Nuclear power plants - Instrumentation and control systems important to safety - Requirements for coping with Common Cause Failure (CCF)

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.

Kernkraftwerke - Leittechnische Systeme mit sicherheitstechnischer Bedeutung - Anforderungen zur Beherrschung von Versagen aufgrund gemeinsamer Ursache

Centrales nucléaires de puissance - Systèmes d'instrumentation et de contrôle commande importants pour la sûreté - Exigences permettant de faire face aux Défaillances de Cause Commune (DCC)

Fournit des exigences relatives à l'évitement des DCC dans les systèmes d'I&C réalisant des fonctions de catégorie A; exige de façon complémentaire la mise en oeuvre de systèmes d'I&C indépendants pour surmonter les DCC, lorsque la probabilité d'occurrence des DCC est déjà réduite en appliquant strictement les principes de sûreté prévalant au SC 45A de la CEI (en particulier ceux énoncés dans les CEI 61226, CEI 61513, CEI 60880 et CEI 60709); donne une vue générale du domaine complet des exigences applicables aux DCC.

Jedrske elektrarne - Merilna in nadzorna oprema za zagotavljanje varnosti - Zahteve za obvladovanje odpovedi iz normalnih razlogov (CCF) (IEC 62340:2007)

Merilna in nadzorna oprema za zagotavljanje varnosti se lahko načrtuje z uporabo konvencionalne fiksno pritrjene opreme, računalniške opreme ali kombinacije obeh vrst opreme. Ta mednarodni standard zagotavlja zahteve in priporočila za celovito arhitekturo merilne in nadzorne opreme, ki lahko vsebuje eno ali obe tehnologiji. Namen tega standarda je: a) podati zahteve, povezane s preprečevanjem odpovedi merilne in nadzorne opreme, ki izvaja funkcije kategorije A, iz normalnih razlogov; b) dodatno zahtevati izvedbo neodvisne merilne in nadzorne opreme za obvladovanje odpovedi iz normalnih razlogov, medtem ko se verjetnost za odpoved iz normalnih razlogov zmanjša s strogim upoštevanjem splošnih varnostnih načel IEC SC 45A (predvsem IEC 61226, IEC 61513, IEC 60880 in IEC 60709); c) podati pregled celotnega področja uporabe zahtev, pomembnih za odpovedi iz normalnih razlogov, ki pa se ne prekrivajo s področji, ki jih že obravnavajo drugi standardi. Ta standard se nanje sklicuje. Ta standard poudarja potrebo po popolni in natančni specifikaciji varnostnih funkcij na osnovi analize projektnih nezgod in z upoštevanjem glavnih varnostnih ciljev elektrarne. Ta specifikacija je predpogoj za oblikovanje celostnega niza podrobnih zahtev, ki jih je treba upoštevati pri projektiranju merilne in nadzorne opreme.

General Information

Status
Published
Publication Date
13-May-2010
Drafting Committee
Parallel Committee
Current Stage
6060 - Document made available
Due Date
01-Nov-2010
Completion Date
14-May-2010

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SLOVENSKI STANDARD
SIST EN 62340:2010
01-september-2010
Jedrske elektrarne - Merilna in nadzorna oprema za zagotavljanje varnosti -
Zahteve za obvladovanje odpovedi iz normalnih razlogov (CCF) (IEC 62340:2007)
Nuclear power plants - Instrumentation and control systems important to safety -
Requirements for coping with Common Cause Failure (CCF) (IEC 62340:2007)
Kernkraftwerke - Leittechnische Systeme mit sicherheitstechnischer Bedeutung -
Anforderungen zur Beherrschung von Versagen aufgrund gemeinsamer Ursache (IEC
62340:2007)
Centrales nucléaires de puissance - Systèmes d'instrumentation et de contrôle
commande importants pour la sûreté - Exigences permettant de faire face aux
Défaillances de Cause Commune (DCC) (CEI 62340:2007)
Ta slovenski standard je istoveten z: EN 62340:2010
ICS:
27.120.20 Jedrske elektrarne. Varnost Nuclear power plants. Safety
SIST EN 62340:2010 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN 62340:2010
---------------------- Page: 2 ----------------------
SIST EN 62340:2010
EUROPEAN STANDARD
EN 62340
NORME EUROPÉENNE
May 2010
EUROPÄISCHE NORM
ICS 27.120.20
English version
Nuclear power plants -
Instrumentation and control systems important to safety -
Requirements for coping with Common Cause Failure (CCF)
(IEC 62340:2007)
Centrales nucléaires de puissance - Kernkraftwerke -
Systèmes d'instrumentation et de contrôle Leittechnische Systeme
commande importants pour la sûreté - mit sicherheitstechnischer Bedeutung -
Exigences permettant de faire face Anforderungen zur Beherrschung
aux Défaillances de Cause Commune von Versagen aufgrund gemeinsamer
(DCC) Ursache
(CEI 62340:2007) (IEC 62340:2007)

