IEC 60951-1:2009

IEC 60951-1 ®
Edition 2.0 2009-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Nuclear power plants – Instrumentation important to safety – Radiation
monitoring for accident and post-accident conditions –
Part 1: General requirements
Centrales nucléaires de puissance – Instrumentation importante pour la sûreté –
Surveillance des rayonnements pour les conditions accidentelles et post-
accidentelles –
Partie 1: Exigences générales
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IEC 60951-1 ®
Edition 2.0 2009-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Nuclear power plants – Instrumentation important to safety – Radiation
monitoring for accident and post-accident conditions –
Part 1: General requirements
Centrales nucléaires de puissance – Instrumentation importante pour la sûreté –
Surveillance des rayonnements pour les conditions accidentelles et post-
accidentelles –
Partie 1: Exigences générales
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
X
CODE PRIX
ICS 27.120.20 ISBN 978-2-88910-346-1
– 2 – 60951-1 © IEC:2009
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.8
2 Normative references .8
3 Terms and definitions .9
4 Design principles.14
4.1 Basic requirements related to functions .14
4.2 Measurement range .16
4.3 Energy response .16
4.4 Minimum detectable activity (or limit of detection).16
4.5 Precision (or repeatability).16
4.6 Accuracy (or relative error).17
4.7 Measurement time.17
4.8 Response time .17
4.9 Overload performance.18
4.10 Ambient background shielding or compensation devices .18
4.11 Requirements related to accident conditions .18
4.12 Reliability .19
4.13 User interface.19
4.13.1 General .19
4.13.2 Display of measured value.19
4.13.3 Alarms.19
4.13.4 Status indication.20
4.13.5 Local indications.20
4.14 System testing, maintenance facilities and ease of decontamination .21
4.14.1 System testing.21
4.14.2 Maintenance facilities .21
4.14.3 Ease of decontamination .21
4.15 Electromagnetic interference .21
4.16 Power supplies.22
4.17 Interfaces .22
4.18 Sampling assembly .22
4.19 Quality .23
4.20 Type test report and certificate .24
5 Functional testing .25
5.1 General .25
5.2 General test procedures .25
5.2.1 General .25
5.2.2 Tests performed under standard test conditions .25
5.2.3 Tests performed with variation of influence quantities.25
5.2.4 Calculations and/or numerical simulations .26
5.2.5 Reference sources .26
5.2.6 Statistical fluctuations.28
5.3 Performance characteristics .28
5.3.1 Reference response .28
5.3.2 Sensitivity and relative response for solid sources.28

60951-1 © IEC:2009 – 3 –
5.3.3 Accuracy (relative error) .29
5.3.4 Response to other artificial radionuclides .30
5.3.5 Response to background radiation.30
5.3.6 Precision (or repeatability).31
5.3.7 Stability of the indication .31
5.3.8 Response time .31
5.3.9 Overload test.32
5.4 Electrical performance tests .33
5.4.1 Alarm trip range.33
5.4.2 Alarm trip stability.33
5.4.3 Fault alarm .33
5.4.4 Status indication and fault alarm tests .34
5.4.5 Warm-up time — Detection and measuring assembly .34
5.4.6 Influence of supply variations .34
5.4.7 Short circuit withstand tests.35
5.5 Environmental performance test .35
5.5.1 Stability of performance after storage .35
5.5.2 Mechanical tests.36
5.5.3 Stability of performance with variation of temperature and humidity.37
5.5.4 Electromagnetic compatibility .39
Bibliography.44

Table 1 – Overview of the standards covering the domain of radiation monitoring.6
Table 2 – Reference conditions and standard test conditions .41
Table 3 – Tests performed under standard test conditions .42
Table 4 – Tests performed with variation of influence quantities.43

– 4 – 60951-1 © IEC:2009
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS –
INSTRUMENTATION 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
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
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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
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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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
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expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60951-1 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 1988. This edition
constitutes a technical revision.
The main technical changes with regard to the previous edition are as follows.
• To clarify the definitions.
• To up-date the references to new standards published since the first issue.
• To update the units of radiation.

