ML16272A219

Oconee, Units 1, 2, and 3, Supplemental Information Re NRC 2008 and 2012 Request for Information Pursuant to 10 CFR 50.54(f) Pertaining to External Flooding, Dated March 6, 2015 (Redacted)

ML16272A219
Person / Time
Site:	Oconee
Issue date:	03/06/2015
From:	Batson S L Duke Energy Carolinas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
Shared Package
ML16070A295	List: ML16070A284 ML16070A287 ML16070A288 ML16070A290 ML16272A216 ML16272A217 ML16272A218 ML16272A220 ONS-2015-028, Supplemental Information Re NRC 2008 and 2012 Request for Information Pursuant to 10 CFR 50.54(f) Pertaining to External Flooding, Dated March 6, 2015 (Redacted)
References
FOIA/PA-2016-0071, ONS-2015-028
Download: ML16272A219 (16)

Text

diLl bU (0AU52a.. Bcott L. Batson4%DUKE vice ,~ ~kI~Df2VOconee Nuclear StationONO1VP l 7800 Rocheste SC 29072o: 864.873.3274S864.873.4208ONS-20 15-028 Scott.sason@duke.energy.cornMarch 6, 201.5ATTN: Document Cont'rol Desk 10 CFR 50.54(f)U.S. Nuc:lear Regulatory Commission (NRC)Washington, DC 20555Duke Energy Carolinas, LLC (buke Energy)Oconee.Nuc;lear Station, Units 1, 2 and 3Docket Numbers 50-269, 50-270, 50-287'Renewed License Numbers DPR-38, DPR-47, and DPR-55

Subject:

Supplemental Information Regarding NRC 2008 and 2012 Requests for InformationPursuant to 10 CFR 50.54(f) Pertaining to External Flooding at Oconee NuclearStation (ONS).

References:

1. NRC Letter, In formation Request Pursuant to 10 CFR 50.54(f) Related to ExternalFlooding, Including Failure of the Jocassee Dam, at Oconee Nuclear Station, Units 1, 2,and 3, (TAC NOS. MD8224, MD8225, and MD8226), dated August 15, 2008(ADAMS Accession No. ML081 640244).2. NRC Letter, ReqUest for Information Pursuant to Title 10 of the Code of FederalRegulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3, of the Near-TermTask Force Review of Insights from the Fukushima Dai-ichi Accidentk datedMarch 12, 2012 (ADAMS Accession No. ML1 2053A340).3. Duke Energy Letter, Revised Flood Hazard Reevaluation Report per NRC's Request forAdditionallInformation, dated March 6, 2015.Ladies and Gentlemen,This letter Supplements Duke Energy's response to the NRC's 10 CFER 50.54(f) letters datedAugust 15, 2008 (Reference 1), and March 12, 2012 (Reference 2), for the purpose ofcommunicating Duke Energy's approach to address the regulatory matters associated withflooding caused by a postulated Jocassee, Dam failure.The approach is discussed in more detail in the enclosure to this letter. The enclosure alsorefers to a letter submitted concurrently with this one, which transmits a revised Flood HazardReevaluation Report (FHRR) for Oconee Nuclear Station (Reference 3).This letter does not create or revise any Regulatory Commitments.

ONS-201 5-028March 6, 2015Page 2Should you have any questions concerning this letter, or require additional information, pleasecontact Brian McCabe at (919) 812-8324.I declare under penalty of perjury that the foregoing is true and correct. Executed onMarch 6, 2015.Sincerely,Scott L. BatsonVice PresidentOconee Nuclear Station

Enclosure:

Supplemental information: 10 CFR 50.54(f) letters dated August 15, 2008, and March 12, 2012.

ONS-201 5-028March 6, 2015Page 3CC:Victor McCree, Regional AdministratorU.S. Nuclear Regulatory Commission -Region IIMarquis One Tower245 Peachtree Center Ave., NE Suite 1200Atlanta, Georgia 30303-1257William Dean, Director, Office of Nuclear Reactor RegulationU.S. Nuclear Regulatory CommissionOne White Flint North11555 Rockville PikeMail Stop O-13H16Rockville, MD 20852-2738Michele Evans, Director, Division of Operating Reactor LicensingU.S. Nuclear Regulatory CommissionOne White Flint North11555 Rockville PikeMail Stop O-8EIARockville, MD 20852-2738Jack Davis, Director, Japan Lessons Learned Project DivisionU.S. Nuclear Regulatory CommissionOne White Flint North11555 Rockville PikeMail Stop O-13H16Rockville, MD 20852-2738Brian Holian, Deputy Director for Engineering and Corporate SupportU.S. Nuclear Regulatory CommissionOne White Flint North11555 Rockville PikeMail Stop O-13H16Rockville, MD 20852-2738Jeffery Whited(by electronic mail only)U.S. Nuclear Regulatory Commission11555 Rockville PikeMail Stop O-BB1ARockville, MD 20852James R. Hall, Project Manager (ONS).(by electronic mail only)U.S. Nuclear Regulatory Commission11555 Rockville PikeMail Stop O-8G9ARockville, MD 20852Eddy CroweNRC Senior Resident InspectorOconee Nuclear Station ONS-201 5-028 EnclosureMarch 6, 2015Encl. Page 1 of 13EnclosureSupplemental information:10 CFR 50.54(f) letters dated August 15, 2008, and March 12, 2012,INDEX1.2.3.4.5.6.7.8.9.PURPOSEEXTERNAL FLOODING LICENSING HISTORY"CONFIRMATORY" ACTION LETTER (JUNE 22, 2010)EXTERNAL FLOODING MODIFICATIONS"FLOOD HAZARD REEVALUATION REPORTPLANT RESPONSE TO EXTERNAL FLOODINGREGULATORY" PATH FORWARDSUMMARY"REFERENCES

