XI.E3A (NUREG-2191 R0)
XI.E3A ELECTRICAL INSULATION FOR INACCESSIBLE MEDIUM-VOLTAGE POWER CABLES NOT SUBJECT TO 10 CFR 50.49 ENVIRONMENTAL QUALIFICATION REQUIREMENTS
Program Description
The purpose of the aging management program (AMP) is to provide reasonable assurance that the intended functions of inaccessible medium-voltage power cables (operating voltages of 2 kV to 35 kV) that are not subject to the environmental qualification 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. This AMP applies to underground (e.g., installed in buried conduit, embedded raceway, cable trenches, cable troughs, duct banks, vaults, manholes, or direct buried installations) medium-voltage cables within the scope of subsequent license renewal (SLR) exposed to wetting or submergence (i.e., significant moisture). Inaccessible medium-voltage cables designed for continuous wetting or submergence are also included in this AMP for a one-time inspection and test.
Most electrical cables in nuclear power plants are located in dry environments. However, some cables are inaccessible or underground, located in buried conduits, cable trenches, cable troughs, duct banks, vaults, or direct buried installations that may be exposed to water intrusion due to wetting or submergence. When an inaccessible medium-voltage power cable is exposed to wet, submerged, or other environments for which it was not designed, age related degradation of the electrical insulation may occur. Electrical insulation subjected to wetting or submergence could have an adverse effect on performance of intended functions, or potentially lead to failure of the cable insulation system. Although variations exist in the aging mechanisms and effects depending on cable insulation material and manufacture, periodic actions are necessary to minimize the potential for insulation degradation.
Periodic actions are taken to prevent inaccessible medium-voltage cables from being exposed to significant moisture. Significant moisture is defined as exposure to moisture that lasts more than 3 days (i.e., long term wetting or submergence over a continuous period) that if left unmanaged, could potentially lead to a loss of intended function. Cable wetting or submergence that occurs for a limited time as drainage occurs by either automatic or passive drains is not considered significant moisture for this AMP.
The inspection frequency for water accumulation is established and performed based on plant-specific operating experience (OE) over time with cable wetting or submergence. Inspections are performed periodically based on water accumulation over time. The periodic inspection occurs at least once annually with the first inspection for SLR completed prior to the subsequent period of extended operation. Inspection frequencies are adjusted based on inspection results including plant-specific OE but with a minimum inspection frequency of at least once annually. Inspections are also performed after event driven occurrences, such as heavy rain, rapid thawing of ice and snow, or flooding.
Examples of periodic actions to mitigate inaccessible medium-voltage cable exposure to significant moisture include inspection for water accumulation in cable manholes and conduits and removing water, as needed. However, these actions may not be sufficient to verify that water is not trapped elsewhere in the raceways. For example, water accumulation and submergence could occur from: (a) a duct bank conduit with low points in the routing, (b) concrete cracking due to soil settling over a long period of time, (c) manhole covers not being watertight, (d) routing locations subject to a high water table (e.g., high seasonal cycles), and (e) wetting and submergence potential even when duct banks are sloped with the intention to minimize water accumulation.
Therefore, in addition to the above periodic actions, in-scope inaccessible medium-voltage power cables exposed to significant moisture are tested to determine the condition of the electrical insulation. One or more tests may be required based on cable application, construction, and electrical insulation material to determine the age degradation of the cable. Cable testing as part of an existing maintenance or surveillance program, with justification, can be credited in lieu of, or in combination with, testing recommended in this AMP. A plant-specific inaccessible medium-voltage cable test matrix that documents inspection methods, test methods, and acceptance criteria for the applicant’s plant-specific in-scope inaccessible medium-voltage power cables is developed based on OE.
Note: Inaccessible medium-voltage cables designed for continuous wetting or submergence are also included in this AMP for a one-time inspection and test with additional periodic tests and inspections determined by the test/inspection results and industry and plant-specific OE.
The first tests for license renewal are to be completed prior to the subsequent period of extended operation with subsequent tests performed at least once every 6 years thereafter. For inaccessible medium power cables exposed to significant moisture, test frequencies are adjusted based on test results (including trending of aging degradation where applicable) and plant-specific OE but with a minimum test frequency of at least once every 6 years.
As stated in NUREG/CR–5643, “the major concern is that failures of deteriorated cable systems (cables, connections, and penetrations) might be induced during accident conditions.” Because the cables are not subject to the environmental qualification requirements of 10 CFR 50.49, an AMP is required to manage the aging effects. This AMP provides reasonable assurance the insulation material for electrical cables will perform its intended function for the subsequent period of extended operation.
Evaluation and Technical Basis
- 1. Scope of Program: This AMP applies to underground medium-voltage (2kV to 35kV) power cable installations (e.g., direct buried, buried conduit, duct bank, embedded raceway, cable trench, vaults, or manholes) within the scope of subsequent license renewal exposed to significant moisture.
- Significant moisture is defined as exposure to moisture that lasts more than 3 days (that if left unmanaged, could potentially lead to a loss of intended function. Cable wetting or submergence that occurs for a limited time as in the case of automatic or passive drainage is not considered significant moisture for this AMP.
- In-scope inaccessible medium-voltage cable splices subjected to wetting or submergence are also included within the scope of this program. Submarine or other cables designed for continuous wetting or submergence are also included in this AMP as a one-time inspection and test with additional periodic tests and inspections determined by the one-time test/inspection results as well as industry and plant-specific OE.
