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The CFD code chosen to carry on the study was NEPTUNE_CFD, -version NEPTUNE_CFD V1.08@Tls- a highly precise code, in particular for heat transfer, based on state-of-the-art physical modelling and a fully unstructured finite volume solver.

 It was developed between EDF (France’s electricity), CEA (French Atomic Energy Commission), and AREVA-NP, in particular for nuclear reactor simulation tools, but the behaviour of different fluids made of several physical phases or components can be modelled using the general Eulerian multi-field balance equations. These several equations are obtained from the fundamentals conservation laws of physics, restricted to Newtonian mechanics: mass conservation, momentum conservation, and energy conservation, which are solved using the Reynolds Averaged Navier Stokes (RANS) approach. These relations are valid inside each fluid phase, whereas additional jump conditions are necessary for the interfaces between the phases.

The models implemented in this CFD tool have been validated for liquid forced convection and nucleate boiling. Subsequently, the Boussinesq model, presented in the previous section, was coded to be able to take into account the natural convection regime.