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View the SSHAC3 Process Project Plan for Technical Use
SSHAC 3 Process | Workshop Summaries
Chapter 2 - SSHAC Level 3 Assessment Process and Implementation[edit]
This chapter describes the SSHAC Level 3 assessment process, how it was implemented to assess the CEUS-SSC model, and how that implementation was accomplished in compliance with the SSHAC guidance.
The “SSHAC assessment process,” which differs only slightly for Level 3 and 4 studies, is a technical process accepted in the NRC’s seismic regulatory guidance (Regulatory Guide 1.208) for reasonably ensuring that uncertainties in data and scientific knowledge have been properly represented in seismic design ground motions consistent with the requirements of the seismic regulation 10 CFR Part 100.23. Therefore, the goal of the SSHAC assessment process is the proper and complete representation of knowledge and uncertainties in the SSC and GMC inputs to the PSHA (or similar hazard analysis). This reasonable representation of knowledge and uncertainties is referred to in the SSHAC guidance as “the center, the body, and the range of the informed technical community.” The SSHAC assessment process, if properly implemented, provides high levels of confidence that the SSHAC goal has been met. Therefore, the way it is conducted is important and subject to “process” as well as “technical” peer view. A key responsibility of the Participatory Peer Review Panel (PPRP) is to ensure that the SSHAC assessment process has been properly implemented.
SSHAC developed guidance for four “study levels” of implementing an assessment that depend on the degree of uncertainty and contention involved and on the intended use of the seismic hazard model. SSHAC recommended that a Level 3 or Level 4 assessment process be used for complex assessments, the products of which have high public importance and attract public scrutiny, such as regional seismic hazard models intended to be used over a sustained time period as base-case models for site-specific PSHAs. Such models require the highest level of assurance that the community uncertainty distribution has been properly represented. For the CEUS-SSC Project, the decision to use a SSHAC Level 3 assessment process was based on experience with implementing the SSHAC guidance, which has shown that a properly executed Level 3 assessment process can provide a level of assurance of meeting the SSHAC goals comparable to that of Level 4, which is more costly and time-consuming to implement (selection discussed in the Project Plan and Section 1.2.1).
Discussion of the SSHAC process in this chapter comes from four sources:
- The SSHAC document itself (Budnitz et al., 1997).
- A summary of workshops conducted to identify lessons learned from the implementation of SSHAC in actual projects (Hanks et al., 2009).
- A summary of the ongoing efforts of the NRC to develop more specific SSHAC guidelines (Coppersmith et al., 2010).
- Draft NRC guidance for the implementation of SSHAC Level 3 and 4 projects (NRC, 2011).
This chapter begins with a discussion of the fundamental SSHAC goals and activities that make up a SSHAC assessment process. This is followed by a discussion of the SSHAC Level 3 assessment process implemented by the CEUS-SSC Project, including the roles of key participants, project organization, key activities, and the PPRP. The final section summarizes how the CEUS-SSC assessment process compares with the process prescribed in the SSHAC guidelines. (Complete SSHAC 3 Process Description)
Project Plan[edit]
Product Description
This project plan outlines the Central and Eastern United States Seismic Source Characterization for Nuclear Facilities (CEUS-SSC) Project, which will replace the Seismic Hazard Methodology for the Central and Eastern United States, EPRI report NP-4726, July 1986. The objective of the CEUS-SSC project is to develop an up-to-date assessment of probabilistic seismic hazard analysis (PSHA) SSC for CEUS. Input to a PSHA consists of both seismic source and ground motion characterization. These two components are used to calculate probabilistic hazard results (or seismic hazard curves) at a particular site.
Results & Findings
The product of this report is a vetted plan to develop a generic CEUS-SSC model. This model includes consideration of an updated database, full assessment and incorporation of uncertainties, and the range of diverse technical interpretations from the informed scientific community. The SSC model will be widely applicable to the entire CEUS, so this project will use a ground motion model that includes generic variations to allow for a range of representative site conditions (deep soil, shallow soil, hard rock). Hazard and sensitivity calculations will be conducted at six demonstration sites representative of different CEUS hazard environments.
