ML13182A087

Sequoyah and Watts Bar Nuclear Plants - 1st Quarterly Update for NTTF Recommendation 2.1, Flooding Hazard Reevaluation Report (Hrr) Extension Request

ML13182A087
Person / Time
Site:	Watts Bar, Sequoyah
Issue date:	06/27/2013
From:	Tennessee Valley Authority
To:	Hon A L Plant Licensing Branch II
Hon A
Shared Package
ML13256A390	List: ML13182A066 ML13182A087
References
Download: ML13182A087 (29)

Text

Sequoyah and Watts Bar Nuclear PlantsSequoyah and Watts Bar Nuclear Plants 1 stQuarterly Update forNTTF Recommendation 21 NTTF Recommendation 2

.1 ,Flooding Hazard Reevaluation Report (HRR) Extension RequestJune 27, 2013 Agenda IntroductionJoe Shea, Vice President,Nuclear LicensingRecommendation 2.1, Flooding Hazard Reevaluation Report Extension Update Joe SheaJosh Best, Project Engineer,NTTF Recommendation2.1Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic EventsPenny Selman, Seismic ProgramManager,NuclearEngineeringDr.Martin McCann, ConsultantJack R. Benjamin & Associates, Inc.

Closing Remarks Joe Shea 2TVA Nuclear Power Group Itdti I n t ro d uc ti onJoe Shea, Vice President, Nuclear Licensing Recommendation 2.1,Fldi Hd Rlti Rt (HRR) Eti Udt Fl oo di ng H azar d R eeva l ua ti on R epor t (HRR) E x t ens i on U p d a t e SQN and WBN HRR Status IntroductionFlooding Hazard Reevaluation Report Extension Re q uest q-Submitted extension request March 12, 2013 (ML13080A073)

-Initial meetin g with NRC staff A p ril 29 , 2013 gp,-Submitted revised commitments May 9, 2013 (ML13133A004)Provide the SQN and WBN Flooding Hazard Reevaluation Reports by March 12, 2015.Provide quarterly status report to the SQN and WBN NRC Project Managers to provide a status of completed actions and progress

to completing the Hazard Reevaluation Reports starting in June 2013.Present a proposed methodology for spatial scenarios to the NRC by June 30, 2013.

5TVA Nuclear Power Group SQN and WBN HRR StatusMain Task Status Update -June 2013TaskStartFinishStatus 1aMain River Modeling Code Migration(SOCH to HEC-RAS)May 2012Nov 2012Complete 1bTributary River Mode ling Code Migration(SOCH to HEC-RAS)March 2013Nov 2013In-progress2Confirm critical storm PMP selectionDec2012Jan 2013Complete 3Perform local intense precipitation analysis for SQN/WBNSept2012May2013 Complete 3 SQN/WBN Sept 2012 May 2013 Complete 4aSunny Day Dam Failure -WBH -east embankment failureJan 2013Feb 2013Complete4bSunny Day Dam Failure -Tributary DamsMarch 2013Nov 2014In-progress5Perform PMF simulations -2 storms -all dams stableFeb 2013March 2013*In-p ro gress*pg6Evaluate Stability of 18 dams under PMF conditionsSept 2012March2014In-progress 7Perform PMF simulations using results of stability analysisApril 2014Dec 2014Not Started 8 DevelopdamspecificseismichazardsFeb2013April2013 Complete 8 Develop dam specific seismic hazards Feb 2013 April 2013 Complete9Evaluate seismic stability of 18 damsSept 2012March2014In-progress 10Perform simulations using re sults of seismic stability analysisApril 2014Dec 2014Not Started11Perform simulations to quantify uncertaintiesJune 2014Dec2014Not Started 6TVA Nuclear Power Group 12Prepare HRRs with results and interim actions, as requiredJan 2015March 2015Not Started* Task completed but indicated as in-progress to allow for revisiting the breach modeling techniquesin light of the dam stability ISG.

SQN and WBN HRR StatusMain Task Status Update -June 2013Task 3 -Perform local intense pr ecipitation analysis for SQN/WBNLoadCasePipedDrainageOpenChannelDrainage Load Case Piped Drainage Open Channel DrainageDBLIP100% BlockedFullyFunctionalCase 2 LIP*100% BlockedPartially Blocked

• IncludechangestounithydrographsperNUREG/CR

-7046AppendixBCase1 LIP*100% BlockedFullyFunctional Include changes to unit hydrographs per NUREG/CR-7046 Appendix BSiteCritical ElevationDB LIPNUREG/CR-7046 LIPCase2 NUREG/CR-7046 LIPCase1 Elevation LIP Case 2 LIP Case 1Sequoyah706706.0706.25705.63 Watts Bar729728.7729.4729.1 7TVA Nuclear Power Group SQN and WBN HRR StatusMain Task Status Update -June 2013Task 8 -Develop dam specific seismic hazardsPerformed Site-S p ecific probabilistic seismic hazard anal y sis (PSHA) for each ppy()potentially critical dam including deaggregationplots for use in multiple dam failure evaluations due to a single seismic event

