IEC 60544-5:2022
(Main)Electrical insulating materials - Determination of the effects of ionizing radiation - Part 5: Procedures for assessment of ageing in service
Electrical insulating materials - Determination of the effects of ionizing radiation - Part 5: Procedures for assessment of ageing in service
IEC 60544-5:2022 covers ageing assessment methods which can be applied to components based on polymeric materials (e.g. cable insulation and jackets, elastomeric seals, polymeric coatings, gaiters) which are used in environments where they are exposed to radiation. The object of this document is aimed at providing methods for the assessment of ageing in service. The approaches discussed in Clause 5 through Clause 9 cover ageing assessment programmes based on condition monitoring (CM), the use of sample deposits in severe environments and sampling of real-time aged components. This edition includes the following significant technical changes with respect to the previous edition:
- added recent references in 7.4 showing that some electrical condition monitoring methods show promising correlations with ageing;
- updated recommendations for implementation of a sample deposit in 9.2, installation of a sample deposit in 9.3 and testing of samples from the deposit in 9.4;
- updated list of references.
Matériaux isolants électriques - Détermination des effets des rayonnements ionisants - Partie 5: Procédures pour l'évaluation du vieillissement en service
L'IEC 60544-5:2022 traite des méthodes d'évaluation du vieillissement qui peuvent être appliquées aux composants à base de matériaux polymères (gaines et isolations de câble, joints en élastomère, revêtements polymères, garnitures) qui sont utilisés dans des environnements où ils sont exposés aux rayonnements. L'objet du présent document est de fournir des méthodes pour évaluer le vieillissement en service des matériaux. Les approches examinées dans les Articles 5 à 9 concernent les programmes d'évaluation de vieillissement fondés sur une surveillance de l'état (CM, Condition Monitoring), l'utilisation de dépôts d'échantillons dans des environnements sévères et l'échantillonnage de composants vieillis en temps réel. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- des références récentes ont été ajoutées en 7.4 afin d'introduire des méthodes de surveillance de l'état qui montrent des corrélations prometteuses vis-à-vis du vieillissement;
- les recommandations ont été mises à jour pour la mise en œuvre d'un dépôt d'échantillons en 9.2, l'installation d'un dépôt d'échantillons en 9.3 et les essais sur les échantillons du dépôt en 9.4;
- la liste de références a été mise à jour.
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IEC 60544-5 ®
Edition 3.0 2022-06
REDLINE VERSION
INTERNATIONAL
STANDARD
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Electrical insulating materials – Determination of the effects of ionizing
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Part 5: Procedures for assessment of ageing in service
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IEC 60544-5 ®
Edition 3.0 2022-06
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Electrical insulating materials – Determination of the effects of ionizing
radiation –
Part 5: Procedures for assessment of ageing in service
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.240; 29.035.01 ISBN 978-2-8322-3936-0
– 2 – IEC 60544-5:2022 RLV © IEC 2022
CONTENTS
FOREWORD . 4
INTRODUCTION . 2
1 Scope and object . 7
2 Normative references . 7
3 Terms, definitions and abbreviated terms . 7
3.1 Terms and definitions . 7
3.2 Abbreviated terms . 7
4 Background . 7
4.1 General . 8
4.2 Diffusion-limited oxidation (DLO). 8
4.3 Dose rate effects (DRE) . 9
4.4 Accelerated radiation ageing . 9
4.5 Accelerated thermal ageing . 10
5 Approaches to ageing assessment . 10
6 Identifying components of concern . 10
6.1 General . 10
6.2 Priorities for ageing management . 10
6.3 Environmental monitoring . 11
6.4 Localized severe environments . 11
6.5 Worst case components . 11
7 Condition monitoring techniques . 11
7.1 General . 11
7.2 Establishing correlation curves for CM methods . 12
7.3 CM methods . 12
7.4 Using CM for short-term troubleshooting . 13
7.5 Using CM for long-term degradation assessment . 16
8 Predictive modelling . 17
9 Sample deposit . 18
9.1 General . 18
9.2 Requirements of a deposit . 18
9.3 Pre-ageing samples for a deposit . 18
9.4 Installation of a sample deposit . 19
9.5 Testing of samples from the deposit . 19
9.6 Determination of sampling intervals . 19
9.7 Real time aged materials . 20
Annex A (informative) Example of a CM correlation curve . 21
Annex B (informative) Use of a deposit . 22
B.1 Typical sample in a deposit . 22
B.2 Typical testing schedule for a deposit . 22
Bibliography . 23
Figure 1 – Development of ageing data on changes in tensile elongation and a
condition indicator (e.g. indenter modulus) – Schematic representation . 15
Figure 2 – Correlation curve derived from data in Figure 1 – Schematic representation . 16
Figure 3 – Estimation of elongation from a correlation curve . 17
Figure 4 – Modification of sampling interval dependent on values of the CM indicator –
Schematic representation . 20
Figure A.1 – Correlation curve for indenter modulus against tensile elongation for a
CSPE cable jacket material [24] . 21
– 4 – IEC 60544-5:2022 RLV © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL INSULATING MATERIALS –
DETERMINATION OF THE EFFECTS OF IONIZING RADIATION –
Part 5: Procedures for assessment of ageing in service
FOREWORD
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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.
This redline version of the official IEC Standard allows the user to identify the changes made to
the previous edition IEC 60544-5:2011. 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 60544-5 has been prepared by IEC technical committee TC 112: Evaluation and
qualification of electrical insulating materials and systems. It is an International Standard.
This third edition cancels and replaces the second edition published in 2011. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) added recent references in 7.4 showing that some electrical condition monitoring methods
show promising correlations with ageing;
b) updated recommendations for implementation of a sample deposit in 9.2, installation of a
sample deposit in 9.3 and testing of samples from the deposit in 9.4;
c) updated list of references.
The text of this International Standard is based on the following documents:
Draft Report on voting
112/523/CDV 112/553/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in the IEC 60544 series, published under the general title Electrical insulating
materials – Determination of the effects of ionizing radiation, can be found on the IEC website.
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 60544-5:2022 RLV © IEC 2022
INTRODUCTION
Organic and polymeric materials provide a significant proportion of the insulation used in
electrical systems. These materials are sensitive to the effects of irradiation and the response
varies widely between different types. It is therefore important to be able to assess the degree
of degradation of these insulating materials during their service lifetimes. This part of IEC 60544
provides recommended procedures for assessing ageing of insulating materials in service.
