ML12348A208

12/13/12 Meeting Slides Re TVA Hydrology Update Slides

ML12348A208
Person / Time
Site:	Watts Bar
Issue date:	12/13/2012
From:	Tennessee Valley Authority
To:	Andrew Hon Plant Licensing Branch II
Hon, Andy
References
Download: ML12348A208 (56)

Text

N l Nuclear TVA Hydrology Update December 13, 2012

Purpose p

• License Amendment Request (LAR) Review Status

• Updated Information on Temporary Dam Modifications

• Status of Fukushima NTTF Recommendation 2.1 Flood Hazards Reevaluation

• Update on June 2012 Commitments 2

Agenda g

• Introduction

• Updated Hydrology Analysis Tools

• License Amendment Request (LAR) Review

• Temporary Flood Barriers at TVA Dams

• NTTF Recommendation 2.1 Flood Hazards Reevaluation

• TVA Flood Mode Operation Improvement Strategy

• Commitment Status

• Closing Remarks 3

Introduction 4

Introduction

• TVA is performing continued analysis of the hydrology off the h TTennessee Ri River

• TVA is implementing commitments from J

June 13, 13 2012 letter l tt

• TVA is deploying a Fleet Flood Mode Operation Improvement Strategy 5

Tennessee River System Overview Sequoyah Plant Browns Ferry Plant 6

Updated Hydrology Analysis Tools 7

Updated Hydrology Analysis Tools

• TVA conversion of hydraulic modeling tools in progress

• TVA converting from SOCH to USACE HEC-RAS for flood routing calculations for the Tennessee River and selected tributaries

- USACE HEC HEC-RAS RAS used sed eextensively tensi el in recentl recently appro approved ed Combined License Applications

- USACE HEC-RAS is easier to implement, shorter computing times

- Easily adopted to Tennessee River Watershed with minimal refinements to inputs

• Can accommodate more refined geographical input than SOCH model

• Volume check performed in SOCH and HEC-RAS to confirm storage input data

• Consistent with Fukushima NTTF Recommendation 2.1 Flood Hazards Reevaluation guidance 8

Updated Hydrology Analysis Tools

• HEC-RAS conversion process

- Input updates for HEC-RAS requirements

- HEC-RAS unsteady flow models for each reservoir calibrated against March 1973 and May 2003 floods

- Certain current licensing basis legacy codes are not used, and will no longer be needed

• CONVEY

• WWIDTH

- Certain current licensing basis legacy codes are currently retained, may be replaced in future by USACE HEC-HMS

• FLDHYDRO

• TRBROUTE

- Certain current licensing basis legacy codes may be retained in the future

• CHANROUT

• UNIGRAPH

• DBREACH 9

Updated Hydrology Analysis Tools

• Status of conversion from SOCH to USACE HEC-RAS

- Updates of inputs to match HEC-RAS requirements - COMPLETE

- Verification and validation of software - COMPLETE

• Validated USACE HEC HEC-RAS RAS code under TVA Quality Assurance Plan

• Significant oversight by TVA Nuclear Power Group of Contractor during implementation

- Application of HEC-RAS to date includes:

• Examined selected current licensing basis cases

• Evaluated consequence of overtopping and breaching selected upstream dam embankments

- Planned application of HEC HEC-RAS RAS includes:

• NTTF Recommendation 2.1 Flood Hazards Reevaluation

• Sensitivity analyses related to HESCO modular flood barrier performance

• Reanalysis of current licensing basis cases 10

License Amendment Request (LAR)

Review 11

License Amendment Request (LAR)

Review

• WBN Unit 1 LAR submitted Julyy 19, 2012

• SQN Units 1 and 2 LAR submitted August 10, 2012

• Update required to WBN Unit 1 LAR to reflect emergent issue involving Main Control Room (MCR) and 6.9kV Shutdown Board Room ((SDBR)) Chillers

- Does not affect the hydrologic analysis as described in the LAR

- Supplement to be submitted by January 31, 2013 12

License Amendment Request (LAR)

Review

• Selected current licensingg basis cases simulated usingg HEC-RAS

- Rainfall induced PMF cases:

