IEC 60951-1:2022

IEC 60951-1 ®
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 1: General requirements
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IEC 60951-1 ®
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 1: General requirements
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.120.20 ISBN 978-2-8322-6146-0
– 2 – IEC 60951-1:2022 RLV  IEC 2022
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 11
2 Normative references . 11
3 Terms and definitions . 13
4 Design principles . 18
4.1 General . 18
4.2 Basic requirements related to functions . 19
4.3 Measurement range . 21
4.4 Energy response . 21
4.5 Minimum detectable activity (or limit of detection) . 21
4.6 Precision (or repeatability) . 21
4.7 Accuracy (or relative error) Linearity . 21
4.8 Measurement time . 22
4.9 Response time . 22
4.10 Overload performance . 22
4.11 Ambient background shielding or compensation devices . 22
4.12 Requirements related to accident conditions . 23
4.13 Reliability . 23
4.14 User interface . 24
4.14.1 General . 24
4.14.2 Display of measured value . 24
4.14.3 Alarms . 24
4.14.4 Status indication . 25
4.14.5 Local indications . 25
4.15 System testing, maintenance facilities and ease of decontamination . 25
4.15.1 System testing . 25
4.15.2 Maintenance facilities . 26
4.15.3 Ease of decontamination . 26
4.16 Electromagnetic interference. 26
4.17 Power supplies . 26
4.18 Interfaces . 27
4.19 Sampling assembly . 27
4.20 Quality . 28
4.21 Type test report and certificate. 28
5 Functional testing . 29
5.1 General . 29
5.2 General test procedures . 30
5.2.1 General . 30
5.2.2 Tests performed under standard test conditions . 30
5.2.3 Tests performed with variation of influence quantities . 30
5.2.4 Calculations and/or numerical simulations . 33
5.2.5 Reference sources . 34
5.2.6 Statistical fluctuations . 35
5.3 Performance Radiation characteristics . 35
5.3.1 Reference response . 35

5.3.2 Sensitivity and relative response for solid sources . 35
5.3.3 Accuracy (relative error) Linearity . 36
5.3.4 Response to other artificial radionuclides . 37
5.3.5 Response to background radiation . 37
5.3.6 Precision (or repeatability) . 38
5.3.7 Stability of the indication . 38
5.3.8 Response time . 39
5.3.9 Overload test characteristics . 39
5.4 Electrical performance tests characteristics . 40
5.4.1 Alarm trip range . 40
5.4.2 Alarm trip stability . 40
5.4.3 Fault alarm . 41
5.4.4 Status indication and fault alarm tests . 41
5.4.5 Warm-up time — Detection and measuring assembly . 41
5.4.6 Influence of supply variations . 41
5.4.7 Short circuit withstand tests . 42
5.5 Environmental performance test characteristics . 43
5.5.1 Stability of performance after storage . 43
5.5.2 Mechanical tests characteristics . 43
5.5.3 Stability of performance with variation of temperature and humidity . 45
5.5.4 Electromagnetic compatibility . 46
Bibliography . 49

Table 1 – Overview of the standards covering the domain of radiation monitoring in
nuclear facilities . 7
Table 2 – Reference conditions and standard test conditions . 31
Table 3 – Tests performed under standard test conditions . 32
Table 4 – Tests performed with variation of influence quantities . 33

– 4 – IEC 60951-1:2022 RLV  IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS FACILITIES – INSTRUMENTATION SYSTEMS
IMPORTANT TO SAFETY – RADIATION MONITORING FOR
ACCIDENT AND POST-ACCIDENT CONDITIONS –

Part 1: General requirements
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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rights. IEC shall not be held responsible for identifying any or all such patent rights.
This redline version of the official IEC Standard allows the user to identify the changes made to
the previous edition IEC 60951-1:2009. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.

IEC 60951-1 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.
The text of this standard is based on the following documents:
Draft Report on voting
45A/1440/FDIS 45A/1449/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.
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.
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.
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.

– 6 – IEC 60951-1:2022 RLV  IEC 2022
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 on 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
Table 1. 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 given in Table 1.

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 series

– 8 – IEC 60951-1:2022 RLV  IEC 2022
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
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

– 10 – IEC 60951-1:2022 RLV  IEC 2022
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.

