Watts Bar nuclear Plant, Unit 1 - Issuance of …changes to the hydrology analysis. A copy of the...

UNITED STATES NUCLEAR REGULATORY COMMISSION

WASHINGTON, D.C. 20555-0001

Mr. Joseph W. Shea Vice President, Nuclear Licensing Tennessee Valley Authority 1101 Market Street, LP 3D-C Chattanooga, TN 37 402-2801

January 28, 2015

SUBJECT: WATTS BAR NUCLEAR PLANT, UNIT 1 -ISSUANCE OF AMENDMENT TO REVISE UPDATED FINAL SAFETY ANALYSIS REPORT REGARDING CHANGES TO HYDROLOGY ANALYSIS (TAC NO. ME9130)

Dear Mr. Shea:

The U.S. Nuclear Regulatory Commission has issued the enclosed Amendment No. 98 to Facility Operating License No. NPF-90 for Watts Bar Nuclear Plant, Unit 1. This amendment consists of changes to the license in response to your application dated July 19, 2012, as supplemented by letters dated March 1, 2013; April 29, 2013; April 30, 2013; June 13, 2013; October 21, 2013; December 18, 2013; January 31, 2014; April2, 2014; September 30, 2014; and December 5, 2014.

The proposed amendment will revise the Updated Final Safety Analysis Report regarding changes to the hydrology analysis.

A copy of the related Safety Evaluation is also enclosed. The Notice of Issuance will be included in the Commission's biweekly Federal Register notice.

Docket No. 50-390

Enclosures: 1. Amendment No. 98 to NPF-90 2. Safety Evaluation

cc w/enclosures: Distribution via Listserv

Sincerely,

()D~~ o. ~ ~-;. Dion, Project Manager Watts Bar Special Projects Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation



TENNESSEE VALLEY AUTHORITY

DOCKET NO. 50-390

WATTS BAR NUCLEAR PLANT, UNIT 1

AMENDMENT TO FACILITY OPERATING LICENSE

Amendment No. 98 License No. NPF-90

1. The U.S. Nuclear Regulatory Commission (the Commission) has found that:

A. The application for amendment by Tennessee Valley Authority (the licensee) dated July 19, 2012, as supplemented by letters dated March 1, 2013; April 29, 2013; April30, 2013; June 13, 2013; October 21, 2013; December 18, 2013; January 31, 2014; April 2, 2014: September 30, 2014; and December 5, 2014, complies with the standards and requirements of the Atomic Energy Act of 1954, as amended (the Act), and the Commission's rules and regulations set forth in Title 10 of the Code of Federal Regulations (10 CFR) Chapter I;

B. The facility will operate in conformity with the application, the provisions of the Act and the rules and regulations of the Commission;

C. There is reasonable assurance (i) that the activities authorized by this amendment can be conducted without endangering the health and safety of the public, and (ii) that such activities will be conducted in compliance with the Commission's regulations;

D. The issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public; and

E. The issuance of this amendment is in accordance with 10 CFR Part 51 of the Commission's regulations and all applicable requirements have been satisfied.

Enclosure 1

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2. Accordingly, the license is amended by changes as indicated in the attachment to this license amendment, and paragraph 2.C.(2) of Facility Operating License No. NPF-90 is hereby amended to read as follows:

(2) Technical Specifications and Environmental Protection Plan

The Technical Specifications contained in Appendix A as revised through Amendment No. 98 and the Environmental Protection Plan contained in Appendix B, both of which are attached hereto, are hereby incorporated into this license. TVA shall operate the facility in accordance with the Technical Specifications and the Environmental Protection Plan.

3. This license amendment is effective as of the date of its issuance, and shall be implemented no later May 31, 2015. Implementation of the amendment shall also include revision of the Updated Final Safety Analysis Report as described in the licensee's request.

Attachment: Changes to the Operating License

FOR THE NUCLEAR REGULATORY COMMISSION

'1/l~~// sie F. Quichocho, Chief

atts Bar Special Projects Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

Date of Issuance: January 28 , 2015

ATTACHMENT TO LICENSE AMENDMENT NO. 98

FACILITY OPERATING LICENSE NO. NPF-90

DOCKET NO. 50-390

Replace the following pages of Facility Operating License NPF-90 with the attached revised pages. The revised pages are identified by amendment number and contain a marginal line indicating the area of change.

REMOVE 3 4a

INSERT 3 4a 4b

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(4) TVA, pursuant to the Act and 10 CFR Parts 30, 40 and 70, to receive, possess, and use in amounts as required, any byproduct, source or special nuclear material without restriction to chemical or physical form, for sample analysis, instrument calibration, or other activity associated with radioactive apparatus or components; and

(5) TVA, pursuant to the Act and 10 CFR Parts 30, 40 and 70, to possess, but not separate, such byproduct and special nuclear materials as may be produced by the operation of the facility.

C. This license shall be deemed to contain and is subject to the conditions specified in the Commission's regulations set forth in 10 CFR Chapter I and is subject to all applicable provisions of the Act and to the rules, regulations, and orders of the Commission now or hereafter in effect, and is subject to the additional conditions specified or incorporated below.

(1) Maximum Power Level

TVA is authorized to operate the facility at reactor core power levels not in excess of 3459 megawatts thermal.

(2) Technical Specifications and Environmental Protection Plan

The Technical Specifications contained in Appendix A as revised through Amendment No. 98 and the Environmental Protection Plan contained in Appendix B, both of which are attached hereto, are hereby incorporated into this license. TVA shall operate the facility in accordance with the Technical Specifications and the Environmental Protection Plan.

(3) Safety Parameter Display System (SPDS) (Section 18.2 of SER Supplements 5 and 15)

Prior to startup following the first refueling outage, TVA shall accomplish the necessary activities, provide acceptable responses, and implement all proposed corrective actions related to having the Watts Bar Unit 1 SPDS operational.

(4) Vehicle Bomb Control Program (Section 13.6.9 of SSER 20)

During the period of the exemption granted in paragraph 2.D.(3) of this license, in implementing the power ascension phase of the approved initial test program, TVA shall not exceed 50% power until the requirements of 10 CFR 73.55(c)(7) and (8) are fully implemented. TVA shall submit a letter under oath or affirmation when the requirements of 73.55(c)(7) and (8) have been fully implemented.

Facility License No. NPF-90 Amendment No. 98

4a

(8) Upon implementation of Amendment No. 70 adopting TSTF-448, Revision 3, the determination of control room envelope (CRE) unfiltered air inleakage as required by SR 3.7.10.4, in accordance with TS 5.7.2.20.c(i), the assessment of CRE habitability as required by Specification 5. 7.2.20.c.(ii), and the measurement of CRE pressure as required by Specification 5.7.2.20.d, shall be considered met following implementation:

{a) The first performance of SR 3.7.10.4, in accordance with Specification 5.7.2.20.c(i), shall be within the specified Frequency of 6 years, plus the 18-month allowance of SR 3.0.2, as measured from April 5, 2004, the date of the most recent successful tracer gas test, as stated in the August 4, 2004, letter response to Generic Letter 2003-01 , or within the next 18 months if the time period since the most recent successful tracer gas test is greater than 6 years.

(b) The first performance of periodic assessment of CRE habitability, Specification 5.7.2.20.c.(ii) shall be within 3 years, plus the 9-month allowance of SR 3.0.2, as measured from April 5, 2004, the date of the most recent successful tracer gas test, as stated in the August 4, 20041etter response to Generic Letter 2003-01, or within the next 9 months if the time period since the most recent successful tracer gas test is greater than 3 years.

(c) The first performance of the periodic measurement of CRE pressure, Specification 5.7.2.20.d, shall be within 18 months, plus the 138 days allowed by SR 3.0.2, as measured from May 10, 2007, the date of the most recent successful pressure measurement test, or within 138 days if not performed previously.

(9) Permanent Dam Modification

(a) The Tennessee Valley Authority (TVA) will take actions to ensure the stability of the Tellico Dam. Watts Bar Dam, Watts Bar West Saddle Dike, Fort Loudoun Dam. Cherokee Dam. Douglas Dam. and the required Douglas Saddle Dams under nuclear probable maximum flood conditions, consistent with TVA's River Operations acceptance criteria. These actions shall be completed prior to implementing the revised hydrologic analysis for the WBN site, including changes to the hydraulic analysis methodology and updates to the TVA River Operations dam stability acceptance criteria by May. 31. 2015.

(b) TVA shall implement permanent modifications to prevent overtopping of the embankments of the Fort Loudoun Darn due to the Probable Maximum Flood by February 1, 2017.

Amendment No. 98

4b

D. The following exemptions are authorized by law, will not present an undue risk to the public health and safety, and are consistent with the common defense and security. Therefore. these exemptions are granted pursuant to 10 CFR 50. 12.

(1) Deleted

Amendment No 98



SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION

RELATED TO AMENDMENT NO. 98 TO FACILITY OPERATING LICENSE NO. NPF-90

1.0 INTRODUCTION

TENNESSEE VALLEY AUTHORITY

WATTS BAR NUCLEAR PLANT. UNIT 1

DOCKET NO. 50-390

By letter dated July 19, 2012 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML 122360173, Reference 8.1 ), as supplemented by the following letters dated:

• March 1, 2013 (ADAMS Accession No. ML 13067 A393) • April29, 2013 (ADAMS Accession No. ML 13126A101) • April 30, 2013 (ADAMS Accession No. ML 13126A295) • June 13, 2013 (ADAMS Accession No. ML 13168A410) • October 21, 2013 (ADAMS Accession No. ML 13296A025) • December 18, 2013 (ADAMS Accession No. ML 13357A721) • January 31, 2014 (ADAMS Accession No. ML 14036A322) • April2, 2014 (ADAMS Accession No. ML 14093A388) • September 30, 2014 (ADAMS Accession No. ML 14289A 1 06) • December 5, 2014 (ADAMS Accession No. ML 14344A394)

Tennessee Valley Authority (TVA, the licensee) submitted a License Amendment Request (LAR) for the Watts Bar Nuclear Plant, Unit 1 (WBN-1 ). These supplements provided additional information that clarified the application, did not expand the scope of the application as originally noticed, and did not change the staff's original proposed no significant hazards consideration determination as published in the Federal Register (FR) on November 13, 2012 (77 FR 67686).

In Reference 8.1, TVA stated that the probable maximum flood (PMF) for WBN-1 was elevation 738.1 feet (ft) at the time of Operating License issuance in 1996, and included assumptions based on the understanding of dam structural stability and capability during seismic and extreme flood events existing in the 1970s. In the 1980s and 1990s, TVA implemented a Dam Safety Program that resulted in dam safety modifications that increased dam structural stability and capability. TVA also stated that it had completed a hydrologic reanalysis to credit the results of the dam safety modifications from 1995 to 1998. This reanalysis resulted in lowering

Enclosure 2

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the WBN-1 calculated PMF to elevation 734.9 ft that became the licensing base for the PMF. It was discovered later that this reanalysis contained an error that caused this elevation to be underestimated. To correct the error and increase the PMF elevation at the WBN-1 site from elevation 734.9 ft to 738.9 ft, TVA submitted this LAR. In its application, TVA chose the 739.2 ft as the design basis floods (DBF) elevation for stillwater PMF, which provides an additional 0.3 ft safety margin.

This LAR seeks approval to revise the WBN-1 Updated Final Safety Analysis Report (UFSAR) to adopt this updated hydrologic analysis for the WBN-1 site. These changes to the WBN-1 UFSAR incorporate updates previously submitted in support of the initial licensing of WBN-1 as well as more recently developed input information. The amendment proposed adoption of a revised hydrologic analysis of the WBN-1 site, and resulted in changes to the flooding protection requirements for certain structures, systems, and components (SSCs) impacted by the revised analysis.

As part of the evaluation of this LAR, on April 23 and 24, 2014, the U.S. Nuclear Regulatory Commission (NRC or the Commission) staff performed an audit of the TVA dam stability calculations. The NRC staff used the Standard Review Plan (SRP, NUREG-0800) to perform its review of this LAR. As a result of the audit (Reference 8.27), the NRC staff transmitted a request for additional information (RAI) (Reference 8.4) for a technical basis to support the changes to UFSAR Section 2.4.3.4, "Probable Maximum Flood Flow," under the "Concrete Section Analysis." The NRC staff also requested that the technical basis for the proposed change include any analysis and calculations, or reference to industry standards, that support the UFSAR change, and that using a factor of safety (FS) greater than 1.0, for sliding, provides an adequate basis that dam structures are considered safe against failure. On May 21, 2014 (Reference 8.17), the NRC requested additional information related to a preliminary TVA response to the RAI provided in Reference 8.4. During subsequent discussions between TVA and the NRC staff, the NRC staff questioned actions taken by TVA to evaluate dam stability and, furthermore, indicated that the dams identified by TVA as requiring additional review (Boone, Cherokee, Fontana, Fort Patrick Henry, Melton Hill, and Tellico) warranted additional changes to the licensing basis. As such, the dams affected are being modified or analyzed to new design and licensing basis criteria that are consistent with those outlined in the SRP.

By letter dated September 30, 2014 (Reference 8.2), TVA submitted a supplement to the LAR to adopt a revised hydrologic analysis for the WBN-1 site. The changes to the LAR incorporated updates to the hydraulic analysis methodology, including the use of the U.S. Army Corps of Engineers (USACE) Hydrologic Modeling System (HEC-HMS) (Reference 8.1 0) and River Analysis System (HEC-RAS) (Reference 8.11) software, and updates for concrete and earthen dams to the TVA River Operations (TVA-RO, the TVA dam authority having jurisdiction) dam stability acceptance criteria.

The NRC staff conducted another multi-phase audit, including site visits between November 3 and December 17, 2014 (Reference 8.28), to validate information contained in TVA's supplement. On November 18, 2014 (Reference 8.18), the NRC staff forwarded an RAI based on the NRC staff audit and review of the LAR supplement (Reference 8.2). On December 5, 2014, TVA provided responses to the NRC staff RAI and proposed two license conditions (Reference 8.3).

