New Plant Seismic IssuesResolution Program

presented to

USNRC

byR. P. Kassawara, EPRI

May 25, 2005

I~r.Ir-.I

Industry Goal

* Resolve generic issues in a timeframe to supportAdministration goals for nuclear power expressed in NP2010

* Change regulatory guidance, where necessary

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Purpose of Meeting

Discuss:

9 Industry resolution plan for new plant seismic issues

• Approach for addressing high frequency issuer

* Seismic hazard improvement tasks

" Revisions .to regulatory guidance

" Industry/NRC interactions

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Seismic Issues

Experience/concerns with RG1.165- Method is based on a reference relative hazards

probability, not a performance-based (safety-based)approach

- Potential for regulatory and technical instability- Process likely to deter many utilities from applying for

ESP or COL* Eastern U.S. ground motion spectra include a high frequencyc-V,

component that is non-damaging but can exceed certifieddesign spectra in the high frequency region

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Resolution Plan

* Evaluate alternate Performance - Based methods fordetermination of site spectra

* Incorporate other technology advances in PSHAimplementation

• Resolve the high frequency issue

* Propose revision to R.G. 1.165 and SRP 2.5.2 (NUREG 0800)

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Project Organization

" Project Management/Technical Lead

- EPRI R. Kassawara

* Industry Oversight - NEI, Seismic Issues Task Force

" Technical coordination

- Bill Schmidt, MPR

*Technical Review and Advisory Group (TRAG)1f1&4&'

- Bob Kennedy, Consultant

- Carl Stepp, Consultant

- Orhan Gurbuz, Consultant

- Don Moore, Southern Co.

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* Task Leads

- G1.1 Risk Engineering R. McGuire

-G1.2 ARES Corp. G. Hardy

- G1.3 N. Abrahamson, C. Stepp

-S2.1 ARES Corp. G. Hardy

G. Hardy- S2.2 ARES Corp.

- 11.1 C. Stepp

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Industry Program

" Demonstrate generic applicability of ASCE/SEI 43-05 -Task G1.1

" Improve seismic hazard estimation methodology to reflecttechnology advances - Tasks G1.2, G1.3

" Update and improve methods for addressing non-damaging high frequency portion of ground motionspectra - Tasks S2.1, S2.2 C c ;>e-

" Develop proposed revisions to RG1.165 and NUREG0800 -Task 11.1

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Task G1.1 Performance Based Methods

" Update EPRI hazard results at 28 sites to reflect latest"codes, attenuation relationships, updated seismicsources and ground motion model

" Compute performance-based seismic spectra for thesesites using ASCE/SEI 43-05- voa '..,, & /P f,'

" Demonstrate generic applicability of performance-based methodology- k-17

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Task G1.2 - Lower Bound Magnitude

" Choice of lower bound magnitude (LBM) has major impact oncomputed hazard levels, especially for higher frequencies

" Task will study- New observations of damage to industrial facilities and

nuclear plant assessments to support a revised LBM.- New data on Cumulative Absolute Velocity (CAV) to

provide the basis for the LBM distribution* A realistic LBM distribution would reduce hazard consistent

with realistic damage potential of small earthquakes

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Task G1.3 - Truncation of Lognormal.Distribution of Variability on Median GroundMotion

* Current hazard analyses model variabilitywiunbounded lognormal distribution of variability (i.e.,aleatory uncertainty)

" Practice of using an unbounded distribution is unrealistic;however, no consensus bound exists

" Task objective is to define rational, defendable bound onvariability (e.g., point where variability deviates fromlognormal distribution)

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Tasks S2,1 and S2.2 - Treatment of HighFrequency (HF) Motions

" Analytical and observational data show that ground motionspectra for CEUS sites will contain high spectral accelerationsat high frequencies (i.e.- over - 10 hz), but the HF content hasnegligible damage potential

" Objectives of tasks S2.1 and S2.2 are to develop genericmethods for accommodating HF motions considering

Effect of seismic wave incoherence (S2.1), and

Effect of limited inelastic behavior on response to HF inputmotions (S2.2) re/ 4,

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Task 11.1 - Revision to Regulatory Guidance

Based on results of above tasks:

