ML13115A020

Public Meeting Summary - Regulatory Conference / Enforcement Conference Sequoyah Nuclear Plant

ML13115A020
Person / Time
Site:	Watts Bar, Sequoyah
Issue date:	04/23/2013
From:	Scott Shaeffer Reactor Projects Region 2 Branch 6
To:	James Shea Tennessee Valley Authority
References
Download: ML13115A020 (82)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION REGION II 245 PEACHTREE CENTER AVENUE NE, SUITE 1200 ATLANTA, GEORGIA 30303-1257 April 23, 2013 Mr. Joseph W. Shea Vice President, Nuclear Licensing Tennessee Valley Authority 1101 Market Street, LP 3D-C Chattanooga, TN 37402-2801

SUBJECT:

PUBLIC MEETING

SUMMARY

- REGULATORY CONFERENCE /

ENFORCEMENT CONFERENCE SEQUOYAH NUCLEAR PLANT - DOCKET NOS. 50-327, 50-328; WATTS BAR NUCLEAR PLANT - DOCKET NOS. 50-390

Dear Mr. Shea:

This refers to the meeting conducted, at your request, at the NRC Region II office, Atlanta GA, on April 22, 2013, at 8:00 a.m. EDT. The meeting's purpose was to discuss apparent violations related to external flooding events for Watts Bar and Sequoyah nuclear plants. Enclosed are a list of attendees and the presentation handouts.

Topics discussed included: Proposed modifications to improve future flood mode capability, TVA hydrology overview and river operations, apparent violations for both Watts Bar and Sequoyah nuclear plants, TVA cultural insights related to these issues, significance determination, and old design issues considerations.

In accordance with 10 CFR 2.390 of the NRC's "Rules of Practice," a copy of this letter will be available electronically for public inspection in the NRC Public Document Room (PDR) or from the Publicly Available Records (PARS) component of NRCs document system (ADAMS).

ADAMS is accessible from the NRC Web site at http://www.nrc.gov/reading-rm/adams.html (the Public Electronic Reading Room). Should you have any questions concerning this meeting, please contact me at 404-997-4521.

Sincerely,

/RA/

Scott M. Shaeffer, Chief Reactor Projects Branch 6 Division of Reactor Projects Docket Nos.: 50-327, 50-328, 50-390 License Nos.: DPR-77, DPR-79, NPF-90

Enclosures:

1. List of Attendees

2. Handout - TVA Nuclear Power Group Hydrology cc w/encls - See next page:

_________________________ X SUNSI REVIEW COMPLETE G FORM 665 ATTACHED OFFICE RII:DRP RII:DRP SIGNATURE /RA By SSHaeffer for/ /RA/

NAME CJones SShaeffer DATE 4/23/2013 4/23/2013 E-MAIL COPY? YES NO YES NO YES YES NO YES NO YES NO N

J. Shea 2 cc w/encls:

J. T. Carlin Donna K. Guinn Site Vice President Manager, Site Licensing Sequoyah Nuclear Plant Watts Bar Nuclear Plant Tennessee Valley Authority Tennessee Valley Authority Electronic Mail Distribution Electronic Mail Distribution P. R. Simmons Terry E. Cribbe Plant Manager Manager, Corporate Licensing Sequoyah Nuclear Plant Tennessee Valley Authority Tennessee Valley Authority Electronic Mail Distribution Electronic Mail Distribution Edward J. Vigluicci J. W. Proffitt Associate General Counsel, Nuclear Manager, Site Licensing Tennessee Valley Authority Sequoyah Nuclear Plant Electronic Mail Distribution Electronic Mail Distribution Gordon P. Arent C. D. Mackaman Senior Manager, Licensing WBN Unit 2 Program Manager, Corporate Licensing Watts Bar Nuclear Plant Tennessee Valley Authority Tennessee Valley Authority Electronic Mail Distribution Electronic Mail Distribution Edward J. Vigluicci County Mayor Associate General Counsel, Nuclear P.O. Box 156 Tennessee Valley Authority Decatur, TN 37322 Electronic Mail Distribution County Executive County Mayor 375 Church Street 208 Courthouse Suite 215 625 Georgia Avenue Dayton, TN 37321 Chattanooga, TN 37402-2801 Tennessee Department of Environment &

Tennessee Department of Environment & Conservation Conservation Division of Radiological Health Division of Radiological Health 401 Church Street 401 Church Street Nashville, TN 37243 Nashville, TN 37243 Ann Harris Site Vice President 341 Swing Loop Watts Bar Nuclear Plant Rockwood, TN 37854 Tennessee Valley Authority Electronic Mail Distribution (cc w/encls contd - See next page)

David H. Gronek Plant Manager Watts Bar Nuclear Plant Tennessee Valley Authority Electronic Mail Distribution

J. Shea 3 cc w/encls contd:

Senior Resident Inspector U.S. Nuclear Regulatory Commission Watts Bar Nuclear Plant 1260 Nuclear Plant Road Spring City, TN 37381-2000 Senior Resident Inspector U.S. Nuclear Regulatory Commission Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy, TN 37379-3624

J. Shea 4 Letter to Joseph W. Shea from Scott M. Shaeffer dated April 23, 2013

SUBJECT:

PUBLIC MEETING

SUMMARY

- REGULATORY CONFERENCE /

ENFORCEMENT CONFERENCE SEQUOYAH NUCLEAR PLANT - DOCKET NOS. 50-327, 50-328; WATTS BAR NUCLEAR PLANT - DOCKET NOS. 50-390 Distribution w/encls:

C. Evans, RII EICS L. Douglas, RII EICS OE Mail RIDSNRRDIRS RidsNrrPMWattsBar1 Resource RidsNrrPMWattsBar2 Resource R. Pascarelli, NRR ((Regulatory Conferences Only))

RidsNrrPMSequoyah Resource NRC Resident Inspector DRP Branch Chief

STAr 3

• p 0

I-U I-I. F\)

b 01

-o Z m C

> C*)

m C)

C I

>--l >o m m

QzocZi mHm i_rn N)(D Q

( 1 ( Z -< l I- - (,,)

m 5m Yz z

P 10 . z I Q Ii 1- I c:, r I.

I I

l

4.

1) 4.

3 N Ct, Iz I

lB LI lCD

) I-1 I F\)

0 C m o

C)

>1 m 0

C I m

>> m 0

>0 t3 ) -m ,

G)ZOC mHmr.

riCD 0>00-I cD 0 Q mz<

H cc m 0

m rn z

C) CI) ci

-I m Cr)

-p CD

- z I. -o Q I 0

-I N

0 z

c

4-i.

5-P 7C) rn j) n Th 1.

1u 3

1 I-Iz r.)

(I

-o m

> C) m 0 I

>1 m 0

C I

0

>o m

-. 5 omG)>Q r-J(D Q 00

-4 -. -%

c. cc ii 0

C 1) 0 m Yz

() z N (t C) Ci)

-I Cl)

-I.

m Cl)

(

- z z a a

-ç 0

-I V

g C) N K

-I.