There are a number of approaches to the assessment of ageing of polymer-based components
exposed to radiation environments [1], [2], [3], [4] . These are based on the better
understanding of the factors affecting ageing degradation which has been developed over
several decades. In nuclear power plants, qualification programmes are normally used for the
selection of components, including those based on polymeric materials. These initial
TM 2 TM
qualification procedures, such as IEEE Std 323 -1974 [5] and IEEE Std 383 -1974Error!
Bookmark not defined. [6], were originally written before there was sufficient understanding
of ageing mechanisms. Most of the methods discussed in this document are therefore used to
supplement the initial qualification process.
This document is the fifth in a series dealing with the effect of ionizing radiation on insulating
materials.
IEC 60544-1 (Radiation interaction and dosimetry) constitutes an introduction dealing very
broadly with the problems involved in evaluating radiation effects. It also provides guidance on
dosimetry terminology, several methods of determining exposure and absorbed dose, and
methods of calculating absorbed dose in any specific material from the dosimetry method
applied.
IEC 60544-2 (Procedures for irradiation and test) describes procedures for maintaining seven
different types of exposure conditions during irradiation. It also specifies the controls that should
be maintained over these conditions so that when test results are reported, reliable comparisons
of material performance can be made. In addition, it defines certain important irradiation
conditions and test procedures to be used for property change determinations and
corresponding end-point criteria.
IEC 60544-3 has been withdrawn and incorporated into the second edition of IEC 60544-2.
IEC 60544-4 (Classification system for service in radiation environments) provides a
recommended classification system for categorizing the radiation endurance of insulation
materials.
___________
Numbers in square brackets refer to the Bibliography.
IEEE Std 323-1974 and IEEE Std 383-1974 are now withdrawn and have been superseded by more recent
revisions.
ELECTRICAL INSULATING MATERIALS –
DETERMINATION OF THE EFFECTS OF IONIZING RADIATION –
Part 5: Procedures for assessment of ageing in service
1 Scope and object
This part of IEC 60544 covers ageing assessment methods which can be applied to components
based on polymeric materials (e.g. cable insulation and jackets, elastomeric seals, polymeric
coatings, gaiters) which are used in environments where they are exposed to radiation.
The object of this document is aimed at providing methods for the assessment of ageing in
service. The approaches discussed in Clause 5 through Clause 9 cover ageing assessment
programmes based on condition monitoring (CM), the use of sample deposits in severe
environments and sampling of real-time aged components.
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 60544-1, Electrical insulating materials – Determination of the effects of ionizing radiation
– Part 1: Radiation interaction and dosimetry
IEC 60544-2, Electrical insulating materials – Guide for determining Determination of the effects
of ionizing radiation on insulating materials – Part 2: Procedures for irradiation and test
IEC TS 61244-1, Determination of long-term radiation ageing in polymers – Part 1: Techniques
for monitoring diffusion-limited oxidation
IEC TS 61244-2, Determination of long-term radiation ageing in polymers – Part 2: Procedures
for predicting ageing at low dose rates
IEC 60780, Nuclear power plants – Electrical equipment of the safety system – Qualification
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.2 Abbreviated terms
For the purposes of this document, the following abbreviations, taken from IEC 60780, apply.
– 8 – IEC 60544-5:2022 RLV © IEC 2022
BWR boiling water reactor
CBQ condition-based qualification
CM condition monitoring
CSPE chlorosulphonated polyethylene
DBE design basis event
DLO diffusion-limited oxidation
DRE dose rate effect
DSC Differential scanning calorimeter
EPR ethylene propylene rubber
EQ environmental qualification
EVA Ethylene vinyl acetate copolymer
IM Indenter modulus
LOCA Loss of coolant accident
NPP nuclear power plant
OIT oxidation induction time
OITP oxidation induction temperature
PE Polyethylene
PVC polyvinyl chloride
PWR pressurized water reactor
TGA thermo-gravimetric analysis
VVER water-cooled, water-moderated energy reactor (type of pressurized water reactor
developed by Russia)
XLPE cross-linked polyethylene
4 Background
4.1 General
There are a number of factors that need to be considered when assessing ageing of polymeric
components in radiation environments. In 4.2 through 4.5, some of these factors are briefly
discussed and references made to more detailed information.
To accelerate radiation-ageing environments, the normal approach is to increase the radiation
dose rate, often combined with an increase in temperature. The two most important potential
complications arising from such increases involve diffusion-limited oxidation (DLO), which is
described in 4.2, and chemical dose rate effects (DRE), which are described in 4.3. The
implications of these factors on the use and interpretation of condition monitoring (CM)
techniques are also discussed. Accelerated ageing programmes are briefly discussed in 4.4
and 4.5.
4.2 Diffusion-limited oxidation (DLO)
When polymers are exposed to an oxygen-containing environment (e.g. air), some oxygen will
be dissolved in the material. In the absence of oxygen-consuming reactions (oxidation), the
amount of dissolved oxygen will be proportional to the oxygen partial pressure surrounding the
polymer (well known from Henry’s Law). Ageing will lead to oxidation reactions in the polymer,
whose rate will increase significantly as the dose rate and temperature of ageing are increased.
If the rate of consumption of dissolved oxygen in the polymer is faster than the rate at which
oxygen can be replenished by diffusion from the surrounding atmosphere, the concentration of
dissolved oxygen in the interior regions will decrease with time (the oxygen concentration at
the sample surface will remain at its equilibrium value). The reduction in internal oxygen
concentration can lead to reduced or negligible oxidation, referred to as "diffusion-limited
oxidation".
The importance of this effect is dependent on the sample thickness (thinner samples giving
smaller DLO effects) and the ratio of the oxygen consumption rate to the oxygen permeability
coefficient P, which is the product of the oxygen diffusion and solubility parameters. Accelerated
radiation environments involve increases in dose rates, which increase the oxygen consumption
rate. If the temperature remains constant as the dose rate is increased, the oxygen permeability
coefficient will be unchanged. This means that DLO effects will become more important as the
dose rate is raised. These effects are described in more detail in IEC 61244-1. For more detail
about these effects, IEC TS 61244-1 shall be consulted.
The effects of DLO may also need to be considered when carrying out CM measurements. This
is not an issue for the many CM techniques which measure properties at ambient temperature,
such as those based on density and modulus measurements. On the other hand, several CM
techniques such as oxidation induction time (OIT) and thermogravimetric analysis (TGA) use
quite elevated temperatures during the measurements. For these techniques, it is quite possible
to have DLO effects present during measurement of the CM parameter. For this reason, detailed
test methods for CM have been developed [8] to ensure that the sample preparation and test
procedure avoid DLO effects. DLO shall be addressed when developing correlation curves for
CM methods, to ensure that representative data are obtained for both radiation and thermal
ageing.
