Dr. Yan Gao - WG Chair (WEC)

Presented by Mr. Ray Schneider -

WG Member (WEC)

1

Federal Agencies PFHA Workshop 

January 29 - 31, 2013 
Topics

 Background

 Objective/Scope

 Probabilistic Approach

 Present Status

 Q & A

ANS-2.8 2
Background

 Historical - ANSI/ANS-2.8 (1992) “Determining design basis flooding at Nuclear Power sites” – administratively withdrawn

 − Scope considered flooding caused by

• Precipitation, snowmelt and any resulting dam failures

• Seismically-induced and “sunny day” dam failures

• Surge and seiche and attendant wind generation

• Local intense precipitation (pluvial flooding)

• Ice effects, and 

• A reasonable combination of these events.

− Intent to establish a methodology for a design basis flood hazard with 

“virtually no risk of exceedance” (i.e. Probable Maximum Floods (PMFs), 

Probable Maximum Hurricanes (PMH), etc.) deterministically defined 

bounding values with anticipated mean as low as < 10-6/yr mean probability of exceedence

− Excluded consideration of tsunamis

− Appendix B (not formally part of standard) estimated expected 

frequencies of recommended combinations

− Withdrawn in 2002 by ANSI rules and not subsequently updated

ANS-2.8 3
Background - continued

 ANSI/ANS-2.8-201X being developed to fill an important nuclear 

standards gap 

 Reflect nuclear site flooding events since 1992

 Insights from Hurricane Katrina surges

 Record Mississippi and Red River floods

 Combined flooding events at a European coastal site 

 Include surge effects of tsunamis

 Integrate consideration of “climate change” effects 

 Reflect state-of-the-art enhancements in technology, 

computation methods and capabilities in fluid dynamics and 

hydrology

 Extend application from power reactors to all nuclear facilities 

which required design basis flood estimation as a function of 

return periods

 Rationalize treatment of “probable maximum”

ANS-2.8 4
Objective

 Develop ANSI/ANS voluntary consensus standard for 

determining a full range of external flood hazards

 Serve as a reference for siting nuclear facilities, SSC 

design, and evaluation of flood protection features

 Deterministic methods screening process

 Deterministic methods focus on bounding flood hazards 

(when possible and desirable) 

 Probabilistic risk informed methods for treating frequencybased hazard requirements and understanding hazard 

uncertainties 

 Identify “best practices” and technologies for 

performing the above assessments using new flood data 

and technical knowledge gained over past 20 years

ANS-2.8 5
Scope

 Riverine flooding

 Rainfall, snowmelt

 Controlled and uncontrolled releases from upstream dams

 Upstream dam failure

- Hydrologic

- Non-hydrologic (seismic, intrinsic, other)

 Hurricane-induced storm surge

 Wind- and earthquake-generated seiche

 Tsunami

 Seismically-initiated

 Landslide-initiated

ANS-2.8 6
Outside of Scope

 Low water

 Dispersion, dilution and travel time of accident release 

of effluents

 Local intense precipitation (ANS-2.31 under 

development)

 Groundwater (Addressed in ANSI/ANS-2.17)

 Internal or external flooding from failure of pipes or 

tanks

 Standard does not specify:

 Requirements regarding acceptability of any particular hazard 

frequency or hazard profile 

 Guidance on appropriateness of facility flood protection or 

mitigation systems

ANS-2.8 7
Probabilistic Approach - example

 Riverine Flood

√ Riverine Probabilistic Flood Hazard Analysis (PFHA)

√ Probabilistic Aleatory Modeling

√ Probabilistic Epistemic Uncertainty Modeling

ANS-2.8 8
Typical Results of Probabilistic Approach 

ANS-2.8 9

• Example 

external 

flood 

hazard 

curve

• Combined 

events 

consideration
Present Status – 21-Member WG

 Y. Gao (Chair), Westinghouse Electric Company

 R. Schneider, Westinghouse Electric Company 

 M. McCann, Jack Benjamin & Associates, Inc

 J. Kanney, U.S. Nuclear Regulatory Commission

 C. Mazzola, Shaw Environmental Inc.

 J. Stevenson, J.D. Stevenson Associates

 K. Bryson, Chair, ANS-25 Subcommittee

 K. Ng, Bechtel Power Corp.

 J. Hunt, B&W technical Services Y-12

 J. August, CORE Inc.

 Q. Hossain, Lawrence Livermore National Laboratory

 V. Anderson, Nuclear Energy Institute

 J. Stedinger, Cornell University

 R. Rishel, Duke Energy

 D. Finnicum, Westinghouse Electric Company

 G. Love, BWSC Co.

 L. Cieslik, HDR Co.

 G. Meyers, Department of Energy HS-32

 P. Watts, Applied Fluids Co.

 V. Titov, NOAA/Pacific National Environmental Laboratory

 G. Gaillot, Shaw Environmental Inc.

ANS-2.8 10
Present Status – continued

 Working draft actively being generated

 Methods and approaches reflect current industry 

practice and capabilities

 This PFHA Workshop will provide extremely 

important insights into method selection and 

application

 Compilation of WG member inputs in process

 Completion target – later this year

ANS 11 -2.8
Questions??

ANS-2.8 12