• Develop proposed technical revisions to RG 1.165 toidentify and characterize seismic sources and determinesite-specific Safe Shutdown Earthquake Ground Motion

• Develop proposed technical updating of the NRC SRP(NUREG-0800) Section 2.5.2, Vibratory Ground Motion toincorporate the updated RG and other technical advancesin seismic design ground motion evaluations, including highfrequency ground motion issues

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Schedule

" Completion of Task G1.1 by July 2005

" Completion of other G and S tasks by end of 2005

*Completion of Task I1.1 (Industry input to NRC) in 2006& ..--- -- '--

OP e~ A6

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3. Industry Program for Resolution of HF Issues

New Plant Structural Tasks

S2,1 & S2.2

Greg HardyARES CorporationMay 25, 2005

IC.-1=1

New Plant Structural Tasks

* Background on Reduction of High Frequency Portionof SSE Ground Motion

1) EPRI New Plant Structural Tasks0 S2.1 Effect of Seismic Wave Incoherence0 S2.2 Negligible Inelastic Behavior Results from

High Frequency Input Motion

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Background: CEUS Ground Motion

Observations of strong ground motion due to smallmagnitude earthquakes occurring in eastern NorthAmerica

- Did not cause damage to engineered structures- Exhibit considerably higher PGAs than would have

been expected based on WUS experience wky

- Response spectral. ordinates appear to be richer inhigh frequency energy, particularly for frequenciesgreater than about 10 Hz

* New SSE Spectra Present Issues* SSE high frequency beyond Advanced Reactor Design

qualification level

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Hypothetical Site specific response spectrafor Soil Site

1

0.9

0.8

0.7

S0.6

0.5

CO 0.4

0.3

0.2

0.1

00.1 1 10

Frequency, Hz

100

rk Copyright © 2004 Electric Power Research Institute, Inc. All rights reserved. C-I~I2I

Hypothetical Site specific response spectrafor Rock Site

1.6

1.4

1.2

1

.2

. 0.8

• 0.6

0.4

0.2

0 4

0.1 1 10

Frequency, Hz

100

r -- Copyright © 2004 Electric Power Research Institute, Inc. All rights reserved.

Background: Development of EngineeringDesign SSE Response Spectrum

* Development of Site Specific UHS

- Utilize ground motion relationships for CEUSconditions

- Characteristic high frequency content in the regiongreater than 10 Hz

* Convert to Risk-Consistent Site-Specific Spectrum(ASCE 43-5)

" Generate Engineering Design SSE- Consideration of Incoherency Effects- Consideration of High Frequency Inelastic

Deformation Effects

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Past Studies on Incoherenceand High Frequency In-Elastic

Deformation Effects

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Prior Incoherence Studies

* NUREG/CR-3805, "Engineering Characterization ofGround Motion" , Vols. 1-5, 1986 developedrecommendations to account for incoherence

* Response spectrum reduction factors weredeveloped as function of foundation plan dimensionand frequency

* These recommendations were incorporated intoEPRI NP-6041, "A Methodology for Assessment ofNuclear Power Plant Seismic Margin", 1991 and alsoDOE Standard 1020-1994

* Since the original publication of theserecommendations there have been several newsources of data on incoherence

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Damage Effectiveness of High FrequencyAccelerations

Several EPRI studies have dealt with this issue:- NP-5930, "A Criterion for Determining Exceedance of theOperating Basis Earthquake, 1988.

- NP-7498, "Industry Approach to Seismic Severe Accident PolicyImplementation", 1991

* These studies document the damage thresholds to structuresand equipment as determined by high frequency events suchas blasting, shock testing, and operational vibration

* One study, TR-102470, "Analysis of High-Frequency SeismicEvents", 1993, investigated an analytical basis for reduction ofhigh frequency response of building mounted equipment byconsidering the effects of in-elastic deformation

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Simplified Procedure for Equipment Models

* TR-1 02470 developed a simplified analysis procedure to reducethe ground motion to account for negligible inelastic responseresults from high frequency input motion

* This reduced level of input motion does not represent an actualreduced ground motion but is rather a Damage ConsistentMotion which results in negligible inelastic motion for acomponent designed to the reduced input level applied to anelastic building model

* Engineering Design SSE Spectra can be generated whichincorporate reductions due to both ground motion incoherencyand component in-elastic deformation in the high frequencyregion

