Mapping of quench front propagation in a heated cylindrical particle bed – MONET tests

Abstract

In case of a severe accident in nuclear reactor, a debris bed may be formed from the fragmentation of the molten core at different stages of the accident. Debris bed coolability is an important issue, as it will determine the accident progression, its termination, and mitigation. One of the major concerns of debris bed coolability investigations is to understand and evaluate the effect of water re-flooding. Many experiments have been conducted to study the two-phase flow and heat transfer in porous medium configuration. However, the understanding of debris bed quenching with multi-dimensional characteristics are limited. Here, a test facility MCCI-mitigatiON through passive cooling Effect Test (MONET) apparatus is established to conduct the porous debris bed re-flooding investigation. The objective is to understand the mechanism of heat transfer and quench front movement inside the cylindrical heated debris bed during quenching by cooling water supplied from the bottom of the bed. Specifically, the effect of Homogeneous bed (with different external boundary conditions) and radially stratified bed (with different internal porosity configurations) conditions of the cylindrical debris bed on the quench front movement has been investigated. The particulate debris bed is formed with two different types of particles (SS 304, alumina) and sizes (2–3.5 mm). The effect on the quench front movement inside the particle bed has been reported by using temperature measurements together with direct visualizations. Present findings suggest non-uniform quench front propagation pattern even for the homogeneous bed conditions. While the tests with the stratified bed indicate a clear influence of low porosity region on the quench front and vapor movement.