AMP209RE-ASSESSMENT QUALIFICATION OF ElectricAL and I&CEQUIPMENTRELEVANT TO AN ENVIRONMENTAL QUALIFICATION
Programme Description
Preliminary considerations
An Environmental qualification (EQ) programmeis established to demonstrate that certain electrical and instrumentation and control(I&C)equipmentisqualified to perform their safety function in their design environmental conditions after the effects of in-service ageing. These environments can be harsh (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 break (HELB), post-LOCA environment or other environments as defined in accordance with the applicable national regulatory requirements for EQ) or mild (Mild environment areas are NPP locations which experience the effects ofseismic events but whose environmental conditions do not significantly change as aresult of a Postulated Initiating Event (PIE). However, certain equipment in mild areas can experience PIE operationalconditions that are significantly different from normal conditions. The effects of significant ageing mechanisms are addressed as part of EQ programme[1-3]
Qualification methods of an EQ programme are type test, and analysis[4]. In the case of the type test method, ageingis evaluated by a phase of appreciation of behavior in the time which precedes the tests in accidental conditions.
The lifetime assumption of the equipmentenablesselectingparameters of the tests(methods or severities), but the correlationwith the considered qualified lifetime assumption (generally 40 years or less for some equipment) is:
-either direct when it is about accelerated ageing (irradiation under normal functioning, room temperature),
-orindirect when regarding robustness or endurance tests (climatic stress, vibrations, cycles of operation).
Regardingenvironmentallyqualified equipment,there is no such methodwhich guaranteesa design lifetime and assesses a residuallifetime.
The lifetimeassumption isaninputfor the qualification processbutis notanoutput data.
In the qualification practice, there isnota time limitbeyondwhich the qualified equipmentshouldbesystematically replaced. However, there are maintenancerequirementscoming fromthe qualification processto replaceatregular intervals equipmentdeemed sensitive.
Sustaining qualificationduring manufacture, assembly and operationof the equipmenthas a fundamental importance recalled here:it isto keepthe equipmentin a known statethat maintainsthe confidencegained duringtheinitial qualificationprocess.
The re-assessmentqualificationprocessis an essential complement to theinitial qualificationprocess. It is part of ageing management and is performed as the ageof the equipmentincreases and getscloser tothe initial lifetimeassumption.
Definition of an On-going QualificationProgramme
Over time, the lifetime assumption can be challenged for several reasons, such as:
•extension of intended operating life,
•anageing faster than expected, more severe operating environment conditions that those taken into account in the initial qualification process,
•a feedback experience identifying new ageing mechanisms,
•a better scientific knowledge of the involved phenomena.
In such cases, and before the operating life of the equipment becomes greater than its lifetime assumption, a re-assessment qualification programmeis be performed.
Re-assessment qualification is a set of six methods that enable to prove the qualified status of equipment when its operating life becomes greater than its qualified lifetime assumption.
Methodology
Re-assessment qualification calls for one or more of thefollowing six methods.
Method 1 (utilization of initial qualification conservatisms): Analysis of the initial qualification conditions to assess the potential conservatisms compared to the required conditions (reducing excess conservatism incorporated in the prior qualification regarding required values, nevertheless some conservatism is preserved).
Method 2 (utilization of service conditions conservatisms): Comparison between the actual stress and ambient conditions (temperature and radiation) really supported by the equipmentduring operating conditions and those taken into account for the qualification. This comparison from the actual operating values can lead toa reassessment of the qualified lifetime (reducing excess conservatisms of the required values regarding actual values).
This method requires monitoring the specific environmental conditions during normal operation of the plant.
Method 3 (end of qualified life parameter or expertise): Monitoring a chosen state parameter or its operating behavior during periodic testing or inspections. This chosen parameterhelps detect a trend of the equipment characteristicswhich otherwise if undetected could render the equipment vulnerable to failure during PIE conditions.The chosen parameter can be called “end of qualified life parameter” [5-6].
That can be:
-Periodic measurement on the equipment (Method 3a), for instance measurement accuracy, insulation resistance, response time,
-Expert assessment of the equipment (method 3b), to characterize its state of on-site ageing.
Method 4 (mitigation of ambient conditions): Reducing the effects of ambientconditionson the equipment.
Twomethodsare possible toreduce the effects ofambient conditions:
-Modification of the ambient conditions (Method 4a). This is for instance using air-conditioning in order to decrease the average room temperature and thus to increase the lifetime of the equipmentwhich is installed there.
