Liquid Film Thickness on Fuel Rod under High Pressure and High Temperature Steam-Water Two Phase Flow

This paper deals with behavior of liquid film on the fuel rod which is very important for the critical power prediction. In this study, the liquid film measurement device using an ultrasonic transducer has been developed and the liquid film thickness data has been obtained for a simulated BWR 4×4 rod bundle under 1MPa condition. The cooling fluid is steam-water mixture and flow direction is vertical. Also the following results were obtained. Firstly, the liquid film thickness becomes thinner with increasing quality and the liquid film thickness is about 0.2mm at 9.3% of quality. Secondary, the time change of liquid film thickness becomes smaller with increasing the quality. It was found that the change of liquid film thickness becomes more smoothly near the dryout condition.