Studies on debris bed formation behavior are of crucial importance for the improved evaluation of core relocation and debris bed coolability that might be encountered in a Core Disruptive Accident (CDA) of Sodium-cooled Fast Reactors (SFR). Motivated to clarify the characteristics of flow regimes underlying this behavior, both experimental investigations and empirical-model development are being performed at the Sun Yat-sen University. As for the experimental study, several series of simulated experiments are being conducted by discharging various solid particles into water pools. To obtain a comprehensive understanding, a variety of experimental parameters, including particle size (0.256∼8mm), particle density (glass, alumina, zirconia, steel and lead), particle shape (spherical and irregularly-shaped), water depth (0∼60cm), particle release pipe diameter (10∼30mm) as well as the particle release height (110∼130cm) were varied. It is found that due to the different interaction mechanisms between solid particles and water pool, four kinds of flow regimes, termed respectively as the particle-suspension regime, the pool-convection dominant regime, the transitional regime and the particle-inertial dominant regime, were identifiable. As for the empirical-model development, by using dimensional analysis technique, a regime map (base map), which is restricted to predictions of spherical particles up until now, was recently suggested. It is shown that a respectable agreement between experiments and the regime-map predictions could be obtained. This work, which gives a large palette of favorable data and insight for a better understanding and an improved estimation of CDAs in SFRs, is expected to benefit future analyses and verifications of SFR severe accident analysis codes in China.

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