ML21105A433

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Final Supplemental Response to NRC Genetic Letter 2004-02 on Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accident at Pressurized-Water Reactors
ML21105A433
Person / Time
Site: Millstone Dominion icon.png
Issue date: 04/15/2021
From: Mark D. Sartain
Dominion Energy Nuclear Connecticut
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
21-016, GL-2004-02
Download: ML21105A433 (34)
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Text

Dominion 5000 Energy Dominion Nuclear Connecticut, Boulevard, Glen Inc.

VA23060 Allen, Qg DominionEnergy.com April15, 2021 Energy" U.S.NuclearRegulatory Commission SerialNo.: 21-016 Attention: Document Control Desk NRA/GDM: R2 Washington, DC20555-0001 Docket No.: 50-423 License No.:NPF-49 MILLSTONE POWER STATION UNIT 3 ONEMERGENCY RECIRCULATION DURING DESIGN BASISACCIDENTS AT PRESSURIzEDWATER REACTORS" FINALSUPPLEMENTALRESPONSE Thepurpose ofthis submittal istoprovide theDominion Energy Nuclear Connecticut, l

Inc., (DENC) finalsupplemental response forM illstone Power Station (MPS) Unit 3 to '

Generic Letter (GL) 2004-02, "Potential impact ofDebris Blockage on Emergency j Recirculation September 13, during 2004.

Design Basis Accidents atPressurized-Water Reactors," dated j On May15,2013(ADAMS Accession No.ML13141A277), DENCsubmitted a letter of l intent per SECY-12-0093, "Closure Options for Generic Safety issue191, Assessment l

ofDebris Accumulation MPS Unit3 wouldpursue onPressurized-Water Closure Reactor Option 2 -

SumpPerformance," indicating Deterministic of the SECY l

j recommendations (refinements to evaluation methods and acceptance criteria).The final I outstanding issue for MPSUnit 3with respect toGL2004-02 isthe in-vessel downstream effects evaluation todemonstrate long-term core cooling canbeadequately maintained postulated for accident scenarios requiringsumprecirculation.

Thein-vessel downstream effects evaluation hasbeenco'mpleted forMPSUnit 3 andis documented identified intheenclosure intheMay15,2013Closure tothis letter.This Option satisfies letter.

thefinal GSl-191 commitment l This response constitutes DENC's finalsupplemental response toGL2004-02 for MPS j Unit3.

I Y

i

Serial No.21-016 Docket No.50-423 Supplemental Final Response toGL2004-02 Page2 of3 Should you haveanyquestions or require additional information, please contact Mr.GaryD. Miller at(804) 273-2771 Respectfully, MarkD.Sartain Vice President-Nuclear Engineering andFleet Support Commitment contained inthis letter:

1 DENCwill update thecurrent licensing basis (Final SafetyAnalysis Report in accordance with10 CFR 50.71(e)) following NRC acceptance of thefinal supplemental response for MPSUnit 3.

Enclosure:

Final Supplemental Response toGL2004-02 COMMONWEALTH OFVIRGINIA )

)

COUNTY OFHENRICO )

Theforegoing document wasacknowledged before me,inandfor theCounty and Commonwealth today aforesaid, byMarkD.Sartain, whoisVice President-NuclearEngineering andFleet Support ofDominion EnergyNuclear Connecticut, Inc.Hehasaffirmed before methat heis duly authorized toexecute andfiletheforegoing document inbehalf Company, ofthat and that the inthedocument statements aretrue tothe best ofhisknowledge andbelief.

Acknowledgedbefore methis /E dayof ;I , 2021 MyCommission Expires:

i GARYDONMILLER taryPublic Notary Public Commonwealth ofVirginia Reg.# 7629412 MyCommission Expires 31, August 2D

Serial No.21-016 No.50-423 Docket Supplemental Final toGL2004-02

Response

Page3 of3 cc: U.S. Nuclear Regulatory Commission -

Region I

2100 Renaissance Blvd, Suite100 Kingof Prussia, Pennsylvania 194062713 NRCSenior Resident Inspector Millstone Power Station Mr.R.Guzman NRCSenior ProjectManager -

Millstone U.S.Nuclear Regulatory Commission OneWhite Flint North Mail Stop 08C2 11555 Rockville Pike Rockville, Maryland 20852-2738

No.21-016 Serial Docket No.50-423 Enclosure SUPPLEMENTAL FINAL RESPONSE TOGL200402 Energy Dominion Nuclear Inc.

Connecticut, (DENC)

PowerStation Millstone Unit 3

Serial No.21-016 Docket No.50-423 Enclosure Table ofContents 1 Overall Compliance.....-----..--...-.-.--....-....-.....-2 1.1 Overview ofMillstone PowerStation Unit 3 Resolution toGL200402-.2 1.2 CorrespondenceBackground ..-....-.................----.3 1.3 General Plant System Description .....----....---...........5 1.4 General Description ofContainment Sump Strainers --....--5 2 General Description andSchedule for Corrective Actions-..,,.-.,-6 3 Specific information for Review Areas.,,,---....-..=.........-......15 3.n Downstream Effects -

Fuel andVessel -.............-.-.-..---..15 3.o Chemical Effects.-,,-....-....-...........=.-.----.28 3.p Licensing Basis ...--..=-...--.----..........-.,-.,,..28 4 References--,..-.-....-.....--...--....-..---...-..-.29 Page1of30

Serial No.21-016 Docket No.50-423 FinalSupplemental Response toGL2004-02 Enclosure 1 Overall Compliance NRCIssue:

Provide information requested inGL 2004-02, "Requested Information," Item2(a) regarding compliancewith regulations. Thatis, provide confirmation that the [Emergency CoreCooling System(ECCS)) ECCSand[Containment Spray System (CSS)) CSS recirculation functions under debris loadingconditions areorwill beincompliance with theregulatory requirements listed in the Applicable Regulatory Requirements section of this generic letter. This submittal should addressthe configuration ofthe plant that will exist once allmodifications required for regulatory compliance have been madeandthis licensing basis hasbeenupdated toreflect the results ofthe analysis described above.

DEbIC Rejiponse.;

Inaccordance with SECY-12-0093 andasidentified inDENCletter totheNRCdated May15,2013(ADAMS Accession No.ML13141A277), Millstone Power Station (MPS)

Unit3 elected topursue GSI-191 Closure Option 2 -

Deterministic andidentified in-vesseldownstream effects asthelast outstanding issue to beresolved. Topical Report (TR)WCAP-17788-P, Rev. 1, provides evaluation methods and results to address in-vessel downstream effects. As discussed inNRC"Technical Evaluation Report of In-Vessel Debris Effects" (ADAMS Accession No. ML19178A252), the NRC staff has performed a detailed review ofWCAP-17788-P. Although theNRC staff did notissue a SafetyEvaluation for WCAP-17788, asdiscussed further in"U.S.Nuclear Regulatory Commission Staff Review Guidance forIn-Vessel Downstream Effects Supporting Review ofGeneric Letter 2004-02 Responses" (ADAMS Accession No. ML19228A011),

thestaffexpects manyofthe methods developed intheTRcanbeused byPressurized WaterReactor (PWR) licensees todemonstrate adequate long-term core cooling (LTCC).

Completion oftheanalyses demonstrates compliance with 10CFR50.46, "Acceptance criteria for emergency core cooling systems for light-water nuclear power plants," (b)(5),

"Long-term cooling," asit relates toin-vessel downstream debris effects for MPSUnit 3.

1.1Overview ofMPSUnit 3 Resolution toGL200402 By letter dated February 29,2008(ADAMS Accession No.ML080650561), DENC submitted a supplemental response toGL2004-02 for MPSUnit 3that provided specific information regarding themethodology usedfordemonstrating compliance with the applicable regulations, aswell asthe corrective actions that hadeither beenimplemented orplanned tosupport theresolution ofGSI-191. Byletter dated December 18,2008 (ADAMS Accession No. ML083650005), DENC updated its supplemental response for MPSUnit 3 toprovide additional information regarding theanalyses performed andthe corrective actions taken that hadnot beencompleted atthe time oftheFebruary 29,2008 response. Thecontent andlevel ofdetail provided wereconsistent with theNRC guidance provided inNRCletter dated November 21,2007(ADAMS Accession No.

ML073110389).

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Serial No.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure Additional information was provided inDENCletters dated March 13,2009(ADAMS AccessionNo. ML090750436), September 2010(ADAMS16, Accession No.

ML102640210), December 20, 2010(ADAMS Accession No.ML103620562), and June 13, 2017(ADAMS Accession No.ML17171A229). DENCcommitted toaddress the resolutionofdownstream in-vessel effects forMPSUnit 3 following theissuance of revised WCAP-16793, "Evaluation ofLong-Term Cooling Considering Particulate, Fibrous andChemical Debris in theRecirculating Fluid," andthe associated NRCSafety Evaluation Report (SER).

By letterdated May15,2013(ADAMS Accession No.ML13141A277), MPSUnit 3 provided its resolution plan for resolving downstream in-vessel effects pursuant tothe Pressurized-Water Reactor Owner's Group (PWROG) comprehensive program underway todevelop newacceptance criteria forin-vessel debris (i.e.,WCAP-17788-P).

