EN IEC 61226:2021
(Main)Nuclear power plants - Instrumentation, control and electrical power systems important to safety - Categorization of functions and classification of systems
Nuclear power plants - Instrumentation, control and electrical power systems important to safety - Categorization of functions and classification of systems
This document establishes, for nuclear power plants2, 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 document is applicable to: - the functions important to safety that are performed by I&C systems and supported by electrical power systems (categorization of I&C functions), - the I&C systems that enable those functions to be implemented (classification of I&C systems), - the electrical power systems that support those functions (classification of electrical power systems). The systems under consideration provide automated protection, closed or open loop control, information to the operating staff, and electrical power supply to systems. These systems keep the NPP conditions inside the safe operating envelope and provide automatic actions, or enable manual actions, that prevent or mitigate accidents, or that prevent or minimize radioactive releases to the site or wider environment. The I&C and electrical power systems that fulfil these roles safeguard the health and safety of the NPP operators and the public. This document follows the general principles given in IAEA Safety Requirement SSR-2/1 and Safety Guides SSG-30, SSG-34 and SSG-39, and it defines a structured method of applying the guidance contained in those codes and standards to the I&C and electrical power systems that perform functions important to safety in a NPP. This document is read in association with the IAEA guides together with IEC 61513 and IEC 63046 in implementing the requirements of the IEC 61508 series. The overall classification scheme of structures, systems and components for NPPs can be summarized as follows by Figure 1.
Kernkraftwerke - Leittechnische Systeme und elektrische Energieversorgungssysteme mit sicherheitstechnischer Bedeutung - Kategorisierung von Funktionen und Klassifizierung von Systemen
Centrales nucléaires de puissance – Systèmes d'instrumentation, de contrôle-commande et d'alimentation électrique importants pour la sûreté – Catégorisation des fonctions et classement des systèmes
l'IEC 61226:2020 établit, pour les centrales nucléaires de puissance , une méthode d'affectation en catégories des fonctions spécifiées pour la centrale, sur la base de leur importance pour la sûreté. Le classement, sur la base de la catégorie attribuée, des systèmes d'I&C et d'alimentation électrique assurant ou contribuant à la réalisation de ces fonctions détermine alors les critères de conception appropriés. Les critères de conception, dès lors qu'ils sont appliqués, garantissent que chaque fonction est réalisée selon son importance pour la sûreté. Les critères retenus dans le présent document concernent la fonctionnalité, la fiabilité, les performances, la qualification aux conditions environnementales (par exemple, la qualification sismique) et l'assurance qualité (AQ). Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente: - l'alignement sur les exigences, les recommandations et la terminologie de l'AIEA, surtout la prise en compte du document SSR 2/1 (ayant remplacé le NS-R-1) et du guide SSG 30; - l'extension du domaine d'application aux systèmes d'alimentation électrique; - le déplacement des exigences détaillées applicables aux fonctions et aux systèmes d'I&C dans une annexe normative, qui sera supprimée à l'issue de la mise à jour de l'IEC 61513.
Jedrske elektrarne - Merilna, nadzorna in elektroenergetska oprema za zagotavljanje varnosti - Kategorizacija funkcij in klasifikacija sistemov (IEC 61226:2020)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-september-2021
Nadomešča:
SIST EN 61226:2010
Jedrske elektrarne - Merilna, nadzorna in elektroenergetska oprema za
zagotavljanje varnosti - Kategorizacija funkcij in klasifikacija sistemov (IEC
61226:2020)
Nuclear power plants - Instrumentation, control and electrical power systems important
to safety - Categorization of functions and classification of systems (IEC 61226:2020)
Kernkraftwerke - Leittechnische Systeme und elektrische Energiesysteme mit
sicherheitstechnischer Bedeutung - Kategorisierung von Funktionen und Klassifizierung
von Systemen (IEC 61226:2020)
Centrales nucléaires de puissance - Systèmes d'instrumentation, de contrôle-commande
et d'alimentation électrique importants pour la sûreté - Catégorisation des fonctions et
classement des systèmes (IEC 61226:2020)
Ta slovenski standard je istoveten z: EN IEC 61226:2021
ICS:
27.120.20 Jedrske elektrarne. Varnost Nuclear power plants. Safety
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EUROPEAN STANDARD EN IEC 61226
NORME EUROPÉENNE
EUROPÄISCHE NORM
July 2021
ICS 27.120.20 Supersedes EN 61226:2010 and all of its amendments
and corrigenda (if any)
English Version
Nuclear power plants - Instrumentation, control and electrical
power systems important to safety - Categorization of functions
and classification of systems
(IEC 61226:2020)
Centrales nucléaires de puissance - Systèmes Kernkraftwerke - Leittechnische Systeme und elektrische
d'instrumentation, de contrôle-commande et d'alimentation Energiesysteme mit sicherheitstechnischer Bedeutung -
électrique importants pour la sûreté - Catégorisation des Kategorisierung von Funktionen und Klassifizierung von
fonctions et classement des systèmes Systemen
(IEC 61226:2020) (IEC 61226:2020)
This European Standard was approved by CENELEC on 2021-07-05. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61226:2021 E
European foreword
This document (EN IEC 61226:2021) consists of the text of IEC 61226:2020 prepared by IEC/TC 45
"Nuclear instrumentation".