4.3 Dose rate effects (DRE)
The existence of radiation dose rate effects and methods for dealing with these effects are
described in IEC TS 61244-2. This standard shall be consulted for more detail about these
effects. Generally, DRE are separated into two types. The first type, which is commonly
observed in accelerated radiation-ageing experiments, is due to the DLO effects described in
4.2. These DLO-based effects represent a physical, geometry-dependent DRE.
The second type of interest to the current discussion concerns chemical DRE. Such chemically
based DRE are much less common. A documented case of chemical DRE is found in PVC and
low density polyethylene materials, caused by the slow breakdown of hydroperoxide
intermediate species in the oxidation reaction [9]. The existence of such chemical DRE shall be
checked at the start of any accelerated ageing programme. If there are no data available in the
literature for the specific materials of interest, this can be checked by including tests at low
dose rates in the ageing programme.
4.4 Accelerated radiation ageing
Accelerated ageing programmes in the laboratory tend to use acceleration factors much lower
than are normally used in equipment qualification. This may avoid some of the problems
associated with DLO and DRE. The ageing produced may then be a better simulation of the
long-term ageing that occurs under service conditions. The data that are obtained in accelerated
ageing tests can be used with predictive models to enable assessments to be made of the
behaviour of the materials under service conditions.
Accelerated ageing programmes require a matrix of test data to be generated over a range of
environmental conditions as described in IEC TS 61244-2. As a minimum, data are needed for
at least three different dose rates at the normal operating temperature but additional data on
thermal ageing and radiation ageing at elevated temperature enables better use to be made of
the available predictive modelling methods. The dose rates and temperatures used for
accelerated ageing should be selected using the principles described in IEC 60544-2 to ensure
that homogeneous oxidation occurs. For each environmental condition used, test data shall be
obtained at several different ageing times, the longest of which should be sufficient to introduce
significant degradation. A typical test programme could take more than 18 months to complete,
dependent on the radiation resistance of the materials being tested.
– 10 – IEC 60544-5:2022 RLV © IEC 2022
The data required in the test matrix are determined by the type of component being evaluated.
The appropriate test parameters are given in IEC 60544-2 for various types of polymeric
materials and components.
4.5 Accelerated thermal ageing
When carrying out thermal ageing as part of an accelerated ageing programme, it is important
that an appropriate value of the activation energy is used in assessing the temperature and
timescale of the accelerated test. In some materials, the ageing mechanism at high
temperatures is different to that which would occur under plant conditions and in many materials
the activation energy decreases significantly at lower temperatures [10], [11].
Samples which have been exposed to accelerated thermal ageing shall be allowed to stabilize
before any CM tests are carried out. Some polymeric materials are hygroscopic and show a
marked dependence of their properties on the moisture content [8]. This is primarily of concern
for a few materials used in older nuclear power plants, but may also be important for those CM
methods that are sensitive to the moisture content of the material.
5 Approaches to ageing assessment
There are a number of complementary methods available for ageing assessment as described
in their respective clauses. Each of these methods has its own advantages and limitations.
Selection of one or more of the methods will be dependent on the requirements of the individual
users.
Several approaches to ageing assessment in-service are described in this document. These
are:
• identifying components of concern to prioritize the application of ageing management
programmes (see Clause 6);
• condition monitoring to assess the condition of materials which have aged for extended time
periods under actual use environments (see Clause 7);
• predictive modelling to use data from laboratory based accelerated ageing programmes to
estimate ageing under real-time ageing conditions (see Clause 8);
• sample deposit to provide samples for the measurement of ageing under real-time ageing
conditions (see Clause 9).
6 Identifying components of concern
6.1 General
Within a nuclear power plant, there are many components containing polymeric insulating
materials, for example there are over 1 000 km of electrical cables in a typical NPP. It is not
practical to assess the ageing of every individual component, and many will not be exposed to
significant environmental ageing conditions. It is therefore necessary to prioritize any ageing
management programme by identifying those components which are of most concern.
6.2 Priorities for ageing management
Not all components have the same priority for ageing management. In general, those
components performing safety functions during and following an accident are of most concern,
together with those important to continued operation. Any components outside of these
categories would initially be assigned to a low priority for ageing management activities.
The normal operating environment of the components shall be examined to identify the
expected impact of the environment on their ageing. Those components identified as being
subject to severe ageing are assigned the highest priority, whereas those subject to moderate
ageing can then be assigned to a medium priority.
For this prioritization to be carried out effectively, environmental monitoring is essential (see
6.3), combined with knowledge of the ageing behaviour of the components. Initial assessment
may make use of design calculations for temperatures and dose rates. The ageing information
may come from equipment qualification data or from supplementary accelerated ageing tests
carried out in the laboratory.
6.3 Environmental monitoring
Ageing of insulating materials in an NPP is dominated by temperature, radiation dose and
radiation dose rate for organic and polymeric materials. A major requirement for ageing
management is a detailed knowledge of the actual temperatures and dose rates at locations
within the plant where high priority components are situated.
The temperature and dose rate distribution within the plant shall be obtained using temperature
recorders and dosimeters. Operational fluctuations and seasonal variations shall be included
by carrying out these measurements over several fuel cycles. It may be necessary to repeat
such measurements when changes are made to the plant, for example power upgrades.
Small self-contained temperature recorders are available and are a practical and flexible
method for localized temperature recording to supplement bulk temperature monitoring
equipment that is already installed in the plant.
Radiation monitoring is best achieved with alanine dosimeters, which are suitable for long term
measurements. These dosimeters are not significantly affected by temperature, can be sealed
to avoid the influence of humidity and are suitable for monitoring over a wide dose range. The
radicals formed under irradiation in alanine are stable over time periods in excess of a year and
can be measured using electron spin resonance (IEC 60544-1). For more detail about radiation
monitoring, IEC TS 61244-1 shall be consulted.
6.4 Localized severe environments
Identification of localized severe environments (hotspots) where high priority components are
located is an important aspect of ageing assessment. Such locations can be identified in a
number of ways, including interviews of plant personnel, operational reviews, review of plant
layout drawings and plant walkdowns [12], [13], [14], [15]. Each will provide a different
perspective on hotspot conditions. Feedback from plant maintenance personnel is an important
aspect of identifying early signs of degradation.