That letter also included a summary ofthe corrective actionsand analyses that hadbeen implemented forMPSUnit 3 toaddress GSl-191, as well as inherent margins and conservatisms included intheanalyses.

Theplant analyses, changes, margins, andconservatisms summarized andupdated in theMay15,2013MPSUnit 3 correspondence remain valid.

By letter dated August 13,2015(ADAMS Accession No. ML15232A026), DENC committed todeveloping plans fordemonstrating compliancewith PWROG WCAP-17788-P in-vessel debris acceptance criteria for MPSUnit 3 andto communicate that plantothe NRCinafinal updated supplemental response tosupport GL 2004-02 closure.

Thiseffort hasbeencompleted, andtheresolution ofin-vessel downstream effects is provided inSection 3.n below. This analysis doesnotcredit alternate flowpaths (AFPs) andconservatively assumes all fibrous debris that enters thereactor vessel will accumulate atthecore inlet,eventhough, inreality, somefraction offibrous debris will penetratethecore inlet orbypass thecore inlet via AFPs.

1.2 Correspondence Background A listirig ofthesalient correspondence issued bytheNRCorsubmitted byDENCfor MPSUnit 3 regarding the resolution ofthe containment sump issues identifiedinGL2004-02isprovided inTable 1.

TABLE1 GENERIC LETTER200402 CORRESPONDENCE AM Document Date A cgeyssionDocument September 13,2004 ML042360586 NRCGL2004-02 March4,2005 ML050630559 First response toGL2004-02 Page3 of30

Serial No.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure TABLE 1 GENERIC LETTER200402CORRESPONDENCE ADA DocumentDate Am"e*rssion Document September1,2005 ML052500378 Follow-up Response toGL2004-02 License Amendment Request (LAR) to September15,2005 ML052580387 modifyTechnical Specifications (TS) regarding oftheMPSUnit initiation 3 Recirculation Spray (RS) system NRCissuance ofLicense Amendment (LA)

September20,2006 ML062220160 233tomodify MPSUnit 3 TSregarding initiation ofthe RSsystem LAR toreviseMPSUnit 3 TStousegeneric September1,2006 ML062480263 terminology forECCScontainment sump strainers NRCissuance ofLA240torevise MPS September18,2007 ML072290132 Unit 3 TSto use generic terminologyfor ECCScontainment sump strainers November21,2007 ML073110389 NRCRevised Content Guide December19,2007 ML090860438 Draft Benchtop Test Plan for determining chemical effects February 29,2008 ML080650561 Supplemental Response toGL2004-02 December17,2008 ML083230469 First NRCRequest for Additional Information (RAI)

December18,2008 ML083650005 Notice ofCompletion ofActivities toaddress GL2004-02 March13,2009 ML090750436 Resppnse NRCRAl tofirst February 4,2010 ML100070068 Second NRCRAI September 2010 ML102640210 16, MPSUnit 3 response tosecond RAI December20,2010 ML103620562 Final response for MPSUnit 3second RAl May15,2013 ML13141A277 GSl-191 Closure Option Letter August 13,2015 ML15232AO26 Regulatory Commitment Change Letter '

June13,2017 ML17171A229 Third NRCRAIresponse Page4of30

Serial No.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure 1.3 General PlantSystem Description MPSUnit 3 is a Westinghouse four-loop PWRdesign. TheNuclear Steam Supply System (NSSS) consists of one reactorpressure vessel (RPV), four steam generators (SGs), four reactorcoolant pumps (RCPs), onepressurizer andtheReactor Coolant System (RCS) piping.Eachofthe four reactor coolant loops (RCLs) consists ofa SG,anRCP,and associated RCSpipingand iscontained ina concrete enclosure referred toasa cubicle.

Thesefour cubicles areessentially equivalent with respect topiping andequipment insulation. Thereactor isoperated insidea reinforced concrete containment structure maintained atasubatmospheric pressure between10.6 and14.0 psia. Thecontainment structureisequipped with a containment sumplocated attheouter wall ofthe containment. Extensive useismade of gratings andopenings intheupper floors and ofthecontainment structures toallowwater entering thecontainment todrain downto thecontainment sump. Also, the compartmentalized containment design slows transport ofdebristothe sump.

Theemergency core cooling system (ECCS) provides borated water tocool thereactor corefollowing a major loss ofcoolant accident (LOCA). This isaccomplished bythe automaticinjection ofwater from the Safety Injection (SI) accumulators into the RCLsand bytheautomatic pumping ofa portion oftheRefueling Water Storage Tank(RWST) contentsinto theloops via thecharging pumps, SIpumps,and Residual Heat Removal (RHR) pumps(low headSI). After theinjection modeofemergency corecooling, long termcorecooling (LTCC) ismaintained byrecirculating water from the containment sump bytheContainment Recirculation Spray System (RSS) pumps, through the RSScoolers, andintotheRCLsdirectly andvia thecharging andSIpumps.

Thecontainment heat removal system consists oftheQuench Spray (QS) system and thecontainment RSS. Following thepostulated design basis accident (DBA),

containment pressure isreduced byemploying both systems. Heat istransferred from thecontainment atmosphere totheQS system andtheRSSspray water. Heat is transferredfrom thecontainment totheService Water (SW) system via theRSSheat exchangers. TheQSsystem sprays borated water from theRWST.TheRSSdraws suction fromthecontainment sump, thecontent ofwhich consists oftheprimary or '

secondary system effluent andthequench spiray. Thestart signal for theRSSpumps (whicharetheonly pumpsthat take suction from thecontainment sumpprior tosump switchover) was changed to automatically start when RWST level reaches the Low-Low Levelsetpoint coincident with a containment depressurization actuation (CDA) signal.

Thisensures thestrainer isfully submerged prior todrawing water through thestrainer for coolant recirculation.

1.4General Description ofContainment SumpStrainers Asstated inthe MPSSupplemental Response dated February 29,2008andtheMPS Unit3 FSAR,a new,replacement ECCSstrainer manufactured byAtomic Energy Page5 of30

Serial No.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure Canada, Ltd. (AECL) wasinstalled toreplace theprevious trash rack,coarse mesh, and finemeshscreen that hada surface area ofapproximately 240ft2. Thefour RSSpumps takesuctionfrom acommon containment sumpthat isenclosed bythe strainer assembly.

Thestrainer consists ofmultiplefins constructed from corrugated perforated platewith 0.0625-inch holes. The fins areerected vertically over thesumpandextend beyond the sumptoachieve therequired surfacearea. Post-accident water covers thestrainer and isfilteredbythestrainer prior toenteringthecontainment recirculation pumps' suctions.

Design ofthe strainer isbased ona thoroughmechanistic analysis anddebris-bed head losstesting todemonstratethat adequate netpositive suction head(NPSH) andpump suctionline flashing margin exists under worst-case debris clogging scenarios. Vortex suppression isprovided bythe design of the strainer asconfirmed byanalysis andhead losstesting. Strainer design also included structural analysis todemonstrate structural adequacy under all possible conditionsof debris blockage. Thus, water will beavailable tothesuctions oftheRSSpumps under DBA conditions.

Thestrainer hasa solid cover plate installedapproximately eight inches above thefins thatprotects the fins from inadvertently dropped debris during outages andalso provides a workplatform. Thefins onthe strainer arenominally seven inches offthecontainment andthe floor, support structure for the strainer comprises a nominal seven-inchcurb. The isdesigned strainer towithstand design basis earthquake loading andhydraulic loading toandduring prior operation. Thesumpstrainer structure's seventeen interconnected modules areanchored toasupport frame, which isinternally anchored tothe containment structurebasement slab. Thestrainer islocated outside ofthe containment structure cranewall intheannulus between thecrane wall andthecontainment exterior wall.

TABLE2 CONTAINMENT SUMPSTRAINER SURFACE AREA Strainer Surface Area(ft2)

MPSUnit 3 Strainer ~5041 2 General Description andSchedulefor Corrective Actions NRCIssue:

Provideageneral description ofactions taken orplanned, anddates for each. For actions planned beyond December 3'1, 2007, reference approved extension requests orexplain howregulatory requirements will bemetasper"Requested Information" Item 2(b). That isprovidea general description ofandimplementation schedule for allcorrective actions, includinganyplant modifications, that youidentified while responding tothis generic letter.

Efforts toimplement the identified actions should beinitiated nolater than the first refuelingoutage starting after April 1,2006.Allactions should be completed by Page6 of30

Serial No.21-016 Docket No.50-423 FinalSupplemental Response toGL2004-02 Enclosure December 31, 2007.Provide justification for notimplementing theidentified actions duringthefirst refueling outage starting afterApril 1,2006. Ifallcorrectiveactions will not be completed by December 31,2007,describe how theregulatory requirements discussed inthe Applicable Regulatory Requirements section will bemetuntil the corrective actionsare completed.

