IEC 60768:2009

Nuclear power plants - Instrumentation important to safety - Equipment for continuous in-line or on-line monitoring of radioactivity in process streams for normal and incident conditions

IEC 60768:2009 provides criteria for the design, selection, testing, calibration and functional location of equipment for the monitoring of radioactive substances within plant-process streams during normal operation conditions and anticipated operational occurrences. Is only applicable to continuous in-line or on-line measurement. This new edition includes the following significant technical changes with respect to the previous edition:
- it clarifies the definitions;
- up-dates the reference to new standards published since the first issue;
- updates the units of radiation.
This publication is to be read in conjunction with IEC 60951-1:2009, IEC 60951-2:2009, IEC 60951-3:2009 and IEC 60951-4:2009.

Centrales nucléaires de puissance - Instrumentation importante pour la sûreté - Matériels pour la surveillance des rayonnements en continu, interne et externe, au niveau des fluides de procédés pour les conditions de fonctionnement normal et incidentel

La CEI 60768:2009 établit des recommandations applicables à la conception, aux choix, aux essais, à l'étalonnage et à l'emplacement fonctionnel de l'équipement de surveillance des matières radioactives présentes dans les fluides de processus des centrales en condition de fonctionnement normal et durant les incidents de fonctionnement prévus. Est uniquement applicable aux mesures internes ou externes faites en continu. Cette nouvelle édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- clarifie les définitions;
- met à jour les références aux nouvelles normes publiées depuis la première édition;
- met à jour les unités relatives aux rayonnements.
Cette publication doit être lue conjointement avec la CE I 60951-1:2009, la CEI 60951-2:2009, la CEI 60951-3:2009 et la CEI 60951-4:2009.

General Information

• Status: Published
• Publication Date: 28-Apr-2009
• ICS: 27.120.10 - Reactor engineering
• Technical Committee: SC 45A - Instrumentation, control and electrical power systems of nuclear facilities
• Current Stage: PPUB - Publication issued
• Start Date: 29-Apr-2009
• Completion Date: 15-May-2009

Standards Content (Sample)

IEC 60768 ®
Edition 2.0 2009-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Nuclear power plants – Instrumentation important to safety – Equipment for
continuous in-line or on-line monitoring of radioactivity in process streams for
normal and incident conditions

Centrales nucléaires de puissance – Instrumentation importante pour la sûreté –
Matériels pour la surveillance des rayonnements en continu, interne et externe,
au niveau des fluides de procédés pour les conditions de fonctionnement
normal et incidentel
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IEC 60768 ®
Edition 2.0 2009-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Nuclear power plants – Instrumentation important to safety – Equipment for
continuous in-line or on-line monitoring of radioactivity in process streams for
normal and incident conditions

Centrales nucléaires de puissance – Instrumentation importante pour la sûreté –
Matériels pour la surveillance des rayonnements en continu, interne et externe,
au niveau des fluides de procédés pour les conditions de fonctionnement
normal et incidentel
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
W
CODE PRIX
ICS 27.120.20 ISBN 978-2-88910-288-4
– 2 – 60768 © IEC:2009
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.8
2 Normative references .8
3 Terms and definitions .10
4 Design principles.10
4.1 Basic requirements related to functions .10
4.2 Measurement range .11
4.3 Energy response .11
4.4 Minimum detectable activity (or detection limit) .12
4.5 Precision (or repeatability).12
4.6 Accuracy (or relative error).12
4.7 Measurement time.13
4.8 Response time .13
4.9 Overload performance.13
4.10 Ambient background shielding or compensation devices .13
4.11 Requirements related to incident conditions .14
4.12 Reliability .14
4.13 User interface.14
4.13.1 General .14
4.13.2 Display of measured value.15
4.13.3 Alarms.15
4.13.4 Status indication.15
4.13.5 Local indications.16
4.14 System testing, maintenance facilities and ease of decontamination .16
4.14.1 System testing.16
4.14.2 Maintenance facilities .16
4.14.3 Ease of decontamination .17
4.15 Electromagnetic interference .17
4.16 Power supplies.17
4.17 Interfaces .17
4.18 In-line detectors mechanical features.18
4.18.1 General requirements .18
4.18.2 Pressure-containing parts.18
4.18.3 Materials .18
4.18.4 Verification of material processing .19
4.19 Quality .19
4.20 Type test report and certificate .19
5 Functional testing .20
5.1 General .20
5.2 General test procedures .21
5.2.1 General .21
5.2.2 Tests performed under standard test conditions .21
5.2.3 Tests performed with variation of influence quantities.21
5.2.4 Calculations and/or numerical simulations .21
5.2.5 Reference sources .22