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2022-07-05
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2024-07-05
document have to be withdrawn
This document supersedes EN 61226:2010 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
As stated in the nuclear safety directive 2009/71/EURATOM, Chapter 1, Article 2, item 2, Member
States are not prevented from taking more stringent safety measures in the subject-matter covered by
the Directive, in compliance with Community law.
In a similar manner, this European standard does not prevent Member States from taking more
stringent nuclear safety and/or security measures in the subject-matter covered by this standard.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN and CENELEC
websites.
Endorsement notice
The text of the International Standard IEC 61226:2020 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards
indicated:
IEC 60671:2007 NOTE Harmonized as EN 60671:2011 (not modified)
IEC 61508-1 NOTE Harmonized as EN 61508-1
IEC 61508-2 NOTE Harmonized as EN 61508-2
IEC 61508-3 NOTE Harmonized as EN 61508-3
IEC 61508-4 NOTE Harmonized as EN 61508-4
ISO/IEC 27001 NOTE Harmonized as EN ISO/IEC 27001
ISO/IEC 27002 NOTE Harmonized as EN ISO/IEC 27002
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here:
www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60709 - Nuclear power plants - Instrumentation, EN IEC 60709 -
control and electrical power systems
important to safety - Separation
IEC 60812 - Failure modes and effects analysis (FMEA EN IEC 60812 -
and FMECA)
IEC 60880 - Nuclear power plants - Instrumentation and EN 60880 -
control systems important to safety -
Software aspects for computer-based
systems performing category A functions
IEC 60964 - Nuclear power plants - Control rooms - EN IEC 60964 -
Design
+EN IEC
60964:2019/AC:201
9-08
IEC 60965 - Nuclear power plants - Control rooms - EN 60965 -
Supplementary control room for reactor
shutdown without access to the main
control room
IEC/IEEE 60980-- Nuclear facilities - Equipment important to EN IEC/IEEE -
344 safety - Seismic qualification 60980-344
IEC 60987 - Nuclear power plants - Instrumentation and prEN IEC 60987 -
control important to safety - Hardware
requirements
IEC 61000-4 series Electromagnetic compatibility (EMC) -- PartE N 61000-4 series
4-1: Testing and measurement techniques
- Overview of IEC 61000-4 series
IEC 61500 - Nuclear power plants - Instrumentation and EN IEC 61500 -
control systems important to safety - Data
communication in systems performing
category A functions
Publication Year Title EN/HD Year
IEC 61513 2011 Nuclear power plants - Instrumentation and EN 61513 2013
control important to safety - General
requirements for systems
IEC 61771 - Nuclear power plants - Main control-room - - -
Verification and validation of design
IEC 61772 - Nuclear power plants - Control rooms - EN 61772 -
Application of visual display units (VDUs)
IEC 61839 - Nuclear power plants - Design of control EN 61839 -
rooms - Functional analysis and
assignment
IEC 62003 - Nuclear power plants - Instrumentation, EN IEC 62003 -
control and electrical power systems -
Requirements for electromagnetic
compatibility testing
IEC 62138 - Nuclear power plants - Instrumentation and EN IEC 62138 -
control systems important to safety -
Software aspects for computer-based
systems performing category B or C
functions
IEC 62566 - Nuclear power plants - Instrumentation and EN 62566 -
control important to safety - Development
of HDL-programmed integrated circuits for
systems performing category A functions
IEC 62645 - Nuclear power plants - Instrumentation, EN IEC 62645 -
control and electrical power systems -
Cybersecurity requirements
IEC 62671 - Nuclear power plants - Instrumentation and - -
control important to safety - Selection and
use of industrial digital devices of limited
functionality
