Page 70 - Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

Thermal-hydraulic experiments 3

with liquid metals—Introduction

J. Pacio
Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany

The development of liquid-metal fast reactors (LMFRs) requires novel experimental
data in many scientific disciplines, such as thermohydraulics and coolant chemistry,
for feasibility and safety assessment, as well as validation of theoretical models.
Following this motivation, many experimental facilities are currently under design,
construction, or operation worldwide. A database recently compiled by the IAEA
(2016) lists over 150 experimental facilities in 14 countries, covering both sodium
(SFR) and lead-alloy (LFR) systems.
Such experimental facilities generally provide invaluable experimental data via
scientific publications in journals and conference proceedings. However, technical
guidelines regarding the design, construction, and operation of liquid-metal facilities
are very limited, possibly due to their individual and specific operational require-
ments. This chapter compiles experiences at several European research institutions
with these systems, covering several aspects from design to operation and studies
in water mockups and specific instrumentation for liquid metals.
In principle, thermohydraulic experiments with liquid metals can be compared with
water at room temperature. On the one hand, they share some common characteristics
related to typical main components (pumps and valves) and associated infrastructure
required for operation and control. On the other hand, the relatively high temperatures
and properties of liquid metals, listed in Table 3.1, present some unique operational
and safety aspects.
The Prandtl number (Pr) is a nondimensional intensive property of a fluid, rep-
resenting the ratio of molecular momentum and thermal diffusivities, thus influencing
the coupling between velocity and temperature profiles. Liquid metals are character-
ized by a low Pr, and it is generally not possible to reproduce all relevant heat pro-
cesses in a water system. Nevertheless, prototypical studies in water are possible in
flow conditions dominated by other nondimensional quantities such as the Reynolds
(e.g., pressure drop and fluid–structure interaction isothermal studies) or Richardson
(e.g., for natural circulation) numbers. The use of water-based facilities presents sev-
eral practical advantages, such as less severe constraints in the selection of equipment
and materials and the possibility of exploiting nonintrusive optical instrumentation, as
described in Section 3.1.
The design (Section 3.2), construction (Section 3.3), and operation (Section 3.4) of
liquid-metal facilities present additional challenges related to the physical properties
themselves. Their liquid range imposes the need of auxiliary heating and thermal

Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors. https://doi.org/10.1016/B978-0-08-101980-1.00003-X
Copyright © 2019 Elsevier Ltd. All rights reserved.