IEC 60544-5:2011
(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 60544-5:2011 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 standard is aimed at providing methods for the assessment of ageing in service. The approaches discussed in the following clauses 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 second edition cancels and replaces the first edition, published in 2003, and constitutes an editorial revision to align it with standards recently developed by SC 45A as well as with other parts in the IEC 60544 series.
Matériaux isolants électriques - Détermination des effets des rayonnements ionisants - Partie 5: Procédures pour l'estimation du vieillissement en service
La CEI 60544-5:2011 couvre les méthodes d'évaluation du vieillissement pouvant être appliquées aux composants à base de matériaux polymères (par exemple, des gaines et isolations de câble, des joints en élastomère, des revêtements polymères, des gaines) qui sont utilisés dans des environnements où ils sont exposés aux rayonnements. L'objet de la présente norme est destiné à fournir des méthodes d'évaluation du vieillissement en service. Les approches examinées dans les articles qui suivent couvrent les programmes d'évaluation de vieillissement fondés sur le contrôle des conditions (CM), l'utilisation de dépôt d'échantillons dans des environnements sévères et l'échantillonnage de composants vieillis en temps réel. Cette deuxième édition annule et remplace la première édition, publiée en 2003, dont elle constitue une éditoriale révisée destinée à aligner ce document avec des normes récemment élaborées au sein du SC 45A, ainsi qu'avec d'autres parites de la série CEI 60544.
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IEC 60544-5 ®
Edition 2.0 2011-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
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'estimation du vieillissement en service
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IEC 60544-5 ®
Edition 2.0 2011-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
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'estimation du vieillissement en service
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX S
ICS 17.240; 29.035.01 ISBN 978-2-88912-836-5
– 2 – 60544-5 IEC:2011
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope and object . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Background . 7
4.1 General . 7
4.2 Diffusion limited oxidation (DLO) . 7
4.3 Dose rate effects (DRE) . 8
4.4 Accelerated radiation ageing . 8
4.5 Accelerated thermal ageing . 9
5 Approaches to ageing assessment . 9
6 Identifying components of concern . 9
6.1 General . 9
6.2 Priorities for ageing management . 9
6.3 Environmental monitoring . 10
6.4 Localized severe environments . 10
6.5 Worst case components . 10
7 Condition monitoring techniques . 10
7.1 General . 10
7.2 Establishing correlation curves for CM methods . 11
7.3 CM methods . 11
7.4 Using CM for short-term troubleshooting . 11
7.5 Using CM for long-term degradation assessment . 13
8 Predictive modelling . 14
9 Sample deposit . 15
9.1 General . 15
9.2 Requirements of a deposit . 15
9.3 Pre-ageing samples for a deposit . 15
9.4 Installation of an sample deposit . 15
9.5 Testing of samples from the deposit . 16
9.6 Determination of sampling intervals . 16
9.7 Real time aged materials . 17
Annex A (informative) Example of a CM correlation curve . 18
Annex B (informative) Use of a deposit . 19
Bibliography . 20
Figure 1 – Development of ageing data on changes in tensile elongation and a
condition indicator (e.g. indenter modulus) – Schematic. 12
Figure 2 – Correlation curve derived from data in Figure 1 – Schematic . 13
Figure 3 – Estimation of elongation from a correlation curve . 14
Figure 4 – Modification of sampling interval dependent on values of the CM indicator . 17
Figure A.1 – Correlation curve for indenter modulus against tensile elongation for a
CSPE cable jacket material [18] . 18
60544-5 IEC:2011 – 3 –
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
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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.
International Standard IEC 60544-5 has been prepared IEC technical committee TC 112:
Evaluation and qualification of electrical insulating materials and systems.
This second edition cancels and replaces the first edition, published in 2003, and constitutes
an editorial revision to align it with standards recently developed by SC 45A as well as with
other parts in the IEC 60544 series.
The text of this standard is based on the following documents:
CDV Report on voting
112/171/CDV 112/191/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
– 4 – 60544-5 IEC:2011
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
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 publication will remain unchanged until
the stability 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.
IMPORTANT – The 'colour inside' logo on the cover page of this publication 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.
