IEC/IEEE 62582 1 2011, Nuclear power plants – Instrumentation and control important to safety – Electrical equipment condition monitoring methods – Part 1 General IEC/IEEE 62582 1 Edition 1 0 2011 08[.]
General
Condition monitoring is essential only when a clear connection exists between the aging degradation of the monitored component and the safety function of the equipment This connection must be established during the equipment qualification process and should consider any diffusion-limited rate effects that may arise during accelerated aging with high acceleration factors.
Condition monitoring programs utilize measurable indicators to assess the degradation of materials To evaluate the condition of naturally aged components, samples can be taken destructively or measured non-destructively in the field Non-destructive methods are favored as they enable the study of materials without disrupting operations However, achieving the necessary repeatability and accuracy for these measurements in the field can be challenging.
Aging in organic materials can negatively affect safety functions due to various chemical reactions, such as chain scission and cross-linking, which change the polymeric structure Therefore, it is crucial for condition monitoring programs to identify methods that track the progression of these reactions, either directly or indirectly While numerous techniques are available for this purpose, this standard will concentrate on general categories of methods rather than detailing each individual approach.
The overall description of these groups is provided below.
Chemical indicators
The degradation of organic materials occurs through a series of chemical reactions that alter the polymer's chemical structure This progressive change allows for the monitoring of degradation as the material ages Various techniques are available to assess this process, including methods that focus on the degradation of the polymer chains and those that observe related side reactions.
Physical indicators
A crucial set of indicators involves techniques that assess the physical properties of materials The deterioration of organic materials is reflected in alterations to these properties, such as tensile strength, elongation, and hardness By evaluating these characteristics, one can establish a relationship with the material's aged condition.
Electrical indicators
A third category of techniques involves measuring electrical properties of the materials Many of these techniques were developed for polymeric materials used in electrical insulation
Within this family there are two basic subsets of methods The first subset involves measuring the dielectric properties of the materials
A second category of methods involves monitoring the electrical response of systems during normal operation In this approach, a signal is transmitted through the electrical system, allowing for the detection of any deviations from the baseline Such changes may indicate degradation due to aging or physical damage.
Miscellaneous Indicators
With the advancement of new technologies, it is essential to create condition monitoring methods that evolve accordingly Consequently, some techniques are tailored specifically for particular types of materials.
5 Applicability of condition indicators to different types of organic materials
Currently, there is no universal condition monitoring method applicable to all organic or polymeric materials For inclusion in IEC/IEEE 62582, condition indicators must be sensitive to aging effects A valuable condition indicator should exhibit a consistent trend that correlates with degradation and safety-related performance Indicators that remain stable for extended periods before experiencing sudden changes are ineffective for prognostic applications, particularly in mechanical condition monitoring of semi-crystalline materials like cross-linked polyethylene and thermosetting resins, which can vary based on their formulation.
Information on the applicability of various condition indicators to different polymeric materials used in instrument and control equipments in nuclear power plants can be found in
NUREG/CR-7000 and in IAEA-TECDOC-1188, see Bibliography
6 Destructive and non-destructive condition monitoring
Condition monitoring methods can be classified as either destructive or non-destructive, based on their impact on the operability and future aging of the material being measured Non-destructive condition monitoring is ideal for field measurements; however, current techniques are primarily applicable to specific equipment types, such as cables, where critical components are easily accessible In other situations, condition monitoring requires the use of deposited or replaceable samples to facilitate accurate assessments.
When deposited samples are accessible or components can be substituted, a wider array of condition monitoring techniques, including destructive methods, can be utilized This approach allows for condition monitoring across various equipment types, particularly where aging materials, typically organic substances used for electrical insulation and sealing, are reachable.
7 Application of condition monitoring in equipment qualification and management of ageing
General
Condition monitoring plays a crucial role in the qualification and management of aging electrical equipment in nuclear power plants Its primary objectives include determining acceleration factors to establish qualified life through artificial laboratory aging, extending the qualified life of equipment, establishing a qualified condition, and conducting periodic assessments of equipment condition post-installation to ensure it aligns with the qualified condition.
