Flow measurement techniques in heavy liquid metals

This paper summarizes several flow measurement systems qualified in the operation of different lead–bismuth loops in the KArslruhe Liquid Metal LAboratory (KALLA) during the last 5 years. There are several experimental techniques which were well proven in air and water and thus could be transferred similarly to liquid metals: these techniques are split into measuring local quantities as temperature, pressure e.g. by means of pressure taps or velocities using Pitot and Prandtl tubes or the Ultrasound Doppler velocimetry (UDV) for local flow velocities, as well as an integral quantity like the flow rate. Since the knowledge of the flow rate acts in terms of the operational safety of nuclear liquid metal systems as one of the most crucial parameters, this aspect is discussed widely herein. Unfortunately, as liquid metals are opaque, an optical access is not possible. Instead, one can take advantage of the high electric conductivity of liquid metals to measure integral and local quantities, like electromagnetic flow meters and miniaturised permanent magnetic probes for local velocity measurements. In this context especially the electromagnetic frequency flow meter (EMFM) is discussed as a prospective and reliable option to measure the flow rate without demanding extensive precognitions with respect to the fluid–wall interface behaviour.This article describes some of the techniques used in KALLA for different liquid metals, explains the measurement principle and shows some of the typical results obtained using these techniques. Also the measurement accuracy as well as the temporal and spatial resolution of each device is discussed and typical error sources to be expected are illuminated. Moreover, some hints for a correct placement of the individual sensor in the liquid metal environment are given.