ML23346A239
| ML23346A239 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 01/17/2024 |
| From: | NRC/NRR/DORL/LPL1 |
| To: | |
| Klett A, NRR/DORL/LPL1 | |
| Shared Package | |
| ML23346A238 | List: |
| References | |
| EPID L-2019-PMP-0061 | |
| Download: ML23346A239 (1) | |
Text
Seismic Hazard Report by the Offi ce of Nuclear Reactor Regulation Peach Bottom Atomic Power Station, Units 2 and 3 Docket Nos. 50-277 and 50-278
1.0 Overview
This report 1 provides the U.S. Nuclear Regulatory Commission (NRC) staffs updated seismic hazard curves and response spectra for the Peach Bottom Atomic Power Station, Units 2 and 3 (Peach Bottom) site 2 that are based on the implementation of (1) a new seismic ground motion model for the central and eastern United States (CEUS) and (2) recent advances in site response analysis. The NRC staffs updated hazard curves (i.e., tables A-1 through A-3) are included in appendix A to this report.
2.0 Background
In response to the March 11, 2011, Great East Japan Earthquake and tsunami, which triggered an accident at the Fukushima Dai-ichi nuclear power plant, the NRC established the Near-Term Task Force (NTTF) to conduct a systematic and methodical review of NRC processes and regulations and determine whether the agency should make additional improvements to its regulatory system. In SECY-11-0093, Near-Term Report and Recommendations for Agency Actions Following the Events in Japan, dated July 12, 2011 (NRC, 2011), the NRC staff recommended actions to clarify and strengthen the regulatory framework for protection against natural hazards. In particular, NTTF Recommendation 2.1 (NTTF R2.1) instructed the NRC staff to issue requests for information to all power reactor licensees pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Section 50.54(f) (50.54(f) letter (NRC, 2012)). Enclosure 1 to the 10 CFR 50.54(f) letter requested that addressees reevaluate the seismic hazards at their sites, using present day NRC requirements and guidance to perform a probabilistic seismic hazard analysis (PSHA) and develop a site-specifi c ground motion response spectrum (GMRS).
To comply with the 10 CFR 50.54(f) request, the Nuclear Energy Institute submitted Electric Power Research Institute (EPRI) Report 1025287, Seismic Evaluation Guidance: Screening, Prioritization, and Implementation Details (SPID) for the Resolution of Fukushima NTTF Recommendation 2.1 Seismic, dated November 27, 2012 (EPRI, 2012). Recipients of the 10 CFR 50.54(f) letter committed to following the SPID to develop seismic hazard and screening reports (SHSRs). By December 2017, the NRC staff had finished assessing the SHSRs for all operating U.S. nuclear power plants.
Under the process for the ongoing assessment of natural hazards information (POANHI),
described in SECY-16-0144, Proposed Resolution of Remaining Tier 2 and 3 Recommendations Resulting from the Fukushima Dai-ichi Accident, dated December 26, 2016 (NRC, 2016), the NRC staff continuously seeks out and integrates new natural hazards information for operating plants in the United States. The Office of Nuclear Reactor Regulations Office Instruction LIC-208, Process for the Ongoing Assessment of
1 Agencywide Documents Access and Manag ement System (ADAMS) Accession Nos.
ML23346A241 (letter) and ML23346A239 (enclosure).
2 Constellation Energy Generation, LLC is the licensee for Peach Bottom.
Enclosure
Natural Hazards Information, issued November 2019 (NRC, 2019), provides guidance to the staff on how to collect, integrate, and evaluate new information for consideration in its regulatory decision-making. This report presents the NRC st affs latest understanding of seismic hazards at the Peach Bottom site following the POANHI framework.
The Peach Bottom site is located on the banks of the Susquehanna River in southern Pennsylvania within the Piedmont physiographic province and is underlain by metamorphosed sedimentary rock.
