Droplet De-entrainment and flooding in an upper plenum during a LOCA

Abstract

An experimental study has been performed to investigate the droplet de-entrainment and air-water countercurrent flow limitation (CCFL) in the upper plenum during a loss-of-coolant accident (LOCA). Three separate experiments are performed in this study: (a) water accumulation and CCFL in the upper plenum with a multi-hole plate; (b) droplet de-entrainment by inertial impact on vertical rods in an air-droplet mixture flow; (c) droplet de-entrainment in the horizontal pipe. In the first experiment, an experimental study is conducted to investigate the onsets of water accumulation and CCFL through perforated plates inside a vertical tank. The thickness of plates is 1 cm and 4 cm, with a relatively large hole diameter of 5 cm. The numbers of holes are 4 and 12. We examine the effects of the number of holes, plate thickness, water injection method and the location of air vent line on the onset of water accumulation or on the onset of CCFL. In addition, we investigate the influence of the location of air vent line on water level distributions. Experimental results show that the onset of water accumulation is promoted as the number of holes decreases and the water injection lines increase, while the plate thickness and the location of air vent line have a negligible effect on the onset of water accumulation. The location of air vent line in the upper plenum does not affect the water level distribution on the plate. For given water flow rate, the onset of CCFL occurs at the nearly same air flow rate regardless of the plate thickness. The negligible effect of the plate thickness on the water accumulation and CCFL means that the water accumulation and CCFL are initiated at the top of the plate rather than at its bottom. The gas flow rate per hole required for the onset of CCFL is relatively higher in the multi-hole plate than in the single tube because some of tubes in the multi-hole plate provide a flow path for liquid with less air-liquid resistance than in the single t...