IEC 61559-1:2009

IEC 61559-1 ®
Edition 1.0 2009-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Radiation protection instrumentation in nuclear facilities – Centralized systems
for continuous monitoring of radiation and/or levels of radioactivity –
Part 1: General requirements
Instrumentation pour la radioprotection dans les installations nucléaires –
Ensembles centralisés pour la surveillance en continu des rayonnements et/ou
des niveaux de radioactivité –
Partie 1: Exigences générales
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by
any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or
IEC's member National Committee in the country of the requester.
If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication,
please contact the address below or your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de la CEI ou du Comité national de la CEI du pays du demandeur.
Si vous avez des questions sur le copyright de la CEI ou si vous désirez obtenir des droits supplémentaires sur cette
publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence.

IEC Central Office
3, rue de Varembé
CH-1211 Geneva 20
Switzerland
Email: inmail@iec.ch
Web: www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.
ƒ Catalogue of IEC publications: www.iec.ch/searchpub
The IEC on-line Catalogue enables you to search by a variety of criteria (reference number, text, technical committee,…).
It also gives information on projects, withdrawn and replaced publications.
ƒ IEC Just Published: www.iec.ch/online_news/justpub
Stay up to date on all new IEC publications. Just Published details twice a month all new publications released. Available
on-line and also by email.
ƒ Electropedia: www.electropedia.org
The world's leading online dictionary of electronic and electrical terms containing more than 20 000 terms and definitions
in English and French, with equivalent terms in additional languages. Also known as the International Electrotechnical
Vocabulary online.
ƒ Customer Service Centre: www.iec.ch/webstore/custserv
If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service
Centre FAQ or contact us:
Email: csc@iec.ch
Tel.: +41 22 919 02 11
Fax: +41 22 919 03 00
A propos de la CEI
La Commission Electrotechnique Internationale (CEI) est la première organisation mondiale qui élabore et publie des
normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications CEI
Le contenu technique des publications de la CEI est constamment revu. Veuillez vous assurer que vous possédez
l’édition la plus récente, un corrigendum ou amendement peut avoir été publié.
ƒ Catalogue des publications de la CEI: www.iec.ch/searchpub/cur_fut-f.htm
Le Catalogue en-ligne de la CEI vous permet d’effectuer des recherches en utilisant différents critères (numéro de référence,
texte, comité d’études,…). Il donne aussi des informations sur les projets et les publications retirées ou remplacées.
ƒ Just Published CEI: www.iec.ch/online_news/justpub
Restez informé sur les nouvelles publications de la CEI. Just Published détaille deux fois par mois les nouvelles
publications parues. Disponible en-ligne et aussi par email.
ƒ Electropedia: www.electropedia.org
Le premier dictionnaire en ligne au monde de termes électroniques et électriques. Il contient plus de 20 000 termes et
définitions en anglais et en français, ainsi que les termes équivalents dans les langues additionnelles. Egalement appelé
Vocabulaire Electrotechnique International en ligne.
ƒ Service Clients: www.iec.ch/webstore/custserv/custserv_entry-f.htm
Si vous désirez nous donner des commentaires sur cette publication ou si vous avez des questions, visitez le FAQ du
Service clients ou contactez-nous:
Email: csc@iec.ch
Tél.: +41 22 919 02 11
Fax: +41 22 919 03 00
IEC 61559-1 ®
Edition 1.0 2009-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Radiation protection instrumentation in nuclear facilities – Centralized systems
for continuous monitoring of radiation and/or levels of radioactivity –
Part 1: General requirements
Instrumentation pour la radioprotection dans les installations nucléaires –
Ensembles centralisés pour la surveillance en continu des rayonnements et/ou
des niveaux de radioactivité –
Partie 1: Exigences générales
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
V
CODE PRIX
ICS 13.280 ISBN 978-2-88910-544-1
– 2 – 61559-1 © IEC:2009
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.9
2 Normative references .9
3 Terms, definitions and abbreviations .11
3.1 Terms and definitions .11
3.2 Test nomenclature.12
3.3 Abbreviated terms .12
4 Design requirements .12
4.1 General remarks.12
4.1.1 General .12
4.1.2 Safety classification.12
4.1.3 System configuration .13
4.1.4 Location of detector assemblies .14
4.2 Design requirements for the assemblies .14
4.2.1 Detector assembly.14
4.2.2 Processing assembly.14
4.2.3 Alarm assemblies .16
4.3 Central computer.17
4.3.1 General .17
4.3.2 Functional requirements of the central computer .17
4.3.3 Checking normal operation of the equipment .18
4.4 Electrical characteristics.18
4.4.1 General .18
4.4.2 Electromagnetic compatibility .19
5 General Test procedures .19
5.1 Test requirements .19
5.1.1 General .19
5.1.2 Test performed under standard test conditions .20
5.1.3 Test performed with variation of influence quantities .20
5.2 Test procedures for the detector assembly .20
5.3 Test procedures for the monitoring assembly .20
5.3.1 Alarm trip range.20
5.3.2 Equipment failure alarms .21
5.3.3 Alarm response time and stability .21
5.4 Test procedures for the central computer .21
5.4.1 Individual tests of access channels.21
5.4.2 Whole tests of access channels.21
5.4.3 Tests for functional validation and verification. .21
5.5 Test procedures for effects of power supply and environmental variations.22
5.5.1 Power supply variations.22
5.5.2 Power supply variations (interruptions and transients) .23
5.5.3 Surges and oscillatory waves .23
5.5.4 Ambient temperature and humidity .24
5.5.5 Electromagnetic compatibility .24
5.5.6 External electromagnetic immunity and electrostatic discharge.24

