AMP207ENVIRONMENTAL QUALIFICATION OF ELECTRICAL AND I&CEQUIPMENT
Environmental qualification(EQ)programmesare established to demonstrate that certain electrical and instrumentation and control (I&C)equipment located in harsh plant environments (that is, those areas of the plant that could be subject to the harsh environmental effects of a loss of coolant accident (LOCA), high energy line breaks (HELB), post-LOCA environment,and/or other environments as defined in accordance with national regulatory requirements for EQ) are qualified to perform their safety function in those harsh environments after the effects of in-service ageing. The effects of significant ageing mechanisms are addressed as part of EQ programme [1-4].
It is common practice in other Member States (MS) to establish EQ requirements to qualify certain electrical and I&C equipment located in mild environments as applicable to national regulatory requirements. For equipment located in mild environments (environments that would at no time be significantly more severe than the environment that would occur during normal plant operation, including anticipated operational occurrences), it is demonstrated that the equipment can meet its functional requirements during normal environmental conditions and anticipated operational occurrences as defined in accordance with national regulatory requirements [4-5]. All operating plants meet the requirements for EQ according to national regulatory requirements for certain electrical and I&Cequipment important to safety. The EQ programme defines the scope of equipment to be included, requires the preparation and maintenance of a list of in-scope equipment, and requires the preparation and maintenance of a qualification file that includes qualified equipment performance specifications, electrical characteristics, the environmental conditions to which the equipment could be subjected, and the qualification report. The EQprogramme contains provisions for ageing that require, in part, consideration of all significant types of ageing degradation (e.g., thermal, radiation, vibration, and cyclical ageing) that can affect component functional capability.
The EQ programme establishes activities in order to preserve the qualification of in-service qualified equipment. These activities are implemented to assure the adequacy of the equipment, function and installation under required conditions (i.e., normal operating condition, abnormal condition, design basis event (DBE), beyond design basis accident (BDBA) if applicable, etc.) for the intended period of operation.
A qualified lifeassumption is established for EQ equipmentduring initial qualification.The ability of the equipment to perform its safety function is demonstrated as required by preconditioning test sample(s) to the state of degradation expected at the end of the assumed qualified life, followed by simulated DBE(s)and/or other environments as defined in accordance with national regulatory requirements for EQ .
The EQprogramme also requires replacement or refurbishment of equipment not qualified for the current operating term prior to the end of qualified life, unless additional life is established through reanalysis. Aneffective EQ programme in accordance with national regulatory requirements establishes methods of demonstrating qualification forageing and accident conditionsand permits different qualification criteria to be applied based on plant and equipment vintage. EQ equipmentand their associated environment are inspected periodically with particular emphasis on the identification of adverse localized environments that may impact equipment’s EQ[8-11]. Compliance with an EQ programme provides reasonable assurance that the equipment can perform its intended functions during accident conditions after experiencing the effects of in-service ageing.
EQ programme managesthe effect of significant ageing mechanisms such as thermal, radiation, and cyclical ageing through the use of ageing evaluations based on the programme qualification methods. As required, EQ equipment not qualified for the current operating term is refurbished, replaced, or have their qualification extended prior to reaching the ageing limits (qualified life or qualified condition)established in the evaluation. Ageing evaluations for EQ equipment that are qualified of at least the current operating term (e.g., 40 years) are considered time-limited ageing analyses (TLAAs) for the intended operating period.
A plant EQ programme in accordance with national regulatory requirements isconsidered anageing management programme (AMP) for the intended operating period. Reanalysis of an ageing evaluation to extend the qualification of componentsfor intended operating period is performed on a routine basis as part of an EQ programme. Important attributes for the reanalysis of an ageing evaluation include analytical methods, data collection and reduction methods, underlying assumptions, acceptance criteria, and corrective actions (if acceptance criteria are not met). These attributes are discussed in the "EQ Component Reanalysis Attributes" section.
This reanalysis programme can be applied to EQ equipment now qualified for the current license term (i.e., equipment that is qualified for at least the current operating term (e.g., 40 years or more)). As evaluated below, an existing EQ programme incorporating a reanalysis program, consistent the AMP 207 programme elements and national regulatory requirements is an acceptable AMP. Thus, for some MS no further evaluation is recommended for long term operation if an operating plant elects this option. The reanalysis showing that qualification is established for intended period of operationis performed prior to the plant entering the intended period of operation.
A record of the qualification is maintained in an auditable form for the entire intended period of operation during which the covered item is installed in the nuclear power plant or is stored for future use; this permits verification that each item of electrical and I&C equipment important to safety covered by this section (a)is qualified for its application and (b) meets its specified performance requirements when it is subjected to the conditions predicted to be present when it must perform a safety function up to the end of qualified life.