0 Vt C

H p jz; ID o

0

-t- \-

I

Enclosure 1 Q

Q ii c1 z w 0 F Cl) Ui Cl) I C)

-(N Lii z ZC) Ui 0

Ui I-> Zc w(xs

- I_

5 00 I0 O<CD o CD LU 0 1 ( *

, 0<

DUi a::

I UJZ -J 1-J F-D Ui 0 4

-J Ui C, a:: C D LU C z I)

(N I ()

N C

-c 0

(

TVA Nuclear Power Group Hydrology NRC Region II Regulatory Conference April 22, 2013 Enclosure 2

Agenda Preston Swafford Opening Remarks TVA Chief Nuclear Officer 3 Don Jernigan Improved Flood Mode Capability SVP TVA Nuclear Support Services 4 Don Jernigan TVA Hydrology Overview SVP TVA Nuclear Support Services 8 John McCormick TVA River Operations SVP TVA River Operations & Renewables 12 Apparent Violations 15 Unrecognized Increase in PMF Levels Unanalyzed Condition Joe Shea, VP TVA Nuclear Licensing 16 Failure to Report Unanalyzed Condition Joe Shea, VP TVA Nuclear Licensing 20 WBN Failure to Maintain Abnormal Operating Instruction (AOl) Tim Cleary, Site VP WBN Plant 25 WBN Thermal Barrier Booster Pump (TBBP) Wall Design Tim Cleary, Site VP WBN Plant 29 SQN Essential Raw Cooling Water (ERCW) Pump Station Barriers... John Carlin, Site VP SQN Plant 33 Don Jernigan Cultural Insights SVP TVA Nuclear Support Seivices 37 Gene Cobey Significance Determination Considerations TVA Nuclear Licensing 40 Gene Cobey Old Design Issue Considerations TVA Nuclear Licensing 67 Preston Swafford Closing Remarks TVA Chief Nuclear Officer 73 TVA Nuclear Power Group 2 Enclosure 2

Opening Remarks Preston Swafford, TVA Chief Nuclear Officer Enclosure 2

Improved Flood Mode Capability Don Jernigan, Senior VP TVA Nuclear Support Services Enclosure 2

Improved Flood Mode Capability TVA recognizes the significance of potential flood risks and has committed to implementing design changes to WBN and SQN that will provide significant margin above our design basis flood scenarios

• The current licensing approach provides reasonable assurance that the public health and safety will be protected against design basis external floods

• Improved Flood Mitigation Capability to be installed at SQN and WBN by December 31, 2016 Sequoyah Nuclear Plant (SQN) Watts Bar Nuclear Plant (WBN)

Soddy Daisy, TN Spring City, TN TVA Nuclear Power Group 5 Enclosure 2

Improved Flood Mode Capability (Contd)

Flood mode equipment will be located on the second floor of the WBN FLEX Equipment Storage Building (FESB) and in additional space of the SQN FESB Features I Advantages:

• Improved flood mitigation equipment will be at least 15 above the Probable Maximum Flood (PMF) elevation

• Use current locations at SQN and WBN

• Flood mode pumps and 3.0 MW Diesel are elevated on 2nd floor at WBN

• 1st floor houses FLEX equipment (e.g., portable pumps)

F-- ----------- ------------

Enclosure 2

Improved Flood Mode Capability (Contd)

The Improved Flood Mitigation Capability will use newly designed equipment as well as elements of the FLEX strategy to provide the following key safety functions

• Reactor Decay Heat Removal Provide new source of clean water Add new pumping capacity to feed the steam generators Provide path to reject decay heat to the atmosphere or another heat sink

• Reactor Coolant System (RCS) Make-up and Criticality Control Establish protected source of borated water Install new injection pump FESB 2 n d Floor (Overhead View)

TVA Nuclear Power Group 7 Enclosure 2

TVA Hydrology Overview Don Jernigan, Senior VP TVA Nuclear Support Seivices Enclosure 2

Timeline of Hydrology Events U Y 2 December2009 .

June 2012 WA recognizes potential HESCO barriers WA design basis

. December2010 for overtopping of earthen installed February 2012 Other WBN hydrology embankments at four calculations completed ye ow as cakDuons July 2012 upstream dams (rim leaka e) complete TVA Actions I found near WBN submitted 2008 2009 I 2010 12011 dam 2012 2013 Ir -r EEJEIE Feb 2008 April 2010 January 2011 June 2012 August 2012 Hydrology model WBN wind/wave WBN U2 submits PMF calculation is SQN LAR reconstitution calculations FSAR Section 2.4 issued to address submitted project started December 2009 updated on hydrology rim leakage.

PMF calculation issued for WBN and SQN July 2Q12 Flood Protection Walkdown NEI procedure August 2012 NRC identified February 2013 required by NRC performance NRC inspection May 2012 deficiency related exit meeting NRC met with WA to Flood reports violation of to discuss WAs Protection Plan I 0CFR50.72 NRC Actions status of hydrology 2008 and reanalysis 2009 2010 2011 2012 2013 I -..-..

I January2012 I NRC issued a letter to Feb / March 2008 July August 2010 December 2012 WA regarding long term NRC issued 3 NOVs NRC held public NRC 8 hr hydrology issues that WA had not meeting with WA and September2012 notification ERCW implemented the issued letter to June 2012 NRC identified Bldg degraded/

Software QA Program address hydrology NRC issued a CAL TBBP wall would nonconforming for SOCH reanalysis for SQN and WBN not perform its during external to address external intended design flooding flooding concerns TVA Nuclear Power Group 9 Enclosure 2

Hydrology Actions Implemented by TVA WA recognized the hydrology issues and implemented actions to mitigate flood risk

• Comprehensive review and updating of TVA Hydrology modeling and calculations

• Fukushima Response Conducted walkdowns to review impacted systems, structures and components and identify physical margins

• 4,

• Ran simulation to show feasibility of closing HESCO barrier openings

• Flood Mode preparation procedure improvements

• Modifications to address flood mode operations Diesel Generator barriers (SQN) (Complete)

Essential Raw Cooling Water (ERCW) barrier (SQN) (In progress)

Flood Mode Spool Piece Reduction (SQN and WBN) (In Design)

Intake Pumping Station (IPS) barrier (WBN) (In Design)

Thermal Barrier Booster Pump (TBBP) barrier (WBN) (Complete)

Main Control Room I Shutdown Board Room chiller barriers (WBN)

(Complete)

Spent Fuel Pool Pumps and Skimmer pumps barrier (WBN)

(Complete)

TVA has committed to complete permanent modifications to replace HESCO barriers at four dams upstream of WBN by October 2015 TVA Nuclear Power Group 10 Enclosure 2

Hydrology Actions Implemented by TVA (Contd)

TVA Nuclear Power Group 11 Enclosure 2

TVA River Operations John McCormick, Senior VP TVA River Operations and Renewables Enclosure 2

WA River Operations Managing the Rivers of the Tennessee Valley TVA is unique in its responsibility and ability to manage the Tennessee River and its major tributaries through a system of 49 dams

• The Tennessee Valley watershed is complex, draining over 40,000 square miles

• River Operations provides operational control of the reservoirs in the Tennessee River System in an integrated fashion, including:

Flood Control Water Quality Navigation Water Supply Hydropower Recreation

• WA has been a leader in river forecasting for several decades The Tennessee River is a well-researched and understood river system Many river modeling systems in place today had origins based in part on consultation with WA experts

• TVA acknowledges historical weakness with internal communications that contributed to these apparent violations TVA Nuclear Power Group 13 Enclosure 2

TVA River Operations Coordination between NPG and River Operations River Operations ability to control river flows, reservoir storage levels, river temperatures and levels presents TVA with unique advantages and opportunities to enhance and protect nuclear plant operations, including:

One vision and mission Owns river system operations and nuclear plants Dam release coordination Shared responsibility for nuclear and dam safety

• The River Forecast Center (RFC) staff utilizes forecasts of significant precipitation events, allowing for implementation of actions that can be taken to mitigate hydrothermal and flood challenges

• The RFC operates 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> a day, 365 days a year Monitors 200+ rain gauges, 60+ stream flow gauges, reservoir headwater, tailwater, and discharge at 49 dams Reviews and revises river discharge schedule 2-4 times a day, and provides flood warning notification based on pre-determined conditions Recent enhancements have been made that now require Nuclear Operations review of any changes and assumptions used to model river conditions to determine impact to site licensing basis (e.g., Intergroup Agreement: Nuclear Operations and River Operations; Coordination of Hydrology Issues)

TVA Nuclear Power Group 14 Enclosure 2

Apparent Violations Enclosure 2

Unrecognized Increase in PMF Levels Unanalyzed Condition Joe Shea, VP TVA Nuclear Licensing Enclosure 2

Unrecognized Increase in PMF Levels Unanalyzed Condition Root Cause Analysis (RCA) Summary Apparent Violation: Inadequate Flood Procedure Prior to Installation of HESCO Barriers During updating of hydrology calculations, TVA identified the potential for several dams upstream of Problem Statement: WBN and SQN to be overtopped during a PMF condition. This condition could have resulted in an increase in the PMF level at WBN and SQN for which flood response procedures were inadequate Latent design input errors existed in TVAs Simulated Open Channel Hydraulics (SOCH) model due RC-O1: to overconfidence in the accuracy of the model and in the calculation process. This resulted in unrecognized inaccuracies in the nuclear plant PMF calculations TVA nuclear management failed to ensure a sufficient focus on nuclear safety with regard to flooding by failing to provide effective oversight and engagement on changes being made to the RC-02: river system and thus ensuring that potential impacts on nuclear site flooding design basis were properly evaluated Formal flood protection programmatic and process controls had not been established for critical CC-O1: safety systems at the nuclear sites WA had less than adequate common internal understanding of the applicable regulatory CC-02: requirements for the nuclear sites with respect to river system operation controls Other: Ineffective completion of BLN corrective actions TVA Nuclear Power Group 17 Enclosure 2

Unrecognized Increase in PMF Levels Unanalyzed Condition

_Extent of Condition I Cause Extent of Condition (EOC0)

Condition #1: The overtopping and failure earthen embankments at Ft. Loudoun, Cherokee, Tellico, and Watts Bar Dams had the potential to increase PMF and adversely affect the plant

• EOCo: Assess the legacy potential for failed embankments to have affected equipment at BEN before compensatory actions were completed. Preliminary calculations completed. No adverse impact on BFN.

Condition #2: Processes and procedures for calculating, quantifying, and mitigating flood events (including a 100%

PMF event) have been insufficient to protect specific plant equipment at WBN and SQN

• EOCo: Assess the potential that programmatic weaknesses in the control of PMF calculations and for the configuration of the river system could impact other processes including communications with the River Scheduling organization and maintenance of the Riverware process.

Extent of Cause (EOCa)

Root Cause #1: Lack of sufficient questioning attitude resulted in the input errors during the development of the Simulated Open Channel Hydraulics (SOCH) model going undetected

• EOCa: The extent of cause examined other portions of the UFSAR that might be affected by SOCH input errors remaining undetected. The extent of cause also examined whether inputs and assumptions used in determining flood stage advisories may not be correct Root Cause #2: WA nuclear management failed to ensure a sufficient focus on nuclear safety with regard to flooding by failing to provide effective oversight and engagement on changes being made to the river system and thus ensuring that potential impacts on nuclear site flooding design basis were properly evaluated

• EOCa: The extent of cause identified the need to examine whether ongoing finite element analyses of certain WA dams have sufficient oversight and engagement by NPG management TVA Nuclear Power Group 18 Enclosure 2

Unrecognized Increase in PMF Levels Unanalyzed Condition Corrective Actions

• Implemented the Integrated Hydrology Advisory Committee

• Issued TVA standard procedure 20.009 for managing hydrology across fl/A organizations

• Develop and revise procedures to establish and implement an External Flood Protection Program to ensure the nuclear plant critical safety systems are protected from all postulated flooding conditions

• Establish procedural requirements to include reviews by Nuclear of any river or dam changes that may affect the Flood Protection Program

• Create a formal risk management process, informed by INPO Excellence in Integrated Risk Management, for all flood-related engineering products to evaluate changes to Nuclear plant designs, river system operations, flood related procedures, project management, and environmental/NEPA standards

• Develop an inventory of Nuclear programs and processes that are important to nuclear safety, to be prioritized in order of relative risk or importance to safety, and ensure controlling procedures exist to assure nuclear safety TVA Nuclear Power Group 19 Enclosure 2

Failure to Report Unanalyzed Condition Joe Shea, VP TVA Nuclear Licensing Enclosure 2

Failure to Report Unanalyzed Condition Root Cause Analysis (RCA) Summary Apparent Violation: Failure to Report Unanalyzed Condition TVA failed to report an unanalyzed condition as required by IOCFR5O.72(b)(3)(ii)(B) when it was Problem Statement: determined in 2009 that upstream dams would overtop and fail during a design basis probable maximum flood (PM F)

RC-O1: Multiple procedures were inadequate with regard to reportability of unanalyzed conditions RC-02: Cultural bias toward not reporting issues that are not fully analyzed CC-O1: Weakness in understanding unanalyzed condition and relationship to reportability CC-02: Erroneous decision by key decision maker CC-03: Failure to adequately challenge erroneous decision TVA Nuclear Power Group 21 Enclosure 2

Failure to Report Unanalyzed Condition

_Extent of Condition I Cause Extent of Condition (EOC0)

Condition #1: Failure to report unanalyzed condition

+ EOCo: Evaluated other failure to report examples Extent of Cause (EOCa)

Root Cause 1: Multiple procedures were inadequate with regard to reportability of unanalyzed conditions:

• EOCa: Other procedures that may not be adequate with regard to reportability requirements and guidance Root Cause 2: Cultural bias toward not reporting issues that are not fully analyzed

• EOCa: - Other instances of cultural bias toward non-reporting TVA Nuclear Power Group 22 Enclosure 2

Failure to Report Unanalyzed Condition Corrective Actions

• Correct procedures to include guidance on conservative decision-making for reporting

• Incorporate revised procedures into operations, engineering and licensing training

• Conduct broad scope reportability training for key organizations with reporting responsibilities

• Develop structured oversight program to assess reportability decisions

• Include case study on hydrology and flooding reporting decision errors in INPO SOER 10-2 training in 2013 TVA Nuclear Power Group 23 Enclosure 2