Condition monitoring is essential for assessing the degradation of age-sensitive materials in equipment, ensuring it remains within established limits These limits are defined to guarantee that any effects on operability under specified service conditions and design basis events are minimal.
Use of condition monitoring in the establishment of qualified life
Establishment of qualified life
The qualified lifespan of equipment is typically determined through accelerated aging tests conducted in a laboratory, which are then validated against performance criteria during a simulated design basis event The acceleration factor represents the comparison between the degradation rate observed in laboratory simulations and that experienced under normal field operating conditions.
Condition monitoring is used to establish activation energies for calculation of the acceleration factor in accelerated thermal ageing.
Determination of acceleration factor in accelerated thermal ageing
The acceleration factor F in accelerated thermal ageing is normally calculated by application of the Arrhenius equation as follows: ằ ẳ ô º ơ ê
F t (1) where t 1 and t 2 are the times to reach a certain level of degradation at the temperatures T 1 and T 2 (in kelvins); E is the activation energy and k is the Boltzmann constant
The Arrhenius equation, expressed as \$ r = A e^{-E/(kT)} \$, describes how the rate \$ r \$ of a chemical reaction depends on temperature In this equation, \$ A \$ represents the pre-factor, also known as the frequency factor for first-order reactions, measured in s\(^{-1}\) The activation energy \$ E \$, measured in eV, is the minimum energy required for a reaction to take place The Boltzmann constant \$ k \$, valued at approximately \$ 8.617 \times 10^{-5} \text{ eV K}^{-1} \$, and the temperature \$ T \$, measured in Kelvin, are also key components of this relationship.
The activation energy of a material is determined by measuring a condition indicator over time at various temperatures These temperature and time pairs, which correspond to a specific degradation level, are represented in an Arrhenius diagram In this diagram, the inverse of the temperatures (in Kelvin) is plotted on a linear scale along the x-axis, while the time is displayed on a logarithmic scale on the y-axis An illustrative example can be found in Figure 1.
Figure 1 – Example of an Arrhenius diagram
The presence of a straight line connecting the points demonstrates an Arrhenius relationship between the degradation rate and temperature The activation energy \(E\) (measured in eV) is determined from the slope of this line.
The acceleration factor and the qualified life are highly sensitive to the activation energy value Any inaccuracies in determining the activation energy can significantly impact the acceleration factor and, in turn, the qualified life derived from tests involving artificial accelerated thermal aging, as demonstrated in Figure 2.
Qual if ied l if e (y ears )
NOTE The normal service temperature is 50 o C E=0,9 eV
Figure 2 – Influence of activation energy on qualified life, determined from artificial thermal ageing for 42 days at 110 °C, followed by simulated design basis event
The example illustrates the need for high accuracy and repeatability of the condition monitoring methods used in measurements for the determination of activation energies.
Use of condition monitoring in the extension of qualified life
Establishing qualified life during initial qualification testing typically involves a high degree of conservatism, accounting for uncertainties in field environmental conditions, acceleration factors for simulated laboratory aging, performance demonstration, production variations, and measurement equipment This conservative approach, combined with time constraints and moderate acceleration factors, can lead to a qualified life that significantly differs from the actual service life tolerable before a design basis event To extend the qualified life, methods often include monitoring the condition of representative samples of installed equipment.
Use of condition monitoring in the establishment and assessment of qualified
Condition based qualification is included in IEEE 323-2003 as a complement or alternative to qualified life
Condition-based qualification involves determining the values of relevant condition indicators at the end of the ageing process before conducting design basis event testing, which represent the qualified condition This approach significantly benefits from establishing trends in these condition indicators over time, particularly through incremental artificial ageing and measurement at each stage Following installation, periodic measurements of the condition of representative samples are conducted and compared to the qualified condition, as illustrated in Figure 3.
Condition development during artificial ageing
Condi ti on i ndi c at or v al ue t 1 t t 2 2 t 3 t i Time at which condition monitoring is carried out
Qualified condition Condition development of installed specimen
Figure 3 – Illustration of condition-based qualification
The qualified condition can be established during the initial qualification testing If this testing aimed solely to determine a qualified life without condition monitoring, it may still be possible to establish the qualified condition later without redoing the design basis event testing Provided that identical samples of equipment are available, either new or stored in controlled environments, the qualified condition can be confirmed by repeating the aging process from the original qualification testing and assessing the relevant condition indicators both during and at the conclusion of this aging.
