Hydrology License Amendment Requests Watts Bar and Sequoyah Nuclear Plants July 30‐31, 2013

1 Background

. In Feb 2008, NRC inspection of the quality assurance processes and procedures for the hydrology and hydraulics model, Simulated Open Channel Hydraulics (SOCH), for the Bellefonte Combined License Application (COLA) resulted in violations regarding: –SOCH software was not in compliance with the procedure for software validation and verification –Design inputs for the hydrology model were not documented in accordance with procedure – Computer input files were not controlled in accordance with the procedure

2 Background

. TVA utilized results from an updated hydrology calculation (circa 1998) for Bellefonte COLA – Primary subject of the Feb 2008 inspection . This calculation was used as the basis for UFSAR Section 2.4 revisions – Watts Bar initiated UFSAR changes in 1998 – Sequoyah initiated UFSAR changes in 2002 . This calculation was updated for River safety improvements (modifications). All other inputs remained the same.

3 Historical Timeline of PMF

1999 & 2001 Watts Bar & Sequoyah UFSAR change 1972 reflect PMF reevaluation, Browns Ferry 1982 – 1997 respectively Dec 2009 TVA Dam Safety HESCO Hydrology Analysis Feb/March 2008 Approved by NRC Modification Program barriers installed Bellefonte NOV & Hydrology model reconstitution project started

June & Aug 1979 & 1982 2012 Sequoyah & Watts Bar 1997-1998 2004 Completion of WBN Hydrology Analysis PMF re-evaluated TVA Reservoir & SQN analysis, approved by NRC, for Operation Study respectively respectively TVA Dam Safety Mods completed

4 System Overview

Bristol Projects (2) Nolichucky Holston River Clinch River French Broad River Little Tennessee Boone South Holston Ft. Patrick Henry Watauga Thorpe (N) Wilbur John Sevier (N) Doakes Creek Douglas Nantahala Cherokee Fontana Cheoah (T) Calderwood (T) Santeetlah (T) Norris Ft. Loudoun Chilhowee (T) Melton Hill Hiwassee River Tellico Chatuge Watts Bar Plant Watts Bar Nottely Hiwassee Sequoyah Plant Apalachia Blue Ridge Elk River Chickamauga Nickajack Ocoee 1, 2, 3 Browns Ferry Plant Raccoon Mountain Tims Ford Guntersville Duck River

Cumberland River Normandy Wheeler Bear Creek Projects (4) Wilson Green River Tennessee-Tombigbee Waterway

Pickwick

Barkley (C) Note: (C) U.S. Army Corps of Engineers Ohio River Beech River Projects (8) (N) Nantahala Power & Light Company Kentucky (subsidiary of Duke Energy) (T) Brookfield Smokey Mountain Hydro Power (Formerly Tapoco)

Mississippi River 5 5 Hydrologic Calculation Flow Chart

6 Updated Analysis

. TVA initiated project in March 2008 to – Validate and verify legacy hydrology software –Verify or regenerate all model inputs . Original model assumptions kept the same unless discrepancies found –Dam discharge rating curves – Reservoir Operations

7 Model Results

WBN SQN LAR Proposed PMF 739.2 722.0 Elevation Original Licensing PMF 738.1 722.6 Elevation 1998 Calculation PMF 734.9 719.6 Elevation

8 SOCH Segment 1

9 SOCH Segment 2

10 Probable Maximum Flood

Potential Seismic Dam Failures •Re‐evaluation of the controlling dam combinations from the original analysis (plus addition of an assumed seismic failure of ) – Failure for Load Case OBE + ½ PMF – Failure for Load Case OBE + ½ PMF –Cherokee and Douglas for Load Case OBE + ½ PMF –Fontana, Hiwassee, Apalachia, and Failures for Load Case OBE + ½ PMF – Norris, Cherokee and Douglas Failures for Load Case SSE + 25 year flood •PMF elevations have enveloped the calculated Potential Dam Failure elevations in previous analyses; Potential Dam Failure analyses have determined warning times in previous analyses

11 Unit Hydrographs

. Unit Hydrographs excluding Wheeler (used for WBN & SQN) –33 directly validated –14 indirectly validated . Unit Hydrographs above (used for BLN model ‐ 2009) –39 directly validated –23 indirectly validated . Norris was previously divided into four gaged sub‐areas and lag‐routed to Norris Dam in early 1970s. The combined area was validated as a single sub‐basin in 2009. . Melton Hill was previously divided into 10 sub‐basins with synthetic unit hydrographs. It was replaced by a single unit hydrograph in 1984.

