIC GAS AND ELECTRIC COMPANY Caie Number: GEO.DCPP.10.02 GEOSCIENCES DEPARTMENT Calc Revision: 0 CALCULATION DOCUMENT Cale Date: 04127/10 Quality related: Y ITR Verification method:A

1. CALCULATION TITLE: Evaluation of Shear-Wave Velocity at the DCPP ISFSI

2. SIGNATORIES:

PREPARED BYY DATE: 'k,4/Z f/10 Norman Abrahamson Geosciences Organization VERIFIED BY: DATE: O 1/29/0C Printed Name Geosciences Organization APPROVED BY: DATE: ______/ ___!_

Printed-Name Geosciences Organization A

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3. RECORD OF REVISIONS:

Rev. Reason for Revision Revision No. Date 0 Initial Caic 04/27/10

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4. PURPOSE:

The recent ground motion models used for the evaluation of the Shoreline fault (PGE, 2009) use the shear-wave velocity in the top 30 m as the site parameter. This parameter is called Vs30. In GEO.DCPP.09.01, the VS 30 value for the powerblock was computed-using a shear-wave profile measured at the powerblock location in 1978 (PG&E, 1988). The methods for measuring shear-wave velocity have improved significantly since' 1978. New measurements of the shear-wave velocity profile were made at the DCPP ISFSI site as part of the ISFSI site characterization (PG&E, 2004). Because the ISFSI is located on the same geologic unit as the powerblock, the NRC staff requested that PG&E review the recent shear-wave velocity measurements that were at the DCPP ISFSI and compare them to the VS30 values used for the ground motion evaluations.

Per Notification 50086062, Task 22, the purpose of this calculation is to estimate the VS30 values from the ISFSI shear-wave profiles and determine if these values indicate that the VS30 value used for the Shoreline fault ground motion characterization (GEO.DCPP.09.01) is still applicable or if it needs to be updated.

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5. ASSUMPTIONS:

No assumptions are made.

6. INPUTS:

6.1. Shear-Wave Velocity Profiles for the ISFSI The shear-wave velocity profile for the ISFSI borings are shown in Figure 6-1 (PG&E, 2004, Figure 2.6-33) 6.2. VS30 for the Powerblock The VS30 for the powerblock of 1212 m/s is given in GEO.DCPP.09.01 (PG&E, 2009) 6.3. Original Elevation of the ground at powerblock The original elevation of the ground in the powerblock area ranges from 85 ft to 200 ft (PG&E, 1988, Figure 5-3) 6.4. Elevation of the powerblock foundation The elevation of the powerblock foundation is 52.6 ft (PG&E, 1988, Figure 5-3)

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7. METHOD AND EQUATION

SUMMARY

7.1 METHODOLOGY

The VS30 is traditionally based on the shear-wave velocity profile in the top 30 m. For the application of the powerblock, we need to use the shear-wave velocity in the 30 m below the foundation. Therefore, the VS30 from the ISFSI is computed from the embedment depth of the powerblock to a depth of 30 below the embedment depth.

7.2 EQUATIONS

7.2.1. VS30 The VS30 is defined by equations I and 2 in Boore (2004):

Vs(30) = 30/1tt(30) (7-1)

Where tt is the travel time over 30 m and is given by 30 d tt(30)=-f d (7-2)

.7.2.2. Conversion of feet to meters 2.54cm m =035 73 Ift = 12in = 0.305m (7-3) in I00cm This is a well known relation.

7. SOFTWARE:

No specialized software was used. All calculations were made by hand using an Excel spreadsheet.

8. BODY OF CALCULATION:

8.1 Digitization of the velocity profiles The velocity profiles for the ISFSI, shown in Figures 6-1 and 6-1, were digitized. The digitized values are listed in Table 8.1 for borings 98BA-1 and 98BA-4. Table 8-2 shows the digitized values for boring 98BA-3.

Page 7 of I I GEO.DCPP. 10.02, Rev 0 Table 8-1. Digitized shear-wave velocity profile for ISFSI borings 98BA-1 and 98BA-4.

Top (M) Bottom (m) VS (m/s) 0.0 5.3 1242 5.3 7.2 1381 7.2 9.3 1251 9.3 10.9 1474 10.9 16.1 1019 16.1 19.3 1592 19.3 23.3 1465 23.3 25.5 1069 25.5 28.3 947 28.3 32.7 1166 32.7 36.8 1524 36.8 49.1 1272 Table 8-2. Digitized shear-wave velocity profile for ISFSI boring 98BA-3.

Top (M) Bottom (m) VS (m/s) 0.0 3.9 464 3.9 5.8 1130 5.8 8.8 1179 8.8 11.6 1090 11.6 14.3 1042 14.3 17.2 1251 17.2 20.0 1502 20.0 26.4 1090 26.4 30.0 1514 30.0 35.9 1110 35.9 39.7 1421 39.7 42.6 1328 At the powerblock, the original surface elevation was between 85 ft and 200 ft (input 6-3). The foundation elevation is 52.6 ft (input 6-4). The lower range of the original elevation of 85 ft is selected as a minimum elevation. The difference between these two elevations gives the embedment depth.

