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Annie Kammerer Bechtel Corporation Pacific Earthquake Engineering Center, UC Berkeley
Nuclear Energy: Resources, Geological Hazards, and Waste Management Energy from the Earth Series March 2014
The US Nuclear Regulatory Commission (NRC) uses a risk-‐informed regulatory framework
Assessing seismic risk requires: Understanding and quantifying seismic hazards Understanding and quantifying plant seismic capacity
Earth science data has a direct impact on nuclear safety by allowing the nuclear industry and the NRC to better quantify the natural hazards that plants must be able to withstand (and their associated uncertainties)
Risk
Seismic Load Capacity
Seismic Motion Parameter
Prob
ability of E
xcee
danc
e
Seismic Motion Parameter
Cond
ition
al Proba
bility of Failure
In 1971 the NRC established General Design Criteria 2, which required that plants be designed to withstand natural phenomena with a consideration of data uncertainty (Appendix A to 10 CFR Part 50).
In 1973, “Seismic and Geologic Siting Criteria for NPPs” provided detailed criteria to evaluate the suitability of proposed sites and the suitability of the plant seismic design basis. (Appendix A to 10 CFR Part 100)
Appropriate data collection and field investigation efforts to meet 10 CFR 100.23 requirements
Site (>1km)
Site Area (>8 km)
Site Vicinity (>40 km)
Site Region (>320 km)
Increasing level of effort close to site.
However, any seismic sources that may impact hazard should be appropriately assessed.
In 1996, the NRC issued an update/reorganiztion to complete the current legal basis for seismic design (10 CFR Part 50 Appendix S):
Defined “Safe-‐shutdown earthquake” (SSE) ground motion
Specified 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.”
Added the explicit requirement to consider uncertainty
In 1997, the commission issued a directive to move towards “risk informed” policies.
2007 NRC issued Regulatory Guide 1.208, which describes the current hazard assessment approach works with risk-‐based engineering guidance (ASCE 43-‐05) Uses 10,000 to 100,000 year ground motions (10-‐4 to 10-‐5 annual probability) for design ground motions.
VERY rare ground motions used for design. Significant earth science needs to quantify these rare events appropriately.
Risk targets: Frequency of damage of individual safety-‐related elements (individual), core damage frequency (systems), and large early release frequency (containment)
The current US risk-‐informed regulatory approach to seismic safety provides a rational framework for decision making that is targeted on risk factors that matter.
The assessment of seismic risk relies directly on quantification of seismic hazard; which itself relies directly on sufficient and robust earth science information from the broader technical community.
Probabilistic Seismic Hazard Analysis • Objective to determine the best estimate (and
uncertainty estimate) of ground motion levels at a particular location over time periods of interest.
• PSHA considers ground motions from all possible earthquakes from all seismic sources that may impact a site, and accounts for the likelihood of any particular earthquake.
• (Approach can be used for any natural hazard)
The PSHA mode is developed through a well defined process that incorporates evaluation and integration of all of the available data, models & methods
NUREG/CR-6372 NUREG 2117 (1989) (2012)
“aleatory” randomness is
integrated
“epistemic” uncertainty from
alternative models is addressed through a
logic tree
Seismic Source Characterization
Ground Motion Characterization
Base figure from Reiter (1990)
Earthquake Recurrence
Source Geometry
Seismic Hazard Model
Seismicity
Geology
Tectonics
Magnetics
Gravity Paleo-‐seismic
Geodetics (GPS)
Crustal stress
Crustal geophysics
Site Characteristics
12
Seismic Source Characterization
PUBLISHED January 2012
Ground Motion Characterization IN PROGRESS expected 2015
15 Courtesy of TEPCO
Fukushima Lessons Learned Report with Significant Recommendations for changing NRC regulations and practices
NRC ML111861807
17
Early
Near term
Long term
2.3
2.1
2.2
Walkdowns
Hazard evaluation
Risk evaluation
Regulatory Actions
10 year update
Walkdowns to assure plants are meeting licensing basis and to look for potential seismic issues. Reports due November 2012. Some equipment
delayed until outage.
Hazard evaluation due in 18 months for plants within the new CEUS SSC (NUREG 2115) model area. 3 years for western US NPPs performing
plant-‐specific studies.
Risk results due 3 years after hazard using seismic probabilistic risk assessments (SPRA)
After receiving the information from the SPRA, the NRC will determine what regulatory action is
appropriate.
Rulemaking to require a reevaluation every 10 years.
11/2012 (+outages)
Spring 2014 (CEUS) 3/2015 (WUS)
3 years after hazard
Depends on findings
Rulemaking timeline
• Operating reactors designed using scenario earthquake (deterministic) approach • No assessment of likelihood of scenario earthquake or resulting
ground motions • Coupled with very conservative “margins” engineering • New assessments provide apples to orange comparisons with old
values
Seismic Motion Parameter
Prob
ability of E
xcee
danc
e ?X
Thank You