METHODS(&(USE(OF(PROBABILISTIC(SEISMIC(HAZARD(ANALYSIS( …

METHODS & USE OF PROBABILISTIC SEISMIC HAZARD ANALYSIS

IN US NUCLEAR POWER PLANTS

Dr. Annie Kammerer, PE Pacific Earthquake Engineering Research Center, UC Berkeley

Annie Kammerer ConsulLng

Korean Atomic Energy Research InsLtute April 2015

Acknowledgements to : Dr. Kevin Coppersmith, Dr. Julian Bommer, and Dr. Jon Ake

ProbabilisLc Seismic Hazard Analysis (PSHA)

¨ Method for assessing seismic load ¨ ObjecLve is to determine the best esLmate (and associated uncertainty) of ground moLon levels at a parLcular locaLon over Lmes periods of interest

¨ PSHA considers all possible earthquakes from all seismic sources that may impact a site, and accounts for the likelihood of any parLcular earthquake

2

Design Level & Total Hazard 3

SPRA

Seismic Load Capacity Seismic MoLon Parameter

Freq

uency of Exceedance

Pi

Seismic MoLon Parameter

Cond

iLon

al Probability of Failure

i

Systems Analysis

Event trees, Fault trees, Containment Analysis

Assessing Hazard & Risk 4

Early AEC Seismic Hazard

¨  Early seismic hazard assessments under the Atomic Energy Commission were for a Design Basis Earthquake (DBE), which was determinisLc with standard spectral shapes Led to a peak ground acceleraLon (PGA) based on past earthquakes in the region (and a lot of expert judgment).

5

NRC Seismic Hazard RegulaLons

¨  In 1971 the NRC established General Design Criteria (GDC 2), which required that SSCs important to safety be designed to withstand the effects of natural phenomena with “appropriate consideraLon of the most severe of the natural phenomena that have been historically reported for the site and surrounding region with sufficient margin for the limited accuracy and quan?ty of the historical data and the period of Lme in which the data have been accumulated” (Appendix A to 10 CFR Part 50). Codifies seismic design & requires consideraLon of uncertainty.

6

NRC Seismic Hazard RegulaLon

¨  In 1973, Appendix A to 10 CFR Part 100, “Seismic and Geologic Si?ng Criteria for NPPs” was established to provide detailed criteria to evaluate the suitability of proposed sites and the suitability of the plant design basis established in consideraLon of seismic and geological characterisLcs. Codified minimum standards for site and hazard evaluaLon and site suitability.

¨  In 1996, the NRC issued 10 CFR Part 50 Appendix S defines SSE as “Safe-‐shutdown earthquake ground mo5on is the vibratory ground moLon for which certain structures, systems, and components must be designed to remain funcLonal” Provides performance-‐based requirement for ground moLon that replaces the determinisLc DBE

7

Current Risk-‐Informed Design Guidance

¨  In 1997 NRC was issued a commission direcLve to move towards “Risk Informed” policies.

¨  1997 issuance of RG 1.165, which was the first seismic hazard guide based on probabilisLc techniques.

¨  2007 NRC issued RG1.208, based on PSHA and developed for use with ASCE 43-‐05 ¤  RG1.208: A Performance-‐Based Approach to Define the Site-‐Specific Ground MoLon

¤  ASCE 43-‐05: Seismic Design Criteria for SSCs in Nuclear FaciliLes

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Recent Seismic Hazard Re-‐evaluaLon

¨  In mid-‐2000s interest was renewed in new NPPs and the NRC received 3 Early Site Permit (ESP) applicaLons for reactors to be co-‐located at exisLng sites. ¤ North Anna, Vogtle, and Calvert Cliffs

¨ Based on the difference in the new PSHA data and the DBEs for the exisLng reactors, NRC Staff iniLated Generic Issue (GI) 199.

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Recent Re-‐evaluaLon

¨ GI-‐199 was a program to reevaluate seismic hazard and risk for central & eastern US NPPs

¨ Prior to Fukushima, the NRC performed and published an iniLal screening required to show that GI-‐199 met program criteria (risk-‐significant changes to mulLple NPPs)

¨ Ajer Fukushima GI-‐199 was extended to all NPPs. GI-‐199 the became part of the Fukushima NTTF recommendaLon 2.1 Program.

