Eddy Current Flow Meter

The Eddy Current Flow Meter (ECFM) is a robust, inductive flow rate sensor, that has been used for several decades in various liquid metal applications worldwide. To achieve local measurements in the vicinity of the sensor, the ECFM is introduced directly into the liquid metal flow, protected by a stainless steel thimble. Here at HZDR a miniaturized ECFM for ambient temperatures up to 700 °C has been developed and tested in collaboration with our cooperation partners. The ECFM, with a diameter of only 11 mm, will be used to monitor the coolant flow and detect coolant blockages during operation in the coming generation IV liquid metal fast breeder reactors (e.g. ASTRID). Because the ECFM will be located at one of the hottest parts of the reactor – roughly 10 cm above the core - extreme demands are made on every sensor component in order to yield reliable results over long time periods. Therefore the ECFM is an important part of the nuclear safety instrumentation.

Figure 1: Basic structure of the ECFM

Functional Principle

he sensor consists of three symmetrical arranged magnetic coils, the middle coil is called primary coil and is used to generate an alternating magnetic field, which leads to the induction of eddy currents within the liquid metal. These eddy currents cause a deformation of the magnetic field that is generated by the primary coil. The secondary coils are used to measure the deformation of the magnetic field: For a stationary liquid metal there is a symmetrical deformation of the field, and therefore the voltage in both secondary coils is equal. With increasing flow rates, the asymmetry will increase and the measured voltages become more and more different. From the voltage difference of the secondary coils, the flow rate of the surrounding liquid metal can be obtained.

Applications

In addition to being used in liquid metal fast breeder reactors, the ECFM can be used to measure the flow rate or velocity of liquid metal flows in pipes or for local measurements in liquid metal pools. The ECFM has been tested successfully in Galinstan (GaInSn), sodium and lead-bismuth eutectic alloy (LBE).

Cooperation

• Commissariat à l’énergie atomique et aux énergies alternatives (CEA, Frankreich)
• Studiecentrum voor Kernenergie - Centre d'Étude de l'énergie Nucléaire (SCK-CEN, Belgien)

Publications

• Ratajczak, M.; Hernández, D.; Richter, T.; Otte, D.; Buchenau, D.; Krauter, N.; Wondrak, T.
  Measurement techniques for liquid metals
  IOP Conference Series: Materials Science and Engineering 228, 2017
• Krauter, N.; Franke, S.; Gerbeth, G.; Eckert, S.; Stefani, F.; Gastaldi, O.; Girard, M.
  Eddy current flowrate and local ultrasonic velocity measurements in liquid sodium
  Proceedings: International Conference on Fast Reactors and Related Fuel Cycles: Next Generation Nuclear Systems for Sustainable Development (FR17), 2016