This European Standard was approved by CENELEC on 2010-05-01. 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 Central Secretariat 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 Central Secretariat 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, Romania, Slovakia, Slovenia,

Spain, Sweden, Switzerland and the United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2010 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 62340:2010 E
---------------------- Page: 3 ----------------------
SIST EN 62340:2010
EN 62340:2010 – 2 –
Foreword

The text of the International Standard IEC 62340:2007, prepared by SC 45A, Instrumentation and control

of nuclear facilities, of IEC TC 45, Nuclear instrumentation, was submitted to the CENELEC formal vote

for acceptance as a European Standard and was approved by CENELEC as EN 62340 on 2010-05-01.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN and CENELEC shall not be held responsible for identifying any or all such patent

rights.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement
(dop) 2011-05-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn
(dow) 2013-05-01
Annex ZA has been added by CENELEC.

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 measures in the subject-matter covered

by this European Standard.”
__________
Endorsement notice

The text of the International Standard IEC 62340:2007 was approved by CENELEC as a European

Standard without any modification.
---------------------- Page: 4 ----------------------
SIST EN 62340:2010
– 3 – EN 62340:2010
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application 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 Where an International Publication has been modified by common modifications, indicated by (mod), the relevant EN/HD

applies.
Publication Year Title EN/HD Year
IEC 60671 - Nuclear power plants - Instrumentation and -
control systems important to safety - Surveillance
testing
IEC 60709 - Nuclear power plants - Instrumentation and EN 60709
control systems important to safety - Separation
IEC 60780 - Nuclear power plants - Electrical equipment of the -
safety system - Qualification
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 60980 - Recommended practices for seismic qualification - -
of electrical equipment of the safety system for
nuclear generating stations
IEC 61000-4 Series Electromagnetic compatibility (EMC) - EN 61000-4 Series
Part 4: Testing and measurement techniques
IEC 61226 - Nuclear power plants - Instrumentation and - -
control systems important to safety - Classification
of instrumentation and control functions
IEC 61513 - Nuclear power plants - Instrumentation and - -
control for systems important to safety - General
requirements for systems
IAEA Safety Guide - Instrumentation and control systems important to - -
NS-G-1.3 safety in nuclear power plants
IAEA Safety Guide - General design safety principles for nuclear power - -
SG-D11 plants; a safety guide
IAEA Safety 2007 Terminology used in nuclear safety and radiation - -
Glossary protection
---------------------- Page: 5 ----------------------
SIST EN 62340:2010
---------------------- Page: 6 ----------------------
SIST EN 62340:2010
IEC 62340
Edition 1.0 2007-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Nuclear power plants – Instrumentation and control systems important to safety
– Requirements for coping with common cause failure (CCF)
Centrales nucléaires de puissance – Systèmes d’instrumentation et de contrôle-
commande importants pour la sûreté – Exigences permettant de faire face aux
défaillances de cause commune (DCC)
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX
ICS 27.120.20 ISBN 2-8318-9452-2
---------------------- Page: 7 ----------------------
SIST EN 62340:2010
– 2 – 62340 © IEC:2007
CONTENTS

FOREWORD...........................................................................................................................3

INTRODUCTION.....................................................................................................................5

1 Scope...............................................................................................................................7

2 Normative references .......................................................................................................8

3 Terms and definitions .......................................................................................................8

4 Abbreviations .................................................................................................................12

5 Conditions and strategy to cope with CCF ......................................................................13

5.1 General .................................................................................................................13

5.2 Characteristics of CCF ..........................................................................................13

5.3 Principal mechanisms for CCF of digital I&C systems............................................13

5.4 Conditions to defend against CCF of individual I&C systems .................................14

5.5 Design strategy to overcome CCF .........................................................................15

6 Requirements to overcome faults in the requirements specification ................................15

6.1 Deriving the requirements specification for the I&C from the plant safety

design base...........................................................................................................15