60951-1 © IEC:2009 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
45A/734/FDIS 45A/756/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of IEC 60951 series, under the general title Nuclear power plants –
Instrumentation important to safety – Radiation monitoring for accident and post-accident
conditions, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – 60951-1 © IEC:2009
INTRODUCTION
a) Technical background, main issues and organisation of the standard
This IEC standard specifically focuses on radiation monitoring systems used for accident and
post-accident operations.
This standard is intended for use by purchasers in developing specifications for their plant-
specific radiation monitoring systems and by manufacturers to identify needed product
characteristics when developing systems for accident monitoring conditions. Some specific
instrument characteristics such as measurement range, required energy response, and
ambient environment requirements will depend upon the specific application. In such cases,
guidance is provided on determining the specific requirements, but specific requirements
themselves are not stated.
This standard is one in a series of standards covering post-accident radiation monitors
important to safety. The full series is comprised of the following standards.
• IEC 60951-1 – General requirements
• IEC 60951-2 – Equipment for continuous off-line monitoring of radioactivity in gaseous
effluents and ventilation air
• IEC 60951-3 – Equipment for continuous high range area gamma monitoring
• IEC 60951-4 – Equipment for continuous in-line or on-line monitoring of radioactivity in
process streams
b) Situation of the current standard in the structure of the IEC SC 45A standard series
The IEC 60951 series of standards are at the third level in the hierarchy of SC 45A standards.
They provide guidance on the design and testing of radiation monitoring equipment used for
accident and post-accident conditions. Other standards developed by SC 45A and SC 45B
provide guidance on instruments used for monitoring radiation as part of normal operations.
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.
Table 1 – Overview of the standards covering the domain of radiation monitoring
Developer ISO SC 45A – Process and safety monitoring SC 45B – Radiation
protection and
Scope Sampling circuits Accident and post- Normal and incident
effluents monitoring
and methods accident conditions conditions
Gas, particulate and ISO 2889 IEC 60951-1 and IEC 60761 series and IEC 62302 (noble
iodine with sampling IEC 60951-2 gases only)
(OFF LINE)
Liquid with sampling N/A N/A IEC 60861
(OFF LINE)
Process streams N/A IEC 60951-1 and IEC 60768 N/A
(gaseous effluents, IEC 60951-4
steam or liquid)
without sampling
(ON or IN-LINE)
Area monitoring N/A IEC 60951-1 and IEC 60532
IEC 60951-3
60951-1 © IEC:2009 – 7 –
Developer ISO SC 45A – Process and safety monitoring SC 45B – Radiation
protection and
Scope Sampling circuits Accident and post- Normal and incident
effluents monitoring
and methods accident conditions conditions
Central system N/A IEC 61504 IEC 61559 series
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.
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.

– 8 – 60951-1 © IEC:2009
NUCLEAR POWER PLANTS –
INSTRUMENTATION 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 during and after an accident. This standard is
limited to equipment for continuous monitoring of radioactivity in accident and post-accident
conditions.
The object of this standard is to lay down mandatory general requirements and give examples
of acceptable methods for equipment for continuous monitoring of radioactivity within the
plant during and after accident conditions in nuclear power plants using light water reactors.
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 standard.
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 60038:2002, 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: Degrees of protections provided by enclosures – IP code
IEC 60780, Nuclear power plants – Electrical equipment of the safety system – Qualification

60951-1 © IEC:2009 – 9 –
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 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 61000-4-3:2006, Electromagnetic compatibility (EMC) – Part 4-3: Testing and
measurement techniques – Radiated, radio-frequency, electromagnetic field immunity test
IEC 61000-4-4:2004, Electromagnetic compatibility (EMC) – Part 4-4: Testing and
measurement techniques – Electrical fast transient/burst immunity test
IEC 61000-4-5:2005, Electromagnetic compatibility (EMC) – Part 4-5: Testing and
measurement techniques – Surge immunity test
IEC 61000-4-6:2008, Electromagnetic compatibility (EMC) – Part 4-6: Testing and
measurement techniques – Immunity to conducted disturbances, induced by radio-frequency
fields
IEC 61000-4-8:2001, 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 61000-6-4:2006, 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, 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 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 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)
ISO 2889:2009, 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.

