X.E1 (NUREG-2191 R0)

X.E1 ENVIRONMENTAL QUALIFICATION OF ELECTRIC EQUIPMENT

Program Description

The U.S. Nuclear Regulatory Commission (NRC) has established nuclear station environmental qualification (EQ) requirements in Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix A, Criterion 4, and 10 CFR 50.49. 10 CFR 50.49 specifically requires that an EQ program be established to demonstrate that certain electrical 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 break and post-LOCA environment] are qualified to perform their safety function in those harsh environments after the effects of inservice (operational) aging. 10 CFR 50.49 requires that the effects of significant aging mechanisms be addressed as part of EQ.

For equipment located in a harsh environment, the objective of EQ is to demonstrate with reasonable assurance that electric equipment important to safety, for which a qualified life has been established, can perform its safety function(s) without experiencing common cause failures before, during or after applicable design basis events.

For equipment located in a mild environment (an environment that at no time would be significantly more severe than the environment occurring during normal operation, including anticipated operational occurrences as defined in 10 CFR 50.49), the demonstration that the equipment meets its functional requirements during normal environmental conditions and anticipated operational occurrences is in accordance with the plant design and licensing basis. Equipment important to safety located in a mild environment is not part of an EQ program per 10 CFR 50.49(c). Documents that demonstrate that a component is qualified or designed for a mild environment include design/purchase specifications, seismic test qualification reports, an evaluation, or certificate of conformance.

Operating plants requesting subsequent license renewal shall meet the qualification requirements of 10 CFR 50.49 and license renewal aging management provisions of 10 CFR Part 54 for certain electrical equipment important to safety. 10 CFR 50.49 defines the scope of equipment to be included in an EQ program, requires the preparation and maintenance of a list of in-scope equipment, and requires the preparation and maintenance of a qualification file that contains the qualification report, with applicable equipment performance specifications, electrical characteristics, and the environmental conditions to which the equipment could be subjected. Licensees are required to maintain a record of qualification in auditable form [10 CFR 50.49(j)] for the entire period during which each covered item installed in the nuclear power plant or is stored for future use.

Additionally, 10 CFR 50.49(e) states that electric equipment qualification programs must include and be based on temperature, pressure, humidity, chemical effects, radiation, aging, submergence, and consideration of synergistic effects. The requirements of 10 CFR 50.49(e) also includes the application of margins to account for unquantified uncertainties, including production variations, and inaccuracies in test instruments. These margins are in addition to any conservatism applied during the derivation of local environmental conditions of the equipment unless these conservatisms can be quantified and shown to contain the appropriate margins. The aging provisions contained in 10 CFR 50.49(e)(5) require, in part, consideration of all significant types of aging degradation (e.g., plant-specific operational aging that includes thermal, radiation, vibration, and cyclic aging) which can have an effect on the functional capability of the equipment.

EQ programs manage equipment thermal, radiation, and cyclic aging through the use of aging evaluations based on 10 CFR 50.49(f) qualification methods. Four methods are established by 10 CFR 50.49(f) to demonstrate qualification for aging and accident conditions, as shown below:

Testing an identical item of equipment under identical conditions or under similar conditions with a supporting analysis to show that the equipment to be qualified is acceptable.
Testing a similar item of equipment with a supporting analysis to show that the equipment to be qualified is acceptable.
Experience with identical or similar equipment under similar conditions with a supporting analysis to show that the equipment to be qualified is acceptable.
Analysis in combination with partial type-test data that supports the analytical assumptions and conclusions [is acceptable.]

Additionally, 10 CFR 50.49(k) and (i) permit different qualification criteria to apply based on plant and electrical equipment vintage.

Supplemental EQ regulatory guidance for compliance with these different qualification criteria are provided in the Division of Operating Reactors (DOR) Guidelines; “Guidelines for Evaluating Environmental Qualification of Class 1E Electrical Equipment in Operating Reactors,” NUREG–0588, “Interim Staff Position on Environmental Qualification of Safety-Related Electrical Equipment (Category 1 and Category 2 requirements),” and Regulatory Guide (RG) 1.89, Revision 1, “Environmental Qualification of Certain Electric Equipment Important to Safety for Nuclear Power Plants,” as applicable. Compliance with 10 CFR 50.49 provides reasonable assurance that the equipment can perform its intended function during accident conditions after experiencing the effects of inservice aging.

For equipment preconditioned and tested to less than an end-of-installed life condition (i.e., preconditioned to a shorter designated life) 10 CFR 50.49(e)(5) requires the equipment to be replaced or refurbished at the end of its designated life unless additional life is established through ongoing qualification.