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Exampme Reductions for Incoherence andInelastic Deformation

Example High Frequency Horizontal Ground Motion Spectra

0.5

0.45 -

0.4

0.35 -

5% Damping

-SAh Ground Motion Spectrum

-SAh x Rs, Incoherence Redued Spectrum

-Sah x Rs/Fu, Incoherence and In-ElasticDeformation Reduced Spectrum

0.3 +

CO,0.25 +

0.2 +

0.15

0.1

0.05 --

00

Aýý

10 20 30 40 50

Frequency, Hz

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60

C-II2i

New Plant Structural Tasks

S2.1 Effect of Seismic Wave Incoherence

S2.2 Effect of Limited Inelastic Behavior

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New Plant ESP Structural Task S2.1

Effect of Seismic Wave Incoherence onFoundation and Building Response

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Motivation for S2.1 Task

" Background

- Ground motion is measured at a point; studies show thatcoherent motion input to reasonable size structures is less thanat a single point

- Structures respond effectively to coherent input motion" Prior High Frequency Response Considerations Used Early

(limited) Incoherence Data* New research effort required to properly address incoherency

- Generate new coherency function based on all current data

- Develop factors to reflect the incoherency effects onfoundations/structures similar to those being considered forAdvanced Reactor purposes

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Motivation for S2.1 Task (Cont.)

Subsequent to 1993 EPRI Study, Significant NewData Exists:- Probabilistic spectra were generated for the Diablo Canyon Long

Term Seismic Program which used measured site coherencyfunctions

- EPRI TR-1 00463, "Spatial Variation of Earthquake GroundMotion for Application to Soil-Structure Interaction", 1992,presented coherency functions based on LLST array (Taiwan)data for fifteen earthquake events

- Arrays used for coherency model also include:* EPRI Parkfield* Chiba, Japan* Coalinga• UCSC ZIYA• Pinyon Flat

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S2.1 Task Objectives

" Develop a state-of-the-art representation of the coherency functionbased on the most applicable data available

• Develop reduction factors for incoherent motion

- apply to the Fourier amplitude spectrum- develop an effective low-pass digital filter

* Perform sensitivity analysis which compare applying reductionfactors to the free-field motion, the base mat motion, or the floorresponse motion

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Task S2.1 - Effects of Seismic WaveIncoherence

" Task will assess recent data and develop incoherencecorrections- Dr. Abrahamson to develop coherency function- ARES to develop incoherence corrections

" Task Status- Initial team meeting April 7, 2005- Coherency function developed- TRAG meeting for review and comment April 21

- ARES developing structural response code withincoherence function and structural models

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Coherency Function for. Horizonta a GroundMotion

Coherency as a Function of Frequency & Separation Distance

0L)

1.000

0.900

0.800

0.700

0.600

0.500

0.400

0.300

0.200

0.100

0.000

I

0 10 20 30 40 50

Frequency (Hz)

- 10 meters - 50 meters - 100 meters

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C~oherency Function for Vertical GroundMotion

Coherency as a Function of FrequencyA& Separation Distance

0L)

1.000

0.900

0.800

0.700

0.600

0.500

0.400

0.300

0.200

0.100

0.000

0 10 20 30 40 50

Frequency (Hz)

I-- 10 meters - 50 meters - 100 meters

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Subtasks for Task S2.1

" Define coherency function and program function into seismic response code" Define the parameters to be included in the seismic response analyses

- site conditions- ground motion characteristics- foundation characteristics- structure characteristics

" Conduct SSI analyses (CLASSI with surface supported rigid behavingfoundations will be used since incoherence is a surface wave phenomena;embedment also reduces high frequency response but is a separatephenomena)

" Develop the reduction factors as a function of foundation size and frequency* Conduct sensitivity studies

- Upper Bound on Coherency Function- 2000 m/s apparent wave velocity

- SASSI Verification Analyses (Bechtel)

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Status/Schedule of S2.1 Tasks

* Coherency function defined (report in process)

* Programming function into CLASSI in process* Parameters for response analysis defined

- Site conditions (soil site and rock site)

- Ground motion characteristics representative of ESP sites- Foundation characteristics representative of Advanced