– 10 – 60951-1 © IEC:2009
3.1
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]
3.3
aerodynamic equivalent diameter
diameter of a unit-density sphere having the same gravitational settling velocity as the particle
in question
[IEV 393-11-41]
NOTE The aerodynamic equivalent diameter concerns particles with a diameter from 0,1 μm to 2 mm.
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]
3.5
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:
n
s 1 1
V = = ()x − x
i
x x n −1
i=1
[IEV 394-40-14]
3.6
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.
60951-1 © IEC:2009 – 11 –
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 %.
3.11
effective range of measurement
absolute value of the difference between the two limits of a nominal range
[IEV 394-40-16]
NOTE In the nominal range the performance of a piece of equipment or an assembly meets the requirements of
its specifications.
3.12
electron beam
electron flux emitted from one source and moving along the exactly determined tracks with
very great velocities
[IEV 841-30-01]
NOTE Such beam routed to a detector causes extremely high dose rates.
3.13
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 equation:
n
()x − x
∑ i
i=1
s =
n −1
x being the result of the ith measurement and ⎯x being the arithmetic mean of the n results
i
considered
[IEV 394-40-40]
– 12 – 60951-1 © IEC:2009
NOTE 1 The expression s n is an estimate of the standard deviation of the distribution of x and is called the
experimental standard deviation of the mean.
NOTE 2 Experimental standard deviation of the mean is sometimes incorrectly called standard error of the mean.
3.14
measuring assembly
assembly designed to measure a quantity
NOTE In this standard, the quantity is volumetric activity or dose rate, although the value may be expressed in
other units.
3.15
minimum detectable (measurable) activity
quantity of radioactivity giving a count which, in the presence of a specified background noise,
has a 95 % probability not to be caused by that of background noise alone
[IEV 394-40-25]
3.16
particle
aggregate of molecules forming a solid or liquid of size ranging from a few molecular
diameters to some tenths of a milimeter (several hundred micrometers)
[ISO 2889]
3.17
process streams
fluid which flows through a system intended to provide a useful purpose.
NOTE 1 Examples of process streams are: primary coolant system, spent fuel cooling system, component cooling
system, etc.
NOTE 2 The process streams within the scope of this standard are those streams in which the level of
radioactivity may significantly increase as a result of accident or post-accident conditions.
NOTE 3 Monitoring of these process streams for radioactivity provides information on the quality or integrity of
the barrier and potential release to the environment.
3.18
reference response
response of the assembly under reference conditions to unit reference dose rate, expressed
as:
v − v
B
R =
ref
v
c
where:
ν is the value measured by the equipment or assembly under test

ν is the background value of the equipment without external influence
B
ν is the conventionally true value of the reference source
c
[IEV 394-40-22]
NOTE The background value may be automatically taken into account by an algorithm included in the
measurement systems.
3.19
relative error
error of measurement divided by a true value of the measurand

