XI.E1 (NUREG-2191 R0)
XI.E1 ELECTRICAL INSULATION FOR ELECTRICAL CABLES AND CONNECTIONS NOT SUBJECT TO 10 CFR 50.49 ENVIRONMENTAL QUALIFICATION REQUIREMENTS
Program Description
The purpose of this aging management program (AMP) is to provide reasonable assurance that the intended functions of electrical cable insulating material (e.g., power, control, and instrumentation) and connection insulating material that are not subject to the environmental qualification (EQ) requirements of [Title 10 of the Code of Federal Regulations (10 CFR) 50.49 are maintained consistent with the current licensing basis through the subsequent period of extended operation.
In most areas within a nuclear power plant, the actual operating environment (e.g., temperature, radiation, or moisture) 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.
An adverse localized environment is an environment that exceeds the most limiting environment (e.g., temperature, radiation, or moisture) for the electrical insulation of cables and connectors. Electrical insulation used in electrical cables and connections may degrade more rapidly than expected when exposed to an adverse localized environment. Cable or connection electrical insulation subjected to an adverse localized environment may increase the rate of aging of a component or have an adverse effect on operability.
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, temperatures, and moisture levels; (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; and (e) 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 cable and connection electrical insulation to an adverse localized environment (e.g., equipment thermal insulation removal and restoration);
- Corrective actions involving in-scope electrical cable and connection electrical insulation material service life (current operating term);
- Previous walk-downs including visual inspection of accessible cable and connection electrical insulation; and
- Environmental monitoring (e.g., long term periodic environmental monitoring–temperature, radiation, or moisture).
Periodic environmental monitoring consists of a representative number of environmental measurements taken over a sufficient period of time and periodically evaluated to establish the environment for condition monitoring electrical insulation. Plant environmental data can be used in an aging evaluation in different ways, such as directly applying the plant data in the evaluation or using the plant data to demonstrate conservatism. The methodology employed for monitoring, data collection, and the analysis of localized component environmental data (including temperature, radiation, and moisture) is documented in the record of the analysis. Documentation is provided, as needed, on the applicability of methodologies utilizing data that are collected and evaluated once, or are of limited duration.
Accessible in-scope cables and connections are visually inspected for degradation. Visual inspection findings may necessitate testing. Testing is comprised of one or more tests utilizing mechanical, electrical, or chemical means implemented on a sampling basis and represents with reasonable assurance, both accessible and inaccessible in-scope cable and connection electrical insulation degradation.
Accessible in-scope cable and connection inspection 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). These potential adverse localized environments are then evaluated, which 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 cable and connector electrical insulation aging degradation.
The cable condition monitoring portion of the AMP utilizes component sampling for cable and connection electrical insulation testing, if deemed necessary. The following factors are considered in the development of the electrical insulation sample: the environment including identified adverse localized environments (high temperature, high humidity, vibration, etc.), voltage level, circuit loading, connection type, location (high temperature, high humidity, vibration, etc.) and the electrical insulation composition. The component sampling methodology utilizes a population that includes a representative sample of in-scope electrical cable and connection types regardless of whether or not the component was included in a previous aging management or maintenance program. The technical basis for the sample selection is documented.
Electrical insulation material for cables and connections previously identified and dispositioned during the first period of extended operation as subjected to an adverse localized environment are evaluated for cumulative aging effects during the subsequent period of extended operation. If an unacceptable condition or situation is identified for cable or connection electrical insulation by visual inspection or test, corrective actions are taken including a determination as to whether the same condition or situation is applicable to other in-scope accessible and inaccessible cable or connection electrical insulation (e.g., extent of condition). As such, this program does not apply to plants in which most cables are inaccessible.
As stated in NUREG/CR–5643, “the major concern is that failures of deteriorated cable systems (cables, connection electrical insulation) might be induced during accident conditions.” Since the cable and connection electrical insulation is not subject to the EQ requirements of 10 CFR 50.49, an AMP is needed to manage the aging mechanisms and effects for the subsequent period of extended operation. This AMP provides reasonable assurance that the insulation for electrical cables and connections will perform its intended function for the subsequent period of extended operation.
