ML17216A744

Proposed Tech Spec 5.3.1 Changing Nominal Active Fuel Length for Reactor Core Fuel Assemblies.Safety Evaluation & NSHC Determination Encl

ML17216A744
Person / Time
Site:	Saint Lucie
Issue date:	10/17/1986
From:	FLORIDA POWER & LIGHT CO.
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ML17216A742	List: ML17216A741 ML17216A744
References
NUDOCS 8610280051
Download: ML17216A744 (10)

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ATTACHMENTIMarked-upTechnicalSpecificationPage:5-48b10280051',Bb1017PDRADOCK05000335)'PDR.'wEJWl/0I6/3 IDESIGNFEATURESAe5.2.l.SHIELDBUILDINGa.Mfnfmuaannularspacelfeet.b.Annuluseafna1volue<5l3>000cubicfeet.c.Nominaloutsfdeheight(aeasuredferniopoffoundationbasetothetopoftheCoca)~230.5feet.d.Nosfna)insidedfaaeter~illfeet.e.Cylinderwallafnfaathickness~3feet.f.Doaeafnfeethfckness~2.5feet.g.hee5nsfderad5us~ll2feet.ESICNPRESSUREANDTEMP5.2.2Thecontafaaentvesselfsdesignedandshallbeaafntafnedfora@life'sinternalpressureofllpsfgandatmperytureof26l'F.PENETRATIONS5.2.3penetratfonsthroughthecontafaaentstructurearedesfgnedandshallbeeafntafnedinaccordancewiththeoriginaldesignprovisionscontainedtnSections3.8.2.1.10and6.2.4oftheFSARwfthallowancefornoraeldegrada-tfonpursuanttotheapplicableSurveillanceRequfresents-REACTORCOREI~Q~g]3V-]o.ndTheinitialcoreloadingshallnttl-235.Reloadfuelshallbeloading.theNRC',allfidelassmblfe5edwithasleevedesignamaximatotalweightof2250grassuranfm.haveaeaxfauNenrfchaentof2.83weightperes&flarfnphysicaldes5gntotheinitialcor5.3.2ExceptforspecialtestasauthorizedundercontroleleaentassmnlfesshallbeslepreviouslyapprovedbytheNRC..~fllII~E5.3.1Thereactorcoreshallcontain217fuelasseaieswitheachfuelasseblycontafnfngaaaxfyuaof176fuckrodsclad5thZfrcaloy-4.Eachfuelrodshallhaveemfnalactivefuellengthof136.7fnchesandcontainST.LllCIE-UNIT1AaenhaentNo.g,44 f'~w'L ATTACHMENT2SAFETYEVALUATIONIntroductionFloridaPowerandLightproposestochangeSt.LucieUnit1TechnicalSpecification5.3.1.Thepurposeofthischangeistopermittheloadingoffuelwithanominalactivefuellengthofbetween134.1and136.7inches.FuelburntinSt.LucieUnit1incycles1through7hasanominalactivefuellengthof136.7inches.Theslightlyshorteractivefuellengthpermitstheuseofafuelroddesignthatismoreresistanttofrettingtypefailuresthanthepresentdesign.DiscussionAslightlyshorteractivefuellengthpermitstheuseofalongersolidzircaloyendcapwhileretainingthesameoverallfuelrodlengthandassemblylengthandconfiguration.Thelongerendcap,whichwillbelengthenedfrom0.4inchesto3.04inches,willextendapproximatelyhalfwayupthroughthelowerspacergridassemblyatwhichpointitisweldedinastandardfashiontothefuelrodcladding.Thepurposeofthislongerzircaloyendcapanditsextensionabovethelowergridspringcontactpointistoofferincreasedprotectionagainstfuelcladdefectsinducedbyfrettingatthelowerendofthefuelrod.Thisprotectionisparticularlyimportantinlowburnupfuelbecauseofthestrongpossibilityoffissionproductreleasesfromcladdefectscausedbysecondaryhydriding.Hydridingoccurswhenhydrogenreactswiththeinsideofthecladtoformzirconiumhydrideblisters,whichcancreatecladdefects.Secondaryhydridingimpliesthathydrogen,intheformofwater,isintroducedintothefuelrodviaaprimarydefectsuchasthatcausedbyfretting.Znafuelpinoflowburnupthereisalargefreevolumebetweenthefuelpelletsandcladwhichfacilitatesthemovementofsteamandfissionproducts.Hydrogenisabletoconcentrateinsignificantquantitiesandusuallyattackstherodnearitshottestlocation(Reference1).Efadefectformswhilethereisstillalargefreevolume,thentheentirefissionproductinventoryofthevolumeistheoreticallyavailableforrelease.Asburnupincreasesonafuelrodthepellet-cladgapwilldecreaseduetoacombinationofthermalexpansion,cladcreepandfuelpelletswellingeffects.Thereisevidence(Reference2)thatpointsofhardcontactbetweenthefuelandclad,whichcausecladridging,formafterapproximately 23GWd/MTUofexposure."Soft"contactpoints,orpellet-cladinteractionthatcreateapositiveforceonthecladwithoutdeformingit,occurmuchearlierintherod'sexposure,atapproxi-mately3.5GWd/MTU(Reference3).Bothhardandsoftcontactpointswillhavetheeffectoflimitingthemigrationoffissionproducts(andhydrogen)tosomefractionofthetotalrodlength.Failuresoccurringathigherburnupsdonot,therefore,adverselyimpactfuelrodintegritytothedegreethatlowerburnupfailuresdo.Pressuredropcalculationsandindustr'yinspectionsoffuelassembliescontainingfuelpinsthathavefailedduetodebrisinducedfrettingdemonstratethatspacergridsserveasexcellentfiltersortrapsforanydebrisinthereactorcoolantthatpassesthroughthecore.Conversely,debris-inducedperforationsseldomoccuratlocationsabovethelowerspacergrid.Byextendingthesolidzircaloylowerendcapthroughthegridspringinthelowerspacerassembly,FPLisassuringthatanydebrisentrappedinfreshfuelbythelowerspacergridwillfretagainstsolidzircaloyinsteadofcladdingmaterial.Thiswillsignificantlylovertheprobabilityoflowburnupfuelfailures.Thepurposeofthisfueldesignchangeisnottomakethepresenceofdebrisinthereactorcoolantsystemacceptable,rather,'tistoprovideadditionalassurancethatanytypeoffretting-relatedfailureswillnotoccur.Thenominalactivefuellengthofreloadfuelwillbereducedfrom136.7to134.1inchesbyremovingapproximately2.64inchesofnaturaluraniumfromtheloweraxialblanket.Thisremovalofmaterialreducestheloweraxialblanketlengthfrom6.0inchesto3.36inches(Figure1).Incycle8theshorteningoftheaxialblanketinthereloadfuelwillresultinatotalreductioni:nthecore'sactivefuellengthofapproximately3250.feet,or0.75%.TheimpactofthisdesignchangeonthecorepowerpeakingandonthemechanicalcompatibilityofreloadfuelhasbeencarefullyevaluatedbyFPL.Resultsindicatethattheproposeddesignchangewillhaveanegligibleeffect-onthesafeoperationoftheplant.Theseresultsarediscussedbelow.PeakinandPowerDistributionTheproposedfueldesignchangesdonotsignificantlyaffectthecorepowerpeakingorpowerdistribution.Toquantifytheseeffects,calculationswereperformedwithtwothree-dimensional,PDQ(Reference4)modelsthatwerespeciallybuiltforthisevaluation.Inthefirstmodel,fuelassembliesincorporatingthelongerlowerendcapdesignwerepositionednexttofuelassembliescontainingrodsofthepresentdesign.Thesecondmodel,whichwasbenchmarkedagainstarepresentativecycle8three-dimensionalnodalmodel,wasidenticaltothefirstmodel