Impurityconcentrationbehaviorsinaboilingtubesheetcrevice:PartII.PackedcreviceOriginalResearchArticle

Theimpurityconcentrationbehaviorofaboilingcrevicepackedwithmagnetiteparticleswasinvestigatedwiththermocouplesandelectrodesforthemeasurementoftemperatureandelectrochemicalcorrosionpotential(ECP),respectively,inordertounderstandchemicalchangeinapressurizedwaterreactor(PWR)steamgenerator(SG)crevice.Asecondarysolutioncomposedof50ppmNaand200ppbhydrogenwassuppliedataflowrateofabout4l/h.Sodiumhydroxide(NaOH)concentrationprocessinthecreviceandtheresultantboilingpointelevationbehaviorwerecharacterizedwithtemperatureandECPdata.Thetemperatureinthepackedcrevicewasabout2–3°Chigherthanthatfortheopencrevice.Inthesameconditions,themagnetite-packedcreviceshowedagreateramountofboilingpointelevationwithalongertimetoreachasteadystatecomparedwiththecaseofanopencrevice.Itwasfoundthatthebottomregionofthecrevicewasinitiallyfilledwithsteam,andthentheconcentratedliquidregioninitiallylocatedatthemiddleofcreviceexpandedtoboththecrevicebottomandtheupperregion.Toanalyticallyestimatethewettedlength,aclosedformmodelwasintroduced.Themodelresultsestimatedtheinitialwettedlengthshorterascomparedwiththemeasurementresults.MeasuredECPresultsofpackedcreviceshowedsimilarbehaviorsascomparedwithcalculatedresultsbyusingNernstequation.ECPresultsreasonablycoincidedwiththeboilingpointelevationestimatedfromthetemperaturedataexceptoneunusualcase.