ML20366A017

NRC-2017-000688 (Formerly FOIA/PA-2017-0690) - Resp 5 - Final, Agency Records Subject to the Request Are Enclosed, Part 9 of 15

ML20366A017
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Issue date:	12/29/2020
From:	NRC/OCIO
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ML20366A007	List: ML20366A008 ML20366A009 ML20366A010 ML20366A011 ML20366A012 ML20366A013 ML20366A014 ML20366A015 ML20366A016 ML20366A017 ML20366A018 ML20366A019 ML20366A020 ML20366A021 ML20366A022 ML20366A023
References
FOIA, FOIA/PA-2017-0690, NRC-2017-000688
Download: ML20366A017 (40)

Text

Serial: RNP-RA/14-0012 MAR l 2*2014 u!s. Nuclear Regu1ato1y Commission Attn: Ooctment Control Desk 11555 Rockville Pike R~.MD~.

H.* B. ROBINSON STEAM.ELECTRIC PLANT, UNIT NO. 2 DOCKET NO. 50-261 / RENEWED LICENSE NO. DPR-23 W.llGlcaalt H.a,.,.,._,Slurn Elide Pin 1H I SlltVb,,.....

a..a,...~

.., W..Ennnc>>Roao

~SC2fl/SIO

,, IUS 1611118 10 CFR so.54(f)

~

Flood Hazasd Reevaluation Report, Response to NRC 10 CFR 50.54(f) Request for lnfonnatian Pwsuant to Title 10 of th& Code Of FedBrat Regulations 50.54(f) teg&Jding

~

-2.1. 2.3 and 9.S of u.*Near-Term Task Force Review of tnsight8 ftrm 1tte t=ukuahima Dai-ichf Acctderit, Dated Mmd1 12; 2012

1. NRC L&ttel to Aft Power Reactor Licensees and Holders of Construction Permits In Aotlve or Deferred Status, Rsqunt for Information Pursuant to Tdle 10 of th9 Co!# of Federal Regulatiorrs SO.S4(f) ~

Rflcorntnenclations 2. 1, 2.3, and 9.3 of the Near-

. Tef!'I Td Force Rfflew ol JnsJghts from the Fukushima Dai-icm Aocldsnt. dated March 12, ~12, Ange~ Documem Access and Management System (ADAMS)

Accession No. ML12053AS40

2. NRC 1-etter to All Power Ruetor Ucensee8 and Holders of ConstructiOn Permits in Active or Deferred Status, Prioritization of R6sponSfl DulJ Dates for Request For Information Pursuant to r,u,, 10 of tlHI Codtt of FedtJraJ Regulations 50.54(f) Regarding Flooding HabJrd Reevalualions for Recommendatfon 2.1 of the N6ar-Tsnn Task FOtCB Review of Insights from the F~

Dai-lchl Aocktent, C$ated May 11, 2012, APAMS AccesslonNo. ML12097A509

3. NRC Letter~ David L. Skeer\\ to Joteph S. Pollock (N~I), TrigglJrConditions for

. Psrforming an Integrated Assessment and Due Da* Rapor,se, dated-December 3, 2012, ADAMS Accession No. ML12326A912

4. D'1ke Energy Lstter, H. 8. Robinson sieam Ellc:trlc Plant. Unit No. 2 Response to RecommendaUon 2.3, Flooding Walk.down, of lhe Near-Term Task Force Review of Insights tron, the Fukushima Oai-lchi kddent. dated November 26~ ao,2. ADAMS Accession No. ML12340A067 Ao10 NfZL

U. S. Nuclear Regulatory Commission Sertm: RNP-RA/14-0012 Page2 of3 Ladies and Gentlemen:

By letter dated March 12, 2012, the Nuclear Regulatory Commission (NRC) Issued Reference 1 to an power reactor licensees and holders of~

permits in active or*deferred status.

~osure 2 d Rafe~ 1 n,questect that each licensee ~O!ffl a ieevaluatlon ot external

~~

sowtes and repoct the resulls _, -~

vwith tti& NRC's prtoritization plan (f:leference 2). The due date eslabltahad for the H: 8. Robinson Steam Bectrtc Plant, Unit No.

2, was Mat'Ch 12, 2014. Enclou'e 1 tothie--~ the -..uired Duke Energy~ "

Hazard ReevHl8tion Report tor H. &. Roblnlon*Steam Electric Plant, Uni*> 2.-*, *

• The. attad.led ftoOd r.ant INY8luation report daacribes the_appn,ach, methods and results from the reevaluation of flood hazarda at H. 8. Robinson Steam Etectrlc Plant, Unit No. 2. The eight (8) flood-causing rnec:hanlsMs. IAIS a combtned effect flood identified in Attactunent 1 to Enclosure ~ d Reference 1 are dNcrl>ed in the fl9port along with the potential effects on H. 8.

Robinson Steam Eledric Plant. Unit No. 2 *.

• The flood hazard~ faport shows lhlt some flood le\\l9l8 exceed 1he Current Ucenslng

• 84si$ (ClB) levels. The increa9ed levels are the resub f1 newer methodologies and guidance whtc.h ereapplcable to new ~r revilwl andlypicallvuoeedthe melhodologies and guidance used to establlah the CUJ for elistlng plants. As such, these differences are not the resufts ot errors wilhin the Cl8 flood eva1ultions.

In accordance with Aefeaence 3, an lnteglated Ass asement (IA) I& required if flood levels determined during lhe flood hazard reevaluation are not bounded by lhe CLB flood levels.

Enclosure *2 of Reference 1 specifies that lhe IA t,e completed and a report submitted within two years of submitting 1he Flooding Huard Reevalultion Report. An IA will be completed and a report swmitted no tater than March 12, 2016.

Aa discussed within Reference 1, the NRC slated that the etment regulato,y approach, and the resultant plant~. gave lie f_fRC the ~idence to conclude that an accidant with consequences slmilaf to the~ accident ts unftk~ to occur in the United States (U.S.).

The NRC concluded that continued plant operatichl and the continuation of Hcensing aetivitieS did not pose an nminen1 nsk to public health and safety. The floodilg walkdowns of H. 8.

Robinson Steam Electric Aant, Unit No. 2 CL8 flood protection features have been pelfonned and the results were provided by Aefaence 4. In general, the flood walkdowns verified that the flood pR>tectiOn eystems fot H. 8. Robinson Steam Beclric Plant, Unit No. 2 are available, functional and implementable and If necessary, any degraded, nonconforming flood protection features were entered In H. e. Robinson Steam Electric Plant, Unit No. 2 Corrective Action Program.

Section 5 of the Flood Hazard Report and Enclosure 2 of this letter, provides a discussion ot the interim evakration and actions taken or plarn,ed 1o address the higher flooding levels relative to the Cl8 flood levels. 'ff18Se actiOn& will erhlnce tbe a.H18nt capability to maintain the plant in 8 safe condition during the ~n-basi& memal flooding events that exceed the CLB

U. $. Nuclear Regulatory Comml$SIOn.

Serial: RNP-RA/14-0012 Page3ot3 flood levels and as a '9SUlt, continued plant operation does not impose an imminent risk to the pubUc health and safety white comp1etlng the Integrated Assessment.

In addition, Duke Energy may determine that addltionat site specific meteorological analyses are realistic for the H. e. Robinson Steam Electric Plant, Unit No. 2 to refine the bounding hazard. Although addiUonaJ analyses may be perfonned, the interim actions described in will be implemented In accordance wtth the dates provided In the table.

This letter contatns regulatory commttrnerfs as listed in the table provided in Enclosure 2. The table provides a Ost of the intartm actions taken or planned to be taken along with the dates by which they have been or will be tmplemented. Duke Energy commits to not modify any of these commitments and associated Implementation dates without notltymg the NRC In advance.

If you nave any questions or require additional Information, please contact Richard Hightower Manager* Regulatory Affairs, at (843)-857-1329.

I declare under the penally of perjury that the foregoing 18 true and COITect.

executed on

hd t~

W. A. Gideon Site Vice President WAG/she Enclosures : 1) H. 8. Robinson Steam Electric Plant, Unit No. 2 Flood Hazard Reevaluation Report

2) H. e. Roblnaon Steam Electric Plant, Unit No. 2 lntertm Actions cc:

Mr. t<. M. Ellis, NRC Senior Resident Inspector Mr. S. P.. Lingam, NRC Project Manager, NRA Mr. V. M. McCree, NAC Region II Administrator

United States Nuclear Regulatory Commission

-Enclosure to Serial: RNP*RA/14--0012 Page 1 of 31 ENCt.08URE 1 11.000NMAROREEYAWA'IIONREPOAT tt. 8. AOIINSON 81£AllaECTRIC PUNT, UNrrNO. 2 DOCKETNO.SNl1

United States Nuclear Regulatory Commls$ion Enclosure to Serial: RNP..RA/14-0012 Page2of 31 1'A8U OF CONTENTS

1.

EXECUTIVE SUMIIMY.................................................................................................. 4

2.

SffE INFOAMATION.................................... ".............................................................,~.4 2, 1 Current Deels,rt 8aell Rood tr PF P 1d...... -...................... "............................................... 4 2.1. t Local Intense Precipitation.......................................................................................... 4 2.1.2 Flooding in Streams and River&.................................................................................. 4 2.1.3 Storm, Sutge.** :............................................................................................................ ~5 2.1

.. 4 Seidle ***********************************************************************************************************************,5 2.1.5 Tauriami.."...................................................... :....................................................................... 5 2.1.6 2.1.7 2.1.8 lce-tndLIC8C:l'Floodir1g................................................................................................................... 5

~net Migration or Diversion.......... **.***........................................... -.**..................... 5 Combirled.Effects Floocls,....................................................................................................... 5 2.1.9 Dam Breaches and Failures....................................................................................... 5 2.2 CutnmtLloenllftgllal*Flood',-,tionancllltlfalltlon,-.............................. s 2.3 FIODCf 9'1illled Clllllgll 1111.Cit Uct1111119,___.................................................... 1

a.

SUIIIIAAY OF FLOOOHAZMD REEVALUA'IIOlt............ "****************************"***.... *"**e a.,

L.Oc11-liltlll.-Preclplt,llton-.................................. "........................................................... e 3.1.1 Methodology / Analyses / Computations..................................................................... 6

3. t.2

• Results/ Conclusions......................................................................... ~...................... :8 3.2 Floodlngln....,,_...._.Duetoltl~IIMimumPNclpllatlon(PIIP),... 11 3.2.1 Hydrologic and HydrauMc Study......................................................................... '....... 11 3.2.2 Results/ Conclusions............................................................................................... 14

$.I, Stoma su,90: ************-**************... *****"*********...........................................