Regulatory Performance and Behaviors Leadership actions to accelerate regulatory performance and behavior change

• Licensing leadership team strengthening

• Issue Licensing Human Capital and Workforce restructuring strategy

• Establish corporate general manager of licensing position

• Implement subcommittee of NSRB focused on licensing and fleet regulatory behaviors

• Develop comprehensive regulatory training and development plan

• Improve senior leadership alignment on regulatory focus issues TVA Nuclear Power Group 24 Enclosure 2

WBN Failure to Maintain AOl Tim Cleary, Site VP WBN Plant Enclosure 2

Failure to Maintain AOl Root Cause Analysis (RCA) Summary Initially unable to implement Abnormal Operating Instruction 7.1 (AOI-7.1) to reconfigure and realign Apparent Violation:

systems necessary for flood mitigation within 27 hours3.125e-4 days <br />0.0075 hours <br />4.464286e-5 weeks <br />1.02735e-5 months <br /> During a walkdown to support the Near-Term Task Force evaluation, WBN did not demonstrate Problem Statement: performance of the AOI-7 Series procedures in the time specified, 27 hours3.125e-4 days <br />0.0075 hours <br />4.464286e-5 weeks <br />1.02735e-5 months <br />, which resulted in the potential failure to complete realignment of the plant for flood mode operation WBN personnel failed to understand the risk significance of issues identified with the stations ability RC-O1: to implement the flood mode protection plan CC-O1: Use of unsubstantiated assumptions Failure to thoroughly evaluate missed opportunities identified by line personnel, our QA organization CC-02: and the NRC Failure to properly train and maintain proficiency of the workers resulted in unfamiliarity with the CC-03: challenges and actions required to optimize implementation of flood mode operations Belief in stations capabilities to implement Flood Mode procedures as written resulted in a low CC-04: priority being placed on concerns identified related to timely implementation of flood mode operations TVA Nuclear Power Group 26 Enclosure 2

Failure to Maintain AOl Corrective Actions

• The implementing instructions, AOIs and Maintenance Instructions (MIs), were revised to capture the learnings from the reasonable simulation that was performed in response to the NRC Order

• A detailed listing of tools and equipment required for each Maintenance Instruction has been incorporated into the procedures. Flood mode tool boxes are staged and locked at the appropriate locations to ensure tools to implement the required actions are available, with a periodic Preventive Maintenance (PM) to validate that tool boxes are still in place and locked

• Operations Training for Flood Mode Implementation Procedures have been reduced from a 4-year frequency to a 2-year frequency

• Technical training has completed training needs analysis to revise and incorporate flood mode training for those organizations responding to a PMF event

• Clear guidance has been incorporated into AOl-7.O1 to aide in organizational response

• Verify that Corrective Actions to Prevent Recurrence (CAPRs) from Pre-HESCO Root Cause are completed and implemented which address developing and establishing a formal Flood Protection Program

• Revise Periodic Assessment of Operations Procedures Related to Natural Disasters to verify flood mode procedures are accurate and can be implemented

• Create a detailed timeline tool for implementing the flood mode plan and incorporate the timeline into AOI-7.O1 TVA Nuclear Power Group 27 Enclosure 2

Failure to Maintain AOl Extent of Condition I Cause Extent of Condition (EOC0)

Condition #1: Other abnormal procedures with time requirements that have not been demonstrated

• EOCo: Identify the population of procedures for the extent of condition, a review was conducted of time requirements and actions identified one procedure in which we could not confirm that we had validated the time requirement to perform the actions. That procedure has since been validated Extent of Cause (EOCa)

Root Cause 1: WBN personnel failed to understand the risk significance of issues identified with the stations ability to implement the flood mode protection plan

• EOCa: The extent of cause review identified the population of procedures at risk for successful implementation as well as looking for other slow developing events. The analysis did not identify any additional procedures TVA Nuclear Power Group 28 Enclosure 2

WBN Thermal Barrier Booster Pump Wall Design Tim Cleary, Site VP WBN Plant Enclosure 2

WBN Thermal Barrier Booster Pump Wall Design Root Cause Analysis (RCA) Summary Failure to correctly translate the design basis related to onsite flooding into the instruction for plant Apparent Violation:

design change TemporaryAlteration Control Form (TACF) 1-09-0006-070 Actions taken by Watts Bar to protect the reactor coolant pumps seals during a design basis Problem Statement:

probable maximum flood (PMF) event were found to be inadequate Engineering management did not provide rigorous oversight and direction in the field and the RC-O1: reinforcement of station expectations and standards during the development of the TACF The process prescribing development of temporary design changes to the plant was less than CC-O1: adequate in that it failed to ensure that all requirements of 10 CFR 50, Appendix B, Criterion Ill would be met Opportunities in various processes of reviewing the temporary alteration process were missed by CC-02: failing to identify non-compliance with regulatory requirements Job performance requirement qualification guide was insufficient in establishing minimum CC-03: knowledge requirements for developing temporary design changes TVA Nuclear Power Group 30 Enclosure 2

WBN Thermal Barrier Booster Pump Wall Design Corrective Actions

• Permanent barrier has been installed around the TBBP

• WBN Engineering is utilizing NEDP-5 (Design Document Reviews) to ensure temporary alterations are properly verified prior to being approved

• Work orders with the sealants RTV-102, -106 and Dow Corning 732 were reviewed to ensure the products are being applied appropriately

• Training Needs and Performance Analysis completed to consider changes to the Temporary Modifications qualification

• Developed formal External Flood Protection Program

• NPG-SPP-09.5 (Temporary Modifications) has been revised to ensure compliance with 10 CFR 50, Appendix B, Criterion Ill

• Site Engineering will develop a case study of this issue highlighting the need to refer back to base-level regulations when assessing a program

• Quality Assurance will evaluate this root cause to identify lessons learned in support of continuous audit and assessment process improvements TVA Nuclear Power Group 31 Enclosure 2

WBN Thermal Barrier Booster Pump Wall Design

_Extent of Condition I Cause Extent of Condition (EOC0)

Condition #1: Inadequate design for the TBBP temporary modification

• EOCo: Initial Extent of Condition covered design changes, both permanent and temporary. Based on research and analysis, permanent design changes have a more rigorous verification process, both in the procedure and in current practice, than do temporary modifications. The team then focused on temporary modifications in the extent of condition and the determined that the plant is not exposed to similar risk as posed by this event Extent of Cause (EOCa)

Root Cause 1: Engineering Management did not provide rigorous oversight and direction in the field and the reinforcement of station expectations and standards during the development of the TACF

• EOCa: Addressed in the Causal Analysis from the WBN Root Cause to address potential cross cutting issue in the area of Human Performance/Work Practices/Oversight. The extent of cause includes cross cutting aspects due to inadequate engineering management standards. The action to address the Extent of Cause will be addressed by implementing the requirement for completion of one Work Oversight Observation per month of each First Line Supervisor by their manager TVA Nuclear Power Group 32 Enclosure 2

SQN ERCW Pumping Station Flood Barriers John Carlin, Site VP SQN Plant Enclosure 2

