Abstract: A passive containment cooling system for a nuclear reactor and a method of cooling a pressurized water reactor thereby has an isolation condensing means for cooling and condensing steam and accumulating and cooling noncondensable gas released from within a containment of a nuclear reactor. A steam-driven air ejector which is driven by steam of high temperature and pressure generated from a steam generator is used to exhaust the noncondensable gas from the isolation condensing means, to flow the noncondensable gas into the containment. A steam generator makeup water storage tank makes up the water inventory of the steam generator and provides security for steam generator water inventory lost by operation of the steam-driven air ejector. This leads to the removal of early decay heat by dumping steam from the steam generator into the tank and injection of makeup water into the steam generator during the early stage of an accident.