Evaluation and Technical Basis
- 1. Scope of Program: This AMP applies to accessible cable and connection electrical insulation within the scope of subsequent license renewal including in-scope cables and connections subjected to an adverse localized environment.
- 2. Preventive Actions: This is a condition monitoring program and no actions are taken as part of this program to prevent or mitigate aging degradation.
- 3. Parameters Monitored or Inspected: Accessible in-scope cable and connection electrical insulation subject to an adverse localized environment are visually inspected for surface anomalies. The cable insulation visual inspection portion of the AMP uses the cable or connection jacket material as representative of the aging effects experienced by the cable and connection electrical insulation. Cable and connection electrical insulation material are evaluated for signs of reduced electrical insulation resistance due to an adverse localized environment of temperature, moisture, radiation and oxygen that includes radiolysis, photolysis (ultraviolet sensitive materials only) of organics, radiation induced oxidation, moisture intrusion, indicated by signs of electrical insulation embrittlement, discoloration, cracking, melting, swelling or surface contamination.
- An adverse localized environment is a plant-specific condition; therefore, the applicant should clearly define the most limiting temperature, radiation, and moisture environments and their basis. For the subsequent period of extended operation, the applicant reviews plant-specific OE for previously identified and mitigated adverse localized environments cumulative aging effects applicable to in-scope cable and connection electrical insulation (i.e., service life). The applicant should also inspect for adverse localized environments for each of the most limiting cable and connection electrical insulation plant environments (e.g., caused by temperature, radiation, moisture, or contamination).
- 4. Detection of Aging Effects: Aging effects resulting from temperature, radiation, or moisture cause surface abnormalities in the cable jacket, and connection material. Accessible electrical cables and connections are visually inspected for cable jacket and connection electrical insulation surface anomalies such as embrittlement, discoloration, cracking, melting, swelling, or surface contamination. Cable and connection electrical insulation are inspected to identify cable and connection insulation installed in an adverse localized environment. Plant-specific OE is also evaluated to identify in-scope cable and connection insulation previously subjected to adverse localized environment during the period of extended operation. Cable and connection insulation are evaluated to confirm that the dispositioned corrective actions continue to support in-scope cable and connection intended functions during the subsequent period of extended operation.
- The inspection of accessible cable and connection insulation material is used to evaluate the adequacy of inaccessible cable and connection electrical insulation. Accessible electrical cables and connections subjected to an adverse localized environment found in the performance of this AMP are visually inspected at least once every 10 years. This is an adequate period to preclude failures of the cables and connection electrical insulation since experience has shown that aging degradation is a slow process. If visual inspections identify degraded or damaged conditions as defined in Element 3 of this AMP, then testing may be performed for evaluation. For a large number of cables and connections identified as potentially degraded, a sample population is tested. The first inspection for subsequent license renewal is to be completed prior to the subsequent period of extended operation. Testing may include thermography and other proven condition monitoring test methods applicable to the cable and connection insulation. Testing as part of an existing maintenance, calibration or surveillance program may be credited in lieu of testing recommended in this AMP.
- This AMP, as noted, is a cable and connection electrical insulation condition monitoring program that utilizes sampling. A sample of 20 percent of each cable and connection type with a maximum sample size of 25 is tested. The following factors are considered in the development of the cable and connection insulation test sample: environment including identified adverse localized environments (high temperature, high humidity, vibration, etc.), voltage level, circuit loading, connection type, location (high temperature, high humidity, vibration, etc.), and insulation material. The component sampling methodology utilizes a population that includes a representative sample of in-scope electrical cable and connection types regardless of whether or not the component was included in a previous aging management or maintenance program. The technical basis for the sample selection is documented.
- 5. Monitoring and Trending: Trending actions are not included as part of this AMP, because the ability to trend visual inspection and test results is dependent on the test or visual inspection program selected. However, condition monitoring of cable and connection insulation utilizing visual inspection and test results that are trendable provide additional information on the rate of cable or connection insulation degradation.