Electrical equipment important to safety to be included in a 10 CFR 50.49 EQ program are specified under 10 CFR 50.49(b). A list of environmentally qualified electrical equipment important to safety is required under 10 CFR 50.49(d). Plant systems, structures, and components within the scope of license renewal established under 10 CFR 50.49 that are within scope of license renewal per 10 CFR 54.4(a)(3) and are considered a time-limited aging analysis (TLAA) under 10 CFR 54.3(a) require an evaluation to demonstrate that the TLAA analysis satisfies 10 CFR 54.21(c)(1)iii.

Along with Generic Aging Lessons Learned for Subsequent License Renewal (GALL-SLR) Report AMP X.E1, plant EQ programs which implement the requirements of 10 CFR 50.49 (as further defined and clarified by the DOR Guidelines, NUREG-0588, and RG 1.89) demonstrate the acceptability of the TLAA analysis under 10 CFR 54.21(c)(1) and are considered an acceptable aging management program (AMP) for the subsequent period of extended operation.

Environmental Qualification – Reanalysis

Reanalysis evaluates the original attributes, assumptions and conservatisms for environmental conditions and other factors of an aging evaluation to demonstrate that equipment qualified life can be extended. Reanalysis of equipment qualified under the program requirements of 10 CFR 50.49(e) is performed as part of an EQ program. Important attributes for the reanalysis of an aging evaluation include analytical methods, data collection and reduction methods, underlying assumptions, acceptance criteria, and corrective actions. These attributes are discussed in the “Environmental Qualification Equipment Reanalysis Attributes” section below.

Environmental Qualification Equipment Reanalysis Attributes

The reanalysis of an existing aging evaluation is normally performed to extend the qualification by reevaluating original attributes, assumptions and conservatisms in environmental conditions and other factors to identify excess conservatisms incorporated in the prior evaluation. Reanalysis of an aging evaluation to extend the qualification of electrical equipment is performed pursuant to 10 CFR 50.49(e) as part of an EQ program. While an electrical equipment life limiting condition may be due to thermal, radiation, or cyclical aging, the majority of electrical equipment aging limits are based on thermal conditions. Conservatism may exist in aging evaluation parameters, such as the assumed service conditions or unrealistically low activation energy. The reanalysis of an aging evaluation is performed according to the station's quality assurance (QA) program requirements, which requires the verification of assumptions and conclusions including the maintenance of required margins.

As already noted, important attributes of a reanalysis include analytical methods, data collection and reduction methods, underlying assumptions, acceptance criteria, and corrective actions. These attributes are discussed below.

Analytical Methods: The analytical models used in the reanalysis of an aging evaluation are the same as those previously applied during the prior evaluation. The Arrhenius methodology is an acceptable thermal model for performing a thermal aging evaluation. The analytical method used for a radiation aging evaluation is to demonstrate qualification for the total integrated dose that includes normal radiation dose for the projected installed life plus accident radiation dose. For subsequent license renewal, one acceptable method of establishing the 80-year normal radiation dose is to multiply the initial 40-year normal radiation dose by two. The result is added to the accident radiation dose to obtain the total integrated dose for the component. For cyclical aging, a similar approach may be used. Other models may be justified on a case-by-case basis.

Data Collection and Reduction Methods: The identification of excess conservatism in electrical equipment service conditions used in the prior aging evaluation is the chief method used for a reanalysis. For example, temperature data, associated margins, and uncertainties used in an equipment EQ evaluation may be based on anticipated plant design temperatures found to be conservative when compared to actual plant temperature data. When used, plant environmental data may be obtained from monitors used for technical specification compliance; other installed monitors, measurements made by plant operators during rounds, dedicated monitors for EQ equipment or combinations of the above. The environmental data gathering and analysis method can be used to identify conservatism in the original qualification and justify additional qualified life for the EQ equipment. Any changes to material activation energy values included as part of a reanalysis are justified by the applicant on a component-specific basis.

Underlying Assumptions: EQ equipment aging evaluations account for environmental changes occurring due to plant modifications, seasonal changes, and events. A reanalysis demonstrates that adequate margin is maintained consistent with the original analysis in accordance with 10 CFR 50.49. 10 CFR 50.49 requires further consideration of certain margins and accounting for unquantified uncertainties such as diffusion limited oxidation, activation energy, synergistic effects, inverse temperature, and dose rate effects. Reanalysis that utilizes initial qualification conservatisms and/or inservice environmental conditions (e.g., actual temperature and radiation conditions) are part of an EQ program.

