Fundamental Experiment of Gas Entrainment Phenomenon From Free Liquid Surface in a Sodium-Cooled Fast Reactor

Abstract The Sodium-cooled Fast Reactor (SFR) is an advanced type of nuclear reactor using liquid sodium as a coolant. However, the structure of the reactor and the flow of the coolant causes Gas Entrainment phenomenon to occur on the surface of the liquid sodium in a reactor vessel. Gas Entrainment causes the inert cover gas, i.e., argon gas, to be trapped inside the reactor vessel which may lead to disturbance of the reactivity. Hence, to maintain safe and stable operations a solution to prevent Gas Entrainment is required. Currently, researchers are developing a method to predict Gas Entrainment based on experimental data. At Tokai University, a special experiment apparatus is used to conduct water experiments to simulate Gas Entrainment phenomenon from a moving vortex dimple on the free liquid surface. Measurements of the inlet velocity and downward velocity were done by using the Particle Image Velocity (PIV) method. Image data of the vortices were recorded with the highspeed video system and the vertical length of the gas core in vortices from the liquid surface were evaluated. In addition, the number of vortices occurred were counted and classify the types of Gas Entrainment. From analyzing these experimental data, we expect to determine the mechanism of Gas Entrainment and how it occurs. In case of the special experiment apparatus at Tokai University, the high downward velocity around the downstream region allows the vortices to extend towards the bottom of the flow channel.