IEC 62859 - Nuclear power plants - Instrumentation and EN IEC 62859 -
control systems - Requirements for
coordinating safety and cybersecurity
IEC 63046 - Nuclear power plants - Electrical power EN IEC 63046 -
system - General requirements
IAEA GSR Part 2 2016 Leadership and Management for Safety - -
IAEA SSG-30 2014 Safety Classification of Structures, - -
Systems and Components in Nuclear
Power Plants
IAEA SSR-2/12016 Safety of nuclear power plants: Design - -
(Rev.1)
IEC/IEEE 60780-- Nuclear facilities - Electrical equipment EN 60780-323 -
323 important to safety - Qualification
IEC 61226 ®
Edition 4.0 2020-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Nuclear power plants – Instrumentation, control and electrical power systems
important to safety – Categorization of functions and classification of systems
Centrales nucléaires de puissance – Systèmes d'instrumentation, de contrôle-
commande et d'alimentation électrique importants pour la sûreté –
Catégorisation des fonctions et classement des systèmes
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.120.20 ISBN 978-2-8322-7973-1
– 2 – IEC 61226:2020 IEC 2020
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 8
2 Normative references . 9
3 Terms and definitions . 10
4 Abbreviated terms . 16
5 Categorization scheme . 16
5.1 General . 16
5.2 Background . 17
5.3 Description of categories . 17
5.3.1 General . 17
5.3.2 Category A . 19
5.3.3 Category B . 19
5.3.4 Category C . 19
5.4 Assignment criteria . 19
5.4.1 General . 19
5.4.2 Category A . 20
5.4.3 Category B . 20
5.4.4 Category C . 20
6 Categorization/classification procedure . 21
6.1 General . 21
6.2 Identification of anticipated operational occurrences (AOO), design basis
accidents (DBA) and design extension conditions (DEC) . 22
6.3 Identification and categorization of functions . 23
6.4 Classification of systems . 23
6.4.1 Classification of I&C systems . 23
6.4.2 Classification of electrical power systems . 25
7 Assignment of technical requirements to categories and classes . 25
Annex A (normative) Assignment of technical requirements to I&C systems . 28
A.1 General . 28
A.2 Requirements related to functions . 28
A.2.1 Basic requirements . 28
A.2.2 Specific requirements . 28
A.3 Requirements related to systems . 29
A.3.1 Basic requirements . 29
A.3.2 Specific requirements . 30
A.4 Requirements related to equipment qualification . 32
A.4.1 Basic requirements . 32
A.4.2 Specific requirements . 32
A.5 Requirements related to quality aspects . 33
A.5.1 Basic requirements . 33
A.5.2 Specific requirements . 34
Annex B (informative) Examples of categories and classes . 36
B.1 General . 36
B.2 Category A/Class 1 . 36
IEC 61226:2020 IEC 2020 – 3 –
B.2.1 Typical functions . 36
B.2.2 Typical I&C systems . 36
B.2.3 Typical electrical power systems. 36
B.3 Category B/Class 2 . 36
B.3.1 Typical functions . 36
B.3.2 Typical I&C systems . 37
B.3.3 Typical electrical power systems. 37
B.4 Category C/Class 3 . 37
B.4.1 Typical functions . 37
B.4.2 Typical I&C and electrical power systems . 37
Bibliography . 39
Figure 1 – Overall classification scheme . 9
Figure 2 – Method of categorization of functions and classification of I&C systems . 22
Figure 3 – Method of classification of electrical power systems . 25
Table 1 – Correlation between classes of systems and categories of functions . 24
Table 2 – Tabular correlation between classes and other IEC standards . 27
– 4 – IEC 61226:2020 IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS – INSTRUMENTATION, CONTROL
AND ELECTRICAL POWER SYSTEMS IMPORTANT TO SAFETY –
CATEGORIZATION OF FUNCTIONS AND CLASSIFICATION OF SYSTEMS
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61226 has been prepared by subcommittee 45A: Instrumentation,
control and electrical power systems of nuclear facilities, of IEC technical committee 45:
Nuclear instrumentation.