3.0 Motivation
After evaluating the SHSR submittals, the NRC staff captured in NUREG/KM-0017, Seismic Hazards Evaluations for U.S. Nuclear Power Plants: Near-Term Task Force Recommendation 2.1 Results, issued December 2021 (Munson et al., 2021), the information used to develop the GMRS at each of the U.S. nuclear power plants. This includes a compilation and synthesis of (1) information provided by licensees in their SHSRs, (2) information collected by the NRC staff during its reviews of the SHSRs, and (3) information subsequently collected by the NRC staff from the scientific and engineering literature pertaining to several of the nuclear power plant site s. In addition, NUREG/KM-0017 includes updated approaches and relationships, relative to those recommended by the SPID, that the NRC staff used to perform its analyses.
After the development of NUREG/KM-0017, a new Senior Seismic Hazard Analysis Committee (SSHAC) Level 3 ground motion model (GMM) for Eastern North America called NGA-East was published by Goulet et al. (2018). In addition, the NRC staff also participated in a SSHAC Level 2 study, documented in Research Information Letter 2021-15, Documentation Report for SSHAC Level 2: Site Response, issued November 2021 (Rodriguez-Marek et al., 2021). This SSHAC Level 2 study implemented the SSHAC approach to performing site response analyses (SRAs). The SSHAC process, described most recently in NUREG-2213, Updated Implementation Guidelines for SSHAC Hazard Studies, issued October 2018 (Ake et al., 2018),
provides a structured and logical framework for the systematic evaluation of alternative data, models, and methods. This seismic hazard report for the Peach Bottom site incorporates the NGA-East GMM in place of the EPRI (2013) GMM; however, because the rock beneath the site is competent with high shear wave velocities ( ) the NRC staff did not perform an SRA (section 4.2 further discusses the NRC staffs basis for not performing an SRA).
4.0 Methods
4.1 Reference Rock Hazard
For the reference rock PSHA, the NRC staff used the distributed seismicity zones (DSZs) from the SSHAC Level 3 Central and Eastern United States Seismic Source Characterization for Nuclear Facilities (CEUS-SSC) model in NUREG-2115, Central and Eastern United States Seismic Source Characterization for Nuclear Facilities, issued January 2012 (NRC, 2012).
Specifically, the NRC staff selected the DSZs that are located within 500 kilometers of the site.
For this reevaluation, the NRC staff used the SSHAC Level 2 update to the CEUS-SSC seismicity catalog and recurrence parameters (Gatlin, 2015), which primarily impacts sites close to the 1886 Charleston earthquake sequence. For the Peach Bottom site, the NRC staff selected the Charleston CEUS-SSC repeated large-magnitude earthquake (RLME) source, which is the only RLME source that is within 1,000 kilometers of the site. To develop the reference rock seismic hazard curves for the site, the NRC staff used the NGA-East
GMM (2018) to compute the median and logarithmic standard deviation of the spectral accelerations. Because the NGA-East GMM implements the rupture distance parameter, the NRC staff developed virtual rupture planes for each of the distributed source zones surrounding the site. For each virtual rupture, the NRC staff used the CEUS-SSC hazard input document (NRC, 2012) to specify the size of the rupture plane and the orientation of the rupture plane in terms of the strike and dip angles, dip direction, and rupture type (e.g., reverse and strike slip).
In contrast, to develop the hazard curves for NUREG/KM-0017, the NRC staff used point source approximations for the CEUS-SSC and EPRI GMM (EPRI, 2013) combination.