12 Unit Hydrographs Revisions

All revisions administrative or technical for Browns Ferry Nuclear only

. CDQ000020080059 Guntersville UH (49 & 50) Revision 2

. CDQ000020080060 Nickajack UH (47A & 47B) Revision 3

. CDQ000020080061 Chickamauga UH (38, 39, 40, 41, 43) Revision 2

. CDQ000020080062 Little Pigeon UH (7) Revision 2

. CDQ000020080064 Chickamauga Local UH (44B & 45) Revision 3

. CDQ000020080070 Little Tennessee above Chilhowee UH (19‐23) Revision 2

13 Inflow Hydrograph Routing

HEC Products used for Dam Failure Outflows Blue Ridge Dam HEC‐RAS HEC‐HMS HEC‐RAS HEC‐HMS Fontana Dam HEC‐HMS HEC‐RAS Norris Dam HEC‐HMS

14 Computational Time Step

. Use of different model configurations and time steps in the SOCH model can produce reasonable, but different, results. . Downstream impact (BLN & BFN) is greater than upstream impact (SQN & WBN). . Model configuration revised (for BLN & BFN) to allow for an increased time step. . Test simulation with revised model configuration with longer time steps results in the same elevation at WBN and a slightly lower elevation at SQN.

15 Revised Configuration

. Segment 1 (for WBN and SQN) –No revisions. Limited to 5 second time step due to ‐Tellico Canal. . Segment 2 (for WBN and SQN) –No revisions. Limited to 5 second time step due to Lick Branch.

16 Revisions to Calculations Resulting from Time Step Issue

. CDQ000020080059 Guntersville UH (49 & 50) Revision 2 due to time‐step issue . CDQ000020080060 Nickajack UH (47A & 47B) Revision 4 due to time‐step issue . CDQ000020080064 Chickamauga Local UH (44B & 45) Revision 3 due to time‐step issue . CDQ000020080039 Chickamauga Calibration Revision 3 . CDQ000020080040 Nickajack Calibration Revision 3 . CDQ000020080041 Guntersville Calibration Revision 3 . Others evaluated, but not changed for WBN and SQN time step: – CDQ000020080054, CDQ000020080080, CDQ000020080081, CDQ000020080082

17 Geometry Revisions

. In general, the two main types of changes to geometry are: –Extension of cross‐sections because of overtopping during simulations – Addition or removal of interpolated cross‐sections for model stability . Additional types of changes include: – Addition of slots in channel bottoms for stability – Adjustment of Manning’s n for stability – Addition of a channel geometry cross‐section in place of a failed dam – Revision of storage calculation for drain down analysis

18 Revisions to Geometry Differing from those used by PNNL

Calculation Geometry Affected Modification CDQ80 Appendices E & F, CDQ82 Extended cross‐section to higher Appendix A15 cross‐sections elevation. CDQ80 Fort Loudoun – Tellico Canal 1 foot slot added for stability CDQ80 Appendix BFort Loudoun – Tellico Canal 14 foot slot added for stability. Interpolated section between TRM CDQ82 Appendix A 0.3 and 33.6 in Cross‐section removed Extended cross‐section to higher CDQ80 Appendix A5 cross‐sections elevation CDQ80 Appendix ACRM 23.1 Copied cross‐section from Lower Clinch Extended cross‐section to higher CDQ80 Appendix B5 cross‐sections elevation CDQ54 Appendices A, B, H, K, and M Extended cross‐section to higher 7 cross‐sections CDQ80 Appendix B elevation Extended cross‐section to higher CDQ82 Appendix A–Fontana Failure 38 cross‐sections elevation Manning’s n value changed for stability CDQ54 RM 2.86 and consistency CDQ54 Appendices E –H and MRM 2.62 Interpolated cross‐section removed

19 Revisions to Geometry Differing from those used by PNNL

Calculation Geometry Affected Modification Cross‐sections between TRM 480.5 CDQ54 and 471.0 Removal of interpolated cross‐sections Manning’s n value changed for stability RM 2.86 CDQ80 and consistency CDQ80 RM 2.62 Interpolated cross‐section removed Cross‐sections between TRM 480.5 CDQ80 and 471.0 Removal of interpolated cross‐sections Manning’s n value changed for stability CDQ82 RM 2.86 and consistency Cross‐sections between TRM 480.5 CDQ82 and 471.0 Removal of interpolated cross‐sections Extended cross‐section to higher CDQ82 30 Cross‐sections elevation. Extended cross‐section to higher CDQ54 Appendices E, F, and G5 cross‐sections elevation. Extended cross‐section to higher CDQ54 Appendices H and M3 cross‐sections elevation. Cross‐section revised to include storage CDQ81 3 cross‐sections available at Lick Branch and North Chickamauga Creek

20 Dam Rating Curve Differences

Changes from FSAR to LAR . Assumed maximum openings . Orifice discharge coefficients . Submergence effects – reference data for spillway free flow used –model data for orifice flow available . HESCO Concertainers . Turbine discharge . Rim Leaks

21 HESCO Concertainers

. Cherokee –North Embankment –South Embankment –Three Saddle Dams . –South Embankment –Marina Saddle Dam . Tellico Dam – Saddle Dams 2 and 3 –Right Bank Saddle Dam –Main Dam Works . –East Embankment