NUCLEAR POWER PLANTS FACILITIES – INSTRUMENTATION SYSTEMS
IMPORTANT TO SAFETY – RADIATION MONITORING FOR
ACCIDENT AND POST-ACCIDENT CONDITIONS –

Part 1: General requirements
1 Scope
This part of IEC 60951 provides general guidance on the design principles and performance
criteria for equipment to measure radiation and fluid (gaseous effluents or liquids) radioactivity
levels at nuclear power plants facilities during and after an accident design basis accidents
(DBA) and design extension conditions (DEC), including severe accident (SA). This document
is limited to equipment for continuous monitoring of radioactivity in design basis accidents
(DBA), design extension conditions (DEC), including severe accident (SA) and post-accident
conditions.
The purpose of this document is to lay down mandatory general requirements and give
examples of acceptable methods for equipment for continuous monitoring of radioactivity within
the plant facility during and after accident conditions in nuclear power plants using light water
reactors design basis accidents (DBA), design extension conditions (DEC), including severe
accident (SA) in nuclear facilities.
It specifies, for the equipment described above, the general characteristics, general test
procedures, radiation, electrical, safety and environmental characteristics and the identification
and certification of the equipment. If this equipment is part of a centralized system for
continuous radiation monitoring in a nuclear facility, there may be additional requirements from
other standards related to this system.
Sample extraction and laboratory analysis, which are essential to a complete programme of
effluent monitoring, are not within the scope of this document.
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 60038:20022009, IEC standard voltages
IEC 60068-2-1:2007, Environmental testing – Part 2-1: Tests – Test A: Cold
IEC 60068-2-2:2007, Environmental testing – Part 2-2: Tests – Test B: Dry heat
IEC 60068-2-6:2007, Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-14:2009, Environmental testing – Part 2-14: Tests – Test N: Change of
temperature
IEC 60068-2-30:2005, Environmental testing – Part 2-30: Tests – Test Db: Damp heat, cyclic
(12 h + 12 h cycle)
– 12 – IEC 60951-1:2022 RLV  IEC 2022
IEC 60068-2-78:20012012, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat,
steady state
IEC 60529, Degrees of protections provided by enclosures (IP code)
IEC 60780, Nuclear power plants – Electrical equipment of the safety system – Qualification
IEC/IEEE 60780-323:2016, Nuclear facilities – Electrical equipment important to safety –
Qualification
IEC 60880, Nuclear power plants – Instrumentation and control systems important to safety –
Software aspects for computer-based systems performing category A functions
IEC 60980, Recommended practices for Seismic qualification of electrical equipment of the
safety system for nuclear generating stations
IEC/IEEE 60980-344, Nuclear facilities – Equipment important to safety – Seismic qualification
IEC 60987, Nuclear power plants – Instrumentation and control important to safety – Hardware
design requirements for computer-based systems
IEC 61000-4-2:2008, Electromagnetic compatibility (EMC) – Part 4-2: Testing and
measurement techniques – Electrostatic discharge immunity test
IEC 61000-4-3:20062020, Electromagnetic compatibility (EMC) – Part 4-3: Testing and
measurement techniques – Radiated, radio-frequency, electromagnetic field immunity test
IEC 61000-4-4:20042012, Electromagnetic compatibility (EMC) – Part 4-4: Testing and
measurement techniques – Electrical fast transient/burst immunity test
IEC 61000-4-5:20052014, Electromagnetic compatibility (EMC) – Part 4-5: Testing and
measurement techniques – Surge immunity test
IEC 61000-4-6:20082013, Electromagnetic compatibility (EMC) – Part 4-6: Testing and
measurement techniques – Immunity to conducted disturbances, induced by radio-frequency
fields
IEC 61000-4-8:20012009, Electromagnetic compatibility (EMC) – Part 4-8: Testing and
measurement techniques – Power frequency magnetic field immunity test
IEC 61000-4-12:20062017, Electromagnetic compatibility (EMC) – Part 4-12: Testing and
measurement techniques – Ring wave immunity test
IEC 61000-4-18:2019, Electromagnetic compatibility (EMC) – Part 4-18: Testing and
measurement techniques – Damped oscillatory wave immunity test
IEC 61000-6-4:20062018, Electromagnetic compatibility (EMC) – Part 6-4: Generic standards
– Emission standard for industrial environments
IEC 61069-1:19912016, Industrial-process measurement, control and automation – Evaluation
of system properties for the purpose of system assessment – Part 1: General considerations
and methodology Terminology and basic concepts
IEC 61226, Nuclear power plants – Instrumentation, control and electrical power systems
important to safety – Classification of instrumentation and control functions Categorization of
functions and classification of systems

