ML13182A087

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:	Andrew Hon Plant Licensing Branch II
Hon A
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ML13256A390	List: ML13182A066 ML13182A087
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Download: ML13182A087 (29)

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Sequoyah and Watts Bar Nuclear Plants 1st Quarterly Update for NTTF Recommendation 2.1,21 Flooding Hazard Reevaluation Report (HRR) Extension Request June 27, 2013

Agenda Joe Shea, Vice President, Introduction Nuclear Licensing Joe Shea Recommendation 2.1, Flooding Hazard Reevaluation Josh Best, Project Engineer, Report Extension Update NTTF Recommendation 2.1 Penny Selman, Seismic Program Manager, Nuclear Engineering Methodology for Evaluating the Potential for Dr. Martin McCann, Consultant Multiple Dam Failures Due to Seismic Events Jack R. Benjamin & Associates, Inc.

Closing Remarks Joe Shea TVA Nuclear Power Group 2

I t d ti Introduction Joe Shea, Vice President, Nuclear Licensing

Recommendation 2.1, Fl di Hazard Flooding H d Reevaluation R l ti Report R t (HRR) Extension E t i Update U d t

SQN and WBN HRR Status Introduction Flooding Hazard Reevaluation Report Extension Request q

Submitted extension request March 12, 2013 (ML13080A073)

Initial meeting g with NRC staff April p 29,, 2013 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.

TVA Nuclear Power Group 5

SQN and WBN HRR Status Main Task Status Update - June 2013 Task Start Finish Status Main River Modeling Code Migration 1a (SOCH to HEC-RAS) May 2012 Nov 2012 Complete Tributary River Modeling Code Migration 1b (SOCH to HEC-RAS) March 2013 Nov 2013 In-progress 2 Confirm critical storm PMP selection Dec 2012 Jan 2013 Complete Perform local intense precipitation analysis for 3 SQN/WBN Sept 2012 May 2013 Complete Sunny Day Dam Failure - WBH - east embankment 4a failure Jan 2013 Feb 2013 Complete 4b Sunny Day Dam Failure - Tributary Dams March 2013 Nov 2014 In-progress 5 Perform PMF simulations - 2 storms - all dams stable Feb 2013 p g March 2013* In-progress*

6 Evaluate Stability of 18 dams under PMF conditions Sept 2012 March 2014 In-progress Perform PMF simulations using results of stability 7 analysis April 2014 Dec 2014 Not Started 8 Develop dam specific seismic hazards Feb 2013 April 2013 Complete 9 Evaluate seismic stability of 18 dams Sept 2012 March 2014 In-progress Perform simulations using results of seismic stability 10 analysis April 2014 Dec 2014 Not Started 11 Perform simulations to quantify uncertainties June 2014 Dec 2014 Not Started Prepare HRRs with results and interim actions, as 12 required Jan 2015 March 2015 Not Started

• Task completed but indicated as in-progress to allow for revisiting the breach modeling techniques in light of the dam stability ISG.

TVA Nuclear Power Group 6

SQN and WBN HRR Status Main Task Status Update - June 2013 Task 3 - Perform local intense precipitation analysis for SQN/WBN Load Case Piped Drainage Open Channel Drainage DB LIP 100% Blocked Fully Functional Case 2 LIP* 100% Blocked Partially Blocked Case 1 LIP* 100% Blocked Fully Functional

• Include changes to unit hydrographs per NUREG/CR-7046 Appendix B Site Critical DB LIP NUREG/CR-7046 NUREG/CR-7046 Elevation LIP Case 2 LIP Case 1 Sequoyah 706 706.0 706.25 705.63 Watts Bar 729 728.7 729.4 729.1 TVA Nuclear Power Group 7

SQN and WBN HRR Status Main Task Status Update - June 2013 Task 8 - Develop dam specific seismic hazards Performed Site-Specific p p probabilistic seismic hazard analysis y ((PSHA)) for each potentially critical dam including deaggregation plots 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 Curves Developed 5% and 7% damped mean and medium horizontal and vertical 1x10-4 uniform hazard response spectra (UHRS)

TVA Nuclear Power Group 8

TVA Dam Stability Analysis PMF and Seismic Stability Analysis Flowchart Note - All activities are sub-tasks to Tasks 6 & 9 TVA Nuclear Power Group 9

TVA Dam Stability Analysis PMF and Seismic Stability Analysis Flowchart (contd)

Develop Dam Specific Seismic Hazards (Task 8) 6 A

Perform Stability Analyses (PMF & Seismic)

(Tasks 6 & 9) 7 Compare Results to Acceptance Criteria 8 Yes No Revise Analysis Meets Acceptance Techniques?

Criteria?

