ML21105A433

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
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)

Text

Dominion EnergyNuclear Connecticut, Inc.

Qg 5000 Dominion Boulevard, GlenAllen, VA23060 DominionEnergy.com Energy" April 15,2021 U.S.NuclearRegulatory Commission Serial No.: 21-016 Attention:

Document Control Desk NRA/GDM: R2 Washington, DC20555-0001 Docket No.: 50-423 License No.:NPF-49 MILLSTONEPOWERSTATION UNIT 3 ONEMERGENCY RECIRCULATION DURING DESIGN BASISACCIDENTS AT PRESSURIzEDWATER REACTORS" FINALSUPPLEMENTALRESPONSE Thepurpose ofthis submittal istoprovide theDominion Energy Nuclear Connecticut, Inc.,

(DENC) final supplemental response for Millstone Power Station(MPS)

Unit3to Generic Letter (GL) 2004-02, "Potential impact ofDebris Blockage on Emergency Recirculation during DesignBasisAccidents atPressurized-Water Reactors,"

dated September 13,2004.

OnMay15,2013(ADAMS Accession No.ML13141A277),

DENCsubmitted a letter of intent perSECY-12-0093, "Closure Options forGeneric Safety issue

191, Assessment ofDebris Accumulation onPressurized-Water Reactor SumpPerformance,"

indicating MPS Unit3 wouldpursueClosureOption2 Deterministic of the SECY recommendations (refinements toevaluation methods andacceptance criteria).The final outstanding issue forMPSUnit 3with respect toGL2004-02 isthein-vessel downstream effects evaluation todemonstrate long-term corecooling canbeadequately maintained forpostulated accident scenarios requiring sumprecirculation.

Thein-vessel downstream effects evaluation hasbeenco'mpleted forMPSUnit 3andis documented intheenclosure tothis letter.

Thissatisfies thefinal GSl-191 commitment identified intheMay15,2013Closure Option letter.

Thisresponse constitutes DENC'sfinal supplemental response toGL2004-02 forMPS Unit 3.

,Y

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

Response

toGL2004-02 Page2of3 Should you haveanyquestions orrequire additional information, please contact Mr.GaryD. Miller at(804) 273-2771 Respectfully, MarkD.Sartain VicePresident

- Nuclear Engineering andFleet Support Commitment contained inthis letter:

1 DENCwill updatethecurrent licensing basis(Final Safety Analysis Report in accordance with10 CFR 50.71(e))

following NRC acceptance ofthefinal supplemental response forMPSUnit 3.

Enclosure:

Final Supplemental

Response

toGL2004-02 COMMONWEALTH OFVIRGINIA))

COUNTYOFHENRICO

)

Theforegoing document wasacknowledged before me,inandfortheCounty and Commonwealth aforesaid, today byMarkD.Sartain, whoisVicePresident

- Nuclear Engineering andFleet Support ofDominion Energy Nuclear Connecticut, Inc.Hehasaffirmed before methat heisduly authorized toexecute andfile theforegoing document inbehalf ofthat

Company, and that the statements inthedocument aretrue tothebestofhisknowledge andbelief.

Acknowledged before methis/E dayof

I

, 2021 MyCommission Expires:

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

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

Response

toGL2004-02 Page3of3 cc:

U.S.

Nuclear RegulatoryCommission

- Region I

2100 Renaissance

Blvd, Suite 100 Kingof Prussia, Pennsylvania 19406

- 2713 NRCSenior Resident Inspector Millstone Power Station Mr.R.Guzman NRCSenior ProjectManager

- Millstone U.S.Nuclear Regulatory Commission OneWhiteFlint North Mail Stop08C2 11555Rockville Pike Rockville, Maryland 20852-2738

Serial No.21-016 Docket No.50-423 Enclosure FINALSUPPLEMENTAL

RESPONSE

TOGL200402 Dominion Energy Nuclear Connecticut, Inc.

(DENC)

Millstone PowerStation Unit3

Serial No.21-016 Docket No.50-423 Enclosure TableofContents 1

Overall Compliance.....-----..--...-.-.--....-....-.....-2 1.1 Overview ofMillstone PowerStation Unit3Resolution toGL200402-.2 1.2 Correspondence

Background

..-....-.................----.3 1.3 General Plant System Description

.....----....---...........5 1.4 General Description ofContainment SumpStrainers

--....--5 2

General Description andSchedule for Corrective Actions-..,,.-.,-6 3

Specific information forReview Areas.,,,---....-..=.........-......15 3.n Downstream Effects

- FuelandVessel -.............-.-.-..---..15 3.o Chemical Effects.-,,-....-....-...........=.-.----.28 3.p Licensing Basis

...--..=-...--.----..........-.,-.,,..28 4

References--,..-.-....-.....--...--....-..---...-..-.29 Page1of30

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

Response

toGL2004-02 Enclosure 1

Overall Compliance NRCIssue:

Provide information requested inGL 2004-02, "Requested Information,"

Item2(a) regarding compliancewith regulations.

That is,provide confirmation that the[Emergency CoreCooling System(ECCS)) ECCSand[Containment SpraySystem(CSS))

CSS recirculation functions under debris loadingconditions areorwill beincompliance with theregulatory requirements listed intheApplicable Regulatory Requirements section of this generic letter.

This submittal should addresstheconfiguration oftheplant that will exist onceall modifications required for regulatory compliance havebeenmadeandthis licensing basis hasbeenupdated toreflect theresultsoftheanalysis described above.

DEbIC Rejiponse.;

Inaccordance withSECY-12-0093 andasidentified inDENCletter totheNRCdated May15,2013(ADAMS Accession No.ML13141A277),

Millstone PowerStation (MPS)

Unit3 elected topursue GSI-191 Closure Option 2 Deterministic andidentified in-vessel downstream effects asthelast outstanding issue to beresolved.

Topical Report (TR)

WCAP-17788-P, Rev.1,provides evaluation methods andresultstoaddress in-vessel downstream effects.

Asdiscussed inNRC"Technical Evaluation Report of In-Vessel Debris Effects" (ADAMS Accession No.ML19178A252),

theNRCstaff has performed adetailed review ofWCAP-17788-P.

Although theNRC staff didnotissue a

Safety Evaluation forWCAP-17788, asdiscussed further in"U.S.Nuclear Regulatory Commission Staff ReviewGuidance forIn-Vessel Downstream Effects Supporting ReviewofGeneric Letter 2004-02 Responses" (ADAMS Accession No.ML19228A011),

thestaff expects manyofthemethods developed intheTRcanbeusedbyPressurized WaterReactor (PWR) licensees todemonstrate adequate long-term core cooling (LTCC).

Completion oftheanalyses demonstrates compliance with10CFR50.46, "Acceptance criteria foremergency corecooling systems forlight-water nuclear power plants,"

(b)(5),

"Long-term cooling,"

asitrelates toin-vessel downstream debris effects forMPSUnit 3.

1.1Overview ofMPSUnit3Resolution toGL200402 Byletter datedFebruary 29,2008(ADAMS Accession No.ML080650561),

DENC submitted asupplemental response toGL2004-02 forMPSUnit 3that provided specific information regarding themethodology usedfordemonstrating compliance withthe applicable regulations, aswell asthecorrective actions that hadeither beenimplemented orplanned tosupport theresolution ofGSI-191.

Byletter datedDecember 18,2008 (ADAMS Accession No.ML083650005),

DENCupdated itssupplemental response for MPSUnit 3toprovide additional information regarding theanalyses performed andthe corrective actions taken that hadnotbeencompleted atthetimeoftheFebruary 29,2008 response.

Thecontent andlevel ofdetail provided wereconsistent withtheNRC guidance provided inNRCletter datedNovember 21,2007(ADAMS Accession No.

ML073110389).

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

Response

toGL2004-02 Enclosure Additionalinformation wasprovided inDENCletters datedMarch13,2009(ADAMS AccessionNo.

ML090750436),

September 16,2010(ADAMS Accession No.

ML102640210),

December 20,2010(ADAMS Accession No.ML103620562),

and June13,2017(ADAMS Accession No.ML17171A229).

DENCcommitted toaddress the resolution ofdownstream in-vessel effects forMPSUnit3 following theissuance of revised WCAP-16793, "Evaluation ofLong-Term Cooling Considering Particulate, Fibrous andChemical Debris inthe Recirculating Fluid,"

andtheassociated NRCSafety Evaluation Report (SER).

Byletter datedMay15,2013(ADAMS Accession No.ML13141A277),

MPSUnit3 provided itsresolution planfor 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).

