XI.E7 (NUREG-2191 R0)
XI.E7 HIGH-VOLTAGE INSULATORS
Program Description
The purpose of the aging management program (AMP) is to provide reasonable assurance that the intended functions of high-voltage insulators within the scope of subsequent license renewal (SLR) are maintained consistent with the current licensing basis through the subsequent period of extended operation. The high-voltage insulator program was developed specifically to age manage high-voltage insulators susceptible to aging degradation due to local environmental conditions.
The high-voltage insulators program includes visual inspections to identify degradation of high-voltage insulator sub-component parts, namely; insulation and metallic elements. Visual inspection provides reasonable assurance that the applicable aging effects are identified and high-voltage insulator age degradation is managed. Insulation materials used in high-voltage insulators may degrade more rapidly than expected when installed in an environment conducive to accelerated aging. The insulation and metallic elements of high-voltage insulators are made of porcelain, cement, malleable iron, aluminum, and galvanized steel. Significant loss of metallic material can occur due to mechanical wear caused by oscillating movement of insulators due to wind. Surface corrosion in metallic parts may appear due to contamination or where galvanized or other protective coatings are worn. With substantial airborne contamination such as salt, surface corrosion in metallic parts may become significant such that the insulator no longer will support the conductor. Various airborne contaminates such as dust, salt, fog, cooling tower plume, or industrial effluent can contaminate the insulator surface leading to reduced insulation resistance. Excessive surface contaminants or loss of material can lead to insulator flashover and failure.
The high voltage insulators within the scope of this program are to be visually inspected at a frequency, determined prior to subsequent period of extended operation, based on plant-specific operating experience (OE). The first inspections for the subsequent period of extended operation are to be completed prior to the subsequent period of extended operation. The high-voltage insulator program provides reasonable assurance that high-voltage insulators will perform its intended function during the subsequent period of extended operation.
Evaluation and Technical Basis
- 1. Scope of Program: This AMP manages the age related degradation effects of high-voltage insulators within the scope of subsequent license renewal, susceptible to airborne contaminants including dust, salt, fog, cooling tower plume, industrial effluent or loss of material.
- 2. Preventive Actions: The high-voltage insulators AMP is a condition monitoring program that relies on visual inspections and high-voltage insulator coating and cleaning to manage high-voltage insulator aging effects. High-voltage insulator periodic visual inspections are performed to monitor the buildup of contaminants on the insulator surface. The periodic coating or cleaning of high-voltage insulators limits high-voltage insulator surface contamination.
- 3. Parameters Monitored or Inspected: The high voltage insulators within the scope of this program are visually inspected at a frequency based on plant-specific OE. High-voltage insulator surfaces are visually inspected to detect reduced insulation resistance aging effects including cracks, foreign debris, salt, dust, cooling tower plume and industrial effluent contamination. Metallic parts of the insulator are visually inspected to detect loss of material due to mechanical wear or corrosion.
- 4. Detection of Aging Effects: Visual inspection is used to detect the following two aging degradations: (a) loss of material in the metallic parts and (b) reduced insulation resistance. The loss of material in the metallic parts is due to corrosion caused by contaminants, where galvanized or other protective coatings are worn, and mechanical wear due to wind-induced movement. Reduced insulation resistance can be caused by the presence of insulator surface contamination. Visual inspections may be supplemented with infrared thermography inspections to detect high-voltage insulator reduced insulation resistance. The first inspection for SLR is to be completed prior to the subsequent period of extended operation.
- 5. Monitoring and Trending: Trending actions are not included as part of this AMP, because the ability to trend visual inspection results is limited. However, inspection results that are trendable provide additional information on the rate of insulator degradation including optimization of inspection frequencies.
- 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.
- High-voltage insulator surfaces are free from unacceptable accumulation of foreign material such as significant salt or dust buildup as well as other contaminants. Metallic parts must be free from significant loss of materials due to pitting, fatigue, crevice, and general corrosion. Acceptance criteria will be based on temperature rise above a reference temperature for the application when thermography is used. The reference temperature will be ambient temperature or a baseline temperature based on data from the same type of high-voltage insulator being inspected.
- 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.
- Corrective actions are taken and an engineering evaluation is performed when the acceptance criteria are not met. Corrective actions will be based on the observed degradation. The evaluation will consider the significance of the inspection results, the extent of the concern, the potential root causes, and the corrective actions required. If an unacceptable condition is identified, a determination is made as to whether the same condition or situation is applicable to other high-voltage insulators. Corrective actions will be implemented when inspection results do not meet the acceptance criteria.
- 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: 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 1001997(revision referenced is archived), “Parameters that Influence the Aging and Degradation of Overhead Conductors.” Palo Alto, California: Electric Power Research Institute. December 2003.
_____. EPRI 1013475, “Plant Support Engineering: License Renewal Electrical Handbook.” Revision 1. Palo Alto, California: Electric Power Research Institute. February 2007.
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. NUREG/CR–5643, “Insights Gained From Aging Research.” Agencywide Documents Access and Management System (ADAMS) Accession No. ML041530264. Washington, DC: U.S. Nuclear Regulatory Commission. March 31, 1992.
_____. Information Notice 93-95: “Storm-Related Loss of Offsite Power Events Due to Salt Buildup on Switchyard Insulators.” ADAMS Accession No. ML031070158. Washington, DC: U.S. Nuclear Regulatory Commission. December 13, 1993.