Two experiments were conducted at the ROSA-V/Large-Scale-Test-Facility to investigate thermal-hydraulic behavior of a gravity-driven passive injection system for a pressurized water reactor under cold-leg small break loss-of-coolant accident conditions. The injection system, used in the tests, consisted of a tank located above the reactor vessel, an injection line, and pressure balance lines. The two tests were conducted using the same break area, corresponding to 2.5% of the scaled cold-leg cross-sectional area, and different actuation logic for the automatic depressurization system (ADS). Both experimental results showed an accumulation of hot water in the upper part of the tank due to the natural circulation, followed by a continuous water level drop, and the existence of a slightly superheated liquid layer near the water surface. Because of the differences in the ADS actuation logic, the system depressurization behavior was different between the two tests. Much larger injection rates from the tank were obtained for the test that experienced the larger depressurization rate. The liquid temperature distributions obtained from these tests were predicted well by an analytical model proposed in a previous paper.
