ML20104C050
| ML20104C050 | |
| Person / Time | |
|---|---|
| Site: | HI-STORM 100, Consolidated Interim Storage Facility |
| Issue date: | 03/31/2020 |
| From: | Holtec |
| To: | Office of Nuclear Material Safety and Safeguards |
| Shared Package | |
| ML20104C047 | List: |
| References | |
| 5021061 | |
| Download: ML20104C050 (4) | |
Text
Attachment2toHoltecLetter5021061 HISTORMUMAXAmendmentRequest#3 RAIResponses-NonProprietary
Page1of4 RAI1ProprietaryRAI RAI2ProprietaryRAI RAI3ProprietaryRAI RAI4ProprietaryRAI RAI5ProprietaryRAI RAI6ProprietaryRAI RAI7ProprietaryRAI RAI8ProprietaryRAI RAI9ProprietaryRAI RAI10ProprietaryRAI RAI11Clarifyhowthemaximumgloadsustainedbythe24PT1DSCcanisterintheHISTORMUMAX VerticalVentilatedModule(VVM)ensuresnuclearcriticalitysafetyhasbeenachievedwhencompared toitsoriginallicensingbasis.
SectionI.3.7ofthefinalsafetyanalysisreport(FSAR)statesinpart:
Thecriticalitysafetyofthestored24PT1DSCisensuredbydemonstratingthatthemaximumgload sustainedbytheCanisterstoredinsidetheHISTORMUMAXVVMsislessthanitslicensingbasisvalue.
Thisconclusionsatisfiestherequirementof10CFR72.124(a),withrespecttostructuralmarginsofsafety forSSCs[structure,system,andcomponent]importanttonuclearcriticalitysafety.
However,itisunclearhowgloadsaloneareabletoensurethatstructuralmarginsofsafetyforSSCs importanttonuclearcriticalitysincetheboundaryconditionsofthe24PT1DSCinitsoriginalNUHOMS modulearenotlikethoseintheHISTORMUMAX.Specifically,the24PT1DSCcanisterintheNUHOMS moduleliesonitssideandissupportedalongitslengthcontinuously,wherethe24PT1DSCintheHI STORMUMAXisorientedverticallyandisconstrainedatitsends.Stressesinthe24PT1DSCandits contentsduetoseismicloadswillresultindifferentsafetymarginsforbothscenarioswhichhavenot beendescribed.ClarifythesafetymarginsandupdatetheFSARasnecessaryforthe24PT1inavertical orientationintheHISTORMUMAXVVM.
Thisinformationisneededtodeterminecompliancewith10CFR72.124(a)and10CFR72.236(l).
HoltecResponse:
Nuclearcriticalitysafetyofthe24PT1DSCisensuredduetothefactthatthemaximumgloadsustained bythecanisterintheHISTORMUMAXVVM,duetotheMostSevereEarthquake(MSE),is toHoltecLetter5021061 HISTORMUMAXAmendmentRequest#3 RAIResponses-NonProprietary
Page2of4 approximatelyonetenthofthedesignbasisgloadevaluatedintheAdvancedNUHOMSUFSAR[I.1.2.1]
forthecasksidedrop.Specifically,themaximumhorizontalaccelerationofthe24PT1DSCduetothe MSEeventis7.48gperFSARTableI.3.4.4versusanappliedloadof75ginSection3.6.1.1.7of[I.1.2.1]
forthecasksidedropevent.Moreover,theMSEearthquakeandthecasksidedroparebothaccident levelevents,andthereforetheacceptancecriteriaforthesetwoeventsareidentical.
Holtecrecognizesthattheexternalboundaryconditionsforthe24PT1DSCaredifferentwhenitis insidetheHISTORMUMAXVVMversusthetransfercask.However,theprimaryshearandbending stressesinthe24PT1DSCcanistershellareasmallfractionofthematerialyieldstrengthundertheMSE loading,indicatingthatthe24PT1DSCinternalbasketassemblyandthestoredfuelarewellsupported againstlateralloading.Thisisdemonstratedbyconsideringthe24PT1DSCcanisterasasimply supportedbeam,withitstotalweightuniformlydistributedalongitslength,andsubjectingittoastatic gloadof7.48g.Theresultingprimaryshearstressandbendingstressinthe5/8thickcylindricalshell areonly2.32ksiand6.63ksi,respectively.Meanwhile,theallowableshearandprimarymembrane stresses(at500°F)forthe24PT1DSCshellassembly,underaccidentconditions,are30.1ksiand43.2 ksi,respectively.ThisadditionalcalculationhasbeenaddedtoHoltecreportHI2167337(seeCalculation No.4inHI2167337Rev.1).
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RAI16Justifyhowthetopseismicrestraintassemblyanddividershellappurtenanceassemblywill restrainthe24PT1DSCcanisterintheUMAXVVMwhensubjectedtoseismicloads.