22 Dam Rating Curve Revisions

. Fort Loudoun Dam Rating Curve – CDQ00002008009 ‐Revision 3 (6/12) – added rim leaks . Tellico Dam Rating Curve – CDQ000020080018 – Revision 2 (7/10) –corrected saddle dam elevation and HESCO barrier elevations . Rating Curve – CDQ000020080013 – Revision 2 (1/10) –corrected turbine shut‐off time . Watts Bar Dam Rating Curve – CDQ000020080020 – Revision 3 (12/11) ‐ corrected overflow length in East Embankment failure, corrected barrier elevations Revision 4 (6/12) – added rim leaks

23 Dam Rating Curve Revisions

. Rating Curve – CDQ000020080006 – Revision 2 (6/11) ‐ added case for south embankment failure for drain down analysis . Rating Curve – CDQ000020080014 – Revision 2 (6/12) – added rim leaks . Rating Curve – CDQ000020080011 – Revision 3 (6/11) – added case for BFN, no impact to WBN/SQN

24 Lock Gate Failure

. Flow over the lock gates is accounted for in the dam rating curves . Stability of the lock gates evaluated for PMF loading –Hydrostatic load of the PMF was compared to the design impact load of the lock gate –Design margin ratios developed for each dam –No catastrophic failure during a PMF event – Operability of the gates during and after the event was not considered • Assumed unavailable during and after the event

25 Fort Loudoun Rim Leak

. A rim leak was identified at Fort Loudoun . Lowest elevation of the rim leak was elevation 835.15 feet . PMF elevation is 835.63 feet . Impact to PMF is negligible

26 Fort Loudoun Rim Leak

27 Nickajack Rim Leak

. A rim leak was identified at Nickajack 2,500 feet northeast of the Dam. . Lowest elevation of the rim leak was elevation 654.54 feet . PMF elevation is 667.41 feet . Impact to PMF is negligible given that Nickajack is a significant distance downstream of Watts Bar and Sequoyah nuclear plants . Nickajack is not failed during the analysis of Watts Bar and Sequoyah nuclear plants

28 Nickajack Rim Leak

Q max = 2,533cfs

29 Watts Bar Rim Leaks

30 Watts Bar Rim Leak Routing

. Seven Rim Leaks were identified –4 east of the dam –3 west of the dam . Discharge of rim leaks 1‐6 are combined with Watts Bar Dam discharge for Segment 1 simulations . Rim leak 7 was removed at TRM 538.40 for Segment 1 simulations

31 Watts Bar Rim Leak Routing

. Segment 2 simulations separated the rim leak discharge from the main dam discharge . West rim leaks were added as a concentrated local at Yellow Creek at TRM 526.82 without attenuation. . East rim leaks were added as a concentrated local at Watts Creek at TRM 528 without attenuation

32 Watts Bar West Saddle Dam

. Total failure postulated for West Saddle Dam (consistent with previous model assumption) . Discharge of West Saddle Dam combined with Watts Bar Dam discharge for Segment 1 simulations . Segment 2 simulations separated the West Saddle Dam discharge and added it as a concentrated local at Yellow Creek at TRM 526.82 without attenuation. – Yellow Creek is the natural drainage path –HEC‐RAS study model for Yellow Creek determined negligible attenuation effect on flow from the West Saddle Dam to the mouth of Yellow Creek.

33 Watts Bar West Saddle Dam

34 Dallas Bay Routing

. Dallas Bay, Lick Branch, and North Chickamauga Creek geometry –Take advantage of storage in the reaches – Account for the submergence effects of the rim leak on the Chickamauga Dam tailwater . Use SOCH to develop an elevation/discharge relationship at the rim leak . Only valid when no failures are postulated at Chickamauga Dam

35 Dallas Bay / Lick Branch Rim Leak

36 Assumptions

Assumption FSAR LAR Chickamauga Lock Configuration Current Lock Current Lock Modeled as a rating curve at Dallas Bay/Lick Branch/North Chickamauga Cr Included in the unsteady SOCH model Chickamauga Dam West Saddle Dam Failure Total Failure Total Failure Modeled as a rating curve at Discharge separated as a local in West Saddle Dam Routing Watts Bar Dam Yellow Creek The average tailwater rating Correction for submergence was Correction for Submergence curve used for each event performed for each event HESCO Concertainers Not included Included for PMF simulations Operational Allowances Not included Evaluated for each simulation Rim Leaks at Fort Loudoun, Watts Bar, and Not included Included Nickajack Melton Hill Reservoir Level pool routing Unsteady SOCH model Hiwassee River (mouth to HRM 18.9) Lag routed Unsteady SOCH model

Turbine Discharge Evaluated for main river dams Evaluated for all dams with turbines

If operating deck was overtopped then Operational Deck/Gate operability Not considered the gates are assumed to be inoperable on the recession side Downstream Dams No failures assumed No failures assumed Loss Method API API Norris Subbasins 4 1 Melton Hill Subbasins 10 1 37