6.5 Worst case components
Having prioritized the components most likely to be affected by ageing, carried out
environmental monitoring and identified localized severe environments, the components will
have been assigned to either a high, medium or low priority for further ageing management. All
components assigned to a high priority shall be subjected to ageing management activities such
as CM or planned replacement.
The evaluation process can be refined as more information becomes available. For example, if
CM of high priority cables indicates that degradation is much less severe than expected, it may
be appropriate to move these components to a lower priority category.
7 Condition monitoring techniques
7.1 General
CM techniques are used to assess the condition of materials which have aged for extended
time periods under actual use environments, such as in nuclear power plants, accelerators,
– 12 – IEC 60544-5:2022 RLV © IEC 2022
reprocessing plants, etc. The approach makes use of test methods which have been shown to
correlate well with ageing degradation.
CM in ageing assessment can be used in a number of ways, ranging from short term trouble
shooting to long term on-going qualification programmes.
7.2 Establishing correlation curves for CM methods
In order to use CM methods effectively, it is important to develop correlation curves between
the monitoring parameter measured and the prime indicator of degradation or functionality. For
low-voltage polymeric cable materials, the prime indicator of degradation is generally
considered to be tensile elongation at break, since changes in electrical properties are small
before physical failure of the cable in many cases. In seal materials, the compression set has
proved to be a useful indicator of the degradation in sealing properties introduced by ageing.
Suitable degradation parameters for other components are given in IEC 60544-2.
Correlation curves shall be determined by measurements of the prime indicator and the relevant
CM parameter on samples aged under identical conditions, as shown schematically in Figure 1.
The measurements shall cover a range of degradation levels, from the unaged condition to a
severely degraded condition. It is recommended that at least five sets of data at different ageing
times be used in establishing the correlation curve (Figure 2), preferably for several different
temperatures and radiation dose rates. An example of a correlation curve for a CSPE cable
sheath material is given in Annex A.
Correlation curves are normally established using accelerated testing. Such tests shall be
carried out using the procedures described in IEC 60544-2. Alternatively, correlation curves can
be established as part of the sample deposit procedure for ageing assessment, as described in
Clause 9, or as part of the initial equipment qualification process.
7.3 CM methods
There is a wide range of methods which have been evaluated for CM of polymeric components,
particularly for cable materials [4], [17]. Of the many methods examined, several have been
identified as being potentially suitable for practical use. Measurement standards for the most
developed of these methods are described in detail in the various parts of the IEC/IEEE 62582
series [8]. For these methods, data correlating the monitoring parameter with degradation of
the polymeric component have been built up and the practical limitations explored. The most
developed methods are
• indenter modulus;
• oxidation induction time (OIT) and oxidation induction temperature (OITP);
• elongation at break.
NOTE There are many other methods which have been investigated for CM and suitable measurement standards
for some of these are expected to be developed over the next few years. A number of these are described in
IAEA-NP-T-3.6 and IAEA-TECDOC-1825, together with their limitations [4], [17].
Visual inspection (including tactile and other sensory inspection) is a qualitative monitoring
method which can be a valuable tool in assessing localized ageing degradation within nuclear
power plants using walkdowns. The practical considerations for in-plant visual inspections
(walkdowns) are described in more detail in [12], [13], [14], [15].
Electrical methods for assessing degradation in cable systems and their associated end-devices
are described in IEC 62465 [18]. These methods primarily relate to cable systems (connectors,
penetrations, etc.) rather than degradation of the insulating materials but some methods are
showing great promise in correlating with thermal ageing degradation [18], [19].
7.4 Using CM for short-term troubleshooting
In short-term tests, the emphasis of CM is in identifying the extent of a problem or in
demonstrating that a problem does not exist. For example, the indenter has been used to
determine the extent of damage to cables from degradation arising from damaged thermal
insulation on a steam line near a cable in a BWR nuclear power plant. By carrying out indenter
measurements along this cable, a profile of the damaged area was obtained. This enabled
replacement of a limited section of cable rather than replacing the entire cable run. Another
example was the use of in-situ electrical CM methods to determine the functionality of a range
of cables in an NPP that had been in operation for 40 years. The results showed that 60 % of
the cables tested were not significantly aged and recommendations could be made for
replacement of those that had aged significantly [20].
– 14 – IEC 60544-5:2022 RLV © IEC 2022
t t t t t t t
1 2 3 4 5 6 7
Ageing time IEC 2680/11
t t t t t t t
1 2 3 4 5 6 7
IEC 2681/11
Ageing time
Condition indicator (e.g. IM)
Tensile elongation (%)
Figure 1 – Development of ageing data on changes in tensile elongation
and a condition indicator (e.g. indenter modulus) – Schematic representation
– 16 – IEC 60544-5:2022 RLV © IEC 2022
Figure 2 – Correlation curve derived from data in Figure 1 – Schematic representation
In some cases, the use of design criteria (e.g. calculation of self-heating of power cable from
current loading) can be very conservative, indicating that the insulation would be expected to
show significant degradation. Checks on the component using CM methods can be used to
demonstrate that the materials have not degraded to the extent predicted, avoiding unnecessary
replacement. This is particularly important where a short, qualified life has been determined
during EQ.
7.5 Using CM for long-term degradation assessment
CM methods can also be used in on-going test programmes which span the lifetime of the plant.
Typical uses of CM methods in such programmes are
• trending of component condition relative to a qualified condition determined during initial
EQ procedures;
• comparison of CM data with predictive modelling, based on accelerated ageing data in the
laboratory and a knowledge of the environmental conditions seen by the component;
• monitoring of components in a sample deposit located in a severe environment in the plant
(this is most frequently used for cables and small electrical components).
Figure 3 illustrates how the elongation at break can be estimated from a CM parameter such as
the indenter modulus.
Condition based qualification (CBQ) is becoming the recommended method for equipment
qualification for new NPPs [12], [13]. For this approach to EQ to be used, CM techniques shall
be applied during the pre-ageing phase of qualification to determine the shape of the ageing
curve and the limiting value of CM parameters at which the component can survive a DBE, i.e.
the qualified condition. Trending of the condition of the component relative to this qualified
condition is an essential part of CBQ.
Figure 3 – Estimation of elongation from a correlation curve
8 Predictive modelling
Data obtained during laboratory accelerated ageing tests can be used to generate model
parameters for predictive ageing models, such as those described in IEC TS 61244-2. These
models can be used to predict the degradation of specific materials under various ageing
conditions of temperature and radiation dose rate. By using the data obtained from
environmental monitoring of the actual temperatures and dose rates in the plant, the
degradation expected to occur in real-time ageing can be assessed.