Thatletter alsoincluded asummary ofthe corrective actionsandanalyses that hadbeen implemented forMPSUnit3 toaddress GSl-191, aswellasinherent margins and conservatisms included intheanalyses.

Theplant

analyses, changes,

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

By letter datedAugust13,2015(ADAMS Accession No. ML15232A026),

DENC committed todeveloping plansfordemonstrating compliancewith PWROG WCAP-17788-P in-vessel debris acceptance criteria forMPSUnit3andto communicate that plan totheNRCinafinal updated supplemental response tosupport GL 2004-02 closure.

Thiseffort hasbeencompleted, andtheresolution ofin-vessel downstream effects is provided inSection 3.nbelow.

Thisanalysis doesnotcredit alternate flowpaths (AFPs) andconservatively assumesallfibrous debris thatenters thereactor vessel will accumulate atthecoreinlet, eventhough, inreality, somefraction offibrous debris will penetrate thecoreinlet orbypass thecoreinlet viaAFPs.

1.2Correspondence

Background

A listirig ofthesalient correspondence issued bytheNRCorsubmitted byDENCfor MPSUnit 3regarding theresolution ofthecontainment sumpissues identified inGL2004-02isprovided inTable 1.

TABLE1-GENERICLETTER200402CORRESPONDENCE AM DocumentDate A cgeyssion Document September 13,2004 ML042360586 NRCGL2004-02 March4,2005 ML050630559 First response toGL2004-02 Page3of30

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

Response

toGL2004-02 Enclosure TABLE 1

- GENERICLETTER200402CORRESPONDENCE DocumentDate Am"e*rssion Document ADA September 1,2005 ML052500378 Follow-up

Response

toGL2004-02 License Amendment Request (LAR) to September 15,2005 ML052580387 modifyTechnical Specifications (TS) regarding initiation oftheMPSUnit 3

Recirculation Spray(RS) system NRCissuance ofLicense Amendment(LA)

September 20,2006 ML062220160 233tomodify MPSUnit 3TSregarding initiation oftheRSsystem LAR toreviseMPSUnit 3TStousegeneric September 1,2006 ML062480263 terminology forECCScontainment sump strainers NRCissuance ofLA240torevise MPS September 18,2007 ML072290132 Unit 3TSto use generic terminologyfor ECCScontainment sump strainers November 21,2007 ML073110389 NRCRevised Content Guide December 19,2007 ML090860438 Draft Benchtop Test Plan for determining chemical effects February 29,2008 ML080650561 Supplemental

Response

toGL2004-02 December 17,2008 ML083230469 First NRCRequest for Additional Information (RAI)

December 18,2008 ML083650005 Notice ofCompletion ofActivities toaddress GL2004-02 March13,2009 ML090750436 Resppnse tofirst NRCRAl February 4,2010 ML100070068 Second NRCRAI September 16,2010 ML102640210 MPSUnit 3response tosecondRAI December 20,2010 ML103620562 Final response forMPSUnit 3second RAl May15,2013 ML13141A277 GSl-191 Closure Option Letter August 13,2015 ML15232AO26 Regulatory Commitment ChangeLetter June13,2017 ML17171A229 Third NRCRAIresponse Page4of30

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toGL2004-02 Enclosure 1.3General PlantSystemDescription MPSUnit 3is a Westinghouse four-loop PWRdesign.

TheNuclear SteamSupply System (NSSS) consists of one reactorpressure vessel (RPV),

four steamgenerators (SGs),

four reactor coolant pumps (RCPs),

onepressurizer andtheReactor Coolant System(RCS) piping.

Eachofthefour reactor coolant loops(RCLs) consists ofa SG,anRCP,and associated RCSpipingand iscontained inaconcrete enclosure referred toasacubicle.

Thesefourcubicles areessentially equivalentwithrespect topiping andequipment insulation.

Thereactor isoperated insidea reinforced concrete containment structure maintained atasubatmospheric pressure between10.6and14.0psia.

Thecontainment structure isequipped witha containment sumplocated attheouterwallofthe containment.

Extensive useismade of gratings andopenings intheupperfloors and structures ofthecontainment toallowwater entering thecontainment todrain downto thecontainment sump.Also, the compartmentalized containment design slows transport ofdebris tothesump.

Theemergency corecooling system(ECCS) provides borated water tocoolthereactor corefollowing amajor lossofcoolant accident (LOCA). Thisisaccomplished bythe automatic injection ofwater fromtheSafety Injection (SI) accumulators into theRCLsand bytheautomatic pumping ofa portion oftheRefueling Water Storage Tank(RWST) contents into theloops viathecharging

pumps, SIpumps,and Residual HeatRemoval (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, andinto theRCLsdirectly andviathecharging andSIpumps.

Thecontainment heatremoval system consists oftheQuench Spray (QS) system and thecontainment RSS. Following thepostulated designbasis accident (DBA),

containment pressure isreduced byemploying bothsystems.

Heatistransferred from thecontainment atmosphere totheQSsystemandtheRSSspray water.

Heat is transferred fromthecontainment totheService Water(SW) system viatheRSSheat exchangers.

TheQSsystemsprays borated waterfromtheRWST.TheRSSdraws suction fromthecontainment sump,thecontent ofwhichconsists oftheprimary or secondary system effluent andthequench spiray.

Thestart signal fortheRSSpumps (which aretheonlypumpsthat takesuction fromthecontainment sumpprior tosump switchover) waschanged toautomatically start whenRWSTlevel reaches theLow-Low Level setpoint coincident withacontainment depressurization actuation (CDA) signal.

Thisensures thestrainer isfully submerged prior todrawing waterthrough thestrainer forcoolant recirculation.

1.4General Description ofContainment SumpStrainers Asstated intheMPSSupplemental

Response

datedFebruary 29,2008andtheMPS Unit3 FSAR,a new,replacement ECCSstrainer manufactured byAtomicEnergy Page5of30

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

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toGL2004-02 Enclosure Canada, Ltd. (AECL) wasinstalled toreplace theprevious trash

rack, coarse mesh,and fine meshscreen thathadasurface areaofapproximately 240ft2.

Thefour RSSpumps take suctionfrom acommon containment sumpthat isenclosed bythestrainer assembly.

Thestrainer consists ofmultiplefins constructed fromcorrugated perforated plate with 0.0625-inch holes. The finsareerected vertically overthesumpandextend beyond the sumptoachieve therequired surfacearea.

Post-accident watercovers thestrainer and isfiltered bythestrainer prior toenteringthecontainment recirculation pumps' suctions.

Design ofthestrainer isbased onathoroughmechanistic analysis anddebris-bed head loss testing todemonstratethat adequate netpositive suction head(NPSH) andpump suction line flashing margin exists under worst-case debris clogging scenarios.

Vortex suppression isprovided bythe design ofthestrainer asconfirmed byanalysis andhead losstesting.

Strainer design also included structural analysis todemonstrate structural adequacy under allpossible conditionsof debris blockage. Thus,water will beavailable tothesuctions oftheRSSpumpsunder DBA conditions.

Thestrainer hasasolid coverplate installed approximately eight inches abovethefins that protects thefins frominadvertently dropped debris during outages andalsoprovides aworkplatform.

Thefins onthestrainer arenominally seven inchesoffthecontainment

floor, andthesupport structure forthestrainer comprises a nominal seven-inchcurb.

The strainer isdesigned towithstand design basis earthquake loading andhydraulic loading prior toandduring operation.

Thesumpstrainer structure's seventeen interconnected modules areanchored toasupport

frame, which isinternally anchored tothecontainment structure basement slab.Thestrainer islocated outside ofthe containment structure cranewall intheannulus between thecranewall andthecontainment exterior wall.

TABLE2-CONTAINMENT SUMPSTRAINERSURFACEAREA Strainer Surface Area(ft2)

MPSUnit 3Strainer

~5041 2

General Description andSchedulefor Corrective Actions NRCIssue:

Provide ageneral description ofactions taken orplanned, anddates foreach.

Foractions planned beyond December 3'1, 2007,reference approved extension requests orexplain howregulatory requirements will bemetasper"Requested Information" Item2(b).

That isprovide ageneral description ofandimplementation schedule forall corrective

actions, including anyplant modifications, that youidentified while responding tothis generic letter.

Efforts toimplement theidentified actions should beinitiated nolater thanthefirst refueling outagestarting after April 1,2006.Allactions should becompleted by Page6of30

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

Response

toGL2004-02 Enclosure December 31, 2007.Provide justification fornotimplementing theidentified actions duringthefirst refueling outage starting afterApril 1,2006.Ifallcorrective actions 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 analysesto determine thepotential foradverse effects ofpost-accident debris blockage anddebris-laden fluids toprevent therecirculation functions ofthe ECCSandRSSforMPSUnit 3.The analyses considered postulated DBAsforwhich therecirculation ofthesesystemsis 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 bytheNRCSafety Evaluation Report (SER),dated December 6,2004 (Reference 4.2):

BreakSelection 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 aDBA.Using theresults oftheanalyses, conservativehead loss testing wasperformed todetermine worst-case strainer headlossanddownstream effects.