DEhL.Resonse; DENCperformed analyses to determine the potentialfor adverse effects ofpost-accident debris blockage anddebris-laden fluids toprevent therecirculation functions ofthe ECCSandRSSfor MPSUnit 3. The analyses considered postulatedDBAs forwhich therecirculation ofthese systemsis required. Mechanisticanalysis supporting the evaluation satisfied thefollowing areasof the NRCapprovedmethodology intheNuclear Energy Institute(NEI) 04-07, "PressurizedWater Reactor SumpPerformance Evaluation Methodology" Guidance Report (GR), assubmitted byNElonMay28,2004(Reference 4.1),asmodified bythe NRCSafety Evaluation Report (SER),dated December 6,2004 (Reference 4.2):

Break Selection Debris Generation andzone ofInfluence Debris Characteristics Latent Debris Debris Transport HeadLoss Vortexing NetPositive Suction Head Available Debris Source Term Structural analysis Upstream Effects Detailed analyses ofdebris generation andtransport wereperformed to ensure that a bounding quantity anda limiting mixofdebris areassumed attheECCScontainment sumpstrainer following a DBA.Using theresults oftheanalyses, conservativehead loss testingwas performed todetermine worst-case strainer headloss anddownstream effects. Chemical effectsbench-top tests conservatively assessed thesolubilities and behaviors ofprecipitates andapplicability ofindustry dataon thedissolution and precipitationtests ofstation-specific conditions andmaterials. Reduced-scale testingwas performed byAECLusing twoseparate test rigs,andmulti-loop testingestablished the influence ofchemical products onthead loss across thestrainer surfacesbysimulating theplant-specific chemical environment present inthewater ofthecontainment sump aftera LOCA.

Inaddition, plant modifications werecompleted forMPSUnit 3 insupport ofGSl-191 resolutionincluding thefollowing:

1.A newMPSUnit 3 ECCSstrainer (withcorrugated, perforated stainless steel fins)was installedwith a totalsurface area approximately replace o f 5041 ft2to the previous trash rack, coarse mesh,andfine meshscreen that hada surface areaof approximately 240ft2. Thereplacement strainer wasdesigned towithstand upto Page7 of30

SerialNo.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure approximately 10pounds persquare inch (psi) ofdifferential pressure andhasa strainer hole sizeof0.0625 inches,which issmaller than theprevious screen size of 0.09375inches.

2.Thestart signal for theMPSUnit 3 RSSpumps (which aretheonly pumps that take suction from thecontainment sumpprior tosumpswitchover) waschanged during the spring 2007refueling outage, as permitted by AmendmentNo.233(ADAMS Accession No.ML062220160). Themodificationchanged theautomatic start signal atapproximately 660seconds following thepostulated accident toanautomatic start whentheRWSTlevel reaches theLow-Low Level setpoint coincident with a CDA signal. This ensures the strainer isfully submerged prior todrawing water through the strainer for coolant recirculation.

Inaddition tothemodifications listed above, the following actions havebeencompleted insupport ofGSl-191 resolution forMPSUnit 3:

1.Detailed analyses ofdebris generation andtransport wereperformed toensure a bounding quantity anda limiting mixofdebris areassumed atthe ECCScontainment sumpstrainer. Using theresults oftheanalyses, conservative headloss testing was performed todetermine worst-case strainer head lossand downstream effects.

2.Chemical effects bench-top tests conservatively demonstrated thesolubility and behaviors ofprecipitates, andapplicability ofindustry dataon the dissolution and precipitation testsofstation-specific conditions andmaterials.

3.Reduced-scale testing wasperformed byAECLandDominion Energypersonnel. The reduced-scale testing established theinfluence ofchemical products on head loss across thestrainer surfaces bysimulating theplant-specific chemical environment present inthe water ofthecontainment sumpafter a LOCA.

4.Downstream effects analyses were performed for clogging/wear ofcomponents inflow streams downstream ofthe strainers.

5. Design controls wereputinplace torequire evaluation ofpotential debris sources in containment created by,oradversely affected by, design changes.

6.Insulation specification changes weremadetoensure that changes toinsulation in containment canbeperformed only after theimpact oncontainment strainer debris loading isconsidered.

To ensure themodifications implemented andtheanalyses performed effectively addressed uncertainties with sufficient margin, thefollowing margins andconservatisms wereincorporated:

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Serial No.21-016 Docket No.50-423 FinalSupplemental Response toGL2004-02 Enclosure 1 Debris generation analysis usedveryconservative zones ofinfluence (zOls) that resulted in theremoval ofvirtually allinsulation within theaffected cubicle.

Conservative zOls from NEl04-07 wereapplied forfibrous insulation, which did not credit themetal encapsulation for muchofthe fibrousinsulation inthe steam generator cubicles. Nocredit was taken inthedebris generation calculation for anyreduction of insulation destruction duetolocation oftheinsulation with respect tothebreak.

2.There arenumeroussurfaces throughout containment whereinsulation andother debris arelikely tosettlefollowing break blowdown andnotbedislodged bywashdown orcontainment spray. Consequently, this material debris would notbeavailable for transport tothe strainer. However, all insulation generated wasassumed inthe debris generation analysis tobeimmediately transported tothecontainment floor, entering thecontainment pool.

3.Although credit istaken inthedesign of thestrainerforleak-before-break in consideration ofpipe whip, jet impingementand missiles, nocredit wastaken for leak-before-break todetermine the amount ofdebris generated ortransported.Analysis of leak-before-break effectsthat reduce the size ofthe break that could occur prior toits detection hasbeenapproved bytheNRCfor useas part ofthe MPSUnit 3 licensing basis. Thereactor coolant pipes areassumed tobreak instantaneously for the debris generation andtransport analysis.

4.Thedebris transport analysis conservatively assumes allfibrous fines are transported tothestrainer surface, 90%oflarge andsmall fibrousdebris pieces areeroded into fines andtransported tothe strainer surface, andall particulate debris is transported tothe strainer surface.

5.Conservative assumptions fromthedebris transport analysis wereadded tothe conservative basis forthedebris headloss determination from testing. The debris head loss testing wasdonewith a particulate surrogate that hasa lower densitythan theepoxy coating that isexpected tomakeupmuchofthe particulate debris. Stirrers wereused inthetest tank tominimize settling ofdebristothe greatest extent possible.

Thetesting evaluated both extremes ofdebris loading (thin-bed debris load andthe fulldebris load) and determined the worst-case head loss. Both t hin-bed andfull debris load testing usedtheparticulate loading generated bythelarge! break LOCA (LBLOCA). The worst-case head loss (thin-bed) isunlikely to occur for a LBLOCA because the quantity offiber transported tothe strainerislikely tobetoohigh toallow forcreation ofa thin-bed. Thethin-bed headloss isalso unlikely tooccur fora small break LOCA(SBLOCA) since the quantity of particulatenecessary for formation ofthe worst-case thin-bed would notbegenerated.

6.Nocredit wastakenfor accident-induced overpressure incalculation ofNPSHmargin forthe ECCSpumps.

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Serial No.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure

7. No credit was taken forsettling of particulate debris on surfaces throughout containment thatwould occur prior toandduring coolant recirculation, including inthe areas ofthe containment pool that have extremely lowvelocities during recirculation asshownby computational fluid dynamics (CFD) analysis.

8.Thereplacement strainer hasa very large surface area andthestrainer footprint is spread over a verylarge region ofcontainment.Foranyonebreak incontainment, thebreak-induced turbulence inthepost-LOCA sumppool would belocalized. The large strainer footprintcombined withthe localized turbulence results inlarge areasof thecontainment sumppoolhaving very lowvelocities, which would enable extensive debris settling onthecontainment floor andmayresult ina nearly clean strainer area oversomeportion ofthestrainer surface. However, clean strainer area wasnot credited inchemical effects orhead loss evaluations, andnosignificant settlingof debris wascredited inthedownstream effects evaluation.

9.Nocredit wastaken for additionalNPSHmargin due tosubcooling ofthe sumpwater.

Thecontainment water sump was conservatively assumed to be saturated for calculation ofNPSHfor theECCSpumps. Nocredit was taken for the several hours required toform theworst-case debrisbed(thin-bed), during which time subcooling of thesumpwater would addsignificant NPSHmargin for theECCSpumps.The analysis conservatively assumes there isnotime delay in transport tothe strainer following thebreak. Formation ofchemical precipitates andtheir subsequent transport tothestrainer debris bedwouldoccurmanyhoursafter the accident when containment heat removal requirements aresignificantly reducedand when significant subcooling ofthesumpwater hasoccurred. Test evaluations demoristrated that a fully formed thin-bed of debris takessignificant time (hours) toform and is dependent onunsettling debristhroughout thetesttank. Consequently, a worst-case thin-bed of debris will bedifficult toformandwill notformuntil several hours after sump recirculation canbeinitiated. Significantdebris settling andsignificant sump water subcooling occurs during the formationofa debris-bed soadditional NPSHmargin is present for chemical effects head loss.

Thedebris

10. load inheadloss testing wastaken from the debris transport calculation, which credits noparticulate settling.

s v 11Debris introduction procedures inchemical effects testing resulted inminimum near-field settling andconservatively high headlosses.

12.

Debris introduction wasaccomplished ina carefully controlled manner toresult inthe highest possible headloss. Particulate wasintroduced initially,which wasfollowed bydiscrete fiber additions the after particulate debris wasfully circulated.