(3D analysis) 9 10 Yes No Stability Analysis Complete 11 TVA Nuclear Power Group 10

TVA Dam Stability Analysis PMF and Seismic Stability Analysis Status by Dam Dam Field Investigation Laboratory Develop Dam PMF and Seismic Stability Project (Borings) Testing Specific Analysis

(# complete/total l t /t t l # borings b i ) Hazards (scheduled completion)

Block 2 Block 3 Block 4 Block 7 1 Apalachia 7/10 - ETC 07/15 ETC 08/16 Complete 03/31/14 2 Blue Ridge Complete - 0/0 N/A Complete 03/31/14 3 Boone B C Completel t - 15/15 Complete Complete 03/31/14 4 Chatuge Complete - 51/51 Complete Complete 03/31/14 5 Cherokee Complete - 41/41 Complete Complete 03/31/14 6 Chickamauga 37/52 - ETC 07/17 ETC 08/07 Complete 03/31/14 7 Douglas Complete - 75/75 ETC 06/28 Complete 03/31/14 8 Fontana Complete - 6/6 ETC 06/28 Complete 03/31/14 9 Fort Loudoun Complete - 57/57 ETC 07/19 Complete 03/31/14 10 Fort Patrick Henry Complete - 6/6 ETC 07/30 Complete 03/31/14 11 Hiwassee Complete - 4/4 ETC 07/15 Complete 03/31/14 12 Melton Hill 3/7 - ETC 07/31 ETC 10/10 Complete 03/31/14 13 Norris 19/20 - ETC 06/28 ETC 07/31 Complete 03/31/14 14 Nottely Complete - 48/48 ETC 06/28 Complete 03/31/14 15 South Holston Complete - 40/40 Complete Complete 03/31/14 16 Tellico Complete - 53/53 Complete Complete 03/31/14 17 Watauga 16/24 - ETC 07/03 ETC 08/09 Complete 03/31/14 18 Watts Bar 55/60 - ETC 07/03 ETC 07/31 Complete 03/31/14 TVA Nuclear Power Group 11

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events - Introduction Commitment to present details for methodology SQN and WBN HRR extension request letter Committed to:

• Present details of a multiple dam failure methodology due to seismic events on or before June 30, 2013 Presenting Generic Methodology TVA plans to use this methodology TVA utilizing outside resources Jack R. Benjamin & Associates, Inc.

TVA Nuclear Power Group 13

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events A general approach has been developed to evaluate the potential that multiple upstream dam failures could be initiated by a seismic event The approach is an additional screening assessment; not a full-scope seismic risk analysis At the point this analysis is performed, an initial screening have/will be conducted that answered the following 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 multiple p dams in such pproximityy to one another that a seismic event could pproduce strongg ground 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 10-6 per year.

TVA Nuclear Power Group 14

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events Methodology has been developed to address seismic risk associated with earthquake ground motion only. Methodology does not address:

Other seismic hazards such as seiche in 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 failure, it is assumed these evaluations have been performed) performed).

TVA Nuclear Power Group 15

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events TVA Nuclear Power Group 16

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events TVA Nuclear Power Group 17

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events The 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 expanded PSHA ground motion model and computational analysis must be expanded to include sources of correlation TVA Nuclear Power Group 18

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events Evaluating the ground motion at multiple dam sites is more complicated than a seismic risk analysis for a single site Factors that must be considered include:

Earthquake magnitude Earthquake source-to-site distance Separation distance between dam sites Inter-earthquake variability (discussed on next slide)

TVA Nuclear Power Group 19

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events There are two aspects to estimating ground motions that must be considered in the risk analysis.

Inter-Event Variability Intra-Event Variability Ground motions for events of the same Ground motions for an individual event at multiple locations are magnitude it d can be b systematically t ti ll different.

diff t correlated, l t d based b d on the th separation ti didistance t between b t sites.

it 1.1 1

Corrrelation Coefficientt 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0 20 40 60 80 100 Distance (km)

TVA Nuclear Power Group 20

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events Systems Analysis The ppurpose rpose of the systems s stems analysis anal sis is to model the combination of upstream pstream dam fail failures res that co couldld 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 analyses will include an assessment to determine whether the dam break flood would fail a downstream dam(s).

An event tree model will be developed p to define the sequences q of multiple p dam failures that could lead to plant 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.

TVA Nuclear Power Group 21

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events Seismic Fragility Analysis The purpose p rpose of the seismic fragilit fragility anal analysis sis is to estimate the conditional probability probabilit of failure fail re 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 dam, and The multiple modes of seismic failure that could lead to uncontrolled release of the reservoir.

TVA Nuclear Power Group 22

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events TVA Nuclear Power Group 23

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events The seismic fragility will be based on an estimate of the HCLPF, as estimated from existing seismic evaluations.

HCLPF = PGAE

• FS

• FP PGAE = peak ground acceleration used in the seismic evaluation FS = calculated factor of safety in the existing analysis FP = estimated margin that may exist between the existing calculations and a more realistic performance state 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.

TVA Nuclear Power Group 24

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events Once the HCLPF is determined, the mean seismic fragility of the dam can determined from the following relationship.

A = HCLPF e 2.645* C C = combined logarithmic standard deviation; includes A and E Estimates of C are available from NPP seismic PRA studies and limited number of seismic fragility assessments for dams and levees.

Typical values of C vary from 0.30 to 0.60.

In this application, the conservative choice is to select a value on the low end of the range.

TVA Nuclear Power Group 25

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events The following figure shows the influence of multiple modes of failure on the fragility for the dam system.

TVA Nuclear Power Group 26

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events In Summary A risk-based risk based screening eevaluation al ation process was as de developed eloped for estimating the likelihood of mmultiple 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 year.

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 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.

TVA Nuclear Power Group 27

Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events TVAs status of the proposed methodology PSHA - completed Systems Analysis - in progress Fragility Analysis - in progress Risk Quantification - TBD Submit methodology in writing TVA Nuclear Power Group 28

Cl i Remarks Closing R k Joe Shea, Vice President, Nuclear Licensing