Experimental study of geometric effect on the debris dispersal phenomenon in a reactor cavity during postulated high pressure melt ejection scenario

Abstract

In order to characterize the debris dispersal fraction from a reactor cavity during postulated high pressure melt ejection (HPME) accident in Nuclear Power Plants, a number of low temperature simulant experiments employing mocks-up of reactor cavities of Kori-1 and YoungGwang 3&4 Nuclear Power Plants have been performed. The parameters which have examined and show the main effect on the debris dispersal in the experiments are breach area of the reactor vessel, primary system pressure, material properties of blowdown gas and melt, and cavity configuration. Using non-dimensional numbers which are known to govern the debris dispersal process in the reactor cavity from the scaling analysis, the experimental data have been analyzed. However, due to the dependency of the debris dispersal process on the cavity geometry, the experimental data from a specific cavity geometry show a limitation for their application to different cavity configurations. To predict the debris dispersal fraction for different types of cavity geometry, a new correlation has been developed, which includes geometric parameters explicitly. It is found that important parameters in the debris dispersal process from the cavity are the available entrainment time as well as the particle flight time. For validation of the proposed correlation, a series of experiments varying geometric factors of the cavity flow area and the cavity exit height have been carried out in two scaled-down HPME facilities. The experimental results show good agreement with the predictions by the developed correlation. As a major geometric parameter of the reactor cavity, when the cavity flow area increases, the debris dispersed fraction decreases due to the decrease of the effective entrainment period and droplet velocity. Along with the increase of the cavity exit height, the debris dispersed fraction also decreases.