Chemical effects bench-top testsconservatively assessed thesolubilities and behaviors ofprecipitates andapplicability ofindustry dataon thedissolution and precipitation tests ofstation-specific conditions andmaterials.

Reduced-scale testing was performed byAECLusing twoseparate test

rigs, andmulti-loop testing established the influence ofchemical products onthead loss across thestrainer surfaces bysimulating theplant-specific chemical environment present inthewater ofthecontainment sump after aLOCA.

Inaddition, plant modifications werecompleted forMPSUnit3 insupport ofGSl-191 resolution including thefollowing:

1.AnewMPSUnit 3ECCSstrainer (with corrugated, perforated stainless steel fins) was installed with atotal surface areaofapproximately 5041ft2 toreplace theprevious trashrack,coarsemesh,andfinemeshscreenthathada surface areaof approximately 240ft2.

Thereplacement strainer wasdesigned towithstand upto Page7of30

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Response

toGL2004-02 Enclosure approximately 10poundspersquare inch(psi) ofdifferential pressure andhasa strainer hole sizeof0.0625

inches, whichissmaller thantheprevious screen sizeof 0.09375inches.

2.Thestart signal for theMPSUnit 3RSSpumps(which aretheonlypumpsthat take suction fromthecontainment sumpprior tosumpswitchover) waschanged during the spring 2007refueling

outage, as permitted byAmendmentNo.233(ADAMS Accession No.ML062220160). Themodificationchanged theautomatic start signal atapproximately 660seconds following thepostulated accident toanautomatic start whentheRWSTlevel reaches theLow-Low Level setpoint coincident witha CDA signal.

This ensures the strainer isfully submerged prior todrawing water through the strainer forcoolant 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 andalimiting mixofdebris areassumed attheECCScontainment sumpstrainer.

Using theresults oftheanalyses, conservative headloss testing was performed todetermine worst-case strainer headlossand downstream effects.

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

3.Reduced-scale testing wasperformed byAECLandDominion Energypersonnel.

The reduced-scale testing established theinfluence ofchemical productson head loss across thestrainer surfaces bysimulating theplant-specific chemical environment present inthewater ofthecontainment sumpafter aLOCA.

4.Downstream effects analyses wereperformed forclogging/wear ofcomponents in flow streams downstream ofthestrainers.

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

6.Insulation specification changes weremadetoensure thatchanges toinsulation in containment canbeperformed onlyafter theimpact oncontainment strainer debris loading isconsidered.

To ensurethemodifications implemented andtheanalyses performed effectively addressed uncertainties withsufficient

margin, thefollowing margins andconservatisms wereincorporated:

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toGL2004-02 Enclosure 1

Debris generation analysis usedveryconservative zonesofinfluence (zOls) that resulted in theremovalofvirtually allinsulation within theaffected cubicle.

Conservative zOls fromNEl04-07 wereapplied forfibrous insulation, whichdidnot credit the metal encapsulation formuchofthefibrous insulation inthesteamgenerator cubicles.

Nocredit was taken inthedebris generation calculation foranyreduction of insulation destruction duetolocation oftheinsulation withrespect tothebreak.

2.Therearenumeroussurfaces throughout containment whereinsulation andother debris arelikely tosettlefollowing breakblowdown andnotbedislodged bywashdown orcontainment spray.

Consequently, this material debris would notbeavailable for transport tothestrainer.

However, allinsulation generated wasassumed inthedebris generation analysis tobeimmediately transported tothecontainment

floor, entering thecontainment pool.

3.Although credit istakeninthedesign of thestrainerforleak-before-break in consideration ofpipe

whip, jet impingementand

missiles, nocredit wastaken forleak-before-break todetermine theamountofdebris generated ortransported.Analysis of leak-before-break effects that reduce thesize ofthe break that could occurprior toits detection hasbeenapproved bytheNRCforuseas part oftheMPSUnit 3licensing basis.

Thereactor coolant pipes areassumed tobreak instantaneously forthedebris generation andtransport analysis.

4.Thedebris transport analysis conservatively assumes all fibrous fines aretransported tothestrainer

surface, 90%oflarge andsmall fibrous debris pieces areerodedinto fines andtransported tothestrainer

surface, andall particulate debris istransported tothestrainer surface.

5.Conservative assumptions fromthedebris transport analysis wereadded tothe conservative basis forthedebris headloss determination fromtesting.

The debris headloss testing wasdonewith aparticulate surrogate that hasalower densitythan theepoxy coating that isexpected tomakeupmuchoftheparticulate debris.

Stirrers wereusedinthetest tank tominimize settling ofdebris tothegreatest extent possible.

Thetesting evaluated both extremes ofdebris loading (thin-bed debris loadandthe full debris load) anddetermined theworst-case headloss.Boththin-bed andfull debris loadtesting usedtheparticulate loading generated bythelarge!

break LOCA (LBLOCA).

Theworst-case headloss(thin-bed) isunlikely tooccurforaLBLOCA because thequantity offiber transported tothestrainer islikely tobetoohigh toallow forcreation ofathin-bed.

Thethin-bed headlossisalsounlikely tooccurforasmall break LOCA(SBLOCA) since thequantity ofparticulate necessary forformation ofthe worst-case thin-bed wouldnotbegenerated.

6.Nocredit wastakenfor accident-induced overpressure incalculation ofNPSHmargin fortheECCSpumps.

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toGL2004-02 Enclosure 7.No credit wastakenforsettling ofparticulate debris on surfaces throughout containment thatwouldoccurprior toandduring coolant recirculation, including inthe areasofthe containment poolthat haveextremely lowvelocities during recirculation asshownby computational fluid dynamics (CFD) analysis.

8.Thereplacement strainer hasaverylarge surface areaandthestrainer footprint is spread overaverylarge region ofcontainment.Foranyonebreak incontainment, thebreak-induced turbulence inthepost-LOCAsumppoolwouldbelocalized.

The large strainer footprint combined with thelocalized turbulence results inlarge areasof thecontainment sumppoolhaving verylowvelocities, which wouldenable extensive debris settling onthe containment floor andmayresult inanearly clean strainer area oversomeportion ofthestrainer surface.

However,cleanstrainer areawasnot credited inchemical effects orhead loss evaluations, andnosignificant settling of debris wascredited inthedownstream effects evaluation.

9.Nocredit wastaken foradditional NPSHmargin duetosubcoolingofthesumpwater.

Thecontainment sumpwaterwasconservatively assumed tobesaturated for calculation ofNPSHfortheECCSpumps.Nocredit was taken fortheseveral hours required toformtheworst-case debris bed(thin-bed),

during whichtime subcooling of thesumpwaterwouldaddsignificant NPSHmargin for theECCSpumps.The analysis conservatively assumesthere isnotimedelay in transport tothestrainer following thebreak.

Formation ofchemical precipitates andtheir subsequent transport tothestrainer debris bedwouldoccurmanyhours after the accident when containment heatremoval requirements aresignificantly reducedand when significant subcooling ofthesumpwaterhasoccurred.

Test evaluations demoristrated that a

fully formed thin-bed ofdebris takes significant time(hours) toform and is dependent onunsettling debris throughout thetest tank.Consequently, aworst-case thin-bed of debris will bedifficult toformandwill notformuntil several hours after sump recirculation canbeinitiated.

Significant debris settling andsignificant sump water subcooling occurs during theformation ofadebris-bed soadditional NPSHmargin is present forchemical effects headloss.

10.Thedebris loadinheadloss testing wastaken fromthedebris transport calculation, whichcredits noparticulate settling.

s v

11Debris introduction procedures inchemical effects testing resulted inminimum near-field settling andconservatively highheadlosses.

12.Debris introduction wasaccomplished inacarefully controlled mannertoresult inthe highest possible headloss.

Particulate wasintroduced initially, whichwasfollowed bydiscrete fiber additions after theparticulate debris wasfully circulated.

13.Thetesttanks werestirred during testing.

However, local areasofturbulence that mayexist inanypost-LOCA containment sumpwater areexpected tobelimited to Page10of30

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toGL2004-02 Enclosure certain portions ofsumpwatervolume.

Consequently, muchofthesumpwaterwill bestilland have nearzerovelocity.

