Experimental Study of Bubble Behavior in a Two-Dimensional Particle Bed With High Solid Holdup

Abstract

In a core disruptive accident of a fast breeder reactor, the post accident heat removal is crucial to achieve in-vessel core retention. Therefore, a series of experiments on bubble behavior in a particle bed was performed to clarify three-phase flow dynamics in debris bed, which is essential in heat-removal capability, under coolant boiling conditions. Although in the past several experiments have been carried out in the gas-liquid-solid system to investigate the bubble dynamics, most of them were under lower solid holdup (≤ 0.5), where the solid-phase influence may be not so important as much as the liquid phase. While for this study, the solid holdup is much higher (> 0.55) where the particle-bubble interaction may be dominated. The current experiment was conducted in a 2D tank with the dimensions of 300 mm height, 200 mm width and 10 mm gap thickness. Water was used as liquid phase, while bubbles were generated by injecting nitrogen gas from the bottom of the tank. Various experimental parameters were taken, including different particle bed height (from 30 mm to 200 mm), various particle diameter (from 0.4 mm to 6 mm), different particle type (acrylic, glass, alumina and zirconia beads), and different nitrogen gas flow rate (around 1.75 ml/min and 2.7 ml/min). By using digital image analysis method, three kinds of bubble rise behavior were observed under current experimental conditions and confirmed by the quantitative detailed analysis of bubble rise properties including bubble departure frequency and bubble departure size. This experiment is expected in the future to provide appropriate quantitative data for the analysis and verification of SIMMER-III, an advanced fast reactor safety analysis code.

Experimental Studies and Empirical Models for the Transient Self-Leveling Behavior in Debris Bed

“…Under these conditions, particles become heavier, making it more difficult to be pushed up by the flow inside the bed. Cheng et al 3,19) have also observed the same trend in their studies of related flow regimes. Again, the good agreement between experimental data and model-predicted data on the influence of particle density provides confirmation of our modeling.…”

“…10; a slower decrease in RðtÞ can be observed as the particle diameter increases. This is because, with the increase in the particle size, the particles tend to be more difficult to be moved by the flow inside the bed, as observed by Cheng et al 3,19) This influence can be well represented by the current model, thereby demonstrating to some degree its ability to predict self-leveling behavior.…”

“…2, defines the term 'debrisbed self-leveling', which is crucial in the relocation of molten core and heat removal capability of debris beds. 1,2) Unfortunately, over the past decades, although some information on debris bed hydrodynamics and heat transfer has been available, 3) very little work related to self-leveling has been performed. Most of these studies generally assume that the upper surface of the debris bed is level.…”

An investigation on debris bed self-leveling behavior with non-spherical particles

“…Extremely, when Re g is large enough, K 3 seems to approach 1.0, the value for spherical particles. This might be because higher Re g means a larger gas flow rate and further a greater impetus for lifting solid particles, as confirmable in our flow-regime investigations [8,11,12], as a result making the additional particle-particle resistance less prominent. On the other hand, from Figure 10 it also seems that a noticeable difference is observable for those particles, indicating that aside from Re g , the differences encountered in the particle properties (e.g.…”

“…In those experiments, to simulate the coolant boiling during CDAs, various experimental methods, including depressurization boiling, bottom-heated boiling as well as gas-injection, have been employed. As for the microscopic flow-regime series [8,11,12], which also consists of several well-organized tests performed at various bubbling conditions (as shown in Figure 3), it was specifically conducted to ascertain the flow characteristics within particle beds, thus providing convincible visual evidence (especially bubble-particle interaction) for supporting the overall understandings. It has been confirmed that by combining the knowledge from flowregime investigations the observed overall leveling characteristics can be understood more effectively [8].…”