Swirling and secondary flows play an important role in several locations of the primary circuit of a PWR. After a brief reminder of the experimental period during the initial designs, few examples such as the lower plenum, the upper Plenum and the hot legs, the fuel assemblies and the U-bend downstream the steam generator are given to illustrate this statement. Although experiments will remain mandatory to understand these complex flows, CFD could bring some light either to perform parametric studies or to analyze the flow structures if not possible in the experiment or in a reactor configuration. In order to have a “clean” approach, one has to first validate the CFD tools on few academic cases dominated by swirling/rotation/secondary effects. A full program for a better understanding of these kinds of flows with CFD computations has been launched at EDF. Examples of the very first calculations are given in the present paper. Although no mature conclusions can be drawn at this stage with the available simulations, one can argue that first moment closures such as k-epsilon or k-omega models can perform well in some configurations while Reynolds Stress Models performs almost always rather well. LES is clearly superior but more expensive. Even the growth of the computing power will not allow us to perform LES computations whatever the configuration, thus focusing on RSM model remains important.

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