SQN ERCW Pumping Station Flood Barriers Root Cause Analysis (RCA) Summary The design basis of the ERCW pumping station was not translated into design requirements and Apparent Violation:

drawings to ensure that the building would not flood WA determined that Sequoyah Unit 1 and 2 were at risk of external flooding inundating the ERCW building through conduit penetrations in manway 33, which would allow flood waters to enter the Problem Statement: ERCW building at a rate greater than the sump pumps capacity creating a condition that could result in the ERCW systems being unavailable to perform their design function during a flood event above plant grade ERCW penetration seals were described in general design documents, but their functional RC-O1 requirements were not specifically addressed in original design documents TVA Nuclear Power Group 34 Enclosure 2

SQN ERCW Pumping Station Flood Barriers

_Extent of Condition I Cause Extent of Condition (EOCo)

• Verify penetrations below maximum flood level in the ERCW Building, EDG Building, and Reactor Building have installed qualified flood barriers Extent of Cause (EOCa)

• Review the adequacy of the flood design basis documentation for installed flood barriers in the ERCW Building, EDG Building, and Reactor Building TVA Nuclear Power Group 35 Enclosure 2

SQN ERCW Pumping Station Flood Barriers Corrective Actions

• Installed high capacity sump pumps in ERCW building

• Sealed two open conduits on north side of ERCW building

• Developed and performed testing beyond vendor testing to ensure the selected conduit sealant would function as intended O Evaluated alternative sealing methods such as CHICO A compound, Polywater FST sealant, RTV and mechanical seals to determine the most appropriate sealant for the conduit penetrations

• Implemented design change to install new penetration seals in Manway 33 to address the initial problem

• Completed Engineering review of Diesel Generator Building and Reactor Building (RB)

• Development of a comprehensive Design Basis Document to fully address external flooding protection for the ERCW, RB and Emergency Diesel Generator (EDG) Buildings

• Issue new exterior flood barrier drawings that identify exterior flood boundaries and contain penetration seal design details TVA Nuclear Power Group 36 Enclosure 2

Cultural Insights Don Jernigan, Senior VP TVA Nuclear Support Services Enclosure 2

Cultural Insights TVA acknowledges a needed focus on cultural contributors with respect to the handling of various aspects of the hydrology-related issues

• Urgency in addressing vulnerabilities in flood protection methods

• Regulatory notifications on newly discovered issues that could potentially place station in an unanalyzed condition

• Sensitivity to external flooding events TVA NPG Hydrology 38 Enclosure 2

Cultural Insights Corrective Actions TVA has taken corrective actions to address cultural issues at TVA nuclear plants Immediate Actions

• Strengthened Licensing departments with the hiring of experienced professionals

• Strengthened reporting procedures to better identify unanalyzed conditions and to adopt a conservative reporting approach when faced with uncertainty

• Enhanced supervisory oversight standards associated with task assignment, pre-job briefs, and other error prevention techniques

• Tightened design standards to ensure consistency with I OCRF5O Appendix B, Criterion Ill

• Strengthened ownership and standards associated with preparing for and executing time-critical response activities Ongoing Actions

• Provide training to Operations, Engineering, and Licensing personnel on improving reportability knowledge and conservative behaviors

• Develop a formal External Flood Protection Program. This program will envelope related procedures, design basis, and risk management TVA NPG Hydrology 39 Enclosure 2

Significance Determination Considerations Gene Cobey, TVA NPG Licensing Enclosure 2

Significance Determination Considerations During this portion of the presentation, TVA will present additional information around four technical areas for consideration in the final significance determination of the apparent violations

• Flooding Initiating Event Frequency

• RCP Seal Performance

• WBN AOl Implementation Timeline

• SQN ERCW Pumping Station Flood Barriers TVA NPG Hydrology 41 Enclosure 2

Flooding Initiating Event Frequency Enclosure 2

Flooding Initiating Event Frequency Analysis Assumptions Critical Storm Selection and Configuration

• WA has confirmed that the critical storm locations were selected for SQN and WBN

• Conservatively, the storm location with the highest rainfall depths were chosen For the 21,400 mi2 storm, a downstream fixed location was selected For the 7,980 mi2 storm, the storm was centered over Bulls Gap Considerations for Downstream Dams

• WA design basis flood analysis does not consider downstream dam failures Realistically, downstream dams would fail in the PMF scenario, reducing flood levels by 6 at WBN and 24 at SQN Flood Modeling Software

• WA has concluded that SOCH and HEC-RAS results are comparable, and has utilized HEC-RAS for probabilistic and risk studies to be discussed today TVA NPG Hydrology 43 Enclosure 2

Flooding Initiating Event Frequency Local Intense (Point) vs. Basin-Average Precipitation There is a well-established inverse relationship between the average precipitation intensity over an area and the size of that area

• Storms over a small area can be much more intense than a storm over a large area, and point precipitation varies significantly from point to point in a watershed

• The precipitation-frequency relationships are different for point precipitation and basin-average precipitation Location Precipitation (in) Duration Method 1

WBN 35.9 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> Local Intense (Point) Precipitation 2

SQN 27.5 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> Local Intense (Point) Precipitation WBN and SQN 3 16.34 (main) + 6.44 (antecedent) 9 days Basin-Average Precipitation HMR56 (1983), 2 1 HMR45 (1973), 3 HMR4I (1965)

• To estimate rainfall over a large area basin using a point precipitation value, an areal reduction factor (ARE) must be applied Recent studies have been published extending the area up to 7,700 mi 2 Allen, R. and DeGaetano, A. (2005). Area! Reduction Factors for Two Eastern United States Regions with High Rain-Gauge Density. J. Hydrol. Eng., 10(4), 327335 By inversely applying an ARF to the 22.8 basin-average precipitation event identified in the NRC analysis, TVA determined that this was equivalent to a 34.2 point precipitation event at WBN

• This event was determined to have an annual exceedence probability (AEP) less than E 6 TVA NPG Hydrology 44 Enclosure 2

Flooding Initiating Event Frequency PMPvs.PMF Although a large precipitation event is typically necessary for a large flooding event, there are a variety of factors that will determine if a precipitation event will result in a flood event, including:

• Soil moisture conditions

• Storage capacity of the basin

• Storm location

• Season of occurrence

• Reservoir operations Due to differences in precipitation and flooding, a better estimate of the frequency of a flood level at the plant is a flood frequency curve

• Statistical hydrologists traditionally use flow-based methods to estimate recurrence of flood events

• Flood flow frequency embeds the precipitation frequency and other contributing factors discussed above TVA NPG Hydrology 45 Enclosure 2

Flooding Initiating Event Frequency Development of Flow-Based AEP Curves Consistent with USGS Bulletin 17b Guidelines for Determining Flood Flow Frequency, which was adopted in 1976 as the U.S. standard for flood-frequency analysis, TVA created maximum annual flood frequency curves

• Natural inflows (flows before they reach dams) were analyzed using historical data and fit to a variety of distributions (Log Pearson Ill, GEV, Kappa)

• 10,000 Monte Carlo simulations for the Log Pearson Ill distribution were used to estimate the confidence bounds All of the various distributions examined were within the confidence bounds Shows the wide uncertainties associated with predicting these rare events

- - - - t L r

4

_j--

f i-;- .

