Page 126 - Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

Design of experimental liquid-metal facilities 99

Fig. 3.2.16 Seven bayonet tube RELAP5 model.

The seven downcomers of each bayonet tube have been assumed thermally insu-
lated (adiabatic) from the annular region, such as the other pipelines.
The thermal connection between the annular region of the bayonet tubes and the
LBE equivalent channel has been realized with seven heat structures, one for each
tube, which represent the second and third tube, and the AISI 316L powder+helium
gap of the double-wall tubes. The gap thermal conductivity adopted for the calculation
is obtained from the correlation given in the following equation as a function of tem-
perature (°C) reported by RELAP5-3D (2018):

6 2
4
C AISI powder He ¼ 5 10 T +8 10 T +1:3981 (3.2.3)

3.2.5.2 Results
This section reports the main results of the preliminary analysis realized with
RELAP5-3D©. The LBE and water temperatures and the steam mass produced when
stationary conditions are reached are reported in Fig. 3.2.17. It can be noticed that the
LBE temperature decreases along the active length, up to the outlet value of 410°C,
with a corresponding thermal power removed of 410kW. In the tube side, the water
firstly reaches the saturation temperature; then, the vaporization occurs (two-phase