Dr. Annie Kammerer

NC State University

10th Structural Engineering &

Mechanics Symposium

March 2011

Risk-informed Seismic Design of

US Nuclear Power Plants

• Atomic Energy Commission (1954)

• Energy Reorganization Act of 1974•Department of Energy

•Nuclear weapons, promotion of nuclear power, care of low-level radioactive waste, and other energy-related work

•Nuclear Regulatory Commission•Regulation of the civilian uses of nuclear materials including power production, medical and other uses

• Nuclear Non-Proliferation Act of 1978•Limits the spread of nuclear weapons. Established

criteria governing U.S. nuclear exports licensed by the

NRC and strengthened international safeguards system

NRC History

• 1950s to 1970s US built plants• 1979 Three Mile Island Accident• 1986 Chernobyl Nuclear Disaster• 435 nuclear plants in 30 countries

generating 16% of total power (104 in US)• Changes in energy policy

•New financial incentives in US energy policy•New financial incentives in US energy policy

•Certified design concept becomes law

•Time limits on NRC response

• NRC now has 20+ applications in-house•COL applications (site specific)

•Certified design applications (nuclear island)

History

Organization

Oversight

Committees

Presidential

Appointees

Existing and

New Reactor

Licensing

Offices

Yucca

Mountain

ResearchResident

Inspectors

• Many types of Regulatory Documents•Code of Federal Regulations (10 CFR)

•Regulatory Guidance

•NUREG-Series Documents

•Standard Review Plan (NUREG 0-800)

•Plant Operating Licenses

• Hearings and proceedings• Oversight committees• Public Meetings• Open public process

US Regulatory Frameword

10 CFR Part 50 Appendix S defines SSE as

“Safe-shutdown earthquake ground motion is

the vibratory ground motion for which

certain structures, systems, and components

must be designed to remain functional”

10 CFR Part 50 also states that “The nuclear

power plant must be designed so that, if the

US Code of Federal Regulations

Safe Shutdown Earthquake Ground Motion

occurs, certain structures, systems, and

components will remain functional and within

applicable stress, strain, and deformation

limits.”

10 CFR Part 50 Appendix A states “Structures, systems, and components important to safety shall be designed to withstand the effects of natural

10 CFR Part 100.23 “Geologic and Seismic Siting Criteria” requires that the applicant determine the SSE and its uncertainty, the potential for surface tectonic and non-tectonic deformations.

US Code of Federal Regulations

be designed to withstand the effects of natural phenomena such as earthquakes, …., without loss of capability to perform their safety functions”.

• Many existing and newcomer nuclear states• Each has their own regulatory body• Many countries use NRC regulations• International Atomic Energy Agency

•UN agency focused on safe nuclear energy and non-proliferation•International Seismic Safety Center•International Seismic Safety Center•Document series similar to NRC

•Binding on IAEA/UN staff and consultants

•Consulting services available•Certified design popular internationally

International Regulation

Safety Standards Series hierarchy

Safety Guides

Requirements

Safety Fundamentals

US Code of

Federal

Regulations

Regulatory

Guides

IAEA

US & IAEA documentation

International Atomic Energy Agency3/17/2010 12

Safety GuidesGuides

NRC

NUREGsSafety Reports &

TECDOCs

IAEA

US documentation and regulations

Seismic

Hazard

NS-G-3.3

NRC

Regulatory

Guide 1.208

STANDARD REVIEW PLAN(NUREG 0-800)

US documentation and regulations

Standard Review Plan

NRC NUREG 0-800 NRC DC/COL-ISG-017

(site response & SSI)

Interim Staff Guidance

• Certified Design Documentation• Site Analysis

•10-4 annual probability ground motion (with design factors)

compared to certified design

•Geotechnical properties assessed for compliance with

requirements

• Combine with other information in COL

US Regulation

GRMS is based on site

characterization and it is

determined from detailed

seismic hazard studies

CSDRS is based on

engineering design of

a plant

Site SSE (GMRS) compared to CSDRS

GMRS is based on

site characterization

and it is determined

from detailed

seismic hazard Certified

Design seismic hazard

studies

CSDRS is based

on engineering

design of a plant.

CSDRS is chosen

by the vendor and

used as review

spectrum Slides provided by NRC

Office of New Reactors

CSDRS

Site Spectrum

GRMS

• Research undertaken to support NRC staff decision making technical basis

• Regulatory infrastructure development• Regulatory guidance• Development of new approaches and tools• Evaluation of operating experience• Evaluation of operating experience• Confirmatory analysis• Special regulatory programs• Codes & Standards • Assistance in reviews

NRC Research Program Activities

• Publicly available plan (in revision for 2011)• Growing program• Targeted on regulatory needs• Strong stakeholder interaction

•Developed with other NRC offices

•Cooperation with industry, other national &

international agencies, and the technical international agencies, and the technical

community

• Developed to advance the science and increase regulatory stability

• Short- and long-term projects & deliverables

NRC Seismic Research Program

Point

“Site”R

fR(r)

+ + =

SSCs

• Site Response•RVT, earthquake records, frequency dependent

damping, direct integration into PSHA…more coming

• Base Isolation•NUREG expected soon

• NRC ESSI Simulator • NRC ESSI Simulator • Advanced QA/QC version of OpenSEES

• Technology Neutral Risk-Informed Design/Review Approaches and Guidance

Earthquake Engineering

• Light water reactors with fuel rods• Heat produces steam that drives a turbine• Pressure water & Boiling water reactors• SSCs cover large frequency ranges• Some Base isolated (non-US currently)• Some with deeper embedment