61559-1 © IEC:2009 – 3 –
5.5.7 Electromagnetic emission .24
6 Documentation .25
6.1 Report on type testing .25
6.2 Certificate .25
6.3 Operating and maintenance manual .25
Annex A (informative) Selection of a measuring unit .31
Annex B (informative) Guidance on location of detector assemblies.32
Bibliography.34

Figure 1 – Monitoring assembly inside monitored area.26
Figure 2 – Monitoring assembly outside monitored area.26
Figure 3 – Centralized configuration .27
Figure 4 – Centralized configuration .28

Table 1 – Reference conditions and standard test conditions .29
Table 2 – Tests performed under standard test conditions .29
Table 3 – Tests performed with variations of influence quantities.30

– 4 – 61559-1 © IEC:2009
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
RADIATION PROTECTION INSTRUMENTATION IN NUCLEAR
FACILITIES – CENTRALIZED SYSTEMS FOR CONTINUOUS
MONITORING OF RADIATION AND/OR LEVELS OF RADIOACTIVITY –

Part 1: General requirements
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 61559-1 has been prepared by subcommittee 45B: Radiation
protection instrumentation, of IEC technical committee 45: Nuclear instrumentation.
This standard cancels and replaces the first edition of IEC 61559 published in 1996. The
document has been updated to take account of the requirements of IEC standards published
since 1996. Specifically, to meet the functional safety lifecycle requirements of IEC 61508
and/or IEC 61513 have been introduced. Additionally, functional validation and verification
tests have been added.
61559-1 © IEC:2009 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
45B/608/FDIS 45B/616/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.
A list of all parts of the IEC 61559 series can be found, under the general title Radiation
protection instrumentation in nuclear facilities – Centralized systems for continuous
monitoring of radiation and/or levels of radioactivity, on the IEC website.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
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.
– 6 – 61559-1 © IEC:2009
INTRODUCTION
a) Technical background, main issues and organisation of this standard
This IEC standard specifically applies to centralized systems intended for continuous
monitoring of radiation and/or levels of radioactivity in nuclear facilities, primarily in support of
radiological protection in the working areas. These centralized systems play an auxiliary or
indirect role in the achievement or maintenance of a nuclear facility’s safety. These are
classified as category C in IEC 61226 since they include functions that have some safety
significance.
This standard is intended for use by purchasers in developing specifications for their plant
specific centralized systems radiation monitoring systems and by manufacturers to identify
needed product characteristics when developing systems.
This standard is one associated with a series of standards which cover process and safety
monitoring, and radiation protection and effluents monitoring in nuclear facilities. The full
series is detailed in paragraph b) below.
b) Situation of the current standard in the structure of the IEC SC 45A/SC 45B
standard series
IEC 60951 series of standards are at the third level in the hierarchy of SC 45A standards.
