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Presentation at December 3, 2014, Category 1 Public Meeting with Duke Energy Carolinas, LLC to Discuss NTTF Recommendation 2.1, Flooding Response
	ML14356A006
Person / Time
Site:	Oconee
Issue date:	12/03/2014
From:	; Duke Energy Carolinas
To:	; Division of Operating Reactor Licensing
	Hall V, NRR/JLD, 415-2915
References
	Download: ML14356A006 (19)
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Jocassee Dam Breach Analysis NRC Technical Presentation Rockville, MD December 3, 2014 For Information Only

For Information Only Dave Baxter, GM, Oconee Regulatory Project Completion Ed Burchfield, GM, Oconee Nuclear Station Engineering Dean Hubbard, Eng. Director, Fukushima External Flooding Benjamin Zoeller, Water Resources Engineer, AMEC Brian Stevens, Water Resources Engineer, AMEC Chris Ey, HDR Civil Engineering Manager Adam Johnson, Oconee Fukushima Engineering 2

For Information Only Agenda Purpose & Scope

Background

Request for Additional Information - Scope Breach Analysis JLD-ISG 2013-01 Conformance Key assumptions Breach Results 2D Modeling - TUFLOW FV TUFLOW FV Selection TUFLOW FV Validation Summary 3

For Information Only Background / Timeline Fukushima 50.54(f) Requires reevaluation of all flooding hazards using present-day guidance and methodologies Deterministic failure of upstream dams required.

Fukushima Hazard Reevaluation Submitted March 12, 2013 Request for Additional Information, September 15, 2014 - Resubmit dam failure analysis applying alternate breach-parameter estimations Jocassee Dam failure reanalyzed using JLD-ISG-2013-01 On schedule to meet submittal of revised FHRR by 2/13/15 Initial results to be discussed today 4

For Information Only NRC Request for Additional Information September 15, 2014

Reanalyze and resubmit the dam failure analyses for the ONS, Units 1, 2 and 3 FHRR after applying alternate breach-parameter estimations.

The staff requests that the model results not rely on a single methodology Instead, the staff requests comparison of results for several models judged appropriate.

Although the Oconee FHRR was submitted before JLD-ISG-2013-1 which was completed in July, 2013, this JLD-ISG may provide useful guidance regarding application of breach models the NRC staff find appropriate for use.

Justification should be provided for the selection of the candidate breach models used as well as the selected value(s) used in the hydraulic model.

Parameter uncertainty as well as parameter sensitivity in the final model results should be explicitly addressed in the response.

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For Information Only JLD-ISG-2013-01 Conformance JLD-ISG 2013-01 Dam Failure Guidance Sunny Day Failure - deterministic failure assumed Hydrologic Failure - not credible Seismic Failure - not credible (separate RAI response)

JLD-ISG 2013-01 7.2 Breach Modeling of Embankment Dams Uses multiple common regression equations for breach parameters sensitivity studies and to predict parameters Uses multiple common regression equations for peak outflow sensitivity studies Multiple modeling methods used including regression, physics based and historical failure comparative analysis Hierarchical hazard assessment (HHA) used with conservative plausible assumptions consistent with available data 6

For Information Only Key Assumptions Starting reservoir elevation 1100 msl (maximum operating level)

Sunny day piping failure initiating at 1020 msl at the West Abutment Breach starts at West Abutment and expands toward dam center Formation in one direction limits the breach size (w/ rock abutment)

Peak outflow occurs prior to full breach based on decreasing head differential and resulting water velocities Breach time recognizes time required to empty the reservoir Bottom of breach at 800 ft msl based on Keowee reservoir full pool elevation. Note the 800 ft msl, the distance from the upstream face to the downstream face of the dam is 1324 feet 7

For Information Only Jocassee Breach Modeling Multiple Methods Applied

Regression equations used for sensitivity input

Von Thun and Gillette (1990)

Froehlich (1995)

Froehlich (2008)

USBR (1982)

Costa (1985)

McDonald Langridge-Monopolis (1984)

Physics based model sensitivity input

NWS Breach Model

Routing Methodologies

HEC-RAS, V4.1

Historical failure comparison to empirical breach equations

Hell Hole

Teton Dam

Oros Dam 8

For Information Only Breach Analysis Summary (Draft) 9 Final Jocassee Dam Breach Parameters Top Width 959 ft Bottom Width 634 ft Side Slopes 0.5 H: 1V Final Bottom Elevation 800 ft Breach Development Time 2.1 hrs Full Formation Time 10.2 hrs Time to Empty Reservoir 19.2 hrs Computed Peak Outflow at Jocassee Dam 2,846,010 cfs

For Information Only Jocassee Dam Breach Progression and Hydrographs 10 0

1,000,000 2,000,000 3,000,000 4,000,000 5,000,000 6,000,000 0.00 0.20 0.40 0.60 0.80 1.00 1.20 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00 24.00 Flow (cfs)

Elevation (ft/1,000) and Fraction of Breach Progression Time (Hours)

Jocassee Dam Breach Progression and Hydrographs Headwater Tailwater Breach Progression Breach Discharge

For Information Only Jocassee HEC-RAS Breach Progression 11 A

Time to Empty Reservoir = 19.2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months B

Full Formation Time as Defined by Froehlich = 10.2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months C

Breach formation to peak outflow = 2.1 hours1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months D

