NEPTUNE_CFD Simulations of DEBORA-Promoteur Experiments : Boiling Freon in a Vertical Pipe with Mixing Vanes
Résumé
The modeling and simulation of two-phase boiling flows are of primal interest for the nuclear industry since boiling regimes are encountered during Anticipated Operational Occurences (AOO) in Pressurized Water Reactor (PWR) cores. A PWR core is a complex medium including rod bundles, grids and mixing vanes. In order to investigate the thermal-hydraulics phenomena in such geometries, EDF and CEA conducted a series of experiments on a test facility called DEBORA-Promoteur which consists of a 4m length vertical tube including a mixing device similar to those used in fuel rod bundles. Liquid freon is injected upwards at the inlet and uniformly heated up to boiling. Void fraction is then measured downstream of the mixing device. Experimental flow conditions reach dimensionless numbers representative of PWR. Measurements of the single-phase velocity field and turbulent intensity were also conducted through the AGATE-Promoteur experiment. In this work, the simulation and modeling of two-phase flows are performed using NEPTUNE CFD (the eulerian multiphase CFD solver co-developed by EDF, CEA, IRSN and Framatome). Boiling flows in a simple tube are first studied (DEBORA). Then, boiling flow in a tube with mixing vanes is simulated to assess the models' validity on such a geometry (DEBORA-Promoteur). Finally, simulations of single-phase flow through mixing vanes are conducted (AGATE-Promoteur) in order to investigate discrepancies observed in the boiling cases through the liquid velocity field. This study finally highlights the key governing parameters and variables to improve the modeling of boiling flows in geometries and conditions similar to PWR.
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