Safety features incorporated into the SMART design enhance the accident resistance of SMART. The integral arrangement of the primary system removes large pipe connections between major components and, thus, fundamentally eliminates the possibility of LB LOCA. The canned motor RCP eliminates the need for an RCP seal, and basically eliminates the potential for a SB LOCA associated with the seal failure. The modular-type once-through steam generators are located relatively high above the core to provide a driving force for natural circulation flow. This design feature along with low flow resistance enables the capability of the system to have residual heat removal with natural circulation when normal means to transfer residual heat from the core are not available. A large volume of in-vessel gas PZR can accommodate a wide range of pressure transients during system transients and accidents. Low core power density lowers the fuel element temperature rise under accident conditions and increases the thermal margin. Negative fuel and moderator temperature coefficients yield beneficial effects on a core self-stabilization, and limit the reactor power during accidents.

15.4.8.2 Safety systems

Besides the inherent safety characteristics of SMART, further enhanced safety is accomplished with highly reliable engineered safety systems. The engineered safety systems designed to function automatically on-demand consist of a passive residual heat removal system, a shutdown cooling system and a containment spray system. Additional engineered safety systems include a reactor overpressure protection system and a severe accident mitigation system.

PRHRS

The PRHRS passively removes the core decay heat and sensible heat by a natural circulation in the case of an emergency such as an unavailability of feedwater supply or a station black-out. Besides, the PRHRS may also be used in the case of a long­term cooling for a repair or refueling. The PRHRS consists of four independent trains with a 50% capacity each. Two trains are sufficient to remove the decay heat. Each train is composed of an emergency cooldown tank, a heat exchanger and a makeup tank. The system is cooled by cooldown water or by air when the cooldown tank is dried out. In the case of a normal shutdown of SMART, the residual heat is removed through the steam generators to the condenser with a turbine bypass system.