0 I -

I I

t4L.VA4IJflF[03DFI0tSD.

TVA NPG Hydrology 46 Enclosure 2

Flooding Initiating Event Frequency Results of Flow-Based AEP Curves for SQN Tennessee River at Sequoyah Nuclear Plant 732.0 Extreme Value Type 1 Plotting Paper Approxima e 95th Percen lie ConfidenL Bound 724.0 i.g..e irson iii 100%PMI-90%PMF

. 716.0 a) 80%PMF -

• 708.0 Se3uOj1hP ant Grade 65% PMF 700.0 5O%PMF 692.0 ased n Relation hip GEVApp oximate 684.0 f-RIve. Level front MF Watersi d-Iode1hig- Mean Freq ncy Curve

,lth Lo Pearson II Distribution or 3-fl y Unregul ed Flows Approximat 5th Percenti e_________

676.0 L g Pearson III onfidence B und AprIl 8 2013 668.0 0.99 0.90 0.50 0.10 0.01 iO- iO- io- iO6 10- 10B ANNUAL EXCEEDANCE PROBABILITY SEQUOYAH NUCLEAR PLANT ANNUAL EXCEEDANCE PROBABILITY RIVER LEVEL (ft) ITEM OF INTEREST th PERCENTILE 95 MEAN FREQUENCY 698.0 50% PMF 5.9 E-7 9.9 E-5 698.0 50% PMF (GEV) 6.6 E-6 nla 705.0 Plant Grade Less Than 1.0 E-8 1.2 E-5 7050 Plant Grade (GEV) 2.0 E-7 nia 712.9 80% PMF Less Than 1.0 E-8 1.5 E-6 720.5 100% PMF Less Than 1.0 E-8 2.5 E-7 TVA NPG Hydrology 47 Enclosure 2

Flooding Initiating Event Frequency Results of Flow-Based AEP Curves for WBN Tennessee River at Watts Bar Nuclear Plant 752.0 Extreme Value Type 1 PlottIng Paper Approxima 95th Percen ic Confidenc Bound 744.0 from Log Pe u-son III GEV

- Appro imate Mean 00% PMF 736.0 Freqi ency Curie 90%PMF w 80%PMF a)

I a) z 728.0 720.0 :_

712.0 LPIIIFreuencyCurve ased n RelatIon hip 704.0 _ f-Rlve eveI from MF Watersl .d-Modellng ilth Lo Pearson II DIstrIbution nr 3-fl jl.Jnregufr ed Flowc Approximat 5th Percent, e 696.0 L g Pearson III onfldence & und April 8, 2013 688.0 0.99 0.90 0.50 0.10 0.01 i0- iO- iD- io- io- 10B ANNUAL EXCEEDANCE PROBABILITY WATTS BAR NUCLEAR PLANT RIVER LEVEL (ft) ANNUAL EXCEEDANCE PROBABILITY ITEM OF INTEREST th PERCENTILE 95 MEAN FREQUENCY 724.0 65% PMF 5.9 E-8 2.3 E-5 728.0 Plant Grade Less Than 1.0 E-8 8.9 E-6 728.0 Plant Grade (GEV) 8.3 E-8 nla 730.9 80% PMF Less Than 1.0 E-8 4.6 E-6 738.7 100% PMF Less Than 1.0 E-8 9.6 E-7 TVA NPG Hydrology 48 Enclosure 2

Flooding Initiating Event Frequency Significance Considerations

• When extending point precipitation events to a large area, an areal reduction factor must be applied, which will result in an initiating event frequency of less than 1 E 6

• The flow method, which is accepted by the hydrological community, supports the conclusion that PMF events are more rare than I E 6 per year TVA NPG Hydrology 49 Enclosure 2

RCP Seal Performance Enclosure 2

RCP Seal Performance TVA has concluded that given a loss of seal cooling during Mode 4 operations with stopped RCPs, the RCP seal failure probability is bounded by that of a very small break LOCA (1 .5E-), per NUREGICR-6928 3

TVAs procedures direct that the plant be shutdown in the case of a flood event

• As part of Stage I flood preparations, TVAs Abnormal Operating Instructions/Procedures (AOl/AOP) direct that the unit be in Mode 4 shutdown (i.e., cooled below 350°F) within 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />, and RCPs stopped

• Thermal barrier booster pump operation is expected for a minimum of an additional 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br /> (Stage II) (i.e., a total of a minimum of 27 hours3.125e-4 days <br />0.0075 hours <br />4.464286e-5 weeks <br />1.02735e-5 months <br />) before water would exceed plant grade and there is potential for a loss of cooling RCP seals are not expected to fail given a loss of seal cooling after Mode 4 is achieved and RCP5 have been stopped

• Westinghouse analysis of stopped RCPs concluded that the RCP seals and 0-rings will perform their design basis function in Mode 4 conditions (< 350°F and pressure 350 psi) for a 100-day duration without seal cooling TVA NPG Hydrology 51 Enclosure 2

WBN AOl Implementation Timeline Enclosure 2

WBN AOl Implementation Timeline Overview of AOl Implementation Timely implementation of the Abnormal Operation Instruction (AOl) is necessary to ensure critical safety functions are provided during a design basis PMF prior to flood waters preventing other actions

• The design basis for WBN includes a 27 hour3.125e-4 days <br />0.0075 hours <br />4.464286e-5 weeks <br />1.02735e-5 months <br /> timeline to implement the AOl

• WBN enters Maximum Probable Flood (AOl-7.O1) instructions when Stage I warning is received from River Operations or indication of extremely high rainfall in the upstream watershed

• Key functions in the AOl provide for:

Decay Heat Removal Reactor Coolant System (RCS) Make-up Reactivity Control Spent Fuel Pool Controls Reactor Coolant System Integrity

• As will be discussed on the following slides, two these functions are most critical to core cooling Decay Heat Removal Reactor Coolant System (RCS) Make-up TVA NPG Hydrology 53 Enclosure 2

WBN AOl Implementation Timeline Decay Heat Removal The timeline below illustrates that at 16:52 High Pressure Fire Protection (HPFP) is aligned to the A train Auxiliary Feedwater (AFW) to support decay heat removal from the steam generators

• Decay Heat Removal actions Remove HPFP pump discharge relief valves (WBN Ml-17.033)

Connect HPFP to AFW systems through spool piece installation (WBN Ml-17.018)

Align systems to inject water into the steam generators (WBN AOl-7.06) 0:00 10:00 27:00 32:27 Stage 1 (10 hrs) Stage 2 (22hrs 27mm) 6 Notification from River Team 3 AtrainHPFP L Operations of impending 1O*02 Ml-17.033 Remove 1402 aligned to feed steam enerators flood conditions HPFP Relief Valves 10:51 AOl-7.06Align HPFPtoATrainAFW 16:52 27:00 Decay Heat Removal Actions Team 2 B train HPFP aligned to feed 13:29 MI-I 7.018 Install A Train 16:22 HPFP spool pieces steam generators Maintenance Team AOl-7.06 Align Operations Team 16.52 19.45 HPFP to B train AFW Team 2 1622 Ml-17.018Install B

