Which statement best describes the purpose of defense-in-depth in nuclear safety?

Which statement best describes the purpose of defense-in-depth in nuclear safety?

• A. To provide multiple layers of protection including prevention, accident assumptions, and worst-case capability.
• B. To rely on a single barrier for safety.
• C. To minimize safety features during peak demand.
• D. To focus only on after-accident response.

Answer: (A)

Defense-in-depth means building multiple independent layers of protection so that a failure in one layer doesn’t lead to an unsafe outcome. It integrates preventative measures to reduce the chance of an event, design and analysis that consider plausible accident scenarios, and robust capability to manage the most severe, worst-case conditions. The statement that best describes this approach emphasizes providing several protective layers that include prevention, accident assumptions, and worst-case capability. This captures the full idea: there are safeguards at different levels, each with its own role, so safety is not left to a single barrier. The other options miss the multi-layer, proactive nature—relying on a single barrier, reducing safety features during peak demand, or focusing only on after-accident response—none of which provide the layered protection essential to defense-in-depth.

Defense-in-depth means building multiple independent layers of protection so that a failure in one layer doesn’t lead to an unsafe outcome. It integrates preventative measures to reduce the chance of an event, design and analysis that consider plausible accident scenarios, and robust capability to manage the most severe, worst-case conditions. The statement that best describes this approach emphasizes providing several protective layers that include prevention, accident assumptions, and worst-case capability. This captures the full idea: there are safeguards at different levels, each with its own role, so safety is not left to a single barrier. The other options miss the multi-layer, proactive nature—relying on a single barrier, reducing safety features during peak demand, or focusing only on after-accident response—none of which provide the layered protection essential to defense-in-depth.