• WBN and SQN 21,400 sq mile winter storm

• WBN and SQN 7,980 sq mile winter storm

• Calculation complete for WBN

• Letter report complete for SQN

- Seismically induced dam failure case:

• Combination Norris Norris-Tellico Tellico Dam seismically induced dam failure (WBN only)

• Operating Basis Earthquake (OBE) with one-half PMF

• Selected because current limiting WBN flood warning time event

• Letter report complete 13

License Amendment Request (LAR)

Review

• Results of selected current licensingg basis cases usingg HEC-RAS

- WBN rainfall induced PMF

• 7,980 sq milel winter storm PMF = 738.0

• 21,400 sq mile winter storm PMF = 738.7 (WBN LAR PMF level = 739.2)

• Surge level in Auxiliary Building = 739.2 (WBN LAR surge level = 739.7)

- SQN SQ rainfall i f ll iinduced d d PMF

• 7,980 sq mile winter storm PMF = 718.7

• 21,400 sq mile winter storm PMF = 720.5 (SQN LAR PMF level = 722.0)

• Wind wave runup for SQN Diesel Generator Building below operating floor elevation

- WBN Norris-Tellico Dam seismically induced dam failure case

• OBE and one-half PMF = 727.8 (below plant grade of 728.0, WBN LAR level = 728.7)

• Current limiting WBN flood wave travel time event

• Flood wave travel time = 28.3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> (WBN LAR time = 27 hours3.125e-4 days <br />0.0075 hours <br />4.464286e-5 weeks <br />1.02735e-5 months <br />) 14

License Amendment Request (LAR)

Review

• Plans forward for reanalysis of all current licensing basis cases using HEC-RAS

- Update of following hydrologic analyses methodology/results

• Rainfall induced PMF cases

• Seismically induced dam failure cases

• Flood warning time cases

- TVA is evaluating the sequencing for reanalyzing the current licensing basis cases with HEC-RAS

- WBN and SQN UFSAR updates will be submitted to reflect these cases upon completion of the reanalysis effort

• TVA requests continued review of WBN and SQN LARs 15

Temporary Flood Barriers at TVA Dams 16

Temporary Flood Barriers at TVA Dams

• Background

• Design of Temporary Flood Barriers

• Actions Completed for Temporary Flood Barriers

• Status of Permanent Modifications at Cherokee, Fort Loudoun, Tellico, and Watts Bar Dams

• Results of Inspections of Temporary Flood Barriers

• Results of Breach Analysis

• y with No Temporary Results of Analysis p y Flood Barriers

• Status of Actions to Address Breach Initiators

• Results of Computational Fluid Dynamics (CFD) Analysis

• Regulatory Process for Temporary Flood Barriers 17

Temporary Flood Barriers at TVA Dams

• In 2009, TVA installed temporary modular flood barriers to preserve the assumption of no embankment failure by overtopping during a rainfall induced PMF event

- Fort Loudon Dam - Cherokee Dam

- Tellico Dam - Watts Bar Dam

• Rainfall induced PMF analysis in the LARs credits increased h h off the height h embankments b k at these h d dams

- Preserves assumption of no embankment failures by overtopping

• Seismically induced dam failure analysis does not credit flood barriers

- Embankments can fail if overtopped in analysis 18

Temporary Flood Barriers at TVA Dams 19

Temporary Flood Barriers at TVA Dams

• Barriers are engineered, interconnected, geotextile lined, and crushed compacted stone filled HESCO Concertainer Baskets

• Geotextile is a heavy-duty, non-woven, permeable, interlocked, polypropylene l l ffabric bi W Welded ld d Wi Wire M Mesh, h coil, il and d pins i Alu-Zinc Al Zi coated Steel, wire diameter of 0.16 inch, with spacing of 3" x 3

• Size: 3X3X3 3 X3 X3 or 3 3X3X4 X3 X4 Weight of One Section: 1 1.6 6 - 2.2 2 2 tons

• Fill Material: #10 crushed stone meeting TDOT Specifications

( ), 903.01(f) 903.01(e), ( ) or 903.22 20

Temporary Flood Barriers at TVA Dams Temporary Flood Barriers at Fort Loudoun Dam 21

