Safety Classification for I&C Systems in Nuclear Power Plants: Comparison of Definitions of Key Concepts

September 2017

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The World Nuclear Association report, Safety Classification for I&C Systems in Nuclear Power Plants – Current Status & Difficulties, by the Cooperation in Reactor Design Evaluation and Licensing Working Group (CORDEL) identified a number of key concepts which are important for the industry to understand and implement correctly in order to meet licensing requirements, but which are often vaguely or inconsistently defined by regulatory bodies.

Where requirements are not clearly defined, there is room for different interpretation. Divergent understanding could have a large impact over the duration of a nuclear project’s lifecycle.

The safety classification report identified the following five concepts as frequently causing problems in the interpretation of requirements:

  • Defence-in-Depth and Diversity.
  • Separation (physical separation / electrical isolation / functional independence / independence of communication).
  • Redundancy.
  • Reliability/Availability.
  • Spurious Activation (inadvertent actuation of I&C functions).

The concept of Independence was added to this list of concepts to be reviewed, as several of the terms stated in the first safety classification report dealt with various aspects of Independence.

Each of the above concepts is defined by a series of terms and associated definitions in different regulatory documents and reference codes & standards. As long as there is no harmonized understanding for such top-level concepts there will be risks of misunderstandings in every project, which may lead to conflicts with contractual requirements and regulatory conformance.

This report compares the various definitions by:

  • identifying all the terms that are associated with the key concepts, and
  • highlighting any inconsistencies in the different regulatory bodies’ definitions of these terms.

Safety Classification I&C


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