This approach can also be used to estimate the effect of changes in the environmental
conditions, for example a short-term increase in temperature arising from damage to thermal
insulation on a nearby steam pipe.
The detailed accelerated ageing tests required to obtain the model parameters are most likely
to be carried out on materials for use in new plants. The use of such models combined with
design data on environmental conditions can be used during the design phase of a new plant
to identify potential problem areas where re-siting of equipment would be appropriate, for
example re-routing of a cable run to avoid a localized hotspot.
Three predictive models which make use of a matrix of accelerated ageing data are described
in detail in IEC TS 61244-2, together with the limitations and data requirements for use of these
models:
• a power law model that has proved useful for materials exposed to radiation environments
where thermal ageing is negligible;
• a time dependent superposition model which can model combined thermal and radiation
ageing for those materials with a single dominant ageing mechanism;
• a dose dependent superposition model which is particularly useful in the low dose rate
radiation ageing range where thermal ageing is important, and for materials with complex
ageing behaviour.
– 18 – IEC 60544-5:2022 RLV © IEC 2022
9 Sample deposit
9.1 General
The testing of materials from a sample deposit in the plant is an alternative approach to
assessment of ageing in service. This makes use of samples specifically installed in the plant
for destructive testing and/or CM as part of an ageing management programme.
Assessment of the long-term properties of components using a sample deposit has advantages
over accelerated ageing programmes. Its use means that the components age under real plant
conditions but can, nevertheless, be checked and monitored without impairing plant operation.
Such deposits are often installed in an area of the plant which has a relatively severe
environment compared with most other areas where such materials are used. In this case, the
sample in the deposit will age more rapidly and therefore will have a lead time over the bulk of
the material in the plant.
Most deposits are primarily used for evaluation of cables and small electrical components and
are mainly set up in a plant which has been in operation for less than five years. However, a
deposit can also be of use in an older plant, provided that the samples are pre-aged using
accelerated ageing before installation in the deposit (9.3). Samples in deposits are partic
...
IEC 60544-5 ®
Edition 3.0 2022-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electrical insulating materials – Determination of the effects of ionizing
radiation –
Part 5: Procedures for assessment of ageing in service
Matériaux isolants électriques – Détermination des effets des rayonnements
ionisants –
Partie 5: Procédures pour l'évaluation du vieillissement en service
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IEC 60544-5 ®
Edition 3.0 2022-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electrical insulating materials – Determination of the effects of ionizing
radiation –
Part 5: Procedures for assessment of ageing in service
Matériaux isolants électriques – Détermination des effets des rayonnements
ionisants –
Partie 5: Procédures pour l'évaluation du vieillissement en service
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.240; 29.035.01 ISBN 978-2-8322-3826-4
– 2 – IEC 60544-5:2022 © IEC 2022
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and abbreviated terms . 7
3.1 Terms and definitions . 7
3.2 Abbreviated terms . 7
4 Background . 8
4.1 General . 8
4.2 Diffusion-limited oxidation (DLO). 8
4.3 Dose rate effects (DRE) . 9
4.4 Accelerated radiation ageing . 9
4.5 Accelerated thermal ageing . 9
5 Approaches to ageing assessment . 10
6 Identifying components of concern . 10
6.1 General . 10
6.2 Priorities for ageing management . 10
6.3 Environmental monitoring . 10
6.4 Localized severe environments . 11
6.5 Worst case components . 11
7 Condition monitoring techniques . 11
7.1 General . 11
7.2 Establishing correlation curves for CM methods . 11
7.3 CM methods . 12
7.4 Using CM for short-term troubleshooting . 12
7.5 Using CM for long-term degradation assessment . 14
8 Predictive modelling . 15
9 Sample deposit . 16
9.1 General . 16
9.2 Requirements of a deposit . 16
9.3 Pre-ageing samples for a deposit . 16
9.4 Installation of a sample deposit . 17
9.5 Testing of samples from the deposit . 17
9.6 Determination of sampling intervals . 17
9.7 Real time aged materials . 18
Annex A (informative) Example of a CM correlation curve . 19
Annex B (informative) Use of a deposit . 20
B.1 Typical sample in a deposit . 20
B.2 Typical testing schedule for a deposit . 20
Bibliography . 21
Figure 1 – Development of ageing data on changes in tensile elongation and a
condition indicator (e.g. indenter modulus) – Schematic representation . 13
Figure 2 – Correlation curve derived from data in Figure 1 – Schematic representation . 14
Figure 3 – Estimation of elongation from a correlation curve . 15
Figure 4 – Modification of sampling interval dependent on values of the CM indicator –
Schematic representation . 18
Figure A.1 – Correlation curve for indenter modulus against tensile elongation for a
CSPE cable jacket material [24] . 19
– 4 – IEC 60544-5:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL INSULATING MATERIALS –
DETERMINATION OF THE EFFECTS OF IONIZING RADIATION –
Part 5: Procedures for assessment of ageing in service
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,
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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
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Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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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.
IEC 60544-5 has been prepared by IEC technical committee TC 112: Evaluation and
qualification of electrical insulating materials and systems. It is an International Standard.
This third edition cancels and replaces the second edition published in 2011. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) added recent references in 7.4 showing that some electrical condition monitoring methods
show promising correlations with ageing;
b) updated recommendations for implementation of a sample deposit in 9.2, installation of a
sample deposit in 9.3 and testing of samples from the deposit in 9.4;
c) updated list of references.
The text of this International Standard is based on the following documents:
Draft Report on voting
112/523/CDV 112/553/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in the IEC 60544 series, published under the general title Electrical insulating
materials – Determination of the effects of ionizing radiation, can be found on the IEC website.
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.
– 6 – IEC 60544-5:2022 © IEC 2022
INTRODUCTION
Organic and polymeric materials provide a significant proportion of the insulation used in
electrical systems. These materials are sensitive to the effects of irradiation and the response
varies widely between different types. It is therefore important to be able to assess the degree
of degradation of these insulating materials during their service lifetimes. This part of IEC 60544
provides recommended procedures for assessing ageing of insulating materials in service.