6.2 Application of the defence-in-depth principle and functional diversity ....................16

6.3 CCF related issues at existing plants.....................................................................17

7 Design measures to prevent coincidental failure of I&C systems.....................................17

7.1 The principle of independence...............................................................................17

7.2 Design of independent I&C systems ......................................................................18

7.3 Application of functional diversity ..........................................................................18

7.4 Avoidance of failure propagation via communications paths ..................................19

7.5 Design measures against system failure due to maintenance activities..................19

7.6 Integrity of I&C system hardware...........................................................................19

7.7 Precaution against dependencies from external dates or messages ......................20

7.8 Assurance of physical separation and environmental robustness...........................20

8 Tolerance against postulated latent software faults ........................................................20

9 Requirements to avoid system failure due to maintenance during operation ...................21

Annex A (informative) Relation between IEC 60880 and this standard .................................

---------------------- Page: 8 ----------------------
SIST EN 62340:2010
62340 © IEC:2007 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS –
INSTRUMENTATION AND CONTROL
SYSTEMS IMPORTANT TO SAFETY –
REQUIREMENTS FOR COPING WITH
COMMON CAUSE FAILURE (CCF)
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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any

equipment declared to be in conformity with an IEC Publication.

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 62340 has been prepared by subcommittee 45A: Instrumentation

and control of nuclear facilities, of IEC technical committee 45: Nuclear instrumentation.

The text of this standard is based on the following documents:
FDIS Report on voting
45A/668/FDIS 45A/676/RVD

Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

---------------------- Page: 9 ----------------------
SIST EN 62340:2010
– 4 – 62340 © IEC:2007

The committee has decided that the contents of this publication will remain unchanged until

the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in

the data related to the specific publication. At this date, the publication will be

• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
---------------------- Page: 10 ----------------------
SIST EN 62340:2010
62340 © IEC:2007 – 5 –
INTRODUCTION
a) Background, main issues and organisation of this Standard

In order to achieve a high safety level, redundancy is applied as one of the key features for

designing instrumentation and control systems (I&C systems) important to safety. Since a

Common Cause Failure (CCF) could compromise the effectiveness of redundancy, it is

essential to take adequate measures against it. The nuclear industry has pioneered systems

design and engineering to address CCF. Over the last thirty years it has implemented and

reached consensus on a number of practices to handle and overcome CCF.

The intention of this standard is to address the whole scope of aspects to overcome Common

Cause Failures (CCFs) and to provide an overview of the relevant requirements for I&C

systems that are used to perform functions important to safety (according to IEC 61226) in

nuclear power plants.

b) Situation of the current Standard in the structure of the IEC SC 45A standard series

IEC 62340 is a second level IEC SC 45A document tackling the issue of CCF.

This international standard supplements IEC 61513 and related standards with requirements

to reduce and overcome the possibility of CCF of I&C functions of category A. The

requirements given by this standard are applicable to category A (IEC 61226) functions if their

failure would be unacceptable with respect to the plant safety design.

For more details on the structure of the IEC SC 45A standard series, see item d) of this

introduction.
c) Recommendations and limitations regarding the application of this Standard

This standard applies to I&C systems important to safety of new NPPs as well as to the

replacement of I&C systems of existing plants. The I&C functions may need to be kept or

upgraded if an I&C system is replaced. The requirements of this standard also consider the

replacement of I&C which entails changes in the structure of I&C systems.

For existing plants, only a subset of the requirements from this standard may be applicable

and this subset should be identified at the beginning of any project. The requirements and

recommendations which are not to be implemented in an I&C upgrading or replacement

project should be justified on a case by case basis by an overall safety assessment. The

potential consequences of not following this standard in some aspects due to plant constrains

should be considered in comparison to the added safety gained through the upgrade as a

whole.

To avoid overlapping requirements, this standard takes advantage of other existing standards

by referring to the relevant (sub)clauses, especially to the nuclear sector standards

IEC 61513, IEC 60709, IEC 60780 and IEC 60880. New requirements are given where not

covered by these standards.

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 document of the IEC SC 45A standard series is IEC 61513. It provides general

requirements for I&C systems and equipment that are used to perform functions important to

safety in NPPs. IEC 61513 structures the IEC SC 45A standard series.

