IEC 60951-3:2022

IEC 60951-3 ®
Edition 3.0 2022-11
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Nuclear power plants facilities – Instrumentation systems important to safety –
Radiation monitoring for accident and post-accident conditions –
Part 3: Equipment for continuous high range area gamma monitoring

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IEC 60951-3 ®
Edition 3.0 2022-11
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Nuclear power plants facilities – Instrumentation systems important to safety –
Radiation monitoring for accident and post-accident conditions –
Part 3: Equipment for continuous high range area gamma monitoring
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.120.20 ISBN 978-2-8322-6055-5
– 2 – IEC 60951-3:2022 RLV © IEC 2022
CONTENTS
FOREWORD . 3
INTRODUCTION . 2
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 11
4 Design principles . 11
4.1 General . 11
4.2 Range of measurement . 11
4.3 Accuracy (relative error). 11
4.4 Location of sensors . 11
4.5 Detector radiation response characteristics Response for other radiation
sources . 12
4.6 Requirements related to accident conditions . 12
5 Functional testing . 12
5.1 General . 12
5.2 Reference sources . 13
5.2.1 General . 13
5.2.2 Gamma . 13
5.2.3 Beta. 13
5.2.4 Neutron . 13
5.3 Performance characteristics . 14
5.3.1 Reference response . 14
5.3.2 Sensitivity and relative response for solid other radiation sources . 15
5.3.3 Variation of response with angle of incidence . 16
5.3.4 Environmental performance . 16
Bibliography . 17

Figure 1 – Energy response .

Table 1 – Overview of the standards covering the domain of radiation monitoring in
nuclear facilities . 7
Table 2 – Additional tests to complement the general tests required in IEC 60951-1 . 13

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS
FACILITIES – INSTRUMENTATION SYSTEMS
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
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This redline version of the official IEC Standard allows the user to identify the changes made to
the previous edition IEC 60951-3:2009. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.

– 4 – IEC 60951-3:2022 RLV © IEC 2022
IEC 60951-3 has been prepared by subcommittee 45A: Instrumentation, control and electrical
power systems of nuclear facilities, of IEC technical committee 45: Nuclear instrumentation.
It is an International Standard.
This third edition cancels and replaces the second edition published in 2009. This edition
constitutes a technical revision.
The main technical changes with regard to the previous edition are as follows:
• Title modified.
• To be consistent with the categorization of the accident condition.
• To update the references to new standards published since the second edition.
• To update the terms and definitions.
This standard is to be read in conjunction with IEC 60951-1.
The text of this standard is based on the following documents:
Draft Report on voting
45A/1441/FDIS 45A/1450/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts of IEC 60951 series, under the general title Nuclear facilities – Instrumentation
systems important to safety – Radiation monitoring for accident and post-accident conditions,
can be found on the IEC website.
Future documents in this series will carry the new general title as cited above. Titles of existing
documents in this series will be updated at the time of the next edition.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.

INTRODUCTION
a) Technical background, main issues and organisation of the standard
This IEC standard specifically focuses on radiation monitoring systems (RMSs) used for
accident and post-accident operations.
According to the lessons learned from the Fukushima-Daiichi accident, it re-acknowledges a
need to provide operators with reliable radiation monitoring data to allow them to understand
the plant state during and after the accident conditions. To support the design of such
instrumentation, it is necessary to provide general guidance on the design principles and
performance criteria for radiation monitoring instrumentation applied during and after the
accident conditions. In addition, the scope of IEC 63147 which provides criteria for accident
monitoring instrumentation for nuclear power generating stations has evolved to include severe
accident (SA) to accident conditions.
Thus to address the specific lessons learned from the Fukushima-Daiichi accident, this standard
categorizes accident condition into design basis accidents (DBA) and design extension
conditions (DEC) including severe accident (SA).
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
equipment characteristics when developing systems for accident monitoring conditions. Some
specific instrument characteristics such as measurement range, required energy response, and
ambient environment requirements environmental withstanding conditions 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 applicable to equipment for continuous monitoring of radiation level
important to safety intended for use during design basis accidents (DBA) and design extension
conditions (DEC) including severe accident (SA), and post-accident conditions. 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
The IEC 60951 series of standards are at the third level in the hierarchy of SC 45A standards.
They provide guidance on specification, 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. The IEC 60761 series provides 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 requirements 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. In addition, IEC 62705 provides guidance on the application of existing
IEC/ISO standards covering design and qualification of RMS. An overview of the standards
covering the radiation monitoring in nuclear facilities is presented in Table 1.

