What term describes a feedback mechanism that increases reactor reactivity?

• A. Positive feedback
• B. Negative feedback
• C. Neutral feedback
• D. Delayed feedback

Answer: (A)

Positive feedback is a mechanism where the response moves the system in the same direction as the initial change, increasing reactivity when conditions change. If a factor causes reactivity to rise, the resulting effects push reactivity higher still, amplifying the initial perturbation. This can lead to rapid, self-reinforcing changes if not controlled. This is different from negative feedback, which opposes the change and tends to stabilize power, neutral feedback which has no effect, and delayed feedback which involves a time lag rather than the direction of the response. An example in some reactor designs is a positive void coefficient, where the formation of steam voids tends to increase reactivity, illustrating how the mechanism amplifies the change.