Apparatus for measuring concentration of radioactivity

Abstract

An apparatus for measuring the concentration of radioactivity in a radioactive fluid discharged from a nuclear power plant. The apparatus comprises a radioactivity concentration measurement pipe arranged to extend vertically, fluid supplying means for supplying the fluid into the measurement pipe in such a manner that the fluid flows down through the measurement pipe along the axis of the measurement pipe without contacting the inner surface of the latter, radioactivity concentration measuring means disposed at the outside of the measurement pipe for measuring the radioactivity concentration in the fluid flowing in the measurement pipe, and means for discharging the radioactive fluid to the outside of the measurement pipe. The apparatus further comprises a gas supply pipe opening at its one end to the atmosphere and communicated at its other end with the inside of the measurement pipe, and a check valve disposed in the gas supply pipe and operated at a pressure higher than the atmospheric pressure. When the pressure in the measurement pipe has come down below the atmospheric pressure, the check valve is operative to always maintain the internal pressure in the measurement pipe at the atmospheric pressure, thereby to prevent the fluid level in the measurement pipe from being raised to reduce the background noise during the measurement of the radioactivity concentration.