The basic nature of the passive safety systems and accident management strategies for the SBWR and ESBWR are similar. The major engineered safety systems and safety grade systems in the ESBWR are:

FIG. VI-1. Schematic of the natural circulation flow inside the RPV.

Gravity driven cooling system (GDCS),

Automatic depressurization system (ADS), which consists of the depressurization valve (DPV) and safety relief valve (SRV),

Isolation condenser system (ICS),

Standby liquid control system (SLCS),

Passive containment cooling system (PCCS), and Suppression pool (SP).

Figure VI-2 presents a schematic of the ESBWR including passive safety system. The GDCS and PCCS are unique to the ESBWR and SBWR. They represent the passive ECCS and containment cooling systems of currently operating BWRs. The ADS is actuated at a prescribed RPV condition and depressurizes the reactor pressure vessel so that the GDCS can be actuated to supply water into the RPV. The goals of the safety systems are to adequately cool the core by maintaining a water level above the active core and to provide a sufficient heat sink via the PCCS and SP in the wetwell (WW) to keep the containment pressure and temperature below the design criteria. The ICS is an engineered safety system, which participates in the most accident transients. It is functionally similar to that in operating BWR and acts as a passive decay heat removal system.