Contactless flowrate sensors for Na, PbBi and Pb flows

Accurate and reliable flow rate measurements are required for various liquid metal systems such as the Na or Lead-flows in fast reactors, the PbBi-flows in transmutation systems, or the flows in liquid metal targets. Commercial flow meters are typically based on the flow-induced electrical voltage, which is measured by electrodes in direct contact to the melt, in a steady magnetic field. For liquid metal flows, a contactless measurement is preferable. We report on the recent development of two types of such flow meters. The former operates by detecting the flow-induced disturbance in the phase distribution of an externally applied AC magnetic field. Such a phase-shift flow meter was developed with an emitting coil at one side of the duct and two sensing coils at the opposite side. The second approach uses a rotatable single cylindrical permanent magnet, which is placed close to the liquid metal duct. The rotation rate of this magnet is proportional to the flow rate. The signal of this sensor is independent on the electrical conductivity of the flowing melt, thus independent on temperature. Both flow rate sensors have been tested at several liquid metal loops: a Na- and a Lead-loop at HZDR, and a PbBi-loop at SCK-CEN Mol (Belgium). In all cases, both sensors show a very good linearity of their signal with the true flow rate in the pipe. For the sodium flow at the NATAN facility of HZDR, the measured flow rates were also compared with measurements of the local velocity profile in the duct performed by ultrasonic Doppler velocimetry.