Page 117 - Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

90 Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

3.2.4.1 CFD core simulator design

CFD as a tool is largely used for design and pretest of the fuel pin simulator. The
developed three-dimensional geometric domain reproduces the fuel pin bundle sim-
ulator in detail. The geometric domain includes an inlet and outlet nonactive region
350mm in length and the three spacer grids adopted to maintain the relative position
between the pins and the wrapper; see Fig. 3.2.5. The spacer grids proposed have been
designed to have a friction coefficient that is as low as possible and are shown in
Fig. 3.2.6. The pin bundle also contains a foot grid holding together the pin foot
and limiting mechanical vibrations; see Fig. 3.2.7. Also this grid is designed for reduc-
ing, as practicable as possible, the related pressure losses.

3.2.4.2 Numerical set-up

The general-purpose code ANSYS CFX 18 (ANSYS, 2018) was used for the numer-
ical simulation here reported. The steady-state transport equations are simultaneously
solved in the whole domain. Considering the periodicity of the geometry, only an
angle of 60° with lateral rotational boundary conditions was used. The spatial dis-
cretization of the domain was generated to provide a reasonable accuracy for the
+
higher Reynolds numbers in the experiments, with y around 1 for the first node.
A mesh independence study was carried out to select the grid discretization, and at

Spacer grid

0 0.200 0.400 (m)
0.100 0.300
Fig. 3.2.5 Axial sketch of the pin bundle (active region in red).