Breach formation limited to 70% at the point of peak outflow

For Information Only Peak Outflow Sensitivity 12 Peak Flow Predictors Peak Breach Outflow (m3/sec)

Peak Breach Outflow (cfs)

USBR 1982 (envelope) 94,069 3,322,010 Froehlich 1995 90,999 3,213,590 Jocassee Outflow 80,590 2,846,010 Costa 1985 (Dam Height) 56,692 2,002,060 Costa 1985 (Dam Factor) 47,376 1,673,070 MLM 1984 44,209 1,561230 Costa 1985 (Reservoir Volume) 31,438 1,110,220

For Information Only Jocassee Dam Peak Outflow vs. Empirical Peak Flow Predictors and Historical Data 13 0

500000 1000000 1500000 2000000 2500000 3000000 3500000 0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0 400.0 Peak Outflow (cfs)

Breach Height (ft)

Jocassee Dam Peak Outflow vs. Empirical Peak Flow Predictors and Historical Data Historical Dams Jocassee Peak Outflow with Recommended Breach Parameters Froehlich 1995 USBR 1982 Costa 1985 (Dam Factor)

Costa 1985 (Volume)

Costa 1985 (Dam Height)

MLM 1984 Linear (Historical Dams)

For Information Only Comparison of Empirical Breach Equations to Historical Failures

Prediction of Embankment Dam Breach Parameters-USBR, states that Froehlich (1995) is the best predictor of breach width for cases with observed breach widths less than 50 meters.

The largest dam included in the database used to develop the Froehlich equations is La Fruta Dam in Texas, with a volume of water above breach of 64,000 acre-feet.

By comparison, Oros Dam had a reservoir storage volume of approximately 535,000 acre-feet and Jocassee Dam has a reservoir storage volume of 1,160,298 acre-feet.

Breach parameters computed using Von Thun and Gillette, Froehlich (1995), and Froehlich (2008) were compared to observed parameters for three of the largest historical dam failures to date where breach data was collected (Hell Hole Dam, Teton Dam, and Oros Dam).

Von Thun and Gillette equations estimated breach parameters provide the best representation for the three historical dam failures, particularly the largest volume dam, Oros Dam. The empirical predicted breach widths with the breach widths of twelve historical dam failures as a function of reservoir volume were compared.

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For Information Only Linear Trend of Historic Breach Width vs.

Reservoir Volume 15 0

200 400 600 800 1000 1200 1400 1600 0

500000 1000000 1500000 2000000 2500000 Average Breach Width (ft)

Volume (acre-ft)

Historical and Empirical Breach Widths as a Function of Volume Database reservoir volume vs.

avg width Von Thun Avg Width NWS BREACH Width Froehlich 1995 Froehlich 2008 Linear (Database reservoir volume vs. avg width)

Dam Reservoir Volume (acre-ft)

Average Breach Width (ft)

Dam Reservoir Volume (acre-ft)

Average Breach Width (ft)

Taum Sauk 4,600 680 Lower Otay 40,000 436 Zhugou 14,900 443 Shimantan 94,900 1,204 Johnsontown, PA 15,300 310 Nanaksagar 170,000 500 Longtun 24,300 392 Teton Dam 251,300 495 Hell Hole Dam 24,800 397 Banqiao 492,500 955 Jiahezi 34,000 392 Oros Dam 535,000 541

For Information Only 2D Modeling - TUFLOW FV TUFLOW FV Selection SRH-2D used in previous analysis (finite-volume numerical scheme)

TUFLOW FV (Finite Volume) represents state of the practice model includes time-varying bed elevation solutions Logic controls provide for dynamic response (automated breach initiation)

Stable platform solving shallow water equations, active development, ability to handle large models Enhanced numerical solution speed (hours vs weeks)

Ability to solve equations using high speed parallel processors 16

For Information Only 2D Modeling - TUFLOW FV cont.

TUFLOW FV Validation Model has been in development since 2008 Model developed for in-house professional use prior to releasing as a commercial product (similar to SRH2D)

UK Environment Agency Benchmarking S&L Validation for OPPD (Appendix B application)

SRH-2D / TUFLOW FV comparison with Oconee data 17

For Information Only Summary

Von Thun Gillette breach equations are best suited for the analysis of Jocassee Dam based on a linear trendline of average breach widths vs. reservoir volume

The key to a conservative and realistic peak outflow lies in the breach progression pattern used in the HEC-RAS

The breach development was limited to 70% during the breach development phase based on sensitivity analysis on breach development time which allows the peak outflow to align with historical data

The breach width was limited to 80% of the total width predicted by the Von Thun and Gillette where the breach is assumed to initiate at one of the abutments and growth would be limited by the abutment in one direction. This is supported by the historic Teton Dam failure where the piping failure and subsequent breach occurred against the abutment

Full formation time using Froehlichs definition is 10.2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months (including part of the 2.1 hours1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months to reach the peak outflow value)

The time to empty reservoir was calculated to be 19.2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months to account for the continuation of breach growth until the reservoir is fully drained. The rate of breach formation after the development time is proportional to the depth of water in the reservoir at each time step in relation to the final pool level

The breach analysis is a refined analysis based on conservative but plausible assumptions based on multiple and diverse methods that are consistent with historical failure data 18

For Information Only Questions or Comments?

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