Reactor Designs

- Structure characteristics representative of AdvancedReactor Designs

* Development of reduction factors in June/July

* Sensitivity Studies in August/September* Final Report in November

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New Plant Structural Task S2.2

Negligible Inelastic Behavior Caused byHigh Frequency Input Motion

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New Plant Structural Task 2.2

* Primary PurposeTo develop reduction (KD) factors to apply tothe high frequency portion of ground responsespectra to conservatively account for the factthat typical power plant equipment andstructures are not damaged by high frequencymotions (i.e. due to extremely limiteddisplacement demand)

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S2.2 Task Objectives

" Reassess key assumptions in TR-1 02470 Report -" Simplify the process of performing reductions" Propose qualification. requirements for high

frequency-sensitive devices" Provide clear documentation of results in an EPRI

report

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S2.2 Project Tasks

* Task 1 - Strengthen Key Assumptions

* Task 2- Develop an improved procedure for knockdown factor implementation

" Task 3 - Define limiting failure modes for nuclear plantequipment

" Task 4- Recommendations for equipment withfunctional failure modes

" Task 5 - documentation of results of S2.2 in a report

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Task 1 -Strengthen Key Assumptions

Task 1-1 Develop Examples to demonstrate thedynamics involved in high frequency response andcapacity

- Simple sliding/rocking models- Non linear inelastic response .

- The simplified models (1 & 2 DOF) used in the TR-102470 study needto be justified as conservative representations of actual equipmentresponsePerform sensitivity analyses to determine the effect of spectral shapedifferences between rock and. soil sites

* Task 1-2 Justify floor spectra amplification assumption- Utilize shear beam models- Model properties representative of New Plant designs

* Task 1-3 Justify bounding example fillet weldassumptions

- Review 0.01 inch limit displacement- Review weld performance under cyclic loading

Review weld faiI meI2Loemaaret&neafthe~e

Task 2 - Develop an Improved Procedure for KnockDown Factor Implementation

Reevaluate Simplified Method within TR-102470

- Purpose of Task 2 is to reevaluate the assumptions

- Conservatisms relate to higher frequencies (> 30 Hz)

- ESP response potentially high in the > 30 region

- Use of more rigorous methods in lieu of conservativeassumptions

* Simplify the high frequency response reduction method bydeveloping a low pass filter

Applied to Fourier amplitude spectra over the specifiedfrequency ranges

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Task 3- Define limiting failure modes fornuclear plant equipment

Small fillet weld selected as the bounding case- Welds often considered relatively non-ductile

- Original study characterized welds as bounding (lessductile) than all other equipment and structure failuremodes with the exception of some functional failuremodes

• Research Limiting Failure Modes to StrengthenAssumption

- SPRA and SMA fragility and HCLPF results- Research studies (e.g. NRC research by LANL on shear

walls)- Document a better basis for defining the fillet welds as the

appropriate bounding configuration

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Task 4- Recommendations for equipmentwith functional failure modes

* Knock down factors not appropriate for functionalfailure modes which are high frequency sensitive

- Relay chatter- Breaker trip

* Goal - develop seismic qualification requirements thatdo not require calculation of floor spectra includinglarge high frequency input

- Floor response in high frequency region not reliable

- Alternate options potentially existo Requirements for military shock and vibration

applicationso Stress screening for modern electrical components

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Status of Task S2.2

* Status- Project Plan Developed and Reviewed April/May 2005- Tasks initiated May 2005- NRC Meeting May 25

e Discuss approach

* Initiate NRC task participation- Identify NRC participant (s)- Technical Meetings in So Cal (June and August 2005)

- Draft Report November 2005

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Backup Slides

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Spatial Variation of Ground Motion

" Wave-passage effect due to difference in arrival times ofseismic waves across a foundation

" Incoherence effect or dispersion due to reflections andrefraction of waves during propagation resulting in loss ofmotion coherency across a foundation

" Local effect due to difference in local foundation soilconditions

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Analysis Cases

* Scattered incoherent rigid massless foundation input - 20 cases- 2 site conditions/ground motion- 2 foundation footprints- 3 directions - H1; H2 (rectangular fdn); V- 2 coherency. functions; NAA, coherent;- Develop knockdown factors

