IVR-ERVC Effectiveness Assessment For Large Scale Pressurized Water Reactor Under Severe Accident Using MELCOR

As a key severe accident management strategy for light water reactors(LWRs), in-vessel retention (IVR) through external reactor vessel cooling(ERVC) has attracted the attention in relevant studies for decades. Greatprogresses have been achieved upon this issue. However, previous studiesonly investigated the final molten pool configurations by steady stateanalysis mainly for reactors of AP600, AP1000. Also, most studies wereperformed to analyze the IVR-ERVC process separately, withoutconsidering the strong coupling features of internal and external reactorpressure vessel (RPV). This paper addressed the IVR-ERVC issues from atransient perspective using the severe accident code MELCOR for1700MW large scale advanced passive power plant, a three-loop,pressurized water reactor with passive safety features. Firstly,comprehensive review works were performed after which the analysismodel of the nuclear power plant was established and verified bysteady-state calculation. Then accident calculations were conducted, duringthe process investigations were mainly focused on the transients in severeaccident including core degradation and relocation, molten pool formation,growth and heat transfer within. Furthermore, internal and external RPVconditions were combined together in IVR-ERVC analysis. MELCORcalculations for lower head heat flux were then compared with critical heatflux (CHF) of lower head to assess the effectiveness of IVR-ERVC. Theresults indicate that lower head heat flux is below the CHF value.Therefore, the IVR-ERVC strategy for1700WM large scale pressurizedwater reactor is considered to be physically effective. At last, sensitivity analysis was performed for several key parameters considered to besignificant in IVR-ERVC assessments. Accordingly, conclusion wasreached and suggestions for further improvement were proposed.