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2.0 REGULATORY EVALUATION

TVA requested a change to the Facility Operating Licensee for WBN-1 in accordance with Title 10 of the Code of Federal Regulations (1 0 CFR) Section 50.90, "Application for amendment of license, construction permit, or early site permit," and 10 CFR 50.59, "Changes, tests and experiments." The proposal changes the UFSAR to adopt a revised hydrological analysis for the WBN-1 site. The NRC staff reviewed the proposed method of analysis in accordance with General Design Criterion (GDC) 2, "Design bases for protection against natural phenomena," of Appendix A, "General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50. GDC 2 states, in part, that, "Structures, systems, and components [SSCs] important to safety shall be designed to withstand the effects of natural phenomena such as earthquakes, tornadoes, hurricanes, floods, tsunami, and seiches without loss of capability to perform their safety functions." The criterion also specifies that the design bases for the SSCs important to safety shall reflect:

(1) Appropriate consideration of the most severe of the natural phenomena that have been historically reported for the site and surrounding area, with sufficient margin for the limited accuracy, quantity, and period of time in which the historical data have been accumulated;

(2) Appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena; and

(3) The importance of the safety functions to be performed.

In addition, the NRC staff used the regulatory positions of the following regulatory guides (RGs) for the identified acceptance criteria:

(1) RG 1.59, "Design Basis Floods for Nuclear Power Plants," Revision 2, describes the design basis floods (DBFs) that nuclear power plants should be designed to withstand in accordance with GDC 2. RG 1.59 guidance directs that a nuclear power plant must be capable of withstanding the DBF without loss of the capability to achieve and maintain cold shutdown. WBN-1 UFSAR Section 2.4 states:

The plant has been designed to have the capability for safe shutdown in floods up to the computed maximum water level, in accordance with regulatory position 2 of Regulatory Guide 1.59, Revision 2, August 1977.

Regulatory position 1 of RG 1.59 describes the flooding conditions to be evaluated in the development of the DBF. In addition, regulatory position 1 directs that all safety-related SSCs be designed to withstand the DBF. Regulatory position 2 allows an exception to providing protection for all safety-related SSCs, provided four criteria are met:

• Sufficient warning time must be available to shut down the plant and implement emergency procedures.

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• All safety-related SSCs must be capable of withstanding a less severe flood, referred to in the guidance as a standard project flood.

• The flooding analyses must consider reasonable combinations of less severe flood conditions for conservatism.

• Hardened protection must be provided for all SSCs necessary to achieve and maintain cold shutdown during the DBF.

Note that the existing DBF for WBN-1 was evaluated in conformance with RG 1.59, with the exception that WBN-1 is required to maintain hot shutdown with Reactor Coolant System temperature below 350 degrees Fahrenheit CF) rather than maintain cold shutdown, as described in the WBN-1 UFSAR Section 2.4.2.2 and 2.4.14.2.2.

(2) RG 1.1 02, "Flood Protection for Nuclear Power Plants," Revision 1, describes the design of flood protection measures that are acceptable to the NRC staff for safety-related SSCs. RG 1.102 is referenced by RG 1.59 in the definition of hardened protection. Where flood barriers (referred to as Incorporated Barriers within the RG 1.1 02) are used to provide protection, the design of these barriers must be sufficient to withstand the static and dynamic forces associated with the DBF and prevent in-leakage. RG 1.102 gives preference to barriers that are permanently installed and maintained in a closed position. However, the use of temporary barriers that must be installed prior to the onset of a flood may be acceptable in response to post-construction changes in the characteristics of the DBF.

3.0 TECHNICAL EVALUATION

3.1 Licensing Basis for Acceptance of the Updated Hydrological Analysis for WBN-1

3.1.1 Hydrologic Engineering Review Overview

TVA stated that the update of the hydrologic analysis for WBN-1 in this LAR includes, but is not limited to, changes as follows:

(1) Description of the current hydrosphere, (2) Use of more recent flood history information, (3) Inputs used for determining probable maximum precipitation (PMP), (4) PMF and DBF elevations at the plant site, (5) Runoff and stream course model, (6) Determination of seismically induced dam failure flood impacts at the

plant site, (7) Analysis for determining that adequate water is available for operation

of WBN-1 , and (8) Flooding protection requirements.

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TVA's updated analysis shows the stillwater PMF to be 738.9 ft, which is produced by the 7,980 mi2 storm computed by TVA's calibrated HEC-RAS model. This is 0.3 ft below the proposed stillwater DBF elevation. TVA decided not to change its stillwater DBF elevation of 739.2 ft, thus providing 0.3 ft of margin. Wind wave activity, including wind setup and wave runup, was estimated to generate wind-wave heights. The wind-wave runup and wind setup plus calculated PMF elevation for various locations of WBN-1 are shown in Table 1.

Table 1: Calculated PMF elevation plus wind-wave setup and wave run up heights

Location Calculated PMF Calculated PMF (Reference 8.2) plus wind setup

and wave runup Diesel Generator Building 738.9' 741.3' West Side of Intake Pumping 738.9' 741.1' Station Auxiliary and Control Buildings 738.9' 740.7'

3.1.1.1 NRC Staff Evaluation

The NRC staff has reviewed TVA's updated watershed hydrologic and river hydraulic models. The NRC staff found that the rainfall-runoff and HEC-RAS models were adequately set-up and calibrated with available large flood records. The models were applied to determine the PMF elevation at WBN-1. Since the models are commonly used in hydrological and hydraulic engineering design and analysis, NRC staff accepted the usage of the calibrated models to calculate the PMF. Based on the accepted models, the NRC staff finds the calculated stillwater PMF elevation of 738.9 ft acceptable, according to the adequate usage of the models and the acceptable calibration of the models. Therefore, the NRC staff concludes that the DBF elevation of 739.2 ft provides a 0.3 ft safety margin. Details of this PMF flood level evaluation are shown in the Section 3.1.3 to Section 3.1.15.1 of this evaluation.

3.1.2 Flood Design Considerations

TVA followed RG 1.59 to evaluate types of flood events to determine the worst potential flood at WBN-1. The evaluated flood events included (1) PMP and potential consequent dam failures, and (2) dam failures in a postulated Safe Shutdown Earthquake (SSE) or Operating Basis Earthquake (OBE) coinciding with RG 1.59 specified flood conditions.

In the application, TVA stated that the proposed DBF elevation is 739.2 ft. Using this proposed DBF elevation, TVA calculated wind wave setup and wave runup both outside and inside the buildings containing safe shutdown equipment shown in Table 2.

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Table 2: DBF PMF elevation plus wind-wave setup and wave runup heights

Building Level of DBF PMF- DBF PMF plus DBF PMF contains safe water still water wind setup plus wind shutdown entry into (Reference 8.2) and wave setup and equipment building+ run up wave runup

(Outside) (Inside) Diesel Generator 742.0' 739.2' 741.6' none Building West side of Intake 728.0' 739.2' 741.7' 741.7' Pumping Station Auxiliary and Control 729.0' 739.2' 741.7' 739.7'* Buildings Note: +Based on information on USFAR Sections 2.4.14.1.1 and 2.4.1.1. *TVA used 739.7' surge level inside of building to design permanent barrier height inside of the building.

Details of TVA's computed wind-wave heights is discussed in Section 3.1.6. Wave runup was estimated at the Diesel Generator Building to be 741.6 ft, or 0.4 ft below the operating floor. However, flood water will enter the Intake Pumping Station (IPS) at 728ft, as well as the Auxiliary and Control Buildings at 729 ft (Reference 8. 7). Safe shutdown equipment located below the expected DBF plus windwave effects in these buildings are protected by either permanent or temporary barriers. Details of TVA's flood protection measures are discussed in Section 3.2.


The NRC staff has conducted a confirmatory calculation of the additional height due to the wind effect on the PMF. The results of the NRC confirmatory calculation were less than the corresponding flood levels proposed by TVA (see Section 3.1.9.1 ). Thus, the TVA proposed flood levels are more conservative. The NRC staff also finds TVA's computed flood elevations at various WBN-1 site locations followed RG 1.59 and used acceptable methods to generate higher total elevations due to wave run up and wind setup heights (see Section 3.1.9.1 ). Thus, the NRC staff concludes that TVA's flood elevations are reasonable flood elevations. Furthermore, the NRC reviewed TVA's measures to protect safe shutdown equipment located in these buildings. Details of the staff evaluations are discussed in Section 3.2

3.1.3 PMF on Streams and Rivers

TVA followed RG 1.59, Appendix A (NRC 1977, Reference 8.6) and adopted the methodology as described in Hydrometeorological Report No. 41 (HMR 41) (Reference 8.20) to generate two PMP storms. The PMP storms were compared to generate the worst flood elevation at WBN-1. According to HMR 41, one is a 21 ,400 square mile (mi2) storm for the watershed above Chattanooga. Another is a 7,980 mi2 storm for the watershed above Chattanooga and below the five major tributary dams (Norris, Cherokee, Douglas, Fontana, and Hiwassee.) TVA

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determined that the storm of 7,980 mi2 produces the greatest PMF elevation at WBN-1. The 21,400 mi2 storm would produce slightly less PMF elevation.

According to TVA's current TVA-RO procedures, TVA has evaluated the stability of 18 critical dams at PMF headwater/tailwater conditions. These dams are Apalachia, Blue Ridge, Boone, Chatuge, Cherokee, Chickamauga, Douglas, Fontana, Fort Loudoun, Fort Patrick Henry, Hiwassee, Melton Hill, Norris, Nottely, South Holston, Tellico, Watauga, and Watts Bar. Among the 18 dams, TVA found Blue Ridge, Chatuge, Chickamauga, Fontana, Hiwassee, Norris, Nottely, South Holston, and Watauga would be stable during the PMF event. The following dams would be stable with corrective action: Cherokee, Douglas, Fort Loudoun, Tellico, and Watts Bar dams. Of the 18 dams evaluated, TVA also found the following dams would not withstand certain PMF scenarios, treated those dams as low margin dams, and assumed they would fail completely under those scenarios: Apalachia, Boone, Fort Patrick Henry, and Melton Hill Dams (Reference 8.2).

Other dams in the tributary system (Ocoee 1, Ocoee 2, Ocoee 3, Chilhowee, Calderwood, Cheoah, Mission, John Sevier, and Wilbur) were not evaluated and are postulated to fail completely during the event.

The failure of low margin dams is considered during two different PMP storms: the 7,980 mi2

storm and the 21,400 mi2 storm. TVA identified the 7,980 mi2 storm as the critical storm that caused the worst flooding condition at WBN-1. TVA evaluated the impact of both storms on dam failure. Among the low margin dams, Boone, Fort Patrick Henry, and Melton Hill Dams were postulated to fail during the 7,980 mi2 storm. Another group of low margin dams, including Boone, Fort Patrick Henry, and Appalachia Dams, were postulated to fail during the 21,400 mi2

storm. In both storms, the West Saddle Dike at Watts Bar Dam (crest elevation 752ft) would be overtopped and is postulated to fail. No other failures are postulated to occur except the non-evaluated dams in the tributary system as indicated above. Maximum discharge at WBN-1 would be 1,158,956 cubic feet per second (cfs) for the 7,980 mi2 storm. The resulting calculated PMF elevation at the plant would be 738.9 ft, excluding wind-wave effects. An additional 0.3 ft of margin is provided for a design basis PMF at elevation 739.2 ft.


To better understand the significance of dam stability on PMF elevation, during the dam safety audit of November 4, 2014, the NRC staff visited Douglas, Tellico, Fort Loudoun, and Watts Bar Dams, as well as the West Saddle Dike. These dams were being structurally strengthened or modified to prevent overtopping during the PMF. Also, through an audit on November 5, 2014, at the TVA office in Knoxville, Tennessee, the NRC staff confirmed that TVA followed TVA's current TVA-RO procedures to evaluate the dam stability. At that time, the NRC staff reviewed the computational results of the dam stability for several major dams, including Douglas, Fort Loudoun, and Watts Bar Dams.

In addition to reviewing dam stability, the NRC staff reviewed TVA's revisions to the hydrologic and hydraulic analysis for the watershed. The hydrologic and hydraulic analyses include recalculation of the PMP, excess rainfall depth, spatial rainfall distribution in the watershed, and precipitation loss and flood simulation. The NRC staff reviewed the LAR submittal provided by TVA (Reference 8.2) and conducted a multi-phase audit on a weekly basis through

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teleconferences, electronic portal reviews and webinars to facilitate the evaluation process for the revised hydrologic analysis. Also, the NRC staff evaluated runoff and stream course modeling, water level determination, and wind-wave effects on the PMF elevation. The details of those evaluations are discussed in the following sections.

The NRC staff further reviewed the supporting documents of hydrologic and hydraulic models in Enclosure 11 of Reference 8.2 to validate the dam failure cases as described by TVA were included in the HEC-RAS model. The NRC staff also verified that the 7,980 mi2 storm would create the maximum flood elevation at the WBN-1 with the dam failure cases. Based on the site field verification, the hydrology audit, confirmatory calculations, and reviews, the NRC staff considers the computed PMF elevation, 738.9 ft, to be reasonable and acceptable.

3.1.4 Probable Maximum Precipitation

TVA calculated PMP for the watershed above Chickamauga and Watts Bar Dams based on the method described in HMR 41. In this report, the PMP storm is a 9-day storm. During the 9 days, the antecedent storm occurs over the first 3 days, the next 3 days are a dry period, and then the PMP storm occurs on the last 3 days. The PMP calculations consider depth-areaduration characteristics, seasonal variations, and antecedent storm potentials, and incorporate orographic effects of the Tennessee Valley. Because there is relatively light snowfall in the watershed, snowmelt is not a factor in generating maximum floods for the Tennessee River at the site.

