IEC 60951-3:2009

IEC 60951-3 ®
Edition 2.0 2009-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Nuclear power plants – Instrumentation important to safety – Radiation
monitoring for accident and post-accident conditions –
Part 3: Equipment for continuous high range area gamma monitoring

Centrales nucléaires de puissance – Instrumentation importante pour la sûreté –
Surveillance des rayonnements pour les conditions accidentelles et post-
accidentelles –
Partie 3: Ensemble de surveillance locale en continu des rayonnements gamma
à large gamme
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It also gives information on projects, withdrawn and replaced publications.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 60951-3 ®
Edition 2.0 2009-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Nuclear power plants – Instrumentation important to safety – Radiation
monitoring for accident and post-accident conditions –
Part 3: Equipment for continuous high range area gamma monitoring

Centrales nucléaires de puissance – Instrumentation importante pour la sûreté –
Surveillance des rayonnements pour les conditions accidentelles et post-
accidentelles –
Partie 3: Ensemble de surveillance locale en continu des rayonnements gamma
à large gamme
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
M
CODE PRIX
ICS 27.120.20 ISBN 978-2-88910-348-5
– 2 – 60951-3 © IEC:2009
CONTENTS
FOREWORD.3
INTRODUCTION.5
1 Scope.7
2 Normative references .7
3 Terms and definitions .8
4 Design principles.8
4.1 General .8
4.2 Range of measurement .8
4.3 Accuracy (relative error) .8
4.4 Location of sensors .8
4.5 Detector radiation response characteristics .8
4.6 Requirements related to accident conditions .8
5 Functional testing .9
5.1 General .9
5.2 Reference sources .9
5.2.1 General .9
5.2.2 Gamma .9
5.2.3 Beta .9
5.2.4 Neutron .9
5.3 Performance characteristics .10
5.3.1 Reference response .10
5.3.2 Sensitivity and relative response for solid sources.11
5.3.3 Variation of response with angle of incidence .11

Figure 1 – Energy response .10

Table 1 – Overview of the standards covering the domain of radiation monitoring.5
Table 2 – Additional tests to complement the general tests required in IEC 60951-1.12

60951-3 © IEC:2009 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS –
INSTRUMENTATION IMPORTANT TO SAFETY –
RADIATION MONITORING FOR ACCIDENT
AND POST-ACCIDENT CONDITIONS –

Part 3: Equipment for continuous high range area gamma monitoring

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 60951-3 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 1989. This edition
constitutes a technical revision.
The main technical changes with regard to the previous edition as are follows:
• To clarify the definitions.
• To update the references to new standards published since the first issue.
• To update the units of radiation.
This standard is to be read in conjunction with IEC 60951-1.

– 4 – 60951-3 © IEC:2009
The text of this standard is based on the following documents:
FDIS Report on voting
45A/736/FDIS 45A/758/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 IEC 60951 series, under the general title Nuclear power plants –
Instrumentation important to safety – Radiation monitoring for accident and post-accident
conditions, can be found on the IEC website.
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.
60951-3 © IEC:2009 – 5 –
INTRODUCTION
a) Technical background, main issues and organisation of this standard
This IEC standard specifically focuses on radiation monitoring systems used for accident and
post-accident operations.
This standard is intended for use by purchasers in developing specifications for their plant-
specific radiation monitoring systems and by manufacturers to identify needed product
characteristics when developing systems for accident monitoring conditions. Some specific
instrument characteristics such as measurement range, required energy response, and
ambient environment requirements will depend upon the specific application. In such cases
guidance is provided on determining the specific requirements, but specific requirements
themselves are not stated.
This standard is one in a series of standards covering post-accident radiation monitors
important to safety. The full series is comprised of the following standards.
• 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 streams
b) Situation of the current standard in the structure of the IEC SC 45A 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. 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 streams in normal and incident conditions. Finally, ISO
2889 gives guidance on gas and particulate sampling. The relationship between these various
radiation monitoring standards is given in the Table 1 below.
Table 1 – Overview of the standards covering the domain of radiation monitoring
Developer ISO SC 45A – Process and safety monitoring SC 45B – Radiation
protection and
Scope Sampling circuits Accident and post- Normal and incident
effluents monitoring
and methods accident conditions conditions
Gas, particulate and ISO 2889 IEC 60951-1 and IEC 60761 series and IEC 62302 (noble
iodine with sampling IEC 60951-2 gases only)
(OFF LINE)
Liquid with sampling N/A N/A IEC 60861
(OFF LINE)
Process streams N/A IEC 60951-1 and IEC 60768 N/A
(gaseous effluents, IEC 60951-4
steam or liquid)
without sampling
(ON or IN-LINE)
Area monitoring N/A IEC 60951-1 and IEC 60532
IEC 60951-3
– 6 – 60951-3 © IEC:2009
Developer ISO SC 45A – Process and safety monitoring SC 45B – Radiation
protection and
Scope Sampling circuits Accident and post- Normal and incident
effluents monitoring
and methods accident conditions conditions
Central system N/A IEC 61504 IEC 61559
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 the standard
It is important to note that this standard establishes no additional functional requirements for
safety systems.
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,
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 standards 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.

