During normal reactor shut down core decay heat is removed by passive means utilizing Isolation condensers (ICs) immersed in a gravity driven water pool (GDWP) located above the steam drum. Core decay heat, in the form of steam enters the IC tube bundles. The steam condenses inside the tubes and heat is transferred to the surrounding water pool. The condensate returns by gravity to the steam drum. The water inventory in the GDWP is adequate to cool the core for more than 3 days without any operator intervention and without boiling of GDWP water. Fig. III-2 depicts the core decay heat removal system comprising isolation condensers. A separate GDWP cooling system is provided to cool the GDWP inventory in case the temperature of GDWP inventory rises above a set value.