Discussion of Seismic Hazard Reevaluation and NRC’s Technical Focus Areas for Columbia Generating Station June 4, 2015 Agenda
Introduction Presentation of Seismic Reevaluation Report ◘ SSHAC Activities ◘ Seismic Sources ◘ Ground Motion Model and Site Response Discussion of Interim Actions and Evaluations ◘ Flexible and Diverse Mitigation Strategies (FLEX) ◘ Seismic Analysis (PSA) ◘ Path Forward
2 Introduction
Energy Northwest followed the approved process for development of seismic hazard reevaluation for the Columbia Generating Station site in response to Enclosure 1 of the NRC’s 10 CFR 50.54(f) Request for Information Screening determination performed in accordance with NRC- endorsed Screening, Prioritization, and Implementation Details (SPID) (EPRI 1025287) Energy Northwest will present a detailed technical basis to demonstrate how process was followed and is prepared to discuss each of the technical focus areas
3 SSHAC Activities
Kevin Coppersmith Coppersmith Consulting, Inc. SSHAC Activities
SSHAC Level 3 (SL3) conducted as “Hanford Site-Wide PSHA” with sponsorship from DOE and Energy Northwest Project planned and conducted to comply with NUREG-2117 and other guidance Roles and responsibilities of all project participants defined and adhered to Project-specific enhancements to SL3 process Participatory Peer Review Panel (PPRP) confirmed acceptability of both technical and process aspects of the project
5 Hanford Site-Wide SSHAC Level 3 PSHA Purpose of Study: to develop a technically defensible PSHA that can be used for design and safety evaluations at the Hanford Site, Washington, including Columbia Generating Station ◘ PSHA must enjoy high levels of regulatory assurance, as indicated by a SSHAC Level 3 process ◘ Must provide outputs that allow use at multiple facility sites within the Hanford Site, including the CGS ◘ Outputs must be compatible in format with site response analyses for site-specific facility input motions ◘ Compliant with NRC requirements, per 50.54(f) letter, and regulatory guidance ◘ Compliant with DOE Order 420.1B (later 420.1C) regarding 10-year update and expectations of DNFSB
6 SSHAC Guidelines and Guidance
NUREG-2117 SSHAC Implementation Guidelines
7 Project Plan for SSHAC Level 3 PSHA Project Plan specifies: ◘ Project organization ◘ Participant roles and responsibilities ◘ Scope ◘ Schedule ◘ Deliverables and instructions for usage Provided a basis for all project planning and contracting Ongoing information for participants and reviewers Recommended elements given in NUREG-2117 Hanford PSHA Enhancements ◘ New data collection activities ◘ PPRP participation ◘ Interfaces between seismic source characterization (SSC), ground motion characterization (GMC), and site response
8 Selection Criteria for SSHAC Participants
Bommer, J.J. and Coppersmith, K.J., 2013, SMiRT-22, Lessons Learned from Application of the NUREG-2117 Guidelines for SSHAC Level 3 Probabilistic Seismic Hazard Studies for Nuclear Sites
9 HanfordProject PSHA Organization Project Organization
10 SeismicSeismic Source Source Characterization Characterization Team Team
Kevin Coppersmith – TI Lead Lorraine Wolf
Kathryn Hanson • Valentina Montaldo-Falero – Hazard Analyst Ryan Coppersmith • Roseanne Chambers – PSHA document integrator • Joe Lettrick – GIS data base manager Jeff Unruh
11 Ground Motion Characterization Team
Julian Bommer - TI Lead Bob Youngs Linda Al Atik Gabriel Toro Adrian Rodriguez-Marek
12 Resource and Proponent Experts – WS1
Individual Affiliation Walt Silva Pacific Engineering & Analysis Carl Costantino Consultant Norm Abrahamson University of California, Berkeley Tuna Onur Onur Seemann Consulting Rob Graves U.S. Geological Survey Art Frankel U.S. Geological Survey Tom Hearns New Mexico State University Alan Rohay Pacific Northwest National Laboratory Tom Pratt U.S. Geological Survey Brian Sherrod U.S. Geological Survey Rick Blakely U.S. Geological Survey George Last Pacific Northwest National Laboratory Harvey Kelsey Humboldt State University Rex Flake Central Washington University Erick Burns U.S. Geological Survey Paul Thorne Pacific Northwest National Laboratory Bruce Bjornstad Pacific Northwest National Laboratory
13 Resource and Proponent Experts – WS2 Individual Affiliation Walt Silva Pacific Engineering & Analysis Carl Costantino Consultant Norm Abrahamson University of California–Berkeley Art Frankel U.S. Geological Survey Alan Rohay Pacific Northwest National Laboratory Suzette Payne Idaho National Laboratory Yousef Bozorgnia University of California–Berkeley Paul Spudich U.S. Geological Survey Jennifer Donahue Geosyntec Consultants Dave Boore U.S. Geological Survey Olga Ktenidou ISTerre, Université Joseph Fourier – CNRS Gail Atkinson University of Western Ontario Nick Gregor Consultant John Zhao Institute of Geological and Nuclear Sciences, New Zealand
Al Rohay Pacific Northwest National Laboratory Tom Pratt U.S. Geological Survey Brian Sherrod U.S. Geological Survey Rick Blakely U.S. Geological Survey Marcia McLaren Pacific Gas and Electric Co. Steve Reidel Washington State University Judy Zachariasen URS Corporation, Tyler Ladins Humboldt State University Craig Weaver U.S. Geological Survey
14 Participatory Peer Review Panel (PPRP)
Bill Lettis Brian Chiou Woody Savage Ken Campbell, Chair Carl Stepp
15 Goal of a SSHAC Process
“The fundamental goal of a SSHAC process is to properly carry out and completely document the activities of evaluation and integration, defined as: Evaluation: The consideration of the complete set of data, models, and methods proposed by the larger technical community that are relevant to the hazard analysis. Integration: Representing the center, body, and range of technically defensible interpretations in light of the evaluation process (i.e., informed by the assessment of existing data, models, and methods).”