Post-installation measurements may be conducted by different personnel and in various laboratories compared to those used during the establishment of the qualified condition This necessitates stringent specifications for condition monitoring methods, along with thorough documentation and repeatability of measurements Detecting even minor changes in the condition indicator values is crucial, which demands a high level of accuracy in the monitoring methods employed.
Use of baseline data
Condition monitoring is essential for assessing degradation limits, ensuring that functionality remains largely unaffected during service conditions and simulated design basis events.
The effectiveness of data on condition indicators, which have shown operability in simulated design basis events, relies heavily on the repeatability and accuracy of the employed methods, as well as the clarity and thoroughness of the condition monitoring definitions and reports.
IEC 60544-5, Electrical insulating materials – Determination of the effects of ionizing radiation
– Part 5: Procedures for assessment of ageing in service
IEC 60780, Nuclear power plants – Electrical equipment of the safety system – Qualification
IEC 62342, Nuclear power plants – Instrumentation and control systems important to safety –
IEEE Std 1205, IEEE Guide for Assessing, Monitoring, and Mitigating Aging Effects on
Class 1E Equipment Used in Nuclear Power Generating Stations
NUREG/CR-6704, Vol 2 (BNL -NUREG-52610), Assessment of Environmental Qualification
Practices and Condition Monitoring Techniques for Low-Voltage Electric Cables, Condition
JNES-SS-0903:2009, The final report of the project “Assessment of cable ageing for nuclear power plant” T Yamamoto & T Minikawa, Japan Nuclear Energy Safety Organisation,
Nuclear Energy System Safety Division
NUREG/CR-7000, Essential Elements of an Electric Cable Condition Monitoring Program
IAEA-TECDOC-1188:2000, Assessment and management of ageing of major nuclear power plant components important to safety: In-containment instrumentation and control cables,
5 Possibilités d’utiliser les indicateurs d’état pour différents types de matériaux organiques 24
6 Surveillance d’état destructive et non destructive 24
7 Utilisation de la surveillance d’état dans le cadre de la qualification des équipements et de la gestion du vieillissement 24
7.2 Utilisation de la surveillance d’état pour déterminer la durée de vie certifiée 25
7.2.1 Détermination de la durée de vie certifiée 25
7.2.2 Détermination du facteur d’accélération en vieillissement thermique accéléré 25
7.3 Utilisation de la surveillance d’état pour l’extension de la durée de vie certifiée 27
7.4 Utilisation de la surveillance d’état pour la détermination et l’évaluation de l’état qualifié 27
7.5 Utilisation de données de base 28
Figure 1 – Exemple de diagramme d’Arrhenius 26
Figure 2 – Influence de l’énergie d’activation sur la durée de vie certifiée, déterminée après une phase de vieillissement thermique artificiel de 42 jours à 110 °C, suivie de la simulation d’un évènement de dimensionnement 26
Figure 3 – Illustration de la qualification basée sur la surveillance d’état 28
CENTRALES NUCLÉAIRES DE PUISSANCE – INSTRUMENTATION ET CONTRÔLE-COMMANDE
IMPORTANTS POUR LA SÛRETÉ – MÉTHODES DE SURVEILLANCE DE L’ÉTAT DES MATÉRIELS ÉLECTRIQUES –
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La Norme internationale CEI/IEEE 62582-1 a été établie par le sous-comité 45A:
Instrumentation et contrôle-commande des installations nucléaires, du comité d'études 45 de la CEI: Instrumentation nuclộaire, en coopộration avec le ô Nuclear Power Engineering
Committee ằ de la ô Power & Energy Society ằ de l'IEEE 1 , selon l'accord double logo CEI/IEEE entre la CEI et l'IEEE
La présente publication est une norme double logo CEI/IEEE
Le texte de cette norme est issu des documents suivants de la CEI:
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Les normes internationales sont rédigées selon les Directives ISO/CEI, Partie 2
Une liste de toutes les parties de la série CEI/IEEE 62582, présentées sous le titre général
Nuclear power plants rely on crucial instrumentation and control systems to ensure safety Effective monitoring methods for the condition of electrical equipment are essential and can be found on the IEC website.
