The rod used for starting/shutting down the reactor is the

The rod used for starting/shutting down the reactor is the

• A. Containment system
• B. Moderator rod
• C. Shim rod
• D. Safety rod

Answer: (D)

Units in a reactor core are designed with different roles in mind: control rods regulate power during normal operation, shim rods provide fine-tuning of reactivity at low power or during startup, and safety rods are built for rapid, reliable shutdown when fast insertion of neutron absorbers is needed. The safety rod is specifically designed to insert quickly to halt fission and shut the reactor down in an emergency or when a rapid SCRAM is required. That rapid shutdown capability is its defining function, which is why this rod is the one most closely associated with the shutdown aspect of starting/stopping sequences. During normal startup, operators use the other rods (like shim or control rods) to bring the reactor to criticality in a controlled manner, not the safety rod. So the rod described as being used for starting/shutting down aligns with the safety rod because its main purpose is to ensure a quick, decisive shutdown if needed.

Units in a reactor core are designed with different roles in mind: control rods regulate power during normal operation, shim rods provide fine-tuning of reactivity at low power or during startup, and safety rods are built for rapid, reliable shutdown when fast insertion of neutron absorbers is needed.

The safety rod is specifically designed to insert quickly to halt fission and shut the reactor down in an emergency or when a rapid SCRAM is required. That rapid shutdown capability is its defining function, which is why this rod is the one most closely associated with the shutdown aspect of starting/stopping sequences. During normal startup, operators use the other rods (like shim or control rods) to bring the reactor to criticality in a controlled manner, not the safety rod.

So the rod described as being used for starting/shutting down aligns with the safety rod because its main purpose is to ensure a quick, decisive shutdown if needed.