Attachment:

June 22, 2010, Confirmatory Action Letter -Commitments to Address ExternalFlooding Concerns ONS-201 5-028 EnclosureMarch 6, 2015 Encl. Page 2 of 131. PURPOSEThis enclosure supplements information provided by Duke Energy in response to the NRC's10 CER 50.54(f) letters dated August 15, 2008 (Reference 1), and March 12, 201.2 (Reference 2).The purpose of this enclosure is to document Duke Energy's regulatory approach associatedwith flooding levels caused by an upstream Jocassee Dam failure including:a) Oconee Nuclear Station (ONS) plans for maintaining ongoing compensatory measuresdocumented in Confirmatory Action Letter (CAL) 2-10-003 (Reference '3),.b) An update on the status of upstream dam failure mitigation modifications, 'andc) The protection and mitigation strategies being implemented to address flood levels up toand including the bounding flood at the Oconee site due to dam failure.The actions discussed in this enclosure reflect Oconee Nuclear Station's robust defense-in-depth approach to mitigate external floods and our commitment to enhancing safety marginsassociated with such floods.Duke Energy has Submitted a revised Flood Hazard Reevaluation Report (FHRR) (Reference 4)concurrent with this letter. Pending NRC staff review, the new FHRR Jocassee Dam breakanalysis will become a new beyond design basis event at Oconee to be documented: in the ONSUpdated Final Safety Analysis Report (hereinafter referred to as the new flooding licensingbasis). This is discussed in more detail in Sections 5 and 7 of this Enclosure.There has been previous correspondence between Duke Energy and the NRC (References 5and 6) pertaining to using the NRC's January 28, 2011, Safety Evaluation (SE) (Reference 7) onthe Oconee inundation study to satisfy the requirements of the March 12, 2012, 10 CFR 50.54(f)"Recommendation 2.1: Flooding" as the dam failure hazard in the FHRR for the site. inReference 6, the NRC indicated, "If your review of Recommendation 2.1 using the standards ofthe RFI (Request for In formation] indicate that the Jocassee Dam will not fail due to overtoppingor seismic failure, and the NRC staff review supports this determination, then the NRC wi~laccept the January 28, 2011 SE as defining the bounding flood at the. Oconee site due to damfailure." Duke Energy has completed its review and concluded that the Jocassee Dam will notfail due to overtopping or seismic failure, and has provided documentation which supports thatconclusion to the NRC (Reference 4). This is discussed in more detail in Section 5 of thisEnclosure. Pending NRC staff review, Duke Energy will use the January 28, 2011, SE asdefining the bounding beyond design basis flood at the Oconee site due to dam failure.Duke Energy is implementing a defense-in-depth flood response strategy at Oconee thatincludes physical protection barriers and mitigation strategies. The physical protection barriersinclude passive design features such as the Standby Shutdown Facility (SSF) flood Walls(803.5' msi) which (b (()above the flood level[ L kJ) in the revised FHRR, and7.5 feet above site grade (796' msl). Diverse and redundant flooding mitigation is beingimplemented at Oconee through the bounding beyond design basis flood (815.0' msl [19.0'above site grade]) due dam failure. These physical protection barriers and mitigationstrategies are discussed in more detail in Sections 4 and 6 of this Enclosure. The mitigationstrategies will be completed in the 4th quarter of 2016.Duke Energy has worked expeditiously and continues to make significant progress on upstreamdam failure mitigation modifications. Those modifications will be completed by June 2016. Thestatus of these modifications is discussed in more'detail in Section 4 of this Enclosure.Duke Energy recently completed a review of the compensatory measures documented inCAL 2-10-003. While these measures were intended to be interim in nature, Duke Energy has ONS-201' 5-028 EnclosureMarch 6, 2015 Encl. Page 3 of. 13concluded that it is prudent to maintain the ongoing compensatory measures. This is discussedin more detail in Section 3 of this Enclosure.The comprehensive actions reflected in the referenced modifications, compensatory measures,physical protection barriers, and mitigating strategies at Oconee reflect our commitment tosafety and our robust defense-in-depth strategy to mitigate external floods. Duke Energy looksforward to continued dialogue with the NRC on this matter, including further discussionS on theregulatory path forward.2. EXTERNAL FLOODING LICENSING HISTORYOconee Nuclear Station was licensed in 1973 and 1974 based on an evaluation that showedthat a Jocassee Dam failure was not a credible event based on the design and construction ofthe dam to prevent hydrologic failure and seismic failure. In 1984, Oconee developed a PRAthat was reviewed by the NRC in 1985 which showed that a random failure of the JocasseeDam had a low event frequency (Reference 8). This Was confirmed during the 1994 GenericLetter (GL) 89-13 Service Water Inspection (Reference 9) and the NRC Staff Assessment of theIPEEE in March of 2000 (Reference 10). NRC questions raised in 2008 concerning DukeEnergy and industry methods for calculating dam failure frequency led to an NRC request toperform a deterministic failure analysis of upstream dams. On August 15, 2008, the NRCissued a 10 CFR 50.54(f) letter that led to a deterministic failure analysis of the Jocassee Dam(Reference 1). Oconee provided the deterministic analysis results on August 2, 201.0(Reference 11), which was then evaluated in a Safety Evaluation issued by the NRC onJanuary 28, 2011 (Reference 7). Duke Energy committed to and implemented compensatorymeasures to mitigate flooding from a Jocassee Dam failure. These compensatory actions weredocumented in the June 22, 2010, CAL (Reference 3). On April 29, 2011, Duke Energy alsoprovided to the NRC a list of proposed modifications and rsoestagisfor mitigating theexternal flooding impacts for a beyond design basis flood (Reference 12).While pursuing the above flooding actionS, on March 12, 2012, Oconee received a second10 CFR 50.54(f) industry letter in response to the 2011 Fukushima accident, requestinginformation regarding Recommendations 2.1, 2.3 and 9.3 of the Near Term Task Force(Reference 2). Both the 2008 and 2012 10 CFR 50.54(f) letter responses included an analysisof~the flooding effects from a postulated failure of the Jocassee Dam, and a proposed responsestrategy to mitigate the new Jocassee flooding hazard. In response to a question from Oconeeon how to address the two overlapping flooding information requests, the NRC issued aSeptember 20, 2012, letter where the NRC provided, the direction that, "The NRC intends tomaintain the CAL dated June 22, 2010 active until it can be superseded by regulatory actionrelated to the Fukushima responses." (Reference 6). The information request associated withRecommendation 2.1 also states that the flooding hazard information gathered in the responsesthereto will be applicable to the resolution of Generic Issue,204, "Flooding of Nuclear PowerPlant Sites Following Upstream Dam Failures," which the NRC had initiated in 2010 based onits determination that, ". ..the. initial regulatory approach to this specific issue has evolvedconsiderably and in a manner that addresses weaknesses in the previous apprOach."(Reference 13).The UFSAR still reflects that the Jocassee Dam was constructed with sufficient seismic marginand overtopping margin such that failure is not considered credible. No site dam floodingprevention features were included as part of the original design and construction of ONS.beyond the robust design and constructionof the Jocassee Dam. An examination of theSubsequent licensing history of ONS concerning external flooding shows that while there hasbeen significant interaction with the NRC, the licensing basis has not changed from what iscurrently reflected in the UFSAR.

