SESAME Newsletter #3 (March 2018)
TALL-3D Solidification Test Section: investigating freezing propagation in a Lead-Bismuth pool
Freezing of the coolant in liquid metal cooled reactors is identified as a potential safety issue. In liquid metal reactors, the highest risk of coolant freezing is thought to occur during shut-down, maintenance, refuelling, and whenever an over-cooling from the secondary system or the (passive) emergency cooling system is established. However, solidification might be expected even in normal operation in case of stagnation zones occurrence in the vicinity of cooled surfaces. The local solidification of the liquid metal will affect the natural convection pattern in the pool with possible impairment of the core cooling.
The TALL-3D test facility is designed for testing of a great variety of thermal-hydraulics processes of the liquid Lead-Bismuth Eutectic (LBE). It is essentially composed of 3 legs 7 m-high and a 3D cylindrical test section in the central leg. The loop is enhanced for SESAME needs by adding a test section in the first leg above the main heater dedicated to the LBE solidification process and its measurement. The main purpose of the SESAME campaign with this test section is to induce, control and check the solidification process under different working regimes and to collect the experimental data for a cross-check control and validation with the associated CFD modelling. The operating regimes of the test section are driven by a controlled LBE flow rate, LBE inlet temperature and water cooling.
The dedicated Solidification Test Section (STS) has an essentially bi-dimensional geometrical pattern. It is a relatively thin (5cm deep) vertical square pool 20 cm-high. The LBE enters the section by a pipe connected to the bottom at a temperature controlled by the facility main heater and exits vertically through another pipe located at the top. Water cooling is provided to the top side and at one lateral (small) side. This configuration allows, by adjusting the balance between water cooling, LBE flow rate and LBE incoming temperature, to develop a freezing front from the lateral and/or top borders. Depending on the front position, a variety of convection pattern is generated.
Three sets of instrumentation have been chosen for the measurement of the solidification front and characterisation of the flow in the STS pool:
- Thermo-Couples (TC)s for temperature measurement outside and inside the pool,
- Fiber Bragg Grating (FBG) sensors for temperature measurement inside the pool,
- Ultrasound Doppler Velocimetry (UDV) sensors, in collaboration with HZDR, for measurement of the LBE flow velocity and location of the solid front.
Since simultaneous application of UDVs and FBGs was not practical, two optional configurations of the experimental setup were suggested: one with UDV and one with FBGs.
The analysis of the measurement and their processing will be performed in such a way to give a quite complete set of reference data. These data will be used for comparison, improvement and validation of the numerical modelling being performed in parallel.
The design facility has been finalised during 2017 and its construction concluded beginning 2018. The experimental campaign will proceed during 2018.
Marti Jeltsov, Dmitry Grishchenko, Kaspar Kööp, Pavel Kudinov “TALL-3D solidification test setup” SESAME deliverable D3.9, 2018