TRANSIENT EXPERIMENTS WITH THERMITE MELTS FOR A CORE CATCHER CONCEPT BASED ON WATER ADDITION FROM BELOW

A core catcher concept is proposed to be integrated into a new pressur ized water reactor. The core catcher achieves coolability by spreading and fragmentation of the ex-vessel core melt based on a process of wa ter inlet from the bottom through the melt. By highly effective heat r emoval that uses evaporating water in direct contact with the fragment ed melt, the cerium melt would solidify in a short time period, and lo ng-term cooling could be maintained by continuous water evaporation fr om the flooded porous or fragmented cerium bed. The key process for ob taining coolability is the coupling of the three effects: (a) water in gression from below and its evaporation, (b) break up and fragmentatio n of the cerium layer, and (c) heat transfer and solidification of the melt. These mechanisms are investigated in transient medium-scale exp eriments with thermite melts. The experimental setup represents a sect ion of the proposed core catcher design. A thermite melt is located on the core catcher plate with a passive water supply from the bottom. A fter generation of the melt, the upper sacrificial layer is eroded unt il water penetrates into the melt from the bottom through plugs in the supporting plate. Fragmentation and fast solidification of the melt a re observed, and long-term heat removal is guaranteed by the coolant w aterflooding the porous melt. Water inflow is sufficient to safely rem ove the decay heat in a comparable cerium layer. The open porosity is created by the vapor streaming through the melt during the solidificat ion process. Fracture of the solid by thermomechanical stresses is not observed. The experiments in their current stage show the principal f easibility of the proposed cooling concept and are used to prepare lar ge-scale experiments to be performed in the modified BETA facility wit h sustained heating of the melt.