ONS-201 5-028 EnclosureMarch 6, 20.15 Encl. Page 4 of 13Going forward, Duke Energy will incorporate the beYOnd design basis flooding results from theupdated FHRR analysis (Reference 4) into the ONS licensing basis as a new, beyond designbasis event analyzed in the UFSAR. These actions are also consistent with the directionestablished in our OCtober 17, 2011, RAt response letter (Reference. 14) issued after theFukushima event and prior to the March 12, 2012, Fukushima 10 CFR 50.54(f) request toreevaluate external flooding hazards using updated hazard information and present-dayregulatory guidance and methodolOgies. Modifications to Support mitigation of this new floodinglicensing basis will be completed in 2016, as directed by the September 20, 2012, NRC letter(Reference 6).Duke Energy will implement mitigation strategies to address a bounding Jocassee Dam floodingevent as :described in the January28, 2011, Safety Evaluation (Reference 7). This beyonddesign basis bounding flood will be addressed with mitigating strategies based on FukushimaNRC Order EA-1 2-049. The mitigating strategies will be documented in the UFSAR.3. CONFIRMATORY ACTION LETTER (JUNE 22, 2010)The safety of the site from a postulated failure of Jocassee Dam continues to be ensured todayby CAL (Reference 3) compensatory actions that were put in place for Jocassee floodingmitigation in 2010, and continue to be maintained. The CAL was issued on June 22, 2010, toconfirm commitments made by Duke Energy in a June 3, 2010, letter. The letter included acommitment to implement compensatory measures at the Oconee site and Jocassee Dam tomitigate external flooding hazards resUlting from a potential failure of the Jocassee Dam. Thecompensatory measures listed in the enclosure were put into place until final resolution of theinundation of the Oconee site from the failure of Jocassee Dam has been determined. Thecompensatory measures that provide Jocassee flooding mitigation (early warning, shutdown,and core cooling) were inspected by the NRC in June 201.0, and no findings were documentedin the associated July 7, 2010, inspection report (ML101880769). The CAL compensatorymeasures were inspected again and documented in the April 2013, NRC TI-I187 Inspection for2.3 Flooding WalkdoWns (ML!31 15A063), and the November 2013, NRC TI-i 90 Inspection ofFukushima Interim Actions (ML13318A936). No findings were identified in the NRC inspectionswhich included reviews of the notification and response procedures, reasonable simulations toverify response time, equipment staging and equipment material condition.Duke Energy recently completed a review of the compensatory measures documented inCAL 2-10-003. While these measures were intended to be interim in nature, Duke Energy hasconcluded that it is prudent to maintain the ongoing .compensatory measures that supportmitigation strategies. Table 1 below lists the CAL compensatory measures by type. The .tablealso describes whether the action is a onetime action or on-going, and whether the action will bemaintained.Table 1June 22, 2010, CAL Compensatory Measures Complete On-going To be.(see Attachment 1 ) (onetime action) action maintainedPerform External FlIood Analysis (1) xInitial Jocassee Dam Failure Table Top Exercise (11)_. XJocassee Inspecti~ons (4). X XJocassee Monitoring (5, 7, 8, 12, & 13) X XJocassee Response Equipment (9, 10, & 14)._._____ X XJocassee Warning Time & X XOconee Response Process (2, 3, 6, & 15)________________