NUREG-2117
16 NUREG-2117
17 18 TI Team Working Meetings (WM)
WM1
WM2 WM3
WM4
• 3-4 days duration • All team members • Conference room with GIS support 19 • PPRP observers Requirements for SSHAC Level 3 PPRP
PPRP Roles and Responsibilities Technical review: ensure that the full range of data, models, and methods have been duly considered in the assessment and all technical decisions are adequately justified and documented Process review: ensure that the project conforms to the requirements of the selected SSHAC level Provide timely perspectives and advice regarding the manner in which ongoing activities can be improved or carried out more effectively Be present at all the formal workshops as observers and subsequently submit a consensus report containing comments, questions, and suggestions Provide one or more representatives of the PPRP to attend as observers the working meetings of the TI Teams Perform detailed review of all project documentation and provide written comments to ensure complete technical justification of integrated distribution Prepare PPRP Closure Letter providing final technical and process review
20 Hanford PPRP Major Activities
Review of Project Plan and attendance at Kick-Off
Full PPRP present at all 3 Workshops
PPRP representative as observers at all 8 Working Meetings
PPRP encouraged to interrogate TI Teams on their preliminary models at WS3
PPRP Briefing to review Final SSC and GMC models
Review of Draft Report
Preparation of PPRP 21 Closure Letter PPRP Closure Letter November 15, 2014
22 Seismic Source Characterization Model
Kevin J. Coppersmith Coppersmith Consulting, Inc. Hanford Site-Wide SSHAC Level 3 PSHA
24 SSC-Related Activities
Compilation of extensive geologic/geophysical/tectonic database Update and analysis of earthquake catalogs: crustal and subduction zone Identification of seismic source zones and future earthquake characteristics Structural geologic and Quaternary analyses of Yakima folds Assessments of behavioral characteristics of fault sources including segmentation and slip rates Incorporation of associated uncertainties, including both aleatory and epistemic components
25 Seismic Sources in SSC Model
Cascadia Subduction Zone sources ◘ Plate interface ◘ Intraslab source
Seismic source zones ◘ YFTB zone: serves as a “background” zone to fault sources ◘ Zones B, C, and D
Fault sources within Yakima Fold and Thrust Belt (YFTB) ◘ 19 faults characterized ◘ More distant faults are implicitly included in source zones
26 New Data Collection and Analyses
Focused studies and analyses designed to reduce uncertainties in key SSC and GMC issues, within the project schedule and budget GMC-related ◘ Velocities at recording sites ◘ Analyses of kappa ◘ Analyses of basin effects SSC-related ◘ Structural analyses of Yakima folds ◘ Quaternary geologic studies ◘ High-resolution earthquake relocation analyses
27 Seismic Source Characterization, Focus Area 1 1. Summarize the information used to constrain the slip rates on the YFTB faults, including: a. Methodology used to evaluate fault slip from topography including associated uncertainties in the ages and offsets. c. How potential effects of surficial erosion were accounted for in the use of an average topographic profile to represent structural relief in individual faults.
