Nuclear power plants - Instrumentation, control and electrical power systems important to safety - Categorization of functions and classification of systems

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.

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.

General Information

Status
Published
Publication Date
28-Apr-2020
Current Stage
PPUB - Publication issued
Completion Date
29-Apr-2020
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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
IEC 61226:2020-04(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
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

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 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

---------------------- Page: 4 ----------------------
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

---------------------- Page: 5 ----------------------
– 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

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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.
---------------------- Page: 6 ----------------------
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.
---------------------- Page: 7 ----------------------
– 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.
---------------------- Page: 8 ----------------------
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.
---------------------- Page: 9 ----------------------
– 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.

---------------------- Page: 10 ----------------------
IEC 61226:2020  IEC 2020 – 9 –
Figure 1 – Overall classification scheme
This 2-phase pr
...

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