XI.E6 (NUREG-2191 R0)
XI.E6 ELECTRICAL CABLE CONNECTIONS NOT SUBJECT TO 10 CFR 50.49 ENVIRONMENTAL QUALIFICATION REQUIREMENTS
Program Description
The purpose of the this aging management program (AMP) is to provide reasonable assurance that the intended functions of the metallic parts of electrical cable connections that are not subject to the environmental qualification (EQ) requirements of Title 10 of the Code of Federal Regulations (10 CFR) 50.49 and susceptible to age-related degradation resulting in increased resistance of the connection are maintained consistent with the current licensing basis through the subsequent period of extended operation. This AMP manages the aging mechanisms and effects associated with the metallic portion of electrical connections that result in increased resistance of connection due to thermal cycling, ohmic heating, electrical transients, vibration, chemical contamination, corrosion, or oxidation such that the metallic portions of the electrical cable connections are maintained consistent with the current licensing basis through the subsequent period of extended operation.
Cable connections are used to connect cable conductors to other cable conductors or electrical devices. Connections associated with cables within the scope of license renewal are part of this AMP. Examples of connections used in nuclear power plants include bolted connectors, coaxial/triaxial connections, compression/crimped connectors, splices (butt or bolted), stress cones, and terminal blocks. Most connections involve insulating material and metallic parts. This AMP focuses on the metallic parts of the electrical cable connections. This AMP provides testing, on a sampling basis, to demonstrate that either aging of metallic cable connections is not occurring and/or that the existing preventive maintenance program is effective. Testing confirms the absence of age-related degradation of cable connections resulting in increased resistance of connection due to thermal cycling, ohmic heating, electrical transients, vibration, chemical contamination, corrosion, or oxidation.
The Generic Aging Lessons Learned for Subsequent License Renewal (GALL-SLR) Report AMP XI.E1, “Electrical Insulation Material for Electrical Cables and Connections Not Subject to 10 CFR 50.49 Environmental Qualification Requirements,” manages the aging of insulating material but not the metallic parts of the electrical connections. The GALL-SLR Report AMP X1.E1 is based on a visual inspection of accessible cables and connections. However, visual inspection alone may not be sufficient to detect the aging effects from thermal cycling, ohmic heating, electrical transients, vibration, chemical contamination, corrosion, or oxidation on the metallic parts of cable connections.
Electrical cable connections exposed to appreciable ohmic or ambient heating during operation may experience increased resistance of connection caused by repeated cycling of connected loads or by the ambient temperature environment. Different materials used in various cable system components can produce situations where stresses between these components change with repeated thermal cycling. For example, under loaded conditions, ohmic heating may raise the temperature of a compression terminal and cable conductor well above the ambient temperature, thereby causing thermal expansion of both components. Thermal expansion coefficients of different materials may alter mechanical stresses between the components and may adversely impact the termination. When the current is reduced, the affected components cool and contract. Repeated cycling in this fashion can cause loosening of the termination and may lead to increased resistance of connection or eventual separation of compression type terminations. Threaded connectors may also loosen if subjected to significant thermally induced stress and cycling.
A sample of cable connections within the scope of license renewal are tested on a one-time test basis or periodically once every 5 years, if only visual inspection is used to provide an indication of the integrity of the cable connections. Depending on the findings of the one-time test, subsequent testing may have to be performed within 10 years of initial testing. The first visual inspections or tests for license renewal are to be completed prior to the subsequent period of extended operation.
The specific type of test to be performed is a proven test for detecting increased resistance of connection, such as thermography, contact resistance testing, or another appropriate test. As an alternative to measurement of cable connections, for the accessible cable connections that are covered with insulation materials such as tape, the applicant may perform visual inspection of insulation material to detect aging effects. The basis for performing only a periodic visual inspection is documented.
This AMP is a sampling program. The following factors are considered for sampling: voltage level (medium and low-voltage), circuit loading (high loading), connection type, and location (high temperature, high humidity, vibration, etc.). The technical basis for the sample selections should be documented. If an unacceptable condition or situation is identified in the selected sample, a determination is made as to whether the same condition or situation is applicable to other connections not tested. The corrective action program is used to evaluate the condition and determine appropriate corrective action.
This AMP is not applicable to cable connections in harsh environments since they are already addressed by the requirements of 10 CFR 50.49. Even though cable connections may not be exposed to harsh environments, increased resistance of connection is a concern due to the cable connection aging mechanisms and effects discussed above.
Evaluation and Technical Basis
- 1. Scope of Program: Cable connections associated with cables within the scope of license renewal that are external connections terminating at active or passive devices, are in the scope of this AMP. Wiring connections internal to an active assembly are considered part of the active assembly and, therefore, are not within the scope of this AMP. This AMP does not include high voltage (>35 kilo-volts) switchyard connections. The cable connections covered under the EQ program are not included in the scope of this program.
