1 Experimental Techniques for Heavy Liquid Metals

This paper summarizes the most interesting measurement systems which were tested in the PbBi loops of the KALLA laboratory in Karlsruhe with 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 Ultra-SoundVelocimetry (UDV) for local flow velocities, as well as global states like flow rate utilizing nozzles, orifices or turbines. Unfortunately, as liquid metals are opaque, an optical access is not given. Instead, one can take advantage of the high electric conductivity of liquid metals to measure integral and local quantities, like electromagnetic flow meters and miniaturized permanent magnetic probes for local velocity measurements. This article describes some of the techniques used in the KALLA for different liquid metals, explains the measurement principle and shows some of the results obtained using these techniques. Additionally a few words are spent with respect to the measurement errors to be expected and some hints for a correct placement of the individual sensor in the liquid metal environment. Introduction The thermo-physical properties of liquid metals with low melting and high boiling temperatures, like the alkali metals with small atomic weight and heavy liquid metals like lead or its alloys, makes them attractive as coolant candidates in advanced nuclear fusion and fission systems. The fast neutron spectrum and the high neutron yield of the spallation reaction enable simple and robust flow structures with high energy densities. Thus, liquid metals are favourized for the development of neutron spallation sources, for fusion blankets, and as core coolant of fast reactors as well as for heavy ion fragmentation. However, the practical use of liquid metals still needs to be demonstrated by experiments and by numerical predictions. The validation of numerical predictions for nuclear systems using lead or eutectic leadbismuth alloys requires measurement technologies especially adapted to them. Besides the relatively high density, corrosivity and opaqueness of these liquids, the sensors being in contact with them are facing elevated temperatures in the range from 200°C to 550°C or even more. Although in the past decades a lot of progress has been achieved in developing liquid metal adapted measurement devices in the context of sodium operated fast breeder reactors, only part of the knowledge can be transferred to lead or lead alloy cooled systems because of its specific properties. Fluid mechanical measurement devices are divided in principle into two classes of systems. One is the measurement of integral quantities, which are mostly scalars like the flow rate, the pressure in the system or the mean temperatures. Such devices are needed to control the nuclear facility or the experimental loop and to define inlet and outlet conditions. The other class is formed by measurement of local quantities like the velocity distribution, temperature profiles or the surface structure and shape, which is necessary to capture effects predicted by computational fluid dynamics (CFD). The detection of these particular effects in benchmark problems allows the development of new physical models and the validation of CFD simulations. Regarding the physical principles, the border between the two classes is not sharply defined. For instance by miniaturisation of pressure measurement devices, the Pitot or Prandtl tube can be scaled down to detect local flow velocities. Many physical principles can be used to determine the flow rate of fluids in pipes, but the physical and chemical properties of lead bismuth exclude some of them right from the beginning. The opaqueness, which is common to all liquid metals, disables all optical methods. The electric