60951-1 © IEC:2009 – 13 –
[IEV 394-40-11]
NOTE 1 Since a true value cannot be determined, in practice, a conventionally true value is used. For this
standard, relative error is calculated as follows.
(ν −ν ) −ν
B c
E =
ν
c
where:
ν is the value measured by the equipment or assembly under test,
ν is the conventionally true value of the reference source,
c
ν is the background value of the equipment without external influence.
B
NOTE 2 The background value may be automatically taken into account by an algorithm included in the
measurement system.
3.20
relative response
value calculated during type testing equal to the ratio between the reference response of the
equipment and the sensitivity of the same equipment to the solid source of interest
NOTE The relative response allows determination of the reference response of identical equipment that has been
type tested from the measurement of the sensitivity of the solid source.
3.21
response time
the period of time necessary for a component to achieve a specified output state from the time
that it receives a signal requiring it to assume that output state
[IAEA Safety Glossary, 2007 edition]
NOTE For the purposes of the tests described in this standard, the input signal is assumed to be a step variation
and the ending output state is the point at which the output signal variation reaches 90 % of its final value for the
first time.
3.22
routine test
conformity test made on each individual item during or after manufacture
[IEV 394-40-03]
3.23
sampling assembly
set of interconnected devices for collecting a representative sample
3.24
sampling collection efficiency
for a given quantity of radioactive material, ratio of the collected activity to the supplied activity, for a
specified time interval
[IEV 394-39-45]
3.25
sensitivity (of a measuring assembly)
for a given value of the measured quantity, ratio of the variation of the observed variable to
the corresponding variation of the measured quantity
[IEV 394-39-07]
– 14 – 60951-1 © IEC:2009
3.26
volumetric activity
quotient of the activity by the total volume of the sample
[IEV 393-14-16]
NOTE 1 For a gas, it is necessary to indicate the temperature and pressure conditions for which the volumic
activity is measured, for example standard temperature and pressure (STP).
NOTE 2 This quantity is expressed in Becquerels per cubic meter (Bq/m ).
4 Design principles
4.1 Basic requirements related to functions
The main purpose of equipment for continuous monitoring of radioactivity in accident or post-
accident conditions is to continuously measure radiation levels in appropriate areas and
processes. These radiation measurements are displayed locally and/or in control rooms
and/or incident control centers to keep plant operators aware of current radiological
conditions. This information is used by operators to assess plant conditions, take appropriate
actions in order to mitigate the consequences of a plant accident and prevent the inadvertent
release of radiation, and by site emergency personnel, national authorities, for actions
necessary to safeguard public and plant personnel. 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 monitoring of radioactivity in accident or post-accident conditions
are plant specific. It is typically split into three key parts, effluent and ventilation radiation
monitoring, process radiation monitoring, and area radiation monitoring:
• Effluent and ventilation radiation monitors measure the radioactivity in gases released into
the environment in accident and post-accident conditions to ensure that the radiation
levels are not hazardous to the public’s safety and to help in early warning and process
isolations, such as containment vent isolation or control room habitability. Effluent
radiation monitors are usually of the off-line type (radioactivity is measured in a sample
drawn from the effluent or ventilation system).
• Process radiation monitors measure the radioactivity in a fluid (either gas, liquid or steam)
and are normally used in plant process to help in early warning and process isolations,
such as detecting reactor coolant pressure boundary leaks into containment and other
systems. Process radiation monitors can be classified into three basic types:
• In-line monitors: the detector is located directly in the process stream (pipe, stack,
tank, duct, etc.).
• On-line monitors: the detector directly faces the process stream.
• Off-line monitors: a sample is drawn from the process stream to the detector located at
some distance.
• Area radiation monitors (wide range type) are strategically located within buildings subject
to high range dose rates in accident and post-accident conditions, such as the reactor
building, and serve as post-accident monitoring devices. Area radiation monitors are wall
mounted in the area or tank to be monitored. Depending on the radiation level at the
detector position, the electronics part of the monitor may be located at some distance from
the detector.
For the purpose of critical data collection, these monitors are usually 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

60951-1 © IEC:2009 – 15 –
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 and accidental operations, and the corresponding
source terms (main 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 emergency 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.).
• 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 sampling
system, if any, and the time to send or to display the information to the plant operator
or the control system).
• Determine the gross characteristics of the detectors (type of radiation and
measurement, sensitivity and range of measurement, energy response and overload
performance, etc.) and of the sampling system, if any.
• Determine the acceptable false alarm rate taking into account the plant conditions and
the consequences of error in measurement (including losses in sampling), 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 manufac
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