Nuclear Regulatory Needs and Activities Related to Liquefaction Assessment

Transcription

1 National Research Council of the National Academies Committee on Geological and Geotechnical Engineering Board on Earth Sciences & Resources Dr. Annie Kammerer Office of Nuclear Regulatory Research December 8, 2010 Nuclear Regulatory Needs and Activities Related to Liquefaction Assessment

2 Status of NRC Guidance Current Activities of Research Program Nuclear Specific Considerations NRC Future Research Needs and Focuses Ideas for moving National Research Council Program Forward Overview

3 Appendix A to 10 CFR Part 100 requires evaluation of geologic features that could impact foundation stability, including liquefaction susceptible materials. Current Regulatory Guide (2003) & Standard Review Plan (NUREG-0800) based on Youd et al. through NUREG/CR-5741 (2000 by Koester, Sharp and Hynes) and NUREG/CR-6622 (1999 by Hynes) Status of NRC Guidance

4 NRC currently conducting an internal research program to update RG1.198 focused on assessing appropriate levels of probability of triggering and deformation and on advanced techniques New NUREG and updated Regulatory Guide expected outcome of research program Status of NRC Guidance

5 NRC conducting an internal research program with current topics focused on addressing a broad range of liquefaction-related issues including: Acceptable probability of liquefaction triggering Deformation-based performance criteria for NPP SSCs Performance of earth structures, including dams and embankments As part of the internal research, confirmatory analyses have been conducted including comparing FS with the P L from Seed et al 2003 using data from license applications Internal work started in 2009 and is expected to run several years Internal Activities of the NRC Seismic Research Program

6 NRC has current research at Pacific Earthquake Engineering Research Center Cooperatively funded with California Department of Water Resources on Engineering Evaluation of Post-Liquefaction Residual Strength. Full and open RFP to be issued early 2011 for project including multi-dimensional element-level testing and development multi-dimensional FE modeling tools for use with NRC ESSI Simulator (new SSI modeling tool) NRC ESSI Simulator developed for NRC internal research by Boris Jeremic of UCD & LBNL based on OpenSEES platform Broad integrated research to address multiple questions including impact of multidimensional loading and nontraditional loading on dense sands, ground motion selection and modification, impact of site variability, etc. External Activities of the NRC Seismic Research Program

7 NRC Seismic Research Program Plan being revised and re-issued in 2011 Seismic Research Program external funding moving from growth to flat funding with limited new research being initiated in the next 2 years Significant internal program being undertaken by and with new NRC staff NRC has initiated a permanent posting on grants.gov NRC Research Program Planning

8 Heavily regulated environment with a public hearing process that requires clear technical basis for reasonable assurance of safety Policy of Risk-Informed decision making with clear accounting for (and assessment of) uncertainties Consideration of ground motions with low annual probabilities (10-4 to 10-6 ) must be coupled with low probability of occurrence of unacceptable performance (and no cliff edge effects beyond) Stated conditions of no liquefaction for Certified Design Plants licensed under CFR Part 52 leads to problems (not absolutely achievable once probability of occurrence is recognized) Nuclear Specific Considerations that Impact Liquefaction Research

9 Seismic probabilistic risk assessment (SPRA) is required prior to loading of fuel. Incorporation of deformations in state-of-the-art SPRA is under discussion. Internal discussion of appropriate plant-level HCLPF value for liquefaction consequences Specifically, some staff are asking if the required HCLPF value for assessment of risk from shaking (1.67*Safe Shutdown Earthquake Ground Motion) applies to other secondary effects. Regardless of value, some technical basis for acceptable risk must be developed. Nuclear Specific Considerations that Impact Liquefaction Research

10 In the US, NPP sites may have looser sands at the surface, but they are removed due to requirements related to shear wave velocity (and no liquefaction ) under the safety related systems. So, NRC internal research is focused on cyclic mobility and deformation in dense sands. Lessons learned in the Kashiwazaki-Kariwa Nuclear plant (impacted by 2007 NCO earthquake) include the importance of liquefaction potential in the non-safety related systems as it relates to time to NPP restart and loss of public confidence. (All safety related systems performed their safety function as designed) Nuclear Specific Considerations that Impact Liquefaction Research

11 Completion of current research Determination of acceptably low probability of liquefaction triggering for guidance that is based on an acceptably low risk of unacceptable performance and a reasonable assurance of safety Deformation-based performance criteria for NPP SSCs Performance of earth structures, including dams/embankments Method of incorporating performance of potentially liquefiable materials into fully integrated probabilistic SSI analysis (from PSHA to probabilistic floor spectra and deformation) and ultimately into the seismic probabilistic risk assessment Future Research Needs & Focuses

12 Plant Level Fragility from Seismic PRA Future Research Needs & Focuses

13 HCLPF Plant Level Fragility HCLPF High confidence (95%) of a low probability of failures (5%) HCLPF value is the value of PGA at which the HCLPF is met Demonstration of a HCLPF value of 1.67*SSE is required for shaking. Leads to acceptably low probabilities of core damage No triggering assessment involved

14 Transparency Broad community participation Development of a full technical basis for final recommendations Clear, Complete Documentation An assessment uses a process that includes a clear, supportable, and documented line of reasoning from data to assertion anything else is just an opinion National Research Council Program

15 A structured framework and procedure for conducting multipleexpert assessments of input to PSHA Procedures defined by the Senior Seismic Hazard Analysis Committee (SSHAC) in NUREG/CR-6372 National Research Council Program

16 The SSHAC assessment process undertakes evaluation followed by integration into PSHA logic tree Evaluation and consideration of all the data, models, and methods that pertain to the inputs to the hazard analysis. Integration: model-building to capture the center, body, and range of the technically defensible interpretations National Research Council Program

17 At least 3 workshops required in a SSHAC assessment process Data collection and identification of critical issues Review of database and discussion of alternative models by proponent Presentation of models (or in this case recommendations) and feedback Not a perfect fit for project needs, but many elements would be helpful National Research Council Program

18 THANK YOU 18