IEC 61513 refers directly to other IEC SC 45A standards for general topics related to

categorization of functions and classification of systems, qualification, separation of systems,

---------------------- Page: 11 ----------------------
SIST EN 62340:2010
– 6 – 62340 © IEC:2007

defence against common cause failure, software aspects of computer-based systems,

hardware aspects of computer-based systems, and control room design. The standards

referenced directly at this second level should be considered together with IEC 61513 as a

consistent document set.

At a third level, IEC SC 45A standards not directly referenced by IEC 61513 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 45A standard series, corresponds to the Technical

Reports which are not normative.

IEC 61513 has adopted a presentation format similar to the basic safety publication

IEC 61508 with an overall safety life-cycle framework and a system life-cycle framework and

provides an interpretation of the general requirements of IEC 61508-1, IEC 61508-2 and

IEC 61508-4, for the nuclear application sector. Compliance with IEC 61513 will facilitate

consistency with the requirements of IEC 61508 as they have been interpreted for the nuclear

industry. In this framework IEC 60880 and IEC 62138 correspond to IEC 61508-3 for the

nuclear application sector.

IEC 61513 refers to ISO as well as to IAEA 50-C-QA (now replaced by IAEA GS-R-3) for

topics related to quality assurance (QA).

The IEC SC 45A standards series consistently implements and details the principles and

basic safety aspects provided in the IAEA code on the safety of NPPs and in the IAEA safety

series, in particular the Requirements NS-R-1, establishing safety requirements related to the

design of Nuclear Power Plants, and the Safety Guide NS-G-1.3 dealing with instrumentation

and control systems important to safety in Nuclear Power Plants. The terminology and

definitions used by SC 45A standards are consistent with those used by the IAEA.
---------------------- Page: 12 ----------------------
SIST EN 62340:2010
62340 © IEC:2007 – 7 –
NUCLEAR POWER PLANTS –
INSTRUMENTATION AND CONTROL
SYSTEMS IMPORTANT TO SAFETY –
REQUIREMENTS FOR COPING WITH
COMMON CAUSE FAILURE (CCF)
1 Scope

I&C systems important to safety may be designed using conventional hard-wired equipment,

computer-based equipment or by using a combination of both types of equipment. This

International Standard provides requirements and recommendations for the overall
architecture of I&C systems, which may contain either or both technologies.
The scope of this standard is:

a) to give requirements related to the avoidance of CCF of I&C systems that perform

category A functions;

b) to additionally require 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);

c) to give an overview of the complete scope of requirements relevant to CCF, but not to

overlap with fields already addressed in other standards. These are referenced.

This standard emphasises the need for the complete and precise specification of the safety

functions, based on the analysis of design basis accidents and consideration of the main plant

safety goals. This specification is the pre-requisite for generating a comprehensive set of

detailed requirements for the design of I&C systems to overcome CCF.

This standard provides principles and requirements to overcome CCF by means which ensure

independence :

a) between I&C systems performing diverse safety functions within category A which

contribute to the same safety target;

b) between I&C systems performing different functions from different categories if e.g. a

category B function is claimed as back-up of a category A function and;
c) between redundant channels of the same I&C system.

The implementation of these requirements leads to various types of defence against initiating

CCF events.

Means to achieve protection against CCF are discussed in this standard in relation to:

a) susceptibility to internal plant hazards and external hazards;
b) propagation of physical effects in the hardware (e.g. high voltages); and

c) avoidance of specific faults and vulnerabilities within the I&C systems notably:

1) propagation of functional failure in I&C systems or between different I&C systems (e.g.

by means of communication, fault or error on shared resources),
—————————

To support a clear addressing of all requirements and recommendations these are introduced by a clause

number.

Independence between I&C systems or between redundant channels of the same I&C system is the capability

that in case of a postulated failure of one system or one channel the other systems or channels perform their

functions as intended.
---------------------- Page: 13 ----------------------
SIST EN 62340:2010
– 8 – 62340 © IEC:2007

2) existence of common faults introduced during design or during system operation (e.g.

maintenance induced faults),

3) insufficient system validation so that the system behaviour in response to input signal

transients does not adequately correspond to the intended safety functions,

4) insufficient qualification of the required properties of hardware, insufficient verification

of software components, or insufficient verification of compatibility between replaced

and existing system components.
2 Normative references

The following referenced documents are indispensable for the application 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 60671, Nuclear power plants – Instrumentation and control systems important to safety –

