IEC 61513:2011

IEC 61513 ®
Edition 2.0 2011-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Nuclear power plants – Instrumentation and control important to safety –
General requirements for systems

Centrales nucléaires de puissance – Instrumentation et contrôle-commande
importants pour la sûreté – Exigences générales pour les systèmes

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IEC 61513 ®
Edition 2.0 2011-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Nuclear power plants – Instrumentation and control important to safety –
General requirements for systems

Centrales nucléaires de puissance – Instrumentation et contrôle-commande
importants pour la sûreté – Exigences générales pour les systèmes

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XD
ICS 27.120.20 ISBN 978-2-88912-663-7

– 2 – 61513  IEC:2011
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 9
1.1 General . 9
1.2 Application: new and pre-existing plants . 9
1.3 Framework . 9
2 Normative references . 12
3 Terms and definitions . 13
4 Symbols and abbreviations . 26
5 Overall I&C safety life cycle . 26
5.1 General . 26
5.2 Deriving the I&C requirements from the plant safety design base . 29
5.2.1 General . 29
5.2.2 Review of the functional, performance and independence
requirements . 29
5.2.3 Review of the categorisation requirements . 30
5.2.4 Review of plant constraints . 31
5.3 Output documentation . 32
5.4 Design of the overall I&C architecture and assignment of the I&C functions . 32
5.4.1 General . 32
5.4.2 Design of the I&C architecture . 33
5.4.3 Assignment of functions to systems . 36
5.4.4 Required analysis . 37
5.5 Overall planning . 38
5.5.1 General . 38
5.5.2 Overall quality assurance programs . 38
5.5.3 Overall security plan . 38
5.5.4 Overall I&C integration and commissioning . 39
5.5.5 Overall operation plan . 41
5.5.6 Overall maintenance plan . 42
5.5.7 Planning of training. 42
5.6 Output documentation . 43
5.6.1 General . 43
5.6.2 Architectural design documentation . 43
5.6.3 Functional assignment documentation . 43
6 System safety life cycle . 44
6.1 General . 44
6.2 Requirements . 46
6.2.1 General . 46
6.2.2 System requirements specification . 47
6.2.3 System specification . 52
6.2.4 System detailed design and implementation . 55
6.2.5 System integration . 57
6.2.6 System validation . 58
6.2.7 System installation . 59
6.2.8 System design modification . 59

61513  IEC:2011 – 3 –
6.3 System planning . 59
6.3.1 General . 59
6.3.2 System quality assurance plan . 60
6.3.3 System security plan . 62
6.3.4 System integration plan . 62
6.3.5 System validation plan . 63
6.3.6 System installation plan . 63
6.3.7 System operation plan . 64
6.3.8 System maintenance plan . 64
6.4 Output documentation . 65
6.4.1 General . 65
6.4.2 System requirements specification documentation . 65
6.4.3 System specification documentation . 66
6.4.4 System detailed design documentation . 67
6.4.5 System integration documentation . 68
6.4.6 System validation documentation. 69
6.4.7 System modification documentation . 69
6.5 System qualification . 70
6.5.1 General . 70
6.5.2 Generic and application-specific qualification . 70
6.5.3 Qualification plan . 71
6.5.4 Additional qualification of interconnected systems . 72
6.5.5 Maintaining qualification . 73
6.5.6 Documentation . 73
7 Overall integration and commissioning . 74
7.1 General . 74
7.2 Requirements on the objectives to be achieved . 75
7.3 Output documentation . 75
8 Overall operation and maintenance . 75
8.1 General . 75
8.2 Requirements on the objectives to be achieved . 75
8.3 Output documentation . 76
Annex A (informative) Basic safety issues in the NPP . 77
Annex B (informative) Categorisation of functions and classification of systems . 80
Annex C (informative) Qualitative defence approach against CCF. 85
Annex D (informative) Relations of IEC 61508 with IEC 61513 and standards of the
nuclear application sector . 89
Annex E (informative) Changes to be performed in later revisions of SC 45A standards
to adapt to this version of IEC 61513 . 96
Bibliography . 98

Figure 1 – Overall framework of this standard . 11
Figure 2 – Typical relations of hardware and software in a computer-based system . 25
Figure 3 – Relations between system failure, random failure and systematic fault . 25
Figure 4 – Connections between the overall I&C safety life cycle and the safety life
cycles of the individual I&C systems . 29
Figure 5 – System safety life cycle . 46

