Characteristics of a Wire Level Sensor in the Measurement of a Free Surface Fluctuation

In the liquid metal reactor using sodium as a coolant, there exists a free surface in the upper plenum of the reactor vessel where the hot coolant contacts with a cold cover gas. The fluctuation of the free surface causes two important phenomena in the reactor. One is to induce a thermal stress to the reactor vessel due to the free surface fluctuation of sodium. Another is the cover gas entrainment at the free surface. If a significant amount of gas is entrained by the fluctuation of sodium, the entrained gas causes a change in the reactivity and also reduces the heat removal capability of the coolant in the core. Therefore it is an important parameter in the design of a liquid metal reactor. An experimental study will be carried out for measuring the fluctuating frequency and amplitude of the free surface in a cylindrical annular vessel where the inner vessel is simulated as a UIS of a reactor. Since the hydraulic property of sodium is similar to that of water, water is used as a working fluid instead of sodium. Because the range of the estimated frequency is about 0.5∼5 Hz in this experiment, a conductivity type wire sensor is used as a level meter in order to get an accurate enough response. But the characteristic of this type level sensor have not been reported in the literature so far. Owing to this reason, an experiment is carried out to find the characteristics of the level sensor before the surface fluctuation measuring experiment. In the present paper the characteristics of the level sensor are described through an experiment