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11/2/70(Reprinted12/1/70)SAFETYGUIDE1NETPOSITIVESUCTIONHEADFOREMERGENCYCORECOOLINGANDCONTAINMENTHEATREMOVALSYSTEMPUMPSA.IntroductionProposedGeneralDesignCriterion41requiresthattheemergencycoolingandcontainmentheatremovalsystemsbecapableofaccomplishingtheirrequiredsafetyfunctionsassumingpartiallossofinstalledcapacity.Incurrentdesignstheabilitytoaccomplishthesesafetyfunctionsreliablydependsinpartontheproperperformanceofsystempumpswhich,inturn,dependsontheconditionsunderwhichthepumpsmustoperate.Oneoftheseconditionsissuctionpressure.Thisguidedescribesasuitablerelationshipbetweenincreasesincontainmentpressurecausedbypostulatedlossofcoolantaccidentsandthenetpositivesuctionhead(NPSH)ofemergencycorecoolingandcontainmentheatremovalsystempumpswhichmaybeusedtoimplementGeneralDesignCriterion41.B.DiscussionAsignificantconsiderationrelatedtoemergencycorecoolingandcontainmentheatremovalsystemsisthepotentialfordegradedpumpperformancewhichcouldbecausedbyanumberoffactors,includinginadequateNPSH.IftheNPSHavailabletoapumpisnotsufficient,cavitationofthepumpedfluidcanoccur.Thiscavitationmayreducesignificantlythecapabilityofthesystemtoaccomplishitssafetyfunctions.Itisimportantthattheproperperformanceofemergencycorecoolingandcontainmentheatremovalsystemsbeindependentofcalculatedincreasesincontainmentpressurecausedbypostulatedlossofcoolantaccidentsinordertoassurereliableoperationunderavarietyofpossibleaccidentconditions.Forexample,ifproperoperationoftheemergencycorecoolingsystemdependsuponmaintainingthecontainmentpressureaboveaspecifiedminimumamount,thentoolowaninternalpressure(resultingfromimpairedcontainmentintegrityoroperationofthecontainmentheatremovalsystemsattoohigharate)couldsignificantlyaffecttheabilityofthissystemtoaccomplishitssafetyfunctionsbycausingpumpcavitation.Inaddition,thedeliberatecontinuationofahighcontainmentpressuretomaintainanadequatepumpNPSHwouldresultingreaterleakageoffissionproductsfromthecontainmentandhigherpotentialoffsitedosesunderaccidentconditionsthanwouldotherwiseresult.ChangesinNPSHforemergencycorecoolingandcontainmentheatremovalsystempumpscausedbyincreasesintemperatureofthepumpedfluidunderlossofcoolantaccidentconditionscanbeaccommodatedwithoutrelianceonthecalculatedincreaseincontainmentpressure.AdequateNPSHcanbeassuredbylocatingpumpsat-suitableelevationswithrespecttothestoragevolumesconnectedtotheirsuctionsides,byusingmultistageorboosterpumps,byacombinationofthesemethods,orbyothertechniques.C.RegulatoryPositionEmergencycorecoolingandcontainmentheatremovalsystemsshouldbedesignedsothatadequatenetpositivesuctionhead(NPSH)isprovidedtosystempumpsassumingmaximumexpectedtemperaturesofpumpedfluidsandnoincreaseincontainmentpressurefromthatpresentpriortopostulatedlossofcoolantaccidents.1.1