Experimental investigation of upper plenum entrainment in AP1000

Upper plenum liquid entrainment can reduce the coolant inventory in the reactor pressure vessel and poses great threats to core uncovering and melting in the accident conditions. To make up for the de ficiency of upper plenum entrainment database, the Automatic Depressurization and Entrainment TEst Loop (ADETEL) was constructed and upper plenum entrainment experiments were conducted. The test matrix was designed with various variables to investigate the upper plenum entrainment comprehensively. Entrainment phenomena and test data were obtained and analyzed. The entrainment deposition effect of reactor internals was also investigated. The test results indicate that the steam flow rate has little on the entrainment rate under stable experimental conditions. The entrainment rate decreases dramatically with the mixture liquid level in the pressure vessel when the liquid level drops below the hot leg elevation. The entrainment rate is promoted after the installation of reactor internals due to the increase of steam velocity in the upper plenum. Huge discrepancy exists between the test data and Kataoka and Ishii's (1984) pool entrainment model in the near surface region suggesting that the upper plenum entrainment is mainly dominated by side branch entrainment mechanism which is different from the pool entrainment mechanism.