– 4 – 61513  IEC:2011
Figure 6 – Product- and plant-application-specific topics to be addressed in the system
qualification plan . 74
Figure B.1 – Relations between I&C functions and I&C systems . 81
Figure C.1 – Examples of assignment of functions of a safety group to I&C systems . 85

Table 1 – Overview of the overall I&C safety life cycle . 27
Table 2 – Correlation between classes of I&C systems and categories of I&C functions . 33
Table 3 – Overview of the system safety life cycle . 44
Table B.1 – Typical classification of I&C systems . 84
Table C.1 – Examples of CCF sensitive in safety groups . 86

61513  IEC:2011 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS –
INSTRUMENTATION AND CONTROL IMPORTANT TO SAFETY –
GENERAL REQUIREMENTS FOR 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
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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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 61513 has been prepared by subcommittee 45A: Instrumentation
and control of nuclear facilities, of IEC technical committee 45: Nuclear instrumentation.
This second edition cancels and replaces the first edition, published in 2001, and constitutes
a technical revision.
The main technical changes with regard to the previous edition are as follows:
• to align the standard with the new revisions of IAEA NS-R-1 and NS-G-1.3, to review the
existing requirements and to update the terminology and definitions;
• to take account of, as far as possible, requirements associated with standards published
since the first edition, especially IEC 60880, IEC 61226, IEC 62138, IEC 62340 and
IEC 60987;
• to take into account the fact that software engineering techniques have advanced
significantly in the intervening years;

– 6 – 61513  IEC:2011
• to integrate requirements for staff training.
The text of this standard is based on the following documents:
FDIS Report on voting
45A/838/FDIS 45A/848/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.
The committee has decided that the contents of this publication will remain unchanged until
the stability 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.
61513  IEC:2011 – 7 –
INTRODUCTION
a) Technical background, main issues and organisation of the standard
This International Standard sets out requirements applicable to instrumentation and control
systems and equipment (I&C systems) that are used to perform functions important to safety
in nuclear power plants (NPPs).
This standard highlights the relations between
• the safety objectives of the NPP and the requirements for the overall architecture of the
I&C systems important to safety;
• the overall architecture of the I&C systems and the requirements of the individual systems
important to safety.
It is intended that the standard be used by designers, operators of NPPs (utilities), systems
evaluators and by licensors.
b) Situation of the current standard in the structure of the IEC SC 45A standard series
IEC 61513 is the first level IEC SC 45A document tackling the issue of general requirements
for systems. It is the entry point of the IEC SC 45A standard series.
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
It is important to note that this standard establishes no additional functional requirements for
safety systems.
To ensure that the standard will continue to be relevant in future years, the emphasis has
been placed on issues of principle, rather than specific technologies.
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
categorisation of functions and classification of systems, qualification, separation of systems,
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 technical reports
which are not normative.
– 8 – 61513  IEC:2011
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.
Regarding nuclear safety, it provides the interpretation of the general requirements of
IEC 61508-1 [1] , IEC 61508-2 and IEC 61508-4, for the nuclear application sector. In this
framework, IEC 60880 and IEC 62138 correspond to IEC 61508-3 [2] for the nuclear
application sector.
IEC 61513 refers to ISO as well as to IAEA GS-R-3 and IAEA GS-G-3.1 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 document 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.
NOTE 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, protection from chemical hazards and process energy hazards),
international or national standards would be applied, that are based on the requirements of such a standard as the
IEC 61508 series.
___________
References in square brackets refer to the bibliography.

61513  IEC:2011 – 9 –
NUCLEAR POWER PLANTS –
INSTRUMENTATION AND CONTROL IMPORTANT TO SAFETY –
GENERAL REQUIREMENTS FOR SYSTEMS