-Shielding or relocation of the equipment(Method 4b). This isfor instance to protectanequipmentof the radiations stemming from a “hot spot”, witha screento reducethe cumulative doseof radiationduring itslifetimeor movethe equipment toa lessradioactive place.
Method 5 (sampling of equipmenton site): Extending qualified lifetime by testing the equipment with an extended life period assumption.
The test maybe performed:
-on anequipment installed on site in excess (Method 5a),i.e.,Installing additional equipment (de-energized) in identical service conditions, and removefor type testing with further age conditioning to establish additional qualifiedlife.
-on an operating aged equipment taken on the site (sample test), preferably when its reference state (or initial state) and the stress endured are known(Method 5b),
-on a new equipment (Method 5c).
Method 6 (replacement or refurbishment): As preventive measure, replacement (Method 6a) or refurbishment of the equipment (Method 6b), completely or partially, identical to or by less sensitive ageingequipment.
Note 1: Re-assessment Qualification Programme includes all the different possible methods that could be used to extend the qualified life time of anequipment.
Methods 1 and 2 are for instance applied in the “Reanalysis Programme” presented in AMP207. This “Reanalysis Programme” usesinitial qualification conservatisms and/or the utilization of conservatisms that may be associated with actual in-service conditions (e.g., actual temperatures and radiation conditions) to extend anequipmentqualified life. This extension is only provided by analytical methods.
AMP207 mentions some other possibilities to extend anequipmentqualified life: they are methods 3, 4, 5 and 6 described above in the present AMP209. If the “Reanalysis Programme” (methods 1 and 2) can’t produce an acceptable result, it is perhaps possible to avoid replacement or refurbishment of the equipment(method 6) by application of methods 3, 4 or 5.
Note 2: Re-assessment Qualification Programme is presented here to cope with harsh environment qualification, but some methods are also adequate for mild environment and seismic qualification.
Note 3: The method chosen is justified and the application is sufficiently documented to give confidence in the extended qualified life.
Strategy of implementation
The general principles of implementation of re-assessment qualification are the following:
-The six methods are neither simultaneously applied on a same equipment.
-Some methods(knowledge of ambient environment, moving of equipment) may be suitablefor multiple equipmentsat the same locationorinthe same ambient environment. Similarly, a sampling decidedonafirst equipment canprovide useful knowledge tootherequipmentofsimilarorclosely related technology.
-Method 1is the first step, whatever the equipment.Its implementationhelpsto review theinitialqualification file. Theuse of conservative marginscoming from the initial qualification is fruitful only if the knowledge of the ageing process of the equipmenthas improved(for example, unrealistically high temperature or low activation energyinitiallychosen, application of theequipment -de-energized versus energized) orif the low ageing sensitivity of the equipmentisdemonstrated. Recommended margins can be found in [4].
-Method 2 isparticularly suitable forequipment installedinhot spots. For that it is necessary to have the actual statement of the ambient conditions (temperature andradiation). Plant data reports can be obtained in several ways, including monitors used for technical specification compliance, other installed monitors, measurements made by plant operators during rounds, and temperature/radiation sensors set up near the equipment to be monitored.
-Method3asupposes that a thresholdforthe chosen parameter (considered as an “end of qualified life parameter” indicator) can be specified,compliance whichensures the properfunctioning ofthe equipmentduringaccidental or seismic conditions, andthe crossing of whichresults inapossible failure duringits safety mission. The validationof such a methodmayrequire prior laboratory tests.As an illustration and regarding only seismic qualification, a maximum thresholdof corrosionwas determined bytestinglead batteries, whichensurescompliancefunctionalityunderearthquake.
-Method 4 israrely usedin early lifeof the plant, the location of theequipment ortheir protection, for exampleby shieldsto reducethe environmental constraints, having alreadybeen takeninto account duringinstallation design studies. Method 4mayfindaninterestfor managingtheequipmentatthe endof the plant’s life.
-Method 5is intended forequipment subjected to harsh plant environments. Generally, otherequipmentforwhichthe accidental operating conditionsare the same asnormal operating conditions, donot use it. Indeed, except in special cases, the controlsduringoperationcan highlightthe developments thatwouldadversely affect theseismic behavior.
-The application ofthe method5bis facilitated bythe implementationofmethod 2 (knowledge of the history)and bydeterminingthe reference state of the selected equipment.
-The useof methods 2, 3 and5bisperformedconsistentlywiththe maintenance strategyof the plant.
-Method 6 is implemented if the qualification cannot be extended by implementing methods 1, 2, 3, 4 or 5, or if it is an economically more attractive solution.