ONS-201 5-028 EnclosureMarch 6, 2015Encl. Page 5 of 134. EXTERNAL FLOODING MODIFICATIONSSite modifications are required to protect the SSCs needed to support flooding mitigation for arange of Potential breach events. The Jocassee flood licensing basis for the site will be theFHRR (Reference 4) Jocassee breach event where peak water levels at site grade will reachI). The flooding modifications that are being constructed at-the site will address a range of postulated breach events, including the ~new flooding licensingbasis, and are grouped in three flooding levels:1. Flooding levels with peak levels below site grade at 796' msl. -2. Flooding levels above site grade but below the top of the SSF flood walls at 803.5' msl.3. Flooding levels above the SSF flood walls from 803.5' msl up to 815' msl.The modifications to respond to the above range of flooding levels are described in Table 2below and will be completed by June 2016. Additional mitigation strategy modifications tocomply with NRC Order EA-12-049 will be included in a separate response associated with thatOrder.Table 2FloodingNo Modification Description Levels100kV FANT)Relocate the back-up powertransmission line towers100kVu (FANT) above the floodplain to supply emergency power throughLin BakuTower CT-5 to the site. This modification includes the acquisition 1Line ower of new right-of-way and relocation of 22 transmissionRelocation towers.____Protect the Condenser Circulating Water (COW.) imbeddedpiping (cooling water supply) by armoring the easternEast Slope slopes supporting the site grade. This modification2Scour includes approximately 150,000 ft2 Of scour protection (rip 1., 2, & 3Protection rap, concrete block, shotcrete, energy dissipaters, gabionmattresses) on the east slopes of the ONS power block, toprevent flood waters from eroding the embankment.,____Protect the intake dike and the imbedded CondenserCirculating Water piping (cooling water supply) byarmoring the intake dike in high water velocity locationsintake Dike and providing grass cover support as approved by FERC.3 Scour, The modification includes scour protection (shotcrete) 1, 2, & 3Protection where the intake dike meets the east bank, and anauxiliary drain system at the bottom of the intake dikeslope to imprtove drainage for the existing good grasscover that is credited for preventing flood waters from_ _ _ _ _ _ _ _ _ _ _ _ e ro d in g th e e m b a n k m e n t. _ _ _ _Protect the Condenser Circulating Water imbedded piping(cooling water supply) and reduce initial flooding levels byDiscarge directing water away from the site grade. The modification4Diversion icagwall includes a 206' long flood diversion wall, with a top 1, 2, & 3elevation of 828' msl, located near the CondenserCirculating Water discharge structure and designed todeflect flood waters away from the ONS Power Block.TurineThe modification includes one manually operated weirTurbinegate located at the entrance of a 72" turbine building drain5 Building Drain line to prevent flood waters from back-flowing into the 1Isolation building .basement.____

ONS-201 5-028 EnclosureMarch 6, 2015 Encl. Page 6 of 135. ,FLOOD HAZARD REEVALUATION REPORTRevised FHRR -2015 Evaluation ResultsOn.September 15, 2014, the NRC issued a Request for Additional Information requesting thatDuke Energy resubmit the 2.10ONS FHRR with a revised darn failure analysis, applyingalternate breach parameter estimations (Reference 15). By following the guidance provided inJLD-ISG-201 3-01 it was determined that the Von Thun and Gillette breach parameter-regression equations would provide a conservative yet plausible estimate for Jocassee Dambreach parameters. By applying the Von Thun and Gillette equations to the input data for theJocassee Dam, as well as exercising engineering judgment, the resulting breach .parametersutilized .in the reVised FHRR are as shown in the Table 3 below.Table 3Revised FHRR Jocassee Dam Breach ParametersTime to Empty Reservoir (99.5% reservoir volume emptied)HEC-RAS Computed Peak Outflow at Jocassee Dam'TO simulate a potential sunny-day failure of the Jocassee Dam, an unsteady flow model of theJocassee/Keowee/Hartwell reservoir system was developed using the USACE HEC-RAS(Version 4.1) program. HEC-RAS is a 1-D dynamic flow model with unsteady flow modelcomponents used in estimating inundation due to hypothetical dam failures. Additionally, aTUFLOW FV 2-D hydraulic model was developed to simulate the complex flow paths movingbetween the Keoweeand Little River arms Of Lake Keowee including the ONS Intake Canal andDike that abuts the ONS site at the south forming an island during dam breach simulations. The2-D analysis was performed to add detail to the HEC-RAS analysis and model the pOtentialinundation in critical areas identified around ONS. The revised FHRR evaluation shows floodingat the ONS site is primarily caused by high Keowee Dam .taiiwater elevations. Table 4 belowshows the results from the 1-D and 2-D models at various locations on site.