13.

Thetest tanks werestirred duringtesting. However, local areas ofturbulence that mayexist inanypost-LOCA containment sumpwater areexpected tobelimited to Page10of30

Serial No.21-016 Docket No.50-423 Supplemental Final Response toGL2004-02 Enclosure certain portions ofsumpwater volume. Consequently, muchofthesumpwater will bestilland have near zero velocity.

14.Particulatesettling inheadloss testing wasconservatively minimized through useof a lower density walnut shell particulate asa surrogate for thehigher density epoxy coating particulate that maybepresent inpost-LOCA sumpwater.

15.Downstream wearanalysis used the LBLOCA particulate load todetermine abrasive anderosive wear. This is a conservative particulate loading, inview ofthe following:

  • Muchoftheparticulate included inanalysis isunqualified coating that isoutside thebreak zOI.This unqualified coating is assumed topotentially dislodge dueto exposure to thecontainment environment. However, an exposure-based mechanism todislodgement, if iotccurs atall, islikelyonly after manyhours and days.
  • Thelowvelocity ofthesumpwater columnand thesignificant number ofsurfaces throughout containment promote significant settling ofparticulate in containment.

Settled coating notbedrawn will through theECCS strainer since the strainer sits approximately seven inches above thecontainment floor. Additionally, qualified coating postulated tofail inthepresence ofthe201 is not buoyant inthesump water column.

  • Thecapture ofparticulate inthe debris-bed onthe strainerdoes not occurin this analysis, maximizing effects ofdownstream wear.

16.The baseconcrete dissolution isconservatively assumed tobeuninhibited bythe presence oftri-sodium phosphate (TSP), eventhough bench scale test solutions demonstrate inhibitionof concrete degradation atcontainment sump water pH levels.

Consequently, calculations ofthe amount ofcalcium tobeadded tothe testtank for headloss tests wereconservative.

17.The amount ofaluminum andassociated testresults concerning itsrelease into the simulated post-LOCA sumpwater through corrosion ofaluminum surfaces was conservative based upon several conditions:

  • Aluminum corrosionamounts werecalculated athigh pHtofavor corrosion, and aluminum precipitation wasevaluated atlowpHtofavor precipitation.
  • Testing with a lowerpHfavors precipitation Rig 89testing wasperformed with a pH7 at770Ftoencourage aluminum compound eventhough precipitation, the actual pH inthesumpwater isapproximated as pH8 at77 0F.Also, TS requirements fortheRWSTandTSPbaskets ensure sumpwater pHis> 7 at 770F.

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Serial No.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure

  • Rig 89 testing was evaluated conservatively with lowshort-term acceptance criteria, along with themaximumaluminum concentration ofthesumpwater that exists only after 30days.

a Analysis conservatively did not account for thepossible inhibitoryeffect ofsilicate, phosphate, orother species onaluminum corrosion.

a The rateofcorrosion was maximized by analysis that doesnotassume development ofpassive films, e.g.,noaluminum oxides remain on aluminum surfaces. Passive films can otherwise beused todecrease the corrosion rate by a factor oftheexposure time. Consequently, having noaluminum oxides remain onaluminum surfaces soall aluminum released bycorrosion enters the solution is conservative.

  • Aluminum notsubmerged incontainment was considered byanalysis tobe exposed tocontainment sprays andtherefore available for corrosion. However, someofthealuminum sources incontainment, such astheout-of-core detector holders, maynotbesubject toa continuous containment spray andwould not contribute tothe total aluminum concentration inthe containment pool.
  • Aluminum released intothesolution wasassumed totransport tothedebris-bed instead ofplating outonthemultiple surfaces throughout containment. During bench-top testing, aluminum plated outonglass beakers andduring reduced scale testing, aluminum plated outonfiber. It isreasonable toexpect a portion ofthe aluminum ions released intosolution willplate out onsomeofthe multiple surfaces incontainment prior toarriving atthe debris-bed onthe strainer.

a Chemical effects test evaluations conservatively neglected theeffectof the presence ofoxygen inthe sumpwater. Corrosion rate ofaluminum inaerated pH 10alkaline water canbea factor oftwolower than whentherate ismeasuredin nitrogen-deaerated water. This dataisinNUREG/CR-6873, "Corrosion Rate

! Measurements and Chemical Speciation of Corrosion Products Using

'Thermodynamic Modeling of Debris Compohents to Support GSI-191,"

'(Jain etal. April 2005).

18.No near-field settlement wascredited intheMPSUnit 3testing.

19.The conservatism oftheRig89 testresults relative tothecontainment was demonstrated bythe following factors:

a Thetest tank size for Rig89wasa 16-in x 16-in x 36-in stainless box.No significant debris transport wasneeded for debris toreach thestrainer surface.

Debris transport distance inthetest tank was essentially zerowhereas in Page12of30

Serial No.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure containment, duetothelarge footprint ofthe strainer, debris transport distances to atleast one leg ofthe strainer areexpected tobesubstantially greater than this test tank size.

  • Walnut shell particulate (used as thesurrogate forepoxy) hasa density of approximately 80 pounds percubic foot (lb/ft3) aS Compared tothehigher density (94 ofepoxy lb/ft3). Thus, epoxy ismorelikely tosettle than theparticulate surrogate used intesting.
  • A significant portion ofthe particulate expected tobegenerated isfrom unqualified coatings that arepostulated tobe dislodgedfromcomponents throughout containment by temperature and humidity in containment post-LOCA.

Degradation ofthese unqualified coatings will take significant time (hours, and probably days), andthus theamount ofparticulate inthedebris-bed (and inthe test tank) is conservative. Additionally, all of the unqualified coating is postulated tofail assmall, transportable particulate when inreality, muchoftheunqualified coating ismorelikely tofailaslarge piecesthat willnot transport.

  • The strainer incontainment sits approximately seven inches abovethe containment floor. Thus, anyparticulate which slides along the floor with the sump water motion isunlikely toreach the strainer surface.

20.Particulate debris settling andcapture could becredited tooccur prior toandduring recirculation, minimizing theamount ofdebris downstream inthe recirculating fluid.

However, the calculation ofwear ofcomponent surfaces duetodebris conservatively neglects this particle debris settling andcapture.

21RSSpumpstart occurs whentheRWSTisapproximately half full.Thewater level continues torise until it isseveral feetabove the topofthestrainer for thefirst few hours after theaccident while theRWSTcontinues tobepumpedinto containment, adding NPSHmargin for theRSSpumps. However, analysis conservatively used the water level from a SBLOCA thatexists atthe startoftheRSSpumps.

t 22.A5D (5 times pipe diameter) 201wasusedfor qualified epoxy coating particulate 1 resulting ina total generation andtransport of10.4 ft3 ofqualified coating particulate tothe strainer. Based onthe April 6,2010 NRCtoNElLetter (ADAMS Accession No.

ML100960495), a 4DzOIisacceptable for qualified epoxy coatings. Useofa4D201 would result inonly 8.0ft3 Ofqualified coating particulate. Thus, thestrainer testing used 23%more(2.4 ft3) qualified coating particulate than what i expected s to occur in containment duetouseofthemoreconservative 5D201 23.A10%margin wasadded tothecoatings particulate debris quantities generated from thezOIandfrom unqualified coatings (atotal of2.1ft3 OfCOatings margin). Reduction Page13of30

Serial No.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure ofcoating debris, which isall modeled asparticulate, would resultina reduction in thin-bed head loss.

Theabovetwo conservatisms result

24. ina total excess of4.5ft3 OfCOating OVerwhat is expected tooccur onthestrainer incontainment. Thetotal particulate coating load onthestrainer was calculated tobe23ft3. A reduction of4.5 ft3 isequivalent toa 20%

reduction incoatingparticulate, which would result ina reduction instrainer head loss for a thin-bed from thetested values.

Unqualified

25. coating wasdeemed tofail immediately astransportable particulate. This isparticularlyconservative since unqualified coating makes up46%ofthe totaltested coating load and39%ofthetotal particulate load onthestrainer. Electric Power Research Institute(EPRI) testing (Reference EPRI Technical Report 1011753 dated September 2005) has shown t hat less than one-third of unqualified coatings actually failed whensubjected toDBAtesting.

Five

26. percent margin wasadded tothefibrous debris quantities generated from the (a

zOI total ofover 60ft3 Offiber margin).

Five

27. percent margin wasadded tothe microtherm debris quantity generatedfrom the (a

zOf total of0.1ft3 OfmiCrotherm margin).

Inboth

28. Rig33andRig89testing, fibrous debris wasconservatively preparedas "single fine."

Onehundred

29. percent debris transport wasassumed for coatings, microtherm, and latent debris.

A sacrificial

30. strainer areaisinstalled incontainment toaccommodate transport of foreign material tothestrainer. Theinstalled strainer area(5041 ft2) exceeds the tested strainerarea (4290 ft2) by at least the amount o f the s acrificialarea.

t Resolution ofDownstream Effects -

Fuel andVessel: This item isdispositioned in Section3.n below. =.