This fourth edition cancels and replaces the third edition published in 2009. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) 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;
b) to extend the scope to electrical power systems;
c) 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 61226:2020 IEC 2020 – 5 –
The text of this International Standard is based on the following documents:
FDIS Report on voting
45A/1301/FDIS 45A/1306/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC 61226:2020 IEC 2020
INTRODUCTION
a) Technical background, main issues and organisation of the standard
This International Standard responds to an International Atomic Energy Agency (IAEA)
requirement to identify and classify nuclear power plants important to safety items on the
basis of their functions and safety significance. With the application of the concept of
Defence in Depth, which is implemented through the combination of a number of
consecutive and sufficiently independent levels of protection, the functions important to
safety are distributed over several systems or subsystems. In addition, with programmable
digital items now being used for NPP instrumentation and control systems, each system or
sub-system often performs many functions. Therefore, it is the intent of this standard to
establish the criteria and methods to be used to:
– identify and assign the functions important to safety into categories, depending on their
contribution to the prevention and mitigation of postulated initiating events (PIE);
– classify accordingly the I&C and electrical power systems which are necessary to
perform these functions.
According to IAEA Safety Standard SSR-2/1 (Requirement 22), the method for classifying
the items important to safety shall be based primarily on deterministic methods,
complemented where appropriate by probabilistic methods. Several possible approaches
for use of probabilistic safety assessment (PSA) for classification are described in
IEC TR 61838.
b) Situation of the current standard in the structure of the SC 45A standard series
IEC 61226 is directly referenced by IEC 61513 and is the second level SC 45A document
that deals with the categorization of functions and classification of I&C and electrical
power systems.
For more details on the structure of the SC 45A standard series, see item d) of this
introduction.
c) Recommendation and limitation regarding the application of this document
Correct categorization of functions is essential to ensure the appropriate degree of
attention by the plant's designers, operators and regulatory authorities to the specification,
design, qualification, quality assurance (QA), manufacturing, installation, maintenance,
and testing of the systems that ensure the safety functions.
This standard establishes the criteria and methods to be used to assign the functions of a
NPP accomplished by I&C and electrical power systems to three categories A, B and C,
which depend on the importance of the function for safety. Functions with no direct safety
role are non categorized (NC).
The category to which a function is assigned determines technical requirements based on
providing the appropriate level of assurance that the function will be executed on demand
with the required performance and reliability and have the necessary environmental
durability and QA. The level of assurance to be shown for each of these aspects shall be
consistent with the importance of the function to safety.
d) Description of the structure of the IEC SC 45A standard series and relationships
with other IEC documents and other bodies documents (IAEA, ISO)
The top-level documents of the IEC SC 45A standard series are IEC 61513 and
IEC 63046. IEC 61513 provides general requirements for I&C systems and equipment that
are used to perform functions important to safety in NPPs. IEC 63046 provides general
requirements for electrical power systems of NPPs; it covers power supply systems
including the supply systems of the I&C systems. IEC 61513 and IEC 63046 are to be
considered in conjunction and at the same level. IEC 61513 and IEC 63046 structure the
IEC SC 45A standard series and shape a complete framework establishing general
requirements for instrumentation, control and electrical systems for nuclear power plants.
_____________
IAEA SSR-2/1 requirement 22 considering also requirements 4, 18 and 27.
IEC 61226:2020 IEC 2020 – 7 –
IEC 61513 and IEC 63046 refer directly to other IEC SC 45A standards for general topics
related to categorization of functions and classification of systems, qualification,
separation, defence against common cause failure, control room design, electromagnetic
compatibility, cybersecurity, software and hardware aspects for programmable digital
systems, coordination of safety and security requirements and management of ageing.
