ML13259A042

Response to March 12, 2012 Information Request Regarding Seismic Aspects of Recommendation 2.1 - 1.5 Year Response for CEUS Sites

ML13259A042
Person / Time
Site:	North Anna
Issue date:	09/12/2013
From:	Grecheck E Virginia Electric & Power Co (VEPCO)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
13-243C
Download: ML13259A042 (13)

Text

VIRGINIA ELECTRIC AND POWER COMPANY 4

RICHMOND, VIRGINIA 23261 September 12, 2013 U.S. Nuclear Regulatory Commission Serial No.

13-243C Attention: Document Control Desk NL&OS/WDC RO Washington, DC 20555 Docket Nos.

50-338/339 License Nos.

NPF-4/7 VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 RESPONSE TO MARCH 12. 2012 INFORMATION REQUEST REGARDING SEISMIC ASPECTS OF RECOMMENDATION 2.1 - 1.5 YEAR RESPONSE FOR CEUS SITES

References:

1. NRC Letter, "Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3, of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident," dated March 12, 2012

2. NRC Letter, Endorsement of EPRI Final Draft Report 1025287, "Seismic Evaluation Guidance," dated February 15, 2013

3. EPRI Report 1025287, Seismic Evaluation Guidance: Screening, Prioritization and Implementation Details (SPID) for the Resolution of Fukushima Near-Term Task Force Recommendation 2.1: Seismic

4. NEI letter to NRC, Proposed Path Forward for NTTF Recommendation 2.1:

Seismic Reevaluations, dated April 9, 2013

5. NRC Letter, EPRI Final Draft Report 3002000704, "Seismic Evaluation Guidance:

Augmented Approach for the Resolution of Near-Term Task Force Recommendation 2.1: Seismic," as an Acceptable Alternative to the March 12, 2012, Information Request for Seismic Reevaluations, dated May 7, 2013 On March 12, 2012, the Nuclear Regulatory Commission (NRC) issued Reference 1 to all power reactor licensees and holders of construction permits in active or deferred status. of Reference 1 requested each addressee in the Central and Eastern United States (CEUS) to submit a written response consistent with the requested seismic hazard evaluation information (items 1 through 7) by September 12, 2013. On February 15, 2013, NRC issued Reference 2, endorsing the Reference 3 industry guidance for responding to Reference 1. Section 4 of Reference 3 identifies the detailed information to be included in the seismic hazard evaluation submittals.

On April 9, 2013, NEI submitted Reference 4 to the NRC, requesting NRC agreement to delay submittal of some of the CEUS seismic hazard evaluation information so that an update to the EPRI (2004, 2006) ground motion attenuation model could be completed and used to develop that information.

NEI proposed that descriptions of subsurface materials and properties and base case velocity profiles (items 3a and 3b in Section 4 of Reference 3) be submitted to NRC by September 12, 2013 as an interim product of seismic hazard development efforts being performed in accordance with Reference 3.

The final seismic hazard and screening information will be submitted to NRC by March 31, 2014. In Reference 5, NRC agreed with this recommendation.

Serial No. 13-243C Docket Nos. 50-338/339 Page 2 of 3 The attachment to this letter contains the requested descriptions of subsurface materials and properties and base case velocity profiles for North Anna Power Station.

If you have any questions regarding this information, please contact Mr. Thomas Shaub at (804) 273-2763.

Sincerely, Eugene S. Grecheck Vice President - Nuclear Engineering and Development COMMONWEALTH OF VIRGINIA COUNTY OF HENRICO The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Eugene S. Grecheck, who is Vice President - Nuclear Engineering and Development of Virginia Electric and Power Company. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that company, and that the statements in the document are true to the best of his knowledge and belief.

Acknowledged before me this 7W of

___________3_...

QLt:..day of Se_______rpm__2__3 My Commission Expires:

VICKI L. HULL MCmsEpe._

Notary Public

,1 Commonwealth of Virginia 1

140542 Nota' Public My Commission Expires May 31, 2014 Commitments made in this letter: No new regulatory commitments

Attachment:

Subsurface Materials and Properties and Base Case Velocity Profiles (SPID Section 4, Items 3a and 3b)

Serial No. 13-243C Docket Nos. 50-338/339 Page 3 of 3 cc:

U.S. Nuclear Regulatory Commission, Region II Regional Administrator Marquis One Tower 245 Peachtree Center Ave. NE Suite 1200 Atlanta, Georgia 30303-1257 Dr. V. Sreenivas Project Manager - North Anna U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 G-9A 11555 Rockville Pike Rockville, MD 20852-2738 K. R. Cotton Gross Project Manager - Surry U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 G-9A 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector North Anna Power Station J. E. Reasor, Jr.