Figure 1 in section 8 shows the distribution of the virtual ruptures for one of the four alternative CEUS-SSC seismotectonic DSZ configurations along with the resulting 10-Hertz (Hz) mean hazard curves developed using the NGA-East GMM. In particular, figure 1 shows the distribution of the surface projection of the updip segments of the virtual rupture planes for each of the six seismotectonic DSZs within 500 kilometers of the site. As expected, the Extended Continental CrustAtlantic Margin (ECCAM) s ource zone, which surrounds the site, is the largest contributor to the 10 Hz reference rock mean hazard curves at the 10 -4 annual frequency of exceedance (AFE) level. Similarly, figure 2 shows the distribution of the virtual ruptures for one of the three alternative CEUS-SSC maximum-magnitude DSZ configurations along with the resulting 10 Hz mean hazard curves developed using the NGA-East GMM. The Mesozoic-and-Younger ExtensionNarrow Configuration (MESEN) source zone, which surrounds the site, is the largest contributor to the 10 Hz reference rock mean hazard curves at the 10-4 AFE level. Figure 3 shows the Charleston RLME source, which is over 600 kilometers from the site, and its contribution to the 1 Hz reference rock mean hazard, from using the NGA-East GMM. Figure 4 shows the contribution from all the DSZs relative to the Charleston RLME, as well as the total mean hazard for the 1 and 10 Hz mean reference rock hazard curves, from using the NGA-East GMM. For both the 1 and 10 Hz mean reference rock hazard curves, the DSZ sources provide the largest contribution at the 10 -4 AFE level. Finally, figure 5 shows the mean 1,000-, 10,000-, and 100,000-year return period mean reference rock uniform hazard response spectra (UHRS) for the Peach Bo ttom site from using the EPRI GMM (blue) and the NGA-East GMM (red). This comparison between the UHRS for the two GMMs shows the results from using the ergodic standard deviation for both the EPRI GMM and for the NGA-East GMM, which is appropriate because, as discussed below, Peach Bottom is a reference condition rock site. As shown in figure 5, the spectral accelerations from using the NGA-East GMM are moderately higher at the 10 -5 AFE level than those from using the EPRI GMM across the entire range of spectral frequencies. However, for the 10 -4 AFE level, the spectral accelerations from using the NGA-East GMM are only slightly higher than those from using the EPRI GMM.
4.2 Site Response Analysis
SRAs, which are used to develop site adjustment (or amplification) factors (SAFs) depend on several factors, including the site strata (material type, stiffness, and thickness) and their response to dynamic loading. Because this information is site specific, the ability to accurately model the site response depends on the quantity and quality of site-specific geologic and geotechnical data available, and on the interpretation and use of these data to develop input models for assessing amplification (or deamplif ication) of ground motions. The resulting SAFs are assessed for a wide range of input ground motions as part of understanding the changes in the soil and rock response as input ground motions increase.
American National Standard ANSI/ANS-2.29-2020, Probabilistic Seismic Hazard Analysis (ANS, 2020) provides guidance for performing a PSHA when developing design and safety
evaluation criteria for nuclear facilities. Section 4.3.6, GMM interface with site response, of the standard states that an SRA may not be necessary for particularly stiff rock sites, the subsurface of which closely match the reference conditions assumed for the GMM. The standard states that the decision to forego an SRA for a stiff rock site shall be justified and provided as part of the analysis. For Peach Bottom, because the GMM already accounts for the stiff rock condition, the NRC staff determined that an SRA is not needed.
4.2.1 Site Exploration
As described in the NTTF R2.1 SHSR submitted by Exelon (Barstow, 2014) 3 and summarized in section 2.2.10 of NUREG/KM-0017, the site investigations for Peach Bottom consist of laboratory measurements (shock-scope tests under a range of confining pressures) to obtain compressional wave velocities ( ) and unit weights from core samples from several boreholes at depths ranging from about 6 meters (m) to 40 m.
