The concept of defence in depth was first utilized in military practice. Scattered defensive outposts are, of course, vulnerable to defeat through local attack. To overcome this weakness, the defence in depth idea estab­lished methodologies through which the outposts were linked together via communication channels and response doctrine that specified assistance from one outpost to others nearby, along with an established deep configu­ration of outposts that together formed a strong network of defence.

Defence in depth

This useful concept has been adopted by the world nuclear industry. A good summary of the application of this concept can be found in the IAEA report titled Defence in Depth in Nuclear Safety (INSAG-10, 1996). This document is based on the original description of this concept published in an earlier
document (INSAG-3, 1988). Similar descriptions have appeared in design and safety-related documents published over the past few decades. Figure 10.3 illustrates the overall concepts of defence in depth. In this view, the processes are separated into two parts — prevention and mitigation, respec­tively. Some reactor designs may have different specific elements in some of these positions; however, the principle remains the same — there are multiple levels of defence against transfer of radioactive materials from their normal positions in the reactor to the public or environment.