1 Scope
1.1 General
I&C systems important to safety may be implemented using conventional hard-wired equip-
ment, computer-based (CB) equipment or by using a combination of both types of equipment
(see Note 1). This International Standard provides requirements and recommendations (see
Note 2) for the overall I&C architecture which may contain either or both technologies.
This standard highlights also the need for complete and precise requirements, derived from
the plant safety goals, as a pre-requisite for generating the comprehensive requirements for
the overall I&C architecture, and hence for the individual I&C systems important to safety.
This standard introduces the concept of a safety life cycle for the overall I&C architecture, and
a safety life cycle for the individual systems. By this, it highlights the relations between the
safety objectives of the NPP and the requirements for the overall architecture of the I&C
systems important to safety, and the relations between the overall I&C architecture and the
requirements of the individual systems important to safety.
The life cycles illustrated in, and followed by, this standard are not the only ones possible;
other life cycles may be followed, provided that the objectives stated in this standard are
satisfied.
NOTE 1 I&C systems may also use electronic modules based on complex electronic components such as ASICs
or FPGA. Depending on the scope and functionality of these components, they may be treated according to the
guidance for conventional electronic equipment, or similar to CB equipment. A significant part of the guidance for
CB equipment is also applicable to the design of equipment with complex electronic components, including e.g. the
concepts of re-using pre-existing designs, and the evaluation of design errors in software or complex hardware
designs.
NOTE 2 In the following, “requirement” is used as a comprehensive term for both requirements and
recommendations. The distinction appears at the level of the specific provisions where requirements are expressed
by “shall” and recommendations by “should”.
1.2 Application: new and pre-existing plants
This standard applies to the I&C of new nuclear power plants as well as to I&C up-grading or
back-fitting of existing plants.
For existing plants, only a subset of requirements is applicable and this subset should be
identified at the beginning of any project.
1.3 Framework
The standard comprises four normative clauses (an overview is provided in Figure 1):
• Clause 5 addresses the overall architecture of the I&C systems important to safety:
– defining requirements for the I&C functions, and associated systems and equipment
derived from the safety analysis of the NPP, the categorisation of I&C functions, and
the plant lay-out and operational context;
– structuring the overall I&C architecture, dividing it into a number of systems and
assigning the I&C functions to systems. Design criteria are identified, including those
to give defence in depth and to minimize the potential for common cause failure (CCF);

– 10 – 61513  IEC:2011
– planning the overall architecture of the I&C systems.
• Clause 6 addresses the requirements for the individual I&C systems important to safety,
particularly the requirements for computer-based systems. This includes differentiation of
requirements according to the safety category of the I&C functions which are
implemented;
• Clauses 7 and 8 address the overall integration, commissioning, operation and
maintenance of the I&C systems.
NOTE Figure 1 outlines the structure of the standard. It does not necessarily present the timely order of activities
which may be in reality partially executed in parallel, or include iterations.
Additionally, the standard provides informative annexes:
• Annex A highlights the relations between IAEA and basic safety concepts that are used
throughout this standard;
• Annex B provides information on the categorisation/classification principles;
• Annex C gives examples of I&C sensitivity to CCF;
• Annex D provides guidance to support comparison of this standard with parts 1, 2 and 4 of
IEC 61508. This annex surveys the main requirements of IEC 61508 to verify that the
issues relevant to safety are adequately addressed, considers the use of common terms
and explains the reason for adopting different or complementary techniques or terms;
• Annex E indicates modifications to be made in future revisions of daughter standards of
IEC 61513 to make them consistent and to minimize overlapping contents.

61513  IEC:2011 – 11 –
5 Overall safety lifecycle: Requirements specification for the overall I&C

5.2  Deriving the I&C requirements from the 5.3 Requirements on output documentation
plant safety design base
5.2.2 Functional, performance and    Overall requirements specification for the I&C
independence requirements systems important to safety

5.2.3 Categorisation requirements

5.2.4 Plant constraints
5 Overall safety lifecycle: Design and planning of the overall I&C architecture and assignment of the I&C functions
to the individual I&C systems
5.4  Requirements on the 5.5   Requirements on the 5.6  Requirements on the
objectives overall planning documentation
5.5.2 O QA programs 5.6.2 Architectural design
5.4.2 Design of the I&C
architecture
5.5.3 O security plan 5.6.3 Functional assignment
5.4.3 Assignment of the
5.5.4 O integration and
functions to the
commissioning plan
individual systems
5.5.5 O operation plan
5.4.4 Required analysis
5.5.6 O maintenance plan
6 System safety lifecycle: Realisation and planning of the individual I&C systems