14.Particulatesettling inheadlosstesting wasconservatively minimized through useof alower density walnut shell particulate asasurrogate forthehigher density epoxy coating particulate that maybepresent inpost-LOCA sumpwater.

15.Downstream wear analysis usedtheLBLOCAparticulate loadtodetermine abrasive anderosive wear.Thisis a conservative particulate

loading, inviewofthefollowing:

• Muchoftheparticulate included inanalysis isunqualified coating thatisoutside thebreak zOI.This unqualified coating isassumed topotentially dislodge dueto exposure tothecontainment environment.

However,an exposure-based mechanism todislodgement, ifit occurs

atall, islikely onlyafter manyhours and days.

• Thelowvelocity ofthesumpwater columnand thesignificant numberofsurfaces throughout containment promote significant settling ofparticulate incontainment.

Settled coating will notbedrawnthrough the ECCS strainer since thestrainer sits approximately seveninches abovethecontainment floor.

Additionally, qualified coating postulated tofail inthepresence ofthe201is not buoyant inthesump watercolumn.

• Thecapture ofparticulate inthedebris-bed onthestrainer does notoccurinthis

analysis, maximizing effects ofdownstream wear.

16.The baseconcrete dissolution isconservatively assumedtobeuninhibited bythe presence oftri-sodium phosphate (TSP),

eventhoughbenchscale testsolutions demonstrate inhibition ofconcrete degradation atcontainment sumpwaterpHlevels.

Consequently, calculations oftheamountofcalcium tobeaddedtothetest tank for headloss tests wereconservative.

17.The amountofaluminum andassociated testresults concerning itsrelease into the simulated post-LOCA sumpwaterthrough corrosion of

, aluminum surfaces was conservative baseduponseveral conditions:

• Aluminum corrosion amounts werecalculated athighpHtofavor corrosion, and aluminum precipitation wasevaluated atlowpHtofavor precipitation.

• Testing with alower pHfavors precipitation Rig89testing wasperformed with a

pH7at770Ftoencourage aluminum compound precipitation, eventhough the actual pH inthesumpwaterisapproximated aspH8 at770F.Also,TS requirements fortheRWSTandTSPbaskets ensure sumpwaterpHis> 7 at 770F.

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toGL2004-02 Enclosure Rig 89 testing wasevaluated conservatively withlowshort-term acceptance

criteria, along withthemaximumaluminum concentration ofthesumpwaterthat exists only after 30days.

a Analysis conservatively didnotaccount forthepossible inhibitory effect ofsilicate, phosphate, orother species onaluminum corrosion.

a Therateofcorrosion was maximized byanalysis thatdoesnotassume development ofpassive films, e.g.,noaluminum oxides remain onaluminum surfaces.

Passive films can otherwise beusedtodecrease thecorrosion rateby afactor oftheexposure time. Consequently, having noaluminum oxides remain onaluminum surfaces soall aluminum released bycorrosion enters thesolution is conservative.

• Aluminum notsubmerged incontainment was considered byanalysis tobe exposed tocontainment sprays andtherefore available forcorrosion.

However, someofthealuminum sources incontainment, such astheout-of-core detector

holders, maynotbesubject toa continuous containment spray andwouldnot contribute tothetotal aluminum concentration inthe containment pool.

• Aluminum released into thesolution 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.

Itisreasonable toexpect a portion ofthe aluminum ionsreleased into solution will plate outonsomeofthe multiple surfaces incontainment prior toarriving atthedebris-bed onthestrainer.

a Chemical effects testevaluations conservatively neglected theeffectof the presence ofoxygen inthesumpwater.

Corrosion rateofaluminum inaerated pH 10alkaline water canbeafactor oftwolower thanwhentherateismeasuredin nitrogen-deaerated water.ThisdataisinNUREG/CR-6873, "Corrosion Rate

!Measurements and Chemical Speciation of Corrosion Products Using

'Thermodynamic Modeling of DebrisCompohents to SupportGSI-191,"

'(Jain etal.April 2005).

18.Nonear-field settlement wascredited intheMPSUnit 3testing.

19.Theconservatism oftheRig89 testresults relative tothecontainment was demonstrated bythefollowing factors:

a ThetesttanksizeforRig89wasa 16-in x 16-in x 36-in stainless box.No significant debris transport wasneeded fordebris toreachthestrainer surface.

Debris transport distance inthetesttankwas essentially zerowhereasin Page12of30

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

Response

toGL2004-02 Enclosure containment, duetothelarge footprint ofthestrainer, debris transport distances to atleast one legofthestrainer areexpected tobesubstantially greater thanthis test tank size.

• Walnut shell particulate (used asthesurrogate forepoxy) hasa density of approximately 80 pounds percubic foot(lb/ft3) aS Compared tothehigher density ofepoxy(94 lb/ft3). Thus, epoxyismorelikely tosettle thantheparticulate surrogate usedintesting.

'

• Asignificant portion ofthe particulate expected tobegenerated isfromunqualified coatings thatarepostulated tobe dislodgedfromcomponents throughout containment by temperature and humidity in containment post-LOCA.

Degradation ofthese unqualified coatings will takesignificant time(hours, and probably days),

andthustheamount ofparticulate inthedebris-bed (and inthe testtank) isconservative.

Additionally, all oftheunqualified coating ispostulated tofail

assmall, transportable particulate when inreality,muchoftheunqualified coating ismorelikely tofail aslarge piecesthat willnottransport.

• The strainer incontainment sits approximately seven inchesabovethe containment floor.

Thus,anyparticulate which slides along thefloor with thesump watermotion isunlikely toreach thestrainer surface.

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

However, thecalculation ofwearofcomponent surfaces duetodebris conservatively neglects this particle debris settling andcapture.

21RSSpumpstart occurs whentheRWSTisapproximately half full.

Thewater level continues torise until itisseveral feet abovethetopofthestrainer forthefirst few hours after theaccident while theRWSTcontinues tobepumpedinto containment, adding NPSHmargin fortheRSSpumps.However, analysis conservatively used the waterlevel fromaSBLOCAthat exists atthestart oftheRSSpumps.

t 22.A5D(5timespipediameter) 201wasusedforqualified epoxycoating particulate 1 resulting inatotal generation andtransport of10.4ft3 ofqualified coating particulate tothestrainer.

BasedontheApril 6,2010NRCtoNElLetter (ADAMS Accession No.

ML100960495),

a4DzOIisacceptable forqualified epoxycoatings.

Useofa4D201 wouldresult inonly8.0ft3 Ofqualified coating particulate.

Thus,thestrainer testing used23%more(2.4 ft3) qualified coating particulate thanwhatisexpected tooccur in containment duetouseofthemoreconservative 5D201 23.A10%margin wasaddedtothecoatings particulate debris quantities generated from thezOIandfromunqualified coatings (a

total of2.1ft3 OfCOatings margin).

Reduction Page13of30

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Response

toGL2004-02 Enclosure ofcoating debris, whichisallmodeled asparticulate, wouldresult inareduction in thin-bed head loss.

24.Theabovetwo conservatisms result inatotal excess of4.5ft3 OfCOating OVerwhatis expected tooccur onthestrainer incontainment.

Thetotal particulate coating load onthestrainer was calculated tobe23ft3.

Areduction of4.5ft3 isequivalent toa20%

reduction incoatingparticulate, which wouldresult inareduction instrainer headloss forathin-bed fromthetested values.

25.Unqualified coating wasdeemed tofail immediately astransportable particulate.

This isparticularly conservative since unqualified coating makesup46%ofthetotal tested coating loadand39%ofthetotal particulate loadonthestrainer.

Electric Power Research Institute (EPRI) testing (Reference EPRITechnical Report 1011753 dated September 2005) hasshownthat less than one-third ofunqualified coatings actually failed whensubjected toDBAtesting.

26.Fivepercent margin wasaddedtothefibrous debris quantities generated fromthe zOI(a total ofover60ft3 Offiber margin).

27.Five percent margin wasaddedtothemicrotherm debris quantity generatedfromthe zOf(a total of0.1ft3 OfmiCrotherm margin).

28.InbothRig33andRig89testing, fibrous debris wasconservatively preparedas "single fine."

29.Onehundred percent debris transport wasassumedforcoatings, microtherm, and latent debris.

30.A sacrificial strainer areaisinstalled incontainment toaccommodate transport of foreign material tothestrainer.

Theinstalled strainer area(5041 ft2) exceeds the tested strainer area(4290 ft2) byatleast theamountofthesacrificial area.

t Resolution ofDownstream Effects

- FuelandVessel:

Thisitemisdispositioned in Section 3.nbelow.

=.