IEC 61504:20002017, Nuclear power plants facilities – Instrumentation and control systems
important to safety – Plant-wide radiation monitoring Centralized systems for continuous
monitoring of radiation and/or levels of radioactivity
IEC 61513:2011, Nuclear power plants – Instrumentation and control important to safety –
General requirements for systems
IEC 61559-2:2002, Radiation in nuclear facilities – Centralized systems for continuous
monitoring of radiation and/or levels of radioactivity – Part 2: Requirements for discharge,
environmental, accident, or post-accident monitoring functions
IEC 62138, Nuclear power plants – Instrumentation and control systems important for to safety
– Software aspects for computer-based systems performing category B or C functions
IEC 62262:2002, Degrees of protection provided by enclosures for electrical equipment against
external mechanical impacts (IK code)
IEC 62566:2012, Nuclear power plants – Instrumentation and control important to safety –
Development of HDL-programmed integrated circuits for systems performing category A
functions
IEC 62566-2:2020, Nuclear power plants – Instrumentation and control important to safety –
Development of HDL-programmed integrated circuits – Part 2: HDL-programmed integrated
circuits for systems performing category B or C functions
IEC 62705, Nuclear facilities – Instrumentation and control important to safety – Radiation
monitoring systems (RMS): Characteristics and lifecycle
ISO 2889:20092015, Sampling airborne radioactive materials from the stacks and ducts of
nuclear facilities
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
absolute error of measurement
difference between the measured value and the conventional quantity value of the measurand
3.2
acceptance test
contractual test to prove to the customer that the device fulfils certain specifications
[IEV 394-40-05]
3.2
accident conditions
deviations from normal operation more severe than anticipated operational occurrences,
including design basis accidents and severe accidents
[IAEA Safety Glossary, 2007 edition]

– 14 – IEC 60951-1:2022 RLV  IEC 2022
3.3
aerodynamic equivalent diameter
diameter of unit-density sphere having the same gravitational settling velocity as the particle in
question of concern
Note 1 to entry: The aerodynamic equivalent diameter concerns particles with a diameter from 0,1 μm to 2 mm.
[SOURCE: IEV 393-11-41 IEC 60050-395:2014, 395-02-34]
3.4
anticipated operational occurrence
operational process deviating from normal operation which is expected to occur at least once
during the operational lifetime of a nuclear power plant but which, in view of appropriate design
provisions, does not cause any significant damage to items important to safety or lead to
accident conditions
[IAEA Safety Glossary, 2007 edition]
3.4
coefficient of variation
ratio of the standard deviation s to the arithmetic mean x of a set of n measurements x given
i
by the following formula:
[IEV 394-40-14]
3.5
collection efficiency
percentage retained by the filter of the total amount of particles initially in a known volume of
air passed through the filter
[ISO 2889]
3.7
conventionally true value
value attributed to a particular quantity and accepted, sometimes by convention, as having an
uncertainty appropriate for a given purpose
[IEV 394-40-10]
NOTE For example, a value and its uncertainty determined from a primary or a secondary standard, or by a
reference instrument which has been calibrated against a primary or secondary standard, may be taken as the
conventionally true value.
3.6
conventional quantity value
quantity value attributed by agreement to a quantity for a given purpose
Note 1 to entry: The term “conventional true quantity value” is sometimes used for this concept, but its use is
discouraged.
Note 2 to entry: Sometimes a conventional quantity value is an estimate of a true quantity value.
Note 3 to entry: A conventional quantity value is generally accepted as being associated with a suitably small
measurement uncertainty, which might be zero.

3.8
decision threshold
fixed value of the activity which allows a decision to be made for each measurement with a
given probability of error as whether the registered measurement includes a contribution from
the physical effect
[IEC 60761-1,3.9]
NOTE The statistical test shall be designed such that the probability of wrongly rejecting the hypothesis (error of
the first kind) is equal to a given value α. In the case of this standard, α equals 5 %.
3.9
Design Basis Accident (DBA)
accident conditions against which a facility is designed according to established design criteria,
and for which the damage to the fuel and the release of radioactive material are kept within
authorized limits
[IAEA Safety Glossary, 2007 edition]
3.10
detection limit
smallest true value of the measurand which is detectable by the measuring method
[IEC 60761-1,3.10]
NOTE The detection limit is the smallest true value of the measurand which is associated with the statistical test
and hypotheses by the following characteristics: if in reality the true value is equal to or exceeds the detection limit,
the probability of wrongly not rejecting the hypothesis (error of the second kind) shall be at most equal to a given
value β. For this standard, β equals 5 %.
3.7
effective range of measurement
absolute value of the difference between the two limits of a nominal range
Note 1 to entry: In the nominal range the performance of a piece of equipment or an assembly meets the
requirements of its specifications.
[IEV 394-40-16]
3.8
electron beam
electron flux emitted from one source and moving along the exactly determined tracks with very
great velocities
Note 1 to entry: Such beam routed to a detector causes extremely high dose rates.
[SOURCE: IEC 60050-841:2004, 841-30-01]
3.9
experimental standard deviation
for a series of n measurements of the same measurand, the quantity s characterizes the
dispersion of the results and is given by the formula:
n
(x − x)
∑ i
i=1
s =
n −1
x being the result of the ith measurement and x being th
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