– 6 – IEC 60951-3:2022 RLV © IEC 2022
IEC 63147/IEEE Std 497™ provides general guidance for accident monitoring instrumentation.
IEEE Std 497™ was directly adopted as a joint logo standard and a technical report, IEC TR
63123, was prepared to discuss the application of the joint standard within the IEC context.
The structure of this standard is adapted from the structure of IEC 63147/IEEE Std 497™, and
the technical requirements of this standard are consistent with the requirements given in
IEC 63147/IEEE Std 497™ together with the application guidance given in IEC TR 63123.

Table 1 – Overview of the standards covering
the domain of radiation monitoring in nuclear facilities
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
Central system N/A IEC 61504 IEC 61559

IEC
Developer ISO
SC45A SC45B
Sampling Calibration Normal
Normal
Scope (Normal (Normal operation, DBA DEC
operation
operation) operation) AOO
IEC 62302,
Radioactive noble
ISO 4037-1, IEC 60951-1, IEC 60761-
gas off-line ISO 2889 N/A N/A
ISO 4037-3 IEC 60951-2 1,
monitoring
IEC 60761-3
IEC 60761-
Radioactive aerosol ISO 4037-1, IEC 60951-1,
ISO 2889 N/A N/A 1,
off-line monitoring ISO 4037-3 IEC 60951-2
IEC 60761-2
IEC 60761-
Radioactive iodine ISO 4037-1,
IEC 60951-1,
ISO 2889 N/A N/A 1,
off-line monitoring ISO 4037-3 IEC 60951-2
IEC 60761-4
Liquid off-line
N/A N/A N/A N/A N/A IEC 60861
monitoring
IEC 62303,
Tritium off-line IEC 60761-
N/A N/A N/A N/A N/A
monitoring 1,
IEC 60761-5
On-line or in-line ISO 4037-1, IEC 60951-1,
N/A IEC 60768 N/A N/A
monitoring ISO 4037-3 IEC 60951-4
ISO 4037-1,
Area monitoring N/A IEC 61031 IEC 60951-1, IEC 60951-3 IEC 60532
ISO 4037-3
Centralized system N/A N/A IEC 61504, IEC 60960 N/A IEC 61559-1
IEC 61513, IEC 60880,
IEC 60987, IEC 61226,
Classification/basic
N/A N/A IEC 62138, IEC 62566, N/A N/A
requirements
IEC 62566-2, IEC 62645,
IEC 61250
IEC/IEEE 60780-323,
Qualification N/A N/A IEC/IEEE 60980-344, N/A IEC 62706
IEC 62003
– 8 – IEC 60951-3:2022 RLV © IEC 2022
For more details on the structure of the IEC SC 45A standard series, see the 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 important to safety.
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.
The IEC SC 45A standard series comprises a hierarchy of four levels. The top-level documents
of the IEC SC 45A standard series are IEC 61513 and IEC 63046.
IEC 61513 provides general requirements for instrumentation and control (I&C) systems and
equipment that are used to perform functions important to safety in nuclear power plants
(NPPs). IEC 63046 provides general requirements for electrical power systems of NPPs; it
covers power supply systems including the supply systems of the I&C systems.
IEC 61513 and IEC 63046 are to be considered in conjunction and at the same level. IEC 61513
and IEC 63046 structure the IEC SC 45A standard series and shape a complete framework