60768 © IEC:2009 – 3 –
5.2.6 Statistical fluctuations.22
5.3 Performance characteristics .23
5.3.1 Reference response .23
5.3.2 Accuracy (relative error) .23
5.3.3 Response to other artificial radionuclides .24
5.3.4 Response to background radiation.24
5.3.5 Precision (or repeatability).25
5.3.6 Stability of the indication .25
5.3.7 Response time .25
5.3.8 Overload test.26
5.4 Electrical performance tests .26
5.4.1 Alarm trip range.26
5.4.2 Alarm trip stability.27
5.4.3 Fault alarm .27
5.4.4 Status indication and fault alarm tests .27
5.4.5 Warm-up time – Detection and measuring assembly.27
5.4.6 Influence of supply variations .28
5.4.7 Short circuit withstand tests.29
5.5 Environmental performance test .29
5.5.1 Stability of performance after storage .29
5.5.2 Mechanical tests.30
5.5.3 Stability of performance with variation of ambient and stream
conditions.31
5.5.4 Electromagnetic compatibility .33
Bibliography.39

Table 1 – Reference conditions and standard test conditions .36
Table 2 – Tests performed under standard test conditions .37
Table 3 – Tests performed with variation of influence quantities.38

– 4 – 60768 © IEC:2009
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS –
INSTRUMENTATION IMPORTANT TO SAFETY –
EQUIPMENT FOR CONTINUOUS IN-LINE OR ON-LINE
MONITORING OF RADIOACTIVITY IN PROCESS STREAMS
FOR NORMAL AND INCIDENT CONDITIONS

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
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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 60768 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 1983. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
• to clarify the definitions.
• to up-date the reference to new standards published since the first issue.
• to update the units of radiation.

60768 © IEC:2009 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
45A/729/FDIS 45A/741/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.
This International Standard is to be read in conjunction with IEC 60951:2009.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – 60768 © IEC:2009
INTRODUCTION
a) Technical background, main issues and organisation of this Standard
This IEC standard specifically focuses on process streams radiation monitoring systems used
for normal and incident 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 normal and incident 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.
b) Situation of this Standard in the structure of the IEC SC 45A standards series
IEC 60768 is at the third level in the hierarchy of SC 45A standards. It provides guidance on
the design and testing of process streams radiation monitoring equipment used for normal
and incident conditions. Other standards developed by SC 45A and SC 45B provide guidance
on instruments used for monitoring radiation as part of normal operations and also for
accident and post accident conditions. 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 60951 standard series establishes
requirements for equipment for radiation monitoring for accident and post accident conditions.
Finally, ISO standard 2889 gives guidance on gas and particulate sampling. The relationship
between these various radiation monitoring standards is given in the table below:
Developer ISO SC 45A – Process and safety 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 2 IEC 60761 series and IEC 62302 (noble
iodine with sampling gases only)
(OFF LINE)
Liquid with sampling N/A N/A IEC 60861
(OFF LINE)
Process streams N/A IEC 60951-1 and 4 IEC 60768 N/A
(gaseous effluents,
steam or liquid)
without sampling
(ON or IN-LINE)
Area monitoring N/A IEC 60951-1 and 3 IEC 60532
Central System N/A IEC 61504 IEC 61559
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.
60768 © IEC:2009 – 7 –
d) Description of the structure of the IEC SC 45A standard series and relationships
with other IEC documents, IAEA and 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 45 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 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.

– 8 – 60768 © IEC:2009
NUCLEAR POWER PLANTS –
INSTRUMENTATION IMPORTANT TO SAFETY –
EQUIPMENT FOR CONTINUOUS IN-LINE OR ON-LINE
MONITORING OF RADIOACTIVITY IN PROCESS STREAMS
FOR NORMAL AND INCIDENT CONDITIONS

1 Scope
Information regarding the levels of radioactive materials in defined process streams of nuclear
power plants is necessary to evaluate plant performance, to provide at an early stage
information on possible radioactive releases, and to allow plant operators to take actions to
control these releases.
This International Standard provides criteria for the design, selection, testing, calibration and
functional location of equipment for the monitoring of radioactive substances within plant-
process streams during normal operation conditions and anticipated operational occurrences.
IEC 60768 is only applicable to continuous in-line or on-line measurement, i.e. monitors of
which the detector measures radioactivity by being positioned in the process stream (i.e.
immerged in) or adjacent to the process stream (i.e. viewing straight through a pipe or tank).
It does not apply to monitors of which the detector measures a representative proportion of
the stream at some remote location (sampling assembly), which are within the scope of
IEC 60861.
IEC 60768 is only applicable to monitors for normal and incident conditions. Process stream
radiation monitoring equipment for accident and post-accident conditions are within the scope
of IEC 60951-4.
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 60038:1983, 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)
IEC 60068-2-78:2001, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat,
steady state
IEC 60529:1989, Degrees of protection provided by enclosures (IP Code)

