Comparison of Several RANS Modelling for the Pavia TRIGA Mark II Research Reactor

Aim of this work is the comparison of different turbulent models based on the Reynolds
Averaged Navier-Stokes (RANS) equations in order to find out which model is the most suitable
for the study of the channel thermal-hydraulics of the TRIGA Mark II reactor. Only the steady
state behaviour (i.e. the full power stationary operational conditions) of the reactor has been
considered. To this end, the RAS (Reynolds-Averaged Simulation) models available in the
open source CFD software OpenFOAM have been applied to the most internal channel of the
TRIGA and assessed against a Large Eddy Simulation (LES) model. The results of the latter
approach, expressed in terms of axial velocity, turbulent viscosity, turbulent kinetic energy, and
temperature have been compared with the results obtained by the RAS models available in
OpenFOAM (k − ε, k − ω and Reynolds Stress Transport). Heat transfer is taken into account
as well by means of the turbulent energy diffusivity parameter.
The simulation results demonstrate how, amongst the RAS models, the k − ω SST is
the one whose results are closer to the LES simulation. This model seems to be the best one
for the treatment of turbulent flow within the TRIGA subchannel, offering a good compromise
between accuracy and computational requirements. Since it is much less expensive than an LES
model, it can be applied even to full core calculation, in order to obtain accurate results with
less computational effort.