Experimental Investigation of Counter-Current Flow in Downcomer of CAP1400

 In order to study the phenomenon of counter-current flow in the downcomer of the CAP1400 reactor under real working conditions, a test bench with the height and  diameter ratio of 1:1 of the downcomer of the pressure vessel and a 60° slice was built using CAP1400 as a prototype. The test working medium was air and water, and the two-phase gas-liquid flow and ECC bypass phenomenon with different mass flow rate and gas flow rate were experimentally studied. The results show that the gas-liquid reverse flow (CCFL) phenomenon is obvious with the increasing of gas injection rate, and when the gas volume reaches 4 kg/s or more, the injection water cannot be in the core completely. In addition, comparing the experimental results with the theoretical formula of CCCL, Kutateladze empirical correlation and UPTF empirical correlation could not accurately describe the CCFL phenomena in the downcomer of CAP1400. Therefore, based on the experimental data, the new correlations were fitted. The comparison of  the test data with and without U-type reflector shows that the U-type reflector can reduce ECC bypass water and enhance the injection ability.