- 2. Preventive Actions: This is a condition monitoring program. However, periodic actions are taken to prevent inaccessible medium-voltage power cables from being exposed to significant moisture, such as identifying and inspecting conduit ends and cable manholes/vaults for water accumulation, and removing the water, as needed.
- The inspection frequency for water accumulation is established and performed based on plant-specific OE with cable wetting or submergence. The inspections are performed periodically based on water accumulation over time. The periodic inspection occurs at least once annually with the first inspection for SLR completed prior to the subsequent period of extended operation. The annual inspection frequency is consistent with U.S. Nuclear Regulatory Commission Inspection Manual, Attachment 71111.06, “Flood Protection Measures.”
- Inspections for water accumulation are also performed after event driven occurrences, such as heavy rain, rapid thawing of ice and snow, or flooding. Plant-specific parameters are established for the initiation of an event driven inspection. Inspections include direct indication that cables are not wetted or submerged, and that cable/splices and cable support structures are intact. Dewatering systems (e.g., sump pumps and passive drains) and associated alarms are inspected and their operation verified periodically. The periodic inspection includes documentation that either automatic or passive drainage systems or manually pumping are effective in preventing cable exposure to significant moisture.
- If water is found during inspection, corrective actions are taken per the applicant’s corrective action program to keep the cables free from significant moisture and to assess cable degradation. The aging management of the physical structures, including cable support structures of cable vaults/manholes is managed by Generic Aging Lessons Learned Subsequent License Renewal (GALL-SLR) Report AMP XI.S6, “Structures Monitoring.”
- 3. Parameters Monitored or Inspected: Inspection for water accumulation is performed based on plant-specific OE with water accumulation over time.
- Inaccessible or underground medium-voltage power cables within the scope of license renewal exposed to significant moisture are tested to determine the age degradation of the electrical insulation.
- 4. Detection of Aging Effects: For inaccessible medium-voltage power cables exposed to significant moisture, test frequencies are adjusted based on test results (including trending of aging degradation where applicable) and plant-specific OE. Cable testing occurs at least once every 6 years. The first tests for license renewal are to be completed prior to the subsequent period of extended operation with additional tests performed at least once every 6 years thereafter. This is an adequate period to monitor performance of the cable and take appropriate corrective actions since experience has shown that although a slow process, aging degradation could be significant.
- The specific type of test performed is determined prior to the initial test. Testing of installed inservice cables is comprised of one or more tests utilizing mechanical, electrical, or chemical means that determines, with reasonable assurance, in-scope inaccessible medium-voltage electrical insulation age degradation. One or more tests may be required due to cable application, construction, and electrical insulation material to determine the age degradation of the cables. Cable testing as part of an existing maintenance or surveillance program, with justification, can be credited in lieu of, or in combination with, testing recommended in this AMP. A plant-specific inaccessible medium-voltage cable test matrix that documents inspection methods, test methods, and acceptance criteria for the applicant’s in-scope inaccessible medium-voltage power cables is developed based on OE.
- 5. Monitoring and Trending: Where practical, identified degradation is projected until the next scheduled inspection. Results are evaluated against acceptance criteria to confirm that the timing of subsequent inspections will maintain the components’ intended functions throughout the subsequent period of extended operation based on the projected rate of degradation. However, condition monitoring cable test and inspection results, utilizing the same visual inspection and test methods that are trendable and repeatable, provide additional information on the rate of cable or connection insulation degradation.
- 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.
- The acceptance criteria for each test or inspection are determined by the specific type of test performed and the specific cable tested. Acceptance criteria for inspections for water accumulation are defined by the direct indication that cable support structures are intact and cables are not subject to significant moisture. Dewatering systems (e.g., sump pumps and drains) and associated alarms are inspected and their operation verified to prevent unacceptable exposure to significant moisture.
- 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 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.
- 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: Operating experience has shown that medium-voltage power cable electrical insulation materials undergo increased degradation either through water tree formation or other aging mechanisms when subjected to significant moisture. Inaccessible medium-voltage cables subjected to significant moisture may result in an increased age degradation of electrical insulation. Minimizing exposure to significant moisture mitigates the potential for age related 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 1205-2014, “IEEE Guide for Assessing, Monitoring, and Mitigating Aging Effects on Electrical Equipment Used in Nuclear Power Generating Stations and Other Nuclear Facilities.” 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 1986-49, “Age/Environment Induces Electrical Cable Failures.” ADAMS Accession No. ML031220698. Washington, DC: U.S. Nuclear Regulatory Commission. June 16, 1986.
_____. Information Notice 2002-12, “Submerged Safety-Related Electrical Cables.” ADAMS Accession No. ML020790238. Washington, DC: U.S. Nuclear Regulatory Commission. March 31, 2002.
_____. Information Notice 2010-26, “Submerged Electrical Cables.” ADAMS Accession No. ML102800456. Washington, DC: U.S. Nuclear Regulatory Commission. December 2, 2010.
_____. Inspection Manual, Attachment 71111.01, “Adverse Weather Protection.” ADAMS Accession No. ML14334A684. Washington, DC: U.S. Nuclear Regulatory Commission. January 1, 2016.
_____. [Inspection Manual, Attachment 71111.06, “Flood Protection Measures.” ADAMS Accession No. ML15140A133. Washington, DC: U.S. Nuclear Regulatory Commission. January 1, 2016.
_____. 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 1.211, “Qualification of Safety-Related Cables and Field Splices for Nuclear Power Plants.” Revision 0. 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.” Revision 0. ADAMS Accession No. ML1035310458. Washington, DC: U.S. Nuclear Regulatory Commission. April 30, 2012.