Analysis of the Nitrogen Entrainment in a Safety Injection Tank with a Small Scaled Experiment

The Korean large pressurized water reactor APR1400 applied passive flow controller for the emergency core cooling system to correspond to the increase of concerns about passive safety. The passive flow controller in the APR1400, which is called fluidic device, controls the flow rate of emergency core cooling (ECC) water from the safety injection tank (SIT). The vortex chamber in the fluidic device controls flow rate. The vortex builds up high flow resistance through the fluidic device and therefore, the discharge flow rate decreases. The performance of the fluidic device was evaluated by experiments with the valve performance evaluation rig (VAPER) facility in the KAERI. The discharge mass flow rate from the SIT over time was demonstrated as expected. However, the experiment did not focus on the nitrogen entrainment phenomena which has been issued recently. The concept of equilibrium water level was brought to analyze the nitrogen entrainment phenomena and to figure out the criteria of the nitrogen entrainment. Deduced equilibrium water level is 19.5 cm for the initial condition of 10 bar. The level increases through the initial pressure increases. The longer stand pipe which can provide enough water level difference between stand pipe and SIT will decrease the amount of entrained nitrogen. The large, short and simple-shaped control pipe which lowers the pressure loss at the pipe will decrease the amount of entrained nitrogen. The results can be used to design a SIT with no nitrogen entrainment to the primary loop of the nuclear reactor.