There are a number of approaches to the assessment of ageing of polymer-based components
exposed to radiation environments [1], [2], [3], [4] . These are based on the better
understanding of the factors affecting ageing degradation which has been developed over
several decades. In nuclear power plants, qualification programmes are normally used for the
selection of components, including those based on polymeric materials. These initial
TM 2 TM 2
qualification procedures, such as IEEE Std 323 -1974 [5] and IEEE Std 383 -1974 [6],
were originally written before there was sufficient understanding of ageing mechanisms. Most
of the methods discussed in this document are therefore used to supplement the initial
qualification process.
This document is the fifth in a series dealing with the effect of ionizing radiation on insulating
materials.
IEC 60544-1 (Radiation interaction and dosimetry) constitutes an introduction dealing very
broadly with the problems involved in evaluating radiation effects. It also provides guidance on
dosimetry terminology, several methods of determining exposure and absorbed dose, and
methods of calculating absorbed dose in any specific material from the dosimetry method
applied.
IEC 60544-2 (Procedures for irradiation and test) describes procedures for maintaining seven
different types of exposure conditions during irradiation. It also specifies the controls that should
be maintained over these conditions so that when test results are reported, reliable comparisons
of material performance can be made. In addition, it defines certain important irradiation
conditions and test procedures to be used for property change determinations and
corresponding end-point criteria.
IEC 60544-3 has been withdrawn and incorporated into the second edition of IEC 60544-2.
IEC 60544-4 (Classification system for service in radiation environments) provides a
recommended classification system for categorizing the radiation endurance of insulation
materials.
___________
Numbers in square brackets refer to the Bibliography.
IEEE Std 323-1974 and IEEE Std 383-1974 are now withdrawn and have been superseded by more recent
revisions.
ELECTRICAL INSULATING MATERIALS –
DETERMINATION OF THE EFFECTS OF IONIZING RADIATION –
Part 5: Procedures for assessment of ageing in service
1 Scope
This part of IEC 60544 covers ageing assessment methods which can be applied to components
based on polymeric materials (e.g. cable insulation and jackets, elastomeric seals, polymeric
coatings, gaiters) which are used in environments where they are exposed to radiation.
The object of this document is aimed at providing methods for the assessment of ageing in
service. The approaches discussed in Clause 5 through Clause 9 cover ageing assessment
programmes based on condition monitoring (CM), the use of sample deposits in severe
environments and sampling of real-time aged components.
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 60544-2, Electrical insulating materials – Determination of the effects of ionizing radiation
on insulating materials – Part 2: Procedures for irradiation and test
IEC TS 61244-1, Determination of long-term radiation ageing in polymers – Part 1: Techniques
for monitoring diffusion-limited oxidation
IEC TS 61244-2, Determination of long-term radiation ageing in polymers – Part 2: Procedures
for predicting ageing at low dose rates
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.2 Abbreviated terms
BWR boiling water reactor
CBQ condition-based qualification
CM condition monitoring
CSPE chlorosulphonated polyethylene
DBE design basis event
– 8 – IEC 60544-5:2022 © IEC 2022
DLO diffusion-limited oxidation
DRE dose rate effect
EPR ethylene propylene rubber
EQ environmental qualification
NPP nuclear power plant
OIT oxidation induction time
OITP oxidation induction temperature
PVC polyvinyl chloride
PWR pressurized water reactor
TGA thermo-gravimetric analysis
VVER water-cooled, water-moderated energy reactor (type of pressurized water reactor
developed by Russia)
XLPE cross-linked polyethylene
4 Background
4.1 General
There are a number of factors that need to be considered when assessing ageing of polymeric
components in radiation environments. In 4.2 through 4.5, some of these factors are briefly
discussed and references made to more detailed information.
To accelerate radiation-ageing environments, the normal approach is to increase the radiation
dose rate, often combined with an increase in temperature. The two most important potential
complications arising from such increases involve diffusion-limited oxidation (DLO), which is
described in 4.2, and chemical dose rate effects (DRE), which are described in 4.3. The
implications of these factors on the use and interpretation of condition monitoring (CM)
techniques are also discussed. Accelerated ageing programmes are briefly discussed in 4.4
and 4.5.
4.2 Diffusion-limited oxidation (DLO)
When polymers are exposed to an oxygen-containing environment (e.g. air), some oxygen will
be dissolved in the material. In the absence of oxygen-consuming reactions (oxidation), the
amount of dissolved oxygen will be proportional to the oxygen partial pressure surrounding the
polymer (well known from Henry’s Law). Ageing will lead to oxidation reactions in the polymer,
whose rate will increase significantly as the dose rate and temperature of ageing are increased.
If the rate of consumption of dissolved oxygen in the polymer is faster than the rate at which
oxygen can be replenished by diffusion from the surrounding atmosphere, the concentration of
dissolved oxygen in the interior regions will decrease with time (the oxygen concentration at
the sample surface will remain at its equilibrium value). The reduction in internal oxygen
concentration can lead to reduced or negligible oxidation, referred to as "diffusion-limited
oxidation".
The importance of this effect is dependent on the sample thickness (thinner samples giving
smaller DLO effects) and the ratio of the oxygen consumption rate to the oxygen permeability
coefficient P, which is the product of the oxygen diffusion and solubility parameters. Accelerated
radiation environments involve increases in dose rates, which increase the oxygen consumption
rate. If the temperature remains constant as the dose rate is increased, the oxygen permeability
coefficient will be unchanged. This means that DLO effects will become more important as the
dose rate is raised. For more detail about these effects, IEC TS 61244-1 shall be consulted.
The effects of DLO may also need to be considered when carrying out CM measurements. This
is not an issue for the many CM techniques which measure properties at ambient temperature,
such as those based on density and modulus measurements. On the other hand, several CM
techniques such as oxidation induction time (OIT) and thermogravimetric analysis (TGA) use
quite elevated temperatures during the measurements. For these techniques, it is quite possible
to have DLO effects present during measurement of the CM parameter. For this reason, detailed
test methods for CM have been developed [8] to ensure that the sample preparation and test
procedure avoid DLO effects. DLO shall be addressed when developing correlation curves for
CM methods, to ensure that representative data are obtained for both radiation and thermal
ageing.
4.3 Dose rate effects (DRE)
The existence of radiation dose rate effects and methods for dealing with these effects are
described in IEC TS 61244-2. This standard shall be consulted for more detail about these
effects. Generally, DRE are separated into two types. The first type, which is commonly
observed in accelerated radiation-ageing experiments, is due to the DLO effects described in
4.2. These DLO-based effects represent a physical, geometry-dependent DRE.
The second type of interest to the current discussion concerns chemical DRE. Such chemically
based DRE are much less common. A documented case of chemical DRE is found in PVC and
low density polyethylene materials, caused by the slow breakdown of hydroperoxide
intermediate species in the oxidation reaction [9]. The existence of such chemical DRE shall be
checked at the start of any accelerated ageing programme. If there are no data available in the
literature for the specific materials of interest, this can be checked by including tests at low
dose rates in the ageing programme.