* SSI inertial interaction foundation & structure response - 6 cases- 1 site condition/ground motion- 1 foundation footprint- 1 structural model- 3 directions - H1; H2; V- 2 coherency functions; NAA, coherent w/knockdown factors

* Parametric Studies- 3 cases- Another apparent wave velocity (2 km/s) for one case- 84% coherency function for one case- Benchmark with SASSI (surface rigid) NAA coherency function- Embedment; foundation flexibility performed in SASSI by Bechtel and compare knockdown

factors with those of CLASSI surface rigid

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High Frequency In-Elastic Deformation Effects

" High frequency accelerations are associated with smalldisplacements

" A 0.4g response at 25 Hz will require a displacement of0.0063 inch while a 0.4g response at 5 Hz will involve adisplacement of 0.157 inch

" A small fillet weld has a yield displacement on the order of0.001 inch and the displacement at weld failure being 0.01 inch

" Thus, the 25 Hz response level is within the yield range of theweld while the 5 Hz response level has failed the weld (which isoften the source of the observed "brittle" nature of weldanchorage)

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Industry Program forImproving PSHAMethodology and UpdatingRG 1.165

J. Carl SteppConsultantEPRI Advanced Nuclear Plants' Systems

I~JI2IE: F= FF. I

Objectives

* Incorporate advances in technologies made during the past15 - 20 years into regulatory guidance- Improve probabilistic seismic hazard methodology

" Revise lower bound magnitude for hazard integration" Assess behavior of upper tail of variability on median ground

motion

- Update RG 1.165

" Update PSHAs for 28 nuclear plant sites" Implement performance based method for determining

site-specific risk-consistent spectrum

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Task G1 .2 Revise lower bound magnitudefor hazard integration

" mb 5.0 established as lower bound in the mid 1980s- Standard magnitude scale used for earthquake catalogs and

for engineering estimation of ground motion at the time

" Mw is current standard magnitude scale

" Current practice is abrupt cut-off at mb 5.0" Develop and implement a distribution on lower bound

magnitude defined in Mw- Technical advances during the past 20 years permit more

confident determination and characterization of theappropriate lower bound magnitude

- A realistic LBM distribution would result in hazard consistent withthe realistic damage potential of small earthquakes

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Task G1.3 Assess upper tail of variability onmedian ground motion

" Current practice is to model ground motion variability (epsilon)using an unbounded lognormal distribution

" Practice is known to be excessively conservative, but to date noconsensus bound on the distribution exists

* Critically important for assessment of hazard uncertainty at verylow annual non-exceedance frequencies required for nuclearplant seismic design and assessment

" Implementation of a bound on epsilon on rock will assure thatsite-specific ground motion (UHS) based on PSHA isreasonable (properly incorporates uncertainty) for the PSHAlevel (annual recurrence frequency).

* Task will implement a Senior Seismic Hazard AdvisoryCommittee (SSHAC) Level 2 assessment

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Task G1.1 Application of performance basedmethod

* Update EPRI 89 hazard results for 28 sites (those used in RG1.165, Appendix B) using updated ground motion and sourcemodels, and site response modeling approaches

* Determine site-specific design response spectra (DRS) at 5 and 10Hz using performance based method described in ASCE/SEI 43-5

* Calculate annual frequencies of plant damage for DRS 5 and 10Hz

- Using simple fragility functions => 13 = 0.3, 0.4, 0.5, 0.6- Definitions of plant damage

e Onset of significant inelastic deformation (OSID) =>HCLPF/DRS = 1.0

* Core damage => HCLPF/DRS = 1.67

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Task G1.1 Application of performance basedmethod

* Form cumulative distributions of annual frequency of OSID andcore damage

* Demonstrate that annual frequency of OSID is Consistent with thesafety of the 25 nuclear plants for which PRAs are available

* Develop technical documentation and support implementation ofperformance based method to update RG 1.165

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Industry Program toSupport Updating SeismicRegulatory Guidance

J. Carl SteppConsultantEPRI Advanced Nuclear Plants' Systems

Objective

Develop state-of-practice technical documents and supportNuclear Regulatory Commission actions to update affectedsections of seismic regulatory guidance- Regulatory Guide 1.165- NUREG-0800

