Experimental investigation of CCFL in pressurizer surge line with air-water

For the passive AP600/AP1000 plant, the first three stages of ADS (automatic depressurization system) valves are attached to the top of pressurizer. The existence of these valves make liquid flow into and out of the pressurizer an important part of the dynamics during a small break loss-of-coolant accident. After the fourth stage ADS is opened, draining of pressurizer water takes place. Steam generated in a reactor core and water condensed in a pressurizer form a Counter Current Fbw (CCF) in the pressurizer surge line. The counter current flow limitation may be taking place at certain flow condition in the surge line and the draining of water from pressurizer is restrained. So the investigation of CCFL is very important for the accurate prediction of coolant inventory and water lever in reactor pressure vessel (RPV). To investigate the counter current flow phenomenon in the surge line of AP1000, CCFL in pressurizer surge line test loop with a scaling ratio of 1:5 is established and visualization experiments are conducted with air-water working fluid. The experiment is conducted at atmospheric pressure and room temperature with dimensional water level from 0.137 to 0.821 in the pressurizer simulator. The counter current flow processes are recorded by high speed camera and analyzed in detail. CCFL data at different water levels in the pressurizer simulator is obtained and compared with existing test data. Obvious difference is found between this present CCFL experimental data and available data in public literatures. This discrepancy may be caused by the differences in fluids physical properties, surge line geometry and boundary conditions. The CCFL data can be well normalized by the Wallis parameter and the Kutateladze parameter respectively. The influence of water level in the pressurizer simulator is small but should not be neglected.