4.4 Accelerated radiation ageing
Accelerated ageing programmes in the laboratory tend to use acceleration factors much lower
than are normally used in equipment qualification. This may avoid some of the problems
associated with DLO and DRE. The ageing produced may then be a better simulation of the
long-term ageing that occurs under service conditions. The data that are obtained in accelerated
ageing tests can be used with predictive models to enable assessments to be made of the
behaviour of the materials under service conditions.
Accelerated ageing programmes require a matrix of test data to be generated over a range of
environmental conditions as described in IEC TS 61244-2. As a minimum, data are needed for
at least three different dose rates at the normal operating temperature but additional data on
thermal ageing and radiation ageing at elevated temperature enables better use to be made of
the available predictive modelling methods. The dose rates and temperatures used for
accelerated ageing should be selected using the principles described in IEC 60544-2 to ensure
that homogeneous oxidation occurs. For each environmental condition used, test data shall be
obtained at several different ageing times, the longest of which should be sufficient to introduce
significant degradation. A typical test programme could take more than 18 months to complete,
dependent on the radiation resistance of the materials being tested.
The data required in the test matrix are determined by the type of component being evaluated.
The appropriate test parameters are given in IEC 60544-2 for various types of polymeric
materials and components.
4.5 Accelerated thermal ageing
When carrying out thermal ageing as part of an accelerated ageing programme, it is important
that an appropriate value of the activation energy is used in assessing the temperature and
timescale of the accelerated test. In some materials, the ageing mechanism at high
temperatures is different to that which would occur under plant conditions and in many materials
the activation energy decreases significantly at lower temperatures [10], [11].
Samples which have been exposed to accelerated thermal ageing shall be allowed to stabilize
before any CM tests are carried out. Some polymeric materials are hygroscopic and show a
marked dependence of their properties on the moisture content [8]. This is primarily of concern
– 10 – IEC 60544-5:2022 © IEC 2022
for a few materials used in older nuclear power plants, but may also be important for those CM
methods that are sensitive to the moisture content of the material.
5 Approaches to ageing assessment
There are a number of complementary methods available for ageing assessment as described
in their respective clauses. Each of these methods has its own advantages and limitations.
Selection of one or more of the methods will be dependent on the requirements of the individual
users.
Several approaches to ageing assessment in-service are described in this document. These
are:
• identifying components of concern to prioritize the application of ageing management
programmes (see Clause 6);
• condition monitoring to assess the condition of materials which have aged for extended time
periods under actual use environments (see Clause 7);
• predictive modelling to use data from laboratory based accelerated ageing programmes to
estimate ageing under real-time ageing conditions (see Clause 8);
• sample deposit to provide samples for the measurement of ageing under real-time ageing
conditions (see Clause 9).
6 Identifying components of concern
6.1 General
Within a nuclear power plant, there are many components containing polymeric insulating
materials, for example there are over 1 000 km of electrical cables in a typical NPP. It is not
practical to assess the ageing of every individual component, and many will not be exposed to
significant environmental ageing conditions. It is therefore necessary to prioritize any ageing
management programme by identifying those components which are of most concern.
6.2 Priorities for ageing management
Not all components have the same priority for ageing management. In general, those
components performing safety functions during and following an accident are of most concern,
together with those important to continued operation. Any components outside of these
categories would initially be assigned to a low priority for ageing management activities.
The normal operating environment of the components shall be examined to identify the
expected impact of the environment on their ageing. Those components identified as being
subject to severe ageing are assigned the highest priority, whereas those subject to moderate
ageing can then be assigned to a medium priority.
For this prioritization to be carried out effectively, environmental monitoring is essential (see
6.3), combined with knowledge of the ageing behaviour of the components. Initial assessment
may make use of design calculations for temperatures and dose rates. The ageing information
may come from equipment qualification data or from supplementary accelerated ageing tests
carried out in the laboratory.
6.3 Environmental monitoring
Ageing of insulating materials in an NPP is dominated by temperature, radiation dose and
radiation dose rate for polymeric materials. A major requirement for ageing management is a
detailed knowledge of the actual temperatures and dose rates at locations within the plant
where high priority components are situated.
The temperature and dose rate distribution within the plant shall be obtained using temperature
recorders and dosimeters. Operational fluctuations and seasonal variations shall be included
by carrying out these measurements over several fuel cycles. It may be necessary to repeat
such measurements when changes are made to the plant, for example power upgrades.
Small self-contained temperature recorders are available and are a practical and flexible
method for localized temperature recording to supplement bulk temperature monitoring
equipment that is already installed in the plant.
Radiation monitoring is best achieved with alanine dosimeters, which are suitable for long term
measurements. These dosimeters are not significantly affected by temperature, can be sealed
to avoid the influence of humidity and are suitable for monitoring over a wide dose range. The
radicals formed under irradiation in alanine are stable over time periods in excess of a year and
can be measured using electron spin resonance. For more detail about radiation monitoring,
IEC TS 61244-1 shall be consulted.
6.4 Localized severe environments
Identification of localized severe environments (hotspots) where high priority components are
located is an important aspect of ageing assessment. Such locations can be identified in a
number of ways, including interviews of plant personnel, operational reviews, review of plant
layout drawings and plant walkdowns [12], [13], [14], [15]. Each will provide a different
perspective on hotspot conditions. Feedback from plant maintenance personnel is an important
aspect of identifying early signs of degradation.
6.5 Worst case components
Having prioritized the components most likely to be affected by ageing, carried out
environmental monitoring and identified localized severe environments, the components will
have been assigned to either a high, medium or low priority for further ageing management. All
components assigned to a high priority shall be subjected to ageing management activities such
as CM or planned replacement.
The evaluation process can be refined as more information becomes available. For example, if
CM of high priority cables indicates that degradation is much less severe than expected, it may
be appropriate to move these components to a lower priority category.
7 Condition monitoring techniques
7.1 General
CM techniques are used to assess the condition of materials which have aged for extended
time periods under actual use environments, such as in nuclear power plants, accelerators,
reprocessing plants. The approach makes use of test methods which have been shown to
correlate well with ageing degradation.
CM in ageing assessment can be used in a number of ways, ranging from short term trouble
shooting to long term on-going qualification programmes.
