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SAFETYGUIDE5ASSUMPTIONSUSEDFOREVALUATINGTHEPOTENTIALRADIOLOGICALCONSEQUENCESOFASTEAMLINEBREAKACCIDENTFORBOILINGWATERREACTORSA.IntroductionSection50.34of10CFRPart50requiresthateachapplicantforaconstructionpermitoroperatinglicenseprovideananalysisandevaluationofthedesignandperformanceofstructures,systems,andcomponentsofthefacilitywiththeobjectiveofassessingtherisktopublichealthandsafetyresultingfromoperationofthefacility.Thesteamlinebreakaccidentisoneofthepostulatedaccidentsusedtoevaluatetheadequacyofthesestructures,systems,andcomponentswithrespecttothepublichealthandsafety.Thissafetyguidegivesaceeptableassumptionsthatmaybeusedinevaluatingtheradiologicalconsequencesofthisaccidentforaboilingwaterreactor.B.DiscussionIntheprocessofreviewingalargenumberofapplicationsforconstructionpermitsandoperatinglicenses,theregulatorystaffhasdeveloped,basedonengineeringjudgmentandonapplicableexperimentalresultsfromsafetyresearchprogramsconductedbytheAECandthenuclearindustry,anumberofappropriatelyconservativeassumptionswhichareusedbytheregulatorystafftoevaluatetheapplicant'sestimateoftheradiologicalconsequencesofvariouspostulatedaccidents.ThissafetyguideliststheassumptionsIusedbytheregulatorystafftoevaluatethesteamlinebreakaccidentforaboilingwaterreactor.C.RegulatoryPositionTheassumptionsrelatedtothereleaseofradioactivematerialare:'Insomecases,plantdesignconditionsmayexistwhichrequirespecialconsiderationanddifferentassumptions.1.ThesteamlinebreaksIwiththereactoratfullpower3andthereactorscrams.2.Thesteamlineisolationvalvescloseinthemaximumtimeincorporatedortobeincorporatedinthetechnicalspecifications.Thisclosuretimewillbeverifiedbysuitableperiodictesting.3.Thetotalmassofcoolantreleasedisthatamountinthesteamlineandconnectinglinesatthetimeofthebreakplustheamountthatpassesthroughthevalvespriortoclosure.(Ruptureswithintheturbinecomplexarenotconsideredinthisguide.)4.Theradioactivityinthecoolantisassumedtobethemaximumamountincorporatedortobeincorporatedinthetechnicalspecifications,providedthatnofurtherfuelfailuresareassumedtooccurasaresultofdelaysinvalveclosure.5.Alloftheiodine(nocreditforplateoutisallowed)andnoblegasesfromthereleasedcoolantarereleasedtotheatmospherewithin2hoursataheightof30meterswithafumigationcondition.6.Theassumptionsfordoseconversionandatmosphericdiffusionare:(a)Nocorrectionismadefordepletionfromtheeffluentplumeofradioactiveiodineduetodepositionontheground,orfortheradiologicaldecayofIodine131intransit.2Forpurposesofthisguideasteamlinebreakisdefinedasacompleteseveranceofthepipeandthepipecenterlineisoffsetbyatleastthepipediameter.'Forcertaindesignsotheroperatingmodes(i.e.,hotstandby)mayrepresentaworsecondition.Thesedesignswillbeevaluatedonanindividualcasebasis.5.1(b)Thebreathingrateofpersonsoff-specialmeteorological,topositeisassumedtobe3.47x10-4graphical,andothercharaccubicmeterspersecond.(Thisteristicswhichmayaffectthevalueisdevelopedfromtheaver-maximumplumeconcentraagedailybreathingrate[2x10'tion.Thesesiterelatedcharcm3/day]assumedinthereportofacteristicsmustbeevaluatedICRP,Committee11-1959.)onanindividualcasebasis.In(c)Theiodinedoseconversionfactorsthecaseofbetaradiation,thearegiveninICRPPublication2,receptorisassumedtobeexReportofCommitteeII,Permis-posedtoaninfinitecloudatsibleDoseforInternalRadiation,themaximumgroundlevel1959.concentrationatthatdistance(d)Externalwholebodydosesarefromthereactor.InthecasecalculatedusingInfiniteCloudofgammaradiation,thereassumptions,i.e.,thedimensionsceptorisassumedtobeexofthecloudareassumedtobeposedtoonlyone-halfthelargecomparedtothedistancethatcloudowingtothepresenceofthegammaraysandbetaparticlestheground.Themaximumtravel.Suchacloudwouldbecon-cloudconcentrationisalwayssideredaninfinitecloudforare-assumedtobeatgroundlevel.ceptoratthecenterbecauseany(2)Theappropriateaveragebetaadditional[gammaand]betaemit-andgammaenergiesemittedtingmaterialbeyondtheclouddi-perdisintegration,asgiveninmensionswouldnotalterthefluxtheTableofIsotopes;Sixthof[gammaraysand]betaparti-Edition;byC.M.Lederer,J.clestothereceptor(MeteorologyM.Hollander,I.Perlman;andAtomicEnergy,Section7.4.1.1UniversityofCalifornia,-editorialadditionsmadesothatBerkeley;LawrenceRadiationgammaandbetaemittingmaterialLaboratoryshouldbeused.couldbeconsidered).Underthese(e)(1)Theequationusedtodeterconditionstherateofenergyab-minetheatmosphericdifsorptionperunitvolumeisequalfusionfromanelevatedretotherateofenergyreleasedperleaseat30meters,uniformunitvolume.4winddirectionwithafumigaThefollowingspecificassumptionstionconditionexistingis:areused:0.0133(1)Thedoseatanydistancefrom/YthereactoriscalculatedbasedWhere:onthemaximumconcentra-x=theshorttermavertionintheplumeatthatdis-agecenterlinevaluetancetakingintoaccountofthegroundlevel4MeteorologyandAtomicEnergy-1968,Chapter7,Fromasemi-infinitecloud,thegammadoseRadioactiveCloud-doseCalculations,liststhefollow-rateinairis:D'=0.25Efx.ingequations:Where:A.ForaninfiniteuniformcloudcontainingxDbetadoseratefromaninfinitecloudcuriesofbetaradioactivitypercubicmeter(rad'sec)thebetadoserateinairatth