ML13206A003
| ML13206A003 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar, Sequoyah  |
| Issue date: | 07/19/2013 |
| From: | James Shea Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML13206A001 | List: |
| References | |
| Download: ML13206A003 (33) | |
Text
Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 July 19, 2013 10 CFR 50.54(f)
ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Sequoyah Nuclear Plant, Units 1 and 2 Facility Operating Licenses Nos. DPR-77 and DPR-79 NRC Docket Nos. 50-327 and 50-328 Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390 Watts Bar Nuclear Plant, Unit 2 Construction Permit No. CPPR-92 NRC Docket No. 50-391
Subject:
References:
First Quarterly Status Report to the Flooding Hazard Reevaluation Report Extension Request Including Technical Pager Regarding Methodology for Multiple Dam Failures Due to Seismic Events
- 1. TVA letter, "Tennessee Valley Authority (TVA) - Extension Request Regarding the Flooding Hazard Reevaluation Report Required by NRC Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendation 2.1, Flooding, of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident," dated March 12, 2013
- 2. TVA letter, "Revised Commitments for the Extension Request Regarding the Flooding Hazard Reevaluation Report Required by NRC Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendation 2.1, Flooding, of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident,"
dated May 9, 2013 Printed on recycled paper
U.S. Nuclear Regulatory Commission Page 2 July 19, 2013 By letter dated March 12, 2013, the Tennessee Valley Authority (TVA) requested an extension to submitting the Flooding Hazard Reevaluation Reports (HRRs) for the Sequoyah Nuclear Power Plant (SQN), Units 1 and 2, and the Watts Bar Nuclear Plant (WBN), Units 1 and 2 (Reference 1). After meeting with the Nuclear Regulatory Commission (NRC) on April 29, 2013, TVA committed in a follow-up letter dated May 9, 2013, to provide the SQN and WBN Flooding HRRs to the NRC by March 12, 2015 (Reference 2). TVA also committed in the Reference 2 letter to provide periodic quarterly status reports to the SQN and WBN NRC Project Managers to provide a status of completed actions and progress to completing the HRRs starting in June, 2013.
The purpose of this letter is to submit the first quarterly status report regarding the status of completed actions and progress to completing the HRRs. This letter also submits the technical paper describing a methodology for evaluating the potential for multiple dam failures due to seismic events. Both of these subjects were presented by TVA in a June 27, 2013 public meeting with the NRC.
During the June 27, 2013 meeting, TVA briefed the NRC regarding the status of completed actions and progress to completing the SQN and WBN HRRs. TVA advised the NRC that Task 3, "Perform local intense precipitation analysis for SQN/WBN," and Task 8, "Develop dam specific seismic hazards," were complete. TVA provided a status of sub-tasks supporting the probable maximum flood and seismic stability analyses. The briefing material presented by TVA during the meeting is provided in Enclosure 1 to this letter. This presentation met Commitment 1 of the Enclosure to the Reference 2 letter.
During the June 27, 2013 meeting, TVA also presented a Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events. This presentation met Commitment 3 of Enclosure 2 to the Reference 1 letter. As discussed in the meeting, TVA plans to implement this methodology in support of the tasks for completion of the SQN and WBN HRRs. Enclosure 2 of this letter provides a description of the methodology for evaluating the likelihood that multiple dams upstream of a nuclear power plant could fail as a result of a seismic event. The methodology in Enclosure 2 of this letter provides an alternative to Section 5.5, "Multiple Dam Failure Due to a Single Seismic Event," of the draft Interim Staff Guidance, JLD-ISG-2013-01, "Guidance for Assessment of Flooding Hazards Due to Dam Failure." TVA is available to meet with the NRC to discuss details of the methodology, if needed.
TVA will provide the second quarterly update regarding the status of completed actions and progress to completing the SQN and WBN HRRs by September 30, 2013, consistent with Commitment 1 in the Enclosure of TVA's letter to NRC dated May 9, 2013.
U.S. Nuclear Regulatory Commission Page 3 July 19, 2013 If you have questions regarding this update, please contact Kevin Casey at (423) 751-8523.