Surveillance testing

IEC 60709, Nuclear power plants – Instrumentation and control systems important to safety –

Separation

IEC 60780, Nuclear power plants – Electrical equipment of the safety system – Qualification

IEC 60880, Nuclear power plants – Instrumentation and control systems important to safety –

Software aspects for computer-based systems performing category A functions

IEC 60980, Recommended practices for seismic qualification of electrical equipment of the

safety system for nuclear generating stations

IEC 61000-4 (all parts), Electromagnetic compatibility (EMC) – Part 4: Testing and

measurement techniques

IEC 61226, Nuclear power plants – Instrumentation and control systems important to safety –

Classification of instrumentation and control functions

IEC 61513, Nuclear power plants – Instrumentation and control for systems important to

safety – General requirements for systems

IAEA Safety Guide NS-G-1.3, Instrumentation and control systems important to safety in

Nuclear Power Plants

IAEA Safety Guide SG-D11, General design safety principles for nuclear power plants

IAEA Safety Glossary Ed.2.0, 2006
3 Terms and definitions

For the purposes of this document, the terms and definitions of IEC 61513 and IEC 61226

apply as well as the following.
3.1
Common Cause Failure (CCF)

failure of two or more structures, systems or components due to a single specific event or

cause
[IAEA Safety Glossary, Ed. 2.0, 2006]
---------------------- Page: 14 ----------------------
SIST EN 62340:2010
62340 © IEC:2007 – 9 –

NOTE 1 The coincidental failure of two or more structures, systems or components is caused by any latent

deficiency from design or manufacturing, from operation or maintenance errors, and which is triggered by any

event induced by natural phenomenon, plant process operation or an action caused by man or by any internal

event in the I&C system.

NOTE 2 Coincidental failure is interpreted in a way which covers also a sequence of system or component

failures when the time interval between the failures is too short to set up repair measures.

3.2
defence-in-depth

the application of more than one protective measure for a given safety objective, such that the

objective is achieved even if one of the protective measures fails
[IAEA Safety Glossary, Ed. 2.0, 2006]
NOTE The protective measures are assumed to be independent.
3.3
diversity

existence of two or more different ways or means of achieving a specified objective. Diversity

is specifically provided as a defence against CCF. It may be achieved by providing systems

that are physically different from each other, or by functional diversity, where similar systems

achieve the specified objective in different ways
[IEC 60880, 3.14]
NOTE See also ”functional diversity”.
3.4
fail-safe design

design of system functions so that they respond to specified faults in a predefined, safe way

3.5
failure

inability of a structure, system or component to function within acceptance criteria

[IAEA Safety Glossary, Ed. 2.0, 2006]

NOTE 1 A failure is the result of a hardware fault, software fault, system fault, or human error, and the associated

signal trajectory which triggers the failure.
NOTE 2 See also “fault”, “software failure”.
3.6
fault
defect in a hardware, software or system component
[IEC 61513, 3.22]

NOTE 1 Faults may be subdivided into random faults, that result e.g. from hardware degradation due to ageing,

and systematic faults, e.g. software faults, which result from design errors.

NOTE 2 A fault (notably a design fault) may remain undetected in a system until specific conditions are such that

the result produced does not conform to the intended function, i.e. a failure occurs.

NOTE 3 See also ”software fault” and “random fault”.
3.7
fault avoidance

use of techniques and procedures which aim to avoid the introduction of faults during any

phase of the safety life cycle
[IEC 61508-4, 3.6.2, modified]
---------------------- Page: 15 ----------------------
SIST EN 62340:2010
– 10 – 62340 © IEC:2007
3.8
fault tolerance

the built-in capability of a system to provide continued correct execution in the presence of a

limited number of hardware and software faults
[IEC 60880, 3.18]
3.9
functional diversity

application of diversity at the functional level (for example, to have trip activation on both

pressure and temperature limit)
[IEC 60880, 3.19]
NOTE See also ”diversity”.
3.10
functional validation

verification of the correctness of the application functions specifications versus the first plant

functional and performance requirements. It is complementary to the system validation that

verifies the compliance of the system with the functions specification
[IEC 61513, 3.24]
3.11
human error (or mistake)
human action that produces an unintended result
[IEC 60880, 3.21]
3.12
independent I&C systems
systems that are independent possess the following characteristics:

a) the ability of one system to perform its required functions is unaffected by the operation or

failure of the other system;
b) the ability of the syst
...

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