60768 © IEC:2009 – 9 –
IEC 60780:1998, Nuclear power plants – Electrical equipment of the safety system –
Qualification
IEC 60880:2006, Nuclear power plants – Instrumentation and control systems important to
safety – Software aspects for computer-based systems performing category A functions
IEC 60951-1:2009, Nuclear power plants – Instrumentation important to safety – Radiation
monitoring for accident and post accident conditions – Part 1: General requirements
IEC 60980:1989, Recommended practices for seismic qualification of electrical equipment of
the safety system for nuclear generating stations
IEC 60987:2007, Nuclear power plants – Instrumentation and control important to safety –
Hardware design requirements for computer-based systems
IEC 61000-4-2:2008, Electromagnetic compatibility (EMC) – Part 4-2: Testing and
measurement techniques – Electrostatic discharge immunity test
IEC 61000-4-3:2006, Electromagnetic compatibility (EMC) – Part 4-3: Testing and
measurement techniques – Radiated, radio-frequency, electromagnetic field immunity test
IEC 61000-4-4:2007, Electromagnetic compatibility (EMC) – Part 4-4: Testing and
measurement techniques – Electrical fast transient/burst immunity test
IEC 61000-4-5:2005, Electromagnetic compatibility (EMC) – Part 4-5: Testing and
measurement techniques – Surge immunity test
IEC 61000-4-6:2008, Electromagnetic compatibility (EMC) – Part 4-6: Testing and
measurement techniques – Immunity to conducted disturbances, induced by radio-frequency
fields
IEC 61000-4-8:1993, Electromagnetic compatibility (EMC) – Part 4-8: Testing and
measurement techniques – Power frequency magnetic field immunity test
IEC 61000-4-12:2006, Electromagnetic compatibility (EMC) – Part 4-12: Testing and
measurement techniques – Ring wave immunity test
IEC 61000-4-18:2006, Electromagnetic compatibility (EMC) – Part 4-18: Testing and
measurement techniques – Damped oscillatory wave immunity test
IEC 61000-6-4:2006, Electromagnetic compatibility (EMC) – Part 6-4: Generic standards –
Emission standard for industrial environments
IEC 61069-1:1991, Industrial-process measurement and control – Evaluation of system
properties for the purpose of system assessment – Part 1: General considerations and
methodology
IEC 61226:2005, Nuclear power plants – Instrumentation and control systems important to
safety – Classification of instrumentation and control functions
IEC 61504:2000, Nuclear power plants – Instrumentation and control systems important to
safety – Plant-wide radiation monitoring
IEC 62138:2004, Nuclear power plants – Instrumentation and control important for safety –
Software aspects for computer-based systems performing category B or C functions
IEC 62262:2002, Degrees of protection provided by enclosures for electrical equipment
against external mechanical impacts (IK code)
—————————
To be published.
– 10 – 60768 © IEC:2009
3 Terms and definitions
The terms and definitions given in IEC 60951-1:2009 apply.
4 Design principles
4.1 Basic requirements related to functions
The main purpose of equipment for continuous in-line or on-line monitoring of radioactivity in
process streams is to continuously measure radiation levels in appropriated pipes or tanks,
either by being positioned in them (i.e. immerged in the process stream) or adjacent to them
(i.e. viewing straight through the process stream). These radiation measurements are
displayed locally and/or in control rooms to keep plant operators aware of current radiological
conditions. This information is used for control purposes and/or initiation of protective actions.
Therefore, the equipment concerned by this standard is capable of actuating alarms and
providing inputs to other plant systems and processes to isolate processes at abnormal
radiation levels.
The basic requirements for the design, selection, testing, calibration and functional location of
equipment for continuous in-line and on-line monitoring of radioactivity in process streams are
plant specific.
Process radiation monitors within the scope of this standard can be classified into two basic types:
– in-line monitors: the detector is located directly in the process stream (pipe, stack, tank,
duct, etc.),
– on-line monitors: the detector faces directly the process stream.
For the purpose of critical data collection, these monitors may be designed to withstand
adverse environmental and seismic conditions, during and after an accident.
Radiation Monitoring requirements and Radiation Monitoring System design should be
addressed early in Plant design to establish effective monitoring at the appropriate sensitivity
level. Thus, for maximum performance capability, the following procedure should be followed
by the purchaser and the manufacturer:
– Establish the required measurement characteristics (purchaser):
– Determine the scenarios of normal conditions and anticipated operational occurrences,
and the corresponding source terms (preponderant isotopes to be measured by the
monitor), including their chemical composition
– Determine the essential information required by the plant operator or the control
system to initiate actions, the functions assigned to the equipment for continuous
radiation monitoring and classify them according to IEC 61226 guidance
– Determine the optimum points of measurement taking into account installation
conditions (location, interfaces to plant protection features, ambient conditions and
qualification requirements, electrical connections through safety barriers, etc)
– Determine the stream characteristics (physical, chemical and dynamic characteristics
of the stream to be monitored) such as: type of fluid, thermodynamic state,
temperature range and rate of change, pressure range and rate of change,
radiochemical properties, etc.
– If necessary, calculate the activity transfers (propagation through pipes or ducts and
through the safety barriers), in order to determine the activity spectrums and the
background at the point of measurement
– Determine the time profile of the postulated release and the required range of
measurement and response time of the complete channel (including the time to send
or to display the information to the plant operator or the control system)