• Maintenance Teams are configured as 5 teams of 3 maintenance staff, pius 2 supervisors Train HPFP spool pieces Teams 1, 4 and 5 are involved with other flood mode preparation activities TVA NPG Hydrology 54 Enclosure 2

WBN AOl Implementation Timeline Reactor Coolant System (RCS) Make-up The timeline below illustrates that RCS make-up utilizing the Flood Mode Boration Make-up system (aka Aux Charging) would be completed within 20.1 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, as demonstrated by simulation

• RCS Make-up (Stage II) actions Injection into the RCS as make-up through the use of Auxiliary Charging System Install flood mode spool pieces from Auxiliary Charging System and the Normal Charging System (WBN procedure MI-I 7.01 9)

Align system to inject into the RCS (WBN procedure SOl-84.01) 0:00 10:00 27:00 32:27 Stage 1 (10 hrs) Stage 2 (22hrs 37mm)

TL_

Notification from River Operations of impending flood conditions Team 3 MI-I 7.019 Aux 14:02 Charging 16:05 RCS Make-up Spool Pieces Actions E Maintenance Team RCS Make-up Aligned J Operations Team SOl-84.01 Flood 16:05 Mode Boration 20:05 Make-up TVA NPG Hydrology 55 Enclosure 2

WBN AOl Implementation Timeline Significance Considerations

• Although TVA was not able to complete the entire AOl process in the prescribed 27 hours3.125e-4 days <br />0.0075 hours <br />4.464286e-5 weeks <br />1.02735e-5 months <br />, the decay heat removal and RCS make-up critical safety functions were satisfied with ample margin (6.9 hrs)

TVA NPG Hydrology 56 Enclosure 2

SQN ERCW Pumping Station Flood Barriers Enclosure 2

SQN ERCW Pumping Station Flood Barriers Overview TVA has concluded that it is highly likely that plant operators would be able to remove decay heat successfully during the flooding events of concern

• The plant will be in Mode 4 and RCPs stopped before ERCW is potentially impacted

• Sufficient staff will be on site to implement mitigating actions

• Procedural guidance exists to take the necessary mitigating actions TVA NPG Hydrology 58 Enclosure 2

SQN ERCW Pumping Station Flood Barriers ERCW Sequence of Events and Flood Timing TVA analyzed three scenarios accounting for water level, timing, and impacted equipment 7101 STAGE I STAGE 2 Available Equipment: I

• HPFP Cooling

• Flood Mode Boration: Scenario 3 705 i I SQN PLANT GRADE 705 LLI Aux Feed (TDAFW)

• Aux Feed I Scenario 2 F

0 SBO Diesel Connected 702 700

• Charging Pump wI Loss of Off-site Power 0 HPFP Cooling DC Power U-698 Water Reaches Strainers (698)

• Assumed loss of ERCW 695

• Assumed loss of EDGs 690 Stage I Flood Warning 0 5 10 15 20 25 30 35 40 Time TVA NPG Hydrology 59 Enclosure 2

SQN ERCW Pumping Station Flood Barriers ERCW Analytical Conservatisms In TVAs analysis, conservative assumptions were made to ensure margin in the worst case scenarios

+ Timing of water level rise Water level rise assumed to be bounding case (0.5 per hour)

Impact of sump pumps not credited Assumed in-leakage driven by maximum flood level

• Timing of loss of ERCW Instantaneous loss of ERCW is assumed once flood waters reach elevation 698 Traveling water screens Strainer fouling

• Availability of diesel generators Assumed that diesel generators become unavailable immediately once flood waters reach elevation 698

• No credit taken for recovery actions that are not procedurally driven TVA NPG Hydrology 60 Enclosure 2

SQN ERCW Pumping Station Flood Barriers SQN ERCW PRA Evaluation Results WA performed a PRA evaluation and concluded that the probability of failure to achieve core cooling a flood event is approximately 6E 6

Unit lIUnit 2 ACDF Results Scenario Mean Value th Percentile Value 5

g Scenario #1 8.51 E° 1 1 .09E° 7

Scenario #2 5.21 E° 9 6 3.34E° Scenario #3 9 2.09E° 6 2.50E° Total 9 8.15E° 6 5.95E° TVA NPG Hydrology 61 Enclosure 2

Application of Technical Topics Summary of Findings TVA feels that the analyses and additional information provided are applicable to multiple apparent violations, as shown below:

P re-H ESCO I

WBN AOl Implementation WBNTBBP I

SQNERCW if I TVA NPG Hydrology 62 Enclosure 2

Application of Technical Topics Impact on Pre-HESCO Condition Finding The following should be considered when assessing the risk significance of this finding:

• TVA agrees that the initiating event frequency of rare flooding events is uncertain

• When translating point precipitation to a large area basin, an areal reduction factor must be applied, which would result in a flood event frequency less than E- 6

• TVAs position is that the flow based method should be used to determine the frequency of these rare flooding events The mean frequency for flooding scenarios of concern at both sites is less than 8 E The 95% confidence interval is approximately 4.6E 6 at WBN and 1 .5E 6 at SQN Tennessee River at Sequoyah Nuclear Plant Tennessee River at Watts Bar Nuclear Plant 732.0 752.0

i. Extreme Value Type 1 Plotting Paper Approximo e 95th Percen Ie Confiden Bound Extreme Value Type 1 Plotting Paper Approxlma 95th Percen Ic Confident Bound 724.0 1.....,. I..,,P ,..,. Ill \ (FII 100% PM ,

/Appro imate Mean 90%PMF 00%PMF Freg ency Curve 716.0 80%PMF . --

90%PMI

\.

80%PMF .

708.0 728.0 Wattr 801 ant Cmd 65%PMF uhF ddi - - -

65% PMF ,,.- ._-

700.0 720.0 -

LP1II Appr Approxi ate Mean 692.0 ised n Relation hip trn t-reque 4iCiJii7e 712.0 GEVApp aximate axed n Relation up 684,0 Hlvc i.euel-froru iMEWatersl d-Modeiln 9

-i,-

n n I-Rise eval-fron !Mf-Watacsl i-Modelksg tb La Pearson II Distribution 676.0

• r34 1Jnragu) adflowL_ pppLmat 5th Percent gPearsun III onfidnncrB und 696.0 -

4th La Pearson II Distribution Approxlmot 5th Percenti e gPrarson III anfidencet und Apr98 2013 Apr98 2013 668.0 0.99 0.90 0.50 0.10 0.01 10 10- 10- 10- 10- 10 688.0 0.99 0.90 0.50 0.10

- 0.01 10 10 10-5 10- 10- 10-ANNUAL EXCEEDANCE PROBABILITY ANNUAL EXCEEDANCE PROBABILITY Therefore, TVA offers for NRC consideration that the significance of this finding can reasonably be considered at least one order of magnitude less significant TVA NPG Hydrology 63 Enclosure 2

Application of Technical Topics Impact on WBN AOl Implementation Finding The following should be considered when assessing the risk significance of this finding:

• TVA agrees that the initiating event frequency of rare flooding events is uncertain

• TVAs position is that the flow based method should be used to determine the frequency of these rare flooding events The mean frequency for flooding scenarios of concern at WBN is less than E 8 The 95% confidence interval is approximately 8.9E 6

• The probability of failure for the Westinghouse RCP seals is bounded by the very small break LOCA frequency of 1.5E 3

• Adequate time exists to complete the procedural steps necessary to fulfill the critical safety functions of decay heat removal and RCS inventory make-up. The HRA failure probability is approximately I .66E Therefore, TVA offers for NRC consideration that the significance of this finding can reasonably be considered to be very low.