According to HMR 41, TVA identified two critical storms. One is a downstream-centered pattern of the 21,400 mi2 PMP, and another is a Bulls Gap centered pattern of 7980 mi2 PMP. The isohyetal pattern of 21 ,400 mi2 PMPs (Figure 2.4-6, Reference 8.1) would produce maximum rainfall on the middle portion of the watershed. The isohyetal pattern of 7,980 mi2

PMP (Figure 2.4.-7, Reference 8.1) would produce maximum rainfall on the upper part of the watershed. In the examination of seasonal variation, HMR 41 specifies the PMP that produces the PMF occurs in March. TVA determined that a 7980 mi2 pattern at Bulls Gap produces a maximum PMF elevation at WBN-1 using the HEC-RAS model. The PMP main storm would produce 16.17 inches of rainfall in 3 days. The antecedent storm produces 6.00 inches of rainfall.


The NRC staff conducted an independent confirmatory analysis for the review of TVA's 2012 LAR submittal (Reference 8.1 ). Time and spatial distribution of the total precipitation over the Tennessee River watershed upstream of WBN-1 were obtained from HMR 41 (Reference 8.20) for a March PMP storm. The NRC staff used geographical information system methods to compute the total area-weighted aggregate depths of precipitation for both the upstream- and downstream-centered 21,400 mi2 storm patterns and the moving 7,980 mi2 storm patterns. The analysis of the 7,980 mi2 storm pattern involved maximizing the PMP depth upstream of WBN-1 by moving the pattern along the primary axis of the Tennessee River watershed as provided for in HMR 41. In that confirmatory analysis, the NRC staff-computed PMP is similar to the TVA-computed 16.17 inches for the 7,980 mi2 storm. The NRC staff considers TVA's computation of the critical PMP to be reasonable and acceptable for use in computing the maximum stillwater PMF elevation at WBN-1.

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The NRC staff noted that the 6.0 inch precipitation depth calculated by TVA for the antecedent storm does not equal 40 percent of the PMP storm precipitation depth of 16.17 inches. For the antecedent precipitation period, the staff found that TVA computed a PMP depth of 14.95 inches over the 24,552 mi2 watershed area upstream of Guntersville Dam. For the PMP period, the NRC staff found that TVA computed a PMP depth of 16.17 inches over the 20,781 mi2

watershed upstream of Chickamauga Dam. This computational result meets HMR 41 requirements based on watershed-area weighted-average PMP. Thus, the NRC staff considers the antecedent precipitation depth of 6.0 inches to be acceptable.

3.1.5 Precipitation Losses

TVA computed precipitation excess using an approach called the antecedent precipitation index (API) method (Reference 8.24). The precipitation excess is equal to the precipitation depth minus precipitation losses. The API method is based on historical storm and flood data from gaged watersheds and considered the effects of weekly variation, runoff location, and antecedent precipitation on precipitation loss. The API method was developed originally by the National Weather service for use by TVA. TVA-ROuses the API method on a daily basis to operate their reservoir system. The computed precipitation excess for the PMP storm is not sensitive to the API because of the large antecedent storm. The precipitation excess is used to calculate the runoff hydrograph for the watershed based on TVA's FLDHYDRO computer code, which is a component of the Simulated Open Channel Hydraulics (SOCH) code. FLDHYDRO was developed by TVA to be used for computing excess rainfall and surface runoff hydrograph. Table 2.4-11 of Reference 8.2 provides computed excess precipitation depths for each sub-basin. The average precipitation loss for the watershed above Chickamauga Dam is 2.32 inches for the 3-day antecedent storm and 1.87 inches for the 3-day main storm. The losses are approximately 39 percent of antecedent rainfall and 12 percent of the PMP, respectively. The precipitation loss of 2.32 inches in the antecedent storm compares favorably with that of historical flood events shown in Table 2.4-12 of Reference 8.2.


The NRC staff reviewed the computations provided by TVA (Reference 8.3}, and the data showed that the API method could generate a conservative excess precipitation. The staff reviewed the computations in detail, including the API equation, API-Runoff Index charts, rainfall accumulation, and surface runoff.

The NRC staff found that TVA's API method of computing precipitation losses was developed according to gaged runoff, which is appropriate, given the size of the Tennessee River basin. The method integrates the effects of land use, land cover, and soil type. TVA considers the API method to be conservative by underestimating the precipitation loss as compared to Soil Conservation Service Runoff and Initial and Constant Methods.

The NRC staff used the data shown in Table 2.4-11 of Reference 8.2, and calculated each sub-basin's percentage of precipitation loss. The NRC staff found that the precipitation losses by sub-basin for the antecedent storm ranged from 26 percent to 57 percent, while TVA's watershed average was a 39-percent loss, which falls within the NRC staff-computed range. The precipitation loss calculated by the NRC staff for the main PMP storm is 11 percent on

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average precipitation loss upstream of Chickamauga Dam, which is in reasonable agreement with the 12 percent computed by TV A.

Based on the NRC staff's review of API detail computations and TVA's conservative excess precipitation, which is shown in the Reference 8.3, and TVA's use of daily API information to operate the Tennessee River System, as well as the method being appropriate for the size of sub-watershed with gaged runoff, the NRC staff considers TVA's computation of the precipitation losses to be reasonable and acceptable for use in computing maximum PMF elevations at WBN-1.

3.1.6 Runoff and Stream Course Model

In Reference 8.2, TVA computed runoff from 40 sub-watershed areas and includes the total watershed above Chickamauga Dam. The precipitation was transformed to runoff using TVA's FLDHYDRO computer code using the unit hydrographs. The unit hydrographs were developed using observed discharge data records and the methodology as described in the American Society of Civil Engineers (ASCE) technical paper presented by Newton and Vineyard (Reference 8.19). Also, the developed unit hydrographs were validated with other storm records and stream discharges. For non-gaged unit areas where a stream gage is not available, unit hydrographs were developed from unit hydrographs of similar watersheds relating the unit hydrograph peak flow to the drainage area size, time to peak in terms of watershed slope and length, and the shape to the unit hydrograph peak discharge in cubic feet per second (cfs) per mt For example, some unit hydrograph plots are provided from Reference 8.2

The surface runoff from the sub-watershed outlet flows through the stream channel to the reservoir upstream boundary. TRBROUTE was a computer code originally developed by TVA for computing flow routing in a stream channel. TVA converted the TRBROUTE code into computational spreadsheets. The output from the spreadsheet is the channel flow hydrograph at a reservoir upstream boundary. TVA adopted the HEC-RAS model to simulate the flow from upstream reservoirs through the Tennessee River System, including dams, locks, and dikes, to the downstream limit at Wilson Dam. The HEC-RAS model river schematic is shown in Figure 2.4-1 a in Reference 8.2.

The HEC-RAS model performs one-dimensional steady and unsteady flow calculations. TVA's validated inputs to the HEC-RAS model included the main river downstream through Wilson Dam and tributaries that enter the main stream from the upstream watershed. TVA's HEC-RAS model development included checking stream geometry, evaluating stream cross-section layout, adjusting distance among cross-sections, and verifying reservoir and stream channel storage volumes. The HEC-RAS model was calibrated through stream segments based on observed 1973 and 2003 floods. The upstream inflows from sub-watersheds are inputs to HEC-RAS as upstream boundary conditions, or as lateral flow that are distributed along the main stream. The reservoir operation rules and dam failure rules are set as flow controls using scripts entered into the HEC-RAS model. The downstream boundary condition is set at Wilson Dam according to the tailwater elevation.

The upstream dams above WBN-1 provide large flood storage and attenuation of peak flow. The initial conditions specified in the HEC-RAS model at the beginning of the simulation of the antecedent event are set at the median pool level for March. A summary of the maximum

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discharge at each dam for the WBN-1 PMF is computed by the HEC-RAS model and is shown in Table 2.4-16 in Reference 8.2.

Discharge rating curves at dams and dikes were determined by headwater elevation, tailwater elevation, and spillway or outlet configurations. Discharges over other components, such as non-overflow sections, navigation locks, saddle dike, and rim leaks were also included in the discharge rating curve. In addition to the discharge rating curves at the dams, reservoir operation rules were incorporated. When the maximum discharge exceeds the operation rules or the operating deck is inundated, the discharge rating curves at the dams are applied. A typical discharge rating curve, as an example, is provided on Figure 2.4-11 of Reference 8.2 for the Watts Bar Dam.

Upstream of WBN-1, TVA has installed temporary flood barriers at Fort Loudoun Reservoir to increase the height of embankments to prevent the PMF from overtopping the dam. The increased embankment height provides additional headwater level. This additional headwater level was included in the discharge rating curves for this dam. Also, permanent flood walls were recently installed on the embankments of Watts Bar, Tellico, and Cherokee Dams. Increasing the height of the embankments at this dam prevents embankment overflow and failure of the embankment for the PMF event.

The discharge rating curve for Chickamauga Dam is for the current lock configuration with all 18 spillway bays available. Reservoir rim leaks were added as additional discharge components to the Watts Bar Dam discharge rating curve. Three of the rim leak locations discharge to Yellow Creek, entering the Tennessee River 3 miles (mi) downstream of Watts Bar Dam. The remaining four rim leak locations discharge to Watts Creek, which enters Chickamauga Reservoir just below Watts Bar Dam.


The NRC staff found that TVA used the methodology presented by Newton and Vineyard (Reference 8.19) to develop unit hydrographs for each sub-watershed. The methodology was one of the recommendations in 5.4.1.1 Unit Hydrographs of American Nuclear Society (ANS) N170-1976/ANS 2.8, which was referenced by RG 1.59. During the weekly audit in November 2014, the NRC staff also confirmed that the correct procedures were used to develop TV A's unit hydrographs.

For a confirmatory check of TVA's unit hydrographs, NRC staff performed independent computations utilizing Snyder's unit hydrograph method, which is based on physical watershed characteristics and is commonly used by the hydrology community. The NRC staff noted that a few of TV A's unit hydrographs have multiple peaks (Figure 2.4-10, Sheets 2 and 6 of Reference 8.2). The shapes of the hydrographs between Snyder and TVA were found to be similar except for the few which had multiple peaks. The NRC staff confirmed that the multiple peaks were due to branch flows converging into the outlet of the specific sub-watershed. In general, the comparison of the peak runoffs of the unit hydrographs showed that on average, TVA's peak flows are higher than the flows computed using the Snyder unit hydrographs. The hydrographs computed by TVA have shorter times to peak than the NRC staff's computed Snyder unit hydrographs. The shorter peak time and higher peak flows computed by TVA can create more severe flooding conditions.

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Further, the NRC staff selected some of TVA's unit hydrographs for technical review to verify that the peak runoffs of unit hydrographs through rainfall-runoff computations could generate comparable peak flows at gage stations. TVA provided rainfall-runoff computational data and results during the weekly hydrology audit for NRC staff review. The NRC staff confirmed that TVA's unit hydrographs that generated the peak flows were larger than, or only slightly less than, the observed peak flows at various gage stations. Based on reviewing the methodology and procedure used by TVA to develop the unit hydrographs, as well as the peak times and peak runoffs of the hydrographs, the NRC staff concluded that TVA's unit hydrographs were conservative and acceptable.

The NRC staff reviewed TVA's application of HEC-RAS model, which is an industry standard model. The review included the following model components: stream cross-section data, model calibration, hydraulic parameters, discharge rating curves, flood operation guides, inflows to reservoirs, unsteady flow rules, reservoir boundary conditions, and flow initial conditions.

The NRC staff reviewed the procedures that TVA used to establish the cross-sections. The NRC staff found the geometry of flow cross-sections in the reservoirs to be properly defined. Since TVA included the procedures of verifying reach storage volumes with reservoir records and GIS-computed storage-volume curves, and verifying effective flow areas with United States Geological Survey (USGS) maps (Reference 8.12) to define the flow cross-sections, the NRC staff considered the stream geometry implemented in the HEC-RAS model as being adequate and acceptable.

The NRC staff reviewed the HEC-RAS model calibration of two stream segments in the Tennessee River. One segment is the reservoir between Watts Bar and Fort Loudoun Dams. Another one is the reservoir upstream of Fort Loudoun/Tellico Dam. For the calibration, the NRC staff examined TVA's computation time step, Manning's roughness (energy loss coefficient), and downstream boundary condition of both stream segments.

The NRC staff evaluated TVA's 5-minute computational time step. The NRC staff executed TVA's model at a 1-minute time step and found the difference in computed flood elevations to be 0.01 ft. Thus, the NRC staff considers a 5-minute time step acceptable for use in calibrating the historical floods of 1973 and 2003.

For TVA's calibrated Manning's roughness, the NRC staff considered the calibrated roughness acceptable, since the roughness was within the common limits as defined by the HEC-RAS reference manual. Further, the NRC staff evaluated the bias of the calibration by examining the sensitivity of Manning's roughness on HEC-RAS model. The NRC staff found that the bias with TVA's calibrated model in the Watts Bar Reservoir is plus(+) 0.1 ft for the 1973 and 2003 floods. The NRC staff then reduced the Manning's roughness in Watts Bar Reservoir by 0.002 and performed computations for the 1973 and 2003 floods (see Section 3.1. 7.1 for PMF sensitivity). The bias computed by the NRC staff's sensitivity test was larger than found from the original TVA calibrated model. Because TVA's smaller bias is preferable, the NRC staff considers that the Manning's roughness used by TVA is reasonable.

Regarding the downstream boundary condition, the NRC staff found that using the observed discharge as the downstream boundary condition could create bias in upstream flood elevations

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for the 1973 flood but not for the 2003 flood. TV A had previously investigated the storage volume based on 1973 discharge data and suspected the inaccuracy of the 1973 discharge record at the downstream dam (Reference 8.3). Consequently, the NRC staff considers using observed stage data as the downstream boundary condition to be more appropriate than using observed discharge data.