N........................ 18 3.3.1 Approach/ Methodology........................................................................................... 16 3.3.2 Computations Oiseussk>n......................................................................................... 1-6 3.4 Selche............................................................................................................................. 17 a.e Tsunami............................................... _........................................................... "............ 17 3.8 lce-lrlclllOlcl ~

............................................................................................ "...... 17

3. 7 Cllan.nel Migration or Dlvtrll011................................................................................... 11

3. 7.1 Approach / Methodology........................................................................................... 18 3.1.2 Results / Conclusion................................................................................................. 19

-Dem a.c11e1 artcl 'Fallula................... n................................................................, * **** 19 3.8 3.8.1 3.8.2 Scenario A - Upstream Dam Breach and Failure..................................................... 19 Scenarto B - Lake Robinson Dam Breach................................................................ 21 Cot9bl"'9d,Effect Flc,od,N**.. ****n*****.. *****---**...__****..... **.... ******.. **---~**********.. *********************22 3,,9 3.9.1 3.9.2 Approach / Methodology........................................................................................... 22 Results....................................................................................................................... 25

4.

CCJM:PARISON-WIIH--e&JAAe. DESIGN BASIS......................................................... 21 Local """'* Preclpllll:lon........................................................................................... r, 4.2 Flaocll.lllt in_,._.. ___,.......................... "........................ _................... "......... 27

United States Nuclear Regulatory CommlssJon Enclosure to Serial: RNP-RA/14-0012 Page3of31 4.a Storm s.,..................................................................................................................... 21 4.4 S.lclle-........................................................_......... *-****************-******H******************.. **-******.. 17 4.5 Taunaml........................... "............................ ~ ******** "."....................................................... ff 4.e lce-lnclu:ceCI flooding................. :...................................................................................... 28 4.7 Chan....a lllgratlort or oav.tlon........................................................... "........................ 21 4.t Dant 111-"* alld lallla1111 ***"**********:.......................... ~.-............................... ~ ****.****.*** 28 4.1 COIIIIIMd Effilcl FIGOCll.............. ;..............................._.~.......................... ~ ** ~ **..***..*. *~***28

5.

-INTERIM: AC-r10NS................................,,................... "................................................... 29 1.1

£vetluatecl Eventa far Sitt FIOOCllag.................. ".,,............. ~."***-****............ -~....................21 5.-1. t Local Intense Precipitation (UP) Event..................................................................... 29

. 5.1.2 Probable "Maximum FIOod (PMF) Event.. ~................................................................. 29 5.2.

lnlpectl d tllt Evtnte......................._..~*********n"*"**N********.. **~**n*h**H................ "............. n 5.3 lvtnt AelPDII*....................................... N................................................................... 29 5.3.1 COre Cooting............................................................................................................. 29 5.3.2 Spent Fuel Pool Cooling........................................................................................... 30 5.3.3 Containment lntegrity................................................................................................ 30 lnlarlm Actlon'I ~1':>tlll I.lit Eflllt............................ "........................................ 80 5.4 5.4.1 5.4.2 5.4.3 Steam Generator Cooling......................................................................................... 30 RCS f nventory and So ration..................................................................................... 30 Spent Fuel Pool Cooling........................................................................................... 31 5.& ln1erlm ActlOlla ~

to tllt NF Evlftl'............... ~***.. **...................................,........ 31 5.5.1 Steam Generator Cooling......................................................................................... 31 5.5.2 ACS Inventory and Boration..................................................................................... 31 5.5.3.*. Spent Fuel Pool Coollng........................................................................................... 31

United States Nuclear Regulatory Commission Enclosure to Serial: RNP-AA/14-0012 Page4of 31

1.

EXICUTIVE SUIIIIAAY This report summarizes the results of the flood hazald. reevaluatioos pelfonned at H. B.

Robinson Steam Electric Plant, Unit No. 2 (HBASEP) in response to the March 12, 2012 NRC 10 CFR 50.54(f) Request for Information, Item 2.1. The flood hazard reevaluation was completed using current regulatory guidance and methodologies used for earty site permits and combined Ucense applications. For each flood hazard. the reevaluated flood elevations were compared to the design basis flood hazard level to determine whether it was bounded.

There were several instances of higher elevations from the expanded flood causing mechanisms versus the site's Current Licensing Basis (CLS) flood level. Therefore, an Integrated Assessment wlll be completed and a report submitted to the NRC on or before March 12, 2016. The iffleglaled aSS8SSinent will be performed to address higher reevaluated flood hazards for Local Intense Precipitation, Flooding In Streams and Rivers, Dam Breaches and Failures, Ston11 Surge, and Combined Effects. Until ful1her assessment is completed, HBRSEP ha$ implemented the requisite interim actions, except for the completion of training on the use of the Portable RCS Boration equipment, which Is In progress and will be completed prior to entering MOOE 4 ctumg plant restart from the current outage (R229F3).

a. SffE INFORMATION The elevation of the plant site is 225 ft Mean Sea Level (MSL), MSL Js equivalent to National Geodetic Vertical Datum of 1m (NGVD29). The main surface water feature in the site vicinity is Lake Robinson, created by Che lmpouncbent of Black Creek at the Lake Robinson Dam f r industrial u

. Robinson Lake normal pool elevation is 220 feet MSL (b)(3) 16 USC § 824o-1(d) (b)(4) (b){7J(F) re were 2.1 CURRENT DESIGN BASIS FLOOD HAZARD Design basis flood haiards were deten11ined by reviewing the CLB. This Includes docketed and currentty effective written commitments for ensuring compliance wtth NRC requirements, and design basis information documented In the plant Updated Final Safety Analysis Report (UFSAR).

2.1.1 Local lnten9e Pl9Clpitdon Local Intense precipitation was not considered applicable In the CLB.

2:1.2 Flooding In StNllmt and RMl'8 The flood hazard detennination was based on peak flows into the lake calcutated for two hypothetical stonns. A design unit hydrograph for the drainage area above the dam was developed from examination of nearby gauging station records that yielded several well defined hydrographs. Two different peak flows were calculated using the design unit hydrograph. No credit was taken for the shape of the drainage area In reducing the rainfall in these calculations,

United States Nuclear Regutatory Commission Enclosure to Serial: RNP-RA/14-0012 Page Sot 31 and maximum antecedent moisture conditions were assumed In estimating Infiltration and retention. The first peak flow condition. was based on a July 1916 stonn transposed from Asheville, NC to the Black Creek drainage area, which yielded a peak discharge Into the lake of 23,000 cubic feet per second (ds). The second peak flow determined resulted from the Probabl$ Maximum Precipitation (PMP) for the area, which was taken from the charts prepared by th& Hydrometeorological Section of the Weather Bureau. Thi$ peak flow yielded a 39,000 cfs discharge into the lake. The two peak flows are bounded by the design basts capacity of the Tainter gates*of 40,000 ds, thus, ensurJng th& fake level would not exceed 222 ft MSL.

2.1.3. $COffll Surge Storm surge was not considered appli~ In the CLS.

~.1.4 Salol'II Seiche was not considered applicable in the CLB.

2.1.s tsunami T$Ufl8ffll was not considered applicable In the CLB.

2.1.6 tCHl1Clucld FIOOdlnf lce*lnduoed flooding was not considered applicable In the CLB.

2.1. 7 Channel Mlgnrtlon or Olvel'IIIOn Flooding due to channel migration or diversion was not considered applicable in the CLB.

2.1.8 Comblnlden.ctaFIOOClt A combined effects flood was not considered applicable In the CLB.

2.1.9 Oam *~

Ind F*Huree Dam breaches and fSJlures were not considered applicable In the CLB.

2,2 CURREHT LICENSING 9.ASIS FLOOD PAOTECflON AND IIITIGATION fEAfURES the Lake Robinson Dam Tainter gates are credited flood protection features In the HBRSEP licensing basis. The function of the Tainter ~ n..tlJ2o~* mtmJtJDit.de;star:LbalSIS..tlaad..lalateJrs.tii.,

• revent the lake from exceedl 222 ft MSL (b){3) 16 USC § 8240-1 (d), (b)(4), (b){7)(F) gau rsonnel utilize a lake level atlons Tainer

United States NUCiear Regulatory Commission Enclosure to Serial: RNP-RA/14-0012 Page6of 31 operation of the plant. tn accordance with the CLB, site flooding will not occur since the site grade is above the maximum lake level which can be maintained by the dam and appurtenant structures.

During the flooding walkdowns performed ii support of Request tor Information Item 2.3, it was confirmed that the Tainter gates* material condition and functionality met the acceptance criteria, there.Is adequate time available for the gate operation personnel to property position the gates during a flooding event conildering weather conditions, and credited operator actions are feasi~le.

a.a FLOOD RELATIDCHANGES SINCE UCENSING 1$SUANCE The local watershed condition on the HBRSEP site has changed slightly. The site has added temporary/portable buffdlnSJ$, pennanent buildings, paved partdng lots, earthen berms and vehicle (~rsey) barriers since the original tlcense was Issued. A new drainage channel and a retention pond have also been constructed.

There have bean no signiflcMt changes to the watersheds of the Black Creek and its tributaries since license issuance.

a.

SUMIIMY OF fLOODHAZAADREEYAUIAllON

a. t I.OCAL INTENSE PAEClftffA1ION The effects of tocal 1ntense precipitation (UP) were evaluated. For the assessment of flood haiarda at safety-refated buildings, the Hierarchical Hazard Assessment (HHA) process, as described in NUREG/CR-7046 (Design-Basis Flood estimation for Stte Characterization at Nuclear Power Plants In the United States of America) was followed. It is assumed that there are no precipitation tosses on-site during thtt.entlre PMP event and runoff proc8$$, and all catch basins, pipelines, smafl culverts, inlets. pumps, siphons and other drainage systems are not functioning. The *local PMP could be caused by tropical stonn or frontaJ precipitation. It ts conservatively assumed that the storm occurs without warning. It is also assumed that topography Win not change during the event due to sediment erosion/accretion.

3.1.1 Methodology/ ----/ ComputatloM A two-dimensional hydroct,r'lamic modet, FL~20 Pro Version, was used to calculate the flow depth and velocity due to the local PMP. The model computational domain encompasses the entire HBRSEP site, the high land on the west and northwest, and part ot Lake Robinson on the east. The FL0-20 model uses the finite volume method to solve the dynamic wave momentum equations.

FL0-20 uses a grid system to calculate the flow field to solve the equations. The computational method for overland flow involves calculating the discharge across each of the boundaries in eight potential flow directions. The fuff dynamic wave equation is a second order non-linear partial differential equation. To solve this non.lilear equation for vek>city at each grid element, an initial estimate of velocity is obtained from the corresponding diffusive wave equation using the average water su.rface slope. Manning's equation Is applied to compute the friction slope.

The estimatad velocity is then plugged back in the dynamic wave equation to calculate the non-

Untte<f States Nuctear Regulatory Commission Enclosure to Serial: ANP-RA/t<<>012 Page 7of 31 1in9-r solution for velocity by applying the Newton-Raphson iteration method. After obtaining the velocity, the discharge across the grid element boundary is computed by multiplying the vafocity by the cross sectional flow area. After the discharge is determined for all eight directions, the net Change of flow volume is calculated. This change in volume Is used to catcutate the change In depth for each grid.

