Results regarding analytical bottom reflooding experiments in a 37- and a 127-heater rod bundle are presented for two different tight lattices. A comparison between these two geometries and with the standard pressurized water reactor (PWR) array shows a degradation of cooling efficiency when the cross section of the subchannels is decreased. The core heat sinks (guide thimbles and “water tubes”) are seen to have a noticeable influence on the overall cooling of the bundle, and it is confirmed that a combined top/bottom injection does not significantly improve cooling efficiency. Calculations with CATHARE 1.3 code adjusted for the standard PWR array are presented (zero heat sinks), but results have to be confirmed over a wider range of parameters.