Development of molten core relocation analysis module MCRA in the severe accident analysis code SAMPSON

IMPACT is a complex software system under development at the Nuclear Power Engineering Corporation, that includes the severe accident analysis code (S AMPSON). SAMPSON is an integration of twelve modules and will be capable of simulating hypothesized severe accidents in a nuclear power plant in the f inal phase of the IMPACT project. As one of these modules, the Molten Core Relocation Analysis (MCRA) module simulates the relocation behavior of a mo lten core during a severe accident. MCRA adopts a multi-phase, multicompone nt, multi-velocity field model to simulate severe accident phenomena mechan istically. Herein, we describe flow regimes, interfacial area modeling and physics models such as the momentum exchange and phase change models. Two s eparate effect analyses are presented as verification of MCRA's models foll owing the model descriptions. First, the fluid dynamics of the multi-veloci ty field model was verified in the calculation of nitrogen gas bubbling thr ough water in Leung's experiment. Second, data of the JRC-Ispra KROTOS-37 e xperiment were adopted for verification of the multi-velocity field model a nd vaporization/condensation model. Calculation results of both analyses co mpared well with the experimental data. Finally, MCRA's integrated function involving the melting/freezing model was demonstrated by calculating two-p hase flow with a fuel rod and molten fuel.