ONS-201 5-028 EnclosureMarch 6, 2015Encl. Page 7 of 13Table 4Comparison of 1-D and 2-0 Model Results:Time to breach and maximum water surface elevations (Elevation in ft msl and Time in hours)-Keowee.D.am Behigintake Dike1-D 2-D 1-D 2-DElevation Time Elevation Tim Elevation Time Elevation JTime817.00 2.75 :817.00 2.681 n/a n/a n/a J n/a_______ Maximum Water Surfaces ____ ____Keowee Dam Intake DikeI-D ] 2-D 1I-D 2-DElevation IfTime Elvton Tm Elevation [Time Elevation] Time821.1 j3.07 821.66 (b)( )(F) 810.32 3.87 809.72 J 3.8Maximum Water surfaces_____Swale " Tailwater ____1-D 2-D0 1-D 2,DElevation JTime Elevation [Time JElevation Tie Elevation] Timen/a' n/a Jf817.2 3.02 J799.4 4:8 [ 00.58 J5.12Maximum Water Surfaces____SSF S SF ____1-D I 2-1-D I-D 2-DElevation1 Time Elevation Time JDepth Time Depth Timen/a n/a JJ800.55 j5.33 j n/a j n/a 4.55 5.33The Keowee dam is nominally at an elevation of 815' msl. The peak water surface elevation atthe dam reaches (l)(7)F) .The ONS Intake Canal Dike crest is nominally at an elevation of 815" msl. The peak watersurface elevation in the ONS Intake Canal Dike reaches 809.72' msl.The nominal elevation of the Yard is 796' msi. The Yard would be exposed to flooding viadownstream backwater from Keowee Darn (Tailwater). The Yard would be inundated toelevation (b)(7)F) during the modeled dam failure (2.92' below the top, ofthe SSF hIooowalls).For further discussion and results, please refer to the revised FHRR.M~thodoloov and Assumntions Used-to Develon AnalysisThe JLD-iSG-201 3-01 guidance document discusses three types of dam failures: hydrologicfailure, seismic failure, and sunny- day failure. The revised FHRR concludes that the first two oftheSe failures are not credible failure modes. As a result of reviewing the dam structures atJocassee and Keowee for criteria outlined in ANS 2.8 for design basis floods, and comparingthem to the design basis requirements required by the regulating agency, FERC, it wasdetermined that the Jocassee Development and Keowee Development have adequate marginto meet the criteria for overtopping and stability as required by NTTF Recommendation 2.1.