The local PMP oalculation. relies on a hydrologk: analysis as shown in Section 3.2 for the downstream boundary condition. For the Lake Robln60n watershed, the analysts showed that the flood from ttl& waterahed PMP took more than 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> to raise the water-elevation to 225 ft NGVD29 in Lake Robinson. The local flood would haw receded before that occurred. Therefore the downstream condition wilt not affect the outflow boundary condition at the lake shoreline for FL0-2D modet.

The 1-hcur, 1-square mHe PMP values were used. fot this computation. Hydrometeorologioal Report (HMR) 52 recommended that no inCrease in PMP values be applied for areas smaller than 1 square mile. 'nle HBRSEP site is approxtmatety 0.3 square mites. The contributing watershed is approximately 0.55 square mHes. The Fl0-20 grid mesh covers about 1.25 square miles area which encloses the contributing watershed completely. The FL0-20 model automatioaffY determines the flow direction based on the ground elevation. Runoff outside of the contributhg watershed is divet'ted toward offsite locations. The effective contributing area for the cornputatiOnal domain In the model is approximately 0.55 square mites. Therefor&, the 1-hour, 1-square mile PMP was applied to the entirlt HBRSEP contributing watershed. The rainfall amounts for the local PMP are fisted In Table 1. The 1-hour, 1-square mlfe PMP amount Is 19.02 indl8$. The 5-, 15-and 30-milute rafnfaff amounts were dete,mined by multiplyilg the 1-hour rainfall by ratios obtained from Figures 38 through 38 of HMR 52. Values of each Increment of PMP are listed In Table 1. The 6-hour PMP (HMR 51) of 30.21 inches Is also Included in the same table in order to genentta the &-hour hyetograph for the computation.

Tettltt.hlc.

forl.oclltPIIP Railfall Duration Parameters Ra1io (inches)

Sources 6-hour, 10-square mite NIA 30.21 HMR 51 F,gure 18 PMP 1-hour 1-square mile 1

19.02 HMR 52 f'tgUre 24 PMP s-to 60-mln ratio 0.325 6.18 HMR 52 -Agure 36 15-to 60-mtn ratio 0.511 9.72 HMR 52 Figure 37 30- to 60-mln ratio 0.737 14.06 HMR 52 Figun, 38 To detennlne the impact of the Locat Intense Precipitation (UP) on the rOOfs of the Containment Building, Auxiliary Building / Control Room, and the Twblne Building, the total volume of water

United States Nuclear Regulatory Commission Enclosure to Serial: RNP-RA/14-0012 Page8of 31 stored or ponding on the roof was compared to the design five load. The LIP event is considered to have no adverse effect on the roofs of the investigated buildings.

3.1.2 Reaultl / ConclutlOna The time series model output shows that there are two different flood elevation peak& at the HBRSEP site. TIiis 18 due to the travel time for offsite runoff to reach the HBRSEP site. Runoff from the westem end of the watershed took about six hours to reach the site. The first peak was generated by the local runoff and occurs abOut 1.1 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> after the start of the storm. event. The second peak was created by the nmoff from the west aid$ of the watershed and occurs -about a.o hours after the start of the storm event. The initial peak elevation Is higher than the second peak elevation.

The flood elevations, velocities and Impact forces at safety-related SSCs under the PMP condition are summarized in Table 2. These flood elevations and resultant static loads represent the water levels and static pressures at the peak flood condition. The maximum v~locitles and resultant Impact toads represent 1he peak flow speed condition of flood flow on the site. Note that the impact load is from flow velocity. Debris Is not expected to influence Impact toads due to the low velocities, low flow depths and the presence of site banters which would intercept offsite debris before It coufd enter the powett>lock area.

As shown in Table 2. maximum flood levels are higher than the finished floor elevations at most bUildings on the list. Th& original design site elevatlOn ls 225 ft NGVD29 for the HBRSEP site as reported in the UFSAR.

As seen 1n Table 2. the potential of erosion from high velocity flow is tow at the site because the maximum velocity is slower than 3.8 ft/a. which is lower than the speed threshold for earth channel erosion (4 ft/sec for coarse sand earth channel). The maximum lmpac.1 force and pressurf are less than the concrete strength 3,000 pound per square inch (psi) (or 432,000 iblft2) at each building. The potential for buildings to be damaged by flood force is therefore minimal.

Teltle2. Su

.* of Reeun. for FL0-20 Model at ICav 8ulldlnaa on HSRSEPSltlt Location Flnllhld llulnun llexlfflum Mu.

Mu.

Finished FIOor Flow Velocity Ae8ubnt A'8Ultant Floorw Elev.Uon Eltvdon Impact Static llaxFlood Load I.cad Ellvatlon ft ft NGVD29 tfGV02t lb/ft tbffl ft FabShop 230.15 230.13 3.80 85.81 179.59

+0.02 Fuel Building 226.13 228.90 0.81 0.45 179.71

-2.77

United States Nuclear Regulatory CommlSsion Enclosure to Serial: RNP-RA/14-()012 Page9of 31 Location flnllhld.....,,. llaxhnum Floor flow Velocity EJeYlltlQn EIIMlllfon ft/a ft ft NGVD21 tlGVD2t Fuel Handling Building 226.13 229.26 2.83 Environmental 226.38 229.67

• 2.12 and Radiation Control Building Turbine 226.00 229.15 3.05 Building:

Turbine Generator and Condensers Condensate 226.36 229.22 2.51 Polishing System Contaminated 226.12 229.47 1.17 Equipment Storage Outage Management Building 234.06 23'.55 3.30 Spent Fuel 240.17 241.04 2.75 Area Aux C Building 225.97 228.66 0.85 Radwaste 226.13 228.69 1.62 Building Reactor 226.13 228.72 0.85 Auxifiary Building Wortt Control 226.65 229.47 2.05 Building Max.

Flntehed Reeuttant AMultant Floor vs Impact Static Maxffood 1,.oeel Load Elevetlon M

Wft ft 53.26 262.30

-3.13 41.8t 299.73

• S.29 68.58 313.80

-3.15 45.72 299.46

• 2.86 6.99 450.18

-3.35 26.90 73.01

-0.49 21.06 46.79

-0.87 3.91 157.36

-2.69 7.24 225.33

-2.56 3.91 229.12

-2.59 12.08 303.70

-2.82

United States Nuclear Regulatory Commission Enclosure to Serial: RNP*RA/14-0012 Page 10of 31 Location flftllMCI llaUftum Malmum FloOr flow Velocllr Elevltion Ellvallon ff/a ft.

ft NGVD29 NGY029 Untt2 226.13 2.29.42 0.8' Containment Building Access 226.13 229.51 2.22 Building Diesel 226.00 229.23 1.82 AFWPump 226.00 229.11 2.05 SOAFWPump 226.00 229.24 1.52 Visitor Center 254.00 254.33 0.14 partcjng lot Flex Building 243 242.85 1.11 Near Barrier 225.97 228.79 1..:3 SE-PA side (135105)

Near Barrier

• 225.97 227.95 1.09 SE*.

Switchyard side (135104)

NearBanier 226.00 229.14 0.77 SW* PA side (129680)

NearBanier 226.00 228.29 2.37 SW*

Switchyard side (129678)

Mu.

Flnlshed Atsultant Resultant Floorva tmpect Static Max Flood Loact Load Elevation lb4ft tblft ft 12.14 315;34

.. -3.29.

17.59 321.93

-3.38 25.81 321.64

• 3.23 31.35 302.53

-3.11 18.24 327.60

-3.24 0.02 3.43

-0.33 3.84 49.64

+0.15 13.97 247.44

• 2.82 5.77 122.80

• 1.98 4.60 307.05

-3.14 31.17 163.81

• 2.29

United States Nuclear Regulatory Commission Enclosure to Serial: RNP-RA/14-0012 Page 11 of 31 3.2 fl.OODING IN S1111AMS ANDAIVEAS OUE TO PAOIABLE MAXIMUM PReCIPn'AnoN (PMP)

Lake Robinson is a cooling water reservoir for HBRSEP and is fed by Black Creek and Its tributaries. lhls section is to detennine the effect of floodiig in rivers and streams near the HBRSEP from the Probable Maximum Flood (PMF) induced by Probable Maximum Precipitation (PMP) In Lake Robinson and Its watershed.

The PMF has been defined as an estimate of the hypothetical flood (peak disdlarga, volume, and hydrograph shape) that is consldered to be the most severe rvasonably possible at a particular location. The PMF f81)r8Sm'1ts an estimated upper bound on the maximum runoff potential for a given watershed.

A comprehensive HEC-GeoHMS and HEc.HMS hydrologlc model of the Lake Robinson Watersbtd was prepared. The model was developed using Economic and Social Research Institute (ESRl) ArcMap Geographic lnformation System (GlS) mapping and the U.S Army Corps of Engineers (USACE)'s HEC-OeoHMS.

the Natural Resources Conservation Service (NRCS), fonnalty mown as the SoH Conservation Service (SCS), Curve Number (CN) methodology was utilized to calculate runoff hydrographs from the 28 watershed sub-basina. Sub-basin sizes, Curve Numbers (CN), land use classifications, and sub-basin times of concentration (Tc) were estimated for the 28 sub-basins.

The hydrologlc model of the Lake Robinson Watershed was expanded to include the USGS stream flow from the gauge station located immediately downstream of Lake Robinson dam.

Sub-basin hydrographs were routed through the watershed channels and combined with hydrographs from tributary sut,..baslns. The upstream ponds and dams are small and have little storage capacity. Therefore. the limited upstream storage was not included In the model, but potential attenuation was captured via calibration of initial abstraction. All upstream reservoirs and ponds are assumed full at the beginning of the postulated PMP event and will not attenuate the peak or volume during any flooding (i.e.* inflow = outflow). Reservoir storage and spUlway discharge characteristics for Lake Robinson Dam were obtai'led from a.built drawings and reports provided by HBRSEP. The MuskJngum-Cunge methodology was used to model channel routing.. Non-linearity adjustments were made according to NUREG/CR-7046 guidance.

3.2.1 Hydrologlc and Hydraulic Study 3.2.1.1 Hydrologlc Methodology/ Anatyela / Computltion A comprehensive HEC,,GeoHMS and HEC-HMS hydrologlc model was utilized to calculate runoff generated by the PMF. Watershed-related input parametena needed for the HEC-HMS model in~ initial rainfall losses, rainfall Infiltration losses, drainage area size, rainfall-runoff lag times, and data for hydrograph routing through the watershed and channels.

Initial ralnfaff tosses (abstra~lon) to account for surface wetting of vegetation and soil and tming of local surface depressions were adjusted using Hurricane Frances 2004 data.

Initial rainfalt infiltration losses were estimated using the NRCS (formerly SCS) Curve Number methodology for which the CN Is the parameter used to define rainfall infiltration losses. CN vatues for each sub-basin were derived based on soil types and land uses in the watershed.