Based on the NRC staff's review of computational time step, Manning's roughness, and the downstream boundary condition, the NRC staff considers the model as being appropriately calibrated. The NRC staff further accepted that TVA's model calibration could ensure reasonable replication of observed river discharges and elevations for known historic events, including the 1973 and 2003 floods.

Also, the NRC staff reviewed the dam rating curves and dam operating rules embedded in the HEC-RAS model. The rules implement the discharge rating curves and flood operations guides that have previously been developed by TVA and TVA-RO. To verify that TVA included the tailwater effect on the discharge at the dam, the NRC staff increased the tailwater elevations at Watts Bar Dam to run the HEC-RAS model and examined the computational results. As expected, the NRC staff found a corresponding decrease in discharge and an increase in headwater elevations with an increase in tailwater elevations. For TVA's reservoir operation rules, which were included in the HEC-RAS model input, the NRC staff found that the computed discharge was comparable to TVA's rating curves. Therefore, the NRC staff considered that the rating curves and the operation rules were properly incorporated into the HEC-RAS model.

Based on the above reviews and analyses, the NRC staff concludes that the use of rainfallrunoff model and the HEC-RAS model is adequate for these PMF computations.

3.1. 7 Probable Maximum Flood Flow

TVA added the components of dam failure, embankment breaches, and watershed rim leaks in the calibrated HEC-RAS model.

For dam failures and embankment breaches, there are configuration parameters used for failure timing or failure elevation in the unsteady flow rules. The configuration parameters are for specific simulations by HEC-RAS. Some dam failure timing and elevations were defined by TVA through multiple iterations of the model, such as the simulation of Watts Bar Dam West Saddle Dike failure.

The rim leak at Fort Loudoun Reservoir is located north of the Marina Saddle Dike. The leak discharges into the Tennessee River at Tennessee River Mile (TRM) 602.3 and was added to the Fort Loudoun Dam discharge rating curve. The seven rim leaks at Watts Bar Reservoir were added to the Watts Bar Dam discharge rating curve. Of the seven leaks, three rim leaks discharge to Yellow Creek and then enter the Tennessee River 3 mi downstream of Watts Bar Dam. The remaining four rim leaks discharge to Watts Creek, which enters Chickamauga Reservoir just downstream of the Watts Bar Dam.

TVA computed the PMF discharge at WBN-1 to be 1,158,956 cfs, which includes the discharges from the rim leaks, the Watts Bar Dam West Saddle Dike, and the effects of upstream dam

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failure. This discharge would result from the 7,980 mi2 storm in March with a Bulls Gap centered storm pattern (Reference 8.2, Figure 2.4-7).

The PMF discharge hydrograph at WBN-1 provided by TVA is shown in Reference 8.2, Figure 2.4-23. During the PMF event, the flow would overtop the Watts Bar Dam West Saddle Dike, which is approximately 2 mi upstream from Watts Bar Dam. The overtopped Watts Bar Dam West Saddle Dike is postulated to fail at the time of maximum head water elevation for Watts Bar Dam. The discharge from the failed Watts Bar Dam West Saddle Dike flows into Yellow Creek and joins the Tennessee River at mile 526.82, 1.18 mi downstream of WBN-1. The location of WBN-1 is at TRM 528. The computed PMF showed that Chickamauga Dam at TRM 471 downstream would be overtopped. TVA considered that the dam was postulated to remain without failure.

TVA addressed the impact of the PMF on dam concrete section, embankment structures, and spillway gates as follows.

Concrete Section Analysis

For concrete dam sections, structure stability was analyzed for the static loadings of maximum headwater and corresponding tailwater levels that would occur in the PMF as described in Section 2.4.3 of Reference 8.2. The force and moment equilibrium must be satisfied without exceeding the limits of concrete, concrete-rock interface, and foundation strength. The tensile strength of the concrete-rock interface is assumed to be zero. Theoretical dam base cracking is allowed, provided that the crack stabilizes, the resultant of all forces remains within the base of the dam, and the required sliding FS is obtained. The acceptable factors of safety for sliding are 1.3 where cohesion is not considered, and 2.0 where cohesion is considered. When the concrete dams were evaluated by TVA and they were outside of these acceptance criteria, dam failure was then postulated within the HEC-RAS model. The dams evaluated to fail during a PMF event are Fort Patrick Henry Dam (total failure in both storms), Boone Dam (total failure in both storms), Melton Hill Dam (total failure only in 7,980 mi2 storm) and Appalachia Dam (total failure only in 21 ,400 mi2 storm).

TVA did not evaluate nine dams in the tributaries and postulated them to fail completely during the PMF event. Those nine dams are Ococee 1, Ocoee 2, Ocoee 3, Chilhowee, Calderwood, Cheoah, Mission, John Sevier, and Wilbur Dams.

To prevent their failure during the PMF, TVA committed to strengthen the following dam components: Watts Bar Dam east flood wall, Watts Bar Dam neck of the non-overflow section, Tellico Dam neck of the non-overflow section, Fort Loudoun Dam non-overflow section, Cherokee non-overflow section, and Douglas non-overflow section. TVA proposed the following license condition in Reference 8.3, Enclosure 3:

(a) TVA will take action to ensure the stability of the Tellico, Watts Bar, Watts Bar West Saddle Dike, Fort Loudoun, Cherokee, Douglas Dam, and Douglas Saddle Dams under nuclear PMF conditions, consistent with TVA-RO's acceptance criteria. Therefore, actions shall be completed prior to implementing the revised hydrologic analysis for WBN-1, including changes to the hydraulic analysis methodology and upgrades to meet the TVA RO dam stability acceptance criteria by May 31,2015.

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The NRC staff reviewed TVA's proposal and found it acceptable, as the permanent modifications will be completed earlier than the previous committed date of October 31, 2015.

Embankment Structures

For embankment dam sections, slope stability was analyzed by TV A for the static loadings of maximum headwater and corresponding tailwater levels that would occur in the PMF as described in Section 2.4.3 of Reference 8.2. TVA used conventional methods to investigate the equilibrium of a soil mass in the slope tending to rupture and slide downslope under the influence of gravity. TVA compared forces, moments, or stresses tending to cause instability of the mass and those that resist instability. TVA stated that the acceptable FS for slope stability is 1.4 using the TVA-RO's criteria. TVA also stated that embankment modifications are required to meet this safety factor for slope stability. TVA stated that the following embankment structures would not fail during the PMF event: Watts Bar Dam east embankment, Douglas Saddle Dams, Cherokee Dam embankments, Fort Loudoun Dam embankments, and Tellico Dam embankments.

TVA is in the process of modifying Watts Bar Dam West Saddle Dike embankment and reduce the crest elevation by 5 ft to 752 ft, so that the Watts Bar Dam West Saddle Dike would be overtopped and fail during the PMF event.

Spillway Gates

According to TVA, during peak PMF conditions, the radial spillway gates of Fort Loudoun and Watts Bar Dams may be wide open with flow over the gates and under the gates. Under this control condition, both the static and dynamic load stresses in the main structural members of the Watts Bar Dam spillway gate are determined to be less than the yield stress, and the stress in the trunnion pin is less than the allowable design stress. The open radial spillway gates at other dams upstream of Watts Bar Dam were determined to not fail by comparison to the Watts Bar Dam spillway gate analysis.

3.1. 7.1 NRC Staff Evaluation

The NRC staff examined the unsteady flow rules and dam discharge rating curve embedded in the model. The rules relate the dam failure timing and headwater level. The NRC staff compared the discharge rating curves between failure and non-failure conditions from HEC-RAS outputs to verify the dam breach outflow. The failure timing and water head level were also examined. The NRC staff found the unsteady flow rules and discharge rating curves were adequately set-up and acceptable to compute the breach outflow.

The NRC staff noted that TVA applied a linear interpolation to compute the discharge and PMF elevations at WBN-1. The HEC-RAS model reports results at cross-section stations 527.8 TRM and 529.89 TRM, whereas WBN-1 is at 528 TRM. The NRC staff noted that the discharge at 527.8 TRM is 0.4 percent larger than reported by TVA at WBN-1. The NRC staff attributes this increase to lateral inflows from local PMP runoff.

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The NRC staff reviewed the HEC-RAS model for the postulated breach and associated flow at the Watts Bar Dam West Saddle Dike caused by overtopping. TVA proposed to reduce the crest elevation of the West Saddle Dike to 752 ft to allow relief and bypass the PMF flows behind Watts Bar Dam. The rating curves were set in the model to simulate the overtopping and breach flows of the Watts Bar Dam West Saddle Dike. The TVA HEC-RAS model is set up to directly discharge the breach flows into the Tennessee River immediately downstream of WBN-1 without peak flow attenuation. To determine if the breach outflow impacts WBN-1 as it enters the Tennessee River, the NRC staff created a steady flow model to simulate the breach outflow and routing through Yellow Creek. The NRC staff's steady flow simulation indicated the breach outflow is expected to have no impact on WBN-1. Also, the NRC staff noted that the flows in Yellow Creek will be constricted as Yellow Creek passes through a gap in the ridge before reaching WBN-1. Therefore, the NRC staff recognizes that the ridge will reduce the impact of breach flow on WBN-1. Based on the staff's steady flow simulation and the constriction of flow at the gap, the NRC staff considers TVA's modeling without peak flow attenuation in Yellow Creek due to the flow constriction at the gap is acceptable.

The NRC staff reviewed the structural analysis of spillway gates during the PMF, and found that the spillway gates of Fort Loudoun and Watts Bar Dams would be fully open to discharge flows. Therefore, under this condition, these gates would not resist the full hydrostatic force and thus would not fail, because most of the PMF discharges would pass under the gates, and the structural members of the gates are capable of withstanding the PMF discharge without failure. The NRC staff further confirmed in the site audit that opening the gates during the PMF event is consistent with TV A-RO's procedures.

The NRC staff examined the discharge rating curves and flood operations guides as input to HEC-RAS rules for Watts Bar and Fort Loudoun Dams. The examination consisted of a line-by-line review of the rules, as well as comparing the stage-discharge rating curves computed by the NRC staff and the stage-discharge curves specified by TVA. From the examination of the HEC-RAS rules of the discharge rating curves and flood operations guides, the NRC staff verified that during the recession of the PMF flood, the water levels follow the discharge rating curves without application of the flood operations guides, indicating that spillway gates are not operational.

During the confirmatory audit from November 4 through 7, 2014, at the TVA Knoxville office, the NRC staff determined that TVA provided an adequate technical basis to support the proposed changes to WBN-1 UFSAR Section 2.4.3.4, "Probable Maximum Flood Flow," under the "Concrete Section Analysis" heading. This section currently reads as follows:

For concrete Dam sections, comparisons were made between the original design headwater and tailwater levels and those that would prevail in the PMF. If the overturning moment and horizontal forces were not increased by more than 20 percent, the structures were considered safe against failure. All upstream Dams passed this test except Douglas, Fort Loudoun, and Watts Bar. Original designs showed the spillway sections of these Dams to be most vulnerable. These spillway sections were examined in further detail and judged to be stable.

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TVA proposed to change the UFSAR as follows:

For concrete Dam sections ... The force and moment equilibrium must be maintained without exceeding the limits of concrete, concrete-rock interface and foundation strength. The tensile strength of the concrete-rock interface is assumed to be zero. Theoretical base cracking is allowed provided the crack stabilizes; the resultant of all forces remains within the base of the dam, and adequate sliding factor of safety is obtained. The acceptable factors of safety for sliding are 1.3, where cohesion is not considered, and 2.0, where cohesion is considered.

The NRC staff found the safety factors to be acceptable, because the proposed changes are consistent with the current dam stability criteria adopted by TVA-RO and are based on guidelines published by the Federal Energy Regulatory Commission (FERC).

Based on the NRC staff's review, TVA's methods for computing PMF discharge and the modeling results are found to be reasonable and acceptable. The NRC staff also found the factors of safety for sliding are 1.3 where cohesion is not considered, and 2.0 where cohesion is considered are acceptable. These TVA proposed changes are consistent with the current dam stability criteria adopted by TVA-RO and are based on guidelines published by FERC.

The NRC staff noted that the ongoing modifications of dams and embankments performed in support of WBN-1 license amendment are credited to support the PMF analysis assumptions for the following embankment structures: Watts Bar Dam east embankment, Douglas Saddle Dike, Cherokee Dam embankments, Fort Loudoun Dam embankments, and Tellico Dam embankments. The crest of the Watts Bar Dam West Saddle Dike will be reduced to the elevation of 752 ft. Since all modifications to the embankments are not expected to be completed by the time this safety evaluation (SE) is issued, TVA proposed a license condition to complete of the embankment modifications by the implementation date of of this LAR on May 31,2015.

Based on the NRC staff's above evaluations, comparisons, and confirmations of TVA's HEC-RAS modeling results, the NRC staff concludes TVA's methods for computing PMF discharge and the modeling results as well as proposed license condition to be reasonable and acceptable.

3.1.8 Water Level Determinations

TVA determined that the maximum stillwater PMF elevation at WBN-1 was 738.9 ft, which is produced by the 7,980 mi2 storm. This is 0.3 ft below the current stillwater DBF elevation. TVA decided not to change its stillwater DBF elevation of 739.2 ft, thus providing 0.3 ft of margin. The 738.9 ft of PMF elevation at WBN-1 was computed by TVA's calibrated HEC-RAS model. The computed PMF discharge hydrographs correspond to the computed PMF elevation hydrograph provided in Reference 8.2, Figure 2.4-23.

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TVA's model calculated the PMF elevation to be 738.9 ft, which provides 0.3 ft of margin to the proposed DBF elevation. The NRC staff examined whether the PMF elevation was sensitive to Manning's roughness or computational time step. The NRC staff notes that there is a difference in the time step used for the PMF simulation versus the calibration simulations. The PMF simulation uses a 1-minute time step, whereas the calibration simulations used a 5-minute time step. In Section 3.1.6, the NRC staff examined the effect of these two time step steps on water surface elevation (WSE) and found a very small difference (0.01 ft). The NRC staff accepted the use of 5 minutes for calibration and found a reduction to 1 minute would not affect the PMF result.

