ML15322A157

McGuire, Units 1 and 2 - Relief Request Serial No. 15-MN-002

ML15322A157
Person / Time
Site:	McGuire, Mcguire
Issue date:	11/09/2015
From:	Capps S D Duke Energy Carolinas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
15-MN-002, MNS-15-088
Download: ML15322A157 (8)

Text

J\ DUKE Steven D. CappsE NERG..Y McGuire Nuclear StationDuke EnergyMG01VP 1 12700 Hagers Ferry RoadHuntersville, NC 280780: 980.875.4805f: 980.875.4809Steven .Capps@du ke-energy~comSerial No. MNS-15-088 10 CFR 50.55aNovember 9, 2015U. S. Nuclear Regulatory CommissionATTN: Document Control DeskWashington, DC 20555-0001

Subject:

Duke Energy Carolinas, LLC (Duke Energy)McGuire Nuclear Station, Units 1 and 2Docket Nos. 50-369 and 50-370Relief Request Serial No. 15-MN-002Pursuant to 10 CFR 50.55a(z)(2), Duke Energy hereby submits the enclosed relief request (RR)for an alternative to defect removal prior to performing repair activities on buried NuclearService Water System (RN) piping.McGuire's Buried Piping Integrity Program requires visual and ultrasonic examination of portionsof buried Class 3 RN piping. This buried piping is shared between Units 1 and 2. If excessivewall thinning or through-wall leakage resulting from internal or external corrosion is detected inthis buried piping, this RR provides an alternative to defect removal prior to performing repairactivities. The proposed alternative will reduce the risk to system and plant operation and willhelp to avoid a hardship without a compensating increase in quality and safety.Staff approval of this RR is requested within one year of the date of this submittal.The enclosure to this letter contains the RR. If you have any questions or require additionalinformation, please contact P.T.. Vu of Regulatory Affairs at (704) 875-4302.Sincerely,Steven D. CappsEnclosure www.duke-energy.com U. S. Nuclear Regulatory CommissionNovember 9, 2015Page 2xc:Victor McCree, Region II AdministratorU. S. Nuclear Regulatory CommissionMarquis One Tower245 Peachtree Center Ave., NE, Suite 1200Atlanta, GA 30303-1257G. Ed Miller, Project ManagerU. S. Nuclear Regulatory Commission11555 Rockville PikeMail Stop O-8G9ARockville, MD 20852-2738John ZeilerNRC Senior Resident InspectorMcGuire Nuclear Station 9fEnclosureDuke Energy Carolinas, LLCMcGuire Nuclear Station, Units 1 and 2Relief Request Serial #15-MN-002Relief Requested in Accordance with 10 CFR 50.55a(z)(2) to use an Alternative to DefectRemoval Prior to Performing Repair/Replacement Activities on Nuclear Service WaterSystem Buried Piping IDuke Energy Carolinas, LLCRelief Request #15-MN-002Page 2 of 61. ASME Code Component(s) AffectedNuclear Service Water (RN) System ASME Class 3 components listed below:1.1. 36 inch and 42 inch diameter buried supply piping from the Low Level Intake (LLI) atCowans Ford Dam to the Auxiliary Building. This piping contains raw water from LakeNorman.1.2. 36 inch diameter buried supply and return piping from the Standby Nuclear ServiceWater Pond (SNSWP) to the Auxiliary Building. This piping contains raw water drawnfrom, and returned to, the SNSWP.1.3. Design data applicable to the above piping is provided below:Nominal Wall Thickness: ANSI "Standard" pipe schedule to 0.5 inchesDesign Pressure: 25 to 35 psigDesign Temperature: 95 to 150 degrees, FMaterial Specification: Carbon steel, consisting of one or more of the followingspecifications and grades:* A-134Gr283C* SA-155GrC55* SA285 Gr C* SA-672 Gr C70, CL. 21* SA-155 Gr KC 70, CL. 11.4. The above piping does not have an internal coating system, but the exterior of thispiping was coated with coal tar epoxy.1.5. The RN System piping above is shared between Units 1 and 2.2. Applicable Code Edition and AddendaASME Code,Section XI, 2007 Edition with the 2008 Addenda.The 4th Inservice Inspection Interval dates for Units 1 and 2 are as follows:* Unit 1 4th Inservice Inspection Interval: December 1, 2011 through November 30,2021* Unit 2 4th Inservice Inspection Interval: July 15, 2014 through December 14, 20243. Applicable Requirement3.1. IWA-4412 requires that welding, brazing, defect removal, and installation activities beperformed in accordance with IWA-4420.3.2. IWA-4420 specifies requirements for defect removal and examination.Relief is requested from the requirement of IWA-4400 that defective portions of componentsbe removed prior to performing a repair/replacement activity by welding.

