(~DUKE ~ ENERG~,

Serial No: MNS-16-062

August 10, 2016

U.S. Nuclear Regulatory Commission A TIN: Document Control Desk Washington, DC 20555-0001

Steven D. Capps Vice President

McGuire Nuclear Station

Duke Energy MGOlVP I 12700 Hagers Ferry Road

Huntersville, NC 28078

. 0 980.875.4805 f 980.875.4809

Steven.Capps@duke-energy.com

10 CFR 50.55a

Subject: Duke Energy Carolinas, LLC (Duke Energy) McGuire Nuclear Station, Unit 1 Docket No. 50-369 Relief Request 16-MN-003 Alternative to Defect Removal Prior to Performing Temporary Repair Activities on Three-Inch-Diameter Nuclear Service Water System Piping

Pursuant to 10 CFR 50.55a(z)(2}, Duke Energy hereby requests U.S. Nuclear Regulatory Commission's approval for an alternative to defect removal prior to performing temporary repair activities on three-inch-diameter Nuclear Service Water System piping associated with the 1 B Diesel Generator Cooling Water Heat Exchanger. Enclosure 1 contains details regarding this request.

Duke Energy requests NRC's approval of this relief request by August 29, 2016, for repair of this piping planned for the week of September 12, 2016.

If you have any questions or require additional information, please contact P.T. Vu of Regulatory Affairs at (980) 875-4302.

Sincerely,

Enclosure

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www.duke-energy.com

U.S. Nuclear Regulatory Commission August10,2016 Page2

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C. Haney, Region II Administrator U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, GA 30303-1257

G. E. Miller, Project Manager U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop 0-8G9A Rockville, MD 20852-2738

V. Sreenivas, Project Manager U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop 0-8G9A Rockville, MD 20852-2738.

A. Hutto NRC Senior Resident Inspector McGuire Nuclear Station

U.S. Nuclear Regulatory Commission August 10, 2016 Page 3

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Mark Pyne (EC05ZB) Mark Ferlisi (EC05ZB) Joe Herrick (MG05SE) John Pring (MG01 RR) Mark Hunt (MG02MO) Greg Shipley (MG02MO) Justin Warren (MG02MO) Jill Morton (MG01 RC) Master File MC-801.01 (MG02DM) ELL (EC02ZF)

Enclosure 1

Duke Energy Carolinas, LLC

McGuire Nuclear Station, Unit 1

Relief Request Serial #16-MN-003

Relief Requested in Accordance with 10 CFR 50.55a(z)(2) to use an Alternative to Defect Removal Prior to Performing Temporary Repair/Replacement Activities on Nuclear Service

Water System Piping

Page 1 of 11

Enclosure 1

1 ASME Code Component(s} Affected

Nuclear Service Water (RN) System ASME Class 3 components listed below:

1.1 The 3 inch drain piping between valve 1 RN-883 and its associated 8" diameter header. This piping is a low point syste.m drain on the supply side of the '1 B' Diesel Generator Cooling Water Heat Exchanger. The associated 8" header ties into the 30" diameter '18' Essential Supply Header. See Attachment 1 (page 9 of 11) for Flow Diagram MCFD-157 4-03.00. See Attachment 2 for the 3" pipe drain configuration at valves 1 RN-883.

1.2 The 3 inch drain piping between valve 1 RN-884 and its associated 8" diameter header. This piping is a low point system drain on the discharge side of the '1 B' Diesel Generator Cooling Water Heat Exchanger. The associated 8" header ties into the 36" diameter '1 B' Essential Discharge Header. See Attachment 1 (page 8of11) for Flow Diagram MCFD-1574-03.00. See Attachment 2 for the 3" pipe drain configuration at valves 1 RN-884.

1.3 Design data applicable to the above piping is provided below from Duke Energy Specification MCS-1206.00-02-0002, "Specification for the Design of Power Piping Systems Materials and Components QA Conditions 1, 2, 3, & 4" and McGuire Flow Diagram MCFD-1574-03.00.

1.4 Design data applicable to the above piping is as follows:

Nominal Wall Thickness: 0.216 inches

Design Pressure: 135 psig

Design Temperature: 102 degrees, Fat 1RN-883; 150 degrees, Fat 1RN-884

Material of Construction: Carbon Steel, SA-106 Grade B

Internal Coatings: None

2 Applicable Code Edition and Addenda

2.1 Original Construction Code is ANSI 831.7 Class Ill, 1969 Edition including Addenda a, b, & c. However, MCS-1206.00-02-0002 specifies that repairs, replacements and modifications performed under ASME XI shall be made in accordance with ASME Ill, Subsection ND, 1971 Edition with Winter 71 Addenda.

2.2 ASME Code, Section XI, 2007 Edition with the 2008 Addenda.

3 . Applicable Requirements

3.1 IWA-4400 specifies requirements for welding, brazing, metal removal, fabrication, and installation.

3.2 IWA-4420 specifies requirements for defect removal, evaluation, and examination.

Relief is requested from the requirement of IWA-4400 that defective portions of components be removed prior to performing a repair/replacement activity by welding.

Page 2of11

Enclosure 1 4 Reason for Request

4.1 On 5/25/2016, during an Engineering system walk down with the Nuclear Regulatory Commission (NRC) Resident, a weeping through wall leak was discovered in a 3" RN drain line upstream of 1 RN-884 in the Auxiliary Feedwater (CA) Pump Room. Unit 1 just completed a refueling outage in April 2016. The leak is in the carbon steel pipe directly adjacent to the toe of the weld to a stainless steel valve. The area was ultrasonically inspected (UT) and qualified for continued operation via Code Case N-513-3. UT examination of the piping for the entire length of pipe between the header and the isolation valve shows the area of excessive thinning to be at the carbon steel to stainless steel interface indicative of galvanic corrosion. The area continued to be inspected by UT monthly as part of the code case requirements. The 7/18/2016 UT data indicated the rate of wall thinning apparently accelerated to a point where the valve and its associated piping would not remain functional until the next refueling outage. The amount of degradation (approximately 0.001 inches per day) experienced is unforeseen and unprecedented at McGuire Nuclear Station (MNS). Based on the data collected on 7/18/2016, the corrosion rate predictions were: 1) a localized pit below the thickness for hoop stress values as soon as 15 days and 2) average wall thinning below structural stress values in 66 days. Subsequent UT measurements indicate the corrosion rate is stabilizing; however, Duke Energy believes the wall thickness margin is at risk should aggressive corrosion resume. . The frequency of UT thickness measurement has been increased to twice weekly to ensure any changes in corrosion rates are quickly identified.

4.2 As part of the extent of condition examinations required by Code Case N-513-3, the comparable 3" RN drain line upstream of 1 RN-883 was inspected. UT examination of the piping for the entire length of pipe between the header and the isolation valve shows the area of excessive thinning to be directly adjacent to the carbon steel to stainless steel interface indicative of galvanic corrosion. Although some thinning was noted in the original inspection, the pipe met all code requirements. When the accelerated corrosion rate was noted at 1RN-884, the area at 1RN-883 was re-inspected via UT examination. Although not as degraded as the area at 1 RN-884, the