THYC calculations in assemblies with staggered grids

This paper is devoted to the validation of the THYC code in 3D configurations. THYC has been developed by EDF, and can be applied to PWR core thermal-hydraulic analysis. It is based on a porous medium approach and a fully three dimensional representation of the flow. Two analytical experiments dealing with in-bundle single-phase 3D flows are presented. One was performed at CEA, the other one at EDF. Both represent a bundle with a few rods, and simplified grids. The grids are arranged so as to cause baffle effects somehow similar to those induced at the border in between two assemblies whose grids are not at the same level. The CEA mock-up includes 5 x 5 rods and two staggered partial grids. The EDF mock-up includes 4 x 10 rods, and one partial grid in between two whole grids. Measured velocities using Laser Doppler Velocimetry are compared with THYC predictions. As the arrangements of the grids are not alike in the two experiments, the mechanisms governing the flow downstream of the baffle are different. The flow deviation around the partial grids is properly predicted by the THYC code, Yet, in the second configuration, the computed flow recovers uniform conditions downstream of the partial grid, on a shorter distance than in the experiment, hinting that the transverse pressure drop modeling could be improved for situations with small inclinations of the flow with respect to rod axis. (author)