The safety design philosophy of ACP100 is to realize a high level of safety and, at the same time, to simplify the design of the systems by means of a passive engineering safety system. No emergency diesel generator is needed. The emergency measures outside the plant boundary should be made technically unnecessary or reduced to a minimum. The passive system of ACP100 include: long-term residual heat removal system to cope with station blackout accident, passive core cooling system to cope with LOCA, cavity flooding during a severe accident, and a passive containment heat-removal system. The passive containment heat-removal system means that the heat is taken away by the gas and steam convection between containment and ultimate heat sink by natural circulation. This ensures the containment integrity under accident conditions.

• The absence of any large-diameter piping associated with the primary system removes the possibility of large-break LOCAs. The elimination of large-break LOCAs substantially reduces the necessity for emergency core cooling system components, alternate current (AC) supply systems, etc.

• The large coolant inventory in the primary circuit results in large thermal inertia and a long response time in the case of transients or accidents.

• Inherent safety features include: an integrated primary coolant system, eliminating large break LOCAs; long characteristic times in the event of a transient or severe accident, due to large coolant inventory and the use of passive safety systems; negative reactivity effects and coefficients.

• Passive safety systems are duplicated to fulfil redundancy criteria. According to Chinese nuclear safety regulations, the shutdown system is diversified. The systems include a residual heat removal system, an emergency injection system, and safety relief valves which protect the reactor pressure vessel against over-pressurization in the case of strong differences between core power and the power removed from the reactor pressure vessel. All safety systems mentioned in this paragraph are passive systems.