ONS-20t 5-028 EnclosureMarch 6, 2015 Encl. Page 8Bof 13As requested by the March 20, 2014, NRC Requestfor Additional Information (Reference 16) toupdate the previous analysis initially submitted in the 20.13 FHRR, Duke Energy performed newseismic analyses for the Jocassee Dam. Duke Energy performed a new combinationdeterministiclProbabilistic analysis using the guidance provided in JLD-ISG-201 3-01 todetermine the darn factor of safety and displacements at the ground motion response spectrum(GMRS) level. The calculated post-earthquake slope stability factors of safety are well above1.0 and the estimated earthquake induced displacements are relatively small; therefore, theJocassee Dam is expected to perform satisfactorily following the design earthquake ground 'motions considered.The NRC Staff position on sunny-day failure States that no widely accepted current engineeringpractice exists for estimnatingfailure rates on the order of 1x10.6 per year, therefore sunny-dayfailure should be assumed to occur and the consequences estimated. Dueto this staff positionDuke Energy has assumed a deterministic sunny-day failure of the Jocassee Dam.Of the various modeling techniques presented in the JLD-ISG-201 3-01, Duke Energy used theHydrologic Model Method, utilizing the Hierarchical Hazard Assessment (HHA) process which isa progressively refined stepwise estimation of the flooding hazard. The advantage to thisapproach is a more realistic representation of the effects upstream dam failures and attenuationto the site. In order to develop the sunny-day failure analysis, Section 7.2 of the JLD-ISG-2013-01, Breach Modeling of Embankment Dams, was used to determine the appropriatemethodologies and assumptions. The breach parameter analysis used multiple commonregression equations for the breach parameters sensitivity studY and to predict parameters.The peak breach outflow, as calculated by the HEC-RAS model, was compared to multiplecommon regressiOn equations for peak outflow. As recommended by the JLD-ISG-2013-01guidance, Duke Energy used multiple modeling methods including regression, physics based,and historical failures to ensure the final results reflected a comparative analysis that is bothconservative and plausible.Comparison of 2010 and 2015 Evaluation MethodologqieSThe 2010 Jocassee breach evaluation developed in response to the 2008 10 CFR 50.54(f) letterbecame the basis for the January 28, 2011, NRC Safety Evaluation. The new revised FHRRevaluation completed in 2015 differs from the 201.0 evaluation with the primary difference beingthe approach used in the evaluations. In 2010, the goal was to maximize a flooding hazard byusing conservative simplifying assumptions and methods. Some of these simplifyingassumptions and methods included: not using regression equations to develop the breachparameters, using the default sinusoidal breach progression curve provided by HEC-RAS, andassuming the peak outfloW OccUrs coincidentally with the breach fully Progressed. TheseassumPtions and methods Were. used to maximize flooding with no refined analysis performedbeyond the initial screening level analysis. This approach is consistent with theNUREG/CR-7046 screening analysis approach.After the natural disaster at Fukushima occurred and the resulting NRC 10 CFR 50.54(f)Request for Information was issued, the goal of the 2015 evaluation was to develop a state-of-the-practice, accurate breach analysis that is both conservative and plausible. By following the*guidance provided in JLD-ISG-201 3-01 Section 7.2 ,MBreach Modeling of Embankment Dams",the analysis complies with the NRC staff positions that the model results not rely on a singlemethodology and include a Comparison of results for several mocdels judged appropriate for thesize and design of Jocassee, Key assumptions and engineering judgments are consistent withthe physics of a dam breach .events and were confirmed by historical data. These assumptionsand engineering judgments include; breach growth in one. direction limiting the breach size dueto the breach initiating at one of the rock abutments, peak outflow occurs prior to full breachbased on decreasing head differential and resulting water velocities, and the breach timerecognizes time required to fully empty a reservoir as large as Jocassee. This approach is ONS-201 5-028 EnclosureMarch 6, 2015 Encd. Page 9 of 13consistent with the HHA approach of refined analysis described in NUREG/CR-7046.Comparing the revised FHRR evaluation with the 2010 evaluation shows that by usingJLD-ISG-201 3-01, the updated breach analysis is founded in more technical rigor than thesimplified screening approach used in 2010. Below in Table 5 is a comparison of the revisedFHRR evaluation breach parameters with the parameters developed in the simplified evaluationcompleted in 2010.Table 5Comparison of Jocassee Dam Breach ParametersBreach Parameter 2015 Revised FHRR 2010 EvaluationBottom Width 634 ft 425 ftSide Slopes 0.5H:IV 1.55H, 0.7H:IVFinal Bottom Elevation 800' msl 800' mslBreach Development Time to Peak Outflow tiF,HEC-RAS Computed Peak Outflow at Jocassee Dam _______________6. PLANT RESPONSE TO EXTERNAL FLOODINGThe dam failure flooding response and associated modifications being constructed at the sitewill address a range of postulated breach events including the new flooding licensing basis andare grouped in three flooding levels:1. Flooding levels with peak levels below site grade at 796' msl.2. Flooding levels above site grade but below the top of the SSF flood walls at 803.5' msl.3. Flooding levels above the SSF flood walls from 803.5' msl up to 815' msl.The common entry point in Abnormal Procedures for all three categories of dam flooding eventswill be the declaration of a Condition "A" (Failure of one or more dam/dike is imminent or hasoccurred), or Condition "B" (Potentially hazardous flooding situation is developing). TheCondition "A" response will require that all Oconee reactors be tripped and mitigating strategiesbe deployed in anticipation of flooding. Condition "B" will require the Shift Manager to evaluatethe Condition "B" conditions and proceed with a shutdown if the conditions are degrading towardmeeting Condition "A" criteria. The Abnormal Procedure response including mitigationstrategies will involve the following parallel actions by procedure:* Connect hoses to feed steam generators (SG)* Portable pump alignments* Energize backup power supply through CT-5* Staff the SSF and ensure flood doors are secured* Activate the TSC/OSC & conduct site assemblyThe deployment of Mitigating Strategies includes the staging and connecting of the equipmentso that the equipment can be activated if required as the flooding scenario progresses based onflooding levels and the loss of SSCs required to keep the reactor cores cool. The subsequentflooding response based on the severity of the event is described below:Flooding levels with peak levels below site grade at 796' msl.* Plant SSCs provide feedwater and reactor coolant makeup* SSF and Mitigation Strategies provide back up to plant SSCs ONSo201 5-028 EnclosureMarch 6,2015 Encl. Page 10 of 13Flooding levels, above site-garade but below the too of the SSF flood walls at 803.5' msi.* Plant SSCs provide feedwater and reactor coolant (RC) makeup until plant SSCs are lost* SSF is staffed andavailable* SSF provides feedwater and reactor coolantl makeup if normal SSCs lost* Mitigation Strategies pr'ovide backup to the SSFFlooding levels above the SSF flood walls from 803.5' msl up to 815' msl.* Plant SSCs provide feedwater and reactor coolant makeup until plant SSCs are lost.* SSF is staffed and availablie* SSF provides feedwater and reactor coolant makeup When normal!SSCs lost* When the SSF is lost, Mitigation Strategies are put into service providing:,/ Feedwater" and reactor Coolant makeuP (diesel powered),I InstrumentationV' Spent fuel pool makeupMitigation Strategies provide div;erse and flexible, capabilities to maintain the key safetyfunctions: core cooling, containment, and spent fuel pool cooling if/when plant SSCs and the-SSF are .lost. Backup equipment is. available consistent with the N+1 guidance to supportmitigation strategies.Oconee's mitigation strategies for flooding provide steam generator feed, reactor coolantmakeuP, and multiple repower strategies; including guidance on where to measure keyinstrument readings using portable instruments for the beyond design basis bounding floodevent. New mechanical and electrical connections are being installed in the plant to allowdiverse capability.The .SG feed strategy uses one .pump to feed all three units. The RC makeup strategy will useone high pressure pump per unit to move inventory from the Borated Water Storage Tanks(BWST) into the RO system via currently installed vents and drains.In response, tO a Jocassee dam failure, Oconee will use site procedures to shutdown the unitsand perform a rapid cooldown, While deploying the SG feed portable mitigation strategy inparallel. The portable pump will be located above the inundation, level and hoses will besecured throughout the yard to ensure capability is maintained through the inundationtimeframe. Based on thermal hydraulicanalysis, RC Makeup. will not be needed until after theflood waters recede. Debris clearing equipment is available if needed in the FLEX StorageBuilding,: which is above the floodplain, to assist in deployment.An External Damage Mitigation Program will manage the mitigation strategies for flooding long-term. This program will include preventative maintenance activities to .ensure health of theequipment. Oconee will house an additional set of equipment needed as well as ensure thestrategies have been designed to utilize Regional Response Center (RRC) equipment forbackup capability to allow indefinite coping.The mitigation strategies are in progress and will be completed during the upcoming refueling`outages (Unit 2 E0C27 fall 201,5, Unit 3 EOC 28 spring 2016, and Unit I E0029 fall 2016) withall required actions in place in 2016 to meet NRC Order EA-12-049.7. REGULATORy pATH FORWARDPending Staff review of the new FHRR submitted concurrent with this ;supplement, the FHRRflood height will become the new licensing basis for Oconee. Specifically, Duke Energyrwillestablish the FHRR (Reference 4).Jocassee beyond design basis' flood where peak water levels ONS-201 5-028 EnclosureMarch 6,.20.15 Encl. Page .11 of 13at site grade ' the SSF flood walls)as the licensing basis for the site to be incorporated into Chapter 2. of the U FSAR.Duke Energy performed a comprehensive review of Oconee's current licensing basis associatedwith external flooding. Based on that review, Duke Energy's currentr directionl is to .update theOconee licensing basis and incorporate .the results of the new FHRR Jocassee Dam. breakanalysis in the UFSAR under 10 CFR 50.59 without a License Amendment. Changes to theUFSAR would be submitted to the NRC in accordance with 10 CFR 50.,7!(e)i. Other regulatoryprocesses are also available to codifY the results of the Oconee external flooding reViews. DukeEnergy looks forward to continued .dialogue with the NRC on this matter.As part of the *site response to address a range of beyond design basis breach events, theanalysis submitted to the NRC on August 2, 2010 (Case 2,1 00W) (Reference 11),. will :be usedto establish the bounding flooding eVent with a peak flooding level of 81 5.0' msl (1i9.0 feet abovesite grade) to be addressed with mitigation strategies. Thisflooding level is also reflected in .theNRC's January 28, 2011, SE (Reference 7).. The mitigation strategies for NRC OrderEA-12-049 including the new bounding flooding event response will be implemented for the sitein the fall of 201.6. The mitigating strategies response as r'equired by .NRC Order EA-1 2-049 willbe included in the Chapter 3 of the site UFSAR.AS noted previously, the modifications discussed in Section 4 will be completed by June 2016.Also, Duke Energy intends to maintain the Compensatory. measures outlined in CAL 2-1.0-003 asdiscussed in Section 3..8. SUMMARYIn summary, pending NRC staff review, the new FHRR Jocassee Dam break analysis willbecome the new licensing basis for external flooding at Oconee tO be documented in the ONSUpdated Final Safety Analysis Report; Chapter 2. This will. continue to be treated as a beyond*design basis event within the context of our licensing basis and plant design basis. Also,pending NRC staff review, Duke Energy will use the January. 28, 20 1, SE to define thebounding flood at the Oconee site due to damnfailure and document mitigation strategies inUFSAR Chapter 3.As noted previously, Duke Energy is *implementing a defense-in-depth flood response strategyat Oconee that includes physical protection barriers and, mitigation strategies. The physicalprotection barriers include passive design features such as the 8SF wall which is above theflood level in the FHRR (Reference 4). Diverse and redundant mitigation :strategies are beingimplemented at Oconee through the bounding flood due to .dam failure. Duke Energy continuesto make significant .progress on upstream dam failure mitigation modificationS, and thesemodifications will be completed by June ,2016. The mitigation strategies are in progress and willbe completed in the 4?h quarter of 2016.. Finally, Duke Energy will maintain the ongoingCAL 2-10-003 compensatory measures. These comprehensive actions reflect our commitmentto safety, and our robust defensmin-depth Strategy to mitigate exter'nal floods at Oconee.'Duke Energy looks forward to continued dialogue with-the NRC on this. matter, including furtherdiscussions on the regulatory path forward.