Temporary Flood Barriers at TVA Dams

• Since the May 31, 2012 TVA presentation, the following actions have been i l implemented d iinvolving l i the h temporary HESCO modular d l fl flood db barriers i

- Made progress on permanent modifications

- Implemented procedures for semi-annual inspections

• Inspection frequency increased to monthly in December 2012

- Submitted summary of the results of an analysis of flood levels at SQN Units 1 and 2 and WBN Unit 1 using SOCH for the 21,400 sq mile storm that assumes a failure off a section ti off ththe b barriers i and d earthen th embankments b k t

- Completed an analysis of flood levels at SQN Units 1 and 2 and WBN Unit 1 using HEC-RAS for the 7,980 winter storm without the barriers

- C Completed l t daC Computational t ti l Fl Fluid id D Dynamics i (CFD) model d l ffor FFortt LLoudoun d and d

Tellico Reservoirs to demonstrate flow velocity profiles in the reservoirs at PMF levels, and to calculate velocities and trajectories of large objects as they pp approach Fort Loudoun Dam

- Initiating corrective actions to ensure 2009 decision to install temporary HESCO modular flood barriers addresses required regulatory process 22

Temporary Flood Barriers at TVA Dams

• Modifications at Cherokee, Fort Loudoun, Tellico, and Watts Bar Dams to be i l implemented d to replace l HESCO modular d l flflooddb barriers i

• Project Status

- TVA published a Notice of Intent (NOI) in the Federal Register in June 2011

- Scoping completed for the Draft Environmental Impact Statement (DEIS) in September 2011

- Initial conceptual design and alternatives developed to support DEIS

- DEIS issued September 2012

- Public meeting to discuss the project and accept comments held on October 25, 2012

• Schedule

- Public comments for DEIS received and being addressed

- Final Environmental Impact Statement (FEIS) scheduled to be complete by February 4, 2013, and Notice of Availability published on February 11, 2013

- TVA Senior Vice President of River Operations and Renewables final decision will be documented in a Record of Decision (ROD) scheduled for March 13 13, 2013

- Completion of modifications scheduled by October 2015 23

Temporary Flood Barriers at TVA Dams

• Results of TVA Nuclear Power Group inspections of the temporary HESCO flood fl dbbarriers i iinstalled ll d at Ch Cherokee,k FFort LLoudoun, d TTellico, lli and dW Watts BBar reservoirs

- Minor deficiencies from visual inspection of modular flood barriers

- No deficiencies d f ffrom inspection off staged d materials l ffor closure l off public bl access gaps in modular flood barriers

- Procedures used to close public access gaps found to be up-to-date

- Contact information in the River Operations and Renewables Emergency Action Plan Supplements found to be up-to-date

• TVA River Operations performs independent inspections on a monthly basis

• TVA Nuclear Power Group increased frequency of independent inspections to monthly

• TVA has performed reasonable simulation of TVA procedures for closure of gaps in the temporary flood barriers 24

Temporary Flood Barriers at TVA Dams

• Analysis of flood levels at SQN Units 1 and 2 and WBN Unit 1 assuming HESCO barrier b i b breaches h

- Failure of HESCO flood barriers and earthen embankments at Fort Loudoun, Cherokee, Tellico, and Watts Bar Dams modeled

- Segment 1 of both 21 21,400 400 sq mile and 77,980 980 sq mile storms revised in model

- SOCH hydraulic modeling consistent with SQN and WBN LAR

- Dam rating curves revised to model embankment failures

- New outflow hydrograph required for Cherokee Dam during the 7 7,980 980 sq mile storm

- Barriers stay in place and then fail at peak headwater elevation or when overtopped

- Portion of embankments with flood barriers at Fort Loudoun and Tellico Dams fails

- Flood wave overtops east wall at Watts Bar DamDam, causing breach of Watts Bar East Embankment

- Segment 1A and 2 of the models same as SQN and WBN LARs

- No downstream dams, including embankments or gates, are assumed to fail 25

Temporary Flood Barriers at TVA Dams

• Analysis of flood levels at SQN Units 1 and 2 and WBN Unit 1 assuming HESCO barrier b i b breachesh ((contd)d)