fDuke Energy Carolinas, LLCRelief Request #f15-MN-002Page 3 of 64.' Reason for Request4.1. McGuire plans to continue to inspect portions of buried Class 3 Nuclear Service Water(RN) piping for visual and ultrasonic examination in accordance with requirements ofthe McGuire Buried Piping Integrity Program, prior to the end of the Unit 1 4th inserviceinspection interval. This program was developed for the purpose of maintaining thesafe and reliable operation of all buried piping systems within its scope, includingportions of the RN System, and was developed in direct response to industryawareness of aging buried pipe issues. Subsequently, NEI and the Buried PipingIntegrity Task Force developed and issued on February 4, 2010 NEI 09-14, "Guidelinefor the Management of Buried Piping Integrity" to facilitate the industry implementationof the Initiative. Duke Energy believes that these examinations will help to confirm thestructural and leak-tight integrity of these components, providing additional assurancethat this system can continue to perform its intended safety function.4.2. If excessive wall thinning or through-wall leakage resulting from internal or externalcorrosion is detected in this buried piping, the defective areas would require repair inaccordance with the ASME Code, Section Xl, 2007 Edition with the 2008 Addenda,IWA-4000. Prior to performing repair/replacement activities by welding, the defectiveportions of the component must be removed. Duke Energy believes that requiringremoval of defective portions of this piping prior to performing repair/replacementactivities represents a hardship or unusual difficulty without a compensating increase inthe level of quality and safety for reasons identified in this request.5. Proposed Alternative and Basis for Use5.1. For piping identified in Section 1.0 of this request that cannot be depressurized anddewatered without entering a Technical Specification LCO, or without requiring ashutdown of both Units 1 and 2, the following alternative is proposed.5.2. In lieu of the requirement of IWA-4400 to remove the defective portion of the componentprior to performing repair/replacement activities by welding, unacceptable wall thicknessloss or through-wall leakage caused by localized general or pitting corrosion on theinterior or exterior surface of the piping may be repaired without removing the defectiveportion of the component, provided the repair/replacement activity complies with therequirements of ASME Code Case N-789-1, with the following exceptions:5.2.1. Pressure pads shall not be used.5.2.2. The requirement of Code Case N-789-1, 1(e) shall not apply.5.2.3. Structural pads shall be designed such that the growth of degradation is notprojected to exceed the limits of dimensions "C" or "L" in Code Case N-789-1,Figure 1 for the design life of the repair/replacement activity. The growth ofdegradation shall be based on a corrosion rate of either 2 times the actualmeasured corrosion rate in that location, or 4 times the estimated maximumcorrosion rate for that portion of the RN system.5.2.4. Structural pads shall be designed such that the minimum required designthickness shall be maintained for the design life of the repair/replacement activity,based on corrosion rates used in the design.

