Experimental Study on Two-Phase Flow and Pressure Drop Characteristics in Stratified Porous Bed

Abstract

Understanding the behavior of coolant flow through porous media in nuclear reactor safety is essential for evaluating the coolability of debris beds formed from Fuel-Coolant Interactions (FCI) during a severe accident. This paper presents an experimental study focusing on the pressure drop within a stratified particulate bed containing varying diameters of spherical glass (1.5 and 6mm) in both single/two-phase flow. Two layers of different sizes of spherical particles are independently packed in a cylindrical test section to create an axially and radially stratified bed. The experiment measures pressure drops in each layer as water and air move upwards through the bed. For this study, the new DEBECO-LT facility (Debris Bed Coolability–Low Temperature) was designed and developed to serve as a platform for controlled experimentation. The concept focuses on a two-phase flow, using water and air with varying porous medium sizes. For accurate real-world replication, two homogeneous and two stratified beds were used. The findings show that in a horizontally stratified bed consisting of small particles above coarse particles, the pressure drop in the upper layer is more significant in comparison to a homogenous bed composed only of smaller particles, and the pressure drop measured at the bottom is comparable to that found in a similar homogeneous bed. However, for the vertically stratified bed, the pressure drops on the left and right sides are nearly equal. A vertically stratified structure can cause lateral flow, redistributing the flow rate throughout various sections of the packed bed.