CFD simulation of turbulent flows over wire-wrapped nuclear reactor bundles using immersed boundary method

A preliminary study for lead-bismuth eutectic (LBE) turbulent flows over wire-wrapped nuclear reactor bundles is performed. The 19-pin hexagonal bundle geometry, representative of NACIE-UP facility and adopted in the MYRRHA reactor [1, 2], is considered. The presence of the helical wire wrap has a strong effect on flow patterns inside the bundle geometry, with induced secondary flows and enhanced mixing [3]. From a computational point of view, the wire-wrapped geometry model is much more complex to realize than the bare rod configuration and simplified models are often used [4, 5]. In order to overcome the difficulties of the model generation, an hybrid body fitted immersed boundary method is used. A computational grid that fits the presence of bundle pins is generated, as for the case of the bare rod configuration, allowing a better control of mesh resolution in the regions close to wall boundaries. The immersed boundary method is used to model the presence of the helical wire wrap so that its effect on fluid motion can be taken into account.