They provide guidance on the design and testing of radiation monitoring equipment used for
accident and post accident conditions.
IEC 60951-1 – General requirements
IEC 60951-2 – Equipment for continuous off-line monitoring of radioactivity in gaseous
effluents and ventilation air
IEC 60951-3 – Equipment for continuous high range area gamma monitoring
IEC 60951-4 – Equipment for continuous in-line or on-line monitoring of radioactivity in
process stream
Other standards developed by SC 45A and SC 45B provide guidance on instruments used for
monitoring radiation as part of normal operations. IEC 60761 series provide requirements for
equipment for continuous off-line monitoring of radioactivity in gaseous effluents in normal
conditions. IEC 60861 provides requirements for equipment for continuous off-line monitoring
of radioactivity in liquid effluents in normal conditions. IEC 60768 provides requirement for
equipment for continuous in-line and on-line monitoring of radioactivity in process stream in
normal and incident conditions. ISO standard 2889 gives guidance on gas and particulate
sampling. The relationship between these various radiation monitoring standards is given in
the table below:
Developer ISO SC 45A – process and safety SC 45B – radiation
monitoring protection and effluents
monitoring
Scope Sampling Accident and post Normal and
circuits accident incident
and conditions conditions
methods
Gas, particulate and ISO 2889 IEC 60951-1 and IEC 60761 series
iodine with sampling -2
(OFF LINE)
Liquid with sampling N/A N/A IEC 60861

61559-1 © IEC:2009 – 7 –
(OFF LINE)
Process stream N/A IEC 60951-1 and IEC 60768 N/A
(gaseous effluents, -4
steam or liquid)
without sampling
(ON or IN-LINE)
Area monitoring N/A IEC 60951-1 and IEC 60532
-3
Central system N/A IEC 61504 IEC 61559

c) Recommendations and limitations regarding the application of this standard
It is important to note that this standard establishes no additional functional safety
requirements for safety systems.
d) Description of the structure of the IEC SC 45A/SC 45B standard series and
relationships with other IEC documents and other bodies’ documents (IAEA, ISO)
The basic safety publication is IEC 61508-7, Functional safety of electrical/electronic/
programmable electronic safety-related systems. It defines the requirements for an overall
safety life-cycle framework and a system life-cycle framework. IEC 61508 should be complied
with when developing instruments with safety functions for centralized systems of radiation
monitoring outside the nuclear power plant sector whilst complying with the requirements
defined in this standard.
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 nuclear power plants. 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,
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/SC 45B 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 45/SC 45B 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 power plant 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 50-C/SG-Q) for
topics related to quality assurance (QA).

– 8 – 61559-1 © IEC:2009
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.

61559-1 © IEC:2009 – 9 –
RADIATION PROTECTION INSTRUMENTATION IN NUCLEAR
FACILITIES – CENTRALIZED SYSTEMS FOR CONTINUOUS
MONITORING OF RADIATION AND/OR LEVELS OF RADIOACTIVITY –