60951-3 © IEC:2009 – 7 –
NUCLEAR POWER PLANTS –
INSTRUMENTATION IMPORTANT TO SAFETY –
RADIATION MONITORING FOR ACCIDENT
AND POST-ACCIDENT CONDITIONS –

Part 3: Equipment for continuous high range area gamma monitoring

1 Scope
This part of IEC 60951 provides general guidance on the design principles and performance
criteria for equipment for continuous high range area gamma monitoring in nuclear power
plants for accident and post-accident conditions.
General requirements for technical characteristics, test procedures, radiation characteristics,
electrical, mechanical, and environmental characteristics are given in IEC 60951-1. These
requirements are applicable in this part unless otherwise stated.
This standard is applicable to installed dose rate meters that are used to monitor high levels
of gamma radiation during and after an accident. It covers equipment intended to isotropically
measure air kerma, ambient dose or other exposure quantities due to gamma radiation of
energy between 80 keV and 7 MeV. The equipment is intended primarily for the purpose of
nuclear plant safety.
Portable instruments for emergency purposes and installed area radiation monitors used to
determine continuously the radiological situation in working areas during normal operation are
within the scope of IEC 60532.
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 60951-1:2009, Nuclear power plants – Instrumentation important to safety – Radiation
monitoring for accident and post-accident conditions – Part 1: General requirements
IEC 60780, Nuclear power plants – Electrical equipment of the safety system – Qualification
IEC 61226, Nuclear power plants – Instrumentation and control systems important to safety –
Classification of instrumentation and control functions
ISO 4037 (all parts), X and gamma reference radiation for calibrating dosemeters and
doserate meters and for determining their response as a function of photon energy
ISO 6980 (all parts), Nuclear energy – Reference beta-particle radiation
ISO 8529 (all parts), Reference neutron radiations

– 8 – 60951-3 © IEC:2009
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60951-1 apply.
4 Design principles
4.1 General
The general requirements of IEC 60951-1 are applicable to all types of monitors within the
scope of the present standard, unless otherwise stated.
4.2 Range of measurement
The purchaser shall specify the required effective range of measurement and the radiation
sources specific to the plant design. The range shall be suitable for the level of and the
variation in radiation in the area during accident and post-accident conditions. It shall be at
least six decades. The low end of the required range shall overlap the highest decade of dose
rate monitors designed for normal operation conditions.
The energy response of the detector in relation to the expected radiation energy spectrum
shall also be specified. Typically detectors should respond to gamma radiation within any
energy range from 80 keV to 7 MeV.
4.3 Accuracy (relative error)
In addition to 4.6 of IEC 60951-1, the following requirements shall apply.
When a detector assembly utilizes more than one radiation detector to cover the full range of
dose equivalent rates indicated by the detector assembly, these requirements apply to the
relevant ranges for each detector separately.
4.4 Location of sensors
The requirements for such equipment are plant specific. Therefore, the locations in which the
monitoring equipment is required shall be determined according to the plant design.
Usually equipment is located within the reactor containment. It shall be located to provide
maximum coverage of the areas being monitored and to minimize shielding effects from other
equipment or structures. As far as is practical, locations should be selected so as to facilitate
maintenance and calibration operations.
Because of the high level of radiation, the equipment is usually designed with a detector
assembly located remotely from any processing assembly (electronics), taking into account
the length of the cable between detector and remote electronics which should be minimized.
4.5 Detector radiation response characteristics
The detector assembly shall be designed to be effectively insensitive to beta and neutron
radiation (compared to its gamma sensitivity) expected to be present during the accident
conditions for which the equipment is intended to operate.
4.6 Requirements related to accident conditions
In addition to 4.11 of IEC 60951-1, the following requirements shall apply.
The type of equipment covered by this standard is typically regarded as essential safety
related equipment. It shall be therefore classified according to IEC 61226 guidance and
environmentally qualified in accordance with the requirements of IEC 60780.

