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KEYWORDSFAILUREANALYSISFRETTINGWEARSIMULATORVIBRATINGSHAFTHIGHTEMPERATUREANDHIGHPRESSUREWATERFRACTURESURFACEMINETHEFAILUREINITIATIONANDFAILUREMODEITWASFOUNDTHATTHEFAILUREHADINITIATEDATAOFTHESENUCLEARFUELRODS,WHICHHAVETHEFOLLOWINGDIMENSIONS；95MMOUTERDIAMETER,06MMWALLTHICKNESSANDABOUTA4MLENGTHBECAUSEOFTHEFIVPHENOMENONBYAPRIMARYCOOLANT,THESESLENDERFUELRODSCOULDEASILYVIBRATE,THUSTHEYARESUPPORTEDBYSEVERALSPACERGRIDSTRUCTURESASSHOWNINFIG1EACHCELLOFASPACERGRIDSTRUCTURECONSISTSOFTWOSPRINGSANDFOURDIMPLESTHEREFORE,ANUCLEARFUELRODISSUPPORTEDBYACERTAINAMOUNTOFSPRINGFORCE,WHICHDEPENDSONTHESPRINGSHAPEANDITSSTIFFNESSUNDERAHIGHTEMPERATUREINANOPERATINGNPPCONDITION,HOWEVER,THECONTACTFORCEBETWEENTHEFUEL13506307/SEEFRONTMATTERC2112008ELSEVIERLTDALLRIGHTSRESERVEDCORRESPONDINGAUTHORTEL8242688761；FAX82428630565EMAILADDRESSLEEYHKAERIREKRYHLEEENGINEERINGFAILUREANALYSIS1620091238–1244CONTENTSLISTSAVAILABLEATSCIENCEDIRECTENGINEERINGFAILUREANALYSISDOI101016/JENGFAILANAL200808013TEMPERATUREC24320C176C,PRESSURIZEDWATERC2415MPAANDRADIOACTIVEENVIRONMENTTHISCONDITIONINEVITABLYRESULTSINMATERIALDEGRADATIONSSUCHASACORROSION,FATIGUE,IRRADIATIONEMBRITTLEMENT,CREEP,ETCDURINGTHEIROPERATIONANOTHERSEVERECONDITIONFORDEGRADINGSTRUCTURALMATERIALSISKNOWNASAFLOWINDUCEDVIBRATIONFIVOFRELATIVELYSLENDERSTRUCTURESDUETOTHERAPIDFLOWVELOCITYOFPRIMARYANDSECONDARYCOOLANTS,WHICHRESULTSINFRETTINGDAMAGESBETWEENTHESESLENDERSTRUCTURESANDTHEIRSUPPORTINGSTRUCTURESTHESEKINDSOFFRETTINGDAMAGESHAVEBEENEXPERIENCEDINTHEMAJORCOMPONENTSOFNPPSSUCHASTHENUCLEARFUELRODS,STEAMGENERATORSGTUBESANDCONTROLRODS1AMONGTHESECOMPONENTS,INOURLABORATORY,THEFRETTINGWEARPHENOMENONOFNUCLEARFUELRODSHASBEENINVESTIGATEDINORDERTOEXAMINEANDDEVELOPAFRETTINGWEARMECHANISMANDADEFECTFREEFUELASSEMBLYFA,RESPECTIVELYGENERALLY,AFACONSISTSOF16C216OR17C2171INTRODUCTIONTHEFAILUREPHENOMENAOFMECHANICALFREQUENTLYINVARIOUSINDUSTRIESONECONTACTREGIONBETWEENTHEVIBRATINGSHAFTANDTHEFUELRODHOLDERJIGANDAFATIGUECRACKWASPROPAGATEDALTHOUGHITWASDIFFICULTTOPROVEITCONCLUSIVELYDUETOTHEHEAVILYOXIDIZEDFRACTURESURFACENEARTHEFAILURELOCATIONS,HOWEVER,THETHREADHOLEWASSUBJECTEDTOAREPEATEDLOADINGDUETOTHEFACTTHATTHESPECIMENHOLDERJIGHADACIRCULARMOTIONFORSIMULATINGAVIBRATIONMOTIONTHISSUGGESTSTHATTHEVIBRATINGSHAFTFAILURERESULTEDFROMCORROSIONFATIGUEPHENOMENONBECAUSETHEFRETTINGTESTHADBEENPERFORMEDATHIGHTEMPERATUREC24320C176CANDPRESSURIZEDDISTILLEDWATERC2415MPACONDITIONSINTHISPAPER,THEREASONSFORTHISFAILUREANDTHEFRACTUREMECHANISMSAREREVEALEDANDDISCUSSEDBYUSINGTHEOMANDSEMRESULTSOFTHEFAILURESURFACEANDTHESTRESSANALYSISOFTHECONTACTREGIONSBETWEENTHEVIBRATINGSHAFTANDTHESPECIMENHOLDERJIGFINALLY,THEABOVERESULTSWEREAPPLIEDTOADESIGNCHANGEOFTHEVIBRATINGSHAFTC2112008ELSEVIERLTDALLRIGHTSRESERVEDSTRUCTURESBYMATERIALDEGRADATIONSINEXTREMEENVIRONMENTSHAVEBEENREPORTEDEXAMPLES,ISINNUCLEARPOWERPLANTSNPPSGENERALLY,NPPSOPERATEINAHIGHFAILUREANALYSISOFAVIBRATINGSHAFTINAFRETTINGWEARSIMULATORYOUNGHOLEE,JAEYONGKIM,HYUNGKYUKIMKOREAATOMICENERGYRESEARCHINSTITUTE,150DUKJINDONG,YUSEONGGU,DAEJEON305353,REPUBLICOFKOREAARTICLEINFOARTICLEHISTORYRECEIVED11JULY2008ACCEPTED1AUGUST2008AVAILABLEONLINE15AUGUST2008ABSTRACTRECENTLY,AFRETTINGWEARSIMULATORWASDEVELOPEDINORDERTOEVALUATETHEFRETTINGWEARBEHAVIOROFNUCLEARCOMPONENTSINHIGHTEMPERATUREANDHIGHPRESSUREHTHPWATERCONDITIONSAFTER500HTESTS,HOWEVER,TWOVIBRATINGSHAFTSAMONGFOURWEREFRACTURED,WHICHWERECONNECTEDTOASPECIMENHOLDERJIGBYUSINGABOLTTHEFRACTURESURFACEWASEXAMINEDUSINGBOTHANOPTICALMICROSCOPEOMANDASCANNINGELECTRONMICROSCOPESEMTODETERJOURNALHOMEPAGEWWWELSEVIERCOM/LOCATE/ENGFAILANALYHLEEETAL/ENGINEERINGFAILUREANALYSIS1620091238–12441239RODANDSPRING/DIMPLEISGRADUALLYDECREASEDDUETOASPRINGRELAXATIONINADDITION,THESPRINGSTIFFNESSISALSOGRADUALLYINCREASEDBECAUSEOFANIRRADIATIONEMBRITTLEMENTOFASPACERGRIDSPRING/DIMPLEEVENTHOUGHACERTAINAMOUNTOFSPRINGFORCEISEXERTEDONTHEFUELRODATITSINITIALOPERATION,ARELATIVELYSMALLSLIPAMPLITUDEONTHECONTACTSURFACEISUNAVOIDABLEUNDERASEVEREFIVCONDITIONCONSEQUENTLY,THECONTACTFORCEISGRADUALLYDECREASEDANDFINALLY,AGAPISOPENEDUPTHISFIG1THESCHEMATICVIEWOFANUCLEARFUELASSEMBLYTHATCONSISTSOF16C216OR17C217FUELRODSANDSEVERALSPACERGRIDASSEMBLYMEANSTHATTHEFRETTINGWEARMODECOULDBECHANGEDFROMASLIDINGWEARTOANIMPACTINGWEARWITHINCREASINGOPERATINGTIMEANOTHERIMPORTANTPOINTISTHATTHEVIBRATIONCHARACTERISTICSOFANUCLEARFUELRODALSOCHANGEDDUETOACONTACTCONDITIONCHANGEOFAFUELRODTHEREFORE,ITISQUITEDIFFICULTTOEXAMINETHEFRETTINGWEARMECHANISMOFANUCLEARFUELRODINNPPOPERATINGCONDITIONSAVERTICALTYPEOFAFRETTINGWEARTESTERFRETONUS,FRTTTINGTESTEROFNUCLEARSYSTEMSFORAHTHPWATERCONDITIONWASDEVELOPEDINORDERTOEVALUATETHEFRETTINGWEARBEHAVIOROFNUCLEARCOMPONENTS2AFTER500HTESTS,HOWEVER,TWOVIBRATINGSHAFTSAMONGFOURWEREFRACTURED,WHICHWERECONNECTEDTOASPECIMENHOLDERJIGBYUSINGABOLTASSHOWNINFIG2ITISFIG2SCHEMATICVIEWSOFTHEASSEMBLINGMETHODBETWEENTHEVIBRATINGSHAFTANDRODSPECIMENHOLDERJIGANDTHEFRACTUREDVIBRATINGSHAFTAFTER500HTESTSATHIGHTEMPERATUREANDPRESSURIZEDWATERCONDITIONESSENTIALTOEVALUATETHEREASONFORTHEIRFAILUREANDTOIMPROVETHEVIBRATINGSHAFTDESIGNTOCONFIRMTHERELIABILITYOFTHEFRETTINGWEARTESTERFORALONGEXPERIMENTINTHISSTUDY,THEREASONSFORTHEFAILUREANDTHEFRACTUREMECHANISMSAREREVEALEDANDDISCUSSEDBYUSINGTHEOMANDSEMRESULTSOFTHEFRACTURESURFACE,MEASUREMENTOFTHEMICROVICKERSHARDNESSANDTHESTRESSANALYSISOFTHEVIBRATINGSHAFTFINALLY,THEABOVERESULTSWEREAPPLIEDTOADESIGNCHANGEOFTHEVIBRATINGSHAFT2FRACTURESURFACEANALYSIS21OMOBSERVATIONTHEVIBRATINGSHAFTISMADEOFACONVENTIONALHIGHCARBONMARTENSITICSTAINLESSSTEELSUS440CANDTHISMATERIALISWIDELYUSEDASTOOLSORBLADESFORUSEINRELATIVELYCORROSIVEATMOSPHERES3THECHEMICALCOMPOSITIONANDMECHANICALPROPERTIESARELISTEDINTABLE1FIG3SHOWSTHEOMRESULTOFTHEFRACTURESURFACEFORTHEVIBRATINGSHAFTDUETOTHEHTHPWATERCONDITION,THEFRACTURESURFACEWASHEAVILYOXIDIZEDANDITWASDIFFICULTTOOBTAINMETALLOGRAPHICPROOFBYUSINGTHEOMOBSERVATIONHOWEVER,ITISEXPECTEDTHATTHEFAILUREWASINITIATEDATACONTACTREGIONBETWEENTHEVIBRATINGSHAFTANDTHEFUELRODHOLDERJIGBECAUSETHESETWOPARTSWASASSEMBLEDBYUSINGABOLTASSHOWNINFIG2DURINGTHEFRETTINGWEARTESTS,FOURVIBRATINGSHAFTSWERERECIPROCATEDINTHEIRAXIALDIRECTIONWITHARANGEOF200LM,AFREQUENCYOF30C176HZANDASINUSOIDALMOTIONBYTWOELECTROMAGNETICACTUATORSTHATWEREARRAYEDATANANGLEOF90OTOGENERATEACIRCULARMOTIONOFTHEFUELRODSPECIMENWHICHISREGARDEDASACONSERVATIVESIMULATIONOFANACTUALFUELRODVIBRATIONINOPERATINGNPPS,THEPHASEDIFFERENCEOFTHESINUSOIDALWAVEFORMFORTHESHAKESIGNALSOFTWOACTUATORSISSETTO90OASSHOWNINFIG4WHENTHEFUELRODSPECIMENISVIBRATEDWITHACIRCULARMOTION,THECONTACTREGIONOFTHEVIBRATINGSHAFTSWITHTHEFUELRODHOLDERJIGISEXPECTEDTOEXPERIENCEFATIGUELOADSGENERALLY,STRIATIONTRACESTHATAREDISTINCTPROOFFORAFATIGUEFAILURECOULDBEFOUNDEASILYONAFRACTURESURFACE,IFTHESTRUCTURALMATERIALSAREFRACTUREDUNDERTHEFATIGUELOADINGCONDITIONSHOWEVER,THEOXIDIZEDFRACTURESURFACEOFTHEVIBRATINGSHAFTWASEXAMINEDBYUSINGSEMWITHOUTANYCLEANINGSBECAUSETHESTRIATIONTRACESCOULDBEEXPECTEDTOREMOVEBYTHEOXIDEREMOVALPROCESSIEACIDCLEANING22HARDNESSVARIATIONBEFORETHESEMOBSERVATION,ITISNECESSARYTOEXAMINETHEMECHANICALPROPERTYCHANGESOFTHEVIBRATINGSHAFT,BECAUSEITWASEXPOSEDTOTHEHTHPWATERCONDITIONDURING500HTESTSSO,AMICROVICKERSHARDNESSOFTHEFRACTUREDVIBRATINGSHAFT1240YHLEEETAL/ENGINEERINGFAILUREANALYSIS1620091238–1244WASMEASUREDANDITSRESULTISSHOWNINFIG5ITISAPPARENTTHATTHEMICROVICKERSHARDNESSVALUEINCREASEDACCORDINGTOTHEEXPOSEDTEMPERATUREFORTHEVIBRATINGSHAFTTHISRESULTCORRESPONDSWELLWITHTHETEMPERINGTEMPERATUREEFFECTTABLE1CHEMICALCOMPOSITIONSANDMECHANICALPROPERTIESROOMTEMPERATUREOFACONVENTIONALHIGHCARBONMARTENSITICSTAINLESSSTEELSUS440C4CMNSIPSCRMOFECHEMICALCOMPOSITIONSWT10101000400317075BALYIELDSTRENGTHTENSILESTRENGTHELONGATIONELASTICMODULUSDENSITYPOISSON’SRATIOMECHANICALPROPERTIES1280MPA1750MPA4200GPA78G/CM303FIG3OMRESULTOFTHEFRACTURESURFACEFORTHEVIBRATINGSHAFTARROWSINDICATETHEEXPECTEDCRACKINITIATIONREGIONYHLEEETAL/ENGINEERINGFAILUREANALYSIS1620091238–12441241FIG4ACTUATINGMECHANISMOFTHEFUELRODBYUSINGTWOELECTROMAGNETICACTUATORSINFRETONUSNOTETHATTHEFUELRODMOTIONSARECHANGEABLEBYADJUSTINGVIBRATIONAMPLITUDESANDPHASEDIFFERENCEBETWEENTWOACTUATORSONTHEMECHANICALPROPERTIESOFSUS440C4INTHISSTUDY,THEHIGHERCARBONMARTENSITICSTAINLESSSTEELISLIKELYTORETAINALARGEAMOUNTOFUNTRANSFORMEDAUSTENITEITISTHOUGHTTHATADELAYEDTRANSFORMATIONMAYOCCURASTEMPERATUREFLUCTUATIONSINSEVERALFRETTINGWEARTESTSBECAUSETHE500HTESTSATABOUT320C176CDIDNOTHAVEANEGLIGIBLEEFFECTONTHESTRESSRELIEVINGOFTHEVIBRATINGSHAFTMATERIALINADDITION,ITISPOSSIBLETHATSOMELOSSINDUCTILITYMAYRESULTFROMAHYDROGENEMBRITTLEMENTTHATISANIMPORTANTCONCERNINMARTENSITICSTAINLESSSTEELSINAHEATTREATINGATMOSPHERECONTAININGHYDROGENINTHEFORMOFDISTILLEDWATER23SEMRESULTSFIG6SHOWSTHEMORPHOLOGYOFTHEFRACTURESURFACEBYUSINGSEMITISAPPARENTTHATTHEFRACTURESURFACEWASALMOSTCOVEREDWITHOXIDESANDITISDIFFICULTTODETECTEVIDENCEOFAFATIGUEFAILURESUCHASSTRIATIONTRACESFROMACAREFULINSPECTIONOFTHERESULTS,HOWEVER,WEAKSTRIATIONTRACESAPPEAREDNEARALATERALOUTERSURFACEALSO,ACRACKPROPAGATIONTRACEWASFOUNDATTHECONTACTREGIONBETWEENTHEVIBRATINGSHAFTANDTHEFUELRODHOLDERJIGEVENTHOUGHITSCHARACTERISTICCOULDNOTBEDEFINEDDUETOTHESEVEREOXIDATIONINTHEHTHPWATERCONDITIONONEOFTHEINTERESTINGRESULTSISTHATANIMPACTINGWEARSCARAPPEAREDINTHEFRACTURESURFACEOFTHEVIBRATINGSHAFTTHISRESULTMEANSTHATTHEIMPACTINGWEARBETWEENTHETWOFRACTUREDSURFACESISGENERATEDAFTERAFRACTUREBECAUSETHEFRACTUREDVIBRATINGSHAFTISCONTINUOUSLYRECIPROCATEDBYANELECTROMAGNETICACTUATORREGARDLESSOFTHESHAFTFAILURESO,ITISEXPECTEDTHATTHEFATIGUESTRIATIONTRACESHADDISAPPEAREDANDWERECOVEREDBYTHEIMPACTINGWEARMOTIONANDBYTHEWEARDEBRISWITHASEVEREOXIDATION,RESPECTIVELYCONSEQUENTLY,THEVIBRATINGSHAFTFAILUREISEXPECTEDTOBEINITIATEDBYACONTACTFATIGUEATTHECONTACTREGIONANDTHENTHECONTACTFORCEEXERTEDBYABOLTFIG5MEASUREMENTRESULTOFTHEMICROVICKERSHARDNESSACCORDINGTOTHEEXPOSEDTEMPERATUREFORTHEVIBRATINGSHAFT
