Page 175 - Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

Measurement techniques for 3.5

liquid metal based nuclear
coolants

T. Wondrak, S. Franke, N. Krauter, S. Eckert
Department of Magnetohydrodynamics, Institute of Fluid Dynamics, Helmholtz-Zentrum
Dresden-Rossendorf, Dresden, Germany

3.5.1 Introduction

The advantages of liquid metal as coolant for nuclear reactors are found in its high
boiling point, its reasonable heat capacity, and its low melting point. Typically,
sodium, lead, or the lead-bismuth eutectic (LBE) are used (Weeks, 1971;
Sakamoto et al., 2013; Cinotti et al., 2011). The opaqueness of those liquids prevents
the use of optical inspection methods and measurement techniques. Additionally, due
to the high temperature, contactless measurement techniques are preferable. Besides
the chemical composition of the liquid, for example, in respect to oxygen, flow prop-
erties are important, because they have direct impact on the heat transfer and therefore
on the cooling behavior of the system. For instance, if a subchannel in the core of the
reactor is blocked, the surrounding structure will be overheated and thus may break
and release some fuel into the cooling circuit. For pool-type reactors, for example, the
reactor developed in the MYRRHA project (Engelen et al., 2015), the flow structure in
the lower plenum has a huge impact on the cooling efficiency of the core. Addition-
ally, in order to detect boiling or gas entrainment into liquid metal, measurement tech-
niques for two-phase flows are needed. All these considerations underline the need for
flow instrumentation in this application.
In this chapter, a short overview about recent measurement techniques for flow
rate, for local velocities, and for bubble detection is given. For a comprehensive
review about measurement techniques for liquid metal, the reader is referred to the
LBE handbook of the OECD (2015).
At the beginning, two techniques based on ultrasound will be described that are
able to measure velocity profiles by means of the ultrasound Doppler velocimetry
(UDV) or to detect the position and size of bubbles by means of the ultrasound transit
time technique (UTTT). In the next section, several methods based on the principle of
electromagnetic induction to measure either the flow rate or local velocities are pres-
ented. These include the transient eddy-current flowmeter (TEC-FM) and the con-
tactless inductive flow tomography (CIFT).

Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors. https://doi.org/10.1016/B978-0-08-101980-1.00015-6
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