United States Nuclear Regulatory Commission Enclosure to Serial: RNP-RA/14-0012 Page 12of 31 The drainage area of the Lake Robinson Dam drainage basin is cflVided into 28 sub-basins. The watershed sub-basins were delineated and the enclosed areas were calculated using HEC Geo-HMS. The sub-basin areal sizes were then Input into the HEC-HMS model for the hydrologlc simulation. In selecting sub-basins for the analyses, special attention was given to potential coincident peaks. dams, flow observation points (USGS gages), and other critical elements (e.g., slope and land use pattem) which could influence the watershed responses during a flood event.

Ralnfall*runoff lag tttnea were calculated from estimates of sub-basin time of concentration (Tc).

Tc is defined as the time it take$ storm water runoff to travel from the hyd,aul~ly most d~tant point of the watershed to an outlet point within the watershed. A Tc value was determined for each sub-basin using the methOd in Natural Resources Conservation Society (formerty SCS)

Teclvtical Release No. SS (TR*S5). Runoff from each sub-basin was dMded into the sheet flow segment (non-concentrated runoff from the most distant point), the shallow concentrated flow ses,nent, and the channel flow.

The Muskingum.Cunge routing procedure waa used for the hydrologic routing of sub-basin hydrographs and combinations of hydrographs throughout the watershed dtannels. This routing procedure is a Stb-routine tn the HEC-HMS model that is designated by the user and only n,qulres Input of the channel geometry. South C.roRna State UDAR based &.point cross-sections were generated using ArcGIS tools for lh8 channels. Routing was Included in the hydrologlc modeling to account for transient dlannal storage attenuation and travel fag times between flow concentration points.

Prgbable Mutmum PdiJallon (PMP) & QJystopment Qf lbl Probat>ft Max;num 8god (PMF}

The PMP estimates for the Lake Robinson Watershed above the main dam of the Lake Robinson Reservoir, South caroNna were determined using the criteria and step-by-step Instructions given in HMR 51 and HMR 52. The data in HMR 51 and HMR 52 indicates that the PMP. event for the Lake Robinson Watershed would result from a tropical stonn event (hurricane) that would be a preclcted severe weather event.

The drainage area of the Lake Robinson Dam drainage basin ls 171.5 square miles: the location of the centroid of the basin Is approximately 34.5826°N, 80.2t37°W. Using HMR 52 as a guide, the PMP for the Lake RobinsOn Dam drainage basin was developed.

The PMF storm was developed by accounting for the antecedent ralnfaD that precedes the PMP

$tonn based on American National Standards Institute (ANSI/ANS)-2.8*1992, Determining Design Basts Flooding at Power Reactor Sites, guidelines and adjusted for non-linearity based upon NUREG/CR-7046. The PMF storm that was used as the rainfall input in the hydrologlc

~ing has the following components:

(1) An antecedent 72-hours stonn that Is comprised of the lesser of 500-year (14.1 In) or 40%.of the PMP (16.1 In),*

(2) Immediately followed by a 72-hours dry period, (3) Immediately followed by the futl 72--hours PMP.

The 50().year rainfall depth over 72-hours Is t4.1 inches and it is lower than 400/o of the PMP and selected for PMF storm antecedent condition.

United States Nuclear Regulatory Commission Enclosure to Serial: RNP-RA/14-0012 Page 13of 31 Parameters needed to route flOOd hydrographs through the Lake Robinson Reservoir and Dam spHlway Include reservoir elevation-storage relatioftships, spillway elevation-discharge characteristics, and initial reservoir storage at the *beginning of the storm event.

The elevatlon-storage refationshlp for Lake Robinson Reservoir was developed based on the bathymetric survey for Lake Robln$0n. The fake has a storage capacity ot 27,560 acre-feet (AF}

below the nonnat pool elevation of 220.0 feet NGV029 and maximwn storage capacity of 51,861 AF below the embankment crest efevatlon of 230.0 feet NGVD29.

Water.etevation In the lake Robinson R8$8t'VQlr is controlled by two 7 F

~bi(Jli-~i~)~t~r *************

~

gates. '1he elevation-discharge relationships were devetop~::'rc-='3"""::'~~=~~

(4) (b)(7)W) operational proctcfurt, For the PMF anatysls, the gate OJ)erational rula was applied, and the Initial reservoir storage elevation at the beginning of the storm event was assumed to be at the plant operation pool elevation, 221.5 feet NGVD29; a historically high reservoir level.

For the PMP auesement of the HBRSEP site *final PMF simulation with nonlinearity effects was selected and applilct to Iha hydraulic model routing. The PMF scenario Is the watershed modet simulation that uses the watershed parameters with corrections to unit hydrographs, the MU$kingum-cunge routing procedure for the hydrologlc routing of slfb..basln hydrographs and comblnaflone of hydrograph& throughout the watershed Channels and 216 hours0.0025 days <br />0.06 hours <br />3.571429e-4 weeks <br />8.2188e-5 months <br /> PMF storm.

3.2.1.2 Hyctrat.tllOtlMllodololv/~/~

The hydraulic analysts completed for this ttudy was baaed on HEC*RAS. HEC-RAS Is a one-dlmenslonal model that can perform unstead-J flow routing through an open channet system that may also include culverts, bridges, levee&, tributaries, storage 8"888, and traveralng dams.

Unstea(ly flow analyses deals with flow conditions that vary ten1>0f'ally and spatially.

Lake Robinson and contributing river segments show that the flow Is mostly one-dlmenslonal, constrained by -natural narrow vaneys with steep side slopes and very little poselbUlty of a two-dimensional flow condition. Apptlcatton of a one-dimensional HEC-RAS model for Lake Robinson Is appropriate.

For the PMF flood wave routing, an unsteady HEC-RAS almulatlon was conducted for a 9.5 mHe segment of Black Creek, extending approximately 8 miles upstream and 1.5 mites downstream of the Lake Robinson Dam. Setectlon o1 this 9.5 mHe ses,nent provides the model with the capability to capture the backwater effects from downstream and the impacts from upstream bridges more accurately.

(b)(3) 16 U SC § 8240-l (d) (b)(4), (b)(7)(F) ea parameters for HEC-RAS model were developed based on fietd assessment and physlcally based earth dam erosion model* BREACH.

United States Nuclear Regulatory Commission Enclosure to Serial: RNP-RA/14-0012 Page 14of 31 (b)(3) 16 USC § 824o-1(d) (b,{4) (b)(7, F) 3.2.2 Allulte I Conclutlol'le Under the analyZed beyond design basis PMF condition, the HEC-RAS model h simulations show that the lake Robinson water swface elevation is J< >

0-1 NGV029 for with and without dam braach~JS~lm!!!U!!!la~tiOna

~

at~ H~BR~S~E~P!...!, !!e~~~~~~~-

§ 824o-1(d1 (b)\\4) (b)(7)(f; 8S com site grade Debris from the upstream watershed wiH not translate to the site due to the low vetocitles in the lake and the constricted crossing of State Road S-13-346 near the north end of the lake.

The estimated PMF elevations at take Robinson Dam with and without dam breach resulting from the HEC-RAS simulations are shown tn Figure 1.

United States Nuclear Regulatory Commission Enclosure to Serial: RNP-RA/14-0012 Page 15of31 (b)(3) 16 US C § 8240-1 (d). (b) (4). (b) (7) (F) 9tart111M......,

<<-t.MVD291 Stllt'l'lnlefnlatflMF-(b)(3) 16 U.S.C § 824o-1(d), (b)(4), (b)n(F)

• ,wpSftr Elnoaon

• 215 (ft, NGVD29}

fnd........... ___ (lld.,.......,....,..,.... ~.........

Claddllloa CoMlltDt'I

• IMF SbHm (11HR SOOWR* n HR DRY PERIOD+ n HR PMPI Begin J'Jme

• 3JOEQOU 1400 Ffgunt 1; Estiffllitecl PIIF Elenlions al...,_llobineon Dam wilt and without Dam8reachbj H!c.RAS Slmulationa (Note that PMF values include adjustment for non-linearity)

United States Nuclear Regulatory Commission Enclosure to Serial: RNP-RA/14--0012 Page 16of 31 3.3 STOAM SURGE 3.3.1 Approacll / Methodology The Probable Maximum Hurricane (PMH) was developed according to the methodoJogy and data provided in *Meteorological Criteria for Standard Project Hurricane and Probable Maximum Hurricane Windfields, Guff and East Coasts of the United States*, referred to hereafter as NWS

23. Because the project site is not at the Immediate coast, the storm strength was reduced using the approach of Kaplan & DeMaria. Due to 1he north-tc>-south orientation of Lake Robinson and the location of the study site at the southam end of the lake, tt was assumed that a wind bloWing north to south would result In the Probable Maximum Storm Surge (PMSS).

3.3.2 Computlllona0ilctlla1oft The storm surge was calculated using PMH wind speeds determined from NWS-23, Inland reduction calculations from Kaplan and DeMaria, topographic data from South Carolina Department of Natural Resources, and bathymetric data. The Inputs were:

depth d = 16.20 feet fetch F = 4.6 mites wind speed U = 119.3 mph angle c:r a 0 Applying these to the Zuider Zee equation yields:

surge S = 2.89 feet = 224.39 feet NGVD'a = 223.47 feet NAVD88 The wave conditions were calculated using the force of graYily, the wind speed, and the lake geometry:

gravity g = 9.81 miff fetch X = 1,268 m wind speed U10 = 119.3 mph= 53.33 mis Applying the calculations in the Coastal Englneerlt,g Manual yields:

wave height Hmo = 1.38 m = 4.47 feet wave period Tp = 2.53 seconde The wave runup and overtopping were calculated from the wave parameters, bathymetric data,

.,d the UOAR data from South Carolina Department of Natural Resources:

freeboard Re = 0.492 m = 1.61 feet slope tan(a) = 0.382

• wave height Hmo = 1.36 m = 4.47 feet wave period T P = 2.53 seconds Applying these to the Coastal Engineering Manual's equations from Ahrens for runup, and van der Meer & Janssen for overtopping yields:

runup ~

= 2.26 m = 7.41 feet= 231.80 feet NGVD29 = 230.87 feet NAVD88

• flux per unit width q c 0.0821 m3/a per meter of crest width = 0.884 ft'ts per foot of crest width Note that the surge elevation Is at 224.39 feet NGVD29 which is below the site grade 225 ft NGVD29. The wave runup may splash at the shoreline near the site. The flow rate is relatively small and will only affect the area along the shoreline. It will not generate any flood for the

United States Nuclear Regulatory CommisSlon enclosure to Serial: RNP*RA/14-0012 Page 17 of 31 interior area of the HBRSEP site. Water will not enter critical structures at the shoreline so long as they are above the runup elevatiOn or are sufficiently enclosed.