ONS-201 5-028 EnclosureMarch 6, 201i5 Encl. Page 12 of 139. REFERENCES1 ) NRC letter, Information Request Pursuant to 10 CFR 50.54(f) Related to ExternalFlooding, Including Failure of the Jocassee at Oconee Nuclear Station, Units 1, 2,and 3 (TAC Nos. MD8224, MD8225, and MD8226), dated August 15, 2008.2) NRC letter, Request for In formation Pursuant to Title 10 of the Code of FederalRegulations 50.54(f) Regarding Recommendations 2.1i, 2.,3 and 9.3, of the Near-TermTask Force Review of Insights from the Fukushima Dai-ichi Accident, datedMarch '12, 2012.3) NRC Confirmatory Action Letter 2-10-003, Confirmatory Action Letter -Oconee NuclearStation, Units 1, 2, and 3 Commitments to Address Exterhal Flooding Concerns (TAC Nos.ME3065, ME3066, and ME3067), dated June 22, 2010.4) Duke Energy Letter, Revised Flood Hazard Reevaluation Report per NRC's Request forAdditional Information, dated March 6, 2015.5) Duke Energy letter, Response to Requests for Additional Information RegardingModifications to Address External Flooding Concerns, dated June 14, 2012.6) NRC letter, Oconee Nuclear Station, Units 1, 2, and3- -Modifications to Address ExternalFlooding Hazards (TAC Nos, ME 7970; ME 7971, and ME7972), datedSeptember 20, 2012.7) NRC letter, Staff Assessment of Duke's Response to Confirmatory Action LetterRegarding Duke's Commitments to Address External Flooding Concerns at the OconeeNuclear Station, Units 1, 2, and 3 (ONS) (TAC ME3065, ME3066, and ME3067)I,dated January 28, 2011.8) NRC letter, Probabilistic Risk Assessment Study, Oconee Nuclear Station, Units 3(Docket No. 50-287), dated AuguSt 14, 1985.9) NRC letter, Notice of Violation, (NRC Inspection Report NOS. 50-269/94-31,50-270/94-31, 50-287/94-31), dated December' 19, 11994.10) NRC letter, Review of Individual Plant Examination of External Events, (TAC NOS.MA83649,. M83650, and M83651), dated March 15, 2000.11 ) Duke Energy letter, Oconee Response to Confirmatory Action Letter (CAL) 2-10-003,dated August 2,, 2010.12) Duke Energy letter, Oconee to Confirmatory Action Letter (CAL) 2-10-003,dated April 29, 2011.13) NRC Generic Issue (GI) 204, Screening Analysis Report for the Proposed Generic Issueon Flooding of Nuclear Power Plant Sites Following Upstream Dam Failures, datedJuly 2011.14) Duke Energy letter, Response to Requests for Additional Information RegardingNecessary Modifications to Enhance the Capability of the ONS Site to Withstand thePostulated Failure of the Jocassee Dam, dated October 2011.15) NRC Letter, Request fOr Additional Information -Oconee Fooding Hazard ReevaluationReport (TAC Nos. MF1012, MFI0I3, and MFI014), dated September 15, 2014.1 6) NRC Letter, Request for Additional Information Regarding Fukushima Lessons LearnedFlood Hazard Reevaluation Report (TAC Nos, MFiOI2, MF1013, and MF1iO4), datedMarch 20, 2014.