EQ Component Reanalysis Attributes
The reanalysis of an ageing evaluation is normally performed to extend the qualification by reducing excess conservatism incorporated in the prior evaluation. Reanalysis of an ageing evaluation to extend the qualification of a component is performed on a routine basis as part of an EQ programme. While a component life limiting condition may be due to thermal, radiation, or cyclical ageing, the vast majority of component ageing limits are based on thermal conditions. Conservatism may exist in ageing evaluation parameters, such as the assumed ambient temperature of the component, an unrealistically low activation energy, or in the application of a component (de-energized versus energized). The reanalysis of an ageing evaluation is documented according to the plant’s quality assurance programme requirements, which requires the verification of assumptions and conclusions. As already noted, important attributes of a reanalysis include analytical methods, data collection and reduction methods, underlying assumptions, acceptance criteria, and corrective actions (if acceptance criteria are not met). These attributes are discussed below.
Analytical Methods: The analytical models used in the reanalysis of an ageing evaluation are the same as those previously applied during the prior evaluation. The Arrhenius methodology is an acceptable thermal model for performing a thermal ageing evaluation. The analytical method used for a radiation ageing evaluation is to demonstrate qualification for the total integrated dose (that is, normal radiation dose for the projected installed life plus accident radiation dose). As an example, for the intended operating period of 60 years, one acceptable method of establishing the 60-year normal radiation dose is to multiply the current operating term (e.g., 40 years)normal radiation dose by 1.5 ( the intended period of operation divided by the current operating term, i.e., 60 years/40 years). The result is added to the accident radiation dose to obtain the total integrated dose for the component. For cyclical ageing, a similar approach may be used. Other models may be justified on a case-by-case basis.
Data Collection and Reduction Methods: Reducing excess conservatism in the component service conditions (for example, temperature, radiation, and cycles) used in the prior ageing evaluation is the chief method used for a reanalysis. Temperature data used in an ageing evaluation is based on plant design temperatures or on actual plant temperature data. When used, plant temperature data can be obtained in several ways, including monitors used for technical specification compliance, other installed monitors, measurements made by plant operators during rounds, and dedicated monitoring equipment for EQ. A representative number of temperature measurements are conservatively evaluated to establish the temperatures used in an ageing evaluation. Plant temperature data may be used in an ageing evaluation in different ways, such as (a) directly applying the plant temperature data in the evaluation, or (b) using the plant temperature data to demonstrate conservatism when using plant design temperatures for an evaluation. Any changes to material activation energy values as part of a reanalysis is justified on a plant-specific basis. Similar methods of reducing excess conservatism in the component service conditions used in prior ageing evaluations can be used for radiation and cyclical ageing.
Underlying Assumptions: EQ equipment ageing evaluations contain sufficient conservatism to account for environmental changes occurring due to plant modifications and events. When unexpected adverse conditions are identified during operational or maintenance activities that affect the normal operating environment of a qualified component, the affected EQ component is evaluated and appropriate corrective actions are taken, which may include changes to the qualification bases and conclusions.A reanalysis demonstrates that adequate conservatism is maintained, consistent with the original analysis, accounting for uncertainties established in the EQ ageing evaluation for the component.
Acceptance Criteria and Corrective Actions: The reanalysis of an ageing evaluation could extend the qualification of the component. If the qualification cannot be extended by reanalysis, the component is refurbished, replaced, or requalified prior to exceeding the period for which the current qualification remains valid. A reanalysis is performed in a timely manner (that is, sufficient time is available to refurbish, replace, or requalify the component if the reanalysis is unsuccessful).
Reanalyses that utilizes initial qualification conservatisms and/or the utilization of conservatisms that may be associated with in-service conditions (e.g., actual temperatures, and radiation conditions) to extend a components qualified life in the intended operating period are an integral part of an EQ programme.In addition, the use of ongoing qualification, including condition basedqualification methodologies, may also be implemented to provide additional assurance that a components-EQ, including qualified life, is maintained during its intended period of operation.Ongoing qualification,as applicable to the component, may include periodic testing, inspections, mitigation, component sampling (e.g., subsequent EQ qualification testing of in-service or representative components) with appropriate acceptance criteria and corrective actions (e.g., mitigation, replacement or refurbishment). The application of additional methodologies to evaluate equipment qualified life is the object of “Re-assessment qualification” presented inAMP 209.
Reanalysis of ageing evaluations, for EQ cables takes into account the effects of the cable EQ process uncertainties, identified in recent international R&D programmes [12-13].
Evaluation and Technical Basis
- Scope of the ageing management programme based on understanding ageing:
This AMP applies to certain electrical and I&C equipment located in harsh plant environments (that is, those areas of the plant that could be subject to the harsh environmental effects of LOCA, HELB, post-LOCA environment, and/or other environments as defined in accordance with national regulatory requirements for EQ).
It is common practice in other MS to establish EQ requirements to qualify certain electrical and I&C equipment located in mild environments as applicable to national regulatory requirements.
- Preventive actions to minimize and control ageing degradation:
An EQ programme does not require actions that prevent ageing effects. EQ programme actions that could be viewed as preventive actions include (a) establishing the equipment service condition tolerance and ageing limits (for example, qualified life or qualification condition limit) and (b) where applicable, requiring specific installation, inspection, monitoring, or periodic maintenance actions to maintain component ageing effects within the bounds of the qualification basis and the assumed qualified life.
