What systems are used to remove decay heat in a nuclear plant?

• A. Decay heat removal systems that provide cooling water flow to the core.
• B. Primary heat exchangers only during operation.
• C. Emergency diesel generators without cooling capacity.
• D. Manual cooling by operators only.

Answer: (A)

Decay heat continues after shutdown, so removing it reliably is essential to keep fuel from overheating. Nuclear plants achieve this with dedicated decay heat removal (DHR) or residual heat removal systems that provide a path for cooling water to flow through the core (or through associated heat exchangers) and reject the heat to a cooling sink. These systems are designed to operate even when the main power and normal heat-removal paths are unavailable, ensuring continuous cooling as long as decay heat is produced.

Emergency diesel generators may power the pumps in these cooling circuits, but they don’t remove heat by themselves without the cooling flow. Likewise, relying on manual cooling by operators alone isn’t the dependable, continuous mechanism designed for long-term heat removal. The key idea is that decay heat is removed by systems that actively provide cooling water flow to the core to carry away the heat.