Nuclear Licensing
Enclosures:
- 1. Slides from TVA's 1st Quarterly Update for NTTF Recommendation 2.1, Flooding Hazard Reevaluation Report (HRR) Extension Request, June 27, 2013
- 2. Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events cc (w/Enclosures):
NRC Regional Administrator - Region II NRR Director - NRC Headquarters NRC Senior Resident Inspector - Sequoyah Nuclear Plant NRC Senior Resident Inspector - Watts Bar Nuclear Plant NRR Project Manager - Sequoyah Nuclear Plant NRR Project Manager - Watts Bar Nuclear Plant, Unit 1 NRR Project Manager - Watts Bar Nuclear Plant, Unit 2
ENCLOSURE I SLIDES FROM TVA'S 1st QUARTERLY UPDATE FOR NTTF RECOMMENDATION 2.1, FLOODING HAZARD REEVALUATION REPORT (HRR) EXTENSION REQUEST, JUNE 27, 2013
Sequoyah and Watts Bar Nuclear Plants Ist Quarterly Update for NTTF Recommendation 2.1, Flooding Hazard Reevaluation Report (HRR) Extension Request June 27, 2013
[nAgenda Introduction Joe Shea, Vice President, Nuclear Licensing Recommendation 2.1, Flooding Hazard Reevaluation Report Extension Update Methodology for Evaluating the Potential for Multiple Dam Failures Due to Seismic Events Closing Remarks Joe Shea Josh Best, Project Engineer, NTTF Recommendation 2.1 Penny Selman, Seismic Program Manager, Nuclear Engineering Dr. Martin McCann, Consultant Jack R. Benjamin & Associates, Inc.
Joe Shea TVA Nuclear Power Group 2
Introduction Joe Shea, Vice President, Nuclear Licensing
Recommendation 2.1, Flooding Hazard Reevaluation Report (HRR) Extension Update
SQN and WBN HRR Status SIntroduction Flooding Hazard Reevaluation Report Extension Request Submitted extension request March 12, 2013 (ML13080A073)
Initial meeting with NRC staff April 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 SMain Task Status Update - June 2013 I
Task I Start -I Finish-T Statu Main River Modeling Code Migration la (SOCH to HEC-RAS)
Tributary River Modeling Code Migration lb (SOCH to HEC-RAS) 2 Confirm critical storm PMP selection Perform local intense precipitation analysis for 3 SQN/WBN Sunny Day Dam Failure - WBH - east embankment 4a failure 4b Sunny Day Dam Failure - Tributary Dams 5 Perform PMF simulations - 2 storms - all dams stable 6 Evaluate Stability of 18 dams under PMF conditions Perform PMF simulations using results of stability 7 analysis 8 Develop dam specific seismic hazards 9 Evaluate seismic stability of 18 dams Perform simulations using results of seismic stability 10 analysis 11 Perform simulations to quantify uncertainties Prepare HRRs with results and interim actions, as 12 required May 2012 March 2013 Dec 2012 Sept 2012 Jan 2013 March 2013 Nov 2012 Complete Nov 2013 In-progress Jan 2013 Complete May 2013 Complete Feb 2013 Nov 2014 Complete In-progress Feb 2013 March 2013* In-progress*
Sept 2012 April 2014 Feb 2013 Sept 2012 April 2014 June 2014 March 2014 In-progress Dec 2014 Not Started April 2013 March 2014 Complete In-progress Dec 2014 Not Started Dec 2014 Not Started 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 i* Main Task Status Update - June 2013 Task 3-Perform local intense precipitation analysis for SQNIWBN Pie Dranag Ope Chne DraS.-inag DB LIP Case 2 LIP*
Case 1 LIP*
100% Blocked 100% Blocked 100% Blocked Fully Functional Partially Blocked Fully Functional
- Include changes to unit hydrographs per NUREG/CR-7046 Appendix B Crtia NUE/R74 NRCC-74 Elvto LI Cas 2
I
-Cs Sequoyah Watts Bar 706 729 706.0 728.7 706.25 729.4 705.63 729.1 TVA Nuclear Power Group 7
SQN and WBN HRR Status Mm Main Task Status Update - June 2013 Task 8-Develop dam specific seismic hazards
- Performed Site-Specific probabilistic seismic hazard analysis (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 lx10-4 uniform hazard response spectra (UHRS)
TVA Nuclear Power Group 8
TVA Dam Stability Analysis
' PMF and Seismic Stability Analysis Flowchart Gather
~
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specific.data Deerin Anlyis Acetac Crtei base
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tes tinge
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fl4 I IL E J fil data
-1 GTS.-dlAN ocrt Note - All activities are sub-tasks to Tasks 6 & 9 A
TVA Nuclear Power Group 9
TVA Dam Stability Analysis i* PMF and Seismic Stability Analysis Flowchart (cont'd) 7 A)
Develop Dam Specific Seismic Hazards (Task 8) 6 Perform Stability Analyses rform S 'a li7 m1c)
(PMF a Seismic)
(Tasks 6 & 9) 4 Yes Yes No No
-ailiyAayi opet TVA Nuclear Power Group 10
TVA Dam Stability Analysis j* 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 # borings)
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 Complete - 15/15 Complete Complete 03/31/14 4 Chatuge Complete - 51151 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 - 75175 ETC 06/28 Complete 03/31/14 8 Fontana Complete - 6/6 ETC 06/28 Complete 03/31/14 a Fort Loudoun Comnlate - 57157 ITC nf7/1 0 rOl
,I,=gf n-A44A TVA Nuclear Power Group 11
Methodology for Evaluating the Potential for g
Multiple Dam Failures Due to Seismic Events
Methodology for Evaluating the Potential for MMultiple 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 M 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 dams in such proximity to one another that a seismic event could produce strong 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 Q6per year.