Withthecompletion ofthedownstream effects analysis forthefuel andvessel, DENC haseffectively resolved forMPSUnit3theissues identified inGL2004-02 andisin compliance withtheapplicable regulations.

Page14of30

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

Response

toGL2004-02 Enclosure 3

Specific Information forReviewAreas Asstated inthe MPS Unit3Supplemental Response datedFebruary 29,2008(ADAMS Accession No.ML080650561) andamended onDecember 18,2008(ADAMS Accession No.ML083650005),as well assubsequent RAIresponses submitted onMarch13,2009 (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),

MPSUnit3 hasaddressed review areas3.athrough 3.m.

Therefore, onlytheoutstanding review areasof3.n through 3.pareaddressed inthissubmittal.

3.n Downstream Effects

- Fuel and Vessel NRCIssue:

Theobjective ofthedownstream

effects, fuel andvessel section istoevaluate theeffects thatdebris carried downstream ofthecontainment sump screen andintothereactor vessel hasoncorecooling.

Showthatthein-vessel effects evaluation isconsistent

with, orboundedby,the industry generic guidance (WCAP-16793),

asmodified by NRC staffcommentson that document.

Briefly summarize theapplication ofthe methods.

Indicate wherethe 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),

theNRCstaff hasperformed a detailed review ofWCAP-17788-P.

Although theNRCstaff didnotissue a Safety Evaluation forWCAP-17788-P, as discussed further in"U.S.Nuclear Regulatory Commission Staff ReviewGuidance forIn-Vessel Downstream Effects Supporting Review ofGeneric Letter 2004-02 Responses" (ADAMS Accession No.ML19228A011),

thestaff expects that manyofthemethods developed intheTRmaybeusedbyPWR licensees todemonstrate adequate LTCC.DENCusedmethods andanalytical results developed inWCAP-17788-P, Rev.1,toaddress in-vessel downstream debris effects for MPSUnit 3andhasevaluated theapplicability ofthemethods andanalytical results from WCAP-17788-P, Rev.1,forMPSUnit 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 fortheMPSUnit 3containment sumpstrainer tofacilitate theevaluation ofthein-vessel debris effects forNRCGL2004-02.

Fromthedebris generation and transport analyses performed forMPSUnit 3,DENChas conservatively determinedthe types andquantities offibrous debris thatcouldbe transported tothestrainers, asdocumented byletter dated February 29,2008(ADAMS Accession No.ML080650562).

The fibrous debris sources considered intheMPSUnit 3

analyses included fiberglass andlatent fiber.

Thetotal fibrous debris quantity fromthese sources thatcould potentially reach the MPS Unit3sumpstrainer wasconservatively calculated tobeapproximately 2053Ibm.

Thestrainer fiber bypass testing performed byAECL thatwasapplied totheMPSUnit 3

strainer didnotmeasure thecumulative quantities offiberbypassedafter eachfiber addition tothetest tank.Thetesting useda"grabsample" methodthat looked atfiber massinawatersample taken downstream ofthe strainer fins atdiscretepoints intime.

Thistesting provided certain

insights, suchaslong-term strainer bypass waslow,butdid notprovide insight into theextent offiber bypass occurring early inECCSoperation.

Consequently, there isnodataforthequantity ofbypassedfiber asthedebris bedis forming; therefore, cumulative fiber bypass fractions cannot bedetermined.

However, otherplants intheindustry haveperformed strainer bypass testing with downstream continuous in-line filters that wereabletodetermine cumulative fiber bypass fractions forvarious debris bedthicknesses.

Consequently, Dominion Energy performed anevaluation todevelop anengineering basis fortheuseofcumulative fiber bypass data fromother plants toapply totheAECLstrainer installed atMPSUnit 3.

M Basedonreview ofstrainer bypass testing dataforthePoint BeachandSouthTexas Project (STP) plants (References 4.6and4.14, respectively),

itwasobserved that asa debris bedforms andcontinues tobuild onastrainer, thefiltration efficiency will plateau atnearly 100%.Eachofthesetests wasperformed withcontinuous in-line filters downstream ofthestrainer assemblies toensure acumulative fiber bypass fraction could bedetermined.

Thefiltration efficiency behavior isalsoconsistent withthat indicated in thebypass testing results fortheDominion Energy fleet that wasperformed byAECL.

Butsince theAECLtests werebasedonly ongrabsamples takenatspecific turnover intervals forthefiber additions, itwasnecessary toutilize other industry testing that used continuous in-line fiber bypass capture todetermine cumulative bypass fractions forthe MPSUnit3 strainer.

ItisnotedAECLtestreports determined, "Fiber bypass concentrations showanearexponential decreasing trend with time."

Thequantity offiber thatbypassed thestrainer wassolowascanning 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, thereisreasonable engineering justification toapplyPoint Beachtestresults, after correcting for differences inapproach

velocity, totheMPSUnit 3strainer.

Using NRCstaff guidance (Reference 4.3) forstrainer fiber bypass andindustry strainer bypass testresults andapproach velocityfromPoint BeachandVogtle, respectively (References 4.4through 4.10), a cumulative strainer bypass fraction wasdeveloped for MPSUnit3.Consistent with NRC staff guidance, thelargest fibrous debris amountfor eachplant thatcould transportto the sump strainerswasassumed andincluded fiber transport anderosion basedonthe bounding fiber break.

Application ofPoint Beach strainer bypass datatoMPSUnit3 was based onfiber bypassatvarious tested and extrapolated theoretical debris bedthicknesses (derived fromfiber massperstrainer area).

TheMPSUnit 3strainer approach velocity ishigher than thePoint Beachtestresults; consequently, itwasnecessary toapply acorrectionfactor toscale thePoint Beachdata tothehigher velocity.

Derivation ofthecorrection factor was basedontheVogtle plant tests that recorded bypass fractions atvarious velocities.

Bypass massnormalized by flowratewasdetermined intheVogtle testreport tobelinearly related toapproach velocity.

Thissupported thecalculation ofcumulative bypass fractions for Vogtle strainers atflowrates comparable toMPSUnit3andPoint Beach.

Then a cumulative bypass correction factor could bedetermined ata given debris bedthickness byscalingthe Vogtle dataattheMPSUnit3 plant velocity tothePointBeach test velocity.

This methodology isbasedonthepremise that theimpact ofapproach velocity on thefiltering efficiency ofadebris bedisnotstrongly dependent onthespecific strainerdesign.

Thegeometry forthePerformance Contracting Incorporated (PCI) furnished Point Beach disk strainer wascompared with theAECLfurnished MPSUnit 3strainer andassessed tobeconceptually equivalent inits hydraulic performance characteristics.

Both strainers haveacentral collection ductthat receives filtered waterfromperforated sheets that is delivered toECCSpumpsuctions.

Debris-laden waterflowing tothestrainers inboth designs will generally beinaperpendicular direction totheperforations.

MPSUnit 3does notutilize anyspecific design features forpromoting evenflow distribution;

however, the AECLstrainer hydraulic report discusses that uniform flow isexpected assoonasasmall fiber layer starts toform.(Reference 4.12).

Withregard tosacrificial areas fortheMPSUnit 3strainer, itwasassumed all oftheareas wouldbeavailable forformation ofthefibrous debris bedsasthis wouldminimize the thickness ofthecalculated theoretical debris bed,which would result inlarger cumulative bypass fractions forthemaximumdebris loads ateachplant.

Page17of30

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

Response

toGL2004-02 Enclosure Casesthat result inthemaximumdesign flowrates fortheMPSUnit3strainer were selected to provide thehighest approach velocity.

Thestrainer perforation sizeforPoint Beach (0.066") isslightly larger thanfortheMPSUnit 3strainer perforation size(0.0625").

Uponconsideration ofthis design attribute, ithasaconservative influence oncumulative bypass fractions when applying Point Beachtest results toMPSUnit 3.

Consentatisg3s.Ap.121[gid Conservatisms applied when determining cumulativebypass fractions fortheMPSUnit 3

include:

a Maximumstrainer design flow rates were usedthatresult inthehighest calculated approach velocities andcumulativebypass fractions.

• TheMPSUnit 3strainer hasaslightly smaller perforation size(0.0625")

ascompared tothePoint Beachstrainer (0.066")

that was used forbypasstest dataapplied tothe MPSUnit 3.

Point Beachtestresults forNukononly insulation were usedsince theyprovided slightly higher bypass thanforother limited insulationmixes thatweretested.

Whentheoretical debris bedthicknesses werecalculated, designated sacrificialareas wereincluded tominimize thethicknesses, whichresult inhigher cumulative bypass.

• A percentage ofthetotal fiber loadontheMPSUnit 3strainer includes intact pieces thatdonoterodeand,assuch,donotcontribute tostrainer fiber bypass.