Part 1: General requirements
1 Scope
This part of IEC 61559 series applies to centralized systems intended for continuous
monitoring of radiation and/or levels of radioactivity installed in nuclear facilities, primarily in
support of radiological protection in the working areas. This standard specifies general
characteristics, general test procedures, radiation, electrical, safety, and environmental
characteristics and the identification certificate for the systems addressed by this standard.
More specifically, it applies to centralized data processing systems, data links, and equipment
sitting and layout. It also applies to indications displayed locally and centrally. It gives general
guidance to the specification, operation, and testing of computers for the centralized
monitoring function.
Typically these centralized systems play an auxiliary or indirect role in the achievement or
maintenance of nuclear facility’s safety. These are classified as category C in IEC 61226
since they include functions that have some safety significance.
It does not directly apply to the design and testing of detection and measurement assemblies.
These should, wherever practical, conform to relevant IEC specifications.
This standard applies to normal monitoring functions. IEC 61559-2 applies to Requirements
for Discharge, Environmental, Accident, or Post-Accident Monitoring Functions.
For Radiation monitoring equipment for accident and post-accident conditions in nuclear
power plants see IEC 60951.
This standard does not apply to criticality alarm systems. These shall conform to IEC 60860.
2 Normative references
The following referenced documents are relevant to 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).
IEC 60038:2002, IEC standard voltages
IEC 60050-151:2001, International Electrotechnical Vocabulary (IEV) – Part 151: Electrical
and magnetic devices
IEC 60050-393:2003, International Electrotechnical Vocabulary (IEV) – Part 393: Nuclear
instrumentation – Physical phenomena and basic concepts
IEC 60050-394:2007, International Electrotechnical Vocabulary (IEV) – Part 394: Nuclear
instrumentation – Instruments, systems, equipment and detectors

– 10 – 61559-1 © IEC:2009
IEC 60532:1992, Radiation protection instrumentation – Installed dose ratemeters, warning
assemblies and monitors – X and gamma radiation of energy between 50 keV and 7 MeV
IEC 60860:1987, Warning equipment for criticality accidents
IEC 61000-4-2:2008, Electromagnetic compatibility (EMC) – Part 4-2: Testing and
measurement techniques – Electrostatic discharge immunity test
IEC 61000-4-3:2006, Electromagnetic compatibility (EMC) – Part 4-3: Testing and
measurement techniques – Radiated, radio-frequency, electromagnetic field immunity test
IEC 61000-4-4:2004, Electromagnetic compatibility (EMC) – Part 4-4: Testing and
measurement techniques – Electrical fast transient/burst immunity test
IEC 61000-4-5:2005, Electromagnetic compatibility (EMC) – Part 4-5: Testing and
measurement techniques – Surge immunity test
IEC 61000-4-6:2008, Electromagnetic compatibility (EMC) – Part 4-6: Testing and
measurement techniques – Immunity to conducted disturbances induced by radio-frequency
fields
IEC 61000-4-11:2004, Electromagnetic compatibility (EMC) – Part 4-11: Testing and
measurement techniques – Voltage dips, short interruptions and voltage variations immunity
tests
IEC 61000-4-12:2006, Electromagnetic compatibility (EMC) – Part 4-12: Testing and
measurement techniques – Ring wave immunity test
IEC/TR 61000-5-1:1996, Electromagnetic compatibility (EMC) – Part 5: Installation and
mitigation guidelines – Section 1: General considerations
IEC 61000-6-4:2006, Electromagnetic compatibility (EMC) – Part 6-4: Generic standards –
Emission standard for industrial environments
IEC 61005:2003, Radiation protection instrumentation – Neutron ambient dose equivalent
(rate) meters
IEC 61187:1993, Electrical and electronic measuring equipment – Documentation
IEC 61226:2005, Nuclear power plants – Instrumentation and control systems important to
safety – Classification of instrumentation and control functions
IEC 61322:1994, Radiation protection instrumentation – Installed dose equivalent rate meters,
warning assemblies and monitors for neutron radiation of energy from thermal to 15 MeV
IEC 61508 (all parts), Functional safety of electrical/electronic/programmable electronic
safety-related systems
IEC 61513:2001, Nuclear power plants – Instrumentation and control for systems important to
safety – General requirements for systems