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Seismic Sources Magnitudes & LocaLons

Earthquake Recurrence

Seismic Source CharacterizaLon Model

Ground MoLon Model

Seismic Hazard Curves

Local Site Response

GMRS (ground moLon)

Overview of PSHA

Seismic Hazard Advances 12

• Central and Eastern US Seismic Source CharacterizaLon project for Nuclear FaciliLes (CEUS SSC Project)

• NUREG 2115 (NRC, 2012)

Source CharacterizaLon

• EPRI Ground MoLon Model Update Project (EPRI, 2013) • Next GeneraLon AlenuaLon RelaLonships for the Central and Eastern (NGA-‐East) (PEER UC Berkeley, 2015)

Ground moLon predicLon equaLons

• PracLcal ApplicaLon of the SSHAC Guidelines • NUREG 2117 (NRC, 2012)

PSHA process guidance

Senior Seismic Hazard Analysis Commilee (SSHAC) Original report provides and procedure for conducLng mulLple-‐expert assessments of input to PSHA New report provides addiLonal details.

NUREG/CR-6372 NUREG 2117 (1989) (2012)

SSHAC Guidelines

ObjecLve of a SSHAC Study

¨ Objective is to develop a model that represents the center, body and range of technically defensible interpretations of the available data ¤ Center-best estimate ¤ Body-shape of the distribution ¤ Range-extreme values of the distribution

¨ Achieved through a process with well defined evaluation and integration phases

Key elements of a SSHAC study

¨ Views of the larger technical community are fundamental

¨ Competing scientific hypotheses can be considered and uncertainties captured

¨ PSHA is a snapshot in time of our knowledge and uncertainties

¨ Notion of the “views of the larger informed technical community” leads to defined expert roles and responsibilities

¨ Experts must be “evaluators” not “proponents”

SSHAC Process Outcomes

¨  Stability ¤  Enjoys public confidence that the views of the larger informed technical community have been considered and properly represented

¤  Public represented by regulator ¤ Not subject to significant change with each new scienLfic finding

¨  Longevity ¤  Results expected to be valid for applicaLons up to at least 10 years in the future

¤  The technical underpinnings will remain valid in the future, despite the development of new data, unLl significant changes in the data or the science

}  Gather data and informaLon from literature }  TI makes assessments including uncertainty }  TI confers with members of technical community to understand alternaLve viewpoints

}  Workshops are held to discuss: ◦  Significant issues and available data ◦  AlternaLve hypotheses ◦  Feedback

}  ParLcipatory peer review of process and technical }  TI team responsible for technical assessments }  Expert panel responsible for making technical assessments

}  TFI facilitates expert interacLons and aggregates expert assessments

Leve

l 1

Leve

l 2

Leve

l 3

Leve

l 4

SSHAC Levels

¨  Stability comes from idenLfying and quanLfying uncertainLes and integraLng them into the PSHA (and SPRA) model

¨  Views of the larger technical community are uncertain ¤  AlternaLve models for the locaLons and rates of future earthquakes

¤  Parameters that define the models are uncertain ¨  Likelihood that the full range of technically defensible interpretaLons is captured increases with SSHAC Study Level (2 versus 3 and 4)

¨  Increasing formalism and involvement of experts ¨  Increasing stability (regulatory confidence) that all viable hypotheses have been considered

Formal Processes for UncertanLes

Uncertainty

Aleatory

Natural variability

Not reducible

Addressed through integraLon over parameter distribuLons

Epistemic Modeling or knowledge

uncertainty

Reducible with more informaLon

Addressed through use of a logic tree

UncertainLes in Hazard & Risk 19

Uncertainty

Aleatory

IntegraLon over distribuLon of expected parameter values

Epistemic

logic tree of technically defensible interpretaLons


Process and Technical R

eview

PPRP

Evaluation of M

odels to Form C

omposite D

istribution

TI Team

Hazard sensi?vity calcula?ons Preliminary database

WORKSHOP 1: Hazard Sensi?ve Issues and Data Needs

Resource Experts

Addi?onal data collec?on & analysis

WORKSHOP 2: Review of Database and Discussion of Alterna?ve Models

Resource Experts

Proponent Experts

Final database Preliminary SSC and GMC models

WORKSHOP 3: Presenta?on of Models and Hazard Sensi?vity Feedback

Final SSC and GMC models, then final hazard calcula?ons, Documenta?on of all technical bases

Database C

ompilation

Technical Staff & Contractors

NUREG 2117 (Level 3)

Seismic Hazard Advances 22

• Central and Eastern US Seismic Source CharacterizaLon project for Nuclear FaciliLes (CEUS SSC Project)