This contrasts with thePoint BeachandVogtle bypass tests thatused shredded fiber, all ofwhich maycontribute tostrainer bypass.

Page18of30

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

Response

toGL2004-02 Enclosure TABLE 3 - CRITICAL PARAMETER COMPARISON FORSUMPSTRAINERBYPASSTESTING Parameter Point BeachValue Millstone Unit3Value Strainer Manufacturer PCI AECL Strainer Perforation 0.066" 0.0625" Size Strainer Areal 1904.6 ft2 5041ft2 FlowRatethrough 2300 gpm (testscaled) 8220gpm Single Strainer Train Approach Velocity 0.0027 ft/sec 0.00363 ft/s Nominal Theoretical 1.5,,

0.60,,

2.037,,

Debris BedThickness Debris Typeand Quantity

(%Fiber MassType)2 Test1 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%

Cumulative Tested 2.01% 2.42%

5.61%

N/A Bypass Notes:

1. Thesacrificial areaisnotdeducted since itismoreconservative tousethemaximumarea available whencalculating thetheoretical fiber bedthickness.

Athinner bedthickness results inahigher cumulative fiber bypass fraction.

Also, there isnoneedforcomparison ofs.urface areas since the terminal Point;Beach cumulative bypass fractions arenotbeing applied totheAECLstrainer.

Determination ofcumulative bypass fractions isonlybeing basedonatheoretical debris bed thickness comparison withPoint Beachandeachplant.

2. Actual fiber quantities arenotprovided asthere isnointent toapply theterminal Point Beach cumulative bypass fractions totheAECLstrainer.

Thebypass fraction forMPSUnit 3isderived by comparison oftheoretical bedthicknesses.

MPSUnit.3 hasa,theoretical debris bedthickness of2.037" that exceeds thefinal nominal theoretical bedthicknesses forthePoint Beachtests.

However, useofthefitted power curveequation withextrapolation isjudged toprovide acceptable results duetothe demonstrated exponential decaybehavior offiber bypass withincreasing debris bed thickness.

Thecumulative bypass fraction ata2.037" thickness isthencalculated using Page19of30

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

Response

toGL2004-02 Enclosure thePoint Beach Test3 curve fitted equation developed inthecalculation:

Cumulative Fiber Bypass

= 0.040303*(Bed Thickness)-o.758434

= 0.040303*(2.037)-o.758434

= 2.3%.

Since the approach velocity fortheMPSUnit 3strainer (0.00363 ft/s) isgreater thanfor thePoint Beachdata (0.0027 ft/s),

a correction factor wasapplied tothecumulative bypass fraction.

The Dominion Energy engineering evaluation includes aspreadsheet that developed cumulative bypass fraction correction factors fromtheAlden TestReport forVogtle (Reference 4.10) that maybeapplied tothePoint Beachderived cumulative bypass fraction forMPSUnit 3. The spreadsheet determined that acorrection factor of 1.514isapplicable fora debris bed thickness of2.037" toscale toa velocity of 0.0043 ft/s, which conservativelybounds 0.00363 ft/s.

Applying this information toMPS Unit 3,thecumulative fiber bypassis 2.3% x1.514

= 3.5%.

TABLE4

SUMMARY

OFFIBERLOAD,DEBRIS BEDTHICKNESS, &VELOCITY ADJUSTED BYPASS FRACTIONS Strainer Characteristic MPSUnit3 Fiber Load 2053.24 Ibm Theoretical Debris BedThickness 2.037 inches Cumulative Bypass Fraction 3.5%

ThedatainTable 4wasusedtoperform theevaluation ofin-vessel effects discussed below.

3.n.2 MPSUnit 3isaWestinghouse 4-loop PWRwith anupflow barrel/baffle configuration.

Per Section 3;0oftheNRCStaff Review Guidance (Reference 4.3),

itisnecessary toconfirm MPSUnitE3 iswithin thekeyparameters oftheWCAP-17788-P, Rev.1,methods and analysis.

Therefore, eachofthekeyparameters isdiscussed below.

3.n.3FuejDesign MPSUnit 3usesWestinghouse 17x17Robust FuelAssembly 2(RFA-2) fuel.

3.n.4WCAP-17788 debris limit Theproprietary total in-vessel (core inlet andheatedcore) fibrous debris limits contained inWCAP-17788-P, Volume1,Rev.1,apply toMPSUnit 3.

Page20of30

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

Response

toGL2004-02 Enclosure 3.n.5 Theamount of fibrous debriscalculated toarrive atthereactor vessel isdetermined for MPSUnit 3following themethod described inWCAP-17788-P, Volume1,Rev.1,Section 6.5.Specifically, an engineering calculation wasperformed todetermine thecoreinlet fibrous debris load forthe Hot LegBreak(HLB) forMPSUnit 3.Thecalculation included thefollowing design inputs and assumptions:

Design Inputs 1 Plantlype-MPSUnit3isafour-loop Westinghouse upflow configuration plant.

2.NumberofAssemblies

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

3.CoreThermal Power

- Thecurrent rated core thermal poweris3650MWt.The analyzed corethermal powerof3723MWt,which includes instrument uncertainty, wasusedforthis evaluation.

4.M

- Thetotal fibrous debris fines mass attheECCSsump

strainer, including fines generated duetoerosion, is380.32 Ibm. Thefiber "fines" are thefibers that aresmall enough tobypass thesumpstrainers and collect atthecore inlet (i.e.,

FuelAssembly LowerEndFittings).

Onaperfuel assembly basis, theinitial sumpfiber load is893.83 g/FA(

= [380.32 Ibm*453.592 g/lbm)/193 FAs).

5.M

- Theactive sumpvolume, alsoreferred toas the active recirculation

volume, isthevolumeofliquid inthecontainment sumpwhich actively participates intherecirculation process.

Thisvolume actsasthesysteminventory whencalculating theconcentration ofdebris tobeinjected intotheRCS.

A conservatively lowsumpvolume wasusedthat accounts forpotential holdup areas within containment.

6.W-Thetime ofSSO,also knownassumprecirculation activation orrecirculation modetransfer (RMT),

isthetimeatwhichfiber isinjected intothereactor vessel/sump screen.Theminimumtimeofsumpswitchover is 33minutes.

7.M

- TheECCSflowrateafter thetimeofSSO(i.e.,

during recirculation mode) isusedtocalculate therate offiber injection into thereactor vessel.

Bothminimum andmaximumECCSflow rates wereanalyzed.

Theminimum ECCSflowrateduring recirculation is965.25 gpm'withoneoperable

train, andthe maximumrecirculation flowrate is1753gpmwithbothtrains 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 tothereactor vessel bydiverting afraction ofdebris that bypasses thesumpstrainer backinto thesump.Perguidance provided inWCAP-17788-P, Rev.1,Volume 1,Section 6.5.2.10, aminimum RSSflowrateshould beanalyzed.

TheminimumRSS flowrateduring ECCSrecirculation alignment is4071gpm.The maximumRSSflow rate duringECCSrecirculation alignment is7202gpm.

9.

- TheMPSUnit3 HLSOtimemustoccur between 3and5hours.Since amaximum HLSOvalue islimiting, avalue of5hours wasusedinthecalculation.

10.Iime.St p.-Atimestepof100seconds wasusedfortheiterative solution.

11.M

- Thetime to chemical

effects, tchem, isthetimeatwhich chemical precipitates areassumed togreatly increase theresistance across the formed debris bed.PerTable 4.4-1 ofReference 4.13,theearliest timeatwhich chemical effects formis24hours forMPSUnit3.

Therefore, avalue of24hours was usedinthecalculation.

12.

Inlet Debris Limit

- Kmax isthemaximumcoreinlet resistance thatcanbetolerated prior tocomplete coreinlet blockage.

tblock istheminimum acceptable time ofcomplete coreinlet blockage.

MPSUnit 3isaWestinghouse upflow plant with Westinghouse fuel; therefore,

• tblock

is143min,

• Thecoreinlet debris limit isthevalue listed inWCAP-17788, Table 6-3, and

• Kmax is5x10E 13.W Thebypassfraction istheportion ofdebris transported tothesumpstrainer that isnotcollected onthesumpstrainer andinstead penetrates through thesumpstrainer andinto thereactor vessel through theECCS.

As notedinSection 3.n.1 above,theMPSUnit3 strainer cumulative bypass percentage wasdetermined tobe3.5%.

s 14.RFA-2.Assenlby P.itch

- TheRFA-2FApitch wasusedinthecalculation.

