NL-15-0075, Additional Information Regarding Seismic Hazard Curves

Additional Information Regarding Seismic Hazard Curves

ML15020A728
Person / Time
Site:	Hatch
Issue date:	01/20/2015
From:	Pierce C Southern Co, Southern Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-15-0075
Download: ML15020A728 (12)

Text

Charles R. Pierce Regulatory Affairs Dtrector JAN 2 0 2015 Docket Nos.: 50-321 50-366 Southern Nuclear Operating Company, Inc.

40 Inverness Center Parkway Post Office Box 1295 Birmingham, AL 35201 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 SOUTHERN.\\.

COMPANY NL-15-0075 Edwin I. Hatch Nuclear Plant - Units 1 and 2 Additional Information Regarding Seismic Hazard Curves

References:

1. NRC Letter, Request for Information Pursuant to 10 CFR 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. Letter to NRC, "Edwin I. Hatch Nuclear Plant-Units 1 and 2, Seismic Hazard and Screening Report for CEUS Sites," dated March 31, 2014.

3. NRC Letter, Supplemental Information related to Development of Seismic Risk Evaluations Regarding the 10 CFR 50.54(f) Request for Information Related to Seismic Hazard Reevaluations for NTTF Recommendation 2.1, dated December 10, 2014 (ML143078707).

Ladies and Gentlemen:

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. Enclosure 1 of Reference 1 requested each addressee in the Central and Eastern United States (CEUS) to submit a Seismic Hazard Evaluation and Screening Report. The requested information was submitted to the NRC for the Edwin I. Hatch Nuclear Plant Units 1 and 2 (HNP) by Southern Nuclear Operating Company (SNC) on March 31, 2014. On June 26, 2014, SNC representatives, along with its contractors, met with the NRC staff at their request, to discuss the information provided in Reference 2.

Based on a teleconference that occurred on December 9, 2014, the NRC acknowledged being aware that HNP has developed seismic hazard curves that slightly predate NTTF 2.1 as part of an in-progress SPRA development initiative which bound the March 2014 submittal. As provided in Reference 3, the use of a bounding curve which predates NTTF 2.1 is an acceptable approach.

U.S. Nuclear Regulatory Commission NL-15-0075 Page2 The Enclosure to this letter provides information on this earlier bounding seismic hazard curve. This information is intended to provide the technical approach used in its development. Included in this information is the source and ground motion models used, the differences between the site response profiles, models and methods used for the earlier curve vs. the March 2014 submittal; and, a table of the Ground Motion Response Spectra (GMRS) spectral acceleration and frequencies presented similar to the March 2014 submittal. SNC understands that the NRC staff plans to document this seismic hazard curve in its staff assessment as the current hazard curve utilized for the Hatch seismic probabilistic risk assessment (SPRA).

This letter contains no NRC regulatory commitments. If you have any questions, please contact John Giddens at 205.992.7924.

Mr. C.R. Pierce states he is Director of Regulatory Affairs of Southern Nuclear Operating Company, is authorized to execute this oath on behalf of Southern Nuclear Operating Company and, to the best of his knowledge and belief, the facts set forth in this letter are true.

Respectfully submitted, Cli~

C.R. Pierce Director-Regulatory Affairs CRP/JMGITWS Sworn o and subscribed before me this.c;;({Q_ day of ~

• ......,. ct Notary Public My commission expires: I u-~- 2 0 ll

Enclosure:

Edwin I. Hatch Nuclear Plant - Units 1 and 2 Seismic Hazard Curve Information

'2015.

U.S. Nuclear Regulatory Commission NL-15-0075 Page 3 cc:

Southern Nuclear Operating Company Mr. S. E. Kuczynski, Chairman, President & CEO Mr. D. G. Bost, Executive Vice President & Chief Nuclear Officer Mr. D. R. Vineyard, Vice President-Hatch Mr. M. D. Meier, Vice President - Regulatory Affairs Mr. B. J. Adams, Vice President-Engineering Mr. D. R. Madison, Vice President-Fleet Operations RTYPE: CHA02.004 U.S. Nuclear Regulatorv Commission Mr. V. M. McCree, Regional Administrator Mr. D. R. Hardage, Senior Resident Inspector-Hatch Mr. R. E. Martin, Senior Project Manager-Hatch State of Georgia Mr. J. H. Turner, Director-Environmental Protection Division

