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 Tennessee River dam 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 Tennessee River 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 Dams 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 Tellico dam) – Norris Dam Failure for Load Case OBE + ½ PMF –Fontana Dam Failure for Load Case OBE + ½ PMF –Cherokee and Douglas for Load Case OBE + ½ PMF –Fontana, Hiwassee, Apalachia, and Blue Ridge Dam 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 Wheeler Dam (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 Cherokee Dam HEC‐HMS Chilhowee Dam HEC‐RAS Douglas Dam HEC‐HMS Fontana Dam HEC‐HMS Hiwassee Dam 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 Fort Loudoun‐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 Tellico Reservoir 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 . Fort Loudoun Dam –South Embankment –Marina Saddle Dam . Tellico Dam – Saddle Dams 2 and 3 –Right Bank Saddle Dam –Main Dam Works . Watts Bar Dam –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 . Melton Hill Dam Rating Curve – CDQ000020080013 – Revision 2 (1/10) –corrected turbine shut‐off time . Watts Bar Dam Rating Curve – CDQ000020080020 – Revision 3 (12/11) ‐ corrected overflow