Development and analysis of a regime map for predicting debris bed formation behavior

Abstract

Studies on debris bed formation behavior are important 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). To clarify the characteristics of flow regimes underlying this behavior, a series of simulated experiments is being performed at the Sun Yat-sen University in China by discharging various solid particles into Two-Dimensional (2D) water pools. Based on the preliminary experimental analyses, it has been recognized that, due to the different interaction mechanisms observed 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. In this work, owing to a much enlarged experimental database, a regime map is developed to describe the regime transition and final bed geometry formed by considering the competitive role between the particle-inertial and water-convection during the particle accumulation process. It is found that a respective agreement on the regime transition between experiments and the regime-map predictions could be obtained given current range of conditions including much difference in particle size (0.125–8mm), particle density (beads of glass, alumina, zirconia, steel and lead), particle release pipe diameter (∼30mm) and water depth (∼60cm). With further improvements, the developed regime map (base map) will be tested under more realistic reactor conditions (e.g. irregularly-shaped particles or larger-scale dimensions) and is expectable to benefit the design of in-vessel core catcher as well as the verifications and improvement of future SFR severe accident analysis codes in China.