The IEC study committee and the IEEE study committee have agreed that the content of this publication will remain unchanged until the stability date specified on the website.
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1 Une liste des participants IEEE est disponible à l'adresse suivante:http://standards.ieee.org/downloads/62582-
INTRODUCTION a) Contexte technique, questions importantes et structure de la présente norme
Généralités
State monitoring should only be conducted if a known relationship exists between the aging degradation of the monitored component and the associated safety function degradation of the equipment This relationship should be established during the equipment qualification process Additionally, it is essential to consider any effects of limited flow diffusion that may occur during accelerated aging associated with high acceleration factors.
State monitoring programs rely on measurable indicators that assess the overall degradation of materials To evaluate the condition of naturally aged components, one must either take destructive samples or conduct non-destructive measurements in the field Non-destructive methods are preferred as they allow for the study of materials without interrupting operations; however, achieving sufficient reproducibility and precision in these measurements directly on-site can often be challenging.
The aging of organic materials can negatively affect critical safety functions due to various chemical reactions, including chain breaks and reassociations that degrade polymer structures Therefore, it is essential to develop methods for monitoring the progression of these reactions in state surveillance programs Numerous techniques are available for this purpose, making it challenging to provide a comprehensive overview of each individual method.
A la place, cette norme va s’intéresser aux principaux groupes de méthodes La description d’ensemble de ces groupes est fournie ci-dessous.
Indicateurs chimiques
The degradation mechanisms of organic materials result from a series of chemical reactions that alter the chemical structure of polymers The gradual changes in the chemical characteristics of these materials provide an opportunity to monitor their degradation over time Various techniques are available for this purpose, with some focusing on the monitoring of polymer chain degradation, while others track related reactions associated with this process.
Indicateurs physiques
Another key family of indicators involves techniques that monitor the physical properties of materials The degradation of organic materials is reflected in changes to these physical properties, such as tensile strength, elongation, and hardness By measuring these physical characteristics, it is possible to establish a correlation with the aging state of the materials.
Indicateurs électriques
A third category of techniques involves measuring the electrical properties of materials, particularly those developed for polymer materials used as electrical insulators This category includes two subsets of methods, with the first subset focusing on the measurement of dielectric properties.
The second subset of methods focuses on monitoring the electrical response of operating systems In these instances, a signal is transmitted through the electrical system, and any deviations from the baseline signal are detected These deviations may indicate degradation caused by aging or physical damage.
Indicateurs divers
Comme de nouvelles technologies sont développées et mises en oeuvre, il devient nécessaire de développer des méthodes de surveillance de l’état pour rester en phase avec l’état de l’art
Ainsi, certaines méthodes sont développées spécifiquement pour certains types de matériaux
5 Possibilités d’utiliser les indicateurs d’état pour différents types de matériaux organiques
There is no single monitoring method suitable for all organic materials and polymers A fundamental requirement for a method to be covered by IEC/IEEE 62582 is that the associated condition indicators must be sensitive to aging effects An important characteristic of a condition indicator is that it shows a monotonic trend in relation to degradation and correlates with safety-related performance An indicator that remains invariant for a long time and then suddenly exhibits significant variations is of no use for applications aimed at establishing prognostics This can occur in the mechanical condition monitoring of semi-crystalline materials, such as cross-linked polyethylene and thermoplastic resins, depending on their compositions.
Information regarding the applicability of various state indicators for different polymer materials used in the instrumentation and control systems of nuclear power plants is available in the documents.
NUREG/CR-7000 et IAEA-TECDOC-1188, voir la Bibliographie
6 Surveillance d’état destructive et non destructive
State monitoring methods are classified as either destructive or non-destructive based on whether the measurements or sampling of materials affect the operability or future aging Non-destructive state monitoring, such as field measurements, is preferred; however, current methods are limited to specific types of equipment, primarily cables, where relevant components for measurement are accessible on-site In other cases, testing samples or replaceable samples are required to conduct state monitoring.
