Rod ejection accident mitigation is achieved by which design feature?

• A. Redundancy in the reactor trip system
• B. Thicker fuel cladding
• C. Faster rod response
• D. Increased boron concentration

Answer: (A)

Rod ejection is a fast, positive reactivity insertion that must be interrupted quickly to prevent a dangerous power surge. The most effective way to ensure this interruption is a reliable automatic shutdown system—the reactor trip (scram). Redundancy in the trip system means multiple independent channels must fail for the trip not to occur, so even if one channel or sensor has a fault, another will still trigger the shutdown. This defense-in-depth approach directly ensures the reactor is promptly driven to a safe state during a rod-ejection event.

The other options don’t provide this immediate, fail-safe shutdown. Thicker fuel cladding won’t stop the rapid reactivity rise. A faster rod response helps, but without a guaranteed trigger, it can still be compromised by a fault. Increased boron concentration affects reactivity chemically, not the quick, automatic action needed to arrest the transient.