- 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: This AMP focuses on the metallic parts of the connection. One-time testing provides an indication of increased resistance of connection due to thermal cycling, ohmic heating, electrical transients, vibration, chemical contamination, corrosion, or oxidation. Representative samples of each type of electrical cable connection are tested. The following factors are considered for sampling: voltage level (medium and low-voltage), circuit loading (high load), connection type, and location (high temperature, high humidity, vibration, etc.). The technical basis for the sample selection is documented.
- 4. Detection of Aging Effects: A representative sample of electrical connections within the scope of license renewal is tested prior to the subsequent period of extended operation. The findings of the initial one-time test are evaluated to determine whether periodic testing of the cable connections is warranted. This finding forms the basis of site-specific operating experience (OE) for age-related degradation and informs the need for subsequent testing on a 10-year periodic basis. The justification and technical basis for not performing subsequent periodic testing is documented. This includes a discussion of the types of unacceptable conditions or degradation identified and whether they were determined to be age-related, requiring periodic maintenance.
- Testing of in-scope connections manages the aging mechanisms and effects requiring management during the subsequent period of extended operation. Testing may include thermography, contact resistance testing, or other appropriate testing methods without removing the connection insulation. One-time testing provides additional confirmation to support industry OE that shows that electrical connections have not experienced a high degree of failures, and that existing installation and maintenance practices are effective. Twenty percent of a connector type population with a maximum sample of 25 constitutes a representative connector sample size. Otherwise a technical justification of the methodology and sample size used for selecting components under test should be included as part of the applicant’s AMP’s documentation.
- The first tests for license renewal are to be completed prior to the subsequent period of extended operation.
- As an alternative to measurement testing for accessible cable connections that are covered with heat shrink tape, sleeving, insulating boots, etc., the applicant may use a visual inspection of insulation materials to detect surface anomalies, such as embrittlement, cracking, chipping, melting, discoloration, swelling or surface contamination. When this alternative visual inspection is used to check cable connections, the first inspection is completed prior to the subsequent period of extended operation and at least every 5 years thereafter. The basis for performing only the alternative periodic visual inspection to monitor age-related degradation of cable connections 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 specific test or visual inspection program selected. However, condition monitoring inspection or test results that are trendable provide additional information on the rate of electrical connection degradation.
- 6. Acceptance Criteria: Cable connections should not indicate abnormal temperatures for the application when thermography is used. Alternatively, connections should exhibit a low resistance value appropriate for the application when resistance measurement is used. When the visual inspection alternative for covered cable connections is used, the absence of embrittlement, cracking, chipping, melting, discoloration, swelling, or surface contamination indicates that the covered cable connection components are not loose. An unacceptable indication is defined as a noted condition or situation that, if left unmanaged, could potentially lead to a loss of 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 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: Electrical cable connections exposed to thermal cycling, ohmic heating, electrical transients, vibration, chemical contamination, corrosion, or oxidation during operation may experience increased resistance of connection. There have been limited numbers of age-related failures of cable connections reported. An applicant’s OE with connection reliability and aging effects should be adequate to demonstrate the AMP effectiveness of GALL-SLR Report AMP XI.E6, “Electrical Cable Connections Not Subject To 10 CFR 50.49 Environmental Qualification Requirements,” including the program’s capability to detect the presence or noting the absence of aging effects for electrical cable connections.
- 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-104213(Archived), “Bolted Joint Maintenance & Application Guide.” Palo Alto, California: Electric Power Research Institute. December 1995.
_____. EPRI TR-109619, “Guideline for the Management of Adverse Localized Equipment Environments.” Palo Alto, California: Electric Power Research Institute. June 1999.
_____. EPRI 1003471, “Electrical Connector Application Guidelines.” Palo Alto, California: Electric Power Research Institute. December 2002.
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.
Licensee Event Report 361/2007-005, “San Onofre Unit 2, Loose Electrical Connection Results in Inoperable Pump Room Cooler.” https://lersearch.inl.gov/LERSearchCriteria.aspx. 2009.
Licensee Event Report 361/2007-006, “San Onofre Units 2 and 3, Loose Electrical Connection Results in One Train of Emergency Chilled Water (ECW) System Inoperable.” https://lersearch.inl.gov/LERSearchCriteria.aspx. 2009.
Licensee Event Report 361/2008-006, “San Onofre 2, Loose Connection Bolting Results in Inoperable Battery and TS Violation.” https://lersearch.inl.gov/LERSearchCriteria.aspx. 2009.
NEI. White Paper, “GALL-SLR AMP XI.E6 (Electrical Cables).” Agencywide Documents Access and Management System (ADAMS) Accession No. ML062770105. Washington, DC: Nuclear Energy Institute. September 5, 2006.
US NRC. NUREG/CR–5643, “Insights Gained From Aging Research.” ADAMS Accession No. ML041530264. Washington, DC: U.S. Nuclear Regulatory Commission. March 31, 1992.
_____. Staff’s Response to the NEI White Paper on Generic Aging Lessons Learned (GALL) Report Aging Management Program (AMP) XI.E6, “Electrical Cable Connections Not Subject to 10 CFR 50.49 Environmental Qualification Requirements.” ADAMS Accession No. ML070400349. Washington, DC: U.S. Nuclear Regulatory Commission. March 16, 2007.