1.1 General 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 (see Note 1). This International Standard provides requirements and recommendations (see Note 2) for the overall I&C architecture which may contain either or both technologies. This standard highlights also the need for complete and precise requirements, derived from the plant safety goals, as a pre-requisite for generating the comprehensive requirements for the overall I&C architecture, and hence for the individual I&C systems important to safety. This standard introduces the concept of a safety life cycle for the overall I&C architecture, and a safety life cycle for the individual systems. By this, it highlights the relations between the safety objectives of the NPP and the requirements for the overall architecture of the I&C systems important to safety, and the relations between the overall I&C architecture and the requirements of the individual systems important to safety. 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. NOTE 1 I&C systems may also use electronic modules based on complex electronic components such as ASICs or FPGA. Depending on the scope and functionality of these components, they may be treated according to the guidance for conventional electronic equipment, or similar to CB equipment. A significant part of the guidance for CB equipment is also applicable to the design of equipment with complex electronic components, including e.g. the concepts of re-using pre-existing designs, and the evaluation of design errors in software or complex hardware designs. NOTE 2 In the following, “requirement” 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”. 1.2 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 should be identified at the beginning of any project. 1.3 Framework The standard comprises four normative clauses (an overview is provided in Figure 1): • Clause 5 addresses the overall architecture of the I&C systems important to safety: – defining requirements for the I&C functions, and associated systems and equipment derived from the safety analysis of the NPP, the categorisation of I&C functions, and the plant lay-out and operational context; – structuring the overall 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 minimize the potential for common cause failure (CCF); – planning the overall architecture of the I&C systems. • Clause 6 addresses the requirements for the individual I&C systems important to safety, particularly the requirements for computer-based systems. This includes differentiation of requirements according to the safety category of the I&C functions which are implemented; • Clauses 7 and 8 address the overall integration, commissioning, operation and maintenance of the I&C systems. NOTE Figure 1 outlines the structure of the standard. It does not necessarily present the timely order of activities which may be in reality partially executed in parallel, or include iterations. Additionally, the standard provides informative annexes: • Annex A highlights the relations between IAEA and basic safety concepts that are used throughout this standard; • Annex B provides information on the categorisation/classification principles; • 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; • Annex E indicates modifications to be made in future revisions of daughter standards of IEC 61513 to make them consistent and to minimize overlapping contents.