1. Plant & Reactor Design Passive Reactor Core Cooling System
Pressurized Core Flooding Tanks (Accumulators)
75% cold borated water
25% nitrogen / inert gas (pressurizer)
Normal condition: Check valves closed due to greater reactor pressure
Accident Incident: Check valves open due to reactor pressure drop
One-time, preliminary cooling system

2. Plant & Reactor Design Passive Reactor Core Cooling System
Elevated Tank Circulation Loops (Core Make-up Tanks)
Contains cold borated water
Tank inflow (top) is connected to reactor coolant system
Accident Incident: Cold borated water flows into hot reactor core & back into the tank
Short-term cooling system (no heat exchanger)

3. Passive Reactor Core Cooling System Elevated Gravity Drain Tanks
Plant & Reactor Design
Passive Reactor Core Cooling System
Elevated Gravity Drain Tanks
Similar to accumulator, except this is driven by gravity rather than pressurized gas
Accident Incident: Check valves open when weight of borated water is greater than reactor pressure
Borated water volume sufficient to flood entire reactor cavity
One-time, preliminary cooling system

4. Plant & Reactor Design Passive Reactor Core Cooling System
Passively Cooled Steam Generator Natural Circulation
Incorporated in PWRs to remove heat from steam generators
Leaves steam generator undamaged from overheating during accident
Continuous cooling system

5. Plant & Reactor Design Passive Reactor Core Cooling System
Passive Residual Heat Removal (PRHR) Heat Exchangers
Similar to passively cooled steam generator natural circulation (previous)
Incorporated in PWRs to remove heat directly from reactor core rather than steam generator
Continuous cooling system during accident

6. Plant & Reactor Design
Passive Systems for Containment & Pressure Suspension
Containment Passive Heat Removal / Pressure Suppression Systems
Steam vented into the containment condenses on incline tubes (red)
Reduces temperature & pressure in containment
Cooling water flows due to natural circulation (heated water rises)

7. Plant & Reactor Design
Passive Systems for Containment & Pressure Suspension
Passive Containment Spray Systems
Hear transferred from containment wall to air outside the wall
Heat outside the containment wall is cooled by cooler air blown from the bottom
Pool on top of containment accelerates cooling process via gravity driven cold water spray