Experimental study on local droplet parameters in a deformed 2 × 2 Rod bundle under air-water annular-mist flow

Abstract

During reflood conditions following a loss-of-coolant accident in pressurized water reactors, droplet flow affects the heat and mass transfer between liquid and steam phases. Flow behavior is further complicated by fuel rod cladding deformation. Accurate knowledge of the large interfacial area liquid droplets characteristics and the effect of rod deformation is essential for understanding the associated thermal-hydraulic process and guaranteeing nuclear safety. This study aims to investigate the effect of fuel rod deformation on the characteristics and distribution of local droplet parameters. Experiments were conducted in a vertical 2 × 2 deformed rod bundle with two deformed test sections with blockage ratios of 25% and 50%. Tests were performed under annular-mist flow conditions at atmospheric pressure over superficial liquid and gas velocities ranges of 0.020–0.040 m/s and 25–35 m/s, respectively. A double-sensor optical fiber probe was used to measure local droplet parameters downstream of the deformed region on the measuring planes. For a quantitative characterization of the effect of rod deformation on local droplet parameter distribution, the results of the deformed bundle tests were compared with those of the previous intact bundle tests. Furthermore, a prediction correlation for the bundle deformation-enhanced droplet mass flux ratio was proposed. The results of this study provide a better understanding of the complex reflood flow behavior and improve the predictability of numerical simulations.