Pertains to these sections of the report ◘ Section 5.2.1 Structural Analyses ◘ Section 8.4.3 Fault Characteristics Included in the SSC Model ◘ Appendix E, Section 5 Evaluation of Long-Term Structural Relief
28 Steps in Characterizing Fault Sources
Measure topographic relief along lengths ◘ Define segments for use in estimating Mchar, Mmax ◘ Alternative rupture length, area relationships Identify polygons on DEM defining fault-related deformation within seismogenic crust ◘ Compare topo relief with structural relief from boreholes: Agree. Define fault dip and uncertainties, given mapped fault location, seismogenic thickness, and polygon Max, average, 60% of polygon width defines uncertainty in fault dip and downdip width for given thickness Include geologic indicators of style of faulting to derive net slip Alternative start times of deformation 10my, 6my for slip rate ◘ Compare with Quaternary rates where known: Agree.
29 Steps in Characterizing Fault Sources (continued) Magnitude frequency distribution model ◘ Compare with fault-related seismicity: Characteristic earthquake model supported Incorporate recurrence interval data, if available Renewal model: elapsed times and alpha unknown Future ruptures: magnitude-dependent rupture areas, lengths can extend across segment boundaries
30 Topographic Analysis of Folds: Defines surface evidence of fault-related deformation within seismogenic crust
31 Identification of Polygons & Possible Segmentation Points
32 Comparison of Topographic Relief with Structural Relief
33 Fault Source Fault Source Acronym Mean Structural Relief (m) Ahtanum Ridge AR 330 Cleman Mountain CM 650 Columbia Hills-Central-East CH-C-E 55 Columbia Hills-East CH-E 105 Mean Structural Relief Columbia Hills-West CH-W 375 Columbia Hills-Central CH-C 135 Columbia Hills-Central-West CH-C-W 230 Frenchman Hills-East FH-E 155 ●Shape of segments Frenchman Hills-West FH-W 155 Horn Rapids Fault HR 90 Horse Heaven Hills-Central HHH-C 485 and slip distribution is Horse Heaven Hills-Central-East HHH-C-E 415 Horse Heaven Hills-Central-West HHH-C-W 575 likely the result of Horse Heaven Hills-East HHH-E 205 Horse Heaven Hills-West HHH-W 270 Manastash Ridge-Central MR-C 300 repeated rupture Manastash Ridge-East MR-E 145 Manastash Ridge-West MR-W 415 ● Average is appropriate Rattles RAW 130 Rattlesnake Hills RH 335 Rattlesnake Mountain RM 619 for assessing slip rate Saddle Mountains-East SM-E 320 Saddle Mountains-West SM-W 335 when have multiple Selah Butte SB 460 Toppenish Ridge-East TR-E 300 measurements along a Toppenish Ridge-West TR-W 310 Umtanum Ridge-Central UR-C 360 Umtanum Ridge-East UR-E 250 fault segment Umtanum Ridge-Southeast Anticline UR-SA 90 Umtanum Ridge-West UR-W 400 Umtanum-Gable Mountain U-GM 160 Wallula Fault WF 250 Yakima Ridge-East YR-E 325 Yakima Ridge-West YR-W 250 Yakima Ridge-Southeast YR-SE 65
34 Uncertainty in Dip Included in Logic Trees
35 Logic Tree Elements Related to Slip Rate
36 Logic Tree for Rattlesnake Mtn Fault Source
37 Net Slip Rate Distributions
38 Seismic Source Characterization, Focus Area 1 1. Summarize the information used to constrain the slip rates on the YFTB faults, including: b. Rationale for excluding thin skinned seismo-tectonic models. d. Bases for excluding listric fault geometries or potential for backthrust structures in structural relief model.