fDuke Energy Carolinas, LLCRelief Request #15-MN-002Page 4 of 65.2.5. Gasket or sealant material, if used between the pipe and the pad, shall bedesigned to allow for pressurization of the pad attachment welds to the pipingduring the pressure test required by Code Case N-789-1, 7. In addition, anyresidual moisture at welding locations shall be removed by heating, prior towelding.5.2.6. Where a structural pad is applied over externally-corroded areas where there ispotential for bulging, the corrosion cavity shall be filled with hardenable fill tominimize the gap beneath the reinforcing pad, prior to installing the pad.5.2.7. The leak tightness of the structural pad and its attachment welds to thecomponent pressure boundary shall be verified by performing a system leakagetest and VT-2 visual examination, as required by Code Case N-789-1, 7.5.2.8. Inservice monitoring requirements of Code Case N-789-1, 8 shall apply, exceptas follows:1. In lieu of the requirement of 8(b), thickness monitoring for structural padsusing ultrasonic or direct thickness measurement shall be performed to verifythat minimum design thicknesses, as required by the Construction Code orSection [II, are maintained. These measurements shall be performed prior tothe date on which no less than 25% of the design life of therepair/replacement activity remains, based on corrosion rates used in thedesign of the structural pad. Subsequent measurements shall be performedprior to the date on which no less than 25% of the remaining design life of therepair/replacement activity remains, based on measured corrosion rates atthe location of the structural pad.2. The requirements of 8(d) and 8(e) shall not apply.5.2.9. Upon completion of the repair/replacement activity, protective coatings shall berestored on exterior surfaces of the piping, including areas affected by therepair/replacement activity.5.3. The basis for the proposed alternative is as follows:5.3.1. For repair of through-wall defects or excessive wall thinning caused by corrosion,compliance with the requirement to remove the defect prior to performing therepair/replacement activity would require that the piping be dewatered prior toperforming repairs, or that repairs be completed using a hot-tapping machine.5.3.2. For repair of excessive wall thinning caused by external corrosion (withoutthrough-wall leakage), restoration of the required component wall thickness couldbe performed by weld overlay on the exterior of the pipe in accordance withapplicable ASME Code requirements. However, the integrity of the pressureboundary could be jeopardized by welding directly on these areas during systemoperation.5.3.3. For repair of defective areas where through-wall leakage is detected, IWA-4400would require the defective area to be removed. The defective areas would thenbe replaced using new pressure retaining material, or by installing a branchconnection that is designed in accordance with the requirements of theConstruction Code. The RN System Low Level Intake supply piping is a singleheader that is shared between Units 1 and 2, and it would be difficult to isolate,depressurize, and drain the piping to permit these types of repairs within the

!Duke Energy Carolinas, LLCRelief Request #15-MN-002Page 5 of 6Technical Specification 3.7.7, Condition A Allowed Outage Time. This difficultywould also be encountered in repairing the RN supply and return piping betweenthe SNSWP and the Auxiliary Building. As such, Duke Energy believes that theonly practical repair methods would require the use of a hot-tapping machine toinstall a branch connection during system operation or to install a line stop(requiring removing the system from service) to dewater the pipe, remove thedefective area, and perform a code-compliant repair. Use of a hot-tappingmachine is not desirable for the following reasons:1. Duke Eneray believes that installation of a line StOD usina a hot-tao)oinamachine (to permit dewatering of the pipe) would necessitate a plantshutdown for both units because Technical Specification 3.7.7 allows onlyone train of the RN System to be taken out of service for no more than 72hours, and Duke Energy believes that it would be difficult to complete thiswork within this timeframe. Also, the risks associated with performing repairsusing a hot-tapping machine (without dewatering the piping) can beeliminated using the proposed alternative.Hot-tapping the RN pipe could result in metal shavings or a portion of thepipe wall dislodging, entering the system, and becoming debris that couldhinder system operation and make it difficult to retrieve the loose material.2.3. Typically, the installation of a branch connection using a hot-tapping machineresults in a mechanical joint being installed on the new branch connectionafter the hot-tap is completed. Installation of a mechanical joint in a buriedapplication is not desirable because it introduces a new path for potentialsystem leakage.4. Removal of material from the pipe wall during hot-tapping could increase therisk of system leakage in the event that difficulties are encountered duringthis process.5.3.4. Structural pads designed and installed in accordance with the proposedalternative will provide sufficient margin against lateral and radial growth of thedefective area due to any internal corrosion of the pipe wall. The proposedinservice monitoring requirements are based on conservative corrosion rates thatprovide reasonable assurance that unacceptable degradation of the pipe wallwould be detected prior to challenging the structural integrity of the pipe. Theproposed alternative includes requirements to ensure the leak-tightness of thestructural pad, and requirements for restoration of protective coatings to minimizethe risk of external corrosion.5.4 For the reasons stated above, Duke Energy believes that compliance with therequirements of the ASME Code, Section Xl, IWA-4400 to remove defective portions ofburied RN System piping prior to performing a repair/replacement activity by weldingwould result in hardship or unusual difficulty without a compensating increase in thelevel of quality and safety achieved by the proposed alternative.6. Duration of Proposed AlternativeThe proposed alternative is requested for the duration of the McGuire Unit 1 4th InserviceInspection Interval, currently scheduled to end on November 30, 2021. Structural pads Duke Energy Carolinas, LLCRelief Request #15-MN-002Page 6 of 6installed in accordance with the proposed alternative may be used for the duration of theirprojected design life, based on measured corrosion rates at the location of the structuralpads.7. References7.1. Letter dated March 28, 2011, providing NRC Safety Evaluation for Duke EnergyCorporation Relief Request #09-MN-002 Revision 1 (ADAMS Accession#ML1 10800426).

