Page 142 - Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

Construction of experimental liquid-metal facilities 115

the main topic of another chapter (Eckert et al., 2017), and a detailed description
exceeds the scope of this work.
On the one hand, their main advantage is being nonintrusive and capable of resolv-
ing low velocities. On the other hand, the obtained signals show a relatively large
dependency on the operating temperature level (Schroer et al., 2011), which makes
proper calibration relatively complicated.

3.3.2.2.2 Differential pressure
Pressure difference is measured in a thermohydraulic facility in order to directly
account for friction or as an intermediate quantity for representing the liquid level
or flow rate. Highly accurate (better than 0.1%) differential pressure gauges are com-
mercially available in many ranges and for high temperatures and pressures, as this is a
well-established technology.
For the special application of liquid metals, the main practical challenge is the
potential freezing that can damage the sensible elastic diaphragm. In order to elimi-
nate this risk, an intermediate fluid, such as mineral oil, can be used for transmitting
the pressure signal to the transducer. On the oil side, this technical solution is already
commercially offered by some pressure gauge vendors. On the liquid-metal side, an
in-house solution must be developed for transmitting the pressure signal to the oil
through a membrane, as in Fig. 3.3.4.
Here, the main practical aspect to take into account is the absence of residual gas,
oxide particles, or frozen plugs in these chambers and in all auxiliary lines. Similarly
as in a water loop facility, a possibility for purging these lines must be available. In the
particular case of LBE due to its high density, a correction for the temperature-
dependent hydrostatic contribution of these auxiliary lines might be necessary. In
principle, if the temperature remains constant, this contribution can be considered
as an offset.

Fig. 3.3.4 Construction for differential pressure measurement with an intermediate fluid.