- Detection of ageing effects:
An EQ programme does not require the detection of ageing effects for in-service equipment. EQ programme actions that could be viewed as detection of ageing effects include (a) inspecting and/or testing EQ equipment periodically with particular emphasis on the identification of adverselocalized environments that may impact a component’s environmental qualification and (b) monitoring or inspection of certain environmental conditions or component parameters to ensure that the component is within the bounds of its qualification basis, or as a means to modify the qualified life.
- Monitoring and trending of ageing effects:
Monitoring and trending of equipment condition or performance parameters is not required to manage the effects of ageing, but may be applicable to ongoing qualification including condition based qualification methodologies. EQ programme actions that could be viewed as monitoring and trending include the verification of how long qualifiedequipment have been installed with respect to its qualified life to ensure that qualified life is not expiredor qualified condition is not exceeded.
A monitoringor trendingprogramme may be used to ensure that the qualifiedequipment is within the bounds of its qualification basis, or as a means to modify qualified life(e.g., programs for monitoring and trending of environmental conditions (such as temperature, radiation levels), may be implemented for EQ components). The monitoring and trending frequency may be adjusted based on component inspection and test results. A modification to qualified life either by reanalysis or ongoing qualification demonstrates that adequate conservatism is maintained, consistent with the original analysis, accounting for uncertainties established in the EQ ageing evaluation for the equipment.
- Mitigating ageing effects:
This is a reanalysis programme. This programme has no specific operations, maintenance, repair or replacement mitigation aspects.
- Acceptance criteria:
The acceptance criteria are that the in-service EQ equipment is maintained within the bounds of its qualification basis, including (a) its established qualified life or qualified conditions and (b) continued qualification for the projected accident conditions. The EQ programme requires refurbishment, replacement, or requalification prior to exceeding the qualified life of each installed equipment. When monitoring and trending is used to modify the equipment qualified life or qualified conditions, plant-specific acceptance criteria are established based on applicable qualification methods in accordance the national regulatory requirements.
- Corrective actions:
If the EQ equipment is found to be outside the bounds of its qualification basis, corrective actions are implemented in accordance with the plant’s corrective action programme. When unexpected adverse conditions are identified during operational or maintenance activities that affect the environment of a qualified equipment, the affected EQ equipment is evaluated and appropriate corrective actions are taken, which may include changes to the qualification bases and conclusions. When an emerging industry ageing issue is identified that affects the qualification of the EQ equipment, the affected equipment is evaluated and appropriate corrective actions are taken, which may include changes to the qualification bases and conclusions. Confirmatory actions, as needed, are implemented as part of the plant corrective action program, pursuant tonational regulatory QA requirements. As discussed in IGALL, the requirements of the national regulatory QA programme are acceptable to address the corrective actions.
- Operating experience feedback and feedback of research and development results:
This AMP addresses the industry-wide generic experience. Relevant plant-specific operating experience is considered in the development of the plant AMP to ensure the AMP is adequate for the plant. The plant implements a feedback process to periodically evaluate plant and industry-wide operating experience and research and development (R&D) results, and, as necessary, either modifies the plant AMP or takes additional actions (e.g. develop a new plant-specific AMP) to ensure the continued effectiveness of the ageing management.
EQ programme include consideration of operating experience to modify qualification bases and conclusions, including qualified life. Compliance with national regulatory EQ requirements provides reasonable assurance that components can perform their intended functions during accident conditions after experiencing the effects of in-service ageing.
The programme includes provisions for the continuous review of plant-specific and industry operating experience, including research and development results, such that the impact on the programme is evaluated and any necessary actions or modifications to the programme are performed.
Sources of external operating experience are OECD-NEA, INPO, Owner’s Groups, WANO, IAEA, VGB Database, NRC information notices and generic communications and Equipment Qualification Data Base (EQDB).
Recent research programs developed in Japan, OECD-NEAand IAEA , on cable EQ and ageing management, describe areas of concern (uncertainties) in the original EQ cables qualification process, performed in the past (e.g. IEEE-323-74).
IAEA Nuclear energy series report D-NP-T.3.6, include detailed information regarding uncertainties and its effects on cable EQ . The uncertainties are related to the following:
- Synergistic effects of sequence applied for the radiation and thermal ageing test.
- Acceleration factors applied in the radiation and thermal ageing tests.
- Oxygen consumption on LOCA chambers effects, during DBE test.
- Dose rate effects.
- Non-conservative or incorrect activation energy values, used in Arrhenius Thermal ageing calculations.
- Inverse temperature effects (semi crystalline polymers XLPE, XLPO).
More recently,SAND 2013-2388 Report results, show the following conclusions, of the uncertainties effects :
- There are different degradation mechanisms for cable polymers, in oxidative or inert environments.
- Neither qualification testing nor accelerated ageing studies have satisfactorily addressed inverse temperature effects (XLPO, XLPE).
- While cable performance in oxygen environments may be satisfactory and EQ process margins may exist, these margins cannot be predicted or validated, from existing qualification and ageing studies.
The above considerations are taken into account in any reanalysis for future qualification or life extension activities on EQ cables.
- Quality management:
Site quality assurance procedures, review and approval processes, and administrative controls are implemented in accordance with the different national regulatory requirements (e.g., 10 CFR 50, Appendix B)