- Breach configurations based on review of different methods discussed in Prediction of Embankment Dam Breach Parameters (U.S. Department of the Interior)

- Breach configuration based on Federal Energy Regulatory Commission (FERC) approach

- Single embankment at each dam postulated to fail

- Size of breach a function of breach depth, assumed failure down to bedrock

- Main embankment adjacent to each dam spillway selected where bedrock elevations known

- Cherokee Dam has barriers on North Embankment, South Embankment, and three Saddle Dams; South Embankment modeled to partially fail

- Fort Loudoun Dam has barriers on South Embankment and the Marina Saddle Dam; South Embankment modeled to partially fail

- Tellico Dam has barriers on Right Bank Saddle Dam, Main Dam Works Embankment, Saddle Dam 2, and Saddle Dam 3; Main Dam Works Embankment modeled to partially fail

- Watts W tt Bar B DamD has h b barriers i on EEastt EEarth th EEmbankment; b k t EEastt EEarth th EEmbankment b k t modeled d l d tto partially fail 26

Temporary Flood Barriers at TVA Dams

• Results provided to NRC by letter dated October 30, 2012

• Results demonstrate need for HESCO modular flood barriers to prevent overtopping of the earthen embankments during PMF events 27

Temporary Flood Barriers at TVA Dams

• Analysis of flood levels at WBN Unit 1 assuming HESCO barriers are not i

installed ll d - and dddams are overtopped d

- Failure of earthen embankments at Fort Loudoun, Cherokee, Tellico, and Watts Bar Dams modeled

- 7,980 7 980 sq mile March storm modeled

- Validated and verified HEC-RAS hydraulic modeling

- DBREACH, a validated and verified code, utilized to establish timing of the failure of the West Saddle Dam at Watts Bar Dam

- No downstream dams, including embankments or gates, are assumed to fail

- Breach failures assumed progressive in nature rather than instantaneous

- Revision of unsteady flow rules required because of breaches

- If upstream dam operating deck overtopped, spillway gates remain open and cannot be closed

- Earthen structures upstream of the site fail at two ft of overtopping, West Saddle Dam at W tt Bar Watts B Dam D fails f il bbased d on DBREACH timing ti i

- Melton Hill non-overflow dam is stable to a flood elevation of 817 ft 28

Temporary Flood Barriers at TVA Dams

• Analysis of flood levels at WBN Unit 1 assuming no HESCO barriers (contd)

- Breach configurations based on review of different methods discussed in Prediction of Embankment Dam Breach Parameters (U.S. Department of the Interior)

- Breach configuration based on Federal Energy Regulatory Commission (FERC) approach

- Single embankment at each dam postulated to fail

- Size of breach a function of breach depth, assumed failure down to bedrock

- Main embankment adjacent to each dam spillway selected where bedrock elevations known

- Cherokee Dam South Embankment modeled to partially fail progressively over one hour starting at peak headwater elevation

- Fort Loudoun Dam Section 1 of the South Embankment modeled to partially fail progressively over one hour starting at two ft overtopping

- Tellico Dam Main Dam Works Embankment modeled to partially fail progressively over one hour starting at same time as Fort Loudoun Dam failure at 1.32 ft overtopping

- Watts Bar Dam East Earth Embankment modeled to partially fail progressively over one hour starting at one ft overtopping

- Total failure of West Saddle Dam at Watts Bar Dam modeled 29

Temporary Flood Barriers at TVA Dams

• Result confirms the need for HESCO modular flood barriers to prevent overtopping during PMF events

• Two breach analyses performed:

- Analysis Anal sis of breach of HESCO barriers and subsequent s bseq ent o overtopping ertopping of dams under PMF conditions

- Analysis of overtopping of dams under PMF conditions (without HESCO b i iinstalled) barriers t ll d)

- Results are similar 30

Temporary Flood Barriers at TVA Dams

• A Computational Fluid Dynamics (CFD) Model for Fort Loudoun and Tellico Reservoirs has been developed

- Demonstrate flow velocity profiles in the reservoirs at PMF levels

- Calculate velocities and trajectories of large objects

• Sources of data include:

- Existing land area elevation data from United States Geological Survey

- Bathymetry data available from TVA (via USACE)

- Boundary conditions available from the TVA SOCH one-dimensional model

• CFD solution algorithms g developed p at the Universityy of Tennessee - Chattanooga (UTC) SimCenter 31

Temporary Flood Barriers at TVA Dams

• Boundary conditions for determining flows:

- Data from the SOCH model from TVA used to determine the inlet heights and flow velocities during the peak of the PMF event at approximately Little Tennessee River Mile (LTRM) 3.6 and Tennessee River Mile (TRM) 605.75

- Conditions C di i used:

d

• Little Tennessee River Inlet: Water height = 833.0 ft, incoming velocity = 2.3 ft/sec

• Tennessee River Inlet: Water height = 835.6 ft, incoming velocity = 7.48 ft/sec

- When necessary (depending on the domain extent used in the flow simulation and the type of simulation used), outflow targets at the Fort Loudoun and Tellico Dams were:

• Tellico Dam Outlet: Water height g = 833.28 ft,, discharge g = 601,898

, cfs

• Fort Loudoun Dam Outlet: Water height = 835.45 ft, discharge = 640,356 cfs 32

Temporary Flood Barriers at TVA Dams

• Tenasi/Incompressible solution method offered the best tradeoff between time to solution and solution fidelity

• Solution domain truncated at the Tellico and Fort Loudoun Dams

- Top boundary defined for the domain at the PMF height of 835 ft

• Flowrates at the dams matched to an PMF SOCH simulation

- Overall mass balance for the domain at solution terminus of 1%

• Solution algorithms used to predict the Tennessee River and Little Tennessee RiRiver er flows flo s at PMF conditions

• Given the flows at PMF conditions, the trajectory of large j

objects like barges g under a zero-powerp condition computed p for a range of release parameters 33

Temporary Flood Barriers at TVA Dams Flow solution obtained using Tenasi/Incompressible solution showing velocity magnitude Fort Loudoun and Tellico Dams Depicted 34

Temporary Flood Barriers at TVA Dams Velocity vectors in the Tellico Channel (connecting Fort Loudoun and Tellico Reservoirs) showing flow from Fort Loudoun to Tellico Reservoir at PMF conditions 35

Temporary Flood Barriers at TVA Dams

• Trajectories computed for objects simulating barges using the inclusion of iinertial i l particles i l iinto the h flflow solution l i

• Trajectory of each particle in the computational domain computed by solving ordinary differential equations for location and velocity

• Barges simulated using a sphere whose wetted area equals that of a 195 ft barge with a width of 35 ft and a draft of 6 ft

- Sphere density chosen as 1000 tons to match the laden weight of a barge

- Continuous phase velocities used to drive the time integration are computed at the free-surface or just below it in order to account for the draft of a barge

• Similar computation performed for 100-ton and 10-ton floating objects

- Simulates a range of objects and debris in the flowstream

• 400,000 independent simulations performed for each case and for each object size 36

Temporary Flood Barriers at TVA Dams

• Four cases run simulating barges and other objects (as independent inertial particles) released at several locations:

- TRM 608.3 located approximately at the northern inlet of the computational domain

- First Class Harbor on western shore between TRM 608 and TRM 609

- First Class Harbor located on southern shore between TRM 606 and TRM 607

- First Class Landing located on opposite shore from Fort Loudoun Dam at TRM 603 37

Temporary Flood Barriers at TVA Dams Computed trajectories for 1000-ton objects, aerial view

• Simulation of objects released at TRM 608 608.3 3

• All objects approach Fort Loudoun Dam, and do not impact the HESCO modular flood barriers 38

Temporary Flood Barriers at TVA Dams Computed trajectories for 1000-ton objects, perspective view

• Simulation of objects released at TRM 608 608.3 3

• All objects approach Fort Loudoun Dam, and do not impact the HESCO modular flood barriers 39

Temporary Flood Barriers at TVA Dams Computed trajectories for 100-ton objects, aerial view

• Simulation of objects released at TRM 608 608.3 3

• All objects approach Fort Loudoun Dam, and do not impact the HESCO modular flood barriers 40