4.2.2 Basecase Profiles
The Peach Bottom site consists of a veneer of residual soils overlying partially weathered rock grading into hard unweathered metamorphic rock. Exelon stated in its NTTF R2.1 SHSR (Barstow, 2014) that the reactor buildings are supported on the Peters Creek schist, which is part of the Wissahickon Formation of late Paleozoic or early Precambrian age. For its NTTF R2.1 SHSR, Exelon selected the top of the moderately weathered rock as the control point elevation for its site response analysis. However, for its seismic probabilistic risk assessment (SPRA; Helker, 2018), Exelon determined its GMRS at the foundation level of the reactor buildings, which is 6 m deeper than the control point elevation that it assumed for the NTTF R2.1 SHSR. Exelon stated that the downward shift of the control point elevation is appropriate because the softer rock and soils above the foundation hard rock were removed prior to the placement of the reactor buildings (Helker, 2018). At this deeper control point, the licensee stated that the rock shear wave velocity ( ) is similar to the reference rock of 2,830 m/sec assumed by the EPRI GMM. As such, Exelon did not perform an SRA to determine the GMRS for the SPRA. Based on its evaluation of the values (about 5,000 m/sec) from the rock samples reported in table 2.5.2 of the Updated Final Safety Analysis Report (Helker, 2023) for depths ranging from 6 m to 20 m and assuming a Poissons ratio of 0.28, the NRC staff estimated a rock of about 2,800 m/sec, which is similar to the reported in the licensees SPRA (Helker, 2018). Although the reference rock for the NGA-East GMM is 3,000 m/sec, which is slightly higher than the reference ro ck velocity used for the EPRI GMM, the NRC staff concluded that an SRA for the Peach Bottom site, using the 6 m deeper control point elevation, will produce close to 1 at the ground motion amplitudes associated with the GMRS and, as such, have no impact on the final GMRS for the site. Because the GMM already accounts for the stiff rock conditions of Peach Bottom, the NRC staff determined that an SRA to adjust the GMM results for this seismic hazard reevaluation was not needed.
4.3 Control Point Hazard and Ground Motion Response Spectra
To determine the GMRS for the Peach Bottom site, the NRC staff used the 10 -4 and 10-5 UHRS, shown in figure 5 of section 8, developed from the reference rock hazard curves. Table 1 in section 8 shows the 10 -4 and 10-5 UHRS and the GMRS spectral acceleration values for the Peach Bottom site. Figure 6 shows the GMRS (red curve) compared to the GMRS (black curve)
3 On February 1, 2022, Exelon Generation Company, LLC was renamed Constellation Energy Generation, LLC.
developed by Exelon for its SPRA (Helker, 2018). The licensees GMRS from the NTTF R2.1 SHSR (Barstow, 2014) and the NRC staffs GMRS from NUREG/KM-0017 are not shown in figure 6 because the downward shift of the control point elevation makes these two GMRS irrelevant for this POANHI evaluation. As shown in figure 6, the final GMRS from this study is very similar but slightly higher (7 percent at 10 Hz) than the licensees GMRS across the entire frequency range. These higher spectral accelerations are due to the NGA-East GMM, which predicts slightly higher median ground motions for sites where the hazard is controlled by lower-to moderate-magnitude earthquakes relative to the EPRI GMM (see figure 5).
5.0 Data Tables
Appendix A provides the data tables for the Peach Bottom site. Tables A-1, A-2, and A-3 give the reference rock mean hazard curves for 23 spectral frequencies ranging from 0.1 to 100 Hz and for peak ground acceleration (PGA). As described above in section 4.2.2, the NRC staff did not perform an SRA for the Peach Bottom hazard reevaluation. As such, the reference rock mean hazard curves and control point mean hazard curves are the same for Peach Bottom.
6.0 References
American Nuclear Society, American National Standard ANSI/ANS-2.29-2020, Probabilistic Seismic Hazard Analysis, La Grange Park, IL, April 16, 2020.
Barstow, J., Letter from Exelon Generation Company, LLC, to the NRC, Response to the NRC Request for Information Pursuant to 10 CFR 50.54(f) Regarding Recommendation 2.1 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident for Peach Bottom Atomic Power Station, Units 2 and 3, March 31, 2014 (ML14090A247).
EPRI, EPRI (2004, 2006) Ground-Motion Model (GMM) Review Project: Final Report, Palo Alto, CA, June 2013 (ML13155A553).
EPRI, Seismic Evaluation Guidance: Scr eening, Prioritization and Implementation Details (SPID) for the Resolution of Fukushima Near-Term Task Force Recommendation 2.1: Seismic. EPRI Report 1025287, Palo Alto, CA, November 27, 2012 (ML12333A170).
Goulet, C.A.; Y. Bozorgnia; N. Abrahamson; N. Kuehn; L. Al Atik; R. Youngs; R. Graves; and G. Atkinson; Central and Eastern North America Ground-Motion CharacterizationNGA-East Final Report, PEER Report 2018-08, Pacific Earthquake Engineering Research Center, Berkeley, CA 2018.