- 6. Acceptance Criteria: Electrical cable and connection insulation material test results are to be within the acceptance criteria, as identified in the applicant’s procedures. Visual inspection results show that accessible cable and connection insulation material are free from unacceptable signs of surface abnormalities that indicate unusual cable or connection insulation aging effects exist. An unacceptable indication is defined as a noted condition or situation that, if left unmanaged, could potentially lead to a loss of the intended function.
- 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 quality assurance (QA) program that are used to meet Criterion XVI, “Corrective Action,” of 10 CFR 50, Appendix B. Appendix A of the Generic Aging Lessons Learned for Subsequent License Renewal (GALL-SLR) Report describes how an applicant may apply its 10 CFR 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.
- Unacceptable test results and visual indications of cable and connection electrical insulation abnormalities are subject to an engineering evaluation. Such an evaluation considers the age and operating environment of the component, as well as the severity of the abnormality and whether such an abnormality has previously been correlated to degradation of cable or connection insulation. Corrective actions include, but are not limited to, testing, shielding, or otherwise mitigating the environment or relocation or replacement of the affected cables or connections. When an unacceptable condition or situation is identified, a determination is made as to whether the same condition or situation is applicable to additional in-scope accessible and inaccessible cables or connections (extent of condition).
- 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 50, Appendix B. Appendix A of the GALL-SLR Report describes how an applicant may apply its 10 CFR 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 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 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: Industry OE has identified cable and connection insulation aging effects due to adverse localized environments caused by elevated temperature, radiation, or moisture. For example, cable and connection insulation located near steam generators, pressurizers, or process may be subjected to an adverse localized environment. These environments have been found to cause degradation of electrical cable and connection electrical insulation that are visually observable, such as color changes or surface abnormalities. These visual indications along with cable condition monitoring can be used as indicators of cable and connection insulation degradation.
- 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.
EPRI. EPRI TR–109619, “Guideline for the Management of Adverse Localized Equipment Environments.” Palo Alto, California: Electric Power Research Institute. June 1999.
IEEE. IEEE Standard 422-2012, “Guide for the Design of Cable Raceway Systems for Electric Generating Facilities.” New York, New York: Institute of Electrical and Electronic Engineers. 2012.
_____. IEEE Standard 576-2000, “Recommended Practice for Installation, Termination, and Testing of Insulated Power Cable as Used in Industrial and Commercial Applications.” New York, New York: Institute of Electrical and Electronics Engineers. 2000.
_____. 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. Generic Letter 2007-01, “Inaccessible or Underground Power Cable Failures that Disable Accident Mitigation Systems or Cause Plant Transients.” Agencywide Documents Access and Management System (ADAMS) Accession No. ML070360665. Washington, DC: U.S. Nuclear Regulatory Commission. February 7, 2007.
_____. Information Notice 2010-2, “Construction Related Experience With Cables Connectors, and Junction Boxes.” ADAMS Accession No. ML090290185. Washington, DC: U.S. Nuclear Regulatory Commission. January 28, 2010.
_____. Information Notice 2010-25, “Inadequate Electrical Connections.” ADAMS Accession No. ML102530012. Washington, DC: U.S. Nuclear Regulatory Commission. November 17, 2010.
_____. Information Notice 2010-26, “Submerged Electrical Cables.” ADAMS Accession No. ML102800456. Washington, DC: U.S. Nuclear Regulatory Commission. December 2, 2010.
_____. NUREG/CR–5643, “Insights Gained From Aging Research.” ADAMS Accession No. ML04153026. Washington, DC: U.S. Nuclear Regulatory Commission. March 31, 1992.
_____. 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 1.218, “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.
SNL. SAND96-0344, “Aging Management Guideline for Commercial Nuclear Power Plants-Electrical Cable and Terminations.” Albuquerque, New Mexico: Sandia National Laboratories. September 1996.