Pertains to these sections of the report ◘ Section 4.1 Tectonic Setting ◘ Section 4.4.1.2 Instrumental Seismicity ◘ Section 6.3 Epicentral Locations ◘ Section 8.4.3.4 Fault Dip ◘ Appendix E, Section 6 Kinematic Analyses Using Earthquake Focal Mechanisms
39 Thin-skinned vs. Thick-skinned
Thin-skinned model called for mechanical decoupling of faults within Columbia River Basalts with those in crystalline basement Former proponents for those models participated in WS1 and WS2 and have abandoned that model Multiple arguments for discounting thin-skinned model are given in pp. 4.5 to 4.10 Additional support was provided by high-resolution earthquake locations, which show no lack of seismicity at sub-basalt sediments Focal mechanisms in CRB and crystalline basement show comparable styles of faulting and stress orientations Geophysical properties of sub-basalt sediments suggest that they are not mechanically “weak”
40 Listric Fault Geometries
Listric geometries were not explicitly “excluded” A planar fault is the simplest geometry and is consistent with the back-limb geometry of essentially all of the YFB folds Historical large-magnitude thrust earthquakes show essentially planar rupture surfaces Backthrusts would have been included if there was good mapped evidence for their presence, and that they extend to the base of the seismogenic crust (i.e., are not confined to shallow depths in the hanging wall of another fault)
41 CGS Ground Motion Characterization
Robert Youngs Amec Foster Wheeler GMC Approach
Use appropriate GMPEs to develop distribution of predicted ground motions Select and appropriate GMPE shape to use as a backbone model Develop distribution of scaling factors to adjust the backbone to represent the distribution of predicted motions Develop scaling factors to adjust for unique site conditions at Hanford
43 Hanford Profile
Several 100 feet of sands and gravels, some with cementation Sequence of basalt flows with well defined and relatively thick sedimentary interbeds – Saddle Mtns Basalts and Ellensburg Formation interbeds Several km of more massive basalts, Wanapum and Grand Ronde Several km of sedimentary rocks above crystalline basement rocks
Waste Treatment Plant (near Site A)
44 Selection of Reference Horizon for Site-wide Study Initial concept to use top of SMB/Interbed sequence However, site response analyses indicate that treatment of the SMB/Interbed sequence as a halfspace produced different surface motions than obtained from explicitly modeling basalts and interbeds Reference horizon moved down to top of massive Wanapum basalts (top of Lolo flow with flowtop removed)
45 Implications for Downstream Site Response Analyses
Assessment of baserock properties required assessment of properties of overlying SMB/Interbeds In order to maintain consistency in downstream use of baserock hazard, properties of SMB/Interbeds specified for use in site response based on properties used to develop GMC Uncertainties in damping within SMB/Interbeds incorporated into uncertainty in baserock hazard in order to minimize computation burden for subsequent analyses.
46 Crustal Earthquakes GMPEs
Primary sources of hazard from shallow crustal earthquakes are reverse and reverse-oblique faulting mechanisms for sites that may be located in the hanging wall Selected candidate models that best represent these types of earthquakes – NGAW2 models, particularly those that explicitly include HW effects Select one of the candidate models to use as the backbone Compute distribution of ground motion predictions from candidate models relative to the selected backbone model Develop distribution of scaling factors to center the backbone model and represent the distribution of ground motion predictions
47 First develop footwall model using ASK14, BSSA14, CB14, and CY14 GMPEs Compute predicted ground motions for a range of magnitudes, distances, fault dips, and depths to top of rupture Compute residuals for all of the predictions as residual = ln(PSA)_i - E[ln(PSA) for 4 NGAW2] for all 4 NGAW2 models Represent epistemic uncertainty in adjustment from CY14 by a mixed effects model
)ln( 21 FF }5.6{ MfR 2)(,1 R MccMccY }5.6{
◘ Fixed coefficients represent change from CY14 to average of selected 4 NGA West2 GMPEs ◘ Random coefficients represent variability in scale factors from individual GMPEs to average
48 Represent Distribution of Scale Factors Discretely
Use period independent scale factors for T <= 2 seconds ◘ Scale factors nearly period independent for periods that contribute to hazard ◘ Allows use of a common Vs-kappa correction Use 9-point approximation of 2-D Gaussian distribution Account for correlation between random scale factor and random adjustment to magnitude scaling
49 Resulting Footwall Models
50 Develop Hanging Wall Adjustments
Use ASK14, CB14, and CY14 HW factors
Compute average scale factor for RJB = 0 sites as difference between mean HW factor [in lnPSA)] and CY14 HW factor Model HW adjustments with function form