Withthecompletion ofthedownstream effects analysis for thefuel andvessel, DENC haseffectivelyresolved for MPSUnit 3 theissues identified inGL 2004-02 andisin compliance with theapplicable regulations.

Page14of30

Serial No.21-016 Docket No.50-423 FinalSupplemental Response toGL2004-02 Enclosure 3 Specific Information for Review Areas Asstated inthe MPS Unit 3 Supplemental Response dated February 29,2008(ADAMS Accession No.ML080650561) andamended onDecember 18, 2008(ADAMS Accession No.ML083650005),as well assubsequent RAIresponses submitted onMarch 13,2009 (ADAMS Accession No. ML090750436), September 16,2010(ADAMS Accession No.

ML102640210), December 20, 2010(ADAMS Accession No.ML103620562), and June13,2017(ADAMS Accession No.ML17171A229), MPSUnit 3 hasaddressed reviewareas 3.athrough 3.m. Therefore, only theoutstanding review areas of3.n through3.p areaddressed inthissubmittal.

3.n Downstream Effects -

Fuel and Vessel NRCIssue:

Theobjective ofthedownstream effects,fuel andvessel section istoevaluate the effects thatdebris carried downstream ofthecontainment sump screen andinto thereactor vessel hasoncore cooling.

Showthat thein-vessel effects evaluation isconsistent with, orboundedby,the industry generic guidance (WCAP-16793), asmodified by NRC staffcommentson thatdocument. Briefly summarize the application ofthe methods. Indicate where the WCAPmethods werenotusedorexceptions weretakenand summarize the evaluation ofthose areas.

Dh TRWCAP-17788-P, Rev. 1provides evaluation methods andresults toaddress in-vessel downstream effects. Asdiscussed inNRC"Technical Evaluation Report ofIn-Vessel Debris Effects," (ADAMS Accession No.ML19178A252), the NRCstaff hasperformed a detailedreview ofWCAP-17788-P. Although theNRCstaff didnotissue a Safety Evaluation forWCAP-17788-P, as discussed furtherin"U.S. Nuclear Regulatory Commission Staff Review Guidance forIn-Vessel Downstream Effects Supporting '

ReviewofGeneric Letter 2004-02 Responses" (ADAMS Accession No.ML19228A011),

thestaffexpects that manyofthemethods developed intheTR maybeusedbyPWR licensees todemonstrate adequate LTCC.DENCusedmethods andanalytical results developed inWCAP-17788-P, Rev. 1,toaddress in-vesseldownstream debris effects for MPSUnit 3andhasevaluated the applicability ofthemethods andanalytical results from WCAP-17788-P, Rev. 1,for MPSUnit 3.

Page15of30

Serial No.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure 3.n.1W An engineering evaluation was performed todetermine a conservative estimated cumulative fiber bypass fraction for theMPSUnit 3 containment sumpstrainer tofacilitate theevaluationofthein-vessel debris effects for NRCGL2004-02.

Fromthe debris generation and transport analyses performed forMPSUnit 3,DENChas conservativelydeterminedthe types andquantities offibrous debris that could be tothe transported strainers, asdocumented byletter dated February 29,2008(ADAMS AccessionNo.ML080650562). The fibrous debris sources considered intheMPSUnit 3 analysesincluded fiberglass andlatent fiber. Thetotal fibrous debris quantity from these sourcesthat could potentially reach the MPS Unit 3 sumpstrainer wasconservatively calculated tobeapproximately 2053Ibm.

Thestrainerfiberbypass testing performed byAECL that wasapplied totheMPSUnit 3 strainer didnotmeasure thecumulative quantities offiberbypassedafter eachfiber tothe addition testtank. Thetesting used a "grabsample" methodthat looked atfiber massina water sample taken downstream ofthe strainer fins atdiscrete points intime.

Thistesting provided certain insights, such aslong-term strainer bypass waslow, but did notprovideinsight into theextent offiber bypass occurring early inECCSoperation.

Consequently, there isnodata for thequantity ofbypassedfiber asthedebris bedis therefore, forming; cumulative fiberbypass fractions cannot bedetermined.

However, other plants intheindustry haveperformed strainer bypass testing with downstream continuous in-linefilters that were able todetermine cumulative fiber bypass fractions forvarious debris bedthicknesses. Consequently, Dominion Energy performed anevaluationtodevelop anengineering basisfor the useofcumulative fiberbypass data fromotherplants toapply totheAECLstrainer installed atMPSUnit 3.

M Basedonreview ofstrainer bypass testing data for thePoint Beach andSouth Texas Project (STP) plants (References respectively),

4.6 and 4.14, itw as observed thatasa bedforms debris andcontinues tobuild ona strainer, the filtrationefficiency willplateau atnearly100%.Eachofthese tests was performed with continuous in-linefilters downstream ofthe strainer assemblies toensure a cumulative fiberbypass fractioncould bedetermined. Thefiltration efficiency behavior isalso consistent with that indicated in thebypass testing results for theDominion Energy fleet that wasperformed byAECL.

ButsincetheAECLtests werebased only ongrab samples taken atspecific turnover for intervals the fiber additions, itwasnecessary toutilize other industry testing thatused continuous in-line fiberbypass capture todetermine cumulative bypass fractions for the MPS Unit 3 strainer. Itisnoted AECLtestreports determined, "Fiber bypass concentrations showa near exponential decreasing trend with time." Thequantity offiber bypassed that thestrainer wassolowa scanning electron microscope evaluation was Page16of30

Serial No.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure required for accurate determination ofconcentration andsize. Considering these results, there is reasonable engineering justification toapply Point Beachtest results, after correcting for differences in approach velocity, totheMPSUnit 3 strainer.

Using NRCstaff guidance (Reference 4.3) forstrainer fiberbypass andindustry strainer bypass test results andapproach velocityfromPoint Beach andVogtle, respectively (References 4.4 through 4.10), a cumulative strainer bypass fraction was developed for MPSUnit 3.Consistent with NRC staff guidance, the largest fibrous debris amount for eachplant that could transport to the sump strainers wasassumed andincluded fiber transport anderosion based onthe bounding fiber break. Application ofPoint Beach strainer bypass data toMPSUnit 3 was based onfiber bypass atvarious tested and extrapolated theoretical debris bedthicknesses (derived from fiber massperstrainer area).

TheMPSUnit 3 strainer approach velocity ishigher than thePoint Beach test results; consequently, it wasnecessary toapply a correctionfactor toscale the Point Beach data tothehigher velocity. Derivation ofthecorrection factor was basedonthe Vogtle plant teststhat recorded bypass fractions atvarious velocities. Bypass massnormalized by flowrate wasdetermined intheVogtle test to be report linearly related to approach velocity.This supported the calculation ofcumulative bypass fractions for Vogtle strainers atflow rates comparable toMPSUnit 3 andPoint Beach. Then a cumulative bypass correction factor could bedetermined ata given debris bedthickness byscalingthe Vogtle data attheMPSUnit 3 plant velocity tothePoint Beach test velocity. This methodology isbased onthe premise that theimpact ofapproach velocity on the filtering efficiency ofa debris bedisnot strongly dependent onthe specific strainer design.

Thegeometry for the Performance Contracting Incorporated (PCI) furnished Point Beach diskstrainer wascompared with theAECLfurnished MPSUnit 3 strainer andassessed tobeconceptually equivalent inits hydraulic performance characteristics. Both strainers havea central collection duct that receives filtered water from perforated sheets that is delivered toECCSpumpsuctions. Debris-laden water flowing tothestrainers inboth designs will generally beina perpendicular direction tothe perforations. MPSUnit 3does notutilize anyspecific design features for promoting evenflow distribution; however, the AECLstrainer hydraulic report discusses thatuniform flow isexpected assoonasa small fiber layer starts toform. (Reference 4.12).

Withregard tosacrificial areas for theMPSUnit 3strainer, it wasassumed allofthe areas would beavailable for formation ofthefibrous debris bedsasthis would minimize the thickness ofthecalculated theoretical debris which bed, would result inlarger cumulative bypass fractions for themaximum debris loads ateachplant.

Page17of30

Serial No.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure Casesthat result inthemaximum design flow rates for theMPSUnit 3 strainer were selected to provide the highest approach velocity. Thestrainer perforation size for Point Beach (0.066") isslightly larger than for the MPSUnit 3strainer perforation size (0.0625").

Uponconsideration ofthis design attribute,it hasa conservative influence oncumulative bypass fractions when applying Point Beach test results toMPSUnit 3.

Consentatisg3s.Ap.121[gid Conservatisms applied when determining cumulative bypass fractions for the MPSUnit 3 include:

a Maximumstrainer design flow rates were used that result inthehighest calculated approach velocities andcumulativebypass fractions.

  • TheMPSUnit 3 strainer hasa slightly smaller perforation size (0.0625") ascompared tothePoint Beach strainer(0.066") thatwas used for bypass test data applied tothe MPSUnit 3.

Point Beachtest resultsfor Nukon only insulation were used since they provided slightly higher bypass thanfor o therlimited insulation mixes that w ere t ested.