-2012 CEUS source model

-2004/2006 EPRI ground motion model

-Developed Mean Hazard CurvesDeveloped5%and7%dampedmeanandmediumhorizontalandvertical

-Developed 5% and 7% damped mean and medium horizontal and vertical 1x10-4 uniform hazard response spectra (UHRS) 8TVA Nuclear Power Group TVA Dam Stability Analysis PMF and Seismic Stability Analysis FlowchartNote -All activities are sub-tasks to Tasks 6 & 9 9TVA Nuclear Power Group TVA Dam Stability AnalysisPMF and Seismic Stability Analysis Flowchart (cont'd)Develop Dam Specific Seismic Hazards(Task 8)6Perform Stability Analyses(PMF & Seismic)

(Tasks 6&9)A Yes (Tasks 6 & 9)7Compare Results to Acceptance Criteria 8 Revise Analysis Techniques?

(3D analysis) 10 NoMeets Acceptance Criteria?

9 10Stability Analysis Complete 11YesNo 10TVA Nuclear Power Group 11 TVA Dam Stability Analysis PMF and Seismic Stability Analysis Status by Dam Dam Project Field Investigation (Borings)(#lt/ttl#bi)LaboratoryTesting Develop Dam Specific HazardsPMF and Seismic Stability Analysis (scheduled completion)

(# comp l e t e/t o t a l # b or i ngs)Block2Block 3 Hazards Block 4 (scheduled completion)

Block 7 1Apalachia7/10 -ETC 07/15 ETC 08/16 Complete 03/31/14 2Blue RidgeComplete-0/0 N/A Complete 03/31/14 BClt 15/15 3 B oone C omp l e t e-15/15CompleteComplete 03/31/14 4 ChatugeComplete -51/51CompleteComplete 03/31/14 5 CherokeeComplete -41/41CompleteComplete 03/31/14 6Chickamauga37/52 -ETC07/17 ETC 08/07 Complete 03/31/14 7 DouglasComplete -75/75ETC06/28 Complete 03/31/14 8 FontanaComplete -6/6 ETC 06/28 Complete 03/31/14 9 Fort Loudoun Complete-57/57ETC07/19 Complete 03/31/14 10Fort Patrick HenryComplete-6/6 ETC 07/30 Complete 03/31/14 11 HiwasseeComplete-4/4ETC07/15 Complete 03/31/14 12MeltonHill 3/7 ETC 07/31ETC10/10 Complete 03/31/14 12 Melton Hill 3/7 -ETC 07/31 ETC 10/10 Complete 03/31/14 13Norris19/20 -ETC 06/28 ETC 07/31 Complete 03/31/14 14 NottelyComplete -48/48 ETC 06/28 Complete 03/31/14 15 South HolstonComplete -40/40 CompleteComplete 03/31/14 16 TellicoComplete -53/53CompleteComplete 03/31/14 11TVA Nuclear Power Group 17Watauga16/24 -ETC 07/03 ETC 08/09 Complete 03/31/14 18Watts Bar55/60 -ETC 07/03 ETC 07/31 Complete 03/31/14 Methodology for Evaluating the Potential for MultipleDamFailuresDuetoSeismicEvents Multiple Dam Failures Due to Seismic Events Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic Events -Introduction Commitment to present details for methodologySQN and WBN HRR extension request letter

-Committed to:Presentdetailsofamultipledamfailuremethodologydue Present details of a multiple dam failure methodology due to seismic events on or before June 30, 2013PresentingGenericMethodologyPresenting Generic Methodology

-TVA plans to use this methodologyTVAutilizingoutsideresourcesTVA utilizing outside resources -Jack R. Benjamin & Associates, Inc.

13TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic EventsA general approach has been developed to evaluate the potential that multiple upstream dam failures could be initiated by a seismic eventThe approach is an additional screening assessment; not a full-scope seismic risk analysisAt the point this analysis is performed, an initial screening have/will be conducted that answered the followin g questions in the affirmative:

-If a combination of multiple upstream dams were to breach during a seismic event, would the resulting flood pose a hazard to a plant located downstream?

-Are multi ple dams in such p roximit y to one another that a seismic event could produce stron g ppypgground motion at each site simultaneously?The methodology is intended as a probabilistic, conservative screening approach to evaluate whether the mean frequency of multiple dam failures is less than 10

-6per year.mean frequency of multiple dam failures is less than 10per year.14TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic EventsMethodology has been developed to address seismic risk associated with earthquake ground motion only. Methodology does not address:Other seismic hazards such as seichein reservoirs, landslides or rock slides, fault displacement, etc.Possible combinations of earthquake and flood events (i.e., 100-year flood).Dam breach and inundation assessments (it is assumed these evaluations have been performed to a level of detail to determine that dam failure combinations would lead to flooding at a plant downstream).Operational features of dams such as opening of gates or other hydraulic systems.Unsatisfactory performance of spillways (e.g., due to high flows). (To the extent that a flood from an upstream dam failure could lead to a dam failure it is assumed these evaluations have been performed)upstream dam failure could lead to a dam failure