3.4$EICH&

The statie wlnd*lnduced water setup at the south end of the lake At\\ = 1.43 m (- 4.69 ft) is the initial seiche amplitude In Lake Robinson along the north-south direction. The potential amplitude of the fake selche in the east-west direction is 0.24 m (- 0.79 ft) near the Robinson Nuclear Plant $1te. Accordtng to.the UFSAR for the Robinson Nuclear Plant, the HBRSEP site grade is at 225 ft (- 68.58 m) NGV029. When the still lake water level is at the maximum allowable water elevation 221.5 ft (- 67.51 m), the water level *could rise to 67.51 m + *1.43 m =

68.94 m (- 226.2 ft) due to wind setup in the north-south dlrectiOn; which Is higher than the HBRSEP site grade (225 ft NGV029); wflife the water level*coufd rise to 67:51 m* + 0.24 m =

67.75 m (- 222.3 ft) due to wind setup In the east*west direction, which is lower than the HBASEP site grade. The results indJcate that the Jake water leYel subject to wind-induced seiche in the north-south direction could exceed the site grade: The maximum flOOd elevation caused by seiche can reach the floor elevation at the shoreline location. Although, away from the shoreline, the water level wtH drop as the flow pushes toward the power block. The flood level is expected to be lower than the floor grade when it reaches the buildings. Hence the seiche wHI not cause any significant flood probtem for the power block.

For the p,tentiaJ seiehe caused by seismic activities in the HBRSEP area, the Jong periods of the fundamental mode S8iche oseiltatlons fall wen outside of the period range where earthquake ground motions carry most energy, and It is thus unlikely that these modes wilt be generated in Lake Robinson. The partlcutar circumstances that could lead to the occurrence of mild sek:hing are not likely to occur in Lake Robinson.

3.5 'l'SUNAMI HBRSEP 1s*1ocated approximately 87 mt inland from the Atlantic coast, where tsunami hazards are relatively low, and 225 ft above sea level. Therefore, the HBRSEP Unit 2 site is not subjected to the effects of tsunami flooding.

3.1 tCE-N>UCED f:LOOOING HBRSEP winters are mild with the cold weather usually tasting from late November to mid-March. ~owever, only about one-third of the days in this period have mininum temperatures below freezing. Winters In the area are mild and there is no history of Lake Robinson freezing.

Consequently, Ice induced floodilg is not considered a viable flood hazard.

3.7 CHANNEL MIGAATIONOR OIVEASION Channel migration or diversion is the lateral movement of a stream channel across its valley and floodplain due to bank erosion or avufslon. Bank erosion occurs when the channel flow is fast enough to $COUF the bank. Most of the bank erosion occurs at the ou1side of meander bends due to the centrifugal fluid ctjnarnic forces exerted by the flow. h can cause the channel to migrate toward the outside of the bends. An erodl>le bank could be eroded rapidly during a high flood and result& in a channel migration. Awlsion is when a river suddenly abandons the old channel and shifts to a new chamel. It typJcally occurs at a meander or a highly active sediment transport river segment such as the river delta. During the avutsion process, the flow

United States Nuclear Regulatory Commission Enclosure to Serial: RNP*RA/14-0012 Page 18of 31 breaches the river bank and splNs out onto a new course. The diversion of water could cause a flood event for low lying areas near the new river course.

Other types of channel migration inch.Ide stream. capture, Whloh is a geomorphological phenomenon describing a stream that is diverted from Its original course and flows down to the course of a neighboring stream. Stream capture coutd cause a flood problem If the neighboring stream is not large enough to cany the flows from both streams.

3.7.1 Approactl/Metflodalogy This study evaluated the rates of lateral channet migration and channel diversion along the Black Creek (upstream of Lake Robinson Dam). to understand the effects of surface discharge variationa and surface flooding reeuttlng from channel migration and channel diversion on the Robinson Nuclear Power Plant site.

Bank erosion, which leads to channeJ migration and diversion, Is a functiOn of several variables:

flow dl8charge. slope and allgnment of the river, charactertatics of bank material, height of the eroding bank, flow depth, stream bank vegetation, seismic activities, and ice expansion.

Seven data 90uroes were established and evaluated for Black Creek for the ahannel migration and channel diversion cafculalion. These data sources are:

1. Aerial Imageries, topographic maps, and utetllle knagertes spanned for more than 70 years from 1941 to 2013.

2. Soll characteristics for the channel, channel banks and the overbank areas.

3. Channet meandering.

4. Riparian wgetatlon cover.

5. Seismic actMtles.

• 6. fee expansion..

7. Shear stress durtng the PMF event.

The seven data sources were supported by field reconnalssaooe and verifications. Stream centertlnes of Black Creek and it8 major tributaries were digitized and the centertlnas were overtak:J. Examination and comparison d the digitized stream llnes of Black Creek and Its major trit.>utaries did not reveal any evidence of natural channel migration or diversion.

Increases In peak flows can requfre a stream to enlarge Its channel cross-sectional area In order to carry the higher depth flows. The type of bank material can Influence a stream bank's yulnerabfflty. Bedrock Is highly resistant to eroek>n. Stream banks that consist of hlgh1y erodible gravels and sand are more sueceptlble to erosion. Most of the Black Creek and Its major tributaries banks are underlain by solt with a sUght to moderate hazard to water erosion, such as sandy foam, sandy day loam, clay loam, silty clay loam, and sHt loam. Banks underlain by soil with severe haZard to water erosk>n such as sand, silt, and gravel are more susceptible to bank erosion. This was found near Black Creek banks but In sman and limited areas which is untikely to *create a basJs for channel migration or diversion.

Riparian vegetation Is an Important factor in reducing the stream bank's susceptibility to erosion.

Stream meander bende before and after a major flood without riparian vegetation were nearly five times as Ukely ae vegetated bends to have undergone bank erosion. The vegetated banks

United States Nuclear Regulatory Commission Enclosure to Serial: RNP-RA/14-0012 Page 19of 31 detected by th& aeriat imageries, topographic "141>$, and field verification for Slack Creek and Its major tributaries are indtcetors of stream bank stabllity.

Black Creek and its major tributaries are charecteriZed by long, straight reaches separated by short, steeper, sinuouS reaches, that yields typically low average sinuosity, thus provides an indication of stream stability.

A seismic fault line and an inferred fault fine cross Siad< Creek In two focatlons. Black Creek and some ot its major tributaries were found to have a fow potential-for soil liquefaction and for the possible occurrence of a landslide t,locking or limiting stream flow.

toe expansion effects in Black Creek are expected-to be Hmited (minor freezing) and are not expected to cause stream flow bloddng that could lead to channel flooding. Therefore, channel migration or diversion during winter months fs not a concem.

Shear strees distribution over c,oss.seotion in open channel is an important factor to assess channef resistance to bank erosion. t1'tl shear stress values in th& reach of Black Creek upstream of Lake R~ Dam during the PMS: event, were reviewed and comparectto typical sheer stresses resisted t,y lhe soil and vegetation types found on the channel banks and the overbenk areas of Stack Creek. The Sheer stresses are lower than the sheer stresses resisted by the soil and vegetation found on the banks and overba.nk areas of Black Creek except for four cross-sections which slightly exceeded the lower limit of the resisted shear stress.

However, the location of these cross-sedionS iS approximately 7.5 miles.upstream of the Robinson Nuclear Power Plant site, and as a result it i8 unlikely to create a basis for channel migration or diversion that would cause flooding at the plant site.

3.7.2 Rte..n.JCoftcfUIIOn The above analySis indiCates that Black Creek (upstream of lake Robinson Dam) has a stable stream alignment with no conclusive evidence of lateral migration and diversion, bank erosion, or sediment bar deP0$ition while maintaining Its sinuosity and gradient.

Therefore, flooding risk to the Robinson Nuclear Power Plant site caused by river channel migration and channel diversion of Black Creek Is tow.

3.8 DAM 8REACHES ANO FAILURE&

Two dam failure flooding scenarios were evaluated for HBRSEP. The first scenario, Scenario A, addresses failure of dams upstream of Lake Robinson and the subsequent flooding in rivers and streams and impact at HBRSSP. The second scenario, Scenario B, addresses the failure of the Lake Robinson Danrdue to PMF.

3.8.1 Scenario A-...... Olnt Breed and Failure 3.8.1.1 Approaob /llltflodology /Coall)Utalion The hydrologic model developed for the Probable Maximum Rood (PMF) simulation was used to svnutate the runoff produced by the 500-year event at lake Robinson Reservoir.

The 600-year watershed model simulation uses the cali>rated and validated model paramete,s, Muskingum-Cunge routing procedure for the hydrologic routing of sub-basin

United States Nuclear Regulatory Commission Enclosure to Serial: RNP*RA/14-0012 Page 20 of 31 hydrographs and combinations of hydrographs throughout the watershed channels and 500-year precipitation with SCS Type II distribution over 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

Acoording to NRC ISG guidance the Initial water surface elevation should be set as the 500-year flood event elevation, which is 221.36 feet NGV029. However, to provide a more conservative approach, the maximum operational poo1 elevation of 221.5 feet, NGV029, was used as the initial water surface etavation for the computations.

According to SCDHEC guidance, dams considered for its inventory were 25 feet or more lo height or that had the capability of impounding SO-acre-foot of water or more. (with water up to tfle top of the dam); additionally. dams smaller than this were also lnefuded In the Inventory If it

• was Judged thelr failure would cause appreciable property damage or any loss of life.

3.s.1.2 1nc*MQIMMlu.t Dim*'

(b)(3) 16 USC § 824o-1(d) (b)14J (b}(?J(F/

a. If Initial water surface elevation is based on 50().year flood event:

500-year flood storage = 30145 acre-foot 50().year flood etevation = 221.36 feet, NGV029 (b)(3) 16 USC § 8240-Hd) (b)(4 1 1b){7)(F 1

• 1,. U Initial water surface elevation Is based on Maximum operattonaJ pool level:

Maximum operational pool flood storage = 30364 acre-foot Maximum operational pool flood elevation = 221.S feet, NGV029 l(b)(3) 16 USC § 824o-t(d) (b}(4) (b)(7XF)

[3.

(b)(3)16USC FoHowing NRC ISG procedures, it was detennined that all

--- additionatseDHECdamsand§a24ti,1cdJ (bl ponds were "tnconsequentiar because they were not identified by the National Inventory of c4,. !bl(7J!FJ (b)(3)16 usc_:~o\\:,~--=V:-~~:':=:~,~~== ~t:

,}2,~~~_{~f (bl These dams would have min*~;;, adverse failure consequences beyond the dam owner's property.

s.a.1*.s NoncrttJcal Dim*

All upstream NIO dams, -,~~-

>l~1-,~e....,f _._%._.

~z-~:-f4...

0

....., were evaluated by the Volume Melhod as described in NRC ISG to identify their potential impact as "noncriticar or *crtttcar dams. According to NRC ISG guidance the initial water surface elevation should be set as the ~year flood event elevation, whk:tl is 221.36 feet. However, to provide a more conservative approach, the maximum operational pool elevation of 221.5, was used as the initial water sulface elevation. In

United States Nuclear Regulatory Canmlssion Enclosure to Serial: RNP~RA/14-0012 Page21 of 31

~b~~l~~~l~<~>-* addition, volume -from each of the+ ********* I was added and the resultant elevations were (4) (b}(?)(Fl determined using elevation-storage relationship.