The standards referenced directly at this second level should be considered together with
IEC 61513 and IEC 63046 as a consistent document set.
At a third level, IEC SC 45A standards not directly referenced by IEC 61513 or by
IEC 63046 are standards related to specific equipment, technical methods, or specific
activities. Usually these documents, which make reference to second-level documents for
general topics, can be used on their own.
A fourth level extending the IEC SC 45 standard series, corresponds to the Technical
Reports which are not normative.
The IEC SC 45A standards series consistently implements and details the safety and
security principles and basic aspects provided in the relevant IAEA safety standards and
in the relevant documents of the IAEA nuclear security series (NSS). In particular, this
includes the IAEA requirements SSR-2/1, establishing safety requirements related to the
design of nuclear power plants (NPPs), the IAEA Safety Guide SSG-30 dealing with the
safety classification of structures, systems and components in NPPs, the IAEA Safety
Guide SSG-39 dealing with the design of instrumentation and control systems for NPPs,
the IAEA Safety Guide SSG-34 dealing with the design of electrical power systems for
NPPs and the implementing guide NSS17 for computer security at nuclear facilities. The
safety and security terminology and definitions used by SC 45A standards are consistent
with those used by the IAEA.
IEC 61513 and IEC 63046 have adopted a presentation format similar to the basic safety
publication IEC 61508 with an overall life-cycle framework and a system life-cycle
framework. Regarding nuclear safety, IEC 61513 and IEC 63046 provide the interpretation
of the general requirements of IEC 61508-1, IEC 61508-2 and IEC 61508-4, for the
nuclear application sector. In this framework IEC 60880, IEC 62138 and IEC 62566
correspond to IEC 61508-3 for the nuclear application sector. IEC 61513 and IEC 63046
refer to ISO as well as to IAEA GS-R part 2 and IAEA GS-G-3.1 and IAEA GS-G-3.5 for
topics related to quality assurance (QA). At level 2, regarding nuclear security, IEC 62645
is the entry document for the IEC SC 45A security standards. It builds upon the valid high-
level principles and main concepts of the generic security standards, in particular
ISO/IEC 27001 and ISO/IEC 27002; it adapts them and completes them to fit the nuclear
context and coordinates with the IEC 62443 series. At level 2, IEC 60964 is the entry
document for the IEC SC 45A control rooms standards and IEC 62342 is the entry
document for the ageing management standards.
NOTE 1 It is assumed that for the design of I&C systems in NPPs that implement conventional safety
functions (e.g. to address worker safety, asset protection, chemical hazards, process energy hazards)
international or national standards would be applied.
NOTE 2 IEC SC 45A domain was extended in 2013 to cover electrical systems. In 2014 and 2015,
discussions were held in IEC SC 45A to decide how and where general requirements for the design of
electrical systems were to be considered. IEC SC 45A experts recommended that an independent standard be
developed at the same level as IEC 61513 to establish general requirements for electrical systems. Project
IEC 63046 is now launched to cover this objective. When IEC 63046 is published, this Note 2 of the
introduction of IEC SC 45A standards will be suppressed.
– 8 – IEC 61226:2020 IEC 2020
NUCLEAR POWER PLANTS – INSTRUMENTATION, CONTROL
AND ELECTRICAL POWER SYSTEMS IMPORTANT TO SAFETY –
CATEGORIZATION OF FUNCTIONS AND CLASSIFICATION OF SYSTEMS
1 Scope
This document 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 document is applicable to:
• the functions important to safety that are performed by I&C systems and supported by
electrical power systems (categorization of I&C functions),
• the I&C systems that enable those functions to be implemented (classification of I&C
systems),
• the electrical power systems that support those functions (classification of electrical power
systems).
The systems under consideration provide automated protection, closed or open loop control,
information to the operating staff, and electrical power supply to systems. These systems
keep the NPP conditions inside the safe operating envelope and provide automatic actions, or
enable manual actions, that prevent or mitigate accidents, or that prevent or minimize
radioactive releases to the site or wider environment. The I&C and electrical power systems
that fulfil these roles safeguard the health and safety of the NPP operators and the public.