Enclosure to NL-15-0075 Edwin I. Hatch Nuclear Plant - Seismic Hazard Curve Information Page E-1

==

Introduction:==

HATCH SEISMIC HAZARD BEING USED FOR THE HATCH SPRA OVERVIEW The Edwin I. Hatch Nuclear Plant (HNP or Hatch) seismic hazard for the Hatch seismic probabilistic risk assessment (SPRA) produces a surface ground motion response spectrum (GMRS) which, for this overview, is called the Hatch SPRA GMRS. The Hatch SPRA GMRS is higher than the NTTF 2.1-Seismic GMRS submitted in March 2014 (Reference 1 ). The primary purpose of the NTTF 2.1-Seismic GMRS was for screening for risk evaluations. Based on the NTTF 2.1-Seismic GMRS, HNP screens in for a risk evaluation that includes a high frequency assessment.

The HNP SPRA project was started in late 2012 to support risk informed applications for Southern Nuclear Operating Company (SNC). The seismic hazard for the Hatch SPRA was developed in early to mid-2013. This included development of the soil seismic hazard at plant grade, EL 129 feet. Foundation input response spectra (FIRS) and associated strain compatible soil profile properties were also calculated at other horizons to support seismic soil-structure interaction analyses.

The following sections provide a brief description of the major steps taken to develop the HNP seismic hazards for the Hatch SPRA including the Hatch SPRA GMRS. These descriptions are based on a set of calculations which provide the details of these steps. In the description for a given step, references are provided to the calculations that support the description.

Rock Seismic Hazard:

Reference 2 provides the description of the probabilistic seismic hazard calculations for hard rock conditions (Vs > 9200 fps) at the HNP site. The following models were used:

Seismic source model published in 2012 identified as the Central and Eastern United States Seismic Characterization (CEUS SSC) project (Reference 8).

Ground motion equations for rock conditions published in 2004 by the Electric Power Research Institute (EPRI) (Reference 9), with modified aleatory uncertainties published in 2006 by EPRI (Reference 10).

The calculation consists of running software that calculates the hazard from seismic sources and combines hazard from multiple sources maintaining the correlation implied by both the seismic source model through activity rates and alternate global models, and through common ground motion equations. In particular, seismic hazards from repeating large magnitude earthquake sources (RLMEs) are combined with seismic hazards from background sources in a manner that depends on ground motion equations, so that the correlation among the hazard results is maintained.

Magnitude/distance de-aggregation results were determined for mean annual frequencies of exceedance (MAFEs) of 1 E-04, 1 E-05, and 1 E-06 at high (5 and 10 Hz) and low {1 and 2.5 Hz)

Enclosure to NL-15-0075 Edwin I. Hatch Nuclear Plant-Seismic Hazard Curve Information Page E-2 spectral frequencies. Mean rock uniform hazard response spectrum {UHRS) for high-and low-frequencies were developed for input to the site response analysis.

Figure 1 below {Reference 2, Figure 14) provides the mean rock hazard curves for the 7 spectral frequencies.

1E*2 PGA 25Hz 10Hz sHz 2.5Hz 1Hz O.SHz 1£7 ~----------~------------~--------~~~

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Figure 1. Mean Rock Hazard by Spectral Frequency Development of Soil/Rock Column Properties:

Reference 3 provides the description of the soil/rock column properties, presents the best estimate shear wave velocity {Vs) profile, provides a variation of this profile, and assigns dynamic properties {G/Gmax and damping versus strain) to the various strata. This information was also provided in the September 12, 2013 submittal to the NRC {Reference 4).

The best estimate V s profile was developed using all available site-specific data and nearby deep offsite data. Site specific subsurface data was obtained from subsurface explorations associated with the HNP FSAR for Units 1 and 2, and the independent spent fuel storage installation {ISFSI) subsurface investigations and foundation evaluations. The deep offsite data was developed from a nearby well {#1 A.P. Snipes well) located about 27 miles southwest of the site. The well data was obtained from the State of Georgia Department of Natural Resources.

The Vs profile of the upper 429 feet is shown on Figure 2, while the entire profile is shown on Figure 3. Site stratigraphy, developed from this data, is also shown on Figures 2 and 3.

Uncertainty was accounted for using a logarithmic standard deviation of 0.5 {cruln = 0.5}

assigned to the best estimate V s profile for use in the randomization process. This uncertainty

Enclosure to NL-15-0075 Edwin I. Hatch Nuclear Plant - Seismic Hazard Curve Information Page E-3 is presented in Figures 2 and 3 as upper and lower range profiles. Note that the best estimate profile presented in Figures 2 and 3 is equivalent to the best estimate profile presented in the March 31, 2014 submittal to NRC (Reference 1 ).

