Thermal detonation wave generation, propagation and reflection from a vessel wall

Abstract

A severe accident at an NPP involving destruction and melting of the core may entail formation of a coarsely dispersed mixture of hightemperature melt with a steam-and-water medium. This, in turn, can lead to a steam explosion as a consequence of very fast transfer of heat from melt to water. The aim of the study is to evaluate the dynamic effects resulting from the steam explosion in the 1D approximation with varying the parameters of the initial mixture. The mathematical model of thermal detonation is briefly described. Fragmentation of molten corium droplets in a shock wave is one of the key processes defining the energy release rate in the medium. The hydrodynamic mechanism governing the droplet fragmentation process is considered as a function of conditions under which the medium flows over the melt droplets. The propagation of a thermal detonation wave in the “corium--water” system and its reflection from a wall is numerically modeled. The qualitative picture of the thermal detonation wave formation and propagation processes, and its reflection from a wall is obtained. The quantitative parameters characterizing the wave's impact on a wall were determined as a function of the initiating point coordinate. The melt’s initial volumetric fraction was also varied in the calculations. A conclusion can be drawn from an analysis of the obtained results that the pressure and its pulse upon the wall have higher values for initiation points that are more distant from the wall. This is attributed to the fact that in such cases, the thermal detonation wave is generated in the largest region containing melt droplets.