Temporary Flood Barriers at TVA Dams Computed trajectories for 10-ton objects, aerial view

• Simulation of objects released at TRM 608 608.3 3

• All objects approach Fort Loudoun Dam, and do not impact the HESCO modular flood barriers 41

Temporary Flood Barriers at TVA Dams Computed trajectories for 1000-ton objects, aerial view

• Simulation of objects released between TRM 608 and TRM 609

• All objects approach Fort Loudoun Dam, and do not impact the HESCO modular flood barriers 42

Temporary Flood Barriers at TVA Dams Computed trajectories for 1000-ton objects, aerial view

• Simulation of objects released between TRM 606 and TRM 607

• All objects approach Fort Loudoun Dam, and do not impact the HESCO modular flood barriers 43

Temporary Flood Barriers at TVA Dams Computed trajectories for 1000-ton objects, aerial view

• Simulation of objects released at approximately TRM 603

• 83% of the objects approach Fort Loudon Dam, with the rest (17%) becoming beached

• Do not impact the HESCO modular flood barriers 44

Temporary Flood Barriers at TVA Dams

• The combined flow and object computational solutions show that the trajectories do not impact the HESCO modular flood barriers placed near the Fort Loudoun Dam

• 1000-ton 1000 ton objects simulating barges barges, and smaller 100 100-ton ton and 10-ton objects, have enough momentum to overcome the Fort Loudoun/Tellico channel suction and therefore approach the Fort Loudoun Dam, rather than being pulled down toward the south and potentially impacting the HESCO modular flood barriers

• Additional modeling considerations 45

TVA Flood Mode Operation Improvement Strategy 46

TVA Flood Mode Operation Improvement Strategy

• TVA Fleet Flood Mode Operation Improvement Strategy

- Corporate C t SSponsored d

- Living Document

- Issuance Expected p byy December 17,, 2012

• Key Personnel

- Corporate Senior Leadership - Jim Morris and Don Jernigan

- Corporate Lead - TBD

- WBN Sponsor - Don Grissette

- WBN Lead - Darlene Viscusie

- SQN Sponsor - John Carlin

- SQN Lead - Melissa Meade

- BFN Sponsor - Keith Polson 47

TVA Flood Mode Operation Improvement Strategy

• Key Elements of Strategy

- Flood Fl d M Mode d AAnalysis l i IImprovements t and d Pl Plantt MModifications difi ti

• Evaluate Modifications to Improve Stage I - Stage II Implementation

• Oversight g of SQN Q Analysis y of RHR Coolingg

- Flood Mode Procedure Improvements

• Oversight of Site Procedure Improvements

• Joint Review of Flood Mode Procedures to Obtain Improvement

- Flood Mode Equipment Reliability Improvement

• Equipment Identification and Classification

• Equipment Assessment

• Long Term Equipment Reliability

• Infrastructure Improvements 48

Commitment Status 49

Commitment Status Commitment Status TVA will submit a License Amendment Request to update the WBN Unit 1 Updated Final Safety Commitment date Analysis Report to reflect the updated hydrologic analysis methods and results, including the July 20, 2012 analysis of the rim leakage paths discussed at the May 31, 2012 public meeting between TVA Submitted and NRC Staff. July 19, 2012 TVA will submit a License Amendment Request to update the SQN Units 1 and 2 Updated Final Commitment date Safety Analysis Report to reflect the updated hydrologic analysis methods and results, including August 10, 2012 the analysis of the rim leakage paths discussed at the May 31, 2012 public meeting between TVA Submitted and NRC Staff. August 10, 2012 TVAss Nuclear uc ea Power o e Group G oup TVA will issue ssue aand d initially t a y pe perform o ap procedure ocedu e for o a se semi-annual a ua Co Commitment t e t date inspection of the compensatory measure for flood protection of the WBN Unit 1 Thermal Barrier August 31, 2012 Booster pumps and motors. The inspection will verify: a. The condition of the permanent First inspection building attachments; and b. The inventory, storage, physical protection, and condition of the conducted materials and consumables required for erection of the temporary flood protection panels August 30, 2012 d i a postulated during t l t d PMF event.t IInspections ti will ill continue ti until til th the compensatory t measure iis replaced by a permanent plant modification.