exceptallfuelrodswereofthepresentdesign.Differencesbetweentheresultsofcalculationsperformedusingthetwomodelswereduetothelowerendcapdesignmodification.Theresultsindicatethatthetotalpeakingfactor,Fqpincreasedbylessthan1%duetotheuseoffuelrodswithalongerlowerendcapdesign.Thiswascausedbyanincreaseintheaxialpeakingfactor,Fz,whichwasalsocalculatedtobelessthan1%.ThesesmallchangesinFzandFqaremuchlessthanthemeasurementuncertaintyofthepeakingfactors(Reference5),andwillbedifficulttodiscernfromnormalstatisticalfluctuationsinthemeasurements.Theincreaseinthesepeakingfactorsisduetoacombinationofeffectsofthereducednominalactivefuellength.Althoughthecore-averagelinearheatraterisesduetotheshortertotalactivefuellength(whichalonewouldcausethepeakingfactorstofall),theremovaloffuelisconfinedtoonereloadbatch,orapproximatelyone-thirdofthefuelassemblies.Thisnon-uniformremovalofmaterialchangesthelocalpeaklinearheatrateintheaffectedfuelassembliesbyaslightlygreaterdegreethantheincreaseincore-averagelinearheatrate;thus,themaximumpeakingfactorsexperienceaslightincrease.Themaximumlinearheatrate,whichistheproductoftheaveragelinearheatrateandthetotalpeakingfactor,thereforeincreasesbyapproximately1%.TheimpactoftheproposeddesignchangeonrelativeassemblypowerwasalsoassessedusingthePDQmodels.Itwasshownthattherelativeassemblypowerdoesnotchangeasaresultoftheproposeddesignchange.Thereislikewisenochangeintheintegratedradialpeakingfactor,FR.Thisisbecausetheshorteningoftheactivefu'ellengthdoesnotsignificantlyaffecttherelativepowerproducedbythehottestpininanassembly,andFRistheproductoftherelativeassemblypowerandtherelativepowerofthehottestpin.Similarly,thechangeinFxywascalculatedandisnegligible.Theeffectsoftheproposedfueldesignchangeoncorepowerpeakingandpowerdistributionaresmallenoughtobeaccommodatedwithinexistingdesignmargins.Therevisedpowerdistributionwillbeaccountedforinthecyclespecificphysicsinputstothesafetyanalysis,whilethespecifiedacceptablefueldesignlimits,initialconditionsassumedforaccidentanalysis,andsafetyanalysismethodologyremain-unchanged.MechanicalComtibilitTheproposedfueldesignchangesdonotadverselyimpacttheperformanceoffuelalreadyresidingi*nthecoreorofthereloadfuelitself.TheeffectsofthedesignchangehavebeencloselyexaminedbybothFPLandENC.Nofuelrodmechanicalpropertieshavebeenchangedwiththeexceptionofthecladdinglength, activefuellengthandlowerendcaplength.Overallfuelrodlengthremainsunchanged.Cladandendcapmaterialcompositionremainunchanged.Theuseoflongerendcapsisnotanewconceptintheindustry.Manufacturersofnuclearfuelforboilingwaterreactorshavehadextensiveexperienceinweldinglongendcapsontofuelcladding.Additionaldrawingspecificationshavebeenwrittenwhichrequirethattherebeverytightangulartolerancesbetweenthecladatthelowerendoftherodandthelowerendcap.Thisensuresthatthereisnochangeintheprobabilityofspacergriddamageduringfuelloadingduetotheproposedfueldesignchange.Theproposednewdimensionsofthelowerendcapandzircaloycladdingwereselectedusingtwocriteria.Thefirstcriteriawastominimizethelengthofaxialblanketmaterialremovedfromthepelletcolumn.Thesecondcriteriawastopositionthecladdingendcapweldabovethe'contactpointofthelowergridspring(giventhattheinter-gridspacingnotbechanged).Thedimensionsselectedensurethatthelowergridspringwillcontactthesolidendcap,whereaspreviouslythelowergridspringcontactedthecladding.Thispositioningofthecontactpointonthesolidendcapshouldalsohelpeliminatelowergridspringfrettingasapotentialfailuremechanism.