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Enclosure to NL-15-0075 Edwin I. Hatch Nuclear Plant-Seismic Hazard Curve Information Page E-5 No site specific data regarding shear modulus and damping versus strain were available; thus, published relationships for these dynamic properties were assigned to the various strata. These relationships included EPRI curves for sands and ldriss and Boulanger curves for weathered and competent rock as presented in Reference 3 and the September 12, 2013 submittal to the NRC (Reference 4). Similar relationships were presented in the March 31, 2014 submittal to NRC (Reference 1 ).

Seismic Site Response Analysis and Site Amplification Functions:

Reference 5 provides a set of 60 simulated profiles to represent the in situ site condition in the main plant area with ground surface at EL 129 feet and uses the input best estimate (BE) properties and their associated uncertainty. The simulated Vs profiles were developed from the best estimate profile shown on Figures 2 and 3. The simulation procedure generates a set of site-specific simulated soil profiles to represent the dynamic properties of the site while considering the uncertainty associated with each of these properties, and correlations between different parameters.

Th~ Vs simulation procedure made use of random field models which describe the statistical correlation between layering and V5

• The default randomization parameters developed in Reference 14 for U. S. Geological Survey C site condition were used for the best estimate profile. Sixty simulated Vs profiles were generated. These random Vs profiles were generated using a natural log standard deviation of 0.5. In the correlation model, a limit of +1-2 standard deviations about the median value in each layer was assumed for the limits on random Vs fluctuations.

To perform the site response analyses for the Hatch site (Reference 6}, a random vibration theory (RVT} approach was er:nployed. The Low Frequency (LF) and High Frequency (HF) rock input spectra are propagated through the soil column starting at bedrock (defined by a shear wave velocity of 9,200 ft/sec). For each of the 60 randomized profiles and input motions, the site amplification is computed as the ratio between 5% damped geologic outcrop pseudo acceleration response spectrum at the control point and bedrock. The analysis is carried out at 301 frequency points ranging from 0.1 to 100 Hz and equally spaced in logarithmic space. The median (computed as the logarithmic mean) and the logarithmic standard deviation (log-SD) of the site amplification at each frequency are then computed.

The 5% damped amplification functions at ground surface for the main plant area in situ soil conditions, corresponding to the LF and HF motions at six hazard levels {1 E-3, 1 E-4, 1 E-5, 1 E-6, 1 E-7 and 1 E-8 mean annual probability of exceedance) are summarized in Reference 6 and shown on Figures 4 and 5.

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Enclosure to NL-15-0075 Edwin I. Hatch Nuclear Plant - Seismic Hazard Curve Information Page E-7 Surface Seismic Hazard:

Reference 7 provides the description of the methodology used to calculate the soil seismic hazard at plant grade, EL 129 feet. The calculation is based on using the 2012 seismic source characterizations (Reference 8), the 2004 EPRI ground motion model (Reference 9) with the revised sigmas of Reference 10, and the site amplification factors developed in Reference 6.

Reference 7 states that the methodology used to calculate the soil seismic hazard at plant grade is well established in the literature (e.g., Reference11). The integration of the various parameters for developing the soil hazard followed Approach 3 (References 12 and 13).

Figure 6 below (Reference 7, Figure 14) provides the mean soil hazard curves for the 7 spectral frequencies.

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Enclosure to NL-15-0075 Edwin I. Hatch Nuclear Plant-Seismic Hazard Curve Information Page E-8 Table 1 below (Reference 7, Table 2) provides tabulation of the mean 1 E-04 and 1 E-05 UHRS and the GMRS associated with the Hatch SPRA seismic hazard.