J\ DUKE Steven D. CappsE NERG..Y McGuire Nuclear StationDuke EnergyMG01VP 1 12700 Hagers Ferry RoadHuntersville, NC 280780: 980.875.4805f: 980.875.4809Steven .Capps@du ke-energy~comSerial No. MNS-15-088 10 CFR 50.55aNovember 9, 2015U. S. Nuclear Regulatory CommissionATTN: Document Control DeskWashington, DC 20555-0001

Subject:

Duke Energy Carolinas, LLC (Duke Energy)McGuire Nuclear Station, Units 1 and 2Docket Nos. 50-369 and 50-370Relief Request Serial No. 15-MN-002Pursuant to 10 CFR 50.55a(z)(2), Duke Energy hereby submits the enclosed relief request (RR)for an alternative to defect removal prior to performing repair activities on buried NuclearService Water System (RN) piping.McGuire's Buried Piping Integrity Program requires visual and ultrasonic examination of portionsof buried Class 3 RN piping. This buried piping is shared between Units 1 and 2. If excessivewall thinning or through-wall leakage resulting from internal or external corrosion is detected inthis buried piping, this RR provides an alternative to defect removal prior to performing repairactivities. The proposed alternative will reduce the risk to system and plant operation and willhelp to avoid a hardship without a compensating increase in quality and safety.Staff approval of this RR is requested within one year of the date of this submittal.The enclosure to this letter contains the RR. If you have any questions or require additionalinformation, please contact P.T.. Vu of Regulatory Affairs at (704) 875-4302.Sincerely,Steven D. CappsEnclosure www.duke-energy.com U. S. Nuclear Regulatory CommissionNovember 9, 2015Page 2xc:Victor McCree, Region II AdministratorU. S. Nuclear Regulatory CommissionMarquis One Tower245 Peachtree Center Ave., NE, Suite 1200Atlanta, GA 30303-1257G. Ed Miller, Project ManagerU. S. Nuclear Regulatory Commission11555 Rockville PikeMail Stop O-8G9ARockville, MD 20852-2738John ZeilerNRC Senior Resident InspectorMcGuire Nuclear Station 9fEnclosureDuke Energy Carolinas, LLCMcGuire Nuclear Station, Units 1 and 2Relief Request Serial #15-MN-002Relief Requested in Accordance with 10 CFR 50.55a(z)(2) to use an Alternative to DefectRemoval Prior to Performing Repair/Replacement Activities on Nuclear Service WaterSystem Buried Piping IDuke Energy Carolinas, LLCRelief Request #15-MN-002Page 2 of 61. ASME Code Component(s) AffectedNuclear Service Water (RN) System ASME Class 3 components listed below:1.1. 36 inch and 42 inch diameter buried supply piping from the Low Level Intake (LLI) atCowans Ford Dam to the Auxiliary Building. This piping contains raw water from LakeNorman.1.2. 36 inch diameter buried supply and return piping from the Standby Nuclear ServiceWater Pond (SNSWP) to the Auxiliary Building. This piping contains raw water drawnfrom, and returned to, the SNSWP.1.3. Design data applicable to the above piping is provided below:Nominal Wall Thickness: ANSI "Standard" pipe schedule to 0.5 inchesDesign Pressure: 25 to 35 psigDesign Temperature: 95 to 150 degrees, FMaterial Specification: Carbon steel, consisting of one or more of the followingspecifications and grades:* A-134Gr283C* SA-155GrC55* SA285 Gr C* SA-672 Gr C70, CL. 21* SA-155 Gr KC 70, CL. 11.4. The above piping does not have an internal coating system, but the exterior of thispiping was coated with coal tar epoxy.1.5. The RN System piping above is shared between Units 1 and 2.2. Applicable Code Edition and AddendaASME Code,Section XI, 2007 Edition with the 2008 Addenda.The 4th Inservice Inspection Interval dates for Units 1 and 2 are as follows:* Unit 1 4th Inservice Inspection Interval: December 1, 2011 through November 30,2021* Unit 2 4th Inservice Inspection Interval: July 15, 2014 through December 14, 20243. Applicable Requirement3.1. IWA-4412 requires that welding, brazing, defect removal, and installation activities beperformed in accordance with IWA-4420.3.2. IWA-4420 specifies requirements for defect removal and examination.Relief is requested from the requirement of IWA-4400 that defective portions of componentsbe removed prior to performing a repair/replacement activity by welding.