3.8.1.4 RetUlttl/Conclutlon (b}(3) 16 USC § 8240 1 (d} (b)(4) (b)(7)(F)

I 3.8.2.1 Approtcb /..... odOlogy /Camputatlon The HBRSEP dam breach eafcufatlons are performed based on the standard assumptions conforming to NUREG/CR-7046 and NTTF 2.1 requirements.

The analysis estimates the dam overtoppfng breach caused by the PMF uu,g the BREACH model. The BREACH model ts a physically based simulation model to predict the breach characteristics and the discharge hydrograph emanating from a breached earthen dam. The BREACH model includes a hydrauHc simulation component which uses conservation of mass to determine reservoir elevation based on Inflows and outflows through the spillway, dam overtopplng, and the overtopping breach opening. However, the model uses a maxJmum of eight points to represent input relationships such as swtace area-etevation of the reservoir, elevation dJscharge of the spillway, and inflow hydrograph. These relationships were stmpllfied from their original high-resolution format to accommodate this model limitation. Therefore, the resulting peak flow timing, pool elevation, and peak flow magnitude are affected by the slmpllflcatlon. Because of the high accuracy of the HEC-RAS model in representing the above mentioned relationships, the breach characteristics Including the elevation at which breach formation starts, breach progression cuNe, and final *breach bottom elevation and width are used in the HEC-RAS model to estimate the maximum pool etevatlon and breach flow.

3:8.2.2 -.u111 I Conclullone The BREACH model results are transferred to the HEC-RAS Hydraulic model to route the full PMF inflow hydrograph through the reservoir using dam breach characteristic& from this

United States Nuclear Regulatory Commission Enclosure to Serial: RNP-RA/14-0012 Page 22of 31 calculation. The HEC-RAS model detem\\ines the maximum reservoir elevation and dam outflow hydrograph.

The results show that the breach initiation starts at about the beginning of dam overtopping and COntinU8SfOr b)(3J16USC §824o-1!dJ (b)l4l (b~7~F 3.9.COUBIN&D EFFECT FLOOD 3.9.1 Approecb/~

Combined-Effect floods 818 events considered f8asonably fDcely to occur at the same time at a given locatJon, and are used to develop an adequate desifJI flood basis. Recommended combinations of events are dlscu$Sed in ANSI/ANS 2.8 1992 Section 9.2, and also in NUREG/CR-7046 Appendbc H. The HBRSEP Unit 2 site is bounded by Lake Robinson on the east and a raHroad on the west. The 171.5 aquere mile Black Creek drainage basin feeds the Lake RobinSon Reservoir and is subject to a PMF resulting from PMP over the watershed. A Probable Maximum Hurricane occurrence was also considered aince the site ts approximately 87 mt tram the nearest coast The Lake Robinson reservoir Is subject to wln(t.generated setup and wave rmup. The HBRSEP site could potentially be flooded bV dam breaks upstream of Lake Robinson due to a seismic event. The plant site itself is subject to locat Intense precipitation. No other flood events such as tsunamis and channel migration have -been identified as potential hazards at the site. Combined events applicable to the site are as follows.

3.9.1.1 Flood$ Caulld By "8olplllllon Ewnta Three altematives for combined precipitation events were analyZad.

(bX3) 16 USC § 8240-l(d) (b){4) (b)(7,(Fl (ii) The wave runup induced by 2-year wind speed, combined with lesser of either one-half the PMF or a 500-year flood coincident with upstream dam faHures. The maximum nonnal pool elevation ts r than the 500- ear flood elevation and was used as a more conservative ti (bX3) 16 USC § 8240-l(d) (b)(4) {b)(7)(F)

(iii) The PMH-lnduced PMSS combined with the maximum controHed lake level. For the PMSS event, the maximum wave runup level on the embankment near the HBRSEP site is 231.80 ft NGVD29. This elevation is higher than the HBRSEP site grade of 225 ft NGVD29.

(b)(3) 16 USC § 8240-l(d) (bJ{4) (b){7)(F)

United States Nuclear Regulatory Commission Enclosure to Serial: RNP-RA/14-0012 Page23 of 31 3.9.1.2 FloodaCauNdby 8'1smlc D-,n Faffur. Ewnt&

ANSVANS 2.8-1992 Section 9.2.1.2 gwes two altematives for ca1culatlng overall PMF due to dam failure. ANSt/ANS 2.8-1992 recommends using the higher result of the two alternative combinations as the design basis for seismic dam failure floods:

Alternative I for dam failure events requires a computation for dam failure that coincides with the 25-year recurrence peak flood. However, Altemative II has a higher flood potentia}

because both the Of'MHlaH PMP and th& 500-year recurrence rainfalls are larger than the 25-year recurrence rainfalt. Thus, only Attemative fl was calculated because of the farger rainfall,

\\\\tllch produces a higher flood as recommended by ANSt/A,&2.8-1992.

Alternative fl also appUes to the fk>od caused by dam failure. The 2-year maximum 1-hr, over-water wind speed was taken to be SO mph. This wind speed was adjusted for fetch lengths ~nd was oriented on any critical fetch that would produce maximum wave runup at or.near any safety-related structure at the peak water level of the PMF.

The flood due to the 500-year 24-hour rainfall coi1cldent with dam failures upstream of Lake Robinson was determined. The 500-year flood elevation Is 221.SS ft NGV029. To provide a conservative approach, the maximum normal pool elevation of 221.50 ft NGVD29 was used Instead of the 500-year etevatlon. The peak flood elevation for this event can be surtimarized as follows:

Maximum Normal Poot Elevation: 221.50 ft r;:

(b)(3) 16 USC flood depth Increase caused by dam faifure GV029,1J,J------------;.§ s240:1 (d), (bl Peak water level including maximum normal pool elevation and dam failure:

(b)(3)16USC I I

~

~.~2.~?~:(?J: (br-----.... -_-_ _,ft NGVOc-;.::,

The wave caused by the 2-year recurrence wind can be calculated as foffows:

2-year recurrence wind: 50 mph Adjusted wind speed for duration of t = 4945 sec: 48.96 mph (21.89 mis)

Wind setup caused by 2-year wind: 0.46 ft Wave height caused by 2-year wind: 3.3 ft Wave period caused by 2-year wind: 2.7 sec

{b}{J} 1ti US t; § 8240 1{d} (b)(4) {b)(7J(F)

Therefore, the peak flood elevation for the scenario of 500-year flood coincident with dam failure and 2-year wind waves is given by (note maximum normal poof starting elevation Is used for additional con$8rv&tism):

United States Nuclear Regulatory Commission Enclosure to Serial: RNP-RA/14-0012 Page24of 31 Peak flood elevation = maximum normal pool with dam failure + 2-year wind setup +

waverunup (b)(3) 16 USC § 824o-1(d) (b)(4), (b)(7)(F) 3.9.1.3 Ftooctt Aloftt the.._ of lnc1oNd9ocliea Of Weter For shore locations of an enclosed water body such as the ~BRSEP site, PMH..fnduced PMSS includes the following altematJvesfor combination (ANS 2.8-1992 Sedkm 9.2.3.1 ):

\\ *...

a) Probable Maximum Surge and seiche with wlnd,,wave activity.

b) 1c,o.year or maximum controlled levet in the water body, whichever Is 1ess The PMH-induced PMSS on Lake Robinson has been evatuated using methods In the Shore Protection Manual, Second Edition. The maximum controlled water levet for Lake Robinson is 221.50 ft NGVD29 per the HBRSEP Lake Robinson Spillway Equipment Operational Manual.

The peak flood elevation for the PMH-induced surge and wave runup is the sum ct the lake elevation (221.50 ft), PMH PMSS (2.89 ft) and wave n.mup (7.41 ft) for a total of 231.80 ft

.NGVD29.

The 100-year flood was calculated using the MEC*HMS model with basin data and the 100-year recurrenc& rainfall from NOAA Atlas 14. The calculated 100-year flood elevation is 221.15 ft NGVD29 which Js less than the maximum controlled level.

For the PMSS event, 1he m*um wave runup level on the embankment near the HBRSEP site is 231.BO ft NGV029. lhis elevation Is higher than the HBRSEP site grade of 225 ft NGVD29.

United States Nuclear Regulatory Commission Enclosure to Serial: RNP-RA/14-0012 Page25of 31 3.9.2 Reeuftt The Combined-Effect flood results are Shown in Table 3.

T1ille.1.:--

Flood Aoocs.CauMClt,r -----

Wlftd-.

~,,...

(NGVD29).

rvnup

,i) PMF with 2-year wind (b)(3) 16 ft (b)

,b) ft causttd wa~ n.,nup USC§

13) 16,

(3) 16 coincident with dam breach 824o-1 USC USC rd) (b)

§ -

§8240

,ii) ~year flood COlncldent (4/ (b)(7, 8240-

-1(d) with upstream darn failures -

(F) ft 1(d) ft (b}(4) rt (b)(4 (b)(7) and 2-year wind (b, 71 (F) lrt:

,Hi) PMSS event. the ".,~

221.50ft 2.89ft 7.41 ft waverunup Floodt Cauaed t,v llllniie SIUI__,..,. 2-,_,wlnct Wave D*t:.nur.*

(NGVD29).. fUl'MIP Maximum nonnal pool wiU1 t;' 3J 18 USC b 3) 16 tb) ft dam failure

,L'ov-1(

b JS C ~ ft

13) 1 4/ (l,7 F J24o-1 USC dt IbJI41

§82do-

~

max. water levtl (NGV029) 233.21 ft 229.56ft 231.80ft

~

"'8X,WJ111rfevel (NGVD29)

(b)(3) 16 U S C

§ 8240-l(d) (b)

(4) (b )(7)(F)

United States Nuclear Regulatory Commission Enclosure to 5erial: RNP-RA/14-0012 Page26of 31

4. C9Mhll9N WJBl<al!BWIDlltt lA§IS For each flood hazard reevaluated, the result was compared to the CL8 flood hazard and protection and mitigation features to determine whether the established site elevations were exceeded. The results are summarized and discussed in Table 4 below.

Tlble4. -

aon Of Flood &.ev9la Floodttazant Location Flnllhtet Protilltile llaxlfflum Floor Flood. ft NBVD29 Ellvallon (FFE),ft NGVDlt CL8

£VAL Local Intense 8eeTable2 Prec!pltatlon Roodlngin Lake ROblnSon 218-hOur NIA (b)(3)16USC §8240-l(d)

Streams and Hee-RAS w/o Robinson lbH4) {b){7)(F)

RiversPMP Dam Failure Lak8 Robinson 216-hour NIA HEc-MS w/ Robln&on Dam Failure Dam Lake Robinson from NIA Bruches and upstream Dama Failures Coollng Water Intake NIA St9nnSurge Wind Setup (Surge)

Along Shore NIA 224.39 WaveRurq>Along NIA 231.8 Shore Seiche Lake Robinson Shoreline NIA 226.2 Tsunami Not an applicable Flood Hazard to this Plant Site.