establishing general requirements for instrumentation, control and electrical power systems for
nuclear power plants.
IEC 61513 and IEC 63046 refer directly to other IEC SC 45A standards for general
requirements for specific topics, such as categorization of functions and classification of
systems, qualification, separation, defence against common cause failure, control room design,
electromagnetic compatibility, human factors engineering, cybersecurity, software and
hardware aspects for programmable digital systems, coordination of safety and security
requirements and management of ageing. The standards referenced directly at this second level
should be considered together with IEC 61513 and IEC 63046 as a consistent document set.
At a third level, IEC SC 45A standards not directly referenced by IEC 61513 or by IEC 63046
are standards related to specific requirements for specific equipment, technical methods, or
activities. Usually these documents, which make reference to second-level documents for
general requirements, can be used on their own.
A fourth level extending the IEC SC 45 standard series, corresponds to the Technical Reports
which are not normative.
The IEC SC 45A standards series consistently implements and details the safety and security
principles and basic aspects provided in the relevant IAEA safety standards and in the relevant
documents of the IAEA nuclear security series (NSS). In particular this includes the IAEA
requirements SSR-2/1 , establishing safety requirements related to the design of nuclear power
plants (NPPs), the IAEA safety guide SSG-30 dealing with the safety classification of structures,
systems and components in NPPs, the IAEA safety guide SSG-39 dealing with the design of
instrumentation and control systems for NPPs, the IAEA safety guide SSG-34 dealing with the
design of electrical power systems for NPPs, the IAEA safety guide SSG-51 dealing with human
factors engineering in the design of NPPs and the implementing guide NSS17 for computer
security at nuclear facilities. The safety and security terminology and definitions used by the
SC 45A standards are consistent with those used by the IAEA.
IEC 61513 and IEC 63046 have adopted a presentation format similar to the basic safety
publication IEC 61508 with an overall life-cycle framework and a system life-cycle framework.
Regarding nuclear safety, IEC 61513 and IEC 63046 provide the interpretation of the general
requirements of IEC 61508-1, IEC 61508-2 and IEC 61508-4, for the nuclear application sector.
In this framework, IEC 60880, IEC 62138 and IEC 62566 correspond to IEC 61508-3 for the
nuclear application sector.
IEC 61513 and IEC 63046 refer to ISO 9001 as well as to IAEA GSR part 2 and IAEA GS-G-3.1
and IAEA GS-G-3.5 for topics related to quality assurance (QA).
At level 2, regarding nuclear security, IEC 62645 is the entry document for the IEC/SC 45A
security standards. It builds upon the valid high level principles and main concepts of the
generic security standards, in particular ISO/IEC 27001 and ISO/IEC 27002; it adapts them and
completes them to fit the nuclear context and coordinates with the IEC 62443 series. At level
2, IEC 60964 is the entry document for the IEC/SC 45A control rooms standards, IEC 63351 is
the entry document for the human factors engineering standards and IEC 62342 is the entry
document for the ageing management standards.
NOTE 1 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, chemical hazards, process energy hazards) international or national
standards would be applied.
NOTE 2 IEC TR 64000 provides a more comprehensive description of the overall structure of the IEC SC 45A
standards series and of its relationship with other standards bodies and standards.

– 10 – IEC 60951-3:2022 RLV © IEC 2022
NUCLEAR POWER PLANTS
FACILITIES – INSTRUMENTATION SYSTEMS
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
facilities for accident and post-accident conditions. This document categorizes accident
conditions into design basis accidents (DBA) and design extension conditions (DEC), including
severe accident (SA).
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 document, unless otherwise stated.
The purpose of this document is to lay down general requirements for equipment for continuous
high range area gamma monitoring of radiation within the facility during and after accident
conditions in nuclear facilities.
This document 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 facility 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
in the scope of IEC 60532.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 60951-1:20092022, Nuclear power plants facilities – Instrumentation systems 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 and electrical power systems
important to safety – classification of instrumentation and control functions Categorization of
functions and classification of systems
IEC 62705, Nuclear power plants – Instrumentation and control important to safety – Radiation
monitoring systems (RMS): Characteristics and lifecycle

ISO 4037 (all parts), Radiological protection – 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 Neutron reference radiations fields
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60951-1 apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
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 document, unless otherwise stated.
The radiation monitor classified for functions important to safety shall comply with the
requirements relating to the characteristics and lifecycle of RMS defined in IEC 62705 and the
standards referenced in IEC 62705 (e.g. IEC 61226).
4.2 Range of measurement
The purchaser shall specify the required effective range of measurement and the radiation
sources specific to the plant facility 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 60951-1:2022, 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 facility specific. Therefore, the locations in which
the monitoring equipment is required shall be determined according to the plant facility design.
For nuclear power plants, usually equipment is located within the reactor containment. It shall
be located to provide maximum coverage of the areas being monitored and to minimize

– 12 – IEC 60951-3:2022 RLV © IEC 2022
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 Response for other radiation sources
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 4.12 of IEC 60951-1:2022, 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.
For nuclear power plants, 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
Gy) as well as
into account specific conditions such as very high integrated dose (up to 1×10
combined high temperature, pressure and humidity.
There may be cases where diversity or multiplexing in detector assembly or monitoring channel
is required for facility accident countermeasures.
5 Functional testing
5.1 General
Except where otherwise specified, all the tests specified in Clause 5 of IEC 60951-1:2022 shall
be carried out.
The tests described hereinafter are only additional tests dedicated to the type of monitors within
the scope of the present document. 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 Table 2.

