A Microwave Open-Ended Cavity as a Void Fraction Monitor for Organic Coolants

A novel application of an open-ended microwave cavity in the field of on-line nuclear instrumentation, specifically to the determination of the void fraction in organic coolants used for cooling nuclear reactors, is presented. The sensor consists of a section of circular waveguide inserted in series with the piping system transporting the coolant. For the selected frequency of operation, the sensor section forms a resonant cavity whose resonant frequency, being a measure of the void fraction, can be automatically and continuously monitored by an electronic system.