61559-1 © IEC:2009 – 11 –
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
The general terminology concerning detection and measurement of ionizing radiation and
nuclear instrumentation is given in IEC 60050-393, IEC 60050-394, and IEC 60050-151.
3.1.1 Manufacturer and purchaser
3.1.1.1
manufacturer
designer and seller of the equipment
3.1.1.2
purchaser
user (operator) of the equipment
3.1.2
category C classification
category that denotes functions that play an auxiliary or indirect role in the achievement or
maintenance of NPP safety; it includes functions that have some safety significance, but are
not category A or B
[IEC 61226]
NOTE Category C denotes systems that have:
a) functions used to prevent or mitigate a minor radioactive release, or minor degradation of fuel, within the NPP
design basis,
b) functions to warn personnel or to ensure its safety during or following events that involve or result in release of
radioactivity in the NPP, or risk of radiation exposure.
3.1.3
detector assembly (DA)
component of the installed radiation monitor that contains detector and may contain
associated electronics (amplifier, discriminator, output pulse shaper), and may also include
programmable electronic circuits
3.1.4
processing assembly (PA)
assembly which converts the output signals of one or more detector assemblies into a form,
generally digital, suitable for transmission down a data link to the central computer; central
computer, and/or which generates alarm outputs to the alarm units at present signal levels
3.1.5
alarm assembly (AA)
assembly which is initiated by the PA. It provides audible and/or visual alarms, in the event of
an alarm threshold being breached or in the case of an equipment fault. It is normally sited
local to the DA
3.1.6
central computer (CC)
central processing and control system for the calculation, display, and storage of data from
the processing units
3.1.7
monitoring assembly (MA)
integrated assembly consisting of combinations of processing, alarm, and detector assemblies

– 12 – 61559-1 © IEC:2009
3.2 Test nomenclature
3.2.1
type test
conformity test made on one or more items representative of the production
[IEV 394-40-02]
3.2.2
acceptance test
contractual test to prove to the customer that the device fulfils certain specifications
[IEV 394-40-05]
3.3 Abbreviated terms
ALI Annual Limit on Intake
DAC Derived Air Concentration
DWL Derived Working Limit
PES programmable electronic system
SIL safety integrity level
VDUs visual display units
4 Design requirements
4.1 General remarks
4.1.1 General
A centralized system for continuous monitoring of the radiation levels in nuclear facilities is
composed of appropriate devices for measurement, acquisition, processing, display and
storage of data. The data is mainly related to detection or measurement of ionizing radiation
and, more generally, to the radiological safety of facilities, premises, and their surrounding
environment.
By monitoring the status of the nuclear facility, the centralized system provides confirmatory
information on the maintenance of a satisfactory working environment, and provides a display
of any developing long-term trends.
This type of monitoring is intended to provide:
– continuous monitoring of all parameters defining the radiological status and especially
those related to the work place (radiation fields, volumetric radioactive contamination in
air) and other associated parameters (e.g. ventilation);
– activation of audible and visual indicators when predetermined thresholds are exceeded;
– storage of data for subsequent processing. For example, this may be used to review
longterm changes in the radiological status of the facility, or to perform historic reviews of
the radiological conditions.
4.1.2 Safety classification
The equipment covered in this standard is installed in facilities such as nuclear power plants,
nuclear fuel storage and processing sites.
The equipment is intended primarily for the purpose of radiological protection and is thus
category C classification as defined in 5.4.3 of IEC 61226 since it may play an auxiliary or
indirect role in the achievement or maintenance of nuclear power plants safety.

