TransformationandfragmentationbehaviorofmoltenmetaldropinsodiumpoolOriginalResearchArticle

Inordertoclarifythefragmentationmechanismofametallicalloy(U–Pu–Zr)fuelonliquidphaseformedbymetallurgicalreactions(liquefactiontemperature=650°C),whichisimportantinevaluatingthesequenceofcoredisruptiveaccidentsformetallicfuelfastreactors,aseriesofexperimentswascarriedoutusingmoltenaluminum(meltingpoint=660°C)andsodiummainlyundertheconditionthattheboilingofsodiumdoesnotoccur.Whentheinstantaneouscontactinterfacetemperature(Ti)betweenmoltenaluminumdropandsodiumislowerthantheboilingpointofsodium(Tc,bp),themoltenaluminumdropcanbefragmentedandthemassmediandiameter(Dm)ofaluminumfragmentsbecomessmallwithincreasingTi.WhenTiisroughlyequivalenttoorhigherthanTc,bp,thefragmentationofaluminumdropispromotedbythermalinteractioncausedbytheboilingofsodiumonthesurfaceofthedrop.Furthermore,evenundertheconditionthattheboilingofsodiumdoesnotoccurandthesolidcrustisformedonthesurfaceofthedrop,itisconfirmedfromananalyticalevaluationthatthethermalfragmentationofmoltenaluminumdropwithsolidcrusthasapotentialtobecausedbythetransientpressurizationwithinthemeltconfinedbythecrust.Theseresultsindicatethepossibilitythatthemetallicalloyfuelonliquidphaseformedbythemetallurgicalreactionscanbefragmentedwithoutoccurringtheboilingofsodiumonthesurfaceofthemelt.