  • Whentheoretical debris bedthicknesses were calculated, designated sacrificialareas wereincluded tominimize the thicknesses, which result inhigher cumulative bypass.
  • A percentage ofthe total fiber load onthe MPSUnit 3 strainer includes intact pieces that do noterode as a nd, such, donotcontribute tostrainer fiber bypass. This contrasts with thePoint Beach andVogtle bypass tests that used shredded fiber, all ofwhich may contribute to strainer bypass.

Page18of30

SerialNo.21-016 Docket No.50-423 FinalSupplemental Response toGL2004-02 Enclosure TABLE 3 CRITICAL PARAMETER COMPARISON FORSUMPSTRAINER BYPASS TESTING Parameter Point BeachValue Millstone Unit 3 Value Strainer Manufacturer PCI AECL Strainer Perforation 0.066" 0.0625" Size Areal Strainer 1904.6 ft2 5041 ft2 FlowRatethrough 2300 gpm (testscaled) 8220gpm Strainer Single Train ApproachVelocity 0.0027 ft/sec 0.00363 ft/s Nominal Theoretical 1.5,, 0.60,, 2.037,,

Debris BedThickness Typeand Debris

(%Fiber Quantity MassType)2 Test 1 Test2 Test3 Fiberglass 40.7% 28.8% 100% 100%

Mineral Wool 59.3% 67.7% 0% 0%

Mineral Fiber 0% 0% 0% 0%

Temp-Mat 0% 3.5% 0% 0%

Paroc 0% 0% 0% 0%

Asbestos 0% 0% 0% 0%

CumulativeTested 2.01% 2.42% 5.61% N/A Bypass Notes:

1. Thesacrificial area isnot deducted since ismore it conservativetousethemaximum areaavailable whencalculating thetheoretical bedthickness.

fiber A thinnerbedthickness ina higher results cumulative fiberbypassfraction.Also,there isnoneed forcomparison ofs.urface areas the since terminal Point;Beachcumulative bypass fractionsare notbeing applied AECLstrainer.

tothe Determination ofcumulative bypassfractionsisonly being based ona theoretical debris bed thickness comparison withPoint Beach andeachplant.

2. Actual quantities fiber arenot providedasthere isnointent toapply Point theterminal Beach bypass cumulative fractionstotheAECLstrainer. Thebypass fraction forMPSUnit 3 isderivedby oftheoretical comparison bedthicknesses.

MPSUnit.3 hasa,theoretical debris bedthickness of2.037" thatexceeds the final nominal theoretical bedthicknesses forthePoint Beach tests. However, useofthefitted power curveequation with extrapolation isjudged toprovide acceptable results duetothe demonstratedexponential decaybehavior offiber bypass with increasing debris bed Thecumulative thickness. bypass fraction ata 2.037" thickness isthencalculated using Page19of30

Serial No.21-016 Docket No.50-423 FinalSupplemental Response toGL2004-02 Enclosure thePoint Beach Test 3 curve equation fitted developed inthecalculation: Cumulative FiberBypass =

0.040303*(Bed Thickness)-o.758434 =

0.040303*(2.037)-o.758434 = 2.3%.

Sincethe approach velocity for theMPSUnit 3 strainer(0.00363 ft/s) isgreater than for thePoint Beachdata (0.0027 ft/s), a correctionfactor wasapplied tothecumulative bypass fraction. The Dominion Energy engineeringevaluation includes a spreadsheet thatdeveloped cumulative bypass fraction factors correction from the Alden Test Report forVogtle (Reference 4.10) that maybeapplied tothePoint Beach derived cumulative bypass fraction for MPSUnit 3. The spreadsheet determined that a correction factor of 1.514 isapplicable fora debris bed thickness of2.037" toscale a to velocity of 0.0043 ft/s,which conservativelybounds 0.00363 ft/s. Applying this information toMPS Unit3,the cumulative fiber bypassis 2.3% x 1.514 = 3.5%.

TABLE4

SUMMARY

OFFIBER LOAD,DEBRIS BEDTHICKNESS, & VELOCITY ADJUSTED BYPASS FRACTIONS Strainer Characteristic MPSUnit 3 Fiber Load 2053.24 Ibm TheoreticalDebris BedThickness 2.037 inches Cumulative Bypass Fraction 3.5%

Thedata inTable 4 wasusedtoperform theevaluation ofin-vessel effects discussed below.

3.n.2 MPSUnit 3is aWestinghouse 4-loopPWRwith anupflow barrel/baffle configuration. Per Section3;0of the NRCStaff Review Guidance (Reference 4.3), iti snecessary to confirm MPSUnitE3 iswithin thekeyparameters oftheWCAP-17788-P, Rev. 1,methods and analysis.Therefore, each ofthekeyparameters isdiscussed below.

3.n.3Fuej Design MPSUnit 3 usesWestinghouse 17x17 RobustFuel Assembly 2 (RFA-2) fuel.

3.n.4WCAP-17788 debris limit Theproprietary inWCAP-17788-P, total Volume (core in-vesselinlet 1,Rev. 1,apply core) andheated fibrous toMPSUnit 3.

debris limits contained Page20of30

Serial No.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure 3.n.5 Theamount of fibrous debris calculated toarrive atthe reactor vessel isdetermined for MPSUnit 3following the method described inWCAP-17788-P, Volume 1,Rev. 1,Section 6.5.Specifically, an engineering calculation wasperformed todetermine thecore inlet fibrous debris load forthe Hot Leg Break (HLB) for MPSUnit 3.Thecalculation included thefollowing design inputs and assumptions:

DesignInputs 1 Plantlype- MPSUnit 3 isa four-loop Westinghouse upflow configuration plant.

2.Number ofAssemblies -

TheMPSUnit 3 core contains 193Westinghouse RFA-2 fuel assemblies (FAs).

3.CoreThermal Power Thecurrent rated core thermal power is3650MWt.The analyzedcore thermal power of3723MWt,which includes instrument uncertainty, wasusedfor this evaluation.

4.M -

Thetotal fibrous debris fines mass atthe ECCSsump including strainer, fines generated dueto erosion, is380.32 Ibm. Thefiber "fines"are thefibersthat aresmall enough tobypass the sumpstrainers and collect atthecore (i.e.,

inlet Fuel Assembly Lower EndFittings). Ona per fuelassembly basis, theinitial sumpfiber load is893.83 (

g/FA [380.32

=

  • Ibm 453.592 g/lbm) /193 FAs).

5.M -

Theactive sumpvolume, also referred toas the active recirculationvolume, isthevolume ofliquid inthecontainment sumpwhich actively participates intherecirculation process. This volume acts asthe systeminventory whencalculating theconcentration ofdebris tobe injected into theRCS. A conservatively lowsumpvolume wasused that accounts for potential holdup areas withincontainment.

6.W-activationorrecirculation Thetime modetransfer ofSSO,also (RMT), isthe known time assumprecirculation atwhich fiber isinjected intothereactor vessel/sump screen. Theminimum time ofsumpswitchover is 33minutes.

7.M -

TheECCSflow rate after thetime ofSSO(i.e.,

duringrecirculation mode) isused tocalculate therate offiber injectionintothe reactor vessel.Both minimum andmaximum ECCSflow rates wereanalyzed. Theminimum ECCSflow rate during recirculation is965.25 gpm' with oneoperable train, andthe maximum recirculation flow rateis1753 gpmwith both trains operating.

Page21of30

Serial No.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure 8.W -

Thecontainment RSShelps reduce thetotal mass ofdebris delivered tothe reactor vessel bydiverting a fraction ofdebris that bypasses thesump strainer back intothesump.Perguidance provided inWCAP-17788-P, Rev. 1,Volume 1,Section 6.5.2.10, a minimum RSSflow rate should beanalyzed.

TheminimumRSS flow rate during ECCSrecirculation alignment is4071gpm.The maximum RSSflow rate duringECCSrecirculation alignment is7202gpm.

9. -

TheMPSUnit 3 HLSOtimemustoccur between 3 and5 hours.Since a maximum HLSOvalue islimiting, a value of5hours wasused inthe calculation.

10.Iime.St p.- A time step of100seconds wasused for the iterative solution.

11.M -

Thetime to chemical effects, tchem,isthe time atwhich chemical precipitates areassumed togreatly increase theresistance across the formed debris bed.PerTable 4.4-1 ofReference 4.13, theearliest time atwhich chemical effects form is24hours for MPSUnit 3. Therefore, a value of24hours was used inthecalculation.

12.

Inlet Debris Limit -

Kmax isthemaximum coreinletresistance that canbetolerated prior tocomplete core inletblockage. is tblock theminimum acceptable timeofcomplete coreinlet blockage. MPSUnit 3 isa Westinghouse upflow plant with Westinghouse therefore, fuel;

  • tblockis143min,
  • Thecore inletdebris limitisthe value listed inWCAP-17788, Table 6-3, and
  • Kmax is5x10E 13.W -

Thebypass fraction istheportion ofdebris transported tothe sumpstrainer that isnotcollected onthe sumpstrainer andinstead penetrates through thesumpstrainer andinto thereactor vessel through theECCS.

As noted inSection 3.n.1 above, theMPS Unit 3 strainer cumulative bypass percentage wasdetermined tobe3.5%. s 14.RFA-2.Assenlby P.itch TheRFA-2 FApitch wasused inthe calculation.

