Control Rod
Absorber rod inserted into reactor core to regulate neutron flux and control reactivity.
Made of neutron poisons like boron-10, hafnium, or cadmium, control rods provide rapid shutdown via SCRAM. In PWRs, clusters of 50-60 rods per assembly yield worth up to 10% delta-k/k. Soluble boron in coolant fine-tunes long-term reactivity.
Why it matters now
Control rod reliability is pivotal for SMR safety cases in 2025-2026 licensing, ensuring passive shutdown for data center PPAs requiring 99.999% uptime.