For calibration, the NRC staff found that a test with the Manning's roughness produced greater bias than computed in TVA's calibration results. Manning's roughness represents a friction coefficient used for computing flow energy loss in the HEC-RAS model. The roughness is used to calculate flow energy loss due to the friction on stream bed or flood plain. In general, larger roughness may cause higher flood elevations and lower flow rates. The typical range of values of Manning's roughness for open channel flow used in hydraulic engineering is from 0.02 to 0.05. The Manning's roughness coefficients used in the TVA calibrated HEC-RAS model ranged from 0.020 to 0.046 in the reservoirs upstream of Chickamauga Dam, which is within the typical range. The NRC staff found that the calibrated Manning's roughness coefficients used in TV A's HEC-RAS model sirnulation of the PMF, which were developed from the 1973 and 2003 flood calibrations, are appropriate.

The NRC staff examined the effect of TVA's computational time step used in the HEC-RAS model on PMF elevation by examining the following time steps: 1 minute, 30 seconds, 15 seconds, and 5 seconds. The NRC staff found the time steps of 30 seconds and 15 seconds to be unstable. The NRC staff compared the flood elevations computed for the 1-minute and 5-second time steps and found the difference was 0.01 ft. The NRC staff confirmed that TVA's use of a 1-minute time step is appropriate.

Based on the NRC staff's review and evaluation of Manning's roughness coefficient and computational time step, along with previous evaluations shown in Section 3.1.5.1, the NRC staff considers TVA's HEC-RAS model for computing the PMF elevation to be reasonable and acceptable.

3.1. 9 Coincident Wind-Wave Activity

To estimate coincident wind waves, TVA used 2-year wind speeds (a wind speed with a 50-percent chance of exceedance in each year) for March, the month in which the PMF is postulated to occur. TVA determined maximum March winds from a statistical analysis of observed winds at Chattanooga, Tennessee. TVA estimated a 2-year, 30-minute wind speed of 21 mi per hour (mph) from the southwest and adjusted the speed based on effective fetch for over water conditions. The effective fetch is the distance over which wind blows in constant duration and speed. TVA estimated an effective fetch of 1.1 mi for the Diesel Generator Building, 1.3 mi for the IPS, and 0.8 mi for the Auxiliary, Control, and Shield Buildings. TVA estimated adjusted wind speeds of 23.8 mph for the Diesel Generator Building, 24.2 mph for the IPS, and 23.4 mph for the Auxiliary, Control, and Shield Buildings.

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TVA used the wind-wave estimation procedure described by USACE, 1966 (Reference 8.8). TVA-estimated wind-wave activity at various locations at WBN-1 is shown in Table 3. As described in Section 3.1.8, TVA calculated the maximum stillwater PMF elevation at WBN-1 to be 738.9 ft. Therefore, the maximum WSEs accounting for wind-wave activity, including wind setup, were estimated to be 7 41.3 ft at the Diesel Generator Building, 7 41.1 ft, at the west face of the IPS,1 and 740.7 ft for the Auxiliary, Control, and Shield Buildings. The effects of these levels on SSC are discussed in Section 3.2.

Table 3: TVA-estimated wind-wave activity at WBN-1

Location Wind Setup Wave Runup Total PMF

(ft) (ft) Calculated (ft) Diesel Generator

0.1 2.3 741.3

Building Intake Pumping Station

0.1 2.4- 3.4* (IPS)

1West Face of Intake 0.1 2.1

741.1 Pumping Station

Auxiliary, Control, and 0.1 1.7 740.7

Shield Buildings


To independently estimate the coincident wind-wave activity, the NRC staff followed the methodology described in Reference 8.9. The NRC staff selected the location of specific safetyrelated SSCs and onsite grading to define runup slopes to represent the worst condition. The NRC staff performed a single, site-wide, wind-wave activity estimation using the longest straight-length fetch. Because other locations at WBN-1 would be exposed to shorter fetches, the NRC staff's wind-wave activity estimates are conservatively applied to all safety-related SSCs. The NRC staff estimated the fetch length as the longest straight-line overwater distance from the site to dry land. The NRC staff's estimate of the fetch length is 4.5 mi. The calculations for wind-wave activity were performed using the Coastal Engineering Manual (CEM) 2.01 Professional Edition software (Reference 8.13). The NRC staff used a concurrent 2-yr overland wind speed of 50 mph based on guidance in American National Standards Institute (ANSI)/ANS-2.8-1992 (ANS 1992). The NRC staff estimated the correction factor for transition from land to water as 0.9 (Figure 11-2-7 of Reference 8.14), but conservatively chose the overland wind speed as the overwater wind speed. The adjusted wind speed was estimated to be 49 mph using CEM guidance under fetch-limited conditions. The NRC staff used topographic and bathymetric data to determine an average water depth of 42.4 ft, along the

1 Note that the maximum PMF elevation including wind-wave effects on the west face of the IPS of 7 41.1 ft is obtained by adding TV A's wind setup of 0.1 ft and wave run up of 2.1 ft to the stillwater PMF elevation of 738.9 ft.

*The wave runup on the east and south faces of the IPS was 2.4 ft. The wave run up on the north face of the IPS was 3.4 ft. The licensee discounted these wave runup heights because there are no plausible entrances on the east, north, and south faces.

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fetch. Using the average depth and adjusted wind speed, the wind setup was calculated using guidance in Reference 8.9 to be 0.2 ft, which was larger than TVA's 0.1 ft as shown in Table 3.

The NRC staff estimated the wave runup using the methods described in Reference 8.9. Using this method, the wave runup was calculated to be 0.8 ft, which was less than TVA's wave runups as shown in Table 3. The NRC staff estimated a combined wind setup plus wave run up of 1.0 ft. Although the NRC staff's computed 0.2 ft for wind setup is higher than TVA's computed 0.1 ft, the NRC staff's computed combined wind setup and wave runup are lower than TVA's computed totals.

In all comparisons of wind-wave heights (Table 3), the NRC staff's computed 1.0 ft wind setup, plus wave runup, are lower than TVA's computational results. The NRC staff concluded that TVA's computational results are acceptable, because they are conservatively estimated by TVA when compared to the NRC staff's 1.0 ft.

3.1.1 0 Potential Dam Failures. Seismically Induced

3.1.1 0.1 Dam Failure Permutations

TVA followed guidance found in RG 1.59, Appendix A, and ANSI/ANS 2.8 (Revised ANSI N170-1976) to evaluate potential flood levels from seismically induced dam failures. Two scenarios were considered:

(1) SSE coincident with the 25-year flood peak and a 2-year wind speed applied in the critical direction, and

(2) OBE coincident with the peak of the one-half PMF and a 2-year wind speed applied in the critical direction.

TVA did not perform any hydrologic analysis for a single dam failure scenario, since the more critical (i.e., highest water level) scenario for WBN-1 involves the simultaneous failure of multiple dams. TVA performed evaluations for five separate scenarios for simultaneous seismic failure, (1) failure of Fontana and Tellico Dams simultaneously in OBE, coincident with one-half PMF; (2) failure of Fontana, Tellico, Hiwassee, Apalachia, and Blue Ridge Dams simultaneously in OBE, coincident with one-half PMF; (3) simultaneous failure of Norris and Tellico Dams in OBE, coincident with one-half PMF; (4) failure of Cherokee, Douglas, and Tellico Dams simultaneously in OBE, coincident with one-half PMF; and (5) simultaneous failure of Norris, Cherokee, Douglas, and Tellico Dams due to the SSE coincident with the 25-year flood. The original analyses did not include the failure of Tellico Dam, but the LAR includes the Tellico Dam in all five of the previously mentioned scenarios due to inconclusive seismic stability analyses of the Tellico Dam.

The resulting flood elevations from all five multiple dam failure scenarios were less than the PMF stillwater elevation of 738.9 ft, as discussed in Section 3.1.3.of this SE.

In En.closure 1 of Reference 8.2, TVA stated that it has evaluated the stability of 18 critical dams at PMF headwater/tailwater conditions. These dams are Apalachia, Blue Ridge, Boone, Chatuge, Cherokee, Chickamauga, Douglas, Fontana, Fort Loudoun, Fort Patrick Henry,

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Hiwassee, Melton Hill, Norris, Nottely, South Holston, Tellico, Watauga, and Watts Bar. Other dams in the tributary system (Ocoee 1, Ocoee 2, Ocoee 3, Chilhowee, Calderwood, Cheoah, Mission, John Sevier, and Wilbur) were not evaluated and are postulated to fail during the event.

Boone, Fort Patrick Henry, Melton Hill, and Apalachia Dams are low margin dams that are postulated to fail for computing PMF. In both 21,400 mi2 and 7,980 mi2 storms, the West Saddle Dike at Watts Bar Dam (crest elevation 752ft) would be overtopped and is postulated to fail. No other dam failure would occur. Maximum discharge at the plant is calculated to be 1,158,956 cfs for the 7,980 mi2 storm. The resulting calculated PMF elevation at the plant is 738.9 ft, excluding wind-wave effects. An additional 0.3 ft of margin is provided for a design basis PMF at elevation 739.2 ft.

In Reference 8.25, the NRC staff asked TVA to provide a description of which stability analysis for the Cherokee and Douglas Dams will be the analysis of record (AOR) if the proposed LAR noted by Reference 8.1 is approved and provides any additional details regarding the stability assumptions for these dams based on the information provided to the NRC in Reference 8.4.

In Reference 8.5, TVA stated that the stability analysis for the Cherokee and Douglas Dams described in Reference 8.5 will remain the AOR for WBN-1. As discussed in Reference 8.4, the results of the analysis completed using current TVA-RO industry standards do not invalidate the WBN-1 Dam stability A OR. TV A also stated that TV A has procedural controls in place that ensure that hydrological-related issues are identified and managed, including the impact of such issues on various aspects of the nuclear plant's current licensing basis.

In Section 2.4.4.1 of the 2012 LAR submittal (Reference 8.1 ), TVA revised the safety factor from 1.52 to 1.0 for the embankment of Watts Bar Dam under an OBE combined with one-half PMF. In Reference 8.2, TVA changed the safety factor of greater than 1.0 back to 1.52 as the same safety factor that WBN-1 was originally licensed.

In Reference 8.18, the NRC staff requested that TVA update the computations according to the OBE concurrent with one-half PMF condition and provide updated slope failure analysis for Watts Bar Dam embankment to the NRC staff for review.

In Reference 8.3, TVA stated that it recently completed simplified analyses on the current embankment configuration with the revised headwater and tailwater elevations. These calculations were completed using a different methodology than the licensing basis, but are used for a more quantitative demonstration of the FS, rather than the qualitative assessment that TVA performed to support the 2012 LAR submittal. TVA also stated that the lowest FS determined from these simplified studies was 1.22; therefore, demonstrating the FS for the Watts Bar Dam is greater than the acceptance (FS=1.0) from TVA-RO's for loading during the earthquake. Therefore, Watts Bar Dam is considered stable in the OBE seismic load case when combined with one-half PMF.

TVA presented the seismic dam failures as described above that indicated the inertia forces acting on the dams were the dominant factor that caused the dam failures, rather than the hydrostatic and hydrodynamic forces acting on the dams when the seismic and flood event simultaneously occurred.

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3.1.1 0.1.1 NRC Staff Evaluation

The NRC staff noted in Reference 8.1 that TVA safety factor changed from 1.52 to 1.0. However, in Reference 8.2, TVA changed the safety factor from 1.0 to 1.52. Subsequently, based on RAI 3.1 (Reference 8.18), TVA revised the safety factor to 1.22 (Reference 8.3). This indicated the FS for the Watts Bar Dam is greater than the TVA-RO acceptance criteria of >1.0 for loading during the earthquake for extreme cases. Therefore, it is acceptable to the NRC staff based on TVA-RO's jurisdictional authority.

The highest flood elevation is caused by the PMF, which is discussed in Section 3.1.2 of this document. The NRC staff reviewed TVA's HEC-RAS model and considers the modeling of the PMF acceptable (see Section 3.1.3.1 ).

The NRC staff found that TVA identified upstream dams had remained in the same failure or non-failure category when compared to the previous analysis for the dam failure induced by seismic loading. The only change to the dam failures was to include the Tellico Dam in the analyses.

In Reference 8.21, TVA made 16 new commitments. In particular, for commitment Nos. 13, 14, 15, and 16, TVA stated:

TVA will implement permanent modifications to prevent overtopping of the embankments of the Cherokee, Fort Loudoun, Tellico, and Watts Bar Dams (respectively), due to PMF. The final solution will be established in an evaluation conducted in compliance with the National Environmental Policy Act (NEPA) Environmental Impact Statement (EIS). Based on the current NEPA EIS schedule, the permanent modifications are scheduled to be installed by October31, 2015.

In Reference 8.22, TVA stated, "In order to complete the planned modifications to Fort Loudoun by October 31, 2015, closure of traffic on highway U.S. 321 is required because approximately 1900 feet of the 4500 feet planned modification is located directly adjacent to the highway ... " In addition, 'Tennessee Department of Transportation (TOOT) is currently constructing a new highway U.S. 321 bridge across the Tennessee River to reroute traffic away from the Fort Loudoun Dam .... The estimated completion date for the TOOT project is December 31, 2016." Therefore, TVA revised commitment 14 (Fort Loudoun) from October 31, 2015, to February 1, 2017. TV A also stated that to extend the life expectancy of the barriers for an additional 2 years, a like-for-like replacement panel will be added to shield the geotextile liner from ultraviolet exposure and prolong the life of HESCO® barriers. TVA further stated that TVA will continue to conduct the temporary modification inspections until the permanent modifications are completed.

