[0013] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. [0014] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure. [0015] Figure 1 is a diagram of a nuclear power generating system including a nuclear reactor and a condenser isolation system and feedwater return system according to the invention; [0016] Figure 2 is a graph comparing reactor pressure vessel pressure for three isolation condenser trains with the condensate returned to the upper plenum verses the downcomer; BRIEF DESCRIPTION OF THE DRAWINGS water inventory is not being depleted. The reactor pressure vessel and attached piping can be designed for a lower pressure. Containment size can be decreased, and/or the design pressure and temperature reduced. Dynamic loads to the containment caused by blowing down of the reactor pressure vessel through relief valves can be eliminated. Mitigation of the anticipated transient without scram by a slower alternate scram mechanism becomes possible so that a backup system for reactivity control via injection of a neutron-observing fluid; i.e., standby liquid control system can be eliminated.