Nuclear Power Plants - Instrumentation and Control for Systems Important to Safety - General Requirements for Systems
|Publication Date:||1 March 2001|
|ICS Code (Nuclear power plants. Safety):||27.120.20|
I&C systems important to safety may be implemented using conventional hard-wired equipment, computer-based (CB) equipment or by using a combination of both types of equipment. This International Standard provides requirements and recommendations (see note) for the total I&C system architecture which may contain either or both technologies.
NOTE In the following, the term requirements is used as a comprehensive term for both requirements and recommendations. The distinction appears at the level of the specific provisions. where requirements are expressed by "shall" and recommendations by "should".
This standard highlights the need for complete and precise requirements, derived from the plant safety goals, as a pre-requisite for generating the comprehensive requirements for the total I&C system architecture, and hence for the individual I&C systems important to safety.
This standard introduces the concept of a safety life cycle for the total I&C system architecture, and a safety life cycle for the individual systems. The life cycles illustrated in, and followed by, this standard are not the only ones possible; other life cycles may be followed, provided that the objectives stated in this standard are satisfied.
Application: new and pre-existing plants
This standard applies to the I&C of new nuclear power plants as well as to I&C up-grading or back-fitting of existing plants.
For existing plants, only a subset of requirements is applicable and this subset is identified at the beginning of any project.
Figure 1 presents the overall framework of this standard, with its normative clauses:
• clause 5 addresses the total architecture of the I&C systems important to safety:
- defining requirements for the I&C functions, and associated systems and equipment (I&C FSE) derived from the safety analysis of the NPP, the categorisation of I&C functions, and the plant lay-out and operation context;
- structuring the totality of the I&C architecture, dividing it into a number of systems and assigning the I&C functions to systems. Design criteria are identified, including those to give defence in depth and to minimise potential for common cause failure (CCF);
- planning the total architecture of I&C systems.
• clause 6 addresses the requirements for the individual I&C systems important to safety, particularly the requirements for computer-based systems;
• clauses 7 and 8 address the overall integration, commissioning, operation and maintenance of the I&C systems;
• annex A highlights the relations between IAEA and basic safety concepts that are used throughout this standard;
• annex B provides information on the
• annex C gives examples of I&C sensitivity to CCF;
• annex D provides guidance to support comparison of this standard with parts 1, 2 and 4 of IEC 61508. This annex surveys the main requirements of IEC 61508 to verify that the issues relevant to safety are adequately addressed, considers the use of common terms and explains the reason for adopting different or complementary techniques or terms.