Passively cooled core isolation condensers are designed to provide cooling to a boiling water reactor (BWR) core subsequent to its isolation from the primary heat sink, the turbine/condenser set. As shown in Figure 7, during power operations, the reactor is normally isolated from the isolation condenser (IC) heat exchanger by closed valves. In the event that the core must be isolated from its primary heat sink, the valves located in the IC lines are opened and main steam is diverted to the IC heat exchanger where it is condensed in the vertical tube section. Heat is transferred to the atmosphere through the heat exchanger and the ICS/PCCS pool. The condensate returns to the core by gravity draining inside the tubes. This is a Category D passive safety system.

FIG. 7. Isolation condenser cooling system.