Experimental investigation of liquid entrainment in AP1000 ADS-4 branch line with air-water

ADS-4 branch line provides a controlled depressurization of the Westinghouse AP600/AP1000 primary loop during a small break LOCA. However, the coolant will be entrained to the containment simultaneously which leads to the loss of liquid inventory. ADS-4 Depressurization and Entrainment TEst Loop (ADETEL) scaled after AP1000 was constructed and visualization experiments were conducted to investigate the entrainment phenomenon at the ADS-4 tee branch line. Entrainment phenomena were recorded by high speed camera and analyzed in detail. The entrainment onset and stabilized entrainment rate data were collected and compared with available data. Discrepancies were found between ADETEL experimental data and available data due to the difference of experimental conditions and test section geometric configuration. The test data reveals that the tee branch liquid entrainment model used in RELAP5 cannot estimate the ADS-4 entrainment for AP1000 accurately and therefore more practicable model should be developed. The ADETEL data also manifest that AP1000 has a higher degree of safety performance during ADS-4 branch depressurization process than AP600 design.