60768 © IEC:2009 – 11 –
– Determine the gross characteristics of the detectors (type of radiation and
measurement, sensitivity and range of measurement, energy response and overload
performance, etc)
– Determine the acceptable false alarm rate taking into account the plant conditions and
the consequences of error in measurement, and specify the precision and accuracy
needed to stay under this threshold
– Check the metrological characteristics of the chosen instrument (agreement between the
purchaser and the manufacturer):
– Calculate the response time of the instrument (measure time related to a specified
accuracy + time for the apparatus to provide an alarm)
– Calculate, at the point of measurement, geometric detection efficiency, decision
threshold and minimum detectable activity (or detection limit), taking into account the
appropriate shielding
– For each characteristic of the instrument, the manufacturer should specify its
variations as a function of the corresponding influence quantities (or variable
parameters). These influence quantities (or variable parameters) should be, at least:
• activity spectrum and time profile of the activity spectrum (during transient operating
conditions) of the source to be measured
• activity spectrum and time profile of the activity spectrum (during transient operating
conditions) of the background
• detection geometry
• number of standard deviations (in order to calculate the minimum detectable activity
or detection limit)
• flow rate of the stream to be measured
• thermodynamic conditions
• precision and time profile of the precision (in order to calculate the measurement
time during steady-state as well as transient operating conditions)
• measurement time and response time (during transient operating conditions)
– For the influence quantities depending on the process or the location, the purchaser
should indicate their range of values. Otherwise, the manufacturer should make any
useful hypothesis in order to take into account the probable conditions of use of the
instrument.
If the signals are used for initiating protective action to mitigate the consequences of
malfunction or failure of structures, systems or components, then the equipment may be part
of the safety-related systems or the protection system. In this case, it shall meet the
requirements of the respective system in accordance with IEC 61226.
If qualification is needed, the equipment shall be environmentally qualified in accordance with
the requirements of IEC 60780 (and IEC 60980 for seismic testing).
4.2 Measurement range
The purchaser shall specify the required effective range of measurement. The range shall be
suitable for the level of radiation during normal and incident conditions. A minimum of four
decades of measurement is required.
4.3 Energy response
The detector may be selected to measure either beta or gamma radiation. The purchaser shall
confirm that the energy response of the detection assembly is suitable for monitoring the
potential activity.
– 12 – 60768 © IEC:2009
4.4 Minimum detectable activity (or detection limit)
The minimum detectable activity (or detection limit) is equal to a number of standard
deviations of the estimation of the signal which would be measured by the instrument without
any activity except the background, and under specified conditions. It should only be
considered in steady-state operating conditions. Its calculation by a formula is possible, using
the measurement time, however it does not give a rigorous statement of the beginning of the
range of measurement.
The required minimum detectable activity (or detection limit) will depend on the particular
application and be subject to local regulations and plant design; it shall be specified by the
plant designer.
The manufacturer shall specify the minimum detectable activity (or detection limit) for nuclides
of interest, taking into account the check sources or provisions incorporated to provide an on-
scale indication on the monitor, as well as all useful data needed to specify the beginning of
the effective range of measurement, even in transient operating conditions. The influence
quantities, their range of values and the variation they cause on the minimum detectable
activity (or detection limit) shall be specified.
4.5 Precision (or repeatability)
Precision (or repeatability) is a measure of the dispersion of the estimations around their
average value. It shall be given by the manufacturer in the effective range of measurement
in % of the signal value for a given confidence interval (or probability of error). Assuming that
the estimations follow a Gaussian distribution, this probability should be expressed in term of
a number of standard deviations.
NOTE For example, the precision could be 20 % of the signal value within a part of the effective range of
measurement with a probability of 95 % (meaning that all the estimations are within ±2σ, with σ the standard
deviation), and 30 % within another part of the effective range of measurement with another probability.
Precision shall be consistent with incident analysis assumptions, operator needs, and
requirements imposed by other systems that use the radiation monitoring signals. Moreover,
they shall be characterized for signal values below the beginning of the effective range of
measurement. The influence quantities, their range of values and the variation they cause on
precision shall be specified by the manufacturer.
Typically, the precision should be within 10 % over the entire effective range of measurement,
all influence quantities taken into account.
4.6 Accuracy (or relative error)
Accuracy (or relative intrinsic error) is a measure of the deviation between the conventionally
true value and the average of the estimations. It shall be given by the manufacturer in the
effective range of measurement in % of the signal value for a given confidence interval (or
probability of error). Assuming that the estimations follow a Gaussian distribution, this
probability should be expressed in term of a number of standard deviations.
NOTE For example, the accuracy could be 20 % of the signal value within a part of the effective range of
measurement with a probability of 95 % (meaning that all the estimations are within ±2σ, with σ the standard
deviation), and 30 % within another part of the effective range of measurement with another probability.
Accuracy shall be consistent with incident analysis assumptions, operator needs, and
requirements imposed by other systems that use the radiation monitoring signals. Moreover,
they shall be characterized for signal values below the beginning of the effective range of
measurement. The influence quantities, their range of values and the variation they cause on
accuracy shall be specified by the manufacturer.
Typically, the accuracy should be within 20 % over the entire effective range of measurement,
all influence quantities taken into account.

