WG 7 - TC 45/SC 45A/WG 7

IEC TR 63400:2021 is intended to augment that description to enable users of individual IEC SC 45A standards to obtain a more comprehensive understanding of the overall structure of the series and its relationship with other standards bodies and standards. This document outlines the scope of the IEC SC 45A standards series and describes the basic structure of the IEC SC 45A standards series, with particular reference to a hierarchy of levels and subdivision into a set of broad topic areas. it presents the structure of the IEC SC 45A standards series in diagrammatic form.

IEC 61226:2020 establishes, for nuclear power plants , a method of assignment of the functions specified for the plant into categories according to their importance to safety. Subsequent classification of the I&C and electrical power systems performing or supporting these functions, based on the assigned category, then determines relevant design criteria.
The design criteria, when applied, ensure the achievement of each function in accordance to its importance to safety. In this document, the criteria are those of functionality, reliability, performance, environmental qualification (e.g. seismic) and quality assurance (QA).
This edition includes the following significant technical changes with respect to the previous edition:
- to align on IAEA requirements, recommendations and terminology, particularly to take into account the replacement of NS-R-1 by SSR 2/1 and publication of SSG 30;
- to extend the scope to electrical power systems;
- to move the detailed requirements applying to functions and I&C systems to a normative annex, which will be removed after updating IEC 61513.

IEC 60709:2018 is applicable to nuclear power plant instrumentation and control (I&C) and electrical systems and equipment, whose functions are required to be independent due to their contribution to:
a redundant or diverse safety group;
different defence in depth levels;
different safety classes and also with non-classified (NC) systems.  This standard is also applicable to temporary installations which are part of those I&C and *electrical systems important to safety (for example, auxiliary equipment for commissioning tests and experiments or mobile power supply systems).
This new edition includes the following significant technical changes with respect to the previous edition:
include requirements referring to the separation principle in electrical systems important to safety;
define separation criteria for I&C and electrical systems in a generic way;
align with the new revisions of IAEA documents and broaden the scope to include other aspects of separation.

IEC TR 62987:2015(E) provides guidance on nuclear-specific issues when applying failure modes and effects analysis (FMEA) and related methods to instrumentation and control systems important to safety in nuclear power plants. The information in this Technical Report complements, for nuclear power plant applications, the procedure for FMEA in IEC 60812.

IEC 62808:2015 establishes requirements for the design, analysis and qualification of isolation devices used to ensure electrical independence of redundant safety system circuits, or between safety and lower class circuits, as specified in IEC 60709. This standard includes guidance on the determination of the maximum credible fault that is applied to the isolation devices. The maximum credible fault can be used as a basis for the test levels used in testing based on other standards (e.g. IEC TS 61000-6-5 or IEC 62003).

IEC 62671:2013 addresses certain devices that contain embedded software or electronically-configured digital circuits that have not been produced to other IEC Standards which apply to systems and equipment important to safety in nuclear power plants, but which are candidates for use in nuclear power plants. It provides requirements for the selection and evaluation of such devices where they have dedicated, limited, and specific functionality and limited configurability. The contents of the corrigendum of September 2016 have been included in this copy.

IEC/TR 61838:2009 provides a survey of some of the methods by which probabilistic risk assessment results can be used to establish "risk-based" classification criteria, so as to allow FSEs to be placed within the four categories established within IEC 61226. The safety principles and the usefulness of a risk-based approach to classification are discussed and a description of four different approaches is presented. The main technical changes in this second edition with regard to the previous edition are as follows:
- to update the references and the terminology;
- to take into account the progress done since edition 1.

IEC 61226:2009 establishes a method of classification of the information and command functions for nuclear power plants, and the instrumentation and control systems and equipment that provide those functions, into categories that designate the importance to safety of the function. The resulting classification then determines relevant design criteria. Is applicable to all the information and command functions and the instrumentation and control systems and equipment that provide those functions. The main changes with respect to the previous edition are listed below:
- to introduce a definition for "non-hazardous stable state";
- to clarify limits of categories;
- to clarify requirements related to equipment used for beyond design events.

Gives requirements related to the avoidance of CCF of I&C systems that perform category A functions; additionally requires the implementation of independent I&C systems to overcome CCF, while the likelihood of CCF is reduced by strictly applying the overall safety principles of IEC SC 45A (notably IEC 61226, IEC 61513, IEC 60880 and IEC 60709); gives an overview of the complete scope of requirements relevant to CCF.

Lays down principles for testing I&C systems performing category A, B and C functions, per IEC 61226, during normal power operation and shutdown, so as to check the functional availability especially with regard to the detection of faults that could prevent the proper operation of the functions important to safety. Covers the possibility of testing at short intervals or continuous surveillance, as well as periodic testing at longer intervals. It also establishes basic rules for the design and application of the test equipment and its interface with the systems important to safety. The main change with respect to the previous edition includes an extension of the scope to cover all systems important to safety, and a requirement gradation for systems and equipment performing category A, B and C functions.