Defense-in-depth

Reactors are designed to be inherently safe based on physical principles, supplemented by redundant equipment and special procedures. Nuclear power benefits from the appHcation of the concept of defense in depth, ie, by using fuel form, reactor vessel, building containment, and emergency backup procedures to ensure safety. 

Eig. 1. The relation between physical barriers and levels of protection in defense-in-depth design of a nuclear faciUty (12). Courtesy of IAEA. 

The fourth level of defense-in-depth is activated if all of the previous levels fail and radioactivity is released from the power-generating system. This level consists of containment systems and accident management processes that prevent the dissernination of radioactivity to the atmosphere even if it is released from the nuclear systems. The fifth level is the provision for emergency planning outside the plant boundary in the highly unlikely event that all of the first four levels of defense were to fad. 

Defense in Depth - Barriers Providing Public Protection... 

An important principle is that security must be built in depth - otherwise known as defense in depth. In this context, it may be helpful to think of security as a set of concentric rings, where the target is located at the center. Each ring represents a level of physical protection (perimeter fence, building shell, security case) but the number of rings and security resistance will vary relative to the risk. The spaces between the rings may represent other defensive measures such as closed-circuit television (CCTV), security lighting, intruder alarm systems, etc. 

A complete security design includes these four concepts in layers of protection or a defense in depth arrangement. The most critical assets should be placed in the center of conceptual concentric levels of increasingly more stringent security measures. In the concept of rings of protection, the spatial relationship between the location ofthe target asset and the location ofthe physical countermeasures is important. 

Defense-in-depth concept, for nuclear power plant design, 17 534-536 Defense Logistics Agency (DLA), 14 201 Defensins, 18 258-259... 

Establish a network protection strategy based on the principle of defense-in-depth. 

Radiological and environmental safety of SPR s being stored is based on the defense-in-depth principles on the way of possible radionuclides penetration into the... 

Because none of the tools in this toolkit can be relied upon to provide the complete solution to the problem, it is necessary to develop a defense-in-depth approach—essentially, a layered defense that exploits the synergies among individual components in order to provide the strongest possible performance of the overall system. The DSB/TRAC BW study describes the utility of such a systems approach as follows ... 

FINESCHI, F., Defense in Depth against the Hydrogen Risk - A European Research Programme, Proc. 34th Annual Conf. of the Canadian Nuclear Association (1994). 

Joseph H. Saleh Amy M. Cummings. 2011. Safety in the mining industry and the unfinished legacy of mining accidents Safety levers and defense-in-depth for addressing mining hazards. Safety Science 49 764-777. 

Produce a safe, economical plant design which meets NRC and user requirements by providing defense-in-depth through pursuit of four Goals ... 

The design of safety class structures, systems and components (SSCs) shall provide defense-in-depth features against the uncontrolled release of radioactive materials to the environment under normal conditions, AOEs, and DBA conditions. 

DISCUSSI ON. The reactor design should be fundamentally safe to ensure that the reactor is capable of being shutdown safely and adequately cooled following postulated accidents. In addition, the reactor facility should be designed to provide defense-in-depth needed to prevent or mitigate the consequences of accidents that could result in uncontrolled release of radioactive materials to the environment. The nuclear safety design criteria ensure that the reactor and the associated safety class SSCs perform their intended safety functions. 

The Nuclear Safety Design Criteria for Fire Protection require the effective implementation of a fundamental fire protection philosophy known as "defense-in-depth". As applied to fire safety, this principle requires each faci I ity to achieve an adequate balance of each of the following elements ... 

Containment and Confinement Barriers. A containment is an essential design feature for providing defense in depth protection for health and safety of the public and on-site workers for large reactors. As such, the codes and standards of the nuclear industry should be applied in a... 

Portions of the HCF structure, along with the steel confinement boxes (SCBs), gloveboxes, fume hoods, and the ventilation systems perform confinement functions. These confinement systems provide defense in depth by ensuring that hazardous materials are retained in specific designated areas within the HCF. They accomplish this function by maintaining an air pressure differential hierarchy from regions of greater contamination to those of lesser contamination within the facility. These differentials are described later in this section. This pressure differential controls the movement of contamination by diffusion and by adverse airflows. The Identified contamination zones in the HCF are as follows ... 

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