fDuke Energy Carolinas, LLCRelief Request #f15-MN-002Page 3 of 64.' Reason for Request4.1. McGuire plans to continue to inspect portions of buried Class 3 Nuclear Service Water(RN) piping for visual and ultrasonic examination in accordance with requirements ofthe McGuire Buried Piping Integrity Program, prior to the end of the Unit 1 4th inserviceinspection interval. This program was developed for the purpose of maintaining thesafe and reliable operation of all buried piping systems within its scope, includingportions of the RN System, and was developed in direct response to industryawareness of aging buried pipe issues. Subsequently, NEI and the Buried PipingIntegrity Task Force developed and issued on February 4, 2010 NEI 09-14, "Guidelinefor the Management of Buried Piping Integrity" to facilitate the industry implementationof the Initiative. Duke Energy believes that these examinations will help to confirm thestructural and leak-tight integrity of these components, providing additional assurancethat this system can continue to perform its intended safety function.4.2. If excessive wall thinning or through-wall leakage resulting from internal or externalcorrosion is detected in this buried piping, the defective areas would require repair inaccordance with the ASME Code, Section Xl, 2007 Edition with the 2008 Addenda,IWA-4000. Prior to performing repair/replacement activities by welding, the defectiveportions of the component must be removed. Duke Energy believes that requiringremoval of defective portions of this piping prior to performing repair/replacementactivities represents a hardship or unusual difficulty without a compensating increase inthe level of quality and safety for reasons identified in this request.5. Proposed Alternative and Basis for Use5.1. For piping identified in Section 1.0 of this request that cannot be depressurized anddewatered without entering a Technical Specification LCO, or without requiring ashutdown of both Units 1 and 2, the following alternative is proposed.5.2. In lieu of the requirement of IWA-4400 to remove the defective portion of the componentprior to performing repair/replacement activities by welding, unacceptable wall thicknessloss or through-wall leakage caused by localized general or pitting corrosion on theinterior or exterior surface of the piping may be repaired without removing the defectiveportion of the component, provided the repair/replacement activity complies with therequirements of ASME Code Case N-789-1, with the following exceptions:5.2.1. Pressure pads shall not be used.5.2.2. The requirement of Code Case N-789-1, 1(e) shall not apply.5.2.3. Structural pads shall be designed such that the growth of degradation is notprojected to exceed the limits of dimensions "C" or "L" in Code Case N-789-1,Figure 1 for the design life of the repair/replacement activity. The growth ofdegradation shall be based on a corrosion rate of either 2 times the actualmeasured corrosion rate in that location, or 4 times the estimated maximumcorrosion rate for that portion of the RN system.5.2.4. Structural pads shall be designed such that the minimum required designthickness shall be maintained for the design life of the repair/replacement activity,based on corrosion rates used in the design.

fDuke Energy Carolinas, LLCRelief Request #15-MN-002Page 4 of 65.2.5. Gasket or sealant material, if used between the pipe and the pad, shall bedesigned to allow for pressurization of the pad attachment welds to the pipingduring the pressure test required by Code Case N-789-1, 7. In addition, anyresidual moisture at welding locations shall be removed by heating, prior towelding.5.2.6. Where a structural pad is applied over externally-corroded areas where there ispotential for bulging, the corrosion cavity shall be filled with hardenable fill tominimize the gap beneath the reinforcing pad, prior to installing the pad.5.2.7. The leak tightness of the structural pad and its attachment welds to thecomponent pressure boundary shall be verified by performing a system leakagetest and VT-2 visual examination, as required by Code Case N-789-1, 7.5.2.8. Inservice monitoring requirements of Code Case N-789-1, 8 shall apply, exceptas follows:1. In lieu of the requirement of 8(b), thickness monitoring for structural padsusing ultrasonic or direct thickness measurement shall be performed to verifythat minimum design thicknesses, as required by the Construction Code orSection [II, are maintained. These measurements shall be performed prior tothe date on which no less than 25% of the design life of therepair/replacement activity remains, based on corrosion rates used in thedesign of the structural pad. Subsequent measurements shall be performedprior to the date on which no less than 25% of the remaining design life of therepair/replacement activity remains, based on measured corrosion rates atthe location of the structural pad.2. The requirements of 8(d) and 8(e) shall not apply.5.2.9. Upon completion of the repair/replacement activity, protective coatings shall berestored on exterior surfaces of the piping, including areas affected by therepair/replacement activity.5.3. The basis for the proposed alternative is as follows:5.3.1. For repair of through-wall defects or excessive wall thinning caused by corrosion,compliance with the requirement to remove the defect prior to performing therepair/replacement activity would require that the piping be dewatered prior toperforming repairs, or that repairs be completed using a hot-tapping machine.5.3.2. For repair of excessive wall thinning caused by external corrosion (withoutthrough-wall leakage), restoration of the required component wall thickness couldbe performed by weld overlay on the exterior of the pipe in accordance withapplicable ASME Code requirements. However, the integrity of the pressureboundary could be jeopardized by welding directly on these areas during systemoperation.5.3.3. For repair of defective areas where through-wall leakage is detected, IWA-4400would require the defective area to be removed. The defective areas would thenbe replaced using new pressure retaining material, or by installing a branchconnection that is designed in accordance with the requirements of theConstruction Code. The RN System Low Level Intake supply piping is a singleheader that is shared between Units 1 and 2, and it would be difficult to isolate,depressurize, and drain the piping to permit these types of repairs within the