Adverse Localized Environment

In most areas within a nuclear power plant, the actual operating environment (e.g., temperature, or radiation), is less severe than the plant design basis environment. However, in a limited number of localized areas, the actual environment may be more severe than the anticipated plant design basis environment. These localized areas are characterized as “adverse localized environments” that represent a limited plant area where the operating environment is significantly more severe than the plant design environment considered in the qualification for EQ equipment.

An adverse localized environment may increase the rate of aging or have an adverse effect on the basis for equipment qualification. An adverse localized environment is an environment that exceeds the most limiting qualified condition for temperature or radiation for the component material. EQ electrical equipment may degrade more rapidly than expected when exposed to an adverse localized environment.

Adverse localized environments are identified through the use of an integrated approach. This approach includes, but is not limited to: (a) the review of EQ program radiation levels and temperatures, (b) recorded information from equipment or plant instrumentation, (c) as-built and field walk down data (e.g., cable routing data base), (d) a plant spaces scoping and screening methodology, (e) plant modifications (e.g., power uprate), and (f) the review of relevant plant-specific and industry operating experience (OE). This OE includes, but is not limited to:

Identification of work practices that have the potential to subject in-scope EQ equipment to an adverse localized environment (e.g., influence of maintenance activity that removes thermal insulation and restoration from hot pipes).
Corrective actions for in-scope EQ equipment involving end-of-installed life, designated life, or qualified life (current operating term).
Observations from previous walk-downs including visual inspection.
Environmental monitoring (e.g., long term periodic environmental monitoring of EQ equipment – temperature or radiation).
Inspection of accessible passive EQ equipment and the evaluation of the equipment environment to identify electrical equipment subjected to an adverse localized environment. The aging impact on accessible EQ equipment located in an adverse localized environment is evaluated and represents, with reasonable assurance, both accessible and inaccessible EQ equipment age degradation.

The inspection portion of the EQ of Electric Components program is considered a visual inspection performed from the floor, with the use of scaffolding as available, without the opening of junction boxes, pull boxes, or terminal boxes. The purpose of the visual inspection is to identify adverse localized environments (employing diagnostic tools such as thermography as applicable). The accessible, passive EQ components located in these adverse localized environments are then visually inspected which depending on the visual inspection results, may require further inspection using scaffolding or other means (e.g., opening of junction boxes, pull boxes, accessible pull points, panels, terminal boxes, and junction boxes) to assess EQ electrical equipment aging degradation. Passive EQ equipment subject to an adverse localized environment may result in surface abnormalities that are visually observable, such as cable jacket surface embrittlement, discoloration, cracking, melting, swelling, or surface contamination. Visual inspection can be used as an indicator of age degradation.

Adverse conditions identified during periodic inspections or by operational or maintenance activities that affect the operating environment of EQ equipment are evaluated and appropriate corrective actions are taken, which may include changes to qualification bases and conclusions (e.g., changes to qualified life).

In-scope accessible passive EQ electrical equipment is inspected at least once every 10 years to identify EQ electrical equipment subjected to an adverse localized environment. The first periodic inspection is to be performed prior to the subsequent period of extended operation.

Acceptance Criteria and Corrective Actions: Reanalysis of an aging evaluation is used to extend the qualification of the component. If the qualification cannot be extended by reanalysis, the equipment is refurbished, replaced, or requalified prior to exceeding the current qualified life. A reanalysis is performed in a timely manner to ensure sufficient time is available to refurbish, replace, or requalify the equipment if the result is unfavorable.

A modification to qualified life by reanalysis must demonstrate that adequate margin is maintained consistent with the original analysis including unquantified uncertainties established in the original EQ equipment aging evaluation.

Environmental Qualification – Ongoing Qualification

Ongoing qualification, for the purposes of this document is defined as the process of requalifying a component through activities similar to the original qualification which may include testing, type testing, or a monitoring program. When assessed, if margins, conservatisms, or assumptions do not support extending qualified life, the following methods may be used:

The retention and continued aging of a test sample from the original EQ test program with demonstration that the qualified life is bounding for the subsequent period of extended operation,
Removal and type testing of additional EQ equipment installed in identical service conditions with a greater period of operational aging,
Monitoring Program – Requires that EQ equipment characteristics subject to aging degradation be monitored at specific intervals and compared to specified acceptance criteria. The acceptance criteria are based on the capability of post aging characteristics for the EQ equipment to retain functional properties during and after enduring design bases environment, as applicable. Condition monitoring intervals are established to prevent age degradation beyond the acceptance criteria prior to corrective action.