Finally, the choice of the methodsdepends on thefamily of equipment consideredandmaintenance policy. Foreasily replaceable equipment, it can lead, for example, to favorareplacement at fixed periodicity(method 6) with respectto aqualification extensiontest (method 5).
The final choiceresults fromatechnical and economicassessment. This assessmentdeterminesthemost effectivegeneric actions(in terms of contributiontoknowledge), coordinating the methodsforrelated equipment(by geographic location, by technology orbyacommon maintenance) and finally,for eachequipment, to select one or moreappropriate methods.
Evaluation and Technical Basis
- Scope of the ageing management programme based on understanding ageing:
An ongoing qualificationprogramme applies to certain electrical and I&C equipment that are important to safety, as defined in accordance with the national regulatory requirements for EQ.
- Preventive actions to minimize and control ageing degradation:
A re-assessment qualification programmerequires actions to take into account ageing effects and may require actions to minimize ageing effects.Re-assessment qualification 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 condition limit) and (b) where applicable, requiring specific installation, inspection, monitoring, or periodic maintenance actions to maintain equipmentageing effects within the bounds of the extended qualification period.
- Detection of ageing effects:
A re-assessment qualification programmemay require the detection of ageing effects (methods 3). Monitoring or inspection of certain environmental conditions or equipment parameters may be usedas a means to modify the qualified life.
- Monitoring and trending of ageing effects:
Monitoring of ambient conditions (such as temperature, radiation levels) or parameters of the state of the equipmentis a part of the re-assessment qualification programme (methods 2, 3 and 4).It may be implemented for EQ in-service equipment.
Monitoring programmes may include any appropriate inspection and test technique(s), supplemented with walk-downs to look for visible signs of anomalies attributable to ageing with particular emphasis on the identification of localized adverse environments that may impact the EQ equipment qualification. The monitoring and its frequency may be adjusted based on equipmentinspection and test results.
- Mitigating ageing effects:
This is a re-assessment qualification programme. This programmecould lead to take specific actions in order to mitigate ageing effects (for instance, method 4: mitigation of ambient conditions).
- Acceptance criteria:
The acceptance criteria isthat an in-service EQ equipment is maintained within the bounds of its qualification basis, including (a) its established qualified life and (b) continued qualification for the projected accident conditions. The re-assessment qualification programme requires application of the 6 methods prior to exceeding the qualified life of each installed device. When monitoring is used to modify anequipment qualified life, plant-specific acceptance criteria are established, based on applicable qualification methods in accordance the national regulatory requirements.
- Corrective actions:
If EQ equipment is found to be outside the bounds of its qualification basis, corrective actions are implemented in accordance with the station's corrective action programme. When unexpected adverse conditions are identified during operational or maintenance activities that affect the environment of 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 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 station's corrective action programme, pursuant to national regulatory QA requirements. As discussed in IGALL, the requirements of the national regulatory QA programme is 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.
An ongoing qualificationprogramme includes consideration of operating experience to modify qualification bases and conclusions, including qualified life. Compliance with national regulatory EQ requirements provides reasonable assurance that equipment can perform their intended functions during accident conditions after experiencing the effects of in-service ageing, including the extended qualification period.
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.
At the time when this AMP was produced, no relevant R&D was identified.
- 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 [7]).
References
[1]INTERNATIONAL ATOMIC ENERGY AGENCY, Ageing Management for Nuclear Power Plants, Safety Guide No. NS-G-2.12, IAEA, Vienna.
[2]French Association for design, construction and in-service inspection rules for nuclear island components (AFCEN)/ RCC-E: Design and construction rules for electrical equipment of nuclear islands – January 2012 Edition
[3]KERNTECHNISCHER AUSSCHUSS, Ageing Management in Nuclear Power Plants, KTA Standard 1403, KTA, Germany,November 2010.
[4]IEC/IEEE 60780-323, Edition 1.0, 2016-02, Nuclear facilities – Electrical equipment important to safety – Qualification
[5]NUCLEAR ENERGY AGENCY, Technical Basis For Commendable Practices On Ageing Management, SCC and Cable Ageing Project (SCAP) Final Report (p.112), NEA/CSNI/R (2010) 15, Paris 13-Apr-2011.
[6]JAPAN NUCLEAR ENERGY SAFETY ORGANIZATION, The final report of the project of assessment of cable ageing for nuclear power plants (p.253), JNES-SS-0903, JNES, 2009.
[7]UNITED STATES NUCLEAR REGULATORY COMMISSION, 10 CFR Part 50, Appendix B, Quality Assurance Criteria for Nuclear Power Plants, Office of the Federal Register, National Archives and Records Administration, USNRC, 2015.
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