Old Dominion Electric Cooperative Innsbrook Corporate Center, Suite 300 4201 Dominion Blvd.

Glen Allen, Virginia 23060

Serial No. 13-243C Docket Nos. 50-338/339 ATTACHMENT SUBSURFACE MATERIALS AND PROPERTIES AND BASE CASE VELOCITY PROFILES (SPID SECTION 4. ITEMS 3A AND 3B)

VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)

NORTH ANNA POWER STATION UNITS I AND 2

Serial No. 13-243C Docket Nos. 50-338/339, Page 1 of 9 North Anna Power Station Units I and 2 Subsurface Materials and Properties and Base Case Velocity Profiles 1

Introduction This document provides the rationale for developing a base profile to be used in computing the ground motion response spectrum (GMRS) consistent with the methodology outlined in the Electric Power Research Institute's (EPRI) Screening Prioritization and Implementation Details (SPID) document (Reference 1).

The following properties are considered in this report:

" geologic setting,

" stratigraphy, safety related structures,

• shear wave velocity,

" layer thickness,

" unit weight and Poisson's ratio,

" shear modulus and material damping versus cyclic shear strain,

" groundwater level, and profile selected for use.

2 Geologic Setting The North Anna Power Station is located in Louisa County, Virginia, on a peninsula on the southern shore of Lake Anna. This places the station in the central portion of the Piedmont physiographic province with the Blue Ridge province about 40 miles to the west and the Coastal Plain province about 15 miles to the east. The Piedmont terrain is characterized by gently sloping upland areas and broad, relatively shallow valleys.

Bedrock within the Piedmont is metamorphic, consisting of granites, gneisses, and schists. The bedrock typically is deeply weathered into a saprolite mantle of up to approximately 100 ft thick.

As described in Reference 2, the Piedmont Upland section is underlain by Late Precambrian and Paleozoic age crystalline rocks.

The crystalline rocks consist of deformed and metamorphosed sedimentary, igneous and volcanic rocks, intruded by mafic dikes and granitic plutons. The North Anna site is located in the Chopawamsic belt which is bounded on the west and east by the Chopawamsic and Spotsylvania thrust faults, respectively.

The Chopawamsic belt comprises the Chopawamsic Formation and the Ta River Metamorphic Suite, which is overlain unconformably by the Quantico Formation and intruded by rocks of the Falmouth Intrusive Suite.

Serial No. 13-243C Docket Nos. 50-338/339, Page 2 of 9 3

Stratigraphy Bedrock at North Anna consists mainly of metamorphic gneiss and schist. There has been extensive in-place weathering of the rock. The rock has weathered completely into saprolitic soil near the ground surface.

The general subsurface profile at North Anna can be divided into 6 zones (Reference 2):

1 Residual clays and clayey silts - all structure of parent rock is lost.

IIA Saprolite - medium dense silty sand, with some fine-grained layers.

1iB Saprolite - very dense silty sand.

III Weathered rock - core stone more than 50% of volume of overall mass.

Ill-IV Moderately weathered to slightly weathered rock.

IV Parent rock - slightly weathered to fresh rock.

The weathering across the site is uneven, and the thickness of the various zones varies widely and randomly throughout the site. The rock zones are defined by both rock quality designation (RQD) and shear wave velocity (Vs).

Considering the original site investigations at Units 1 and 2 site and the more recent site investigations at the proposed Unit 3 site (which shares the same geologic characteristics), the North Anna site is well-characterized and extensively investigated with abundant high-quality data

(>200 borings, including five deep borings with P-S Suspension shear wave velocity measurements), which reduces epistemic uncertainty in the site properties. These data also provide information to characterize the aleatory variation in layer thickness and shear-wave velocity across the site. These variations will be included in considerations of aleatory uncertainties for the base-case profile.

No alternate profiles were considered because of the relative insignificance of epistemic uncertainty with respect to the aleatory variability for this site.

4 Safety-Related Structures Reference 1 provides very specific guidelines on how a nuclear power facility is to identify the Safe Shutdown Earthquake (SSE) Control Point elevation for a plant or unit if this control point was not identified in the Updated Final Safety Analysis Report (UFSAR).

In the case of a plant designated as a rock site, the SSE control point is defined as the foundation bearing elevation of the highest rock-supported, safety-related structure. According to Reference 3, at the North Anna Power Station, the highest rock-founded, safety-related structure is the Casing Cooling Tank and Pumphouse structure.

This is a single slab-supported structure founded above weathered bedrock and on concrete backfill. The concrete backfill was placed to create a level, bearing surface above the varying elevation of the exposed bedrock surface.