HWadjustment p4 5 coshln)cos(1 6 X pRpp 7 0),/max(ln( Compute coefficients for mean adjustment and sigma of adjustments ◘ Add the mean adjustment to the mean FW adjustment ◘ RSS the HW sigma and the sigma of fitting the mean adjustment in with the FW random C1 component
51 Crustal GMPE Logic Tree
52 Subduction Zone GMPE
Selected backbone model BC Hydro model (Abrahamson et al., 2014) ◘ Developed as part of a SSHAC Level 3 study as a response to shortcomings of existing relationship ◘ Global dataset ◘ Includes epistemic uncertainty in magnitude scaling ◘ Includes forearc/backarc scaling
53 Modifications to BC Hydro GMPE to Address Ground Motions at Large Distances
Modify dataset ◘ Re-evaluate censoring of data ◘ Additional data (KiKnet, Arango et al. for Central America, Maule EQ) ◘ Remove Taiwan data for sites where forearc/backarc is unknown ◘ Use Arango et al. data for El Salvador Earthquake ◘ Exclude Tohoku mainshock and aftershocks . Attenuation rate at high frequencies is high – low motions at large distances . Still used to constrain epistemic uncertainty in large-magnitude scaling
54 Modifications to BC Hydro GMPE (2 of 2) Modify functional form controlling anelastic attenuation Assess modified model coefficients applying higher weight to data at distances > 200 km Include forearc/backarc scaling uncertainty ◘ Nisqually earthquake data from Hanford site consistent with BC Hydro backarc attenuation predictions ◘ Regions other than Japan do not show clear difference in forearc/back arc, but data is often limited ◘ Numerical simulation based model of Atkinson and Macias (2009) derived using a Q model similar to that of Phillips et al (2014) for the Cascadia-Hanford travel path show low attenuation similar to BC Hydro Forearc model
55 Subduction Zone GMPE Logic Tree
56 Adjustments to Hanford Baserock Conditions
For Crustal GMPE adjust for Vs and kappa For Subduction zone GMPE adjust for Vs only Vs and Vs-kappa adjustments made using the Inverse Random Vibration Theory Approach of Al Atik et al. (2013)
57 GMC, Focus Area 2a: Provide additional detail on the Vs-Kappa corrections applied to the scaled backbone GMPEs - Rational for not applying a kappa correction for the subduction zone GMMs Hazard sensitivity analyses indicated that the distant, large magnitude Cascadia subduction zone interface (CSZ) earthquakes primarily contribute to the hazard at low frequencies where the effects of kappa are small Because of the large distance to the CSZ (>200 km), the effects of Q are expected to dominate over the effects of kappa. Therefore, incorporation of uncertainty in Q was the focus Because the subduction zone GMMs are defined primarily by data at large distances, separation of kappa effects from Q effects in the host GMMs is difficult.
58 GMC, Focus Area 1 (1 of 10) Provide additional detail on the process used to define the target site kappa values and their uncertainties, including the rationale for logic tree weightings.
Utilize recordings of small earthquakes from 6 sites located on basalt or a few meters of soil over basalt to assess kappa for basalts ◘ Some sites located on SMB with interbeds, some on outcropping layers of deeper basalts Apply alternative approaches to estimate site kappa and its uncertainty ◘ Inversion of Fourier spectra of recordings ◘ Anderson and Hough (1984) Apply kappa estimates in forward sense considering uncertainty in contribution of deeper sediments to kappa for large earthquakes
59 GMC, Focus Area 1 (2 of 10): Target site kappa
Target kappa logic tree ◘ Uncertainty in Vs profile ◘ Alternative approaches ◘ Uncertainty in estimates from each approach ◘ Uncertainty in depth range contributing to kappa for larger earthquakes
60 GMC, Focus Area 1 (3 of 10): Target site kappa
Alternative Vs Profiles ◘ Differ in SMB Vs ◘ Differ in subbasalt sediment Vs ◘ Favor Profile 1 2:1 over Profile 2 – prefer downhole Vs measurements over suspension logging in basalt ◘ Difference in subbasalt Vs had small impact on assessments
61 GMC, Focus Area 1 (4 of 10): Target site kappa
kappa estimated by inversion ◘ Used recordings from 15 earthquakes recorded in 2005 to 2013; 10 recordings at HAWA from 2004 study ◘ Hypocenter depths ≥ 5 km to avoid double paths ◘ accelerograph recordings at HAWA; all other recordings were on BB velocity instruments
Inversion process estimates kappa along with source (fC) and path (Q) parameters by nonlinear least-squares fit to FAS using point- source model ◘ Q(f) was fixed at 500(f)0.6 due to limited distance range and limited bandwidth
◘ Determined parameters: fC, kappa
62 GMC, Focus Area 1 (5 of 10): Target site kappa
Assessed correlation of kappa assessed from inversion with: ◘ Thickness of SMB ◘ Total thickness of interbeds ◘ Thickness of subbasalt sediments Conclusion that entire profile above basement contributed to kappa from the small, deeper earthquakes
63 GMC, Focus Area 1 (6 of 10): Target site kappa