In Reference 8.23, TVA re-performed the hydrological analysis (Calculation CDQ000020080080). In this reanalysis, the sand baskets were not credited to increase the height of the Fort Loudoun embankment. As a result of this reanalysis, the flood level at WBN-1 increased from 731.11 ft to 731.17 ft, which is lower than the 739.8 ft PMF elevation at the plant, as addressed in the LAR (Reference 8.2).

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In Reference 8.3, Enclosure 3, TVA proposed license conditions as follows:

(a) TVA will take action to ensure the stability of the Tellico, Watts Bar, Watts Bar West Saddle Dike, Fort Loudoun, Cherokee, Douglas Dam, and Douglas Saddle Dams under nuclear PMF conditions, consistent with TVA-RO's acceptance criteria. Therefore, actions shall be completed prior to implementing the revised hydrologic analysis for WBN-1, including changes to the hydraulic analysis methodology and upgrades to meet the TV A-RO's dam stability acceptance criteria by May 31 , 2015.

The NRC staff reviewed TVA's proposal and found it acceptable, as the permanent modifications will be completed earlier than the previous committed date of October 31, 2015.

(b) TV A shall implement permanent modifications to prevent overtopping of the embankments of the Fort Loudoun Dam due to the PMF by February 1, 2017.

The NRC staff reviewed TVA's proposal and found it acceptable, because: (1) the existing HESCO barriers will continue to function to prevent overtopping the embankment, (2) TVA will continue to maintain the HESCO barriers to extend the barrier life and conduct inspections until the permanent modifications are completed, and (3) TVA re-performed the hydrological analysis (Calculation CDQ000020080080, Reference 8.23), under seismic scenarios without crediting the sand baskets to increase the height of the Fort Loudoun embankment for the seismic scenarios. The NRC staff concluded that the resultant flood level at WBN still did not exceed the proposed DBF level.

3.1.1 0.2 Unsteady Flow Analysis of Potential Dam Failures

TVA used the HEC-HMS model to estimate the dam failure outflow hydrographs for the tributary dams only. The only exceptions were for Hiwassee, Apalachia, and Blue Ridge, which were postulated to fail completely. The failure outflow hydrographs for these dams were developed using either the TVA SOCH or HEC-RAS hydraulic models. For Tellico Dam, the complete failure was analyzed with the SOCH model.

TVA used TRBROUTE (part of the SOCH code) to estimate the failure time that corresponds with the time of maximum headwater and the initial reservoir elevations at each dam. TVA used HEC-HMS to calculate the failure outflow hydrographs. To validate these outflow hydrographs, TVA compared the results obtained from HEC-HMS to those obtained with TRBROUTE.


As part of the effort to successfully resolve the three Notices of Violation regarding the SOCH code (ADAMS Accession No. ML 1 01760332), the NRC staff reviewed software specification requirements, software design documents, software verification and validation documents, and the user manuals for SOCH including TRBROUTE (ADAMS Accession No. ML 100840221).

Both HEC-HMS and SOCH are valid software applications for developing hydrographs for rivers and reservoirs. Comparing the output from one software application to another is a commonly accepted way to validate the output from the other application.

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The NRC staff further verified that TVA used the SOCH model to simulate dam breach flow for seismically induced dam failure combined with flood events. Since the SOCH model had been calibrated with the two largest flood events, including the 1973 and 2003 floods (Reference 8.3), the NRC staff considers that the SOCH model is acceptable to be applied in the dam breach flow simulation for the seismically induced dam failure cases. Although the HEC-RAS model is the up-to-date model and it can simulate complex breach flow using control rules or breach parameters, the SOCH model is valid to be used when the dam breach rating curve is appropriately used to predict the flood elevation at WBN-1.

The NRC staff finds the approaches discussed in this section to be acceptable.

3.1.10.3 Water Level at WBN-1

As stated by TV A, the maximum flood elevation of 731.17 ft at WBN-1 was generated by the simultaneous failure of Norris, Cherokee, Douglas, and Tellico Dams due to the SSE coincident with the 25-year flood scenario (scenario 5). This flood was assumed to occur in the summer when the reservoir levels are presumed to be higher.

Coincident wind-wave activity for the PMF is described in Reference 8.1, Section 2.4.3.6. Wind waves were not computed for the seismic events, but superimposed wind-wave activity from RG 1.59 specified 2-year wind speed would result in WSEs several feet below the PMF elevation 738.9 ft described in Section 3.1.7.


Since the PMF stillwater elevation is 738.9 ft, and is discussed in Section 3.1. 7 of this SE, the NRC staff concluded that flood level from seismic dam failure is well below the PMF stillwater elevation, even when considering wind-wave activity as described in Section 3.1.8 of this SE and is, therefore, acceptable.

3.1.11 Low Flow in Rivers and Streams

TVA made editorial changes to Section 2.4.11.1 of the UFSAR and made some minor changes in the probable minimum water level at WBN-1. TVA updated the probable minimum water level from 673 ft to 675 ft based on Chickamauga Dam operation. The estimated minimum flow requirement for the essential raw cooling water system is 50 cfs. However, in order to guarantee both ample depth and supply of water, a minimum flow of 3,200 cfs will be released from Watts Bar Dam. With flow of a 3,200 cfs, water surface elevation would be at 665.9 ft and producing a 5.9-ft depth in the intake channel to the IPS.


The NRC staff evaluated the expected WSE at WBN-1 based on a release 3,200 cfs from Watts Bar Dam. The NRC staff computed flow elevation at WBN-1 under these low flow conditions. The computational results showed that the flow elevation was 681.77 ft. This elevation is 15.9 ft higher than TVA's LAR results of 665.9 ft. Therefore, based on the comparison, the NRC staff considers TVA's methods for low-flow WSE to be conservative and acceptable for use.

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3.1.12 Warning Plan

TVA made editorial changes to this section of the UFSAR. Additionally, TVA made changes to the warning plan. TVA's warning plan is implemented in two stages. The first stage, Stage I, is intended to provide sufficient time to make preparations for operating in flood mode while minimizing cost and other economic consequences. The second stage, Stage II, is intended to achieve safe plant shutdown. This stage is implemented if the water level is predicted to reach an elevation of 727 ft or greater.

TVA changed the forecasted flood elevation of when it will begin implementing Stage I of its warning plan from 714.5 ft to 715.5 ft for winter, and from 726.5 ft to 720.6 ft for summer. TVA will begin implementing Stage II of its warning plan if the forecasted flood elevation at WBN-1 is projected to rise above elevation 727 ft.


TVA's warning plan is based, in part, on observed rainfall on the ground at gage stations located throughout the watershed(s). The observed rainfall is used to forecast water levels in the reservoir system. (For more information, see Section 3.1.13.1 of this document.) Typically, daily forecasts for water levels in the Chickamauga Reservoir are provided. During major flood events, site specific forecasts are made every 4-6 hours.

The NRC staff recognized that for the purposes of managing their watershed, TVA no longer assigns a specific time frame to a particular season. For example, the time frame of October 1 -April 15 used to be considered the "winter" season. TV A now refers to the "winter" or "summer" season without referring to a specific time frame. See Section 3.1.12 of this document for additional discussion.

The warning plan is also affected by the season. See Table 4 below for information regarding the seasonal impact on the forecasted water levels used in TVA's warning plan.

Table 4: Forecasted Elevations in Chickamauga Reservoir for Implementing TVA Warning Plan at WBN-1

Season Stage I Stage II

Winter 715.5' 727'

Summer 720.6' 727'

Although TVA changed the trigger levels in Chickamauga Reservoir as shown in Table 4 for implementing its warning plan, TVA did not change the amount of time needed to implement the warning plan. The NRC staff reviewed the arrival time of the PMF, or the flood wave, due to seismic failure of upstream dams for inundation at WBN-1, as shown in Figure 2.4-23 and Figures 2.4-114 through 116 (Reference 8.2). The arriving time would be longer than or equal to 27 hours. Based on maintaining the 27 -hour warning time, the NRC staff finds this change to be acceptable.

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3.1.13 Hydrologic Basis for Warning System

TVA no longer assigns a specific time frame to a particular season. For example, the time frame of October 1 -April 15 used to be considered the "winter" season. TV A now refers to the "winter" or "summer" season without referring to a specific time frame. TVA also repeated earlier statements regarding when Stage I and Stage II procedures will be implemented. (See Section 3.1.11.1, Table 4, for details.)


The removal of a specific seasonal time frame reference provides additional operational flexibility in the reservoir system. This change also acknowledges that the seasons do not follow a specific daily schedule. TVA continues to maintain 27 hours of warning time to implement flood protection and shutdown procedures. Based on maintaining this amount of warning time, the NRC staff finds these changes to be acceptable.

3.1.14 Hydrologic Basis for Warning Times and Elevation

TV A provided information supporting existing figures that describe the basis for establishing the warning time during the winter and summer time periods. Figure 2.4-110, sheet 1 (Reference 8.2) presents the fastest rising PMP at WBN-1 for the winter time period. The hyetograph pattern that produced the least amount of warning time (fastest rising flood) is one with rising precipitation amounts throughout, with the largest precipitation occurring in the last time interval (in this case, 6 hours). This scenario would provide 31 hours of warning time (including 4 hours for communication) for implementing its warning plan before the WSE reaches 727 ft.

TVA provided information regarding flood forecast elevations used to initiate its warning plan. This information is shown in Section 3.1.11.1, Table 4.


TV A's warning system provides sufficient time for TV A to take action and to ensure that WBN-1 is protected. This warning system is based in part, on observed rainfall amount(s) on the ground. The amount(s) of observed rainfall on the ground needed to implement TVA's warning plan has been estimated by TVA-ROusing hydrologic and hydraulic models.

Although TVA made changes to their estimated precipitation amounts used to design its warning plan, these new values still provide 27 hours of warning time (31 hours with communication) to implement its warning plan and, therefore, the NRC staff finds them to be acceptable.

3.1.15 Basis for Flood Protection Plan In Seismic-Caused Dam Failures

TVA identified three seismic dam failure scenarios that would cause flooding above site grade at WBN-1.

The first scenario is the simultaneous failure of Norris, Cherokee, Douglas, and Tellico Dams due to occurrence of the SSE ground motions coincident with a 25-year flood. This combination

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of events follows guidance in ANSI/ANS-2.8. TVA assumes considerable debris from Norris Dam remains immediately downstream, affecting flow through the channel. The estimated warning time until the WSE reaches 1 ft below site grade (i.e., elevation 727ft) is 35 hours, with the maximum WSE reaching 731.17 ft.

The second scenario is the simultaneous failure of Norris and Tellico Dams due to occurrence of the OBE ground motion coincident with one-half of the PMF. This combination of events follows guidance in ANSI/ANS-2.8. TVA assumes considerable debris from Norris Dam remains in the channel immediately downstream, affecting flow through the channel. The estimated warning time until the WSE reaches elevation 727ft (1 ft below plant grade) is 27 hours, with the maximum WSE reaching 728.67 ft. This is 10.2 ft below the PMF level of 738.9 ft. The failure of Melton Hill Dam is included with the effects of failing Norris Dam. Melton Hill Dam is 56.5 mi downstream of Norris Dam.

The third scenario is the simultaneous failure of Cherokee, Douglas, and Tellico Dams due to the OBE ground motion coincident with one-half of the PMF. The estimated warning time until the WSE reaches elevation 727ft is 44 hours, with the maximum WSE reaching 729.07 ft.

TVA stated that random dam failure during non-flood conditions (i.e., so-called "sunny-day" failure) is bounded by the three above seismic-failure scenarios and, therefore, was not evaluated further in the LAR.

TVA-RO's flood forecast system is used to warn when flood conditions from rain, dam failure, or a combination, could cause a flood exceeding plant grade at WBN-1. Stage I of the warning plan will be implemented once the failure of any large upstream dam has been confirmed, or if one of the following three combination failures is confirmed: (1) failure of Norris, Cherokee, Douglas, and Tellico Dams; (2) failure of Norris and Tellico Dams; or (3) failure of Cherokee, Douglas, and Tellico Dams. Once started, the warning plan procedures will be carried out to completion, unless new information determines that WBN-1 is no longer expected to flood.


To evaluate TVA's second scenario that produced the shortest warning time of 27 hours, the NRC staff performed an independent confirmatory analysis using an HEC-RAS model to compute the flood wave from a breach at Norris Dam and also a breach at Tellico Dam due to OBE and one-half PMF. The computed flood wave would reach elevation 727ft, which is lower than the grade elevation at 728 ft, within 25.5 hours, according to the hydrologic conditions of TV A's submittal for LAR (Reference 8.1) in 2012. However, the crest of flood wave would reach WBN-1 later, at 31 hours, and the crest would be 0.5 ft below the grade elevation 728ft. Thus, it would not challenge the safe shutdown equipment at higher elevations.

3.2 Plant Modifications for Flood Protection

As shown in Table 2 in Section 3.1.2 of theSE, TVA stated that large rainfall and seismically induced dam failures can lead to flood elevations that exceed the plant grade at WBN-1. The Reactor Building and Diesel Generator Buildings will remain dry during flood mode. However, part of the Service, Turbine, Auxiliary, and Control Buildings and part of the Intake Pumping Structure (IPS) are assumed to flood. The Essential Raw Cooling Water (ERCW) in the IPS

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and the thermal barrier booster pump motors in the Auxiliary Building are required to function after the PMF to achieve and maintain safe shutdown. In addition, TVA found that the spent fuel pool cooling pump motors also needed plant modification, because the safety margin was reduced due to the updated PMF. Subsequent to the original LAR submittal, TVA identified that main control room chillers and shutdown board room chillers in the Auxiliary Building would also be affected by the updated PMF (Reference 8.15).

