Simulations of KROTOS alumina and corium steam explosion experiments: Applicability of the improved solidification influence modelling

Abstract The KROTOS steam explosion experiments revealed important differences in the energy conversion efficiency among the melts. The differences observed in the experiments are due to the differences in the jet fragmentation, the melt droplet solidification and the void production. These are limiting processes in the steam explosion phenomenon and have to be modelled adequately in fuel–coolant interaction codes. The presented research focuses on the solidification effect which inhibits the fine fragmentation of the melt droplets and therefore influences directly the strength of the steam explosion. The solidification influence modelling in fuel–coolant interaction codes is strongly related to the modelling of the temperature profile inside the melt droplets and to the modelling of the mechanical effect of the formed crust on the fine fragmentation process. An improved model was developed and implemented into the exploratory version of the MC3D code. This enables a more accurate prediction of the amount of droplets participating in the fine fragmentation process during the explosion phase. The general applicability of the proposed improved modelling and its potential for reliable extrapolations of experimental findings to reactor conditions was assessed. For the assessment the KROTOS alumina K44 and corium K53 explosion experiments were selected. The simulations support the key role of the solidification in the steam explosion phenomenon. The application of the improved modelling enhances the geometrical extrapolation capabilities of fuel–coolant interaction codes to cover reactor cases.

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