Anderson and Hough (1984) approach: ◘ Select data for R < 200 km that show linear trend in FAS at high frequencies ◘ Select frequency window for linear trend ◘ Smooth FAS and noise with Konno and Omachi (1998) filter ◘ Select records with signal to noise ratio > 3 ◘ Estimate kappa by fitting
a(f)=A0exp(-πκf) ◘ Extrapolate trend with distance back to 0 distance
64 GMC, Focus Area 1 (7 of 10): Target site kappa
Assess site kappa removing effects of shallow soils and scattering from SMB interbeds ◘ Soil kappa assessed using Campbell (2009) ◘ Scattering kappa assessed by comparing response of an equivalent uniform Vs profile with damping to layered profile without damping Assuming Qs = γVs develop estimates of γ to assign kappa to SMB and to deeper layers ◘ Based on κ = H/Vs/Q
65 GMC, Focus Area 1 (8 of 10): Target site kappa
Favored inversion over A&H 2:1 ◘ Based on fit of broader frequency range of FAS ◘ A&H produced variable assessments of Qs ◘ Application of A&H method required use of shallow earthquakes with potential multiple paths Epistemic uncertainty in A&H kappa assessed based on statistics of fit Epistemic uncertainty in Inversion kappa based on assessments of parametric variations in inversion parameters ◘ Produced an asymmetric distribution ◘ In addition, best estimate kappa based on Q(f) larger than Phillips et al. (2014), thus may be biased high. Weights adjusted to account for potential bias (lower Q would lead to lower kappa)
66 GMC, Focus Area 1 (9 of 10): Target site kappa
Final component – depth extent of subbasalt sediment contribution ◘ Results for small, deep earthquakes indicates all of sediments ◘ No data available to assess contribution for shallower earthquakes or large earthquakes ◘ Considered three equally weighted alternatives All, half, or none
67 GMC, Focus Area 1 (10 of 10): Target site kappa
Resulting baserock kappa distribution
68 GMC, Focus Area 2b: Provide additional detail on the Vs-Kappa corrections applied to the scaled backbone GMPEs - Comparison of the Vs-kappa scaled median GMPEs and NGA-West 2 models
M 7, Rrup 11 km, HW ◘ Red curve - Median Crustal
for VS30 760
◘ Black curves – Median PSA Crustal scaled by Vs-kappa corrections 0.01 0.05 0.10 0.50 1.00 5.00
0.01 0.05 0.10 0.50 1.00 5.00 10.00
Period
69 GMC, Focus Area 2c: Provide additional detail on the Vs-Kappa corrections applied to the scaled backbone GMPEs - Whether any observational data from the region was used to assess the Vs-kappa corrected GMPEs
Available ground motion data from small crustal earthquakes in the region recorded on basalts or shallow soil over basalt were used to assess kappa Recorded crustal earthquake data is generally from earthquakes too small to make meaningful comparisons with the developed GMPEs Data from the M 6.8 Nisqually earthquake was used to assess attenuation from distant CSZ earthquakes
70 Aleatory Variability Model
Utilized single station sigma concept Development very similar to that of the SWUS model with similar results Specified minimum level of epistemic uncertainty in characterizing site response to address: ◘ Lack of variability in site response at very low frequencies ◘ Possible basin effects in surficial sediments at intermediate periods
71 GMC, Focus Area 3: (1 of 5) Provide additional discussion regarding bases for bump seen at T=0.1sec in the mean tau values for the NGA-West2 models and the decision for smoothing through this peak in developing single-station sigma.
A peak in the event-to-event variability (τ) is commonly seen in the results of analyses of empirical strong motion data τ is a measure of the differences in the average motions from earthquake to earthquake ◘ May be due to source differences ◘ May be due to differences in average site conditions for each earthquake Possible mechanisms for peak explored ◘ Using point-source stochastic simulations ◘ Examination of data from limited geographical regions
72 GMC, Focus Area 3: (2 of 5) Bump in τ at T=0.1sec.
Performed point-source stochastic model simulations ◘ Random variation in stress parameter (stress drop) ◘ Random variation in site κ Simulated motions ◘ 200 earthquakes with lognormally distributed stress drops ◘ For each earthquake, ground motions at 25 sites with lognormally distributed site κ ◘ Fit results with mixed effects model to compute variance components τ and ϕ Two cases analyzed ◘ No correlation in site κ between earthquakes –- produces a peak in ϕ (within event variability) but not in τ ◘ Half of the variance is assigned to event-to event variability in median κ and remaining to within-event site-to-site variability in κ –- produces a peak in both τ and ϕ
73 GMC, Focus Area 3: (3 of 5) Bump in τ at T=0.1sec.
Results of fitting mixed effects model to simulations
74 GMC, Focus Area 3: (4 of 5) Bump in τ at T=0.1sec.
Fits to CY14 residuals for only California data Inclusion of site- to-site variability term shifts peak at 10 Hz from τ to ϕS2S for M < 5.5 Less conclusive for larger M, but limited data from sites recording multiple earthquakes