This document follows the general principles given in IAEA Safety Requirement SSR-2/1 and
Safety Guides SSG-30, SSG-34 and SSG-39, and it defines a structured method of applying
the guidance contained in those codes and standards to the I&C and electrical power systems
that perform functions important to safety in a NPP. This document is read in association with
the IAEA guides together with IEC 61513 and IEC 63046 in implementing the requirements of
the IEC 61508 series. The overall classification scheme of structures, systems and
components for NPPs can be summarized as follows by Figure 1.
_____________
The scope of this document is consistent with IAEA SSR-2/1 and SSG-30, upon which it is based.
IEC 61226:2020 IEC 2020 – 9 –
Figure 1 – Overall classification scheme
This 2-phase process is defined for purpose of comprehensiveness; it enables the capture of
all the functions and all the systems important to safety, including I&C systems, as well as
electrical power systems.
In this scheme, functions are defined and categorized regardless of the physical means that
are implemented to fulfill them. In the framework of this document, the functions to be
categorized are performed by I&C systems. Accordingly, they are called I&C functions.
This document applies to I&C and electrical power systems for new nuclear power plants as
well as for modification and modernization of existing plants.
For existing plants, only a subset of requirements can be applicable, and this subset is
identified at the beginning of any project.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 60709, Nuclear power plants – Instrumentation, control and electrical power systems
important to safety – Separation
IEC/IEEE 60780-323, Nuclear facilities – Electrical equipment important to safety –
Qualification.
IEC 60812, Failure modes and effects analysis (FMEA and FMECA)
IEC 60880, Nuclear power plants – Instrumentation and control systems important to safety –
Software aspects for computer-based systems performing category A functions.
IEC 60964, Nuclear power plants – Control rooms – Design.
IEC 60965, Nuclear power plants – Control rooms – Supplementary control room for reactor
shutdown without access to the main control room.
IEC 60980, Recommended practices for seismic qualification of electrical equipment of the
safety system for nuclear generating stations
– 10 – IEC 61226:2020 IEC 2020
IEC 60987, Nuclear power plants – Instrumentation and control important to safety –
Hardware design requirements for computer-based systems.
IEC 61000-4 (all parts), Electromagnetic Compatibility (EMC) – Part 4: Testing and
measurement techniques
IEC 61500, Nuclear power plants – Instrumentation and control systems important to safety –
Data communication in systems performing category A functions.
IEC 61513:2011, Nuclear power plants – Instrumentation and control important to safety –
General requirements for systems.
IEC 61771, Nuclear power plants – Main control-room – Verification and validation of design
IEC 61772, Nuclear power plants – Control rooms – Application of visual display units (VDUs)
IEC 61839, Nuclear power plants – Design of control rooms – Functional analysis and
assignment
IEC 62003, Nuclear power plants – Instrumentation and control important to safety –
Requirements for electromagnetic compatibility testing
IEC 62138:2018, Nuclear power plants – Instrumentation and control important for safety –
Software aspects for computer-based systems performing category B or C functions.
IEC 62566, Nuclear power plants – Instrumentation and control important to safety –
Development of HDL-programmed integrated circuits for systems performing category A
functions.
IEC 62645, Nuclear power plants – Instrumentation and control systems – Requirements for
security programmes for computer-based systems.
IEC 62671, Nuclear power plants – Instrumentation and control important to safety – Selection
and use of industrial digital devices of limited functionality
IEC 62859, Nuclear power plants – Instrumentation and control systems – Requirements for
coordinating safety and cybersecurity
IEC 63046:— , Nuclear power plants – Electrical power systems – General requirements
IAEA GSR Part 2:2016, Leadership and Management for Safety
IAEA SSR-2/1 (Rev.1):2016, Safety of nuclear power plants: Design
IAEA SSG-30:2014, Safety Classification of Structures, Systems and Components in Nuclear
Power Plants
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
_____________
Under preparation. Stage at the time of publication: IEC CDV 63046:2019.
IEC 61226:2020 IEC 2020 – 11 –
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
anticipated operational occurrence
AOO
deviation of an operational process from normal operation that is expected to occur at least
once during the operating lifetime of a facility but which, in view of appropriate design
provisions, does not cause any significant damage to items important to safety or lead to
accident conditions
Note 1 to entry: This note applies to the French language only.