Challenges & Objective(s)
The generic CEUS-SSC model will be of value to readers who are involved in PSHA work, and who wish to use an updated SSC model. This model will be based on a comprehensive and traceable process, in accordance with Senior Seismic Hazard Assessment Committee (SSHAC) guidelines in NUREG/CR-6372, Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts. The model will be used to assess the present-day composite distribution for seismic sources along with their characterization in the CEUS and uncertainty. In addition, this model will be in a form suitable for use in PSHA evaluations for regulatory activities, such as Early Site Permit (ESP) and Combined Operating License Applications (COLA).
Applications, Values & Use
Development of a generic CEUS seismic hazard model will provide value to members who 1) have submitted an ESP or COLA for Nuclear Regulatory Commission (NRC) review before 2010, 2) will submit an ESP or COLA for NRC review after 2010 and 3) must respond to safety issues resulting from NRC Generic Issue 199 (GI-199) for existing plants. This work replaces a previous study performed approximately 20 years ago. Since that study was completed, substantial work has been done to improve the understanding of seismic sources and their characterization in the CEUS. Thus, a new generic SSC model will provide a consistent, stable basis for computing PSHA for a future time span. Use of a new SSC model will reduce the risk of delays in new plant licensing due to more conservative interpretations in the existing and future literature.
EPRI Perspective
The purpose of this study, jointly sponsored by EPRI and the U.S. Department of Energy (DOE), is to develop a new CEUS-SSC model. The team assembled to accomplish this purpose is comprised of distinguished subject matter experts from industry, government, and academia. The informed scientific community, it is not likely to be repeated for a number of years.
Approach
The goal of this report was to present the work plan for developing a generic CEUS-SSC model.The work plan, formulated by a technical integration team, consists of a series of tasks designed to meet the project objectives. This report was reviewed by a participatory peer review panel (PPRP) and sponsor reviewers. Comments from the PPRP are reflected in the report. EPRI held a meeting on May 8, 2008, to facilitate resolution of comments received regarding the project plan. The SSC model is slated for completion in mid-2010.
Keywords
Seismic Sources
Probabilistic Seismic Hazard Assessment (PSHA)
Seismic Source Characterization (SSC)
Seismic Source Characterization Model
Central and Eastern United States (CEUS)
Other Documentation[edit]
1) USGS letter dated April 8, 2010 with feedback on the data sets, methods, and models pertaining to the Central and Eastern U.S. Seismic Source Characterization (CEUS-SSC).
2) USGS letter dated April 9, 2010 stating no further USGS comments regarding the earthquake catalog and data, models and methods.
3) TI Team and PM response dated April 9, 2010 to USGS letter dated April 8, 2010.
4) USGS review dated August 30, 2010 of CEUS-SSC draft report dated July 31, 2010.
5) NRC review dated September 2010 of CEUS-SSC draft report dated July 31, 2010.
6) NRC review dated August 31, 2011 of CEUS-SSC final report dated 2011.
7) DNFSB Board Staff (Paul C. Rizzo) review dated September 7, 2010 of CEUS-SSC draft report dated July 31, 2010.
8) DOE (Joe Hunt) review of CEUS-SSC draft report dated July 31, 2010.
9) DOE (Brent Gutierrez) review of CEUS-SSC draft report dated July 31, 2010.
10) DOE (Richard Lee) review dated October 4, 2010 of CEUS-SSC draft report dated July 31, 2010.
11) EPRI Structural Reliability and Integrity (SR&I) Working Group (Dhiren Pandya) review dated September 1, 2010 of CEUS-SSC draft report dated July 31, 2010.
12) Other stakeholder comment tables including TI Team response