Page 139 - Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

112 Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

Fig. 3.3.2 Electromagnetic pumps installed at KIT. (Left) Flat linear induction pump (FLIP) at
ALINA (Na). (Right) Permanent magnet pump (PMP) at DITEFA (GaInSn).

Alternatively, liquid metals can be pumped by conventional methods, for example,
using a mechanical pump. This option has the main advantage of relying on the exten-
sive experiences and commercial market of water systems, including high-efficient
components capable of providing large flow rates and pressure heads, available
off-the-shelf. On the other hand, the moving parts in the fluid result in challenges
related to sealing and corrosion/erosion.
The following scaling laws from Grote and Feldhusen (2012) must be taken into
account in order to accommodate for the high density of LBE. All inertial forces,
for example, at the bearings, are proportional to the density and square velocity
2
(ρu ). Moreover, the torque at the axis is similarly proportional to the density and
2
square rotational velocity (ρω ). All these considerations lead toward operating at a
reduced rotational velocity (ω) if the fluid density (ρ) is higher, in order to keep
the mechanical integrity of the pump components. However, this results in a reduced
2
flow rate (proportional to ω) and head (proportional to ω ). The remaining challenges
of transmission and sealing at elevated temperatures can be solved using a submerged
pump as in THEADES.
If sufficient height is available, the fluid can be also driven by buoyant forces given
by differences in density, for example, in natural-circulation heated tests. Further-
more, the injection of bubbles can promote additional buoyancy, in the so-called
gas-lift concept. Although this technique is not used at KIT, large experience is avail-
able at European Nuclear Energy Agency (ENEA), for example, in the CIRCE facil-
ity; see, for example, Benamati et al. (2007).

3.3.2.1.2 Heat exchangers

In an experimental thermohydraulic facility, heat exchangers are key components,
acting as final heat sink, internal recuperator, or a test section itself for detailed
measurements. At KIT, several facilities include liquid-metal-to-liquid-metal,
liquid-metal-to-air, and/or liquid-metal-to-oil heat exchangers.