Ice Induced Not an applicable Rood Hazard to this f'lant Site.

RQodlng.

Channel MlgratiOn or Not an applicable Flood Hazard to this Plant Sita.

Diversion Combined Floods caused by NIA (b)(3) 16 Effects oreciDltation events USC §8240 1 (d) (b)(4 ),

F1ooda caused by seismic dam fatture NIA (b){7)(F)

Floodl caUl,ld by atonn NIA 231.8 surge events

United States Nuctear Regulatory Commissk>n Enclosure to Serial: RNP-RA/14-0012 Page27ot31

.t.1 LOCAL tNTENSE PAECJPff'AtlON Local Intense Precipitation is not considered in HBRSEP's CLB. Therefore, the analyzed flood levels were compared to -the finished floor elevations of the various buildings to detennine if potential flooding of components could be Impacted. The results of the evaluation indicate that the predicted flood levels witl be above the floor elevation of several of the onslte buildings and, therefore, this mechanism wiH beeonsidered in the integrated assessment.

4.2 f1..000ING IN.,._.MOANERS (b)(3) 16 USC § 824o-1(d) (b)(4} (b}(7)(F) wJ I be cons a

4.3 STORM 8UAGE Local Stonn Surge was not considered in HBRSEP't CLB. The surge elevation was evaluated to be at 224.39 ft NGVD29 Ytttich Is below the sit& grade 225 ft NGVD29. The wave runup value of 231.80 ft NGVD29 Is a hypothetical runup at grOWld level whlth may &plash at the shoreline near the site. The flow rate Is retativety small and.will only affect the area along the shoreline. tt-wiU not generate any flood for the interior area of HBRSEP site. Water will not enter critical structures at the shoreline as tong as they are above the runup elevation or are sufficientJy enclosed.

4.4 SEICHE Seiche was not considered tn HBRSEP's CLB. The reevaluated values indicate that the lake water levet subject to wind-induced sek:he In Che norttKouth direction could exceed the site grade; however, th& floor grade of each building is one foot above the ground at 226 ft NGV029 or* higher. The maximum flood elevation caused by selche, 226.2 ft NGVD29, may reach the floor elevation at the shorellne location; however, away from the shoreline, the water level will drop as the flow pushes toward the power block. The flood level will be tower than the floor grade when it reaches the buildings. Hence the selche wUI not cause any significant flood problem for the power block.

For the evaluated potential eeiche caused by seismic activities in the HBRSEP area, the long periods of the fundamental mode seiche oscillattons are well outside of the period range where earthquake ground motions carry most energy, and it is unlikely that these modes* wiU be generated in the Lake Robinson.

4.5

• TSUNAMI Flooding from tsunami was not considered in HBRSEP's CLB and was screened out of the analysis based on the plant's inland location.

United States Nuclear Regulatory Commission Enclosure to Serial: RNP.. RA/14-0012 Page28of 31 4.6 tCE-INDlfCEO R.OODeNQ Ice-Induced Flooding was not considered in HBRSEP's CLS and was SCf88fled out of the anarysis based on the historically mHd winter temperatures at the site.

4.7 CHANNEL MIGRA1IONOR DNERSION Flooding from channel migration or diversion was not oonsidered in HBRSEP's CLB. Based on the current and historical characteristicS of the Black Creek tributary, the evatuatlon concluded that the expeded flooding risk to the &He is minimal.

4.8 DAM8AEACHEl,ANDFMURES

• Dam brea or failures (b){3 16 USC § 8240-l(dl (b)<4\\ (bi 7)(F)

NGVD29) and, therefore. wilt not affect any e (225 ft The evaluation of the Lake Robinson dam for PMF~cosm-idi tmitiOnS

!ffl' m..1a~H[;tha

~ t~LQ.'sl:@mm?.!J[)Qj2l, breached.

(b)\\3) 16 USC § 8240-1 (d) (b)(4} (b){7)(F) 4.8 COMIINIOEFFECfR.OODS Combined effect floods were not considered in HBRSEP's CLB. Three tnstances were evaluated: floods caused by precipitation events, floods caused by seismic dam failure events and floods aJong the shores of enclosed bodies of water.

For the oombined effects associated with precipitation events, the peak water level Included the sum of the PMF flood level, Wind setup and lit wave heights, and was detennined to be

• • • • • • • • • . ?~~~~!~Js(;,

ft NGVD29. This elevation is higher than the HBRSEP's site grade of 225 ft NGVD29 an wit (4J (bJ(7J(FJ oonsidered in the integrated assessment.

for floods caused by seismic dam falture including the 500-year event (221.36 ft), for conservatism 1he maximum nonnal pooto*

of 221.50 ft was used coincident with 2-year (b)(3) my.~. ~... ~Ind waves,.the peak flooclelevation was ft NGVD29. This elevation Is also higher than

~.~2,~?:~,{~: (b) HBRSEP's site grade of 225 ft NGVD29 conaldered in the integrated assessment.

For floods along 'the shores of enclosed bodies of water for the PMH-lnduced Probable Maximum Storm Surge event. the maximum wave runup level on the embankment near the HBRSEP site Is predicted to be 231.80 ft NGVD29, which Is 6.8 ft above the HBRSEP site grade of 225 ft NGVD29.

United States Nuclear Regulatory Commission Enclosure to Serial: ANP-AA/14-0012 Page29of 31

5.

INTERIM ACffl>NS Duke Energy has determined that some flood levels exceed the Current Uoensing Basis (CLB).

Of the flood hazard reevaluations perfonned for Robinson Nuclear Plant (HBRSEP), two events were *selected as a basis for developing Interim actions. The Local Intense Precipitation (UP) event is a rainfall event that causes on-site flooding and is conservatively assumed to occur without warning. The probable maximum flood (PMF) event causes the highest on-site flood levels.

&.1 EVAL.UAt£D&VEN1'SFOR811ER.OOOING 5.1.1 Local lntenttflrtclpllttion (UP) Event The LIP event is descrt,ed in Section 3.1. As the stonn is conservatively assumed to occur without wamlng, no manual actions are credited prior to the storm. Peak flood levels occur approximately one hour Into the event, and flOoding occurs across the entire powar block area.

Rain continues tofall for six hours and water starts to recede after the rain ends.

5.1.2 Prob;ble llalfflum Flood (PMF) Evtnt The PMF event is described in Section 3.2. This event Is assumed to occur with sufficient advanced warning that enables a safe plant shutdown. The entire storm event consists of an antecedent storm of 500-year probability that lasts for 72 hr, a dry period of 72 hr, and a 72-hr Probable Maxmum Precipitation (PMP) event. Water flow from the antecedent storm Is within the HBRSEP spillway design basis. and no site flooding occurs during the antecedent storm and the following dry period.

5.2 IMPACTS OF 11tE EVENTS (b)(3) 16 U.S C § 8240-l(d) (b)\\4) (b)(7)(F) 5.3 EVENT RESPONSE Interim adlons have been developed in response to the events. The interim actions do not adversely affect any existing site structures, systems or components. Procedures have been prepared and training performed for the interim actions, except for the completion of training on the use of the Portable RCS Boration equipment, whieh is in progress and will be completed prior to entering MODE 4 during plant restart from the current outage (R229F3).

5.3.1 Core CooliftO HBRSEP will mmtaln core cooling by supplying Auxiliary Feedwater (AFW) to the Steam Generators (SGs) for decay heat removal consistent with existing plant emergency procedures.

United States Nuclear Regulatory Commission Enclosure to Serial: ANP*RA/14-0012 Page30of 31 Valve alignment would be performed locally per procedure. In addition, HBRSEP will preserve or re-establish the capability to add water to 1he RCS for Inventory control and r&activity control with boration.

Additional actions to achieve core cooting related to each specific flooding event are detailed in Sections 5.4 and 5.5.

5.3.2 8plM F*Pool Cooling Loss of AC power will result In a loss of power to the Spent Fuel Poot (SFP) Cooling pumps. An existing procedure is In place to deploy a portable pump to deliver water to the SFP prior to uncovering the top of the fuel.

5.3.3 As long as water is supplied to the SGs and th& ACS is borated, containment Integrity will be maintained for a minimum of two days. After two days, the Emergency Response *OtganiZation (ERO) will take any additional actions needed.

5.4 INfERIII AC1'0N8RELAtEO TO 11tE UPMNI' 5.4, 1 **-Genlwllo,Coollng Feedwater flow must be provided to the SOa within 61 min d the reactor ~

due to flooding to provide adequate decay heat removal. Steam generator COOiing will be provided from the "C" AFW pump. The diesel generator that powers the *c: AFW pump, fs protected from the LIP event. The *c-AfW plffll> is supptied t,v the Condensate StOJage Tank. This tank may be re-fnled with the "C" Oeepwell pump powered by its installed diesel generator. The UP event does not affect the "C" Oeepwetl pump or its associated diesel generator.

Manual actions consist of starting the <<c" AFW pump and its diesel to provide AFW for SG cooling during the UP.,.,.., per procecllre. The diesel may be started remotely from the "C" AFWpump.

5.4.2 RCS Inventory and 8oratJon HBRSEP has the capability to add borated water to the RCS using the guidance provided in Westinghouse WCAP-17601 P, "fleactor Coolant System Response to the Extended Loss of AC Power Event for Westinghouse, Combustion Engineering, and Babcock & Wilcox NSSS Designs," Revision 0, August 2012.

To suppty a source of borated water, dry boric acid will be mixed in a portable tank. This tank will be fiffed using a portable pump currently stored on-site. The borated solution wiU be injected Into the RCS using a new high pressure, portable diesel-driven pump. HBRSEP will relocate this portable equipment near the Refuelilg Water Storage Tank (RWST) after flood levels have receded. It Is not necessary to pre-stage the equipment as there Is sufficient tine to Initiate boratlon with the portat,te equipment following the reactor trip. All required equipment wm be stored on--site in an area that will maintain the equipment available following a UP event.

United States Nuclear Regulatory Commission Enclosure to Serial: RNP-RA/14-0012 Page31 of 31 5.4.3

~llt FUii l'ool Cooling Existing procedures wiH be ~ilized to fill the SFP after the LIP event. The necessary equipment does not need to be pre-staged for this event as the flood tevel wilt have sufftcientty receded before cooling water must be delivered to the SFP.

5.5 IN1'eAIM ACtlONS RElAlEO TO 1ME PIIF EVENT The trigger for this Interim action is notification of a severe stonn system approaching that has the potential for significant rainfalt. Response to Ute notification wiU be to utili%e the Event Response and Notification procedure.

Additionally, lake elevation may atso trigger plant r8$pOl'IS9. The Tainter gates for the dam can control 1ake elevation and prevent flooding during the antecedent stonn. An additional response for the PMF event was Jmplemented such that If the gates are opened to meat the criteria in the plant's Emergency Notillcation Procedur&. the Unit Threat Team will be activated.

s.s.1 s... GtnM&ot CooHnt Procedures were revised to include guidance for the Unit Threat T earn review of actions for a PMF event. If a known ma;or stonn ts heading toward the plant, the conservative decision*

making process of the Unit lhraat Team will ensure a safe plant shutdown prior to site flooding that provides enough time for adequate core decay heat removal Tempc,ra,y equipment could then be utilized as needed. The ptanfe £Jdreme Damage Mitigation Guidelines (EDMGs) have been revised to address pr~

a new pul'l1) above the expected flood elevation to provide AFW to the SQs from the Condensate Storage Tank or an attemate source.