ONS-201 5-028 EnclosureMarch 6, 2015 Encl. Page 13 of 13AttachmentJune 22, 2010, Confirmatory Action Letter -Commitmentsto Address External Flooding Concerns1. Perform flooding studies using the Hydrologic Engineering Center-River Complete Analysis.System (HEC-RAS) model for comparison with previous DAMBRK models to moreaccurately represent anticipated flood heights in the west yard following postulated failure ofthe Jocassee Dam.2. Maintain plans, procedures (Jocassee and Oconee) and guidance documents implemented(Oconee) to address mitigation of postulated flood events which could render the StandbyShutdown Facility inoperable and are consistent with current perspectives gained followingthe HEC-RAS sensitivity studies and. the subsequent 2D inundation studies. To the extentpractical, the mitigation strategy is similar to existing extensive plant damage scenario(B.5.b) equipment, methods and criteria.3. Duke Energy Hydro Generation will create a guidance document to consolidate rivermanagement and storm management processes. (Includes the Jocassee Development andthe Keowee Development.).4. Maintain a dam safety inspection program that includes: (1) weekly dam safety inspectionsof the Jocassee Dam by Duke Energy personnel, (2) dam safety inspections following any2-inch or greater rainfall or felt seismic event, (3) annual dam safety inspections by DukeEnergy, (4) annual dam safety inspections by FERC representatives, (5) five year safetyinspections by FERC approved consultants, and (6) five year underwater inspections.5. Maintain a monitoring program that includes: (1) continuous remote monitoring from theHydro Central Operating Center in Charlotte, NC, (2) monthly monitoring of observationwells, (3) weekly monitoring of seepage monitoring points, and (4) annual surveys ofdisplacement monuments.6. Assign an Oconee engineer as Jocassee Dam contact to heighten awareness of Jocasseestatus.7. Install ammeters and voltmeters on Keowee spillway gates for equipment conditionmonitoring..8. Ensure forebay and tailrace level alarms are provided for Jocassee to support timelydetection of a developing dam failure.9. Add a storage building adjacent to the Jocassee spillway to house the backup spillway gateoperating equipment (e.g., compressor and air wrench).10. Obtain and stage a portable generator and electric drive motor near the Jocassee spillwaygates to serve as a second set of backup sPillway gate operating equipment.11. Conduct Jocassee Darn failure Table Top Exercise with Oconee participation to exerciseand improve response procedures.12. Instrument and alarm selected seepage monitoring locations for timely detection ofdegrading conditions.13. Provide additional video monitoring of Jocassee Dam (e.g., dam toe, abutments, and groinareas) for timely assessment of degrading conditions.14. Obtain and stage a second set of equipment (including a B.5.b-type pump) forimplementation Of the external flood mitigation guidance.15. Conduct Jocassee Dam/Oconee Emergency Response Organization Drill to exercise and~improve response procedures.