TVA Nuclear Power Group 14
Methodology for Evaluating the Potential for MMultiple 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, it is assumed these evaluations have been performed).
TVA Nuclear Power Group 15
Methodology for Evaluating the Potential for MMultiple 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 i
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)
A series of dams on a river system
" In the CEUS, the PSHA will be based on:
Earthquake Source U
-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 M Multiple Dam Failures Due to Seismic Evw 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)
A series of dams on a river system Earthquake Source Source-to-site distance TVA Nuclear Power Group 19
Methodology for Evaluating the Potential for M 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 Ground motions for events of the same magnitude can be 'systematically different.
Intra-Event Variability Ground motions for an individual event at multiple locations are correlated, based on the separation distance between sites.
C0 03 V*
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.2 0
C
.2 0
0 L.)
1.1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0
20 40 60 80 Distance (kin) 100 Distance (km)
TVA Nuclear Power Group 20
Methodology for Evaluating the Potential for M Multiple Dam Failures Due to Seismic Events Systems Analysis
- The purpose of the systems analysis is to model the combination of upstream dam failures that could 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 to define the sequences of multiple 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 MMultiple Dam Failures Due to Seismic Events Seismic Fragility Analysis
- The purpose of the seismic fragility analysis is to estimate the conditional probability of failure 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 0.8-.....-.......
C L--
U,.
08, 0
0.5 -,------------
-- -2 0
(g) d ia ---
_-----_-------------------_Mdan(0h 0
Media (50gh TVA Nuclear Power Group 23
Methodology for Evaluating the Potential for MMultiple 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. 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.
S 0.9 -
HCLPF = ground motion LL 0.8 --
corresponding to a m ean 0 7 conditional probability of failure of 0.01 0
- t.
0-4--
c 0.3 ---------------------------
X Median 0 1 0
0.5 1
1.5 2
2.5 3
PGA (g)
..,...uclear Power Group 24
Methodology for Evaluating the Potential for 0
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*UC 07C = combined logarithmic standard deviation; includes (A and GE Estimates of cy are available from NPP seismic PRA studies and limited number of seismic fragility assessments for dams and levees.
Typical values of cy 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.
0 0
1-0.9 0.8 -
07 06-0.5-0A4 03-0.2 0.1 0
HCLPF = ground motion corresponding to a mean conditional probability of failure of 0.01 Eilliiiiiiii.iii......i;ilii;;iiiliiiil.iiiiiiil 0
0.5 1
15 PGA (g) 2 25 3
TVA Nuclear Power Group 25
Methodology for Evaluating the Potential for MMultiple Dam Failures Due to Seismic Events The following figure shows the influence of multiple modes of failure on the fragility for the dam system.
Dam System with Th ree Failu re Modes
'- 0 5................ i......
............ I................................ :................
o,
0 5 -----------
i aQ 0 4 ----------------- -
I-
& 3 --- - - - - - -
.0
/
-Failure M ode 1 0
2 ----------
Failure N ode 2
- 06 C-f*-
- Failure NI, ode 3 0o0 005 1
5 2
25 PGA (g)
TVA Nuclear Power Group 26
Methodology for Evaluating the Potential for M Multiple Dam Failures Due to Seismic Events In Summary
- A risk-based screening evaluation process was developed for estimating the likelihood of multiple 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, 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 MMultiple Dam Failures Due to Seismic Events
- TVA's 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
Closing Remarks Joe Shea, Vice President, Nuclear Licensing