The above methods are considered ongoing qualification. Other methods or approaches may be acceptable. A modification to extend qualified life must be justified including program documentation and auditable evidence that adequate margin is maintained consistent with the original analysis including unquantified uncertainties established in the original EQ equipment aging evaluation.

Evaluation and Technical Basis

1. Scope of Program: EQ programs apply to certain electrical equipment that are important to safety and could be exposed to harsh environment accident conditions, as defined in 10 CFR 50.49 and RG 1.89, Revision 1. Plant EQ programs along with GALL-SLR Report AMP X.E1 demonstrate acceptability of the EQ electrical equipment TLAA analysis under 10 CFR 54.21(c)(1).

2. Preventive Actions: 10 CFR 50.49 does not require actions that prevent aging effects. EQ program actions that could be viewed as preventive actions include (a) establishing the equipment service condition tolerance and aging limits (e.g., qualified life or condition limit) and (b) where applicable, requiring specific installation, inspection, monitoring, or periodic maintenance actions to maintain electrical equipment aging within the bounds of the qualification basis (e.g., identification of adverse localized environments or shielding for temperature and/or radiation).

3. Parameters Monitored or Inspected: Qualified life is not based on condition or performance monitoring. However, pursuant to RG 1.211 and RG 1.89, Revision 1, such monitoring programs are an acceptable basis to modify a qualified life to establish a revised qualified condition. Monitoring or inspection of certain environmental conditions, including adverse localized environments, or equipment parameters may be used to verify that the equipment is within the bounds of its qualification basis, or as a means to modify the qualified life.

4. Detection of Aging Effects: 10 CFR 50.49 does not require the detection of aging effects for inservice EQ equipment. EQ program actions that could be viewed as detection of aging effects include (a) inspecting EQ equipment periodically with particular emphasis on monitoring or condition assessment and (b) monitoring of plant environmental conditions or component parameters used to verify that the equipment is within the bounds of its EQ basis including attributes, assumptions, and conservatisms for equipment/environmental conditions and other factors. Monitoring or inspection of certain environmental conditions or component parameters may provide a means to maintain equipment qualified life.

Visual inspection of accessible, passive EQ equipment is performed at least once every 10 years. The purpose of the visual inspection is to identify adverse localized environments that may impact qualified life. Potential adverse localized environments are evaluated through the applicant’s corrective action program. The first periodic visual inspection is to be performed prior to the subsequent period of extended operation.

5. Monitoring and Trending: 10 CFR 50.49 does not require monitoring and trending of component condition or performance parameters of inservice equipment to manage the effects of aging. Monitoring, trending, or inspection of certain environmental, condition, or component parameters may be used to verify that EQ equipment is within the bounds of its qualification basis, or as a means to modify the qualification.

6. Acceptance Criteria: An unacceptable indication is defined as a noted condition or situation, if left unmanaged, could potentially lead to a loss of intended function.

10 CFR 50.49 acceptance criteria are that inservice EQ equipment is maintained within the bounds of its qualification basis, including its established qualified life and continued qualification for the projected accident conditions. 10 CFR 50.49 requires refurbishment, replacement, or requalification prior to exceeding the qualified life of each installed component. When monitoring is used to modify equipment qualified life, plant-specific acceptance criteria are established based on applicable 10 CFR 50.49(f) qualification methods.

Visual inspection results show that accessible passive EQ equipment is free from unacceptable surface abnormalities that may indicate age degradation.

7. Corrective Actions: Results that do not meet the acceptance criteria are addressed in the applicant’s corrective action program under those specific portions of the QA program that are used to meet Criterion XVI, “Corrective Action,” of 10 CFR Part 50, Appendix B. Appendix A of the GALL-SLR Report describes how an applicant may apply its 10 CFR Part 50, Appendix B, QA program to fulfill the corrective actions element of this AMP for both safety-related and nonsafety-related structures and components (SCs) within the scope of this program.

If an EQ component is found to be outside the bounds of its qualification basis, corrective actions are implemented in accordance with the station’s corrective action program. When an unexpected adverse localized environment or condition is identified during operational or maintenance activities that affect the qualification of electrical equipment, the affected EQ equipment is evaluated and appropriate corrective actions are taken, which may include changes to qualified life.

8. Confirmation Process: The confirmation process is addressed through those specific portions of the QA program that are used to meet Criterion XVI, “Corrective Action,” of 10 CFR Part 50, Appendix B. Appendix A of the GALL-SLR Report describes how an applicant may apply its 10 CFR Part 50, Appendix B, QA program to fulfill the confirmation process element of this AMP for both safety-related and nonsafety-related SCs within the scope of this program.

