CFD analysis of steam jet injection in a hybrid SIT

In the safety water injection system of an advanced nuclear power plant, APR+, steam is injected onto water inside a tank called a hybrid SIT. Depending on the condensation rate of steam and the rising time of pressure inside the tank, the performance of the system is determined. To understand the phenomena, an experiment with visualization and finely installed instrumentation was conducted. In parallel, simulation of the steam jet development and subsequent condensation was performed using a CFD code, STAR-CCM+. Each phenomenon was first validated by comparing with existing experiments; then, simulation on our hybrid SIT experiment was conducted. In the simulation, three domains of gas (steam and air), water, and wall were considered with fixed gas-water interface for convergence. As a result, pressure and temperature trends were compared between experiments and simulation. Pressure was over-predicted in simulation because of reduced water circulation under the fixed interface. The additional momentum source in the water interface enhanced the direct contact condensation and retarded the pressure rise, narrowing the gap between the experiment and the calculation.