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Approach

" Work with NRC staff and management to establishprocedures and a schedule of interactions to implementrevisions of seismic regulatory guidance [this meeting]

" Prepare industry technical reports supporting the scope ofproposed technical updating of the affected sections RG1.165 and NUREG-0800

" Work interactively with NRC staff in a series of meetings toimplement specific updated technical revisions

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Proposed industry technical reports

Implementation of performance based method fordetermining site-specific ground motions 4 13 el

* Technical basis for bounding the variability of ground motionabout. median estimated motions ,-1..r- <

" Technical basis for establishing a distribution on lower boundmagnitude for seismic hazard integration

" EPRI 04 Ground Motion Model for the CEUS -* Technical basis for treatment of high frequency ground

motion spectraz> Le

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Proposed industry technical reports

* Implementation of performance based method fordetermining site-specific ground motions

- Provides technical. basis for updating RG 1.165, AppendixB and other affected sections of the Guideline r.,a ,.. ,,,

Provides for Risk-Informed basis for determining designbasis ground motions across nuclear plant sites

Preserves safety consistency with the population ofcurrent operating plants and with the Commission'sdetermination that the current population of plants isadequately safe

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Proposed industry technical reports

Technical basis for bounding the variability of ground motion aboutestimated median motions

- Provides technical basis for advancing the quantification of uncertaintyin ground motion modeling in PSHA

- Provides technical basis for updating affected sections of RG 1.165and NUREG-0800

* Technical basis for establishing a distribution on lower bound magnitudefor seismic hazard integration

- Updates lower bound magnitude determination using the currentearthquake magnitude measure, Mw

- Provides technical basis for advancing probabilistic seismic hazardmodeling by using a distribution on lower bound magnitude

- Provides technical basis for updating affected sections of RG 1.165

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Proposed industry technical reports

• EPRI 04 Ground Motion Model for the CEUS- Updates ground motion modeling incorporating technical

advances made during the past 12 years- Provides a model that incorporates current epistemic and

aleatory uncertainty of the informed scientific community- Model derived using current state of practice for

assessing uncertainty - SSHAC Level 3- Uncertainty assessment fully suitable for implementation

in PSHA- Generic implementation will stabilize ground motion

modeling for PSHA and nucFear plant siting into the future

- Provides technical basis for revising affected sections ofRG 1.165 and of NUREG-0800

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Proposed industry technical reports

Technical basis for treatment of high frequency groundmotion spectra- Provides transparent technical basis for treatment of high

frequency components of response spectra, which havenegligible potential to cause damage to nuclear plant-tructLres, systems and components

- Provides technical basis for updating affected sections ofNUREG-0800

- Generic acceptance will contribute significantly to thestability of nuclear plant seismic regulation

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NRC Technical Reports

* Update affected sections of NUREG-0800 and RG 1.165considering- NUREG/CR-6728: Technical basis for revision of

regulatory guidance on design ground motions: hazard-and risk-consistent ground motion spectra guidelines, and

- NUREG/CR-6769: Technical basis for revision of

regulatory guidance on design ground motions:rý 1,( 1, 2.,•development of hazard- and risk-consistent seismic

spectra for two sites* Technical guidance for assessing site-specific hazard- and

risk-consistent seismic design spectra

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Proposed NRC-industry meetings toimplement specific updated technicalrevisions of seismic guidance

* Mid October 2005- Review technical basis for updating RG 1.165

implementing the performance based method for derivingsite-specific SSE ground motions

- Review proposed technical updating of the affectedsections of RG 1.165 and NUREG-0800 incorporatingtechnical advances provided by the results of:e NUREG/CR-6728e NUREG/CR-6769, and

* EPRI TR-1 009684- the EPRI 04 Ground Motion Model

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Proposed NRC-industry meetings toimplement specific updated technicalrevisions of seismic guidance

* Late February 2006- Review proposed technical updates of affected sections

of RG 1.165 and NUREG-0800 based on technicaladvances for:* bounding the variability of ground motion about median

estimated motions

9 establishing a distribution on lower bound magnitude forseismic hazard integration

* treatment of high frequency ground motion spectra

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'7e-

1.o4

-f~ c e, 5' (0A)'~~~-'4e~~~~~ýt bý o liL't f 4-~ '~.~