🧨 AP1000 Automatic Depressurization System (ADS)
The Automatic Depressurization System is a key AP1000 passive safety feature that rapidly reduces reactor coolant system pressure during accidents. This enables gravity‑driven injection from passive safety tanks and ensures core cooling without pumps.
ADS Stages
- Stage 1–3 Valves: Vent steam from the pressurizer to containment to lower pressure gradually.
- Stage 4 Valves: Large squib valves that rapidly depressurize the RCS.
- Integration with CMTs: Depressurization enables passive injection from core makeup tanks.
- Passive Actuation: Valves open automatically on low water level or high pressure.
Functional Behavior
- Rapid Pressure Reduction: Allows low‑pressure injection systems to function.
- Supports Natural Circulation: Enhances passive cooling pathways.
- Complements PRHR: Works with residual heat removal for long‑term cooling.
Why It Matters
- Eliminates reliance on high‑pressure safety injection pumps.
- Enables fully passive LOCA response.
- Defines AP1000’s accident mitigation strategy.