Experimental analysis of off-take phenomena at the header–feeder system of CANDU

An experimental study has been performed to investigate the off-take phenomena at the T-junction installed between the header and feeder pipes in CANadian Deuterium Uranium (CANDU) reactor. Previous works have been made to correlate the onset condition and the quality at the branch for the representative directions such as top, side and bottom. However, for the actual branches with specific direction such as ±36° and ±72° to the horizontal header in the header–feeder system of CANDU, the direct application of the conventional correlations to the safety analysis needs experimental verification. A 1/2 scaled test facility from the prototype plant of Wolsong Units 2, 3 and 4 (CANDU 6 type) is used to measure the onset conditions for the gas pull though and liquid entrainment in the seven different orientations of the branch pipe with 0°, ±36°, ±72° and ±90° angles. The horizontal pipe has a diameter of 184 mm. The branch pipes are attached on the horizontal pipe with, and have diameters of 16.7, 20.7 and 24.8 mm, respectively. Air and water are used as working fluids under the conditions of room temperature and of pressures up to 0.95 MPa. The present experimental data were compared with the existing experimental data set such as UCB and KfK and with the horizontal stratification entrainment model (HSEM) in RELAP5/MOD3.3. It was found that The HSEM does not show good agreements with the present data obtained from the specific branch angles, ±36° and ±72°. At the bottom branch, the quality data are compared with the previous data in terms of h/D. The present data can be used for an improvement of the off-take model in order to predict the onset of off-take and the branch quality at specific angles between −90° and +90° in CANDU.