60951-3 © IEC:2009 – 9 –
Moreover, the detector assembly of such equipment is usually located within the reactor
building which is submitted to a harsh environment during and after an accident. The
qualification program, agreed upon between the manufacturer and the purchaser, shall take
into account specific conditions such as very high integrated dose (up to 1⋅10 Gy) as well as
combined high temperature, pressure and humidity.
5 Functional testing
5.1 General
Except where otherwise specified, all the tests specified in Clause 5 of IEC 60951-1 shall be
carried out.
The tests described hereinafter are only additional tests dedicated to the type of monitors
within the scope of the present standard. As for tests stated in IEC 60951-1, these tests are to
be considered as type tests, although any or all may be considered as acceptance tests by
agreement between manufacturer and purchaser.
These tests are carried out under standard conditions or with variation of the influence
quantities. They are listed in Table 1.
5.2 Reference sources
5.2.1 General
In addition to 5.2.5 of IEC 60951-1, the following requirements shall apply.
All tests shall be carried out using a monodirectional radiation field unless otherwise agreed
between manufacturer and purchaser.
5.2.2 Gamma
All tests shall be conducted with Cs-137 unless specified otherwise. As an alternative, Co-60
may be used. In this case correction shall be made for the difference in response of the
detector assembly between Co-60 and Cs-137. These radiation qualities are specified in the
ISO 4037 series. For very high dose rates an electron beam may be used.
The conventional true dose rate shall be known with an accuracy better than 5 %.
5.2.3 Beta
If the detector is sensitive to beta radiation, a test for the detector assembly response to
gamma radiation in the presence of beta radiation shall be conducted when agreed between
manufacturer and purchaser. The response of the detector assembly to beta radiation from a
Sr-90/Y-90 source shall be stated by the manufacturer. The reference beta radiation fields are
specified in the ISO 6980 series.
If the detector is not sensitive to beta radiation, the manufacturer should provide a
demonstration of this non-sensitivity by analysis.
5.2.4 Neutron
If the detector is sensitive to neutron radiation, the response to neutron radiation shall be
stated when agreed between manufacturer and purchaser. A test for neutron response shall
be carried out if the detector assembly is intended to be used in the presence of neutron
radiation. Cf-252 should be used for neutron tests. The reference neutron radiation fields are
specified in the ISO 8529 series.

– 10 – 60951-3 © IEC:2009
If the detector is not sensitive to neutron radiation, the manufacturer should provide a
demonstration of this non-sensitivity by analysis.
5.3 Performance characteristics
5.3.1 Reference response
In addition to 5.3.1 of IEC 60951-1, the following requirements shall apply.
The variation of response with photon radiation energy between 100 keV and 3 MeV shall be
within ±30 %.
In principle, this test should be performed at the same dose rate for each radiation energy. In
practice, this may not be possible, in which case the indicated dose rate of each radiation
energy should be corrected for the non-linearity (interpolated if necessary) at the indicated
dose rate and for the reference gamma radiation.
The energy corresponding to the medium sensitivity: S = (S + S )/2, shall be taken
medium max min
as a reference,
with S the maximum sensitivity in the energy range (between 100 keV and 3 MeV),
max
and S the minimum sensitivity in the energy range (between 100 keV and 3 MeV).
min
In this condition, S shall not exceed more than 30 % of S , and S shall not go
max medium min
below 30 % of S , which means (S – S )/S < 30 % and (S –
medium max medium medium medium
S )/S < 30 % (see Figure 1).
min medium
Sensitivity
Bad
S
max
<30 %
S = (S + S )/2
medium max min
<30 %
S
min
Good
Energy
100 keV 3 000 keV
IEC  977/09
Figure 1 – Energy response
If for specific applications it is necessary to extend the energy range, the energy response
shall be defined and agreed between the manufacturer and the purchaser. In this case it can
be performed either by real tests or by Monte Carlo simulations.

60951-3 © IEC:2009 – 11 –
5.3.2 Sensitivity and relative response for solid sources
5.3.2.1 General
In addition to 5.3.2 of IEC 60951-1, the following requirements shall apply.
5.3.2.2 Response to beta radiation
The response of the detector assembly to beta radiation from a Sr-90/Y-90 source shall be
stated by the manufacturer who shall also indicate the response to beta radiation for energies
up to 4 MeV.
If agreed upon between the manufacturer and the purchaser, the test for the response to beta
radiation shall be carried out and the response shall be expressed as the ratio of the detector
assembly indication to the conventional true absorbed dose rate (due to the Sr-90/Y-90
source) in air at the detector reference point when the detector is not present.
5.3.3 Variation of response with angle of incidence
5.3.3.1 Requirements
The response to a reference gamma source shall be within ±30 % of the reference response
(corresponding to 0°) for the following angles of incidence: ±15°, ±30°, ±45° ±60° in the plane
including the reference direction and in a plane perpendicular to that and also including the
reference direction.
The manufacturer shall state the relative variation of the response for ±90°.
If another range of angles is required, it shall be selected according to the agreement
between the manufacturer and the purchaser.
5.3.3.2 Test method
For this test, the reference point of the detector assembly shall be placed at a point of test
where the dose rate is known.
Firstly, the direction of radiation shall be changed in steps of 15° in a plane including the
reference direction specified by the manufacturer (reference response as determined in
5.2.1).
Secondly, the direction of radiation shall be changed in steps of 15° in a plane perpendicular
to that used above and also including the reference direction.
...