Helker, D.P., Letter from Exelon Generation Company, LLC, to the NRC, Seismic Probabilisitc Risk Assessment Report, Response to NRC Request for Information Pursuant to 10 CFR 50.54(f) Regarding Recommendation 2.1 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, August 28, 2018 (ML18240A065).
Helker, D.P., Letter from Constellation Energy Generation, LLC, to the NRC, Submittal of the Updated Final Safety Analysis Report (Revision 29 ), Fire Protection Program (Revision 24) and Reference Drawings, April 10, 2023 (ML23110A266).
U.S. Nuclear Regulatory Commission (NRC), Near-Term Report and Recommendations for Agency Actions Following the Events in Japan, SECY-11-0093, Washington, DC.
July 12, 2011 (ML11186A950).
NRC, 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, Leeds, E., and Johnson, M., Washington, DC, March 12, 2012 (ML12053A340).
NRC, Proposed Resolution of Remaining Tier 2 and 3 Recommendations Resulting from the Fukushima Dai-ichi Accident, SECY-16-0144, Washington, DC, December 29, 2016 (ML16286A552).
NRC, Central and Eastern United States Seismic Source Characterization for Nuclear Facilities, NUREG-2115, Washington, DC, January 2012 (ML12048A776).
NRC, Updated Implementation Guidelines for SSHAC Hazard Studies, Ake, J.; C. Munson; J. Stamatakos; M. Juckett; K. Coppersmith; and J. Bommer; NUREG-2213, Washington, DC, October 2018 (ML18282A082).
NRC, Seismic Hazards Evaluations for U.S. Nuclear Power Plants: Near-Term Task Force Recommendation 2.1 Results, Munson, C.; J. Ake; J. Stamatakos; and M. Juckett; NUREG/KM-0017, Washington, DC, December 2021 (ML21344A126).
NRC, Process for the Ongoing Assessment of Natural Hazards Information, Office of Nuclear Reactor Regulation Office Instruction LIC-208, Washington, DC, November 2019 (ML19210C288).
Rodriguez-Marek, A.; E. Rathje; J. Ake; C. Munson; S. Stovall; T. Weaver; K. Ulmer; and M. Juckett, Documentation Report for SSHAC Level 2: Site Response, Research Information Letter 2021-15, Washington, DC, November 2021 (ML21323A056).
7.0 Principal Contributor
Dated: January 17, 2024
8.0 Table 1 and Figures 1 Through 6
Table 1 GMRS and UHRS for Peach Bottom
Frequency (Hz) UHRS 1E-4 (g) GMRS (g) UHRS 1E-5 (g) 0.100 0.002760 0.003800 0.007908 0.133 0.004122 0.005800 0.011921 0.200 0.006949 0.009800 0.020306 0.250 0.009589 0.013500 0.027964 0.333 0.013895 0.020600 0.043069 0.500 0.024862 0.037200 0.077981 0.667 0.033978 0.052600 0.111022 1.000 0.054071 0.084800 0.179832 1.333 0.072805 0.116100 0.247054 2.000 0.105166 0.167600 0.356578 2.500 0.125668 0.204000 0.435934 3.333 0.155079 0.254200 0.544654 4.000 0.175218 0.289100 0.620504 5.000 0.204933 0.335700 0.719157 6.667 0.247108 0.413000 0.889287 10.000 0.309350 0.526500 1.138920 13.333 0.350977 0.606900 1.317975 20.000 0.393488 0.685700 1.492030 25.000 0.380687 0.666200 1.451073 33.333 0.344711 0.606000 1.321442 40.000 0.320247 0.562900 1.227449 50.000 0.282082 0.499000 1.089825 100.000 0.198454 0.350200 0.764260 200.000 0.170101 0.303600 0.664609
Figure 5 1,000-, 10,000-, and 100,000-Year Return Period Mean Reference Rock UHRS for CEUS-SSC and EPRI GMM (Blue Curves) and CEUS-SSC and NGA-East GMM (Red Curves)
Figure 6 GMRS for the Peach Bottom Site
Appendix A
Data Tables