🧪 CANDU Moderator Poison Systems (Liquid Zone Control & Adjuster Rods)
CANDU reactors use moderator‑based reactivity control systems instead of soluble boron in the coolant. Liquid zone control compartments and adjuster rods provide fine reactivity management and power shaping across the core.
Liquid Zone Control (LZC)
- Distributed Compartments: 14–16 water‑filled zones embedded in the moderator.
- Variable Water Level: Adjusting level changes neutron absorption.
- Fast Response: Provides continuous fine reactivity control.
- Power Shaping: Balances flux distribution across the core.
Adjuster Rods
- Non‑Safety Rods: Made of stainless steel or Inconel, not boron.
- Long‑Term Reactivity Control: Used to compensate for fuel burnup.
- Flux Shaping: Inserted asymmetrically to manage local power peaks.
- Withdrawn During Shutdown: Not part of SDS1 or SDS2.
Why It Matters
- Enables boron‑free operation — a defining CANDU feature.
- Supports precise power distribution control.
- Improves fuel efficiency and burnup management.