Table 2 – Additional tests to complement the general tests required in IEC 60951-1
Tests Tests conditions Limits of variation of Reference (subclause)
indication
Range of photon radiation ±30 % of the medium
Reference response 5.3.1
energy between 80 keV and sensitivity between 100 keV
7 MeV
and 3 MeV
Value to be stated by
agreement otherwise if
necessary
Response to beta radiation Range of beta radiation In accordance with 5.3.2.2
energy from a Sr-90/Y-90 manufacturer's
source up to 4 MeV specifications
Variation of response with Different angles of ±30 % 5.3.3
angle of incidence incidence (±15°, ±30°, ±45°
±60°) in the plane including
the reference direction and
in a plane perpendicular to
that.
NOTE For assemblies having a non-linear scale, a linear instrument may be substituted for the indicating meter of
the assembly to verify the performance specified in this table.

5.2 Reference sources
5.2.1 General
In addition to 5.2.5 of IEC 60951-1:2022, 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 value of 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.
– 14 – IEC 60951-3:2022 RLV © IEC 2022
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 60951-1:2022, the following requirements shall apply.
The variation of response with photon radiation energy between 100 keV and 3 MeV shall be
within ±30 %.
For assemblies intended for use in energies higher than 3 MeV, the variation shall be subject
to agreement between the purchaser and manufacturer.
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 following energies should be used for low air kerma rates (taken from the ISO 4037 series):
• Mean energy (keV): quality (tube voltage, kV);
• 100 keV(N-120) or 109 keV(L-125);
• 118 keV(N-150);
• 164 keV(N-200) or 149 keV(L-170);
• 208 keV(N-250) or 211 keV(L-240);
• 662 keV (Cs-137);
• 1 250 keV (Co-60).
Energy response to other photon energies might be demonstrated by real tests or Monte Carlo
simulations.
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 below 30 %
max medium min
of S , which means (S – S )/S < 30 % and (S – S )/S < 30 % (see
medium max medium medium medium min medium
Figure 1).
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
The energy corresponding to the average energy range shall be taken as a reference energy.
For this purpose, Cs-137 or Co-60 should be chosen.
The variation of response for other energies within the energy range shall be within ±30 % of
the reference response to the reference energy.
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.
For specific severe accident applications, additional thermal shielding may be required. This
may additionally affect the energy response of the system; in this case the required energy
response shall be agreed between purchaser and manufacturer.
5.3.2 Sensitivity and relative response for solid other radiation sources
5.3.2.1 General
In addition to 5.3.2 of IEC 60951-1:2022, 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 value of absorbed dose rate (due to the Sr-90/Y-
90 source) in air at the detector reference point when the detector is not present.
The detector assembly shall be exposed at 0° angle of radiation incidence to beta reference
radiation specified in ISO 6980.

– 16 – IEC 60951-3:2022 RLV © IEC 2022
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°.
The results should be expressed as a ratio of the response per unit dose rate for each radiation
source utilized to the response per unit dose rate for zero degrees angle of incidence.
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
The assembly shall be mounted so as to most conveniently enable measurements to be made
at the required angle.
For this test, the reference point of the detector assembly shall be placed at a point of test
where the dose rate is known. The photon radiation qualities of the narrow spectrum series and
the gamma sources Cs-137 specified in the ISO 4037 series should be used if possible.
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.
a) The direction of radiation shall be changed in steps of 15° in a plane including the calibration
direction specified by the manufacturer and the response determined throughout the range
of angles specified in 5.3.3.1.
b) The procedure of a) above shall be repeated for the plane perpendicular to that used in a),
but still including the calibration direction.
5.3.4 Environmental performance
Tests considering the dose rate, temperature, pressure, humidity and vibration shall be
performed by assuming the environment of design extension conditions (DEC) including severe
accident (SA).
Bibliography
IEC 60532, Radiation protection instrumentation – Installed dose rate meters, warning
assemblies and monitors – X and gamma radiation of energy between 50 keV and 7 MeV
IEC 60761-1:2002, Equipment for continuous monitoring of radioactivity in gaseous effluents –
Part 1: General requirements
IEC 60761-2:2002, Equipment for continuous monitoring of radioactivity i
...