Two-fluid equation for two-phase flow considering change in volume porosity

Abstract During loss-of-coolant accidents, nuclear fuels may undergo swelling and ballooning owing to fuel deformation. This can affect the cooling performance because of change in the flow area. In this regard, numerous studies have been conducted to investigate the cooling performance of partially blocked rod bundles. However, the cases in which the coolant flow areas vary with time have not been considered. In this regard, the purpose of this study is to develop and verify the two-fluid equations applicable to a channel whose flow area varies spatially and temporally. Toward this end, we derive volume-averaged two-fluid equations including volume porosity, which may vary spatially and temporally. To verify the developed equations, we perform one-dimensional simulations of simple conceptual problems for single-phase and two-phase flows using the SPACE code. Our simulation results exhibit an improvement over the conventional approach in terms of the mass conservation and velocity aspects.