Frequency 104 UHRS 10-5 UHRS GMRS 100 0.183 0.400 0.205 90 0_183 0.409 0_209 80 0_183 0.420 0_213 70 0.184 0.433 0.219 60 0.184 0.447 0.225 50 0.186 0.465 0_232 45 0_188 0.475 0_237 40 0.190 0.488 0_242 35 0.194 0_503 0.249 30 0.199 0.520 0.258 25 0.215 0_548 0.273 20 0.242 0.550 0.280 15 0.274 0_555 0.289 12_5 0.307 0_592 0.311 10 0.328 0_652 0_341 9

0.351 0.692 0_362 8

0.371 0.750 0.391 7

0.365 0.772 0.399 6

0.365 0_776 0.400 5

0.390 0.811 0.420 4

0.367 0.811 0.415 3

0.375 0.823 0.422 2.5 0.379 0_815 0.420 2

0.362 0_807 0.413 1.5 0.338 0.742 0.380 1.25 0.304 0.653 0.336 1

0.254 0.563 0.288 0.9 0.236 0.541 0.275 0.8 0.211 0.492 0.249 0.7 0.188 0.445 0.225 0.6 0.156 0.406 0.201 0.5 0.126 0_347 0_170 0.4 0.0942 0_270 0.131 0.3 0.0740 0.204 0.100 0.2 0.0513 0.138 0.0679 0.167 0.0392 0.104 0.0514 0_125 0.0225 0.0593 0.0293 0.1 0_0156 0.041 1 0.0203 Table 1. Hatch SPRA Seismic Hazard

Enclosure to NL-15-0075 Edwin I. Hatch Nuclear Plant-Seismic Hazard Curve Information Page E-9

==

Conclusions:==

As provided in this overview, the rock hazard for HNP was based on the CEUS sse model (Reference 8) and a ground motion model based on References 9 and 1 0. The site soil profile is defined as a single best estimated soil profile with the dynamic properties previously provided to the NRC (Reference 4). Seismic site response and the development of site amplification functions was based on sixty simulation profiles with input based on LF and HF rock motions.

Finally, the surface seismic hazard at EL 129 feet was based on the integration of the rock hazard with site amplification functions following Approach 3. In consideration of the bases used for this seismic hazard curve, it is appropriate for HNP to utilize this information and curve as the current hazard curve for the Hatch SPRA.

References:

1. of SNC letter NL-14-0343, NTTF 2.1-Seismic entitled "Seismic Hazard and Screening Report-Hatch," March 31, 2014.

2.

Lettis Consultants International, Inc., HAP001-PR-01 Rock seismic hazard at Hatch using the CEUS seismic source model, 7/10/13.

3.

SCNH-12-075 Dynamic Soil/Rock Column for Hatch Site for SPRA, 2/6/13.

4.

SNC Sept. 12, 2013 Submittal (NL-13-1955) Edwin I. Hatch Nuclear Plant Units 1 and 2 Geological Data.

5.

SCNH-12-074 Soil Profile Simulation for Hatch Site for SPRA, 2/14/13.

6.

SCNH-12-076 Seismic Site Response Analysis for Hatch Site for SPRA, 3/11/13.

7.

Lettis Consultants International, Inc., HAP001-PC-03 Soil hazard calculations for Hatch, 7/24/13.

8.

NRC, EPRI, DOE (2012), Central and Eastern United States Seismic Source Characterization for Nuclear Facilities, NRC Report NUREG-2115, EPRI Report 1021097, DOE Report DOE/NE-0140, 6 Volumes.

9.

EPRI (2004), CEUS Ground Motion Project Final Report, Electric Power Research Institute, Palo Alto, CA.

Report 1008910, December 2004.

10. EPRI (2006), Program on technology innovation: truncation of the lognormal distribution and value of the standard deviation for ground motion models in the central and eastern United States, Electric Power Research Institute, Palo Alto, CA, Report 1014381, August 2006.

11. McGuire, R.K. (2004), Seismic Hazard and Risk Analysis, Earthquake Eng. Res. lnst., Monograph MN0-10.

12. Risk Engineering, Inc. (2002). Technical basis for revision of regulatory guidance on design ground motions:

Development of hazard-and risk-consistent seismic spectra for two sites, US Nuclear Regulatory Commission Report NUREG/CR-6769.

13. Risk Engineering, Inc. (2001). Technical basis for revision of regulatory guidance on design ground motions:

Hazard-and risk-consistent ground motion spectra guidelines, US Nuclear Regulatory Commission Report NUREG/CR-6728.

14. Toro, G.R. (1996). Probabilistic Models of Site Velocity Profiles for Generic and Site-Specific Ground Motion Amplification Studies. Published as Appendix C in Silva, W.J., N. Abrahamson, G. Toro and C. Costantino.

"Description and validation of the stochastic ground motion model." Report Submitted to Brookhaven National Laboratory, Associated Universities, Inc. Upton, New York 11973, Contract No. 770573.