Explain why a strongly negative temperature coefficient aids reactor shutdown.

• A. As temperature rises, reactivity decreases due to negative feedback, naturally damping power and aiding shutdown.
• B. As temperature rises, reactivity increases, accelerating shutdown.
• C. Temperature has no effect on reactivity.
• D. Negative coefficient prevents any shutdown.

Answer: (A)

Temperature feedback governs how a reactor responds to changes in power. A strongly negative temperature coefficient means that when the reactor heats up, reactivity drops. Since reactivity controls neutron multiplication and thus power, this drop in reactivity reduces neutron production, causing the power to fall. As the power decreases, the temperature trend is damped, steering the system toward a shutdown state automatically. The stronger the negative coefficient, the more pronounced this self-correcting effect is, so the reactor is more easily driven toward shutdown without external action. If the coefficient were positive, a temperature rise would boost reactivity and power, fighting shutdown. If temperature had no effect, there would be no automatic regulation, and if a statement claimed the negative coefficient prevents shutdown, that would contradict how negative feedback promotes cooling and shutdown.