61559-1 © IEC:2009 – 13 –
If a safety classification applies, appropriate requirements shall apply concerning
specification, design, manufacturing, installation and operation of the equipment with respect
to the necessary quality of computer hardware and software. The requirements shall be
agreed between manufacturer and purchaser. In particular the purchaser (operator) shall
decide the appropriate safety standard applicable to the site in which the system will function.
The basic safety standards IEC 61508 series apply.
When IEC 61508 is selected, then the requirements of that standard shall apply as
appropriate to the required safety integrity level specified for the system.
Compliance with IEC 61513 facilitates consistency with the requirements of IEC 61508 series
as they have been interpreted for the nuclear industry.
4.1.3 System configuration
The type of equipment defined in this standard generally comprises up to four types of
assemblies, which may be interconnected in a number of configurations and to the central
computer (CC) (see Figures 1 to 4).
These assemblies are:
– detector assembly (DA);
– processing assembly (PA);
– alarm assembly (AA);
– monitoring assembly (MA).
The monitoring assembly is an integrated assembly consisting of combinations of processing,
alarm, and detector assemblies.These assemblies may be located in a single package
(instrument), or as individual assemblies.
Each installation is unique; some typical examples are illustrated.
Figure 1 shows a monitoring assembly located within the monitoring area.
Figure 2 shows an example where the detector assembly is located within the monitored area,
whilst the processing assembly is located in an area of lower radiation or volumetric
radioactive contamination in air. In this example, the alarm assembly must be located within
the monitoring area to warn personnel. The detector assembly measuring volumetric
radioactive contamination in air may be located outside the monitoring area, but the air
sample must be drawn from within the area. The need to position a second alarm unit at the
entry point to prevent access, should be considered. Further alarm assemblies triggered by
the processing assembly may be required to adequately cover the geographical area.
The links from detector assembly to processing assembly and processing assembly to alarm
assembly shall be standardized and ideally independent of assembly type.
The elements forming a monitoring assembly shall have the ability to be grouped, and to
operate in autonomous mode. The monitoring assembly to CC link shall be standardized.
The central computer has to collect the data transmitted from the various monitor units data
links. Additionally diverse digital alarm status inputs may also be accepted.
All data links shall be a good quality, commercially available protocol. Additionally the
installation of the detector assembly to processor unit link and processing unit to alarm unit
link and links to the central computer, shall follow the electromagnetic compatibility
requirements of IEC 61000–5-1.

– 14 – 61559-1 © IEC:2009
The monitoring assembly or processing assemblies can be linked to the central computer in
various ways:
– either all are linked directly to the central computer, that is a centralized configuration;
– or are linked via a CC outstation. Such a configuration reduces the length of the cables.
Figures 1 to 4 detail such arrangements.
4.1.4 Location of detector assemblies
The design and location of detector assemblies and/or monitoring assemblies shall be
considered in relation to the radiological protection requirements of the particular plant
concerned. Generally, the extent of the provision shall be related to the type and degree of
hazard, and the extent of occupancy by plant personnel. Guidance on the criteria which may
be used is given in Annex B.
4.2 Design requirements for the assemblies
4.2.1 Detector assembly
The monitoring sensors are specified for the quantity and radiation type they have to detect
(electron, photon, and neutron radiations, gas contamination, alpha and/or beta aerosol
contamination), and they shall meet the relevant IEC standards applicable to the
measurement being carried out. In some cases, there are directly applicable standards, for
example, IEC 60532 for gamma radiation monitors, and IEC 61322 and IEC 61005 for neutron
monitors. In other cases, relevant requirements may be identified in standards dealing with
equipment specifically designed for other, technically similar applications. (For example,
IEC 60761 series dealing with gaseous effluent monitors.) In such cases, the applicability of
the standards shall be agreed between manufacturer and purchaser.
It is intended that this standard should allow interchangeability of detector assemblies from
different manufacturers. To facilitate this, regardless of the quantity being measured, when
the detector assembly is separate from the processing unit, the attributes of the output signal
from the detector assembly shall be agreed between manufacturer and purchaser.
The output of the detector assembly shall be made directly proportional to the activity being
measured.
4.2.2 Processing assembly
4.2.2.1 General
The processing assembly converts the output signal from the detector assembly into data
representing the quantity to be measured. It also activates the alarm assembly, if the quantity
to be measured exceeds preset thresholds.
The quantity being measured is typically either dose equivalent rate or volumetric
concentration of radioactive contamination in air. Dose equivalent rate and gas volumetric
activity are proportional to the detector output, whereas aerosol volumetric activity is
proportional to the rate of change of the detector output signal.
The processing assembly therefore may simply be required to take the signal from the
detector assembly, modify it by a defined function, and compare the result with a preset alarm
level.
In other cases, it may be required to receive signals from a number of sources, combine them
as defined by an appropriate algorithm, and then compare the computed result with a preset
alarm level.
Selection of a measuring unit is described in Annex A.