Embedment depth = 85 ft - 52.6 ft = 32.4 ft The depth in ft is converted to depth in m using equation 7-3.

Embedment depth = 32.4ft

• 0.305 rn/ft = 9.88; m

Page 8 of I I GEO.DCPP.10.02, Rev 0 This embedment depth is rounded to 10 m.

Tables 8-3 and 8-4 shown the VS profiles at the ISFSI from 10 m depth to 40 m depth.

The VS30 is computed using equations 7-1 and 7-2. Combining these two equations and converting the integral to discrete layers leads to:

VS3 0 = A'30m (8-I) i-1 VSi H.

Where H is the thickness of the layer. For borings 98BA-l&4, the values of Hi and are listed vsi in Table 8-3. The summation of the travel times is listed in the bottom of the table. Using the values from Table 8-3 and eq. 8.1, the VS30 is given by 30m KIV30 30 =1228mls 0.02443 sec For boring 98BA-3, the values of Hi and , are listed in Table 8-4. The summation of the travel PSi times is listed in the bottom of the table. Using the values from Table 8-4 and eq. 8. 1, the Vs30 is given by Vs30o 0.02470sec = 1215mls

Page 9 of I1 GEO.DCPP. 10.02, Rev 0 Table 8-3. VS profile for ISFSI boring 98-I & 98-4 from a depth of 10 to 40 m.

Top Bottom H VS Travel (m) (m) (in) (m/s) Time (sec) 10.0 10.9 0.9 1474 0.00060 10.9 16.1 5.3 1019 0.00513 16.1 19.3 3.2 1592 0.00199 19.3 23.3 4.0 1465 0.00276 23.3 25.5 2.2 1069 0.00204 25.5 28.3 2.8 947 0.00295 28.3 32.7 4.4 1166 0.00373 32.7 36.8 4.1 1524 0.00273 36.8 40.0 3.2 1272 0.00250 Sum: 0.02443 Table 8-4. VS profile for ISFS! boring 98-3 from a depth of 10 to 40 m.

Top Bottom H VS Travel (m) (m) (m) (m/s) Time (sec) 10.0 11.6 1.6 1090 0.00149 11.6 14.3 2.7 1042 0.00259 14.3 17.2 2.9 1251 0.00229 17.2 20.0 2.8 1502 0.00187 20.0 26.4 6.4 1090 0.00585 26.4 30.0 3.6 1514 0.00239 30.0 35.9 5.9 1110 0.00535 35.9 39.7 3.8 1421 0.00266 39.7 40.0 0.3 1328 0.00021 I Sum: 0.02470

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9. RESULTS AND CONCLUSIONS RESULTS The computed VS30 values from the ISFSI site are compared to the VS30 value for the powerblock in Table 9-1. The VS30 values from the ISFSI are within 2% of the Vs30 values previously estimated for the powerblock.

Table 9-1. Computed VS30 values (for 10 m embedment) for the powerblock and the ISFSI borehole sites.

VS30 (m/s) for 10 m Embedment (applicable to the powerblock)

Powerblock 1212 ISFSI 98BA-l&4 1228 ISFSI 98BA-3 1215 CONCLUSIONS Previous studies have shown that there is significant variability of VS30 for sites within a given geologic unit. The coefficient of variation for Tertiary rock geologic units (e.g. Tss) is about 40% (Chiou et al. 2008,. Table 2). The range of the VS30 values for the ISFSI sites and the powerblock shown in Table 9-1 are well within this 40% range.

We conclude that the VS30 values measured from the ISFSI boreholes using modem methods are consistent with the VS30 values from the earlier surveys at the powerblock. The Vs 30 of 1210 m/s used in the Shoreline Fault ground motion calculations (GEO.DCPP.09.01) is an appropriate value for characterizing the VS30 at the powerblock.

10. LIMITATIONS The digitization of the ISFS! profiles has a limited accuracy of a few percent. This limits the accuracy of the computed VS30 values to a few percent.

11. IMPACT EVALUATION This calculation shows that the previously used Vs3o values for the powerblock are still valid.

Therefore, there is no impact of the results of this calculation.

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12. REFERENCES Boore, D. M (2004). Estimating Vs(30) (or NEHRP Site Classes) from Shallow Velocity Models (Depths < 30 m, Bulletin of the Seismological Society of America, Apr 2004; 94: 591 - 597.

Chiou, B., R. Darragh, N. Gregor, and W. Silva (2008). NGA project strong motion data base, Earthquake Spectra, 24:23-44.

PG&E (2009). Comparison of the response spectra for the Shoreline and Hosgri faults with the ISFSI Long Period (ILP) Response Spectrum", Geosciences Calculations GEO.DCPP.09.01.

PG&E (2004).Diablo Canyon ISFSI Safety Analysis Report. Nuclear Regulatory Commission Docket No. 72-26 PG&E (1988). Final report of the Diablo Canyon Long-Term Seismic Program, U.S. Nuclear Regulatory Commission Docket Nos. 50-275 and 50-273.