60544-5 IEC:2011 – 5 –
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 [1–4] . 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
selection of components, including those based on polymeric materials. These initial
qualification procedures, such as IEEE-323 [5] and IEEE-383 [6], were originally written
before there was sufficient understanding of ageing mechanisms. Most of the methods
discussed in this part of IEC 60544 are therefore used to supplement the initial qualification
process.
This part is the fifth in a series dealing with the effect of ionizing radiation on insulating
materials.
Part 1 (Radiation interaction and dosimetry) constitutes an introduction dealing very broadly
with the problems involved in evaluating radiation effects. It also provides guidance to
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.
Part 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.
Part 3 has been incorporated into the second edition of IEC 60544-2.
Part 4 (Classification system for service in radiation environments) provides a recommended
classification system for categorizing the radiation endurance of insulation materials.
___________
Figures in square brackets refer to the bibliography.
– 6 – 60544-5 IEC:2011
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 standard is aimed at providing methods for the assessment of ageing in
service. The approaches discussed in the following clauses 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, in whole or in part, are normatively referenced in this document and
are indispensable for its application. 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, Guide for determining the effects of ionizing radiation on insulating materials –
Part 2: Procedures for irradiation and test
IEC 61244-1, Determination of long-term radiation ageing in polymers – Part 1: Techniques
for monitoring diffusion-limited oxidation
IEC 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
60544-5 IEC:2011 – 7 –
3 Terms and definitions
For the purposes of this document, the following abbreviations, taken from IEC 60780, apply.
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 the following clauses 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, 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
– 8 – 60544-5 IEC:2011
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.
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 61244-2. 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 [10]. The existence of such
chemical DRE shall be checked at the start of any accelerated 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 61244-2. As a minimum, data are needed for at
least 3 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.
60544-5 IEC:2011 – 9 –
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 material.
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 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 plant, 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 standard. 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, e.g. there are >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
– 10 – 60544-5 IEC:2011
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
6.2), 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 a 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, e.g. 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).
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 [11,12]. 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 subject 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,
60544-5 IEC:2011 – 11 –
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 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 5 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]. 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 IEC 62582 [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 [4].
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
plant using walkdowns. The practical considerations for in-plant visual inspections
(walkdowns) are described in more detail in [11,12].
Electrical methods for assessing degradation in cable systems and their associated end-
devices are described in IEC 62465 [14]. These methods primarily relate to cable systems
(connectors, penetrations etc.) rather than degradation of the insulating materials.
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
– 12 – 60544-5 IEC:2011
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.
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
Figure 1 – Development of ageing data on changes in tensile elongation
and a condition indicator (e.g. indenter modulus) – Schematic
Condition indicator (e.g. IM)
Tensile elongation (%)
60544-5 IEC:2011 – 13 –
Correlation curve
0 20 40 60 80 100 120 140 160
Tensile elongation (%)
IEC 2682/11
Figure 2 – Correlation curve derived from data in Figure 1 – Schematic
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 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.
Condition indicator (e.g. IM)
– 14 – 60544-5 IEC:2011
Measured value
of CM parameter
Estimated value
of elongation
Elongation at break
IEC 2683/11
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 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, e.g. 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 plant. The use of such models combined with
design data on environmental conditions can be used during the design phase of new plant to
identify potential problem areas where re-siting of equipment would be appropriate, e.g. 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 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.
Condition monitoring parameter
60544-5 IEC:2011 – 15 –
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 5 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. Samples in deposits are particularly
useful for on-going qualification programmes.
9.2 Requirements of a deposit
A major prerequisite for the implementation of a sample deposit is a good knowledge of the
radiation dose and temperature distribution at the deposit position and at positions in the
plant where the material being tested is in routine use.
Environmental monitoring can be used to select a position in the plant that is exposed to a
higher dose than most of the real positions. It may even be possible to find a location where
the temperature is also similar to the maximum design temperature. Experience has shown
that the loop line between the reactor pressure vessel and the steam generator is suitable for
this purpose in pressurized water reactors (PWRs) and the reactor water clean-up system in
boiling water reactors (BWRs). In VVER type reactors, the main circulation pipe, either hot or
cold leg, is also a suitable location for a deposit.
In selecting a posi
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