Due to its limited horizontal extent, the concrete backfill will not be included in the GMRS calculation.

Serial No. 13-243C Docket Nos. 50-338/339, Page 3 of 9 With plant grade at El. 271 ft (Reference 4), the base of the Casing Cooling Tank and Pumphouse foundation is at El. 268 ft. The GMRS will thus be calculated at El. 268 ft.

Outside the foundation, there is 3 ft of saprolite from El. 268 ft to El. 271 ft.

5 Shear Wave Velocity Bedrock The dynamic rock profile for Units 1 and 2 up to plant grade at El. 271 ft, developed for the North Anna Unit 3 COLA and modified for Units 1 and 2, is shown in the following table:

Elevation Shear Wave Velocity (ft/s)

(ft)

Profile I (VLB)

Profile 2 (VuB)

Best Estimate, VBE 271 -224 3,115 5,800 4,251 224 - 205 4,475 6,635 5,449 205-170 3,450 7,770 5,177 170-135 8,800 8,800 8,800 135-25 9,740 9,740 9,740 The best estimate value is the log-mean of the Profile 1 (VLB) and Profile 2 (VuB) values:

VBE = 1 0^{Average[Log(Vcg), Log(VuB)]}

The Profile 1 and Profile 2 values capture the majority of the measured Vs values in the bedrock, as well as Vs values correlated from other parameters (such as RQD). Thus (VBE -

Profile 1) and (Profile 2 VBE) are assumed to approximate one standard deviation.

The VBC profile (base case) using VBE is shown in Table 1.

Saprolite The saprolite Vs profile developed from the Vs measurements in saprolite (including those developed for the North Anna Unit 3 COLA) can be used in this situation. Using the original ground surface in the area at about El. 290 ft, the 3 ft of saprolite between El. 271 ft and El. 268 ft would have been at 19 ft to 22 ft depth. The rounded Vs values of the saprolite between 20 and 25 ft depth are VBE = 795 ft/sec, VLB = 560 ft/sec, and VUB = 1,030 ft/sec. These can be used for the El. 271 ft to El. 268 ft interval. VUB and VLB = VBE +/-

1 standard deviation.

Serial No. 13-243C Docket Nos. 50-338/339, Page 4 of 9 The VBC profile (base case) using VBE is shown in Table 1.

This base case Vs profile is plotted in Figure 1.

6 Zone Thickness The following approximate Vs and RQD limits for the various zones were developed for the North Anna Unit 3 COLA:

Zone IIA Vs < 1,200 ft/sec RQD = 0 Zone liB Vs = 1,200 - 2,000 ft/sec RQD = 0 Zone III Vs = 2,000 - 4,000 ft/sec RQD < 50%

Zone Ill-IV Vs = 4,000 - 8,000 ft/sec RQD 50% - 90%

Zone IV Vs > 8,000 ft/sec RQD > 90%

Comparing the Vs values with the values in Table 1, it is concluded that:

El. 271 ft to El. 268 ft (3 ft thickness) is Zone IIA.

El. 268 ft to El. 224 ft (44 ft thickness) is primarily Zone III (with some overlap into Zone IIl-IV).

El. 224 ft to El. 170 ft (54 ft thickness) is Zone Ill-IV.

Below El. 170 ft is Zone IV.

These thicknesses are shown in Table 1. Note that the considerable variation in zone thickness will be accounted for later in the randomization process.

7 Unit Weight & Poisson's Ratio Unit weights and Poisson's ratio values were developed for the North Anna Unit 3 COLA. Values are shown in Table 1.

8 Shear Modulus & Damping Ratio versus Shear Strain Shear Modulus The shear modulus values of the Zone Ill-IV and Zone IV bedrock are independent of shear strain.

The ratios of shear modulus values (G) to the maximum shear modulus value (GMAX) of the Zone IIA saprolite are the average of the 0 to 20 ft and 20 ft to 50 ft curves provided in Reference 5, and are based on the results of Resonant Column and Torsional Shear (RCTS) tests on the saprolite. These values are shown versus shear strain in Table 2 and are plotted in Figure 2.

Serial No. 13-243C Docket Nos. 50-338/339, Page 5 of 9 The G/GMAx values of the Zone III weathered rock are based on values for relatively soft rock in Reference 6. These values are shown versus shear strain in Table 2 and are plotted in Figure 2.

The variation in G/GMAx values will be accounted for later in the randomization process.

Damping Ratio As with the shear modulus, the damping ratio (D) values for the Zone Ill-IV and Zone IV bedrock are independent of shear strain. The value of D for these materials is 1%.