Assumptions 1.Thefiber andparticulate arewellmixedinthesumpfluid suchthat ahomogeneous mixture ispresent atthetimeofsumprecirculation.

Therefore, thedebris transport is proportional toECCSflow rate.

2.Nodebris isheldupinanylocation other thanthesumpstrainer(s),

coreinlet, orwithin thecore.Further, nosettling ofdebris iscredited inanylocation oftheRCS.

Page22of30

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

Response

toGL2004-02 Enclosure Therefore, themaximumamountofdebris reaches thecore.

3.Chemicalprecipitates areassumed toformat24hours.

4.Thefiber isin its constituent form,i.e.,

individual

fibers, whichisconsistent with maximum transport assumptions.

5.AFPswerenotcredited.

Per PWROG-16073-P, Rev.0,(Reference 4.13),

theNRC staff expects thedebris bed atthecoreinlet will notbeuniform duetothevariations inflowvelocities atthecoreinlet.

Therefore, itwill takemoredebris thandetermined byWCAP-17788-P, Rev.1,toresult inactivation oftheAFPsandredirection ofsome flowanddebris totheheatedcore.

Because ofthenon-physical nature ofthe assumption ofa uniform debris bed (which remains conservative inother aspects),

credit fordebris bypassing thecore inlet and entering theheated coreshould notbe used.Assuch, thevalues for "M-split" inthe engineering calculation weresettozero.

6.Itwasassumednodebris exits thebreak (i.e.,

once itisintheRCS,itstays inthe RCS).

Therefore, themaximumamountofdebris reaches thecore.

7.Itwasassumed sumpdebris will build-up across thecore inletinauniform

manner, andblockage isonly considered atthecoreinlet.

Thisis a simplifying, conservative assumption.

8.AtthetimeofHLSO,thecharging pumps(high head) continue to deliver coolingflow tothecoldlegs, andthe(low head)

SIpumpsarerealigned todeliver cooling flowto thehotlegs.

Amaximumflow ratewill deliver themostfiber into the reactor pressure vessel (RPV),

whichisconservative, sowithtwopumpsoperatingfor both the charging andSIpumps,themaximumflowratesare876.1and830.7

gpm, respectively.

Therefore, 51.3%oftheflow isdelivered tothecoldlegsand48.7%

is delivered tothehotlegs.

Thesumofthese twoflow rates is45.2gpmless than the total ECCSflowrateprior torecirculation, butbecause a higher flowrateis conservative andresults inmorefiber being delivered into

thecore, theflowsplit was applied tothetotal ECCSflow ratebefore HLSO.

Analysis i

TheHLBdebris isthesumofthefiber that iscaptured atthecoreinlet andthein-core fiber:

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

a Mr,HLeisthetotal fiber massforthehotlegbreak Mr, ciisthemassoffiber atthecoreinlet Mr,in-core isthemassoffiber intheheated core Page23of30

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

Response

toGL2004-02 Enclosure Themassof fiber that reaches theheated corecantravel through

twopaths, either the AFPorfromthe hot leg post-HLSO:

Mr,in-core

= Mr, AFP+ Mr, ce Where:

a Mr,AFPisthemassof fiber that reaches thecorethrough theAFP,and a

Mr,ceisthemassoffiber that reaches thecoreviathecoreexit (i.e.,

fiber injection post-HLSO)

Theabovequantities were determined iteratively ateachtimestep.Thecalculation was terminated atthetimeatwhichthesump fiber loadwasless thanorequal to1%ofthe initial sumpfiber load.

Aspreviously

noted, AFPswerenotcredited in the analysis.

Therefore,Mf, AFPWill always equal zero.Ifthetermination criteria isreached before thetimeofHLSO,thenMr,cewill alsoequal zero.Ifthat isthecase,thentheMr, in-coreterm iszero,andthetotal massof fiber fortheHLBissimply thefiber atthecoreinlet.

Acceptance Criteria Thetotal injected fiber mustbeless thanorequal tothecoreinlet fiber load limit included inWCAP-17788-P, Vol.

1,Ref.1,Table 6-3, forWestinghouse fuel.

3.n.6 Using thedesign inputs andassumptions noted

above, themaximumamountoffiber for MPSUnit 3calculated topotentially reachthereactor vessel is9.6g/FA, which isless thantheproprietary in-vessel fibrous debris limit provided inSection 6.5ofWCAP-17788-P, Volume1,Rev.1.

3.n.7Confirmation thatthecoreinlet fiber amountislessthantheWCAP-17788-P Rev.1threshold MPSUnit 3isaWestinghouse 4-loop design with Westinghouse 17x17RFA-2FAs.The applicable coreinlet fiber threshold forWestinghouse fuelisprovided inTable 6-3of WCAP-17788-P, Rev.1 Thecalculated coreinlet fiber amountforMPSUnit3 is 9.6g/FA, whichislessthantheapplicable WCAP-17788-P, Rev.1,coreinlet fiber threshold limit forWestinghouse fuel.

Page24of30

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

Response

toGL2004-02 Enclosure 3.n.8 r

Aspreviously stated, theearliest possible SSOtimeforMPSUnit 3wasdetermined to be33minutes.

3.n.9 Chemical precipitation timingis dependent ontheplant

buffer, sumppoolpH,volume and temperature, anddebris typesand quantities.

Table 4.4-1 ofPWROG-16073 (Reference 4.13) identifies TestGroup35as representative ofMPSUnit3,andthepredicted chemical precipitation timing (tchem)iS 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

3.n.10 Confirmation thatchemical effects will notoccurearlier thanlatest timeto W

MPSUnit3 performs injection realignment tomitigate thepotential forboric acid precipitation (BAP) nolater than5hours, whichisless than 24hours.

3.n.11 MPSUnit3 isaWestinghouse 4-loop upflow configuration design.

BasedonWCAP-17788-P, Rev.1,Volume1,Table 6-1,tblockfor MPSUnit 3is143minutes.

3.n.12 Theearliest timeofchemical precipitation forMPSUnit 3wasdetermined tobe 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, which isgreater thantheapplicable tblockValue of143minutes.

3.n.13 dgtsign.categoy TheMPSUnit 3rated core thermal power(RTP) is3650MWt.Theanalyzed core thermal poweris3723MWt,whichincludes instrument uncertainty.

MPSUnit3 'isa Westinghouse 4-loop

design, andtheapplicable analyzed thermal poweris3658MWtas provided inWCAP-17788-P, Rev.1,Volume4,Table6-1Therefore, theMPSUnit 3

analyzed thermal powerisgreater thantheWCAP-17788-P analyzed value.

TheWCAP-17788-P, Vol.1,Rev.1,thermohydraulic analysis assumes anSSOtimeof 20minutes together with anRTPof3658MWt.Tojustify theuseoftheanalysis andfuel limit described inWCAP-17788-P, itisnecessary todemonstrate thedecayheatforMPS Unit 3atthetimeofSSO(i.e.,

whenfibrous debris begins toarrive atthecoreinlet) is lessthanthedecayheatintheWCAP-17788-P thermohydraulic analysis atthetimeof SSOasdiscussed inPWROG-16073 (Reference 4.13).

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

Response

toGL2004-02 Enclosure Table 4.5-2 of PWROG-16073 provides adecayheatat20minutes of87.4MWt,which isthedecayheat available atthetimeofSSOintheWCAP-17788-P thermohydraulic analysis.

Thedecay heatmodelisbasedonthe1971ANSInfinite Standard plus20%

uncertainty

[PWROG-16073, Section4.5.1.2).

Asnoted

above, theearliest timeofSSO forMPSUnit 3is33minutes, whichwill result inadditional timeforthecoretodecayand thusalower normalized core power thanthat resulting at20minutes.

TheMPSUnit3 plant-specific post-LOCAdecay heatfraction is0.0216 at30minutes.

Thisdecayheat fraction includes a20%uncertainty andisconservativeforanSSOtime of33minutes.

Thedecayheatatthetime ofSSO isthen calculatedtobe80.5MWt(0.0216

• 3723 MWt),whichislessthanthedecay heat fromtheWCAP-17788-P thermohydraulic analysis atthetimeofSSO(87.4 MWt). Therefore, theWCAP-17788-Pthermohydraulic analysis andfuel limits arestill bounding for MPS Unit 3.Inaddition, there issignificant margin tothemaximumcoreinlet fiber load to help offset this powerlevel difference.

3.n.14 MPSUnit3isaWestinghouse upflow barrel/baffle configuration plant.

Theproprietary analyzed AFPresistance isprovided inTable 6-1ofWCAP-17788-P, Volume4,Rev.1.