75 GMC, Focus Area 3: (5 of 5) Bump in τ at T=0.1sec.
Conclusion – peak in τ near 10 Hz (0.1 s) likely due to differences in average site conditions from earthquake to earthquake rather than variability in earthquake source properties Uncertainty in site effects for Hanford sites is explicitly addressed in development of GMC model Therefore, peak in τ is smoothed through in developing aleatory variability model
76 Provided Recommended Vertical/Horizontal Spectral Ratios for Development of Surface Vertical Spectra
Gulerce and Abrahamson (2011) modified at long periods to match trends in data from the Maule earthquake
77 Baserock Hazard Results at Site C - CGS
78 Source Contributions
79 Contributions to Uncertainty (1 of 2)
80 Contributions to Uncertainty (2 of 2)
81 Development of Input Motions for Site Response
Deaggregated mean hazard at each frequency Developed 4 scenarios to represent deaggregation M, R and weight of event varies Developed conditional mean spectrum for each scenario
82 CGS Site Response
Farhang Ostadan, Bechtel Robert Youngs, Amec Foster Wheeler Site Profile
Site profile consists of two zones: 1. Upper sands and gravels (525 ft thick) 2. Sequence of basalt flows (765 ft thick) to top of Lolo Flow Sand and gravel properties based on FSAR data Basalt flows characterized in PSHA study Simulated profiles generated for each zone and then joined
Labeled depths not for CGS
84 Upper Sands and Gravels Profile
Velocities obtained by cross- hole and down-hole measurements at CGS (formerly WNP-2) and nearby WNP-1 and WNP-4 Considered:
◘ one velocity profile with σln 0.15 to 0.30 ◘ EPRI and Peninsular Range (PR) nonlinear curves (D ≤ 15%)
85 Site response, Focus Area 1a Provide additional detail regarding the bases for only a single profile for the upper 525 ft.
The geology and depositional processes are also known from the nearby DOE facilities in Hanford (e.g. WTP) The soil properties, specifically shear-wave velocity data, are consistent with the soil type and density The distinctive velocity profile in the top 525 ft is common to the 3 adjacent sites (CGS, WNP-1 and WNP-4) Similar Vs measurements were obtained using different methods with different instruments (cross-hole & down-hole) Seismic refraction measurements agreed well with cross-hole measurements in the top 105 ft at CGS Given the relatively small amount of variation among the measured results, there is a high degree of confidence that any additional measurements would fall close to the base case Vs profile (i.e., low epistemic uncertainty) The variation in soil velocity is adequately covered by consideration of the aleatory uncertainty
86 Site response, Focus Area 1d Provide additional detail regarding the adequacy of EPRI and Peninsular curves for covering range of nonlinear behavior for the Pasco Gravel.
As recommended by the SPID, the EPRI and Peninsular Range curves were used These two sets of nonlinear curves are considered to span the range of nonlinearity for cohesionless soils More recent RCTS data (from other sites) often confirm the adequacy of generic curves for sands and gravels The generic curves were considered appropriate for screening analyses
87 Basalt Flows Profile
Provided by PSHA study Velocities measured with PS logging and Downhole (DH) methods ◘ Two alternative profiles ◘ Weighted 2:1 (DH:PS) Nonlinear curves for interbeds computed with Darendeli (01) (D ≤ 15%) Site attenuation (κ₀) calibrated by recordings
88 Site response, Focus Area 1b Provide additional detail regarding the bases for two Vs profiles and their associated weights for the SMB stack.
For interbeds, DH and PS Vs values in agreement For basalts Vs from PS ~25% higher than Vs from DH Two Vs profiles created to capture epistemic uncertainty in basalt Vs Vs based on DH favored 2:1 over Vs based on PS ◘ DH Vs measured a frequencies near those of interest while PS Vs measured at 1 kHz ◘ Experts suggested that reliable PS values in stiff basalts may require use of 5-10 kHz frequencies
89 Site response, Focus Area 1c (1 of 2) Provide additional detail regarding the thickness of the interbed deposits including their lateral extent.
Based on numerous deep borings, thickness and extent of Ellensburg Formation interbeds mapped across Hanford site Example for Mabton interbed from Rohay and Reidel (2005)
90 Site response, Focus Area 1c (2 of 2) Provide additional detail regarding the thickness of the interbed deposits including their lateral extent
Deep wells used to develop SMB stratigraphy at Site C (CGS). Details are in Last (2014) Uncertainty/variability in thickness was included in randomization of layer thicknesses
HSPSHA Fig. 7.11
91 Site response, Focus Area 1e Provide additional detail regarding the bases for randomizing the small strain damping for the basalt layers in the SMB stack in view of the uncertainty already incorporated into the determination of the site kappa.
Randomization is used to address ◘ Uncertainty in properties due to measurement error and extrapolation from other locations ◘ To characterize spatial variability within the facility footprint. ◘ To compensate for simplifications used in conventional 1-D site response analysis methodology Randomization would be applied in SPID methodology even if median properties were known with a high degree of certainty
92 Site response, Focus Area 2 In view of the relatively high shear wave velocities (> 760 m/s) and high confining stresses in the interbed layers, provide the rationale for not considering linear behavior of these materials and instead using a single sand curve which demonstrates significant non-linear behavior.
