Gravity-driven cooling systems

GDCS- Gravity driven cooling system (SBWR feature). 

Passive Containment Cooling System Start-Up Gravity-driven Cooling System Discharge Long-term Passive Decay Heat Removal Overload at Pure-Steam Conditions Release of Hidden Air... 

The Automatic Depressurization Subsystem (ADS) consists of the eight SRVs and six depressurization valves (DPVs) and their associated instrumentation and controls. The ADS quickly depressurizes the RPV in sufficient time for the Gravity-Driven Cooling System (GDCS) injecting flow to replenish core coolant to maintain core temperature below design limits in the event of a LOCA. It also maintains the reactor depressurized for continued operation of GDCS after an accident without need for power. 

Gravity driven cooling system X Passive emergency core cooling (3 independent divisions)... 

Figure 14.11 The mixed spectrum supercritical water-cooled reactor safety system. ICS, isolation cooling system GDCS, gravity-driven cooling system ACC, accumulators ADS, automatic depressurization system PCCS, passive cote cooling system SLCS, standby liquid control system. 

Gravity driven cooling system (GDCS) system (ADS) Standby liquid control system (SLCS)... 

Increased reliability of the emergency core cooling (ECC) system achieved through depressurization of the primary system and passive injection of cooling water from the gravity driven water tank (GDWT) directly into the core ... 

An independent poison ball safety system is provided to assure that the reactor is driven and maintained subcritical in the event of failure of part or all of the Horisontal Hod System due, for example, to an earthquake, or in the event of actuation of the emergency raw-water cooling system which would result from primary loop depressurisation. Upon receipt of a trip signal, the balls are released to fall by gravity into vertical channels in the active sone of the reactor Excess hopper capacity is provided to assure that the balls fill the channels to a level above the top of the active zone. 

In design basis accidents, when abnormal conditions are detected, the shutdown rods are automatically injected between the cassettes, driven by gravity. The shutdown rod worth is sufficient to maintain cold shutdown conditions with a one-rod stuck margin. If shutdown by the rods fails, boron balls stored in the workbench fall between the cassettes, a system similar to that adopted in high temperature gas cooled reactors (HTGRs). 

A fail-safe passive control system is assumed to govern the reactor system. In this system, numerous signals from various redundant detectors of different origin enter the circuit. When all signals are within the pre-defmed ranges of values, then the pump power will be in the on position. In any other situation, the coolant pump is in its normal switched off position, and the fuel elements leave the reactor core, driven by gravity, and become deposited in a passively cooled fuel chamber. 

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