50

Commitment Status Commitment Status TVA s Nuclear Power Group will issue and initially perform a procedure for a semi TVAs semi-annual annual Commitment date inspection to verify the condition of the SQN Units 1 and 2 Spent Fuel Pit Cooling Pump August 31, 2012 Enclosure caps. Inspections will continue until the design change is completed to document the First inspection SQN Units 1 and 2 Spent Fuel Pit Cooling Pump Enclosure caps as a permanent plant feature. conducted August 28, 2012 TVAs Nuclear Power Group will issue and initially perform a procedure for a semi-annual Commitment date inspection to verify the inventory, storage, physical protection, and condition of the materials August 31, 2012 and consumables required to implement the compensatory measure for the common SQN Units First inspection 1 and 2 Diesel Generator Building. Inspections will continue until the compensatory measure is conducted replaced l db by a permanent plant l modification.

difi i August 28, 2012 TVA will perform an analysis of the Design Basis Flood for SQN Units 1 and 2 and WBN Unit 1 Commitment date that assumes a failure of a section of the HESCO flood barriers and earthen embankments at August 31, 2012 Fort Loudoun, Cherokee, Tellico, and Watts Bar dams. Completed August 3131, 2012 51

Commitment Status Commitment Status TVA s Nuclear Power Group will issue and initially perform procedures for semi-annual TVAs semi annual Commitment date inspections of the temporary HESCO flood barriers installed at Cherokee, Fort Loudoun, Tellico, August 31, 2012 and Watts Bar reservoirs. These inspections will: a. Ensure the temporary HESCO flood barriers First inspection remain in place and are not structurally degraded as specified by the manufacturers written conducted specifications and recommendations; b. Verify the inventory and staging of the material August 29, 2012 required to fill the gaps that exist; and c. Ensure that adequate physical security (e.g., fences and locks) is provided for the staged material against theft. These inspections will continue until a permanent modification is implemented to prevent overtopping the Cherokee, Fort Loudoun, Tellico, and Watts Bar dams due to the Probable Maximum Flood.

TVA will review the information contained in the updated hydrologic analysis and determine if Commitment date any information provided in the Final Environmental Statement (FES) related to the operation of from WBN LAR WBN Units 1 and 2 (NUREG-0498, Supplement 1, November 1994), and the WBN Unit 2 Draft October 1, 2012 Final Environmental Impact Statement (FEIS) (Draft NUREG-0498, Supplement 2, September Submitted 2011)) is affected,, and submit the results of this review to the NRC. October 1,, 2012 TVA to provide a summary of the results of TVA's analysis of the Design Basis Flood for SQN Obligation date Units 1 and 2 and WBN Unit 1 that assumes a failure of a section of the HESCO flood barriers from CAL and earthen embankments at Fort Loudoun, Cherokee, Tellico, and Watts Bar dams to the NRC October 30, 2012 within 60 days after its completion. Submitted October 30, 2012 52

NTTF Recommendation 2.1 Flood Hazards Reevaluation 53

NTTF Recommendation 2.1 Flood Hazards Reevaluation

• Analyses y to be completed p byy March, 2013

- Sunny day upstream dam failure

- Updated PMF for 21,400 and 7,980 sq mile March storms

- Loss L off d downstream t d dam withith 21 21,400 400 sq mile il MMarchh storm t PMF

- Local intense precipitation flooding with partially blocked site drainage channels and existing conditions

- Cherokee and Douglas Dam partial failure and Ft. Patrick Henry Dam failure with 21,400 sq mile March storm PMF 54

NTTF Recommendation 2.1 Flood Hazards Reevaluation

• Challenges g to March, 2013 completion p

- Methodology and analyses for seismic dam failures and combinations of seismic dam failures pending NRC guidance development

- TVA completing evaluation of upstream dam stability during PMF and seismic conditions using FERC criteria

- Sensitivity analyses as necessary to quantify uncertainties

- Sediment S di t ttransportt with ith sunny d day embankment b k t ffailures il and d with ith 21,400 sq mile March storm PMF 55

Closing Remarks 56