60768 © IEC:2009 – 13 –
4.7 Measurement time
The measurement time is the average time during which the measurement is to be performed
to obtain an estimation of the signal in stated conditions. It should only be considered in
steady-state operating conditions. Its calculation by a formula is possible, however it does not
take into account the processing algorithms implanted in the monitor.
The manufacturer shall specify the measurement time as well as all useful data (standard
deviation or precision) needed to know the precision of the estimations and the false alarm
rate. The influence quantities, their range of values and the variation they cause on the
measurement time shall be specified.
4.8 Response time
The response time is the time needed for the monitor, after a sudden variation of the signal to
measure (for example a step), to have its output signal or indication reaching for the first time
90 % (increasing transition) or 10 % (decreasing transition) of the variation.
NOTE For integrating systems, it is a percentage of the equilibrium value of the first derivative of the output
signal in function of time that should be considered.
The response time is to be considered only in transient operating conditions. It shall take into
account the processing algorithms of the monitor.
Therefore, its calculation by a formula is not relevant, and the manufacturer shall specify it by
performing tests or numerical simulations, and give all useful data to determine its
relationship with the precision of the estimations and the false alarm rate. The influence
quantities, their range of values and the variation they cause on the response time shall be
specified.
4.9 Overload performance
The indicated measurement shall not decrease or fall to zero during and following exposure
beyond the maximum measuring range. It shall maintain a full-scale indication or an
unambiguous indication. When the exposure returns to within the maximum range, the system
shall recover within the time interval specified by the purchaser.
4.10 Ambient background shielding or compensation devices
Shielding or electronic compensation shall be provided as necessary to reduce the effects of
background radiation on the measurement of process radiation.
It may be agreed between the manufacturer and the purchaser that significant background
radiation is only to be expected from defined directions or sources (vessels, pipes, etc.). In
such cases, the construction of shielding may take this into account. In the absence of such
agreement, shielding shall give virtually identical radiation attenuation in all directions seen
from the sensitive volume of the detector, taking into account the structural materials of the
detection assembly, and the angular response of the detector.
If the equipment cannot easily be removed from the shielding, such shielding should be easily
removable. The maximum mass of the elements, or the appropriate handling means, should
be agreed between manufacturer and purchaser.
When electronic techniques incorporating additional detectors are used to reduce the effect of
background radiation, these detectors shall be chosen and located to give the best practicable
compensation, taking account of the range of energies and the direction of the radiation.

– 14 – 60768 © IEC:2009
4.11 Requirements related to incident conditions
Equipment design shall assure that the equipment supports the necessary system functions
and that the equipment will not fail due to environmental conditions experienced during
normal and incident conditions.
The incident time interval during which system operation is required shall be specified by the
purchaser.
The local environmental conditions in which the different compo
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