[SOURCE: IAEA Safety Glossary, 2018]
3.2
common cause failure
CCF
failures of two or more structures, systems or components due to a single specific event or
cause
[SOURCE: IAEA Safety Glossary, 2018]
3.3
controlled state
plant state, following an anticipated operational occurrence or accident conditions, in which
fulfilment of the fundamental safety functions can be ensured and which can be maintained
for a time sufficient to implement provisions to reach a safe state
Note 1 to entry: See 4 for the list of fundamental safety functions.
Note 2 to entry: See 3.21 for definition of safe state.
[SOURCE: IAEA Safety Glossary, 2018]
3.4
design basis accident
DBA
postulated accident leading to accident conditions for which a facility is designed in
accordance with established design criteria and conservative methodology, and for which
releases of radioactive material are kept within acceptable limits
[SOURCE: IAEA Safety Glossary, 2018]
3.5
design extension conditions
DEC
postulated accident conditions that are not considered for design basis accidents, but that are
considered in the design process of the facility in accordance with best estimate methodology,
and for which releases of radioactive material are kept within acceptable limits
Note 1 to entry: Design extension conditions comprise conditions in events without significant fuel degradation
and conditions in events with melting of the reactor core.
– 12 – IEC 61226:2020 IEC 2020
Note 2 to entry: A set of design extension conditions shall be derived on the basis of engineering judgement,
deterministic assessments and probabilistic assessments for the purpose of further improving the safety of the
nuclear power plant by enhancing the plant's capabilities to withstand, without unacceptable radiological
consequences, accidents that are either more severe than design basis accidents or that involve additional
failures. These design extension conditions shall be used to identify the additional accident scenarios to be
addressed in the design and to plan practicable provisions for the prevention of such accidents or mitigation of
their consequences.[IAEA SSR-2/1]
[SOURCE: IAEA Safety Glossary, 2018]
3.6
diversity
presence of two or more independent (redundant) systems or components to perform an
identified function, where the different systems or components have different attributes so as
to reduce the possibility of common cause failure, including common mode failure
[SOURCE: IAEA Safety Glossary, 2018]
3.7
electrical/electronic/programmable electronic item
E/E/PE item
item based on electrical (E) and/or electronic (E) and/or programmable electronic (PE)
technology
[SOURCE: IEC 62138:2018, 3.15]
3.8
electrical power system
system performing electrical power generation, transmission and distribution; performing
supply functions to operate plant equipment (pumps, valves, heaters, etc.) and to I&C
systems
Note 1 to entry: An electrical system can integrate E/E/PE items to perform its internal electrical control and
protection.
[SOURCE: IEC CDV 63046:2019, 3.12]
3.9
equipment
one or more parts of a system; an item of equipment is a single definable (and usually
removable) element or part of a system
[SOURCE: IEC 61513:2011, 3.16, modified – The notes to entry have been omitted.]
3.10
function
specific purpose or objective to be accomplished, that can be specified or described without
reference to the physical means of achieving it
3.11
functionality
attribute of a function which defines the operations which transform input information into
output information
[SOURCE: IEC 61513:2011, 3.24, modified – The note has been omitted.]
IEC 61226:2020 IEC 2020 – 13 –
3.12
human factor engineering programme
programme that describes at least the human factors organisation, role and mission of human
factors specialists and team, human factors activities and their integration in the design and
validation process, list of deliverables to be provided at each step of the program
3.13
item important to safety
item that is part of a safety group and/or whose malfunction or failure could lead to radiation
exposure of the site personnel or members of the public
Note 1 to entry: Items important to safety include:
a) those structures, systems and components whose malfunction or failure could lead to undue radiation
exposure of the site personnel or members of the public.
b) those structures, systems and components that prevent anticipated operational occurrences from leading to
accident conditions
c) those features which are provided to mitigate the consequences of malfunction or failure of structures, systems
or components.
Note 2 to entry: Items important to safety considered in this standard are I&C and electrical power systems.
[SOURCE: IAEA Safety Glossary, 2018]
3.14
I&C system
system, based on E/E/PE items, performing I&C functio
...
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