6.3   Requirements on 6.4  Requirements on
6.2  Requirements on the
objectives of the thesystem planning output documentation
system life-cycle
phases
6.2.2 Requirements  6.3.2 S quality plan 6.4.2 Requirements

specification specification
6.3.3 S security plan
6.2.3 Equipment selection & 6.4.3 Specification
6.3.4 S integration plan
system specification
6.4.4 Detailed design
6.3.5 S validation plan
6.2.4 Detailed design &
6.4.5 Integration
6.3.6 S installation plan
implementation
6.4.6 Validation
6.3.7 S operation plan
6.2.5 Integration
6.4.7 Modification
6.3.8 S maintenance plan
6.2.6 Validation
6.2.7 Installation
6.2.8 Modifications
6.5 Qualification
6.5.2, 6.5.4  6.5.3, 6.5.5 6.5.6
Requirements on system S Qualification plan Requirements on
qualification qualification documents

7 Overall integration and commissioning

7.2 Requirements on the objectives 7.3 Requirements on output documentation

8 Overall operation and maintenance

8.2 Requirements on the objectives 8.3 Requirements on output documentation

IEC  1895/11
Key QA: Quality Assurance; O: Overall; S: System
Figure 1 – Overall framework of this standard

– 12 – 61513  IEC:2011
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 60880:2006, Nuclear power plants – Instrumentation and control systems important to
safety – Software aspects for computer-based systems performing category A functions
IEC 60964:2009, Nuclear power plants – Control rooms – Design
IEC 60965, Nuclear power plants – Control rooms – Supplementary control points 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
IEC 60987:2007, Nuclear power plants – Instrumentation and control important to safety –
Hardware design requirements for computer-based systems
IEC 61000-4-1, Electromagnetic compatibility (EMC) – Part 4-1: Testing and measurement
techniques – Overview of IEC 61000-4 series
IEC 61000-4-2, Electromagnetic compatibility (EMC) – Part 4-2: Testing and measurement
techniques – Electrostatic discharge immunity test
IEC 61000-4-3, Electromagnetic compatibility (EMC) – Part 4-3: Testing and measurement
techniques – Radiated, radio-frequency, electromagnetic field immunity test
IEC 61000-4-4, Electromagnetic compatibility (EMC) – Part 4-4: Testing and measurement
techniques – Electrical fast transient/burst immunity test
IEC 61000-4-5, Electromagnetic compatibility (EMC) – Part 4-5: Testing and measurement
techniques – Surge immunity test
IEC 61000-4-6, Electromagnetic compatibility (EMC) – Part 4-6: Testing and measurement
techniques – Immunity to conducted disturbances, induced by radio-frequency fields
IEC 61226:2009, Nuclear power plants – Instrumentation and control systems important to
safety – Classification of instrumentation and control functions
IEC 61500, Nuclear power plants – Instrumentation and control important to safety – Data
communication in systems performing category A functions
IEC 61508-2:2010, Functional safety of electrical/electronic/programmable electronic safety-
related systems – Part 2: Requirements for electrical/electronic/programmable electronic
safety-related systems
61513  IEC:2011 – 13 –
IEC 61508-4:2010, Functional safety of electrical/electronic/programmable electronic safety-
related systems – Part 4: Definitions and abbreviations
IEC 62138:2004, Nuclear power plants – Instrumentation and control important for safety –
Software aspects for computer-based systems performing category B or C functions
IEC 62340, Nuclear power plants – Instrumentation and control systems important to safety –
Requirements for coping with common cause failure (CCF)
ISO 9001:2008, Quality management systems – Requirements
IAEA INSAG-10:1996, Defence in Depth in Nuclear Safety
IAEA NS-R-1:2000, Safety of Nuclear Power Plants: Design
IAEA GS-R-3:2006, The Management System for Facilities and Activities Safety –
Requirements
IAEA GS-G-3.1:2006, Application of the Management System for Facilities and Activities –
Safety Guide
IAEA NS-G-1.3:2002, Instrumentation and Control Systems Important to Safety in Nuclear
Power Plants
IAEA 75-INSAG-3 Rev. 1 – INSAG 12:1999, Basic Safety Principles for Nuclear Power Plants
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
application function
function of an I&C system that performs a task related to the process being controlled rather
than to the functioning of the system itself
NOTE 1 See also “I&C function”, “I&C system”, “application software”.
NOTE 2 An application function is normally a subfunction of an I&C function.
3.2
application software
part of the software of an I&C system that implements the application functions
NOTE 1 See also “application function”, “application software library”, “system software”.
NOTE 2 Application software contrasts with system software.
NOTE 3 See also Figure 2.
NOTE 4 In the context of complex electronic components, the term “application logic” may be inferred instead of
“application software” where appropriate throughout this standard.
3.3
application software library
collection of software modules implementing typical application functions
NOTE 1 When using pre-existing equipment, such a library is considered to be part of the system software and
qualified as such.
– 14 – 61513  IEC:2011
NOTE 2 See also Figure 2.
3.4
category of an I&C function
one of three possible safety assignments (A, B, C) of I&C functions resulting from
considerations of the safety relevance of the function to be performed. An unclassified
assignment may be made if the function has no importance to safety
NOTE 1 See also “class of an I&C system”, “I&C function”.
NOTE 2 IEC 61226 defines categories of I&C functions. To each category there corresponds a set of
requirements applicable on both the I&C function (concerning its specification, design, implementation, verification
and validation) and the whole chain of items which are necessary to implement the function (concerning the
properties and the related qualification) regardless of how these items are distributed in a number of
interconnected I&C systems. For more clarity, this standard defines categories of I&C functions and classes of I&C
systems and establishes a relation between the category of the function and the minimal required class for the
associated systems and equipment.
3.5
channel
an arrangement of interconnected components within a system that initiates a single output. A
channel loses its identity where the single-output signals are combined with signals from
another channel (e.g., from a monitoring channel or a safety actuation channel).
[IAEA Safety Glossary, 2007 Edition] [3]
3.6
class of an I&C system
one of three possible assignments (1, 2, 3) of I&C systems important to safety resulting from
consideration of their requirement to implement I&C functions of different safety importance.
An unclassified assignment is made if the I&C system does not implement functions important
to safety
NOTE See also “category of an I&C function”, “items important to safety”, “safety systems”.
3.7
commissioning
the process by means of which systems and components of facilities and activities, having
been constructed, are made operational and verified to be in accordance with the design and
to have met the required performance criteria
NOTE Commissioning may include both non-nuclear/non-radioactive and nuclear/radioactive testing.
[IAEA Safety Glossary, 2007 Edition]
3.8
common cause failure
CCF
failure of two or more structures, systems or components due to a single event or cause
[IAEA Safety Glossary 2007 Edition, Modified]
NOTE 1 Common causes may be internal or external to an I&C system.
NOTE 2 The IEC definition differs from the IAEA definition in two points:
1) The term “specific” was deleted because otherwise the definition of CCF is not consistent with the definition
of CMF “Common mode failure”. Furthermore, this additional word is not necessary in order to understand
the definition.
2) The word “and” was replaced by “or” because IEC/SC 45A experts thought it was a typing fault. In the
online IAEA dictionary (NUSAFE) this correction was already done.