• NUREG 2115 (NRC, 2012)

Source CharacterizaLon

• EPRI Ground MoLon Model Update Project (EPRI, 2013) • Next GeneraLon AlenuaLon RelaLonships for the Central and Eastern (NGA-‐East) (PEER UC Berkeley, 2015)

Ground moLon predicLon equaLons

• PracLcal ApplicaLon of the SSHAC Guidelines • NUREG 2117 (NRC, 2012)

PSHA process guidance

Central and Eastern US Sites

Process

Recent Advances in PSHA

Source Characteriza?on Ground Mo?on Characteriza?on

PUBLISHED January 2012 IN PROGRESS Expected 2015

23

• Advances in applying SSHAC process on a site-‐specific basis in the US. New assessments submiled the NRC March 2015.

Western Sites

• First applicaLon of the SSHAC Level 3 process in a developing naLon

• Assessment for new NPPs • Sponsored by uLlity with ongoing review by the regulator

South Africa

Site-‐Specific Seismic Hazard 24

Bommer et al (2013), “A SSHAC Level 3 ProbabilisLc Seismic Hazard Analysis for a New-‐Build Nuclear Site in South Africa” Earthquake Spectra

ProbabilisLc Flood Hazard Advances 25

¤ Ongoing US efforts towards probabilisLc flooding methods to support more uniform treatment of hazard in risk-‐informed decision making

¤ January 2013 Joint Workshop on ProbabilisLc Flood Hazard Assessment Workshop

¤ Recent NRC & FERC staff workshop on PFHA and applicaLon of the SSHAC guidelines (proceedings expected to be published)

hlp://www.nrc.gov/public-‐involve/public-‐meeLngs/meeLng-‐archives/

research-‐wkshps.html

Regulatory Documents

¨  Code of Federal RegulaLons ¤  10 CFR parts 50 & 52, Federal law

¨  Regulatory Guidance ¤  States staff posiLons on meeLng the code

¨  NUREG-‐Series Documents ¤  Technical supporLng documents ¤  NUREG (staff) & NUREG/CR (contractors)

¨  Standard Review Plan (NUREG 0-‐800) ¤  NRC review standards for staff

¨  Plant OperaLng Licenses ¤  Become part of 10CFR (and are therefore federal law)

¨  CerLfied Designs ¤  Become part of 10CFR

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AEC Atomic Energy Commission ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers CDF Core Damage Frequency CFR Code of Federal RegulaLons COL Combined OperaLng License DBE Design Basis Earthquake EDMG Extreme Damage MiLgaLon Guideline FOSID Frequency of the Onset of Significant InelasLc

DeformaLon HCLPF High Confidence of a Low Probability of Failure GDC General Design Criteria GL Generic Leler (to Licensees) IEEE InsLtute of Electrical and Electronics Engineers

Acronyms 27

JLD Japan Lessons Directorate NPPs Nuclear Power Plants NRC Nuclear Regulatory Commission NTTF Near Term Task Force (on Fukushima) PEER Pacific Earthquake Engineering Research PGA Peak Ground AcceleraLon QME QualificaLon of Mechanical Equipment RG Regulatory Guide SAMG Severe Accident MiLgaLon Guideline SEP SystemaLc EvaluaLon Program SSE Safe Shutdown Earthquake SSC Structures, Systems and Components SSC Seismic Source CharacterizaLon Acronyms

28

Thank You

QuesLons?

29

Uncertainty

Aleatory Epistemic

AcceleraLon (g)

Annu

al Prob of Exceedance

Aleatory variability gives the curve its

shape.

Epistemic uncertainty leads to uncertainty

bands 85%

Median

15%

30

UncertainLes in Hazard & Risk

Uncertainty

Median Curve

AcceleraLon (g)

Annu


85%

Median

15%

31

UncertainLes in Hazard & Risk

Uncertainty

Mean Curve

AcceleraLon (g)

Annu


85%

Median

15%

The mean curve is used in risk assessment and design to beler account for epistemic uncertainty.

Mean Curve

The mean curve exceeds the median due to the log-‐normal distribuLon of most parameters


Uncertainty

Mean Curve

AcceleraLon (g)

Annu


85%

Median

15%

Greater epistemic uncertainty due to lack of data leads to a higher mean curve. This leads, in turn, to higher assessments of risk. There is a benefit to accumulaLng data.

Mean Curve

UncertainLes Hazard & Risk 33