Measuring the critical conditions for gas entrainment inception at the free surface of water

In a liquid metal nuclear reactor using a sodium as coolant, the upper plenum of reactor vessel has a free surface where the coolant sodium contacts with the cover gas. If the cover gas is entrained by the sodium flow at the free surface, the gas causes a change in reactivity of the core and also reduces the heat removal capability of the intermediate heat exchanger. It is important to investigate the critical conditions for the inception of gas entrainment at the free surface. An experimental study has been carried out to measure the critical conditions in the 1/4 section of KALIMER upper plenum with 1/4 length scale in the water test facility. The experimental variables are the mean water level and the flow rate. The measurements have been carried out according to three cases of inception condition. In all of the cases, the relations between the mean level (H) and the flow rate (Q) are represented as H=b1n(Q-a). but the constants a and b are different. Also it is observed that the gas entrainment in the free surface occurs easily when the vane level becomes higher