CONCEPT OF A CORE COOLING SYSTEM AND EXPERIMENTS PERFORMED

One of the problems which must be solved in severe accidents is the me lt-concrete interaction which does occur when the core debris penetrat es the lower pressure vessel head and contacts the basement. To preven t these accident consequences, a core catcher concept is proposed to b e integrated into a new pressurized-water reactor design. The core cat cher achieves coolability by spreading and fragmentation of the ex-ves sel core melt based on the process of water inlet from the bottom. In order to justify the dominant process during flooding of the melt from the bottom, prototypic experiments with thermite melts in laboratory scale have been carried out. In these experiments flooding and early c oolability of the melt is demonstrated. To obtain more detailed inform ation on the important process of water penetration into the melt, a s imulant experiment has been conducted using a transparent plastic melt with the typical viscosity behaviour of an oxidic corium melt and a t emperature allowing evaporation of water. In every experiment the melt is flooded, and complete freezing in the form of a porous layer occur s within a few minutes only.