When samples from a deposit are available or when components can be replaced, a wider range of methods, including destructive techniques, can be employed In this context, condition monitoring can be applied to all types of equipment for which access to aged materials—typically organic materials used for electrical insulation, sealing, and more—is possible.
7 Utilisation de la surveillance d’état dans le cadre de la qualification des équipements et de la gestion du vieillissement
Général
State surveillance, as part of the qualification and management of aging electrical equipment in nuclear power plants, aims to achieve one or more of the following objectives: determining acceleration factors to assess certified lifespan based on artificial aging in the laboratory; extending the certified lifespan; declaring the qualified state; and conducting periodic evaluations of the equipment's condition post-installation for comparison with the qualified state.
State surveillance can also be employed to assess whether the degradation of materials sensitive to aging exceeds specified limits These limits are established to ensure that the effects on operation under defined service conditions and for design events are negligible.
Utilisation de la surveillance d’état pour déterminer la durée de vie certifiée
Détermination de la durée de vie certifiée
The certified lifespan of equipment is typically established through accelerated aging tests conducted on samples in a laboratory, followed by an assessment of their operational suitability against acceptance criteria under simulated sizing events The acceleration factor is defined as the ratio of the degradation rate observed during laboratory simulations to that observed during normal field operation Condition monitoring is utilized to determine the activation energies used in calculating the acceleration factors for accelerated thermal aging.
Détermination du facteur d’accélération en vieillissement thermique accéléré
Le facteur d’accélération F du vieillissement thermique accéléré est normalement calculé en utilisant l’équation d’Arrhenius suivante: ằ ẳ ô º ơ ê
Où t 1 et t 2 sont les instants correspondant à l’atteinte d’un certain niveau de dégradation à des températures T 1 et T 2 (en kelvins); E est l’énergie d’activation et the k est la constante de
The Arrhenius equation, given by \$ r = A e^{-E/kT} \$, illustrates the relationship between temperature and the rate of a chemical reaction (\$ r \$) In this equation, \$ A \$ represents the pre-factor, also known as the frequency factor for first-order reactions, measured in s\(^{-1}\) The term \$ E \$ denotes the activation energy, expressed in electronvolts (eV), while \$ k \$ is the constant involved in the equation.
Boltzmann (0,861 7 ã 10 –4 eV ã K –1 ) et T est la tempộrature (exprimộe en K) L’ộnergie d’activation est dộfinie comme l’énergie qui doit être dépassée pour que la réaction chimique survienne
L’énergie d’activation d’un matériau est normalement calculée à partir des résultats de mesure des indicateurs d’état en fonction du temps et à différents niveaux de température
The Arrhenius diagram illustrates the relationship between temperature values and the time required to reach a specific level of degradation In this diagram, the inverse of the temperatures, expressed in Kelvin, is plotted against a linear scale on the x-axis, while the time \( t \) is represented on a logarithmic scale on the y-axis An example of this can be seen in Figure 1.
Figure 1 – Exemple de diagramme d’Arrhenius
A straight line connecting the points indicates an Arrhenius-type dependence between the degradation level and temperature The activation energy \(E\), expressed in eV, is calculated from the slope of the line.
The acceleration factor and the certified lifespan are significantly influenced by the activation energy value Inaccuracies in determining the activation energy greatly affect the calculation of the acceleration factor, which in turn impacts the certified lifespan derived from tests involving artificial accelerated thermal aging This relationship is illustrated in Figure 2.
Energies d’activation Durée de v ie c e rti fi é e (an s ) 30
NOTE La température de fonctionnement en service normal étant de 50 o C E=0,9 eV
Figure 2 – Influence de l’énergie d’activation sur la durée de vie certifiée, déterminée après une phase de vieillissement thermique artificiel de 42 jours à 110 °C, suivie de la simulation d’un évènement de dimensionnement
The high precision required for state monitoring methods used in measuring activation energies, along with the necessity for these methods to be reproducible, is exemplified in this case.
