Which statement about rod worth curves is accurate?

• A. They are graphs of reactivity versus control rod position used to calibrate control strategy and ensure shutdown margins.
• B. They primarily measure rod mechanical insertion speeds and associated reactivity change.
• C. They indicate the color coding of rods for identification.
• D. They measure the time to a reactor scram.

Answer: (B)

Rod worth curves show how the reactor’s reactivity changes as a control rod is moved to different positions. They quantify the worth of the rod—how much reactivity is added or removed per unit of insertion at each position—which is exactly what you need to calibrate control strategies and ensure adequate shutdown margins. The curve is fundamentally a position-dependent measure of reactivity, not a record of how fast the rod moves. Insertion speed relates to dynamic behavior, which is studied separately, but the worth curve itself focuses on the static reactivity change associated with each rod position. The other ideas—color coding for identification, or measuring the time to scram—don’t describe what the curve represents.