Theproprietary MPSUnit 3specific AFPresistance isprovided inTableRAl-4.2-24of WCAP-17788-P, Volume 4,Rev.1.TheMPSUnit 3specific AFP resistance isless than theanalyzed value; therefore, theMPSUnit3 AFP resistance isbounded bythe resistance applied totheAFPanalysis.

3.n.15 W

MPSUnit 3isaWestinghouse upflow barrel/baffle configuration plant.

TheAFPanalysis forWestinghouse upflow plants analyzed arange ofECCSrecirculation flow ratesfrom 8

- 40gpm/FA, asshowninTable 6-1ofWCAP-17788-P, Volume4,Rev.1.TheMPS Unit3 ECCSrecirculation flowratecorresponding totheworst-case GSl-191 hotleg break scenario is9gpm/FA, whichiswithin therangeofECCSrecirculation flowrates considered intheAFPanalysis.

t WhiletheMPSUnit3 ECCSrecirculation flowratecorresponding totheworst-case GSI-191 hotlegbreakscenario iswithin therangeofECCSrecirculation flowrates considered intheAFPanalysis, theminimum plant-specific ECCSflow

rate, 5gpm/FA, isless thantheminimumanalyzed ECCSflowrateusedtodevelop Kmax inReference 4.14.

Debris bedresistance increases asECCSflowratedecreases, soanunbounded lowflow hasthepotential tocausetheKmax usedinthecalculation tobenon-conservative.

However, themaximumECCSflowrateatMPSUnit3creates themostlimiting

case, whichhassignificant margin totheWCAP-17788 coreinlet fiber limit.

Assuch,the Page26of30

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

Response

toGL2004-02 Enclosure unbounded minimum ECCSflowrateisacceptable because itdoesnotcreate thelimiting fiber loadat the coreinlet; therefore, Kmax isvalid forthelimiting fiber loadcase.

3.n.16 Summa.ry Thecomparison ofkey parameters usedintheWCAP-17788 AFPanalysis totheMPS Unit3 specific valuesis summarized inTable 5.Basedonthese comparisons, MPS Unit 3isbounded bythekey parameters, andtheWCAP-17788 methods andresults are applicable.

TABLE5

- KEYPARAMETER VALUES FORIN-VESSELDEBRISEFFECTS MPS Unit3 Parameter WCAP17788Value Evaluation MaximumTotal In-

< than the Maximumin-vessel fiber Vessel Fiber Load Volume 1,Section 6.5 WCAP-17788 loadisless thanWCAP-(g/FA) value 17788limit.

Maximum coreinlet fiber MaximumCoreInlet 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 heatatthe time ofdebris Switchover Time 20 33

arrival, reducing the (min) potential for debris induced core uncovery andheatup.

Potential forcomplete coreinlet blockage dueto Minimum Chemical chemical product 2.4(tblock) 24(tchem)

Precipitate Time(hr),

generation would occur muchlater than assumed.

Latest hotlegswitchover MaximumHotLeg occurs well before the Switchover Time 24(tchem) 5 earliest potential (hr) chemical product generation.

Thisvalueisnotbounded RatedThermal 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 Final Supplemental

Response

toGL2004-02 Enclosure TABLE 5-KEYPARAMETER VALUESFORIN-VESSEL DEBRISEFFECTS MPSUnit3 Parameter WCAP-17788 Value Evaluation AFPresistance isless Maximum AFP Volume4 Volume 4

thantheanalyzed

value, Resistance Table6-1 Table RAl-4.2-24 which increases the effectiveness oftheAFP.

ECCSrecirculation flow rate corresponding tothe ECCSRecirculationVolume 4

mostlimiting fiber 9

Flow(gpm/FA)

Table6-1 injection hotlegbreak scenario iswithin the analyzed flowrange.

3.o Chemical Effects NRCIssue:

Theobjective ofthechemical effects section istoevaluate theeffect thatchemical precipitates haveonheadloss andcorecooling.

1)Provide asummaryofevaluation results that showthat chemical precipitates formed inthepost-LOCA containment environment, either bythemselves or combined with

debris, donotdeposit atthesumpscreen totheextent that anunacceptable headloss

results, ordeposit downstream ofthesumpscreen totheextent that long-term core cooling isunacceptably impeded.

DENCResponst TheMPSUnit 3chemical effects analysis ofthesumpstrainers wassubmitted inthe MPS Unit3 Supplemental

Response

datedFebruary 29,2008(ADAMS Accession No.

ML080650561) andamendedon December18,2008(ADAMS Accession No.

ML083650005).,

aswell assubsequent RAlresponses submitted onMarch13,2009 (ADAMS Accession No.ML090750436),

September 16,2010(ADAMS Accession No.

ML102640210),

!andDecember 20,2010(ADAMS Accession No.ML103620562).

The MPSUnit 3sumpstrainer chemical effects analysis isunchanged.

3.p Licensing Basis NRCIssue:

Theobjective ofthelicensing basis section istoprovide information regarding any changes totheplant licensing basis duetothesumpevaluation orplant modifications.

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

Response

toGL2004-02 Enclosure 1)

Provide theinformation requested inGL04-02Requested Information Item2(e) regardingchanges totheplant licensing basis.

Theeffective dateforchanges tothe licensing basis should bespecified.Thisdateshould correspond tothat specified inthe 10CFR50.59evaluation forthechange tothelicensing basis.

DENC'sFebruary 29,2008 Supplemental Responsediscussed thelicensing bases changes that hadbeenimplemented forMPSUnit 3associated with theresolution ofthe sumpissues considered inGSl-191 andGL2004-02.Thesechanges arerestated below:

MPSUnit 3FSAR TheMPSUnit 3FSARwasrevised toreflect the installation ofthenewcontainment sump strainer.

DENCwill update thecurrent licensing basis (Final Safety Analysis Report in accordance with10CFR50.71(e))

following NRC acceptance ofthefinal supplemental response forMPSUnit 3.

MPSUnit 3License Amendments Twolicense amendments related toGL2004-02 corrective actions wereapproved and implemented.

a Achange tothestart signal fortheRSSpumpswassubmitted and approved toensure thestrainer wasfully submerged andadequate NPSHexisted for the RSS pumps prior totheir start considering a mechanistic debris blockage analysis.

Amendment No.233wasapproved forMPSUnit3 byNRCletter dated September 20, 2006 (ADAMS Accession No.ML062220160).

Implementation ofthis change was completed during theMPSUnit 3spring 2007refueling outage.

• An amendment wasapproved andimplemented foranadministrative changeto replace obsolete textintheTSSection 4.5.2.d sumpsurveillance requirement with generic terminology forECCScontainment sumpstrainefs.

MPSUnit 3Amendment No.240wasapproved byNRCletter dated September 18,2007(ADAMS Accession No.ML072290132).

4 References 4.1 NEl04-07, Revision 0,"Pressurizer WaterReactor SumpPerformance Evaluation Methodology",

May28,2004.

4.2 NRCSERforNEl04-07,"Safety Evaluation bytheOffice ofNuclear Reactor Regulation Related toNRCGeneric Letter 2004-02, Nuclear EnergyInstitute Page29of30

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

Response

toGL2004-02 Enclosure Guidance Report(Proposed Document NumberNEl04-07),

'Pressurized Water Reactor Sump Performance Evaluation Methodology',"

datedDecember 16,2004.

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

4.4 AREVACalculation 32-9201054-000, "PWRStrainer FiberBypassLength Distribution" (Framatome Proprietary).

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

4.6 AldenTestReport 1142PBNBYP-R2-01, "Point BeachLargeScale Fibrous Debris Penetration TestReport."

4.7 AldenCalculation 1142PBNBYP-600-00,"Fibrous DebrisPenetration Modelfor Point BeachCalculation."

4.8 NextEra Energy Point BeachLetter No.NRC2017-0045; "Updated Final

Response

toNRCGL2004-02,"

December 29,2017.

4.9 NRCDocument ML15320A087

- "Vogtle GSl-191 Resolution PlanandCurrent Status NRCPublic Meeting,"

November 5,2015.

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

4.11MIL3-34325-TR-001, Rev.0;"Reduced-Scale Testing forMillstone 3Replacement Containment SumpStrainers",

AECLTestReport.

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

Replacement Containment SumpStrainers Millstone 3PowerStation 4.13.

PWROG-16073-P, Rev.0,"TSTF-567 Implement'ation

Guidance, Evaluation ofIn-Vessel Debris

Effects, Submittal Template forFinal

Response

toGeneric Letter 2004-02 andFSARChanges,"

February 2020.

4.14WCAP-17788-P, Rev.1,"Comprehensive Analysis andTestProgram forGSl-191 Closure (PA-SEE-1090)"

December 2019.

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