This standard establishes a method and considerations to identify and classify nuclear power plant Instrumentation and Control (I&C) and Electrical systems on the basis of their functions and safety significance. Applying the concept of defense in depth is implemented through the combination of the number of consecutive and sufficiently independent levels of protection. Therefore, the functions important to safety are distributed over several systems or subsystems. In addition, with programmable digital items now being used for Nuclear Power Plant (NPP) instrumentation and controls and electrical systems, each system or subsystem often performs many functions. Therefore, this standard establishes criteria and methods to be used to:
* Identify and assign the functions into categories, depending on their contribution to the prevention and mitigation of postulated initiating events (PIE); and
* Classify accordingly the I&C and Electrical systems which are necessary to perform these functions.