References:

1.Tong,L.S.,Weisman,J.,ThermalAnalsisofPressurizedWaterReactors,AmericanNuclearSociety,LaGrangePark,Illinois,19792.Djurle,S.,"TheStudsvikOver-RampProject",EPRI-NP-3007,April19833.RODEX2FuelRodThermal-MechanicalResonseEvaluationModel,Revision2,XN-NF-81-58(P).(A),February9,1983.4.PD-7/HARMONYUser'sManual,Revision1,Electric'PowerResearchInstitute,March31,1983.5.Johnsonn,A.,etall,"INCA/CECORPowerPeakingUncertainty",CENPD-153-NP,Revision1-NP-A,May1980 940III,I~I1CO$2llk.MJOOCOOliCOOTtC1JttlIC$OCCtooovCTOttCISICOTIONT.O~1.00OAT00II$2AIITS.TOCOOICIITO00I$IOT.O)$.$1NlT00($$.$I$.0iIT$.2I$I.OC0$~0$ITII14.~1~$220.1$p'eC~4IKI~~Q~h~tIwea~e~rWos~S~eve~aICE$(ONNUCLEAIICOMPANY,INC,FUELRODASSEMBLYSWOKtkeIoctootoaTklTt.Sea>>1<tooXNNF.SK.30I,987IIo2FIGURE1

'~ATTACHMENT3DETERMINATIONOFNOSIGNIFICANTHAZARDSCONSIDERATIONThestandardsusedtoarriveatadeterminationthatarequestforamendmentinvolvesnosignificanthazardsconsiderationareincludedintheCommission'sregulations,10CFR50.92,whichstatesthatnosignificanthazardsconsiderationsareinvolvediftheoperationofthefacilityinaccordancewiththeproposedamendmentwouldnot(I)involveasignificantincreaseintheprobabilityorconsequencesofanaccidentpreviouslyevaluated;or(2)createthepossiblityofanewordifferentkindofaccidentfromanyaccidentpreviouslyevaluatedor(3)involveasignificantreductioninamarginofsafety.Eachstandardisdiscussedasfollows:(I)Operationofthefacilityinaccordancewiththeproposedamendmentwouldnotinvolveasignificantincreaseintheprobabilityorconsequencesofanaccidentpreviouslyevaluated.ModificationtothenominalactivefuellengthwillresultinnochangestotheplantproceduresasdescribedintheFinalSafetyAnalysisReport(FSAR).Therewillbenochangestotheplant'sstructure,systems,orcomponentsotherthanthefuelrodsinnewfuelassemblies.Theonlychangetothesefuelrodsistoreducethecladandactivefuellengthwhileincreasingthelowerendcaplength.Boththeoverallfuelroddimensionsanditsspatialorientationinthefuelbundleareunchanged.Thecore'stotalactivefuellengthisshortenedbyabout0.75%.Analysisofthisdesignchangeindicatesanegligibleimpactonsafeoperationoftheplantasaresultofthedesignchangeimpactsonthecorepowerpeakingandmechanicalcompatibilityofreloadfuel.Byextendingthelowerspacerassembly,FPLisassuringthatanydebrisentrappedinfreshfuelbythelowerspacergridwillfretagainstsolidzircaloyinsteadoffuelcladdingmaterialsignificantlyloweringtheprobabilityoflowburnupfuelfailures.Thisprovidesadditionalassurancethatanytypeoffretting-relatedfailureswillnotoccur.Finally,thereisnochangeintheprobabilityofspacergriddamageduringfuelloading.EJWI/016/7 Attachment3(con't)(2)Useofthemodifiedspecificationwouldnotcreatethepossibilityofanewordifferentkindofaccidentfromanyaccidentpreviouslyevaluated.Theproposedamendmentwillresultinnochang'estotheplant'sprocedures,structures,systems,modeofoperationorcomponentsotherthanthefuelrodmodification.Nonewordifferentmaterialsormanufacturetechniqueswillbeusedtoproducefuelrods.NoadditionaltestsorexperimentsnotdescribedintheFSARarenecessarytoimplementtheproposedchange.Theproposedfueldesignchangesdonotadverselyimpacttheperformanceoffuelalreadyresidinginthecoreorofthereloadfuelitself.Nofuelrodmechanicalpropertieshavebeenchangedwiththeexceptionofthecladdinglength,activefuellengthandlowerendcaplength.Overallfuelrodlengthandcladandcapmaterialcompositionremainunchanged.(3)Useofthemodifiedspecificationwouldnotinvolveasignificantreductioninamarginofsafety.Noinputsorresultsfromplantsafetyanalysisrequiremodificationsasaresultoftheproposedchange.Neithertheplant'sprocedures,structures,systems,orcomponentshavechangedotherthanthefuelroddesign.Theimpactofthedesignchangeoncorepowerpeakingisnotsignficantandiswellwithinthemeasurementuncertaintiesoftheseparameters.Thedifferencebetweenfuelsafety'limitsandtheresultsofthesafetyanalysis,whichisrepresentativeofthemarginofsafety,isunchanged.Basedontheabove,wehavedeterminedthattheamendmentrequestdoesnot(I)involveasignificantincreaseintheprobabilityorconsequencesofanaccidentprevisouslyevaluated,(2)createtheprobabilityofanewordifferentkindofaccidentfromanyaccidentpreviouslyevaluated,or(3)involveasignificantreductioninamarginofsafety;andthereforedoesnotinvolveasignificanthazardsconsideration.EJWl/0l6/8