New

Generation

of US Plants

• Generation 3+

Generation 3+ Nuclear Power Plants

Plant designs are diverging greatly• Pebble bed reactors• Sodium cooled gas reactors• Small modular reactors• Deeply embedded designs• Additional base-isolated designs• Additional base-isolated designs

Advanced Plants – Generation 4

NEED TECHNOLOGY NEUTRAL FRAMEWORK

• A Performance-Based Approach to Definethe Site-Specific Earthquake Ground Motion

• Hazard x Performance Risk

• NRC is “Risk Informed” as per 1997 commission directive and uses probabilistic inputs and performance-based design

• Overall plant risk assessed through Seismic Probabilistic Risk Assessment (SPRA)

Risk-Informed Regulation

• SSC performance target risk goals (core damage ~10-6/year)

• Above coupled with robustness of containment leads to even smaller risk of radiological consequences in the population and environmentand environment

• Defense-in-Depth Concept• Prevent• Prepare• Mitigate

Risk-Informed Regulation

To be withdrawn

Hazard + Adequate

Performance

Acceptable

Risk

Key Documents for Understanding

Technical Basis of Approach

Performance Based Design

Risk Reduction Ratio reduces

performance goals below hazard

Hazard Modified to Obtain SSE

DF=0.6 (AR)0.8

AR=UHRS at 10-5

UHRS at 10-4

Slope of the

hazard

curve

with a minimum of 1

Outcome of the NRC 1x10-5 Frequency of Onset

of Significant Inelastic Deformation (FOSID)

HCLPF

• Now the key is to appropriately define the Hazard…which is the goal of RG1.208

• The Ground Motion Response Spectrum (GMRS) is the site-specific uniform hazard response spectrum with an annual probability of 10-4 spectrum for an elevation in the soil or rock column that is meaningful for the facility

Use of RG1.208 to Determine Hazard

rock column that is meaningful for the facility

• GMRS should be developed for horizontal and vertical components

• Determination of GMRS requires many inputs:

– Seismic source characterization

– Ground motion prediction equations (GMPE)

– Dynamic site properties for site response

• And appropriate approaches to develop and combine them:

- SSHAC guidelines for determination of source

characterization and GMPEs (NUREG/CR-6372)

- PSHA techniques

- Integrated site response (NUREG/CR-6728)

Use of RG1.208 to Determine Hazard

Source

Characterization

Ground motion

prediction equations

Central and Eastern US Seismic

Source Characterization project for

Nuclear Facilities (CEUS SSC)

Next Generation Attenuation

Relationships for the Central and

Eastern (NGA-East)

Framework for large

PSHA studies

Eastern (NGA-East)

Recommendations for Application

of the SSHAC Guidelines

Seismic Hazard Assessment

• Appropriate data collection and field investigation efforts to meet 10 CFR 100.23 requirements

Site (>1km)

Site Area (>8 km)

Site Vicinity (>40 km)

Increasing level of

effort close to site.

However, any seismic

sources that may

impact hazard should

be appropriately

Data Collection in RG1.208

Site Vicinity (>40 km)

Site Region (>320 km)

be appropriately

assessed.

Regional source

models (e.g. new CEUS SSC model)

must still be refined

with site-specific

information

SSHAC Guidelines

• NUREG/CR-6372, “Recommendations for

Probabilistic Seismic Hazard Analysis: Guidance

on Uncertainty and Use of Experts”

• SSHAC provides a framework for incorporating

experts into scientific assessments through

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experts into scientific assessments through

structured processes and interactions

• Fundamental concepts behind guidelines• Views of the larger technical community are fundamental inputs

• Competing scientific hypotheses can be considered and uncertainties captured

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

Goals of SSHAC

• “To represent the center, the body, and the range of the technical interpretations that the larger informed technical community would have if they were to conduct the study”

35

conduct the study”

– Increases assurance that uncertainties have

been captured

– Leads to regulatory stability

– Can be peer reviewed by those with

comparable knowledge of the community

SSHAC Guidelines

• NRC Undertaking Program to develop NUREG

on “Implementation of SSHAC Guidelines for

Level 3 and 4 Processes”

– NRC Sponsored USGS

Workshops resulting in USGS

36

Workshops resulting in USGS

OFR 2009-1093

– Draft NUREG (exp. 2010)

– Public Workshop on Level 3

studies to capture additional

lessons learned

– Finalize NUREG

• Geotechnical hazards beyond ground shaking (e.g. liquefaction, direct fault rupture)

• Choice of epsilon cutoff in PSHA

• Site response approaches and application of de-aggregation for simplified methods (e.g. NUREG/CR-6728 method 2a)

• Earthquake record development for time-history based analyses

Additional topics in RG1.208

• Operating Basis Earthquake (OBE) is legally defined in Licensing Basis

•Typically1/2 to 1/3 of Safe Shutdown Earthquake (SSE)

•If both OBE motions and CAV criteria are exceeded the

plant must shutdown within 4 hours

• Regulatory Guide 1.66 describes recommended criteria for shutdown if recommended criteria for shutdown if equipment is unavailable

•Greater than MMI VI or greater within 5 km of plant

•Earthquake was felt within the plant and was of

magnitude 6 or greater

•Magnitude 5 or greater within 200 km of the plant

•Used as guidelines for NRC staff for request to plant

Shutdown Criteria

Thank You

Title Goes HereRisk-informed seismic design of

US Nuclear Power Plants