7.2 Establishing correlation curves for CM methods
In order to use CM methods effectively, it is important to develop correlation curves between
the monitoring parameter measured and the prime indicator of degradation or functionality. For
low-voltage polymeric cable materials, the prime indicator of degradation is generally
considered to be tensile elongation at break, since changes in electrical properties are small
before physical failure of the cable in many cases. In seal materials, the compression set has
proved to be a useful indicator of the degradation in sealing properties introduced by ageing.
Suitable degradation parameters for other components are given in IEC 60544-2.
– 12 – IEC 60544-5:2022 © IEC 2022
Correlation curves shall be determined by measurements of the prime indicator and the relevant
CM parameter on samples aged under identical conditions, as shown schematically in Figure 1.
The measurements shall cover a range of degradation levels, from the unaged condition to a
severely degraded condition. It is recommended that at least five sets of data at different ageing
times be used in establishing the correlation curve (Figure 2), preferably for several different
temperatures and radiation dose rates. An example of a correlation curve for a CSPE cable
sheath material is given in Annex A.
Correlation curves are normally established using accelerated testing. Such tests shall be
carried out using the procedures described in IEC 60544-2. Alternatively, correlation curves can
be established as part of the sample deposit procedure for ageing assessment, as described in
Clause 9, or as part of the initial equipment qualification process.
7.3 CM methods
There is a wide range of methods which have been evaluated for CM of polymeric components,
particularly for cable materials [4], [17]. Of the many methods examined, several have been
identified as being potentially suitable for practical use. Measurement standards for the most
developed of these methods are described in detail in the various parts of the IEC/IEEE 62582
series [8]. For these methods, data correlating the monitoring parameter with degradation of
the polymeric component have been built up and the practical limitations explored. The most
developed methods are
• indenter modulus;
• oxidation induction time (OIT) and oxidation induction temperature (OITP);
• elongation at break.
NOTE There are many other methods which have been investigated for CM and suitable measurement standards
for some of these are expected to be developed over the next few years. A number of these are described in
IAEA-NP-T-3.6 and IAEA-TECDOC-1825, together with their limitations [4], [17].
Visual inspection (including tactile and other sensory inspection) is a qualitative monitoring
method which can be a valuable tool in assessing localized ageing degradation within nuclear
power plants using walkdowns. The practical considerations for in-plant visual inspections
(walkdowns) are described in more detail in [12], [13], [14], [15].
Electrical methods for assessing degradation in cable systems and their associated end-devices
are described in IEC 62465 [18]. These methods primarily relate to cable systems (connectors,
penetrations, etc.) rather than degradation of the insulating materials but some methods are
showing great promise in correlating with thermal ageing degradation [18], [19].
7.4 Using CM for short-term troubleshooting
In short-term tests, the emphasis of CM is in identifying the extent of a problem or in
demonstrating that a problem does not exist. For example, the indenter has been used to
determine the extent of damage to cables from degradation arising from damaged thermal
insulation on a steam line near a cable in a BWR nuclear power plant. By carrying out indenter
measurements along this cable, a profile of the damaged area was obtained. This enabled
replacement of a limited section of cable rather than replacing the entire cable run. Another
example was the use of in-situ electrical CM methods to determine the functionality of a range
of cables in an NPP that had been in operation for 40 years. The results showed that 60 % of
the cables tested were not significantly aged and recommendations could be made for
replacement of those that had aged significantly [20].
Figure 1 – Development of ageing data on changes in tensile elongation
and a condition indicator (e.g. indenter modulus) – Schematic representation
– 14 – IEC 60544-5:2022 © IEC 2022
Figure 2 – Correlation curve derived from data in Figure 1 – Schematic representation
In some cases, the use of design criteria (e.g. calculation of self-heating of power cable from
current loading) can be very conservative, indicating that the insulation would be expected to
show significant degradation. Checks on the component using CM methods can be used to
demonstrate that the materials have not degraded to the extent predicted, avoiding unnecessary
replacement. This is particularly important where a short, qualified life has been determined
during EQ.
7.5 Using CM for long-term degradation assessment
CM methods can also be used in on-going test programmes which span the lifetime of the plant.
Typical uses of CM methods in such programmes are
• trending of component condition relative to a qualified condition determined during initial
EQ procedures;
• comparison of CM data with predictive modelling, based on accelerated ageing data in the
laboratory and a knowledge of the environmental conditions seen by the component;
• monitoring of components in a sample deposit located in a severe environment in the plant
(this is most frequently used for cables and small electrical components).
Figure 3 illustrates how the elongation at break can be estimated from a CM parameter such as
the indenter modulus.
Condition based qualification (CBQ) is becoming the recommended method for equipment
qualification for new NPPs [12], [13]. For this approach to EQ to be used, CM techniques shall
be applied during the pre-ageing phase of qualification to determine the shape of the ageing
curve and the limiting value of CM parameters at which the component can survive a DBE, i.e.
the qualified condition. Trending of the condition of the component relative to this qualified
condition is an essential part of CBQ.
Figure 3 – Estimation of elongation from a correlation curve
8 Predictive modelling
Data obtained during laboratory accelerated ageing tests can be used to generate model
parameters for predictive ageing models, such as those described in IEC TS 61244-2. These
models can be used to predict the degradation of specific materials under various ageing
conditions of temperature and radiation dose rate. By using the data obtained from
environmental monitoring of the actual temperatures and dose rates in the plant, the
degradation expected to occur in real-time ageing can be assessed.
This approach can also be used to estimate the effect of changes in the environmental
conditions, for example a short-term increase in temperature arising from damage to thermal
insulation on a nearby steam pipe.
The detailed accelerated ageing tests required to obtain the model parameters are most likely
to be carried out on materials for use in new plants. The use of such models combined with
design data on environmental conditions can be used during the design phase of a new plant
to identify potential problem areas where re-siting of equipment would be appropriate, for
example re-routing of a cable run to avoid a localized hotspot.
Three predictive models which make use of a matrix of accelerated ageing data are described
in detail in IEC TS 61244-2, together with the limitations and data requirements for use of these
models:
• a power law model that has proved useful for materials exposed to radiation environments
where thermal ageing is negligible;
• a time dependent superposition model which can model combined thermal and radiation
ageing for those materials with a single dominant ageing mechanism;
• a dose dependent superposition model which is particularly useful in the low dose rate
radiation ageing range where thermal ageing is important, and for materials with complex
ageing behaviour.
– 16 – IEC 60544-5:2022 ©
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