!Duke Energy Carolinas, LLCRelief Request #15-MN-002Page 5 of 6Technical Specification 3.7.7, Condition A Allowed Outage Time. This difficultywould also be encountered in repairing the RN supply and return piping betweenthe SNSWP and the Auxiliary Building. As such, Duke Energy believes that theonly practical repair methods would require the use of a hot-tapping machine toinstall a branch connection during system operation or to install a line stop(requiring removing the system from service) to dewater the pipe, remove thedefective area, and perform a code-compliant repair. Use of a hot-tappingmachine is not desirable for the following reasons:1. Duke Eneray believes that installation of a line StOD usina a hot-tao)oinamachine (to permit dewatering of the pipe) would necessitate a plantshutdown for both units because Technical Specification 3.7.7 allows onlyone train of the RN System to be taken out of service for no more than 72hours, and Duke Energy believes that it would be difficult to complete thiswork within this timeframe. Also, the risks associated with performing repairsusing a hot-tapping machine (without dewatering the piping) can beeliminated using the proposed alternative.Hot-tapping the RN pipe could result in metal shavings or a portion of thepipe wall dislodging, entering the system, and becoming debris that couldhinder system operation and make it difficult to retrieve the loose material.2.3. Typically, the installation of a branch connection using a hot-tapping machineresults in a mechanical joint being installed on the new branch connectionafter the hot-tap is completed. Installation of a mechanical joint in a buriedapplication is not desirable because it introduces a new path for potentialsystem leakage.4. Removal of material from the pipe wall during hot-tapping could increase therisk of system leakage in the event that difficulties are encountered duringthis process.5.3.4. Structural pads designed and installed in accordance with the proposedalternative will provide sufficient margin against lateral and radial growth of thedefective area due to any internal corrosion of the pipe wall. The proposedinservice monitoring requirements are based on conservative corrosion rates thatprovide reasonable assurance that unacceptable degradation of the pipe wallwould be detected prior to challenging the structural integrity of the pipe. Theproposed alternative includes requirements to ensure the leak-tightness of thestructural pad, and requirements for restoration of protective coatings to minimizethe risk of external corrosion.5.4 For the reasons stated above, Duke Energy believes that compliance with therequirements of the ASME Code, Section Xl, IWA-4400 to remove defective portions ofburied RN System piping prior to performing a repair/replacement activity by weldingwould result in hardship or unusual difficulty without a compensating increase in thelevel of quality and safety achieved by the proposed alternative.6. Duration of Proposed AlternativeThe proposed alternative is requested for the duration of the McGuire Unit 1 4th InserviceInspection Interval, currently scheduled to end on November 30, 2021. Structural pads Duke Energy Carolinas, LLCRelief Request #15-MN-002Page 6 of 6installed in accordance with the proposed alternative may be used for the duration of theirprojected design life, based on measured corrosion rates at the location of the structuralpads.7. References7.1. Letter dated March 28, 2011, providing NRC Safety Evaluation for Duke EnergyCorporation Relief Request #09-MN-002 Revision 1 (ADAMS Accession#ML1 10800426).