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For AOEs, the offshore floating plant relies on the traditional systems that have been developed for Light Water Reactor (LWRs), i.e., control rods and standby liquid boron control system (for redundant and diverse emergency shutdown), and shutdown cooling through the auxiliary feedwater system.
For DBEs, the plant relies on the passive safety systems developed for terrestrial SMRs, but modified to take advantage of the underwater nuclear island design. Therefore, for decay heat removal given a DBE at operational pressures, there is a dedicated Direct Reactor Auxiliary Cooling System (DRACS) that is based on natural circulation from the Reactor Pressure Vessel (RPV) to an intermediate closed water loop and ultimately to seawater (see figure below). This system can function indefinitely without AC power or refilling of any tanks.
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For a DBE that causes depressurization of the primary system (e.g., a Loss-Of-Coolant Accident or LOCA), short-term core cooling is achieved by gravity-driven injection, from core-makeup tanks or accumulators. For long-term accident response, the floating plant adopts a Passive Containment Cooling System (PCCS) similar to the Westinghouse SMR, in which the normal design of near-vacuum conditions allow for very efficient condensation heat transfer at the inner surface of the containment shell, conduction through the steel shell, and then convective heat transfer in the gap between the containment shell and the hull, flooded with seawater upon detection of a major accident (see figure below). The containment water inventory circulates back to the reactor core to keep it submerged under all postulated conditions. Note that no seawater is ever present within the containment or the RPV. This PCCS also operates indefinitely without AC power or refilling of tanks. As such, the floating plant design has eliminated the loss of ultimate heat sink accident altogether.
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