| Based on the study in thermal-hydraulic and core model, a feasibilityanalysis is developed to achieve code combined analysis of RELAP5andMELCOR. The results show that, the RELAP5major edit and MELCORinput deck can be used as data exchange interface. Consequently, Acombined analysis method utilizing thermal-hydraulic system code RELAP5and severe accident integral code MELCOR is developed to study thetransient response of a traditional three-loop PWR under the severe accidentTMLB’, DECLG and SBLOCA scenarios. In order to utilize RELAP5to themaximum degree and guarantee the accuracy of system response beforeentering into severe accident situation, the minimum cutoff temperature forzircaloy oxidation model of MELCOR, default value of1100K, is used asthe criterion to switch RELAP5transient calculation to MELCOR severeaccident analysis. Required data to initiate MELCOR will be extractedthrough the major edit of RELAP5output. The results show that the datatransferring process is relatively continuous. As observed in combinedcalculation, differences to varying degree are concluded comparing theparameters of primary system pressure, core/pressurizer collapsed waterlevel and fuel/cladding temperature calculated by two methods, as well asthe timing of core heat transfer degradation and vessel failure. Since systemtransient responses were calculated by RELAP5before entering into severe accident, the results from combined calculation are more accurate than thecalculation based on MELCOR alone. Consequently, this combinedcalculation can improve the accuracy and reliability of the severe accidentsimulation.Besides, sensitivity study of the code switch criterion is analyzed, byselecting the RELAP5limiting PCT temperature1477K and MELCORdefault gap release temperature1173K as reference parameters. The resultsshow that the main parameters predicted by different combined analysisbasically have the same trend, but the timing of core materials and vesselfailure are still different. |
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