Experiments and modeling of particulate debris spreading in a pool

Melt fragmentation, quenching and long term coolability in a deep pool of water under reactor vessel are employed as a severe accident mitigation strategy in several designs of light water reactors. Success of the strategy is contingent upon effectiveness of natural circulation in removing the decay heat generated by the porous debris bed. Geometrical configuration of the bed is one of the factors which affect coolability of the bed. Boiling and two-phase turbulent flows in the pool serve as a source of mechanical energy which can affect the initial geometry as well as dynamically change the shape of already formed debris bed. The main goal of this work is to provide experimental data on spreading of solid particles in the pool by large scale two-phase flow structures induced by gas injection from the bottom. These data are necessary for development and validation of predictive capabilities of computer codes allowing numerical modeling of the debris bed formation at prototypic severe accident conditions. In PDS-P experiments air injection at the bottom of the test section is employed in order to create large scale flow in the pool. The test section is constructed as a rectangular tank. It has close to 2D geometry with fixed width (72 mm), variable length (up to 1.6 m) and allows water filling depth of up to 1 m. The variable pool length and depth allows formation of the different in size and pattern two-phase circulating flows. Experimental conditions such as gas-phase flow rate and particle properties (density and size) are scaled to maintain relevancy to the prototypic accident conditions. The average void fraction in the pool is determined by video recording and image processing. Particles are supplied from the top of the facility above the water surface. In the separate-effect studies of the influence of two-phase currents on particle trajectories and bed formation, a low particle flow rate is required in order to minimize or completely exclude particle-particle
QC 20160614