Risk-informed Seismic Design of US Nuclear Power Plants

Transcription

1 Dr. Annie Kammerer NC State University 10 th Structural Engineering & Mechanics Symposium March 2011 Risk-informed Seismic Design of US Nuclear Power Plants

2 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

3 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 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

4 Organization Presidential Appointees Oversight Committees Existing and New Reactor Licensing Offices Resident Inspectors Yucca Mountain Research

5 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

6 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 Safe Shutdown Earthquake Ground Motion occurs, certain structures, systems, and components will remain functional and within applicable stress, strain, and deformation limits. US Code of Federal Regulations

7 10 CFR Part Geologic and Seismic Siting Criteria requires that the applicant determine the SSE and its uncertainty, the potential for surface tectonic and non-tectonic deformations. 10 CFR Part 50 Appendix A states Structures, systems, and components important to safety shall be designed to withstand the effects of natural phenomena such as earthquakes,., without loss of capability to perform their safety functions. US Code of Federal Regulations

8 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 Document series similar to NRC Binding on IAEA/UN staff and consultants Consulting services available Certified design popular internationally International Regulation

9 Safety Standards Series hierarchy US Code of Federal Regulations Regulatory Guides NUREGs Safety Fundamentals Requirements Safety Guides 3/17/ International Atomic Energy Agency Safety Reports & TECDOCs NRC IAEA US & IAEA documentation

10 Regulatory Guide NRC Seismic Hazard NS-G-3.3 IAEA US documentation and regulations

11 STANDARD REVIEW PLAN (NUREG 0-800) NRC NUREG NRC DC/COL-ISG-017 (site response & SSI) Standard Review Plan Interim Staff Guidance US documentation and regulations

12 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

13 Site SSE (GMRS) compared to CSDRS GMRS is based on site characterization and it is determined from detailed seismic hazard studies CSDRS is based on engineering design of a plant. CSDRS is chosen by the vendor and used as review spectrum Certified Design CSDRS Site Spectrum GRMS Slides provided by NRC Office of New Reactors

14 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 Confirmatory analysis Special regulatory programs Codes & Standards Assistance in reviews NRC Research Program Activities

15 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 community Developed to advance the science and increase regulatory stability Short- and long-term projects & deliverables NRC Seismic Research Program

16 Point Site f R (r) + + = R SSCs

17 Site Response RVT, earthquake records, frequency dependent damping, direct integration into PSHA more coming Base Isolation NUREG expected soon NRC ESSI Simulator Advanced QA/QC version of OpenSEES Technology Neutral Risk-Informed Design/Review Approaches and Guidance Earthquake Engineering

18 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

19 Generation 3+ Generation 3+ Nuclear Power Plants

20 Plant designs are diverging greatly Pebble bed reactors Sodium cooled gas reactors Small modular reactors Deeply embedded designs Additional base-isolated designs NEED TECHNOLOGY NEUTRAL FRAMEWORK Advanced Plants Generation 4

21 A Performance-Based Approach to Define the 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

22 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 environment Defense-in-Depth Concept Prevent Prepare Mitigate Risk-Informed Regulation

23 Hazard + Adequate Performance To be withdrawn Acceptable Risk

24 Key Documents for Understanding Technical Basis of Approach

25 Performance Based Design

26 Risk Reduction Ratio reduces performance goals below hazard

27 Hazard Modified to Obtain SSE DF=0.6 (A R ) 0.8 with a minimum of 1 A R = UHRS at 10-5 UHRS at 10-4 Slope of the hazard curve

28 Outcome of the NRC 1x10-5 Frequency of Onset of Significant Inelastic Deformation (FOSID)

29 HCLPF

30 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 GMRS should be developed for horizontal and vertical components Use of RG1.208 to Determine Hazard

31 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

32 Source Characterization Ground motion prediction equations Framework for large PSHA studies Central and Eastern US Seismic Source Characterization project for Nuclear Facilities (CEUS SSC) Next Generation Attenuation Relationships for the Central and Eastern (NGA-East) Recommendations for Application of the SSHAC Guidelines Seismic Hazard Assessment

33 Appropriate data collection and field investigation efforts to meet 10 CFR requirements Site (>1km) Increasing level of effort close to site. Site Area (>8 km) Site Vicinity (>40 km) Site Region (>320 km) However, any seismic sources that may impact hazard should be appropriately assessed. Regional source models (e.g. new CEUS SSC model) must still be refined with site-specific information Data Collection in RG1.208

34 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 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 34

35 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 Increases assurance that uncertainties have been captured Leads to regulatory stability Can be peer reviewed by those with comparable knowledge of the community

36 SSHAC Guidelines NRC Undertaking Program to develop NUREG on Implementation of SSHAC Guidelines for Level 3 and 4 Processes 36 NRC Sponsored USGS Workshops resulting in USGS OFR Draft NUREG (exp. 2010) Public Workshop on Level 3 studies to capture additional lessons learned Finalize NUREG

37 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 timehistory based analyses Additional topics in RG1.208

38 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 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

39 Thank You Title Goes Here Risk-informed seismic design of US Nuclear Power Plants