3.2.1 Thermal Barrier Booster Pumps

The LAR identified the Thermal Barrier Booster (TBB) Pump Motors as being impacted by the proposed DBF. The TBB Pump Motors are located in the auxiliary building at elevation 739.3 ft. The Service, Turbine, Auxiliary, and Control Buildings, where the TBB Pump Motors are located, are allowed to flood in the event of a DBF and the water level, including the windwave surge, within these buildings would reach elevation 739.7 ft. Because the TBB Pump Motors are required to remain functional for safe shutdown during a DBF, they require additional flooding protection measures.

In the July 19, 2012, LAR, TVA stated that a temporary flood protection barrier had been designed to protect the TBB Pump Motors in the event of a DBF. Subsequently, TVA stated (Reference 8.26) on June 13, 2013, that the temporary flood barrier had already been replaced by a permanent modification, in response to an RAI. The permanent flood barrier for the TBB Pumps is a steel wall designed to Seismic Category I criteria and capable of withstanding the hydraulic pressure associated with the DBF. The wall encloses the Train A and Train B pumps and extends to elevation 7 41.7 ft, providing 2 ft of margin above the DBF elevation within the auxiliary building. Where the wall meets the auxiliary building structure, all seams are sealed and watertight. However, there are several portions of the flood barrier wall that have gaps and removable door panels must be installed in advance of a DBF. These removable door panels will be used to close and seal the personnel and equipment access opening, and the seal leak-off floor drain will be plugged to prevent back flow through the drain system.


The permanent portions of the TBB Pumps flood barrier wall meet the guidance of RG 1.1 02. The removable door panels are not normally maintained in a closed position and are, therefore, considered a temporary barrier. These panels provide allow access to the TBB Pumps during normal operation, but must be installed in advance of a DBF. TVA has stated that the removable door panels will be stored at the flood barrier access opening, ensuring the availability of the panels when required. As described in the LAR, the flood warning plan provides a minimum of 27 hours from the receipt of a Stage I flood warning to install these removable door panels. This constitutes sufficient time to accomplish the installation of the removable door panels. The floor drain plug is also a temporary barrier. The floor drain plug is included in WBN-1 abnormal operating procedures, which ensure the staging of the component and direct the installation of the plug within the available warning time. The staging of the temporary barriers, the capability to complete these actions within the available time, and their inclusion in WBN-1 procedures constitute sufficient justification for their use. Therefore, the NRC staff finds that the flooding protection provided for the TBB Pumps is acceptable.

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3.2.2 Essential Raw Cooling Water

The LAR identified equipment associated with the Essential Raw Cooling Water (ERCW) system on the 722ft elevation of the IPS as being impacted by the revised DBF. The IPS is allowed to flood and the resulting wind wave water level within the IPS reaches elevation 7 41.7 ft. Water may enter the 722 ft elevation of the IPS through two doors at the 7 41 ft elevation, but otherwise equipment on the 722 ft elevation is protected from flooding. These two doors have 0.5 ft concrete berms at the opening. As a result, the 722ft elevation of the IPS is protected from flooding up to elevation 741.5 ft. The revised flood elevation within the IPS exceeds this elevation; therefore, additional flooding protection measures are required.

TVA stated in the July 19, 2012, LAR that sandbags will be employed as a compensatory measure to provide additional flood protection at the two doors at the 7 41 ft elevation leading to the 722ft elevation of the IPS. These sandbags are staged and will be constructed into a berm at least 12 inches high, in order to protect the ERCW equipment on the 722ft elevation of the IPS from flooding up to an elevation of 742ft. In an RAI response (Reference 8.26) dated June 13, 2013, TVA stated that the sandbags will be staged on the Raw Cooling Water exterior deck inside metal gang boxes. The action to build the sandbag berm at these two doors is captured in WBN-1 abnormal operating procedures for flood preparations. Additionally, the LAR identified two available sump pumps connected to safety-related power sources that can expel leakage into the 722ft elevation of the IPS.

The LAR stated that the corrective action program requirements have captured the need for additional compensatory measures, including the need for permanent plant modifications. Finally, TVA stated in the December 5, 2014, supplement (Reference 8.3) that a permanent plant modification had been performed to install passive flooding barriers via removable door panels at two doors on the 741ft elevation. These removable door panels now provide protection up to the DBF level within the IPS. The removable door panels are not normally maintained in a closed position and are, therefore, considered a temporary barrier. These panels allow access to the 722ft elevation of the IPS during normal operation, but will be installed in advance of a DBF. TVA has stated that the removable door panels will be stored at the door access openings, ensuring the availability of the panels when required. As described in the LAR, the flood warning plan provides a minimum of 27 hours from the receipt of a Stage I flood warning. This constitutes sufficient time to accomplish the installation of the removal door panels.


TVA installed the flood protection needed to protect the ERCW required for safe shutdown at the DBF level inside the IPS, including having procedures in place to install removable door panels upon flood warning. Although removable door panels are considered temporary, the use of temporary, passive flood barriers conforms to the guidance of RG 1.1 02. Therefore, based on the review of these modifications at the IPS, the NRC staff finds that the flooding protection provided for safe shutdown equipment within the IPS is acceptable.

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3.2.3 Spent Fuel Pit Cooling Pumps

The LAR also identified a reduction in flooding protection margin for the Spent Fuel Pit Cooling Pump Motors. TVA stated that a permanent modification would be completed to restore flooding protection margin for these pumps. The NRC staff issued an RAI concerning details of this modification. In its response (Reference 8.26) dated June 13, 2013, TVA stated that the permanent modification was completed and provides flooding protection to elevation 7 41.7 ft.

The permanent flood barrier for the Spent Fuel Pit Cooling pumps is a steel wall designed to Seismic Category I criteria and capable of withstanding the hydraulic pressure associated with the DBF. The wall encloses the three Spent Fuel Pit Cooling pumps and extends to elevation 7 41.7 ft, providing 2ft of margin above the DBF elevation within the auxiliary building. Where the wall meets the auxiliary building structure, all seams are sealed and watertight. In advance of a DBF, removable door panels will be used to close and seal the personnel and equipment access opening, and the floor drain will be plugged to prevent back flow through the drain system.


The permanent portions of the Spent Fuel Pit Cooling Pumps flood barrier wall meet the guidance of RG 1.1 02. The removable door panels are not normally maintained in a closed position and are, therefore, considered a temporary barrier. These panels allow access to the Spent Fuel Pit Cooling Pumps during normal operation but must be installed in advance of a DBF. TVA has stated that the removable door panels will be stored at the flood barrier access opening, ensuring the availability of the panels when required. As described in the LAR, the flood warning plan provides a minimum of 27 hours from the receipt of a Stage I flood warning. This constitutes sufficient time to accomplish the installation of the removal door panels. The floor drain plug is also a temporary barrier. As described in TVA's April29, 2013, report (Reference 8.16), the floor drain plug is included in WBN-1 abnormal operating procedures, which ensure the staging of the component and direct the installation of the plug within the available warning time. The staging of the temporary barriers, the capability to complete these actions within the available time, and their inclusion in WBN-1 abnormal operating procedures constitutes sufficient justification for their use. Therefore, the NRC staff finds that the flooding protection provided for the Spent Fuel Pit Cooling Pumps is acceptable.

3.2.4 Main Control Room and Shutdown Board Room Chillers and Ancillary Equipment

In a supplement (Reference 8.15) to the LAR, dated March 1, 2013, TVA identified that the Main Control Room (MCR) chillers and Shutdown Board Room (SDBR) chillers as being impacted by the revised DBF. These chillers are located at elevation 737ft in the auxiliary building, which would be flooded during a DBF event, because the water level within the auxiliary building could reach 739.7 ft. Thus, additional flooding protection measures are needed for these chillers.

TVA stated in the supplement that a permanent flood barrier was being designed to protect the MCR and SDBR chillers and ancillary equipment up to elevation 739.7 ft. The proposed modification added an enclosure constructed from 1 0-gauge steel sheet metal reinforced to withstand the hydrostatic pressure associated with a DBF. All seams between the flood barrier and the auxiliary building structure are sealed and watertight. A drain line has been installed

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where the manual valve penetrates the enclosure to prevent the enclosure from flooding due to damage to a pump during normal operation. This drain line will be closed following receipt of a Stage II flood warning. This action is captured in WBN-1 abnormal operating procedures. A portable submersible pump will be installed inside the flood barrier following a Stage I flood warning to remove any in-leakage that may occur. The pump can be powered from normal and emergency power supplies. The installation of the submersible pump is captured in WBN-1 procedures.

The NRC staff requested additional information concerning the modifications to protect ancillary equipment associated with these chillers. TVA's response (Reference 8.26) dated June 13, 2013, described modifications to various components in order to provide protection up to the revised DBF elevation within the auxiliary building. Electrical conduit located below the DBF elevation of 739.7 ft was modified to support submerged operation. All seams and openings on equipment or junction boxes located below the DBF elevation of 739.7 ft (with the exception of junction box covers and weep holes) were sealed to support submerged operation. Upon receipt of a Stage I flood warning any unsealed openings on the junction boxes will be sealed to ensure that the boxes are capable of being submerged. This action is captured in WBN-1 abnormal operating procedures to be completed in the first three hours after receipt of the Stage I flood warning.


The permanent flood barrier for the MCR and SDBR chillers meets the guidance of RG 1.1 02. The valve that penetrates the flood barrier is not maintained in a normally closed position and is considered a temporary barrier. This valve can be closed manually in the available time following a Stage II flood warning and this action is captured in WBN-1 procedures. The capability to complete this action within the available time and the inclusion of this action in WBN-1 abnormal operator procedures constitutes sufficient justification for the use of a temporary barrier. The installation of the portable submersible pump is not required for flooding protection, but provides additional margin against any in-leakage or leakage from the chillers within the permanent flood barrier. The action to install the submersible pump is captured in WBN-1 procedures and can be performed in the time available following a Stage I flood warning. The submersible pump and permanent flood barrier together provide protection up to the DBF elevation with additional capacity to remove any in-leakage. Therefore, the NRC staff finds that the flooding protection provided for the MCR and SDBR chillers is acceptable.

Ancillary equipment below elevation 739.7 ft that has been modified to function while submerged without further action meets the guidance of RG 1.1 02. The junction boxes require actions to apply sealant in advance of a DBF which is considered a temporary barrier. The tools and materials required to perform this action are staged in the auxiliary building. There is sufficient time available following receipt of a Stage I flood warning to complete this action and the action is captured in WBN-1 procedures. The staging of the temporary barriers, the capability to complete these actions within the available time, and their inclusion in WBN-1 procedures constitutes sufficient justification for the use of temporary barriers.

Therefore, the NRC staff finds that the flooding protection provided for the ancillary equipment associated with the MCR and SDBR chillers is acceptable.

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3.2.5 WBN-1 UFSAR Changes Related to Flooding Protection

WBN-1 UFSAR Section 2.4.2.2 states, "TVA has planned the Watts Bar project to conform with regulatory position 2 of RG 1.59."

TVA has proposed the revision of UFSAR Section 2.4.2.2 to state, "TVA has planned the Watts Bar project to conform with RG 1.59, including regulatory position 2."

This revision is editorial in nature and did not change the current licensing bases. The change reflects the conformance of WBN-1 to the guidance of RG 1.59 in general, and not only regulatory position 2. The NRC staff reviewed the LAR and the UFSAR to evaluate the continued compliance of WBN-1 with regulatory positions 2.b and 2.d of RG 1.59, which are related to physical barriers for flooding protection.

Regulatory position 2.b states that all safety-related SSCs should be designed to withstand the Standard Project Flood. RG 1.59 states that this flood is generally 40 to 60 percent of the PMF. TVA states in the LAR that the one-half PMF using the revised hydrologic analysis would result in a flood elevation of 717.2 ft. WBN-1 UFSAR Section 2.4.2.2 states that all safety-related SSCs are protected from flooding up to the site grade elevation of 728 ft. Therefore, all safetyrelated SSCs are able to withstand the standard project flood, and the WBN-1 design conforms to regulatory position 2.b.

Regulatory position 2.d states that those SSCs necessary to achieve and maintain cold shutdown should be designed with hardened protection against the DB F. For those systems not impacted by the revised DBF elevation, the existing flooding protection requirements are sufficient. With respect to cold shutdown, when WBN-1 was first licensed in 1995, the NRC staff stated in WBN-1 's Supplemental Safety Evaluation Report, NUREG-0847, Section 3.4.1, "Flood Protection":

The applicant has stated that all equipment required to maintain plant safety during the flood and for 100 days after the beginning of the flood is either designed to operate submerged or located above the maximum flood level. The Watts Bar flood warning plan provides for a minimum of 27 hours for preparation for flood operation and sufficient time to accomplish a controlled reactor shutdown to the hot-shutdown condition. The reactor will remain in the hotshutdown condition for the duration of flood operation. The staff has reviewed the applicant's list of safety-related equipment, which will be affected by flooding, and concurs that the unavailability of those systems and components will not prevent or adversely affect the accomplishment of a controlled reactor shutdown to the hot-shutdown condition for the duration of the flood operation (up to 100 days).

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A review of the WBN-1 UFSAR by the NRC staff did not identify other SSCs, beyond those identified in the LAR, necessary to achieve and maintain safe shutdown that were impacted by the revised DBF elevation. Temporary flood barriers proposed in the LAR are staged and maintained in accordance with WBN-1 procedures. These temporary flood barriers are designed watertight and can withstand the static and dynamic forces associated with the DBF, in accordance with RG 1.1 02. Permanent flood barriers proposed in the LAR are designed watertight and can withstand the static and dynamic forces associated with the DBF in accordance with RG 1.1 02. With the proposed modifications, those SSCs necessary to achieve and maintain safe shutdown that were impacted by the revised DBF have been provided with protection that ensures their capability to withstand the revised DBF. While the temporary flood barriers do not meet the definition of hardened protection provided in RG 1.59, they do provide adequate flooding protection in accordance with the guidance of RG 1.1 02. Therefore, the NRC staff finds that the WBN-1 design conforms to the guidance of regulatory position 2.d of RG 1.59.

