Lateral Mixing Between Interconnected Subchannels

Abstract

The thermalhydraulic analysis of nuclear fuel assemblies used in power reactors requires detailed information on coolant parameters such as: pressure, flow velocity, quality, void fraction, etc. Subchannel analysis is known as useful method to predict local flow conditions in fuel bundles. The use of this technique consists of dividing the bundle into small cells called subchannels and writing one dimensional conservation equations for each subchannel. The multidimensional nature of the flow is then recovered by means of the lateral interaction between adjacent subchannels, i.e., mixing mechanisms. Therefore, an accurate prediction of the flow distribution in the fuel bundle depends on the appropriate modelling of these mechanisms which for vertical two-phase flow are identified as: diversion cross-flow, turbulent mixing and void drift. In this paper, experimental two-phase turbulent mixing data obtained under hydrodynamic equilibrium flow conditions using two-identical interconnected subchannels is used to develop a drift flux model. Predictions of the proposed model are compared with similar predictions obtained using Lahey's model and the data of Tapucuet al. [1]. In general it is observed that the proposed model is better able to predict the experimental trends.