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© 2017 Electric Power Research Institute, Inc. All rights reserved.
John E. WeglianSenior Technical Leader
3rd NRC External Flooding Research Workshop
December 4-5, 2017
EPRI Flooding Research Program
Overview
2© 2017 Electric Power Research Institute, Inc. All rights reserved.
Challenge with External Flooding
External flooding hazards are assessed based on limited data In most places the historical record for events of interest are
limited to just over 100 yearsDesign basis analyses use the concept of a Probable
Maximum Flood (PMF), but make no attempt to calculate the frequency of occurrence of such a floodExtrapolation to extremely low frequencies is required to
probabilistically assess risk at nuclear power plants– PRA models assess risks down to a frequency of 10-7/yr or lower– The PFHA may be required to assess the hazard frequency down to
as low as 10-6/yr – equivalent to an Annual Exceedance Probability (AEP) of 10-6
3© 2017 Electric Power Research Institute, Inc. All rights reserved.
Techniques to Assess Low Frequency Flooding
Extrapolation beyond twice the historical record is not considered to be credibleA variety of methods are used to extend the effective
historical record– Use of independent, but applicable measurements (e.g., rain gauges)– Transposition of observed storms from one location to another– Development of synthetic storms to simulate flooding impact with
Monte Carlo analysis– Use of paleo (i.e., outside of the historical record) evidence to inform
the data
All of these techniques involve uncertainty, so it is important to characterize the uncertainty
4© 2017 Electric Power Research Institute, Inc. All rights reserved.
EPRI Flooding Research Topics
Hazard Assessment – State of knowledge of external flooding analysis – 3002005292– Riverine flooding – 3002003013– Local intense precipitation – 3002004400– Storm surge – 3002008111– Deterministic hazard assessment – 3002008113
Analysis Techniques– Use of 3-D modeling techniques for flooding – 3002010673
Managing existing design and licensing bases for flood protection barriers– Flood Protection Systems Guide – 3002005423– External Flood Protection Design/License Basis Management Best
Practices Guide – 3002010620
5© 2017 Electric Power Research Institute, Inc. All rights reserved.
State of Knowledge of External Flooding Analysis
3002005292 – External Flooding Hazard Analysis: State of Knowledge AssessmentFreely available to the publicExamines the probabilistic methods currently available to
assess external flooding hazard– Local intense precipitation– Riverine flooding– Dam failure– Storm surge
6© 2017 Electric Power Research Institute, Inc. All rights reserved.
Riverine Flooding
3002003013 – Riverine Probabilistic Flooding Hazard Analysis Pilot: Proof-of-Concept Study for a Nuclear Power PlantTwo stochastic models used to
simulate riverine flooding at a site– Stochastic Event Flood Model (SEFM)– Stochastic Runoff Routing Monte Carlo
(RORB_MC)
Includes evaluation of uncertainties, expert judgement, and sensitivities of flood-hazard estimates to the various modeling components
7© 2017 Electric Power Research Institute, Inc. All rights reserved.
Local Intense Precipitation
3002004400 – Local Precipitation-Frequency Studies: Development of 1-Hour/1-Square Mile Precipitation-Frequency Relationships for Two Example Nuclear Power Plant SitesFreely available to the publicMaximizes available data by finding independent and
applicable data sources and combining them
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Storm Surge
3002008111 – Probabilistic Flooding Hazard Assessment for Storm Surge with an Example Based on Historical Water LevelsProvides process for performing
a probabilistic storm surge hazard assessmentProvides an example using
historical water levels rather than simulating the storm parameters
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Deterministic Hazard Assessment
3002008113 – Evaluation of Deterministic Approaches to Characterizing Flood HazardsFreely available to the publicUses the Hierarchical Hazard Assessment (HHA) process in
NUREG/CR-7046Examines the assumptions, inputs, and methods used for
assessing external flooding hazards– Provides suggestions where changing of assumptions, inputs, and
methods might provide a more realistic, yet still bounding assessment
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Use of 3-D Modeling Techniques for Flooding
3002010673 - Investigation into the Use of Three-Dimensional Modeling Techniques to Assess Internal Flooding ScenariosFreely available to the publicEPRI examined the use of Smoothed Particle
Hydrodynamics (SPH) for modeling of internal flooding scenarios– Conclusions found that in most cases, the use of 1-D techniques is
sufficient– SPH can be beneficial to capture spray or splash effects or when the
PRA is sensitive to the timing of component failures
EPRI did not investigate the use of SPH for external flooding, but the technique may be useful for those scenarios
11© 2017 Electric Power Research Institute, Inc. All rights reserved.
EPRI’s NMAC Flood Protection Research
3002005423 – Flood Protection Systems Guide– Characterizes the flood protection systems in place
3002010620 - External Flood Protection Design/License Basis Management Best Practices Guide– Collects the administrative best practices across the industry on how
to manage the design and licensing bases
12© 2017 Electric Power Research Institute, Inc. All rights reserved.
Near-Term EPRI External Flooding Research
Collection of paleoflood evidence - 3002010667– Report at end of 2017
Guidance on conducting PRA external flooding walkdowns– Publication and training in 2018
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Potential Future External Flooding Research
Hazard assessment – Use of paleoflood data in risk-informed approaches– Estimation of frequency of hurricane-driven storm surge – Seiche and tsunami frequency estimation– Dam failure
Analysis technique– External flooding PRA model development guidance– Correlated hazards modeling (e.g., storm surge and wind)
Flood barrier fragility
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Together…Shaping the Future of Electricity
John E. WeglianSenior Technical [email protected]
Hasan CharkasSenior Technical [email protected]