61513  IEC:2011 – 15 –
3.9
complexity
degree to which a system or component has a design, implementation or behaviour that is
difficult to understand and verify
[IEEE 610, modified] [4]
3.10
component
one of the parts that make up a system. A component may be hardware or software and may
be subdivided into other components
[IEEE 610]
NOTE 1 See also “I&C system”, “equipment”.
NOTE 2 The terms “equipment”, “component”, and “module” are often used interchangeably. The relationship of
these terms is not yet standardised.
NOTE 3 This IEC/SC 45A definition is in principle compatible with the sub-definition of “Component” given in the
frame of the 2007 edition of the IAEA Safety Glossary definition of “Structures Systems and Components (SCC)”.
Nevertheless as only examples of hardware components are given, this can mislead the reader and IEC/SC 45A
prefer to use a definition which explicitly covers software components.
3.11
computer-based system
I&C system whose functions are mostly dependent on, or completely performed by
microprocessors, programmed electronic equipment or computers
NOTE Equivalent to digital system, software-based system, programmed system.
3.12
configuration management
the process of identifying and documenting the characteristics of a facility’s structures,
systems and components (including computer systems and software), and of ensuring that
changes to these characteristics are properly developed, assessed, approved, issued,
implemented, verified, recorded and incorporated into the facility documentation
[IAEA Safety Glossary, 2007 Edition]
3.13
data
representation of information or instructions in a manner suitable for communication,
interpretation, or processing by computers
[IEEE 610, modified]
NOTE See Figure 2.
3.14
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, 2007 Edition]
NOTE See also Clause A.4.
3.15
diversity
presence of two or more 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

– 16 – 61513  IEC:2011
[IAEA Safety Glossary edition 2007, modified]
NOTE 1 When “Diversity” is used with an additional attribute, the term diversity indicates the general meaning
“Existence of two or more different ways or means of achieving a specified objective”, where the attribute indicates
the characteristics of the different ways applied, e.g. func
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