9. Administrative Controls: Administrative controls are addressed through the QA program that is used to meet the requirements of 10 CFR Part 50, Appendix B, associated with managing the effects of aging. Appendix A of the GALL-SLR Report describes how an applicant may apply its 10 CFR Part 50, Appendix B, QA program to fulfill the administrative controls element of this AMP for both safety-related and nonsafety-related SCs within the scope of this program.

10. Operating Experience: EQ programs include consideration of OE to modify qualification bases and conclusions, including qualified life such that the impact on the EQ program is evaluated and any necessary actions or modifications to the program are performed. Compliance with 10 CFR 50.49 provides reasonable assurance that EQ equipment can perform their intended functions during accident conditions after experiencing the effects of operational aging.

The program is informed and enhanced when necessary through the systematic and ongoing review of both plant-specific and industry OE including research and development such that the effectiveness of the AMP is evaluated consistent with the discussion in Appendix B of the GALL-SLR Report.

References

10 CFR Part 50, Appendix B, “Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants.” Washington, DC: U.S. Nuclear Regulatory Commission. 2016.

10 CFR 50.49, “Environmental Qualification of Electrical Equipment Important to Safety for Nuclear Power Plants.” Washington, DC: U.S. Nuclear Regulatory Commission. 2016.

10 CFR 54.21, “Contents of Application—Technical Information.” Washington, DC: U.S. Nuclear Regulatory Commission. 2015.

EPRI. EPRI 1003057(Archived), Revision 1, “Plant Support Engineering: License Renewal Electrical Handbook.” Palo Alto, California: Electric Power Research Institute February 2007.

IEEE. IEEE Standard 1205-2014, “IEEE Guide for Assessing, Monitoring and Mitigating Aging Effects on Class 1E Equipment Used in Nuclear Power Generating Stations.” New York, New York: Institute of Electrical and Electronics Engineers. 2014.

US NRC. Denton, H.R., U.S. Nuclear Regulatory Commission, letter to V. Stello, Office of Inspection and Enforcement. Agencywide Documents Access and Management System (ADAMS) Accession No. ML032541214. Washington, DC: U.S. Nuclear Regulatory Commission. November 13, 1979.

_____. Generic Letter 2007-01, “Inaccessible or Underground Power Cable Failures that Disable Accident Mitigation Systems or Cause Plant Transients.” ADAMS Accession No. ML070360665. Washington, DC: U.S. Nuclear Regulatory Commission. February 7, 2007.

_____. NUREG–0588, “Interim Staff Position on Environmental Qualification of Safety-Related Electrical Equipment.” Revision 1. ADAMS Accession No. ML031480402. Washington, DC: U.S. Nuclear Regulatory Commission. July 31, 1981.

_____. NUREG/CR–7000, “Essential Elements of an Electric Cable Condition Monitoring Program.” ADAMS Accession No. ML100540050. Washington, DC: U.S. Nuclear Regulatory Commission. January 31, 2010.

_____. Regulatory Guide 1.100, “Seismic Qualification of Electrical and Active Mechanical Equipment and Functional Qualification of Active Mechanical Equipment for Nuclear Power Plants.” Revision 3. ADAMS Accession No. ML091320468. Washington, DC: U.S. Nuclear Regulatory Commission. September 30, 2009.

_____. Regulatory Guide 1.211, “Qualification of Safety-Related Cables and Field Splices for Nuclear Power Plants.” ADAMS Accession No. ML082530205. Washington, DC: U.S. Nuclear Regulatory Commission. April 1, 2009.

_____. Regulatory Guide 1.218, “Condition-Monitoring Techniques for Electric Cables Used in Nuclear Power Plants.” ADAMS Accession No. ML103510458. Washington, DC: U.S. Nuclear Regulatory Commission. April 30, 2012.

_____. Regulatory Guide 1.89, “Environmental Qualification of Certain Electric Equipment Important to Safety for Nuclear Power Plants.” Revision 1. ADAMS Accession No. ML14070A119. Washington, DC: U.S. Nuclear Regulatory Commission. May 20, 1984.

_____. Regulatory Issue Summary 2003-09, “Environmental Qualification of Low-Voltage Instrumentation and Control Cables.” ADAMS Accession No. ML03120078. Washington, DC: U.S. Nuclear Regulatory Commission. May 2, 2003.

X.E1 (NUREG-2191 R0)

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