IEC 62340:2007

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)

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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
T
CODE PRIX
ICS 27.120.20 ISBN 2-8318-9452-2

– 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 .

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
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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.

– 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.
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 NP
...