TVA NPG Hydrology 64 Enclosure 2

Application of Technical Topics Impact on WBN TBBP Finding The following should be considered when assessing the risk significance of this finding:

• Initiating event frequency is at least an order of magnitude lower as previously discussed

• The HEC-RAS model results and consideration of downstream dam failures, indicate that the flood level will not reach the base plate of the TBBP motor

• The probability of failure for the Westinghouse RCP seals is bounded by the very small break LOCA frequency of 1.5E-3 NOTES:

1. Values in square bradcets are outside-building rairfall-inducod PMF; Elevations si,own are these levels with a 0.5, surge Included ([)F).

m,PWt!nd 2. Puriiiarnetl bsirie, iiistallud uidvi DCN 54018 prutU puirip Lu El. 742.0 rnmpPrweEfid - 740.5 I IARSubmIttaIPMF 739.7 [739.2]

HEC-RA3 P.4F 739.2 [738.7]

Loss of Downetresm Dam i L738.31

L__ original PMF(199) 734.6 [738.1]

.1 5 1

--currentFSRPMF(1998Reassessment 735.4 [734.9]

Therefore, TVA offers for NRC consideration that the significance of this finding can reasonably be considered to be very low. 65 Enclosure 2

Application of Technical Topics Impact on SQN ERCW Finding The following should be considered when assessing the risk significance of this finding:

• TVA agrees that the initiating event frequency of this combination of flooding events is uncertain

• The results of TVAs significance determination is Unit 1!Unit 2 ACDF Results Scenario Mean Value 9 t

5 h Percentile Value Scenario#1 ° 1

8.51E 7 1.09E° Scenario #2 5.21 E° 9 6 3.34E° Scenario #3 9 2.09E° 6 2.50E° Total 9 8.15E° 6 5.95E° Therefore, TVA offers for NRC consideration that the significance of this finding can reasonably be considered at least one order of magnitude less significant.

TVA NPG Hydrology 66 Enclosure 2

Old Design Issue Considerations Gene Cobey, TVA NPG Licensing Enclosure 2

Old Design Issue Considerations Overview TVA offers for NRC consideration that both the Pre-HESCO condition at SQN and WBN and the ERCW Pumping Station Flood Barrier issue at SQN satisfy the criteria for treatment as an Old Design Issue

• It was licensee-identified as a result of a voluntary initiative, such as a design basis reconstitution

• It was or will be corrected, including immediate corrective actions and long-term comprehensive corrective actions to prevent recurrence, within a reasonable time following identification. For the purpose of this criterion, identification is defined as the time when the significance of the finding is first discussed between the NRC and the licensee

• It was not likely to be previously identified by recent ongoing licensee efforts, such as normal surveillance, quality assurance activities, or evaluation of industry information

• It does not reflect a current performance deficiency associated with existing licensee programs, policy, or procedure Therefore, TVA offers for NRC consideration that both the Pre-HESCO condition at SQN and WBN and the ERCW Pumping Station Flood Barrier issue at SQN satisfy the criteria for treatment as an Old Design Issue TVA NPG Hydrology 68 Enclosure 2

Old Design Issue Considerations Unrecognized Increase in PMF Levels Unanalyzed Condition

• It was licensee-identified as a result of a voluntary initiative, such as a design basis reconstitution WA identified the non-conservatisms with the dam spitiway coefficients in July 2009 as part of hydrology design basis reconstitution

• It was or will be corrected, including immediate corrective actions and long-term comprehensive corrective actions to prevent recurrence, within a reasonable time following identification. For the purpose of this criterion, identification is defined as the time when the significance of the finding is first discussed between the NRC and the licensee WA took immediate actions

• Bulldozer staged to breakup earthen embankment at Fort Loudoun Dam

• Installation of HESCO barriers WA conducted a comprehensive root cause assessment and is currently implementing corrective actions WA will implement permanent modifications to the upstream dams to prevent overtopping (to be completed by October2015)

Modify facilities to significantly improve margin and reduce flood risk at WBN and SQN TVA NPG Hydrology 69 Enclosure 2

Old Design Issue Considerations Unrecognized Increase in PMF Levels Unanalyzed Condition

• It was not likely to be previously identified by recent ongoing licensee efforts, such as normal surveillance, quality assurance activities, or evaluation of industry information The unanalyzed condition due to upstream dams overtopping was not likely to have been discovered by ongoing efforts such as normal surveillances, quality assurance activities or evaluation of industry information It was discovered during a significant effort to reconstitute the hydrological models for the Tennessee Valley watershed

• It does not reflect a current performance deficiency associated with existing licensee programs, policy, or procedure The original spillway coefficient was introduced as part of the original calculations and was corrected in 2009 Therefore, TVA offers for NRC consideration that the pre-HESCO condition satisfies the criteria for treatment as an Old Design Issue TVA NPG Hydrology 70 Enclosure 2

Old Design Issue Considerations SQN ERCW Pumping Station Barriers

• It was licensee-identified as a result of a voluntary initiative, such as a design basis recons titution Discovered while performing walkdowns in accordance with NEI 12-07, Guidelines for Perform ing Verification Walkdowns of Plant Flood Protection Features In the NRC Inspection Report 050-327/2013-10, the NRC characterized this apparent violati on as licensee identified

• It was or will be corrected, including immediate corrective actions and long-term compr ehensive corrective actions to prevent recurrence, within a reasonable time following identification. For the purpos of e this criterion, identification is defined as the time when the significance of the finding is first discussed betwee n the NRC and the licensee TVA took immediate actions

• Installed high capacity sump pumps

• Repaired conduit flood seals Develop an external flood design basis document to fully address flood protection in the ERCW

, EDG, and Reactor buildings Issue new exterior flood barrier drawings that identify exterior flood boundaries and contain penetration seal design requirements Modify facilities to significantly improve margin and reduce flood risk at WBN and SQN TVA NPG Hydrology 71 Enclosure 2

Old Design Issue Considerations SQN ERCW Pumping Station Barriers

• It was not likely to be previously identified by recent ongoing licensee efforts, such as normal surveillance, quality assurance activities, or evaluation of industry information The performance deficiency occurred at the time of the development of the original design basis used for plant construction It is not reasonable to assume that the work activities conducted since original construction would have involved revalidation of the original design basis assumptions/values

• It does not reflect a current performance deficiency associated with existing licensee programs, policy, or procedure Current Design Engineering programs require the capture of design details in plant docum ents and prints Therefore, TVA offers for NRC consideration that the ERCW issue satisfies the criteria for being treated as an Old Design Issue TVA NPG Hydrology 72 Enclosure 2

Closing Remarks Preston Swafford, TVA Chief Nuclear Officer Enclosure 2