5.5.2 RCStrMtdOtf*8orlliOn A safe shutdown 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> prior to the main flooding event wlft ensure that RCS boration will be accomplished. Thereafter. for RCS inventory control, a high pressure, pe>rtable diesel-driven pump will be available for use after the flood recedes.

5.5.3

~Fuel Poof Cooling Existing OUidance provided in the EDMGs will be utiUzed to fill the SFP. The necessary equipment will be available above the *flood elevation to ensure It is unaffected by the PMF event.

United States Nuclear Regulatory Commission to Serial: RNP-RA/14-0012 Page 1 of6 EHCI.OSURE2 FLOODING ttneMI ACTIONS FOA tt. e. R09IN80N S1'EAM EI.ECTRIC PUNT, UNJTNO. 2 DOCKITNO. 50-211

United States Nuclear Regulatory Commission to Serial: RNP-AA/14-0012 Page 2 of6 Introduction Duke Energy has determined that some flood ievels included Jn the Flood Hazard Reevaluation Report contained in Enclosure 1 of this submittal exceed the Current Licensing Basis (CLB) flood levels for H. e. Robinson Steam Elednc Plant, Unit No. 2 (HBRSEP). As stated In Reference 1, Required Response Item 2, in ac=cordance with the NRC's prioritization plan, within 1-to 3-years from the date of this information request, submit the Hazard Reevatuatlon Report.

Include the interim action plan requested in item 1.d, which states that the report should contain interim evaluation and actions taken or planned to address en, higher flooding haZards relative to the design ~sis, prior to completion of the integrated ~*nt. If necessary.

1. EvalcMtdE.,_forSil*FIOodlnf Of the flood hazard reevaluations performed for HBRSEP, two events were selected as a basis for developlng Interim actions. The locat intense ~ltation (LIP) event is a rainfaft event that causes on-site flooding and is conservatively assumed to occur Without waming. The probable n\\&Jdmum flood (PMF) event causes the highest on-site flood levels.

1.1. ~I Intent. Preclplullon (UP) £vent The UP eveht is described il Section 2.1 of the Robinson Nuclea; Plant Flood Hazard Reevaluation Report. As the storm is assumed to occur without warning. no manual actions are credited prior to the storm. Rainfall occurs at the beginning of the event with peak flood levels occurring within the first hour. Maximum flood tevels vary above finished floor elevations across the entire power block area.

1.2. P10Nb1t....._ Aood(flllF) E-nt 1'he PMF event Is described In Section 3.2 of the Robinson Nuclear Plant Flood Hazard Reevaluation Report. The entire storm event consists ot an antecedent stOfm of 500-year probability that laSts for 72 houri, a dry period ot 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, and a 72-hour probable maximum precipitation (PMP) event. The PMP event Is assumed to occur with sufficient advanced wamtng to enable a safe plant shutdown. The antecedent storm delivers rainfall amounts included in the current licensing basis, and the PMP storm provides additional ralnfaU amounts that ar, beyond design basis. Water surface elevations at Lake Robinson overtop the dam eventually causing dam failure.

No site flooding occurs during the antecedent stonn and the following dry period. S.lte flooding begins approximately 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> after the start ot the PMP event. Flood levels Increase until the dam fails. Flood levels recede to below site elevation withln approximately 9.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />.

1.3. lmpacta of the henle

United States Nuclear Regulatory commission to Serial: RNP-RA/14-0012 Page3of6 2.EventRfspo,u,t The ~nterim actions do not adversely affect any existing site structures, systems or components.

Procedures have been prepared and training performed for the Interim actions, except for the completion of training on the use of th& Portable AGS Boration equipment, which is in progress and wfll be completed prior to entering MODE 4 during plant restart from the current outage (R229F3}.

C.Coo1tng HBRSEP wilt maintain core cooling by supplying auxiliary feedwater (AFW) to the steam generator for decay heat removal consistent with existing plant emergency procedures: Valve alignment WOUid be pelfonned locely per procedure. In addition, HBRSEP will preserve or reestablish the capabiity to add water to the reactor coolant system (RCS) for inventory control and readlvlty controt with boratk>n.

• Additionel actions to achieve core cooling related to each specific flooding event are detailed in Sections 2.1 and 2.2.

Splftt Fuel Pool Cooftng Loss of AC power will result in a lo$& of power to the spent fuel pool (SFP) cooling pumps.

HBASEP estmates that the top of the fuel could be uncovered after approximately 45 hours5.208333e-4 days <br />0.0125 hours <br />7.440476e-5 weeks <br />1.71225e-5 months <br />. An existing procedure is In place to deptoy a portable putnp to deliver water to the SFP. Additional actions related to each specific flooding event are detailed In Sections 2.1 and 2.2.

Contatrunent lnllgrlty As tong as "8ter is suppfted to the SGs and the RCS is borated, containment integrtty will be malr}~in_ed for a minimwn of two days. After two days, the Emergency Response Organization (ERO) win take any additional actions needed.

2.1.,-rlmAttioneRe1attdtotlleUPEvent

...... Generator Cooling FeedWater flow must be provided to the steam generators within 61 minutes ot the reactor trip to provide adequate decay heat removal. Steam generator cooling wiD be provided from the "C" AFW pump. The diesel generator that powers the "C' AFW pump, is protected from this flooding event. The "C' AFW pump ia supplied by the condensate storage tank. This tank may be r&-

fllted with the "C' Oeepweff pump and installed diesel generator. The UP event does not affect the "C' Oeepwell pump or Its diesel generator.

Manual actions consist of starting the "C" MW IU1'1P and diesel to provide AFW for steam generator cooling during the flood per procedure within 61 minutes.

ACS tnveMCMy and 8orallon HBRSEP has the capability to add borated water to the RCS as shown in W~use WCAP-17601 P, Reactor Coolant System Response to Che Extended Loss of AC Power Event for Westinghouse, Combustion Engjneering, and Babcock & Wilcox NSS Designs, Revision O, August 2012.

United States Nuclear Regulatory Commission to Sertal: RNP-RA/14-0012 Page4 of6 To supply borated water to the RCS, dry boric acid will be mixed in a portable tank. This tank wlH be filled using a pot1able pump. The borated solution witl be injected Into the RCS using a new high pressure, portable dlesel driven pump. HBRSEP will start relocating this portable equipment near 1he RWST after flood fevets have receded. ft is not necessary to pre-stage the equipment as there Is sufficient time to Initiate boratlon with the portable equipment following the reactor trip. AH required equipment will be stored on-site Jn an area that wm maintain the equipment available following a LIP event Spent Fuel Pool Cooling Existing procedures will be utilized to fut the spent fuel pool after the flOOding event. The necessary equipment does not need to be pnJ*staged for this event as the flood level will have receded.

2.2. tntertm Action* Allltld to the IMF Evtnt Trlaaer The trigger for this Interim action Is notfflcatton of a severe storm system approaching that ha&

the potential for significant rainfall. Response to the notification will be to utHize the Event Response and Notification procedure.

Additionally, lake elevation may also trigger plant response. The talnter gates for the dam are able to controt lake elevation and prevent floodiig during the antecedent storm. An additional response to the PMF event has been Implemented such that If the gates are opened to meet the criteria fn the Event Response and Notification procecllre the unic Threat Team wlH be activated.

Ste*m GeneratorCoolfnt Procedures have.been revised to lnctude guidance for the PMP flood event for the Unit Threat Team to review.,,. a known major storm la heading toward the plant, the conservative declalon.

making process of the Unit Threat Team will ensure a safe plant shutdown prior to the main flooding event for adequate core decay heat removal. Temporary equipment could then be utilized as needed. Procedures have been revised and addresses pre-staging a new pump above the expected flood elevation to provide AFW to the steam generators from the condensate storage tank or alternate source.

ACS Inventory and 80..-tlon A safe shutdown within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> prior to 1he main flooding event wm ensure that RCS boratlon will be accomplished. Thereafter, for RCS Inventory control, the new high pressure, portable dJeseklriven pump will be available for use after the flood recedes per new procedures.

Spent Fuel Pool Cooling Existing procedures wlU be utiJIZed to fill the SFP. The necessary equipment will be available above the flood elevation to ensure that sufficient water Is supplied to the SFP from the RWST or attemate source.

United States Nudear Regulatory Commission to 5erial: RNP*RA/14-0012 Page5of6

3. Summary of Interim Action CoMIQitmenta 1be following table summarizes interim actions taken or planned and their respective completion dates.

Robinson Steam Electric f:>>lant, Unit No. 2 - Flood Hazard Interim Action Commitments 111M

........... ~

• --~T--or... nNtoT--ll~fnllle Number N..._.....,ll11811c,nReport 1

LocaliZed Intense Precipitation (LIP)

1. lnsta11ed flood protectiOn for the -c* AFW diesel and startup panel.

Event

2. fmplementect new procedures that Inject borated water into 1he RCS, using portable temporary equipment, It needed.

3. Maintain the existing procedure to fill the SFP, if needed.

4. Training on the use of the Portable RCS Boratton equipment Is In progress.

ltftplelMnlltiob Date March 12, 2014 March 12, 2014 March 12, 2014 Prior to entering MOOE 4 during plant restart from lhecurrent maintenance outage {R229F3)

United States Nuclear Regulatory Commission to Serial: RNP-RA/14-0012 Page6of6 1111m Initiating Event Numller

2.

Probable Maximum Rood (PMF) 11am Numltar Trtgglr bllttrim ActioM Taken er Pfenne'CO fate*

lnc1udl'! tn Ille Hazard Reevllueliolttte,Olt Notification of a severe

1. Revised the tainter gate operating procedure storm system to activate the Unit Threat Team when preset approachln9 that has limits are reached.

1he potential for significant ralnfaff, or lake elevation. either of

2. Revised the severe weather procedure to which will activate the Unit Threat Team.

inelude guidance, based on-tainter gate operating limits being met and an ensuing mal<>r storm to safely shut doWn the plant.

3. Developed and Implemented procedures to pre-stage equipment capabte of filling the SG and 1ha SFP after the plant Is shutdown.

4. Revtsed the severe weather procedure to plUg the drain valves at the *u DeepweB pump enclosure to ensure Its availability as a long term water source.

5. Training on the use of 1he Portable RCS Boration equipment is in progress.

SUIIUARV

3.

A ROOdlng Integrated Assesement win be completed and report submitted to the NRC on or before fmplemenlatian Dale March 12, 2014 March 12, 2014 March 12, 2014 March 12, 2014 Prior to entering MODE 4 during plant restart from the current maintenance outage (R229F3)

I March 12, 2016.