CFD analysis of porous flow blockage in a gas-lift enhanced LBE-cooled fuel assembly

Porous blockage is likely to occur in wire-wrapped fuel assemblies and cause severe consequences such as overheating and mass flow decrease. In this study, flow behavior upstream, inside and downstream of the blockage is obtained for different porosities to analyse the overheating and pressure change. Additionally, the effect of reactivity feedback considering the void fraction and radial and axial power distributions on LBE-cooled porous blockage are given. It is concluded that flow separation upstream and recirculation downstream is the main reason for the overheat phenomenon due to poor convective heat transfer. Static pressure has a local rise both upstream with small porosities and in the flow recovery region downstream, while the gradient of pressure drops inside the blockage is large and begins forwards for small porosities because of flow resistance. The study of reactivity insertion reveals that although the effect of the void fraction on the reactivity and heat power is straightforward, the volume-averaged coolant and rod temperatures are virtually unaffected within 0.02 s. The wall and bulk temperature of central blockage C1 is generally higher than that of edge blockage E1.