An example of an active safety system is

• A. Emergency Core Cooling System
• B. Gravity-driven fall of a control rod
• C. Passive containment cooling
• D. Operator-initiated valve closure

Answer: (A)

An active safety system is one that uses powered actuation to respond automatically to a transient. The Emergency Core Cooling System does this by employing pumps and valves that are energized to inject cooling water into the reactor core during a loss-of-coolant event, providing an automatic, powered response even if operators aren’t actively acting.

The gravity-driven fall of a control rod is a passive mechanism that operates without pumps or external power. Passive containment cooling relies on natural heat transfer and circulation rather than powered equipment. Operator-initiated valve closure depends on human action, which means it isn’t an automatic safety response.