When the water inventory evaporates during a hypothetical loss of coolant accident in the core of a pressurized water reactor, the fuel rods temperature increases substantially, resulting in the clad ballooning and the formation of blocked sub-channels. During the reflooding phase, where water is injected into the core and a steam-droplets flow is created above the water level, the presence of ballooned zone forces the steam flow to redistribute towards intact sub-channels, which degrades the cooling of ballooned clads within blocked sub-channels. Looking to better understand this flow redistribution process, this study presents experimental results of magnetic resonance velocimetry measurements of three-component velocity fields in several 49-element ballooned bundles to evaluate geometric effects (blockage ratio, length and coplanarity) on the flow dynamics, as well as the flow rate effect (Reynolds number from 1,936 to 9,599). The flow redistribution occurred in the transition zone upstream of the balloon. Moreover, the transverse velocities at this location are higher for higher blockage ratios and they can reach nearly the same magnitude of the axial velocity. The amount of deviated flow is approximately equal to the sub-channel’s blockage ratio and is virtually insensitive to the blockage length or the flow rate. Furthermore, the flow’s axial velocity reduces up- and downstream of blocked sub-channels and this reduction is more substantial as the blockage ratio increases. Results with non-coplanar balloons showed that a less intense flow redistribution takes place; however, a downstream balloon can affect the flow redistribution dynamics caused by an upstream ballooned zone. Finally, for all the tested bundles and tested flow rate ranges, the flow was remarkably homogenized by the downstream mixing spacer grid, restricting the clad ballooning effects only to the portion between the two spacer grids where the ballooned zone is located regardless of the balloon geometry and the flow rate. The present results may be useful as well for other research areas involving flow blockages in heat exchangers.