The D values of the Zone IIA saprolite are the average of the 0 to 20 ft and 20 ft to 50 ft curves provided in Reference 5, and are based on the results of RCTS tests on the saprolite. These values are shown versus shear strain in Table 3 and are plotted in Figure 3.

The D values of the Zone III weathered rock are shown in Table 3 and plotted in Figure

3. Note that for analysis, values of D are typically truncated at 15%.

The variation in D will be accounted for later in the randomization process.

9 Groundwater Level Reference 4 indicates that structures for Units 1 and 2 were designed and analyzed using a uniform groundwater level at El. 256 ft.

10 Profile Selected for Use As discussed in Section 4, considering the original site investigations at Units 1 and 2 site and the more recent site investigations at the proposed Unit 3 site, the epistemic uncertainty is considered insignificant relative to the observed aleatory variability for this site. Thus, a single base-case profile is considered for the site as presented in Table 1 and Figure 1.

The variations in shear-wave velocity, layer thicknesses, and shear-modulus reduction and damping curves will be included in considerations of aleatory uncertainties for the base-case profile through the randomization process.

11 References

1. Electric Power Research Institute (EPRI).

Seismic Evaluation Guidance, Screening, Prioritization and Implementation Details (SPID) for the Resolution of Fukushima Near-Term Task Force Recommendation 2.1: Seismic, Final Report No. 1025287, Electric Power Research Institute, Palo Alto, CA, 2013.

Serial No. 13-243C Docket Nos. 50-338/339, Page 6 of 9

2. North Anna Early Site Permit Application, Rev. 9, 2006.

3. Dominion, "Seismic Screening GMRS Subsurface Profiles for Millstone and North Anna Power Stations," ETE-CCE-2013-0001, Revision 0.

4. North Anna Power Station Units 1 and 2 Updated Final Safety Analysis Report (UFSAR), Revision 48.

5. Electric Power Research Institute (EPRI). Guidelines for Determining Design Basis Ground Motions, Vol. 1-5, EPRI TR-102293, Palo Alto, CA.

6. Sun, J.l., Golesorkhi, R., and Seed, H.B. Dynamic Moduli and Damping Ratios for Cohesive Soils, Earthquake Engineering Research Center, University of California

- Berkeley California, Report No. EERC-88/15, 1988.

Serial No. 13-243C Docket Nos. 50-338/339, Page 7 of 9 Table 1: Base Case Vs Profile and Related Properties Material Elevation Thickness VBC Poisson's Unit Wt (ft)

(ft_

Ratio (Ib/ft3)

Zone IIA 271-268 3

795 0.35 125 Zone III 268-224 44 4250 0.40 150 Zone Ill-IV 224-205 19 5450 0.33 163 Zone Ill-IV 205-170 35 5180 0.33 163 Zone IV 170-135 35 8800 0.27 164 Zone IV

<135 9740 0.27 164 Note:

Groundwater at El. 256 ft Table 2: Modulus Reduction Relationship Shear Strain (%)

GIGMAx, Zone IIA GIGMAx, Zone III Saprolite Weathered Rock 0.0001 1.00 1.00 0.000316 1.00 1.00 0.001 0.99 1.00 0.00316 0.94 1.00 0.01 0.79 1.00 0.0316 0.57 0.98 0.1 0.32 0.87 0.316 0.15 0.63 1.0 0.05 0.33 Table 3: Damping Ratio Relationship Shear Strain (%)

D (%) for Zone IIA D (%)for Zone III Saprolite Weathered Rock 0.0001 1.3 0.6 0.000316 1.3 0.6 0.001 1.6 0.6 0.00316 2.4 0.6 0.01 4.4 0.6 0.0316 8.2 0.6 0.1 14.3 2.7 0.316 20.6 8.2 1.0 27.9 17.0 Notes:

D = 1% for Zone Ill-IV, Zone IV For analysis, values of D are typically truncated at 15%

Serial No. 13-243C Docket Nos. 50-338/339, Page 8 of 9 Shear Wave Velocity, Vs (ftls) 0 2000 4000 6000 8000 10000 280 -

260 -

240 220

-Best Estimate 0

200 180 t

160 4 140 120 100 Figure 1: Base Case Vs Profile

Serial No. 13-243C Docket Nos. 50-338/339, Page 9 of 9 0.90 0.80 0.70 0.60 0.50

-Lone hA

-Zone III 0.30 0.20 0.10 0.00 0.0001 0.0010 0.0100 0.1000 1.0000 Shear Strain (%)

Figure 2: Modulus Reduction Relationship 30 25 20 Zone IIA 10

-Zone III 5

0 0.0001 0.0010 0.0100 0.1000 1.0000 Shear Strain (%)

Figure 3: Damping Ratio Relationship