61559-1 © IEC:2009 – 15 –
4.2.2.2 Main characteristics
The processing assemblies shall, as far as practicable, be designed to be "fail safe"; that is,
be so arranged that interruption or failure of the power supply, or component failure, shall
result in actuation of a trip circuit to produce an alarm. Failure of the power supply shall not
disable the alarm. Indication of power supply failure shall be provided.
If system functions can be controlled, or data manipulated from a remote unit, hardware or
software controls shall be instituted to prevent unauthorized operation from remote locations.
4.2.2.3 Processing assembly alarm specification
Alarm circuits should be operable either to hold an alarm condition until specifically reset by a
reset control, or to auto-reset when the alarm condition disappears. The two modes of
operation should be available by a simple modification onto all equipment.
All alarm functions should be provided with test facilities to allow checking of alarm operation.
In the case of adjustable alarms, checking should be possible over the range of adjustment,
with indication of the actual alarm operation point.
The following alarm facilities normally should be provided.
a) High level alarms
One or more adjustable alarms to cover at least the full measurement range should be
provided. The time taken to activate the alarm trip circuit should be minimised such that
the dose equivalent or the committed effective dose (e.g. derived aerosol activity
3 –1
⋅h ).resulting from this delay is as
concentration and a standard breathing rate of 1,2 m
low as reasonably practical.
A second alarm with the same specification may be incorporated if required by the
purchaser.
b) Low level alarm
A low level alarm facility should be provided. It should be possible to set this low level
alarm at some point below the minimum of the range of measurement, so that in the event
of detector failure, this alarm will operate. The design shall ensure that with the low level
alarm set to this requirement, the frequency of false alarms when the unit is operated
under normal conditions should be an acceptably low frequency.
There is generally an inter-relationship between the time for the alarm to operate, the
frequency of false alarms, and the margin between background level and alarm level. If an
instrument is required to measure low dose rates approaching background, the alarm level
may also be set low, and a long time constant for alarm operation may also be necessary
to minimize false alarms.
c) Fault alarms
An alarm should normally be provided to indicate as many electronic circuit faults as
reasonably practicable, together with any cable break or disconnection faults; separate
indication of the source of any fault is desirable. In deciding on the extent of fault alarms,
the provision of a low level alarm may be taken into account.
An alarm should be provided to indicate as many other faults in other services (e.g. low
air sample flow in volumetric radioactive contamination in air monitors) as reasonably
practicable.
4.2.2.4 Processing assembly outputs
The processing assembly should provide the following outputs:
– at least one set of relay contacts or digital output for each alarm function;
– a data link output for transmission of alarm to an indicating unit and for a local display;

– 16 – 61559-1 © IEC:2009
– outputs intended for recording the measurement, and/or to provide a local analogue
display;
– indicating lights for alarms and other functions on the front panel.
These various outputs allow the monitoring assemblies to operate without a central computer
for small configurations.
The processing assembly shall provide the following outputs for transmission to the central
computer:
– a digital output for transmission of each alarm;
– a data link which shall at least include:
• the measurement;
• the monitor status, including alarms;
• the value of the preset parameters (alarm thresholds and operational parameters).
The data link should be of the RS 485, RS 422, 20 mA current loops, Ethernet,
...