Abstract
Past histories of fuel assembly blockage incidents had made investigation of flow channel blockage in rod bundle a compelling field of thermal-hydraulic safety. This study experimentally investigate flow field structural characteristics in a 5 × 5 rod bundle under two sub-channel blockages with geometries; 2 × 5 and 2 × 3, in a non-mixing spacer grid. The blockage effects on velocity distribution and turbulence characteristics is examined under laminar, transitional and turbulent flow regimes across a range of Reynolds number between 1108 ∼ 8103. Under laminar flow, result of spatiotemporal analysis for flow downstream of the blocked spacer grid-SP2, showed formation of a large symmetric vortex pair shedding in wake formed at both edges of the blockage. For transitional and turbulent flow, the vortex gradually dissipate especially towards the flow channel’s wall due to interference of friction effect. Damping effect of blockage on upward velocity flow and pressure in the vortex dominated region creates a backflow zones accompanied by flow reversal. Analysis of turbulence characteristics examined for 2 × 5 blockage across adjacent bundle gaps and sub-channels showed immense variations with Reynolds number and channel wall impact. The study aimed to provide relevant reference basis to compare and analyze similar scenario under unsteady flow condition.
