METHOD FOR DETECTING LEVEL OF TANK

PROBLEM TO BE SOLVED: To detect level without being influenced by a change in the specific gravity of radioactivity or a fluid by a method wherein a gas is injected into an airtight tank in which a liquid from a constant-quantity-gas injection tank is contained and the level is computed on the basis of a change in the pressure of a gas-phase part inside the airtight tank. SOLUTION: A gas pipe 14 which supplies a gas G is connected to the upper pat (gas-phase part) of a waste-liquid tank 1, and a constant-quantity-gas injection tank 2 is connected to the other end of the pipe 14. Signals of a gas pressure before and after the injection of the gas in the gas-phase part in the waste-liquid tank 1 are input to a tank-level operating unit 16 from a waste-liquid-tank pressure gage 10. In addition, the signal of a set pressure inside the constant-quantity-gas injection tank 2 is input to the tank-level operating unit 16 from a constant-quantity-gas- injection-tank pressure gage 7. Then, in the tank-level operating unit 16, the volume in the liquid-phase part of the waste-liquid tank 1, i.e., the level of a waste liquid inside the waste-liquid tank 1, is computed. In this manner, by means of a change in the pressure in the gas-phase part of the airtight waste-liquid tank 1, the volume in the liquid phase of the waste-liquid tank 1, i.e., the level of the waste liquid inside the waste-liquid tank 1, can be detected.