Thetopseismicrestraintassemblyanddividershellappurtenanceassembly,transferlateral/vertical loadstothe24PT1DSCcanisterwhenitisintheUMAXVVMandsubjectedtoseismicloadings.Full contactbetweenthesecomponentshasbeenassumedthroughouttheseismicevent.Somecalculations whichconsidercontact/frictionforceshavebeenprovidedtosupportthedesignofthetopseismic restraintassemblysystem,buttheydonotconsiderthefulldynamicinteractionbetweenthecavity enclosurecontainer(C.E.C.)oftheUMAXVVM,the24PT1DSC,andthetopseismicrestrainsystem.
DynamicseismicanalysesconductedinLSDYNAdonotincludethetopseismicrestraintassemblyorthe dividershellappurtenanceassemblyexplicitly.
Staffisconcernedthatthecalculationsprovideddonotconsidergapsformingbetweenthetopseismic restraintassembly,theC.E.C,andthe24PT1DSCduringaseismiceventwhichcouldallowthe24PT1 DSCtobesubjectedtopounding.AqueryoftheoutputfilesindicatesthatthediameteroftheC.E.C.
itselfexpandsandcontractsduringtheseismicanalyses,whichcouldimplythatthetopseismic restraintassemblyisnotincontactwiththe24PT1DSC.Similarfindingshavebeennotedwithregards tothedividershellappurtenanceassembly.
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NotethatthecanisterandtheC.E.C.oftheUMAXVVMmostlikelyarenotuniformlyrounddueto manufacturing,andthatasthesystemcontinuestocool,additionalgapscouldformbetweenthetop seismicrestraintassemblyand/ordividershellappurtenanceassembly,theC.E.C.,andthe24PT1DSC canisterasafunctionoftime.Gapsformedbymanufacturingandpotentiallynonuniformexpansion shouldbeconsideredintheevaluationofthetopseismicrestraintassemblyandthedividershell appurtenanceassembly.UpdatetheLSDYNAmodelsandsupportingdetailsintheFSARasnecessary.
Thisinformationisneededtodeterminecompliancewith10CFR72.236(l).
HoltecResponse:
Thetapereddesignofthetopseismicrestraintassembly(TSRA),alongwiththeindependentvertical movementofthesupportarms,ensuresthatthe24PT1DSCwillbelaterallyrestrainedwhensubjectto seismicloads.
Perdrawings10574and10576,thereisaonetoonecorrespondencebetweentheDSCspacerblocks ontheTSRAandthedividershellappurtenanceassemblies(DSAA),witheightofeachequallyspaced aroundthecircumferenceofthe24PT1DSCat45degreeintervals.TheTSRAandDSAAtogetherprovide adirectradialpathwayfortheseismicreactionloadstobetransmittedfromthe24PT1DSCtotheCEC shell,whichinturnisfullybackedby3,000psiconcretefortheHISTORMUMAXVersionMSE(seeFSAR Table2.3.10).
ThetaperedprofileoftheDSCspacerblocks(items2and4ondrawing10574)andtheinterfacing wedgeblocksontheDSAA(seedrawing10576)arespecificallydesignedtoovercomevaryingradialgap sizesduetoslightlyeccentricpositioningofthe24PT1DSCinsidetheUMAXVVM,outofroundnessof the24PT1DSCshell,manufacturingtolerances,etc..SinceeachDSCspacerblocksupport(item2on drawing10574)hangsfreelyfromaslottedholeintheshieldring(item1ondrawing10574),eachone canindependentlyfinditsnaturalrestingpositionasitisbeinglowered.Inotherwords,iftheradial gapsaredifferentafterthe24PT1DSCissetinplaceinsidetheUMAXVVM,thentheeight(8)DSC spacerblockswillcometorestatslightlydifferentverticalelevationsandclosethegapateachlocation.
Forthistohappen,theDSCspacerblocksupports(item1ondrawing10574)mustbesufficientlylongto guaranteethatthespacerblockswillcometorestbetweenthe24PT1DSCshellandtheDSAAwedge blocksbeforetheshieldring(item1ondrawing10574)landsontheTSRAsupportlugs(seedrawing 10576).ThisdesignfeaturealsoenablestheDSCspacerblockstolowerthemselvesfurther,under gravity,asthe24PT1DSCcanistercoolsovertimeandthegapsizesgrowduetoduetothermal shrinkage.
Finally,thecalculationsperformedinHoltecreportHI2167337(seeCalculationNo.2)showthatthe11 degreetaperedangleassociatedwiththeDSCspacerblocks,andthewedgeblocksontheDSAA,issmall enoughtopreventtheDSCspacerblocksfrombeingdisplacedordislodgedwhensubjectedtoseismic loads.Thisisbecausewhentheseismicloadisresolvedintotwoorthogonalcomponents,onenormal andoneparalleltotheDSCspacerblock/wedgeinterface,theparallelcomponentisnotcapableof overcomingtheinterfacefrictionatshallowangles.
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Page4of4 Tosummarize,theDSCspacerblocksandtheDSAAhavebeencarefullyengineeredtoaccommodate varyinginitialgapconditions,toselfadjustovertimeasthecanistercools,andtoremaininplaceunder seismicloads.
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