Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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 [Cavaro M., Payan C. and J.P. Jeannot. 3rd International Conference on Advancements in Nuclear Instrumentation, Measurement Methods and their Applications (ANIMMA), Marseille, France, 2013.].
We propose a contactless inductive bubble detection (CIBD) method. In a laboratory table-top experimental set-up we utilize the method to detect rising Argon bubbles in the liquid metal alloy Gallium-Indium-Tin (GaInSn) that is used as a non-dangerous model fluid. CIBD consists of an excitation coil generating an alternating magnetic field that induces eddy currents in the fluid. Non-conducting gas bubbles in the conducting fluid act as obstacles to these eddy currents and lead to slight changes of the current distribution, that can be detected outside of the fluid. A combination of two pickup coils positioned on top of each other which are wound in opposite direction and connected in series gives a so-called planar gradiometer that is only sensitive to asymmetric magnetic field distributions. Gundrum et al. [Sensors 16, 63. 2016.] used one planar gradiometer positioned opposite to the excitation coil to detect the rising velocity of Argon bubbles in GaInSn as well as liquid Sodium. We extend this approach by the use of several planar gradiometers at different sides of the vessel and with different orientations to determine the size and position of the bubbles as was not possible with only one detection coil. First experimental results will be presented.
The laboratory experiments are accompanied by COMSOL simulations for different bubble radii, positions and excitation frequencies of the excitation coil that reflect in the penetration depth of the magnetic field.
The CIBD method offers a high degree of practicality and flexibility e.g., additional detection coils could be mounted and the use of more than one excitation coil would extend the system towards a tomographic sensor.