TheimpactofdesignonthedecayheatremovalcapabilitiesofamodularpebblebedHTROriginalResearchArticle

ThedecayheatremovalcapabilitiesareanimportantsafetyfeatureofthemodularpebblebedHTR.Itisdesignedinawaythatalsoduringlossofcoolingaccidentsthedecayheatcanberemovedpurelybypassivemeanswithoutexceedingpredefinedtemperaturelimitsforfuelandstructures.Suchaplantdesign,however,yieldslimitationsonthepoweroutput.Thus,fromthethermalhydraulicpointofviewareactorwithmaximumpowerwhichstillobeysthetemperaturelimitsoffuelandcomponents,representsanoptimaldesignofamodularpebblebedHTR. Inthispaper,designoptionsforamodularpebblebedHTRarediscussedwithrespecttotheircapabilitiesofdecayheatremoval. Bothpressurizedanddepressurizedlossofcoolantaccidentsareinvestigated.Optimizationofdesignfeaturesisconsideredwithreferencenotonlytothemaximumfueltemperatureduringtheaccidents,butalsotothetemperatureofstructures,mainlythatofthereactorpressurevessel.Itispointedoutthatannularcorescanproducehigherpowerwithoutexceedingfueltemperaturelimits,especiallyduringdepressurizationaccidents.Thisismainlyduetogeometricaleffects.Heatstorageeffectsoftheinnercolumnalsohaveaninfluenceonthemaximumfueltemperaturebyincreasingthetimeatwhichthistemperatureisreached.Whileathermalinsulationofthecoreandthereflectorincreasesthefueltemperature,maximumtemperatureofthepressurevesselandthecorebarrelisdecreased.Thus,carbonblocksrepresentanimportantelementforoptimizationofthedesign