, it is assumed these evaluations have been performed)

.15TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic Events 16TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic Events 17TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic EventsThe probabilistic seismic hazard analysis (PSHA) input should be same as that required for plant evaluations (SSHAC Level 3 or 4)In the CEUS, the PSHA will be based on:

-USNRC/EPRI/USGS CEUS seismic source characterization (SSC) model, and

-EPRI (2004 & 2006) ground motion attenuation model.For western U.S. plants, it is conceivable the SSC model would need to be expandedPSHA ground motion model and computational analysis PSHA ground motion model and computational analysis must be expanded to include sources of correlation 18TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic EventsEvaluating the ground motion at multiple dam sites is more complicated than a seismic risk analysis for a single siteanalysis for a single siteFactors that must be considered include:

-Earthquake ma g nitude-Earthquake source-to-site distance

-Separation distance between dam sites

-Inter-earthquake variability (discussed on next slide) next slide) 19TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic EventsThere are two aspects to estimating ground motions that must be considered in the risk analysis.Inter-Event VariabilityIntra-Event VariabilityGround motions for events of the same Ground motions for an individual event at multiple locations areitdb'ttilldifftltdbdthtiditbtit magn it u d e can b e 'sys t ema ti ca ll y diff eren t. corre l a t e d , b ase d on th e separa ti on di s t ance b e t ween s it es.11.1 t0.5 0.60.70.8 0.9 relation Coefficien t0.2 0.30.4020406080100Distance (km)Cor r 20TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic Events Systems AnalysisThe prpose of the sstems analsis is to model the combination of pstream dam failres that cold lead The p urpose of the systems analysis is to model the combination of upstream dam fail ures that co uld lead to flooding at the plant.The basis for determining the combinations of failures is derived from a series of dam break and inundation calculations. These anal yses will include an assessment to determine whether the dam break flood would fail a downstream dam(s).An event tree model will be develo ped to define the se quences of multi ple dam failures that could lead to pqpplant flooding. The event tree sequences provide the basis for estimating the conditional probability that a given sequence could occur, given the occurrence of ground motion at each dam site.

21TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic Events Seismic Fragility AnalysisThe prpose of the seismic fragilit analsis is to estimate the conditional probabilit of failre of each The p urpose of the seismic fragility analysis is to estimate the conditional probability of fail ure of each dam.The fragility analysis will be a conservative estimate, based on existing information. The analysis will include:

-Estimate of the aleatory and epistemic uncertainty in the estimate of the seismic capacity of the Estimate of the aleatory and epistemic uncertainty in the estimate of the seismic capacity of the dam, and -The multiple modes of seismic failure that could lead to uncontrolled release of the reservoir.

22TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic Events 23TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic EventsThe seismic fragility will be based on an estimate of the HCLPF, as estimated from existing seismic evaluations.

PGA E= peak ground acceleration used in the seismic evaluation F S= calculated factor of safe ty in the existing analysis F=estimatedmarginthatmayexistbetweentheexistingcalculationsandamorerealisticperformancestateThis P S E F F PGA HCLPF**F P= estimated margin that may exist between the existing calculations and a more realistic performance state. This is a parameter that will be specific to the failure modes being evaluated and the analysis method that was performed.

For cases in which there is no information, this parameter will be 1.0.

24TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic EventsOnce the HCLPF is determined, the mean seismic fragility of the dam can determined from the following relationship.

• 645 2= combined logarithmic standard deviation; includes A and E C e H CLP F A*645.2C Estimates of Care available from NPP seismic PRA studies and limited number of seismic fragility assessments for dams and levees.

CTypical values of Cvary from 0.30 to 0.60.In this application, the conservative choiceis to select a value on the low end of the

range.25TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic EventsThe following figure shows the influence of multiple modes of failure on the fragility for the dam system.

26TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic EventsIn SummaryA riskbased screening ealation process as deeloped for estimating the likelihood of mltiple A risk-based screening e v al u ation process w as de veloped for estimating the likelihood of m u ltiple upstream dam failures that might occur as a result of a seismic event.The methodology is a probabilistic, conservative approach to evaluate whether the mean frequency of multiple dam failures is less than 10

-6 per y ear.The methodology is based on:

-Site-specific PSHA,-Conservative estimate of the seismic fragility of dams as determined from existing seismic analyses and any new data that is available andand any new data that is available

, and-The results of deterministic calculations that have identified the possible combinations of upstream dam failures that could lead to flooding at a downstream nuclear power plant.

27TVA Nuclear Power Group Methodology for Evaluating the Potential forMultiple Dam Failures Due to Seismic EventsTVA's status of the proposed methodology

-PSHA -completed

-Systems Analysis -in progress

-Fragility Analysis -in progress

-Risk Quantification

-TBDSubmit methodology in writing 28TVA Nuclear Power Group Cli Rk Cl os i ng R emar k sJoe Shea, Vice President, Nuclear Licensing