In-depth principle

Ideally, in a perfect world, all chemical facilities would be secured in a layered fashion (aka the barrier approach). Layered security systems are vital. Using the protection in-depth principle, requiring that an adversary defeat several protective barriers or security layers to accomplish its goal, chemical industry infrastructure can be made more secure. Protection in depth is a term commonly used by the military to describe security measures that reinforce one another, masking the defense mechanisms from the view of intruders, and allowing the defender time to respond to intrusion or attack. 

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... 

A comprehensive work planning and control system applying the defence in depth principle should be implemented so that work activities can be properly authorized, scheduled and carried out by either plant personnel or contractors, in accordance with appropriate procedures, and can be completed in a timely manner. The work planning system should maintain high availability and reliability of important plant SSCs. 

The fact that TMI didn t result in a public health catastrophe has to be ascribed to the Defence in Depth principle systematically adopted as Western safety practice. The concept provides multiple redundant and diverse barriers against radioactive releases, well beyond what could be thought strictly necessary. TMI showed that this principle offers protection against the unforeseen and the unknown possible events. 

The complete adoption of the Defence in Depth principle has to be noted in its more evolved version, which includes five superimposed levels of defenee, concisely summarized as follows good design, good control, adequate emergency systems, accident management (various levels of seriousness eonsidered), internal and external emergeney plans. 

The defense-in-depth principle remains the fundamental principle of safety for the nuclear power plants of the next generation, with an implementation of several levels of protection. A good way to contribute to achieve a good level of defense in depth is to reduce the number of significant incidents. This involves to look for improvements of the equipment and systems used in normal operation, with a view to reduce the frequencies of transients and incidents and hence to limit the possibilities of accident situations developing from such events. 

Worldwide, designers, safety authorities and advisory groups (e g. INSAG) recommend that the design of NPPs should be based on the Defense in Depth principle. 

According to the defence-in-depth principle, the KLT-20 design provides for a protective shell, which is a leak-tight metallic structure containing the reactor and the equipment and systems with radioactive coolant, Fig. VI-3. 

In recognition of the defence-in-depth principles, the strategy of severe accident prevention is first realized in the plant design and includes measures to control these accidents and limit their consequences. 

The defence-in-depth principle is incorporated in the SVBR-75/100 design to ensure protection against radioactivity release into the environment. The following barriers exist on the potential pathway of radioactive release fuel matrix cladding of the fuel element primary circuit coolant, reactor vessel, guard vessel, tight box of the reactor installation and the... 

The design shall include the appropriate application of the defence in depth principle so that there are several levels of protection and multiple barriers to prevent releases of radioactive materials, and to ensure that failures or combinations of failures that might lead to significant radiological consequences are of very low probability. 

In one plant, revised technical specifications, which were to be approved, include unit fallback times for combinations of unavailability of vital equipment. The fallback times are based on results of probabilistic safety assessments. In the event of a simultaneous unavailability of vital equipment, a decision tree guides the operators to easily determine the unit fallback time that results from the combination of two or more items of equipment being unavailable. This approach maintains the defence in-depth principle by prescribing more conservative limits for multiple unavailabilities. 

The reactor protection system was designed with the most advanced technology for nuclear power plants, the defence-in-depth principle and early failure detection, with the objective of avoiding the occurrence of accidents beyond the design basis. 

The defence in depth principle prescribes the following barriers to confine radioactive products within the specified limits ... 

The design is such that any single failure of an element of the safety case will not invalidate the above fundamental safety design philosophy. This is achieved by applying the defence in depth principle. 

Until now, the commonly applied approach to the decision-making on nuclear facilities was based on Deterministic Safety Assessment (DSA), where a set of rules and requirements has been defined in order to ensure a high level of safety. This was done by applying the defense in depth principles and adequate criteria for safety margins (IAEA 2009). 

This short summary of the chemistry and biology of rhabdoviruses is intended to provide certain background information required to interpret the mechanisms by which rhabdoviruses perturb cell functions. These comments are not intended to serve as a comprehensive analysis of the structure and function of rhabdoviruses other reviews and current literature must be consulted for in-depth principles of rhabdovirology. Unless indicated otherwise, all properties described here refer to those of the Indiana serotype of vesicular stomatitis virus (VSV-Indiana), which serves as the prototypic model of all rhabdoviruses. 

Defence in depth principles Defence in depth Accident prevention Accident mitigation ... 

In practice, systems designers use the defence-in-depth principle to mitigate the impact of dangerous failures in subsystems [7, 10, 20], for example,... 

For systems important to safety, particular attention should be paid to facihtat-ing maintenance activities that preserve the qualification of the system for the environments in which this system must operate. Minimizing the time necessary to make repairs contributes to the overall reliability and availabihty. Maintainability is an important element in implementing the defence in depth principles set out in paras 2.9-2.II of Ref. [I]. 

These objectives are reached by application of the well-known Defence-in-Depth principle, consisting of several levels of prevention, protection and mitigation provisions. 

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