Interbeds are relatively soft rock-like materials even at depth ◘ Vs < 1000 m/s Some degree of non-linearity expected in such materials at high loading levels, especially because of the large velocity contrasts with the basalts and resulting strain concentrations. Selected the Darendeli (2001) model because it provided a means of incorporating the effect of depth of the interbeds on the G/Gmax and damping relationships. Used only one set of curves with randomization because differences in average response between using alternative sets of median relationships expected to be much smaller that overall uncertainty in defining site ground motions developed for the GMC.
93 Simulated Profiles
94 Input Motions
PSHA study provided CMS motions at: ◘ 20 frequencies ◘ 27 MAFEs ◘ 4 events M, R and weight of event varies Site response computed for each motion
95 Site Response Analysis
Total of 2,160 input rock spectra Two velocity profiles: 1. C1 (downhole) 2. C2 (PS logging) Two nonlinear models for the upper zone: 1. EPRI 2. PR Total of 518,400 soil column analyses
96 Site Response
Performed with PSHAKE ◘ Uses random vibration theory (RVT) ◘ Equivalent-linear wave propagation Control point defined at surface Extracted the site amplification values at the controlling frequency of the CMS motion
97 1D Site Amplification
98 1D log Mean Site Amplification
99 GMRS – Approach 3 Approach 3 (Bazzurro and Cornell, 2004): | |
Gz(z) = Horizon specific hazard curve
px(xj) = probability of rock input level (i.e., slope of input hazard curve) | | | | where 1 is the complementary standard Gaussian CDF
| ) = mean amplification factor
| = sigma of amplification factor
100 GMRS – Approach 3
Input Hazard Curves from PSHA Input Site Amplification Results ◘ Two Profiles: • Profile C1 (0.67) • Profile C2 (0.33) ◘ Two Material Curves: • EPRI (0.5) • Peninsular Range (0.5) No Minimum Amplification Factor
101 Hazard Curves: PGA
102 UHRS: Mean, AEP=10-4
103 UHRS: Mean, AEP=10-5
104 Surface UHS and GMRS
105 Site response, Focus Area 3 Provide additional detail regarding the decision not to implement a minimum site amplification value and the effect of this decision on the development of the uncertainty in the site amplification function as well as on the final hazard curves for the site.
The 0.5 limit is not used in the calculation of the surface hazard because the intended purpose of this report is to obtain the realistic and unbiased median based site amplification for SRA The basis for limitation of 0.50 is not well documented and is more relevant for additional conservatism under design applications
106 Interim Actions and Evaluation Dave Swank Michael Kennedy Energy Northwest Interim Actions – FLEX strategy
Columbia has significant flexibility for connection of portable electrical supplies following a seismic event ◘ Two portable 480 VAC diesel generators on-site ◘ Two redundant 480 VAC connection points to two safety divisions ◘ One additional 480 VAC connection point to either of two safety divisions ◘ 4160 VAC diesel generators available through SAFER ◘ Two 4160 VAC connection points to two safety divisions ◘ One additional 4160 VAC connection point capable of supplying either safety division ◘ Installed breakers and cabling allow safety divisions to be cross-tied if needed
108 Interim Actions – FLEX strategy
Columbia has significant flexibility for connection of portable pumps to supply cooling water to the core and suppression pool ◘ Two portable diesel powered pumps (high head) available onsite ◘ Injection points available on all three divisions of Residual Heat Removal (RHR) ◘ High capacity pump available through SAFER ◘ Injection point available on the Condensate system ◘ Connection points on the both divisions of Standby Service Water (SW) with piping cross-connected to RHR ◘ Inventory source is the normal plant ultimate heat sink (two SW spray ponds)
109 Interim Evaluation – Seismic
Current Seismic Probabilistic Risk Assessment (SPRA) - Mean Seismic Core Damage Frequency is calculated to be 4.9 x10-6 ◘ Based upon a hazard curve developed in terms of peak ground acceleration (PGA) and fragilities in terms of PGA ◘ Current SPRA maintained in alignment with the RG 1.200-compliant Internal Events modeling and is significantly advanced beyond IPEEE requirements ◘ Reanalysis of Mean Seismic Core Damage Frequency at PGA using new ground motion response spectrum indicates margin remains Seismic walk downs completed satisfactory as required by Enclosure 3 of the NRC’s CFR 50.54(f) Request for Information ◘ All results satisfactory
110 Path Forward
Energy Northwest is initiating the Expedited Seismic Evaluation Process ◘ Report due Jan 2016 Energy Northwest is initiating SPRA in accordance with SPID requirements ◘ Submittal due Jun 2017
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