Evaporation and Flow of Coolant at the Bottom of a Particle-Bed modelling Relocated Debris

Subject of the presented work is the experimental investigation of cooling-mechanisms which set in after the relocation of molten debris to the lower plenum during a nuclear accident with core melt. Emphasis is put on the influence of the bottom area of the porous debris. Experiments are carried out with a bed of steel balls (Diam = 2 and 4 mm), heated with an induction coil. The particle-bed is located inside a glass trough with inclining bottom. The particle-bed represents a section from the lower plenum of the RPV. At present, the model-fluid R134a is used and heating rates of up to 560 kW/m2 per unit horizontal cross-sectional area of the article-bed are realized. With these experiments, the evaporation inside the particle-bed and the resulting flow of liquid and gaseous coolant and the influence of an inclining bottom are investigated in detail. The results obtained in the first steady-state experiments and transient experiments are presented and discussed. (authors)