Turbulent flow in a model nuclear fuel rod bundle containing partial flow blockages

Local velocity and turbulence intensity measurements were obtained with a laser Doppler anemometer near flow blockages in an unheated 7 × 7 rod bundle. Sleeve blockages were positioned on the center nine rods to create area reductions of 70 and 90% in the center four subchannels of the bundle. Experimental results indicated that extensive flow disturbances existed downstream from the blockage clusters and showed that only minor disturbances can be expected upstream from the blockages. Recirculation zones for both 70 and 90% blockages were detected downstream from the blockage clusters and persisted for approximately three to five subchannel hydraulic diameters, depending on the degree of the blockage. The experimental velocity results obtained with blockage clusters located midway between grid spacers were successfully predicted using the COBRA subchannel computer program.