Utilisation de la surveillance d’état pour l’extension de la durée de vie certifiée
Significant margins are typically applied to establish the certified lifespan during initial qualification testing These margins account for uncertainties related to environmental conditions in the field, acceleration factors used to derive the certified lifespan from laboratory aging simulations, and the satisfactory operational performance of the equipment Additionally, they consider normal variances from commercial production and uncertainties associated with testing and measurement equipment Due to these margins and the limited time available for testing, as well as the use of modest acceleration factors for laboratory aging simulations, the initial qualification may result in a certified lifespan that differs considerably from the actual service life before a sizing event occurs Common methods for extending the certified lifespan usually involve condition monitoring of representative samples of the installed equipment.
Utilisation de la surveillance d’état pour la détermination et l’évaluation de l’état qualifié
La qualification basộe sur la surveillance d’ộtat apparaợt dans l’IEEE 323-2003 comme une solution alternative ou un complément pour l’évaluation de la durée de vie certifiée
State-based qualification relies on determining appropriate values that represent condition indicators at the end of aging before conducting a test simulating a sizing event These values signify the qualified state The benefits of using state-based qualification as a complementary or alternative solution for determining certified lifespan are significantly enhanced when trends (time-dependent variations) of condition indicator values are assessed during aging This can be achieved through incremental artificial aging, measuring condition indicator values at each increment After installation, identical condition measurements are periodically conducted on representative samples and compared with the qualified state, as illustrated in Figure 3.
Evolution de l’état durant le vieillissement artificiel
V al eur de l ’indi c a teur d’ ét a t t 1 t t 2 2 t 3 t i Instant auquel on réalise la surveillance d’état
Etat qualifié Evolution de l’état du spécimen installé
Figure 3 – Illustration de la qualification basée sur la surveillance d’état
The establishment of a qualified state can be part of the initial qualification tests If the initial qualification was solely aimed at assessing the certified lifespan without planned state monitoring, it may be possible to establish the qualified state retrospectively without repeating the tests related to sizing events If identical samples of the equipment, either new or stored under controlled environmental conditions, are available, the qualified state can be established by repeating the aging approach used in the initial qualification tests and determining the appropriate state indicator values during and at the end of this aging phase.
Post-installation measurements can be conducted by personnel using instrumentation in laboratories different from those used for establishing the qualified state This necessitates high standards for the specification of condition monitoring methods, associated documentation, and the reproducibility of measurements.
Il est important que des petites variations des valeurs des indicateurs d’état puissent être détectées Ceci impose un niveau de précision élevée pour les méthodes de surveillance d’état.
Utilisation de données de base
State surveillance can be employed to assess degradation limits, below which functionality during service conditions and simulated sizing events is typically understood to remain largely unaffected.
The general usefulness of available data regarding the values of state indicators, for which the operational capability of the equipment for simulated sizing events has been demonstrated, relies on the reproducibility and accuracy of the methods employed, as well as the quality of the monitoring definitions and associated reports.
CEI 60544-5, Matériaux isolants – Détermination des effets des rayonnements ionisants –
Partie 5: Procédures pour l'estimation du vieillissement en service
CEI 60780, Centrales nucléaires – Equipements électriques de sûreté – Qualification
CEI 62342, Centrales nucléaires de puissance – Systèmes d'instrumentation et de contrôle- commande importants pour la sûreté – Gestion du vieillissement
IEEE Std 1205, IEEE Guide for Assessing, Monitoring, and Mitigating Aging Effects on
Class 1E Equipment Used in Nuclear Power Generating Stations
NUREG/CR-6704, Vol 2 (BNL -NUREG-52610), Assessment of Environmental Qualification
Practices and Condition Monitoring Techniques for Low-Voltage Electric Cables, Condition
JNES-SS-0903:2009, The final report of the project “Assessment of cable ageing for nuclear power plant” T Yamamoto & T Minikawa, Japan Nuclear Energy Safety Organisation,
Nuclear Energy System Safety Division
NUREG/CR-7000, Essential Elements of an Electric Cable Condition Monitoring Program
IAEA-TECDOC-1188:2000, Assessment and management of ageing of major nuclear power plant components important to safety: In-containment instrumentation and control cables,