The proposed modifications ensure adequate protection against the proposed DBF in conformance with the guidance of regulatory positions 2.b and 2.d of RG 1.59. As a result, the NRC staff finds the proposed revision of WBN-1 UFSAR section 2.4.2.2, above, acceptable.

4.0 SUMMARY AND CONCLUSION

Based on the NRC staff's review and evaluation of the proposed changes to WBN-1, UFSAR, regarding Hydrological Engineering, the NRC staff finds TVA's methods of evaluation and results to be acceptable. The NRC staff's acceptance of these changes was based on the review of TVA's updated watershed hydrologic and river hydraulic models, the latest available information from USAGE; Hydrologic Engineering Center; National Weather Service HMR 41, "Probable Maximum and TVA Precipitation over the Tennessee River Basin above Chattanooga"; and the USGS, as well as National Water Information System.

The NRC staff also reviewed the flooding protection modifications for the impacted systems. The modifications provide protection from the revised DBF in accordance with RG 1.1 02. The WBN-1 design, as modified by the LAR, conforms to the guidance of RG 1.59 related to flooding protection. Thus, the NRC staff finds the changes to flooding protection requirements described in the LAR to be acceptable.

Additionally, the NRC staff, supported by Region II inspectors, performed an audit of the dam stability of the Watts Bar, Fort Loudoun, and Douglas Dams. The audit validated the assumptions for dam stability in the hydrological analysis provided in this submittal. No concerns were identified during this audit regarding the stability of these dams. Therefore, the NRC staff finds UFSAR acceptable with the following TVA proposed license conditions:

License Condition (a):

TVA will take actions to ensure the stability of the Tellico Dam, Watts Bar Dam, Watts Bar West Saddle Dike, Fort Loudoun Dam, Cherokee Dam, Douglas Dam, and the required Douglas Saddle Dams under nuclear PMF conditions, consistent with TVA-RO acceptance criteria.

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These actions shall be completed prior to implementing the revised hydrologic analysis for WBN-1, including changes to the hydraulic analysis methodology and upgrades to meet the TVA-RO dam stability acceptance criteria by May 31, 2015.

License Condition (b):

TVA shall implement permanent modifications to prevent overtopping of the embankments of the Fort Loudoun Dam due to the Probable Maximum Flood by February 1, 2017.

5.0 STATE CONSULTATION

In accordance with the Commission's regulations, the Tennessee State official was notified of the proposed issuance of the amendment. The State official had no comments.

6.0 ENVIRONMENTAL CONSIDERATION

The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (77 FR 67686). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.

7.0 CONCLUSION

The Commission has concluded, based on the considerations discussed above, there is reasonable assurance that (1) the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.

8.0 REFERENCES

8.1 Letter from J. W. Shea, TVA, to NRC Document Control Desk, "Application to Revise Watts Bar Nuclear Plant Unit 1 Updated Final Safety Analysis Report Regarding Changes to Hydrologic Analysis, TAC No. ME8200 (WBN-UFSAR-12-01)," dated July 19, 2012 (ADAMS Accession Nos. ML 12236A167 and ML 12236A164).

8.2 Letter from J. W. Shea, TVA, to NRC Document Control Desk, "Supplement to Application to Revise Watts Bar Nuclear Plant Unit 1 Updated Final Safety Analysis Report Regarding Changes to Hydrologic Analysis," dated September 30, 2014 (ADAMS Accession No. ML 14289A106).

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8.3 Letter from J. W. Shea, TVA, to NRC Document Control Desk, "Response to Request for Additional Information Regarding Final Safety Analysis Report Section 2.4- Hydrologic Engineering, for Watts Bar Nuclear Plant Unit 1," dated December 5, 2014 (ADAMS Accession No. ML 14344A394).

8.4 Electronic Mail from Andrew Hon (NRC) to Joseph W. Shea (TVA), "Watts Bar Nuclear Station, Unit 1 - RAI Related to LAR to Updated FSAR Changes Associated With Hydrologic Analysis from Mechanical And Civil Engineering Branch - Dam Stability Safety Factor (TAC No. ME9130}," dated May 9, 2014 (ADAMS Accession No. ML 14129A316).

8.5 Letter from J. W. Shea, TVA, to NRC Document Control Desk, "Response to Request for Additional Information Regarding License Amendment to Update the Final Safety Analysis Report Regarding Changes to Hydrologic Analysis for Watts bar Nuclear Plant Unit 1," dated April 2, 2014 (ADAMS Accession No. ML 14093A388).

8.6 NRC (U.S. Nuclear Regulatory Commission). 1977. Design Basis Flood for Nuclear Power Plants. Regulatory Guide 1.59, Rev. 2, Washington, D.C.

8.7 TVA (Tennessee Valley Authority). 2013. Response to NRC Request for Additional Information Related to License Amendment Request to Update Final Safety Analysis Report Changes Associated with Hydrologic Analysis from Mechanical And Civil Engineering Branch (TAC ME9130). Submitted October 21, 2013 (ADAMS Accession No. ML 13296A025).

8.8 USACE (U.S. Army Corps of Engineers). 1966. "Computation of Freeboard Allowances for Waves in Reservoirs," Engineering Technical Letter No. 1110-2-8, August 1966, Washington, D.C.

8.9 Burcharth, H. F., and S. A. Hughes. 2011. Fundamentals of Design. In: Coastal Engineering Manual, Part VI, Design of Coastal Project Elements, Chapter Vl-5, Engineer Manual1110-2-1100, U.S. Army Corps of Engineers, Washington, D.C. Available at http:/1140.194. 76.129/publications/eng-manuals/EM 1110-2-1100 voi/PartVI/cem-vi-5. pdf.

8.10 USACE (U. S. Army Corps of Engineers). 201 Oa. Hydrologic Modeling System HEC-HMS, Version 3.5. U. S. Army Corps of Engineers, Institute for Water Resources, Hydrologic Engineering Center. Davis, California. Available at http://www. he c. usace. army. mil/software/hec-hms/.

8.11 USACE (U. S. Army Corps of Engineers). 201 Ob. HEC-RAS River Analysis System, Version 4.1. U. S. Army Corps of Engineers, Institute for Water Resources, Hydrologic Engineering Center. Davis, California. Available at http://www. hec. usace. army. mil/software/hec-ras/.

8.12 USGS (U. S. Geological Survey). 2013. The National Map Viewer. Accessed August 20, 2013, at http://viewer.nationalmap.gov/viewer/.

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8.13 Veri-Tech (Veri-Tech Inc.). 2013. Coastal Engineering Manual Professional Edition Software Version 2.01. Veri-Tech, Inc., Summit, Mississippi. Available at http://www. veritechinc. com/products/cem/index. php.

8.14 Resio, D.T., S.M. Bratos, and E. F. Thompson. 2008. Meteorology and Wave Climate. In: Coastal Engineering Manual, Part II, Coastal Hydrodynamics Chapter 11-2, Engineer Manual1110-2-1100, U.S. Army Corps of Engineers, Washington, D.C. Available at http:/1140.194. 76. 129/publications/eng-manuals/EM 1110-2-1100 voi/Partii/Part 11-Chap 2.pdf.

8.15 Letter from J.W. Shea, TVA, to NRC Document Control Desk, "Supplement to Application to Revise Watts Bar Nuclear Plant Unit 1 Updated Final Safety Analysis Report Regarding Changes to Hydrologic Analysis," dated March 1, 2013 (ADAMS Accession No. ML 13067A393).

8.16 Letter from J.W. Shea, TVA, to NRC Document Control Desk, "Completion of Commitments Related to Updated Hydrologic Analysis Results for Sequoyah Units 1, 2, and 3; and Watts Bar Unit 1 ," dated April 29, 2013 (ADAMS Accession No. ML13126A101).

8.17 Electronic Mail from Siva Lingam (NRC) to Joseph W. Shea (TVA), "Watts Bar, Unit 1, Hydrology LAR with UFSAR Changes (TAC No, ME9130)," dated May 21,2014 (ADAMS Accession No. ML 14149A217).

8.18 Electronic Mail from Andrew Hon (NRC) to Joseph W. Shea (TVA), "Watts Bar Nuclear Station, Unit 1 - RAI Related to License Amendment Request to Updated Final Safety Analysis Report Changes Associated With Hydrologic Analysis (TAC No. ME9130)," dated November 18, 2014 (ADAMS Accession No. ML 14322B018).

8.19 Newton, Donald W., and Vineyard, J. W., "Computer-Determined Unit Hydrographs from Floods," Journal of the Hydraulics Division, ASCE, Volume 93, No. HY5, September 1967.

8.20 U.S. Weather Bureau, "Probable Maximum and TVA Precipitation over the Tennessee River Basin above Chattanooga," Hydrometeorological Report No. 41, 1965.

8.21 Letter from J. W. Shea, TVA, to NRC Document Control Desk, "Commitments Related to Updated Hydrologic Analysis Results for Sequoyah Nuclear Plant, Units 1 and 2, and Watts Bar Nuclear Plant, Unit 1 ," dated June 13, 2012 (ADAMS Accession No. ML 12171A053).

8.22 Letter from J. W. Shea, TVA, to NRC Document Control Desk, "Change in Commitment Related to External Flooding Concerns (TAC Nos. ME8805, ME8806 and ME8807)," dated April 25, 2014 (ADAMS Accession No. ML 14122A219).

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8.23 Letter from J. W. Shea, TVA, to NRC Document Control Desk, "Results of the Hydrology Analysis without Use of Sand Baskets," dated October 31, 2011 (ADAMS Accession No. ML 11306A193).

8.24 Hydrology for Engineering (Chapter 8, Section 8-4), R. K. Linsley, Jr.; M.A. Kohler; J. L. H. Paulhus, McGraw-Hill (1982).

8.25 Electronic Mail from Andrew Hon (NRC) to Joseph W. Shea (TVA), "Watts Bar Nuclear Station, Unit 1 - Request for Additional Information Related to LAR to Updated Final Safety Analysis Report Changes Associated with Hydrologic Analysis (TAC No. ME9130)," dated March 21, 2014 (ADAMS Accession No. ML 14080A335).

8.26 Letter from J. W. Shea, TVA, to NRC Document Control Desk, "Response to NRC Request for Additional Information Related to License Amendment Request to Updated Final Safety Analysis Report Changes Associated with Hydrologic Analysis (TAC No. ME9130)," dated June 13, 2013 (ADAMS Accession No. ML 13168A410)

8.27 Tennessee Valley Authority (TVA)- Watts Bar Nuclear Plant, Unit 1 (WBN-1), Section 2.4, Hydrological Engineering Audit Report (TAC No. ME9130), Audit Dates April23 and 24, 2014, dated June 17. 2014 (ADAMS Accession No. ML 14163A758)

8.28 Tennessee Valley Authority- Watts Bar Nuclear Plant, Units 1 & 2, Section 2.4, Hydrological Engineering - Dam Breach and Stability Determination Audit Report (TAC Nos. ME9130 and ME4620), Audit Dates November 4-7, 2014 (ADAMS Accession No. ML 14323A340)

Principal Contributors: Y. Cheng, NRR E. Davidson, NRR D. Hoang, NRR A. Hon, NRR M. Keefe, NRR K. See, NRO S. Breithaupt, NRO

Date: January 28, 2015

Mr. Joseph W. Shea Vice President, Nuclear Licensing Tennessee Valley Authority 1101 Market Street, LP 3D-C Chattanooga, TN 37402-2801

January 28, 2015

SUBJECT: WATTS BAR NUCLEAR PLANT, UNIT 1 -ISSUANCE OF AMENDMENT TO REVISE UPDATED FINAL SAFETY ANALYSIS REPORT REGARDING CHANGES TO HYDROLOGY ANALYSIS (TAC NO. ME9130)

Dear Mr. Shea:

The U.S. Nuclear Regulatory Commission has issued the enclosed Amendment No. 98 to Facility Operating License No. NPF-90 for Watts Bar Nuclear Plant, Unit 1. This amendment consists of changes to the license in response to your application dated July 19, 2012, as supplemented by letters dated March 1, 2013; April 29, 2013; April 30, 2013; June 13, 2013; October 21, 2013; December 18, 2013; January 31, 2014; April2, 2014; September 30, 2014; and December 5, 2014.

The proposed amendment will revise the Updated Final Safety Analysis Report regarding changes to the hydrology analysis.

A copy of the related Safety Evaluation is also enclosed. The Notice of Issuance will be included in the Commission's biweekly Federal Register notice.

Docket No. 50-390

Enclosures:

Sincerely,

IRA/ Jeanne A. Dion, Project Manager Watts Bar Special Projects Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

1. Amendment No. 98 to NPF-90 2. Safety Evaluation

cc w/enclosures: Distribution via Listserv

DISTRIBUTION: PUBLIC RidsNrrDraAphb LRonewicz, NRR RidsNrrDoriLWBSP

LPL2-2 R/F RidsNrrPMWattsBar1 RidsNrrPMWattsBar2

RidsNrrDeEmcb RidsNrrDssSbpb RidsNrrLABCiayton RidsRgn2MaiiCenter RidsAcrsAcnw_MaiiCTR RidsNrrDoriDpr

ADAMS Accession No· ML 15005A314 .. OFFICE NRR/DORLILPL2-2/PM NRRIDORLILPL2-2/LAiT NRRIDORL/LPL2-2/LA NRRIDE/EMCB/BC* NRRIDSS/SBP/BC

NAME AHon LRonewicz BCiayton TLupold GCasto

DATE 1/8/15 1/8/15 1/27/15 1/8/15 1/8/15

OFFICE NRRIDRA/APHB/BC OGC- NLO NRR/DORL/LWBSP/BC NRR/DORL/LWBSP/PM

NAME SWeerakkody EWilliamson JQuichocho JDion

DATE 1/8/15 1/9/15 1/23/15 1/28/15

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