Inductive bubble detection for liquid sodium

We present an inductive measurement technique for the identification of gas bubbles in liquid metals e.g., liquid sodium as is used as coolant in fast fission reactors. Gas bubbles in the coolant are an indication of damage to the tubing of the steam generator unit and can lead to severe accidents by chemical reactions of the liquid sodium. The contactless inductive bubble detection (CIBD) consists of an excitation coil generating an alternating magnetic field that induces eddy currents in the fluid. Electrically non-conducting gas bubbles in the otherwise conducting fluid act as obstacles to these eddy currents and the slight change of current distribution can be detected outside of the fluid by magnetic field sensors. One sensor is sufficient to verify the existence of gas bubbles robustly and it is possible to estimate the bubble velocity without any calibration. We outline how the use of multiple sensors enables to extract additional quantities of gas bubbles as size and position.