Assumptions 1.Thefiber andparticulate arewell mixed inthesumpfluid such thata homogeneous mixture ispresent atthe time ofsumprecirculation. Therefore, the debris transport is proportional toECCSflow rate.

2. Nodebris isheld upinanylocation other than thesumpstrainer(s), coreinlet, orwithin thecore.Further, no settling ofdebris iscredited inanylocation RCS. ofthe Page22of30

Serial No.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure Therefore, the maximum amount ofdebris reaches the core.

3.Chemicalprecipitates areassumed toform at24hours.

4.Thefiber isin its constituent form, i.e., individual fibers, which isconsistent with maximum transport assumptions.

5.AFPswerenotcredited. Per PWROG-16073-P, Rev. 0,(Reference 4.13), theNRC staff expects thedebris bed atthe core inlet will notbeuniform duetothevariations inflow velocities atthe coreinlet. Therefore, itwilltake moredebris than determined byWCAP-17788-P, Rev. 1,toresult in activation of the AFPsandredirection ofsome flow anddebris totheheatedcore. Because ofthenon-physical nature ofthe assumption ofa uniform debris bed (which remains conservative inother aspects),

credit for debris bypassing thecore inlet and entering the heated core should notbe used. Assuch, thevalues for inthe engineering calculation "M-split" were set tozero.

6.It wasassumed nodebris exits thebreak (i.e., once it isintheRCS,it stays inthe RCS). Therefore, the maximum a mount o fdebris reaches the c ore.

7.It wasassumed sumpdebris willbuild-up across thecore inlet ina uniform manner, andblockage isonly considered atthe core inlet. Thisis a simplifying, conservative assumption.

8.Atthetime ofHLSO,the charging pumps (high head) continue to deliver coolingflow tothecold legs, andthe (low head) SI pumps a rerealigned todeliver cooling flow to thehot legs. A maximum flow ratewill deliver themostfiber into the reactor pressure vessel (RPV), which isconservative, so with twopumpsoperatingfor both the charging andSI pumps, themaximumflowrates are876.1 and 830.7 gpm, respectively. Therefore, 51.3% ofthe flow isdelivered tothecold legs and48.7% is delivered tothe hot legs. Thesumofthese twoflow rates is45.2 gpmless than the total ECCSflow rate prior torecirculation, butbecause a higher flow rateis conservative andresults inmorefiber being delivered intothecore, the flow split was applied tothe total ECCSflow ratebefore HLSO.

Analysis i

TheHLBdebris isthesumofthefiber that iscaptured atthecore inlet andthein-core fiber:

Mr, HLB= Mr, ci+ Mr, in-core Where:

a Mr, HLeis thetotal fiber massfor thehot leg break Mr, ciis the massoffiber atthe core inlet

  • Mr, in-coreisthemassoffiber inthe heated core Page23of30

Serial No.21-016 DocketNo.50-423 Final SupplementalResponse toGL2004-02 Enclosure Themassof fiber that reaches theheated core cantravel through twopaths, either the AFPorfromthe hot leg post-HLSO:

Mr, = Mr, in-core AFP + Mr, ce Where:

a Mr,AFPisthe massof fiber that reaches the core throughthe AFP,and a Mr,ceisthe massoffiber that reaches the core via core the exit fiber (i.e., injection post-HLSO)

Theabove quantitieswere determined iteratively ateach time step. Thecalculation was terminated atthetime atwhich thesump fiber load wasless than orequal to1%ofthe initial sumpfiberload.

Aspreviously noted, AFPswere notcredited inthe analysis. Therefore,Mf, AFPWillalways equal zero. It fhetermination criteria isreached before thetime ofHLSO,then Mr, cewill also equalzero. If that isthecase, then theMr,in-coreterm iszero,andthetotal massof fiberfortheHLBissimply the fiberatthe core inlet.

Acceptance Criteria Thetotal fiber injected must beless than orequal tothe core fiber load limit inlet included inWCAP-17788-P, Vol. 1,Ref. 1,Table 6-3, for Westinghouse fuel.

3.n.6 Using thedesign inputs andassumptions noted above, themaximum amount offiber for MPSUnit 3 calculated topotentially reach thereactor vessel is9.6 g/FA, which is less thantheproprietary in-vessel fibrous debris limit provided inSection 6.5ofWCAP-17788-P, Volume 1,Rev. 1.

3.n.7 Confirmation that thecore inletfiber amountisless than theWCAP-17788-P Rev. 1threshold MPSUnit 3isaWestinghouse 4-loop design with Westinghouse 17x17 RFA-2 FAs.The applicablecoreinlet fiber threshold for Westinghouse fuelisprovided inTable 6-3of WCAP-17788-P, Rev.1 Thecalculated coreinlet fiberamount forMPSUnit 3 is 9.6g/FA, which isless than theapplicable WCAP-17788-P, Rev.1,coreinlet fiber thresholdlimit forWestinghouse fuel.

Page24of30

SerialNo.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure 3.n.8 r Aspreviously stated, theearliest possible SSOtime for MPSUnit 3 wasdetermined to be33minutes.

3.n.9 Chemicalprecipitation timing is dependent onthe plant buffer, sumppool pH,volume and temperature,anddebris types a nd quantities. Table 4.4-1 ofPWROG-16073 (Reference 4.13)identifies Test G roup 3 5 as representative of MPS Unit 3 ,andthe predicted chemicalprecipitation timing(tchem) iS 24 hours.

3.n.10 Confirmation that chemical effects will notoccur earlier thanlatest timeto W

MPS Unit 3 performs injection realignment to mitigate thepotential forboric acid precipitation (BAP) nolaterthan 5 hours, which isless than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

3.n.11 MPSUnit 3 isa Westinghouse 4-loop upflow configuration design. Based onWCAP-17788-P,Rev. 1,Volume 1,Table 6-1, tblockfor MPSUnit 3 is143 minutes.

3.n.12 Theearliest time ofchemical precipitation for MPSUnit 3wasdetermined tobe 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, whichisgreater than the applicable tblockValue of143minutes.

3.n.13 dgtsign.categoy TheMPSUnit 3rated core thermal power (RTP) is3650MWt.Theanalyzed core thermal poweris3723MWt, whichincludes instrument uncertainty. MPS Unit 3 'is a Westinghouse 4-loop design,andthe applicable analyzed thermal power is3658MWtas providedinWCAP-17788-P, Rev. 1,Volume 4,Table 6-1 Therefore, theMPSUnit 3 analyzedthermal power isgreater than the WCAP-17788-P analyzed value.

TheWCAP-17788-P, Vol. 1,Rev.1,thermohydraulic analysis assumes anSSOtime of 20minutestogether withanRTPof3658 MWt.Tojustify theuseofthe analysisandfuel described limit inWCAP-17788-P, it isnecessary todemonstrate the decay heat forMPS Unit 3 atthetime ofSSO(i.e., whenfibrous debris begins toarrive atthecoreinlet) is less than thedecay heat intheWCAP-17788-P thermohydraulic analysis atthe time o f SSOasdiscussed inPWROG-16073 (Reference 4.13).

Page25of30

SerialNo.21-016 Docket No.50-423 FinalSupplemental Response toGL2004-02 Enclosure Table4.5-2 of PWROG-16073 provides a decay heat at20minutes of87.4 MWt,which isthedecayheat available atthetime ofSSOintheWCAP-17788-P thermohydraulic analysis. Thedecay heatmodel isbased onthe1971 ANSInfinite Standard plus 20%

uncertainty[PWROG-16073, Section4.5.1.2). Asnoted above, thee arliesttime ofSSO forMPSUnit 3 is33minutes, which willresult inadditional time forthe core todecay and thusa lower normalized core power than that resulting at20minutes. TheMPSUnit 3 plant-specificpost-LOCAdecay heatfraction is0.0216 at30minutes. This decay heat fraction includes a 20%uncertainty andisconservativefor anSSOtime of33minutes.

Thedecay heat atthe time ofSSO isthen calculated tobe80.5 MWt(0.0216

  • 3723 MWt), which isless than thedecay heat fromtheWCAP-17788-P thermohydraulic analysisatthetime ofSSO(87.4 MWt). Therefore, theWCAP-17788-P thermohydraulic analysisandfuel limitsarestillbounding for MPS Unit 3.Inaddition, there issignificant margintothe maximum i nlet core fiber load to help offset this power level difference.

3.n.14 MPSUnit 3 isa Westinghouse upflow barrel/baffle configuration plant. Theproprietary analyzedAFPresistance isprovided inTable 6-1ofWCAP-17788-P, Volume 4,Rev. 1.

Theproprietary MPSUnit 3 specificAFPresistance isprovided inTableRAl-4.2-24 of WCAP-17788-P, Volume 4,Rev. 1.TheMPSUnit 3 specific AFP resistance islessthan theanalyzed value; therefore, theMPSUnit 3 AFP resistance is bounded bythe resistanceapplied totheAFPanalysis.

3.n.15 W

MPSUnit 3 isaWestinghouse upflowbarrel/baffle configuration plant. TheAFPanalysis forWestinghouse upflow plants analyzed a range ofECCSrecirculation flow ratesfrom 8 40gpm/FA, asshown inTable 6-1ofWCAP-17788-P, Volume 4,Rev. 1.TheMPS Unit3 ECCSrecirculation flowrate corresponding totheworst-case GSl-191 hotleg breakscenario is9 gpm/FA, which iswithin therange ofECCSrecirculation flow rates considered inthe AFPanalysis. t WhiletheMPSUnit 3 ECCSrecirculation flow rate corresponding totheworst-case GSI-191 hotlegbreak scenario iswithin therange ofECCSrecirculation flow rates considered intheAFPanalysis, theminimum plant-specific ECCSflow rate, 5 gpm/FA, islessthan theminimum analyzed ECCSflow rate usedtodevelop Kmax inReference 4.14.Debris bedresistance increases asECCSflow rate decreases, soanunbounded lowflowhasthe potentialtocause theKmax used inthe calculation tobenon-conservative.

However, themaximum ECCSflow rate atMPSUnit 3 creates themostlimiting case, whichhassignificant margin totheWCAP-17788 coreinlet fiberlimit. As such, the Page26of30

Serial No.21-016 Docket No.50-423 Final SupplementalResponse toGL2004-02 Enclosure unbounded minimum ECCSflow rateisacceptable because it does notcreate the limiting fiberloadat the coreinlet;therefore, Kmax isvalid for fiber thelimiting load case.

3.n.16 Summa.ry Thecomparison ofkey parameters usedinthe WCAP-17788 AFPanalysis totheMPS Unit 3 specific valuesis summarized inTable 5. Based onthese comparisons, MPS Unit 3isbounded bythekey parameters, andthe WCAP-17788 methods andresults are applicable.

TABLE5 KEYPARAMETER VALUES FORIN-VESSEL DEBRIS EFFECTS Parameter WCAP17788 Value MPS Unit 3 Evaluation Maximum Total In- < than the Maximum in-vessel fiber Vessel FiberLoad Volume 1,Section 6.5 WCAP-17788 load isless than WCAP-(g/FA) value 17788 limit.

Maximum CoreInlet Maximum core inlet fiber Fiber Load (g/FA) Volume 1,Table 6-3 96 load isless than WCAP-17788 threshold.

Later switchover time resultsin a lower decay Minimum Sump heat atthe time ofdebris Switchover Time 20 33 arrival,reducing the (min) potential for debris induced core uncovery andheatup.

Potential for complete core inletblockage dueto Minimum Chemical 2.4 24(tchem) chemical product Precipitate Time(hr), (tblock) generation would occur muchlater than assumed.

Latest hotleg switchover Maximum HotLeg occurs well before the Switchover Time 24(tchem) 5 earliest potential (hr) chemical product generation.

This value isnotbounded Rated Thermal bytheWCAP-17788-P 3658 3723 value arid is Power (MWt) dispositioned inSection 3.n.13 above.

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Serial No.21-016 Docket No.50-423 Supplemental Final Response toGL2004-02 Enclosure TABLE 5 KEYPARAMETER VALUESFORIN-VESSEL DEBRIS EFFECTS Parameter WCAP-17788 Value MPSUnit 3 Evaluation AFPresistance isless Maximum AFP Volume 4 Volume4 than the analyzed value, Resistance Table6-1 Table RAl-4.2-24 which increases the effectiveness oftheAFP.

ECCSrecirculation flow rate corresponding tothe ECCSRecirculationVolume 4 9 mostlimiting fiber (gpm/FA)

Flow Table6-1 injection hot leg break scenario is within the analyzed flow range.

3.o Chemical Effects NRCIssue:

Theobjective ofthechemical effectssectionistoevaluate theeffect that chemical precipitates have onhead loss andcore cooling.

1)Provide a summary ofevaluation results that showthat chemical precipitates formed inthepost-LOCA containmentenvironment, eitherby themselves or combined with donotdeposit debris, atthe sumpscreen totheextentthat anunacceptable head loss ordeposit results, downstream ofthesumpscreen totheextent that long-term core isunacceptably cooling impeded.

DENCResponst TheMPSUnit 3chemicaleffectsanalysisofthesumpstrainers wassubmitted inthe MPS Unit 3 Supplemental Response dated February29,2008(ADAMS Accession No.

ML080650561) andamended December 2008(ADAMS on 1 8, Accession No.

ML083650005)., aswell assubsequent RAlresponses submitted on March 13,2009 (ADAMS Accession No.ML090750436), September16, 2010 (ADAMS Accession No.

ML102640210), !andDecember 20,2010(ADAMS Accession No.ML103620562). The MPSUnit 3 sumpstrainer chemical effects isunchanged.

analysis 3.p Licensing Basis NRCIssue:

Theobjective ofthelicensing basis sectionistoprovide information regarding any changestothe plantlicensing basis duetothesumpevaluation or plant modifications.

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Serial No.21-016 Docket No.50-423 Supplemental Final Response toGL2004-02 Enclosure 1)Provide theinformation requested inGL 04-02 Requested Information Item 2(e) regarding changes tothe plant licensing basis. Theeffective date for changes tothe licensing basis should bespecified. This date should correspond tothat specified inthe 10CFR50.59evaluation for the change tothe licensingbasis.

DENC'sFebruary 29,2008 Supplemental Response discussed thelicensing bases changes that hadbeenimplemented for MPSUnit 3 associated with theresolution ofthe sumpissues considered inGSl-191 andGL2004-02. These changes arerestated below:

MPSUnit 3 FSAR TheMPSUnit 3 FSARwasrevised toreflect the installation ofthenewcontainment sump strainer. DENCwill update thecurrent licensing basis (Final Safety Analysis Report in accordance with 10CFR50.71(e)) following NRC acceptance ofthefinal supplemental response for MPSUnit 3.

MPSUnit 3License Amendments Twolicense amendments relatedtoGL2004-02 corrective actions wereapproved and implemented.

a A change tothestart signalforthe RSSpumpswassubmitted and approved to ensure the strainer wasfully submerged andadequate NPSHexisted for the RSS pumps prior totheir start considering a mechanistic debris blockage analysis. Amendment No.233wasapproved forMPSUnit 3 byNRCletter dated September 20, 2006 (ADAMS Accession No. ML062220160). Implementation ofthis c hange was completed during the MPSUnit 3 spring 2007refueling outage.

  • An amendment was approved andimplemented foran administrative changeto replace obsolete text inthe TS Section 4.5.2.d sump surveillance requirement with generic terminology for ECCScontainment sumpstrainefs. MPSUnit 3 Amendment No.240wasapproved byNRCletter dated September 18,2007(ADAMS Accession No.ML072290132).

4 References 4.1 NEl04-07, Revision 0,"Pressurizer Water Reactor SumpPerformance Evaluation Methodology", May28,2004.

4.2 NRCSERforNEl04-07, "Safety Evaluation bytheOffice ofNuclear Reactor Regulation Related toNRC Generic Letter 2004-02, Nuclear Energy Institute Page29of30

SerialNo.21-016 Docket No.50-423 Final Supplemental Response toGL2004-02 Enclosure Guidance Report (Proposed Document Number NEl04-07), 'Pressurized Water Reactor Sump Performance EvaluationMethodology'," dated December 16,2004.

4.3 NRCStaff Review Guidance forIn-Vessel Downstream Effects Supporting Review ofGenericLetter 2004-02 Responses, ADAMSAccessions No.ML19228A011, September 2019.

4.4 AREVA Calculation 32-9201054-000, "PWR Strainer Fiber BypassLength Distribution" (Framatome Proprietary).

4.5 AREVA SummaryTest Report 66-9199574-000, "Fiber BypassSize Characterization Test Report."

4.6 Alden Test Report 1142PBNBYP-R2-01, "Point Beach Large Scale Fibrous Debris Penetration Test Report."

4.7 Alden Calculation 1142PBNBYP-600-00,"Fibrous DebrisPenetration Model for Point Beach Calculation."

4.8 NextEra Energy Point Beach LetterNo.NRC2017-0045; "Updated Final Response toNRCGL2004-02," December 29,2017.

4.9 NRCDocument ML15320A087"Vogtle GSl-191 Resolution Plan andCurrent Status NRCPublic Meeting," November 5,2015.

4.10Alden TestReport 1130VNPBYP-R2-00-NONQA, "Vogtle Nuclear Plant Fiber Penetration Testing."

4.11MIL3-34325-TR-001, Rev. 0;"Reduced-Scale Testing for Millstone 3 Replacement Containment Sump Strainers", AECLTest Report.

4.1!2 MIL3-34325-AR-001, Rev.2 w/Addendum 00A;"Hydraulic Performance of

Replacement Containment SumpStrainers Millstone 3Power Station 4.13.

PWROG-16073-P, Rev. 0,"TSTF-567 Implement'ation Guidance, Evaluation ofIn-Vessel Debris Effects, Submittal Template for Final Response toGeneric Letter 2004-02 andFSARChanges," February2020.

4.14WCAP-17788-P, Rev. 1,"Comprehensive Analysis andTest Program for GSl-191 Closure (PA-SEE-1090)" December 2019.

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