Experimental investigations on the two-phase water entrainment phenomenon at inclined branch T-junctions and numerical simulations based on neptune_cfd

Two-phase water entrainment at T-junctions on the hot leg is known to pose a risk of additional coolant loss in accident scenarios. Currently, intensive studies have focused on top branches, where many experimental and theoretical studies are available. However, the phenomena in inclined branches at arbitrary angles remain to be fully analysed. Therefore, our aim was to carry out experimental investigations on liquid entrainment at Tjunctions with inclined branches and to develop a CFD model capable of representing the phenomenon. Experimental investigations on an air-water stable entrainment test have shown that water entrainment phenomena at inclined branch T-junctions differ from those at the top branch in terms of more continuous entrainment and smoother free surface, due to different entrainment mechanisms governed by the angle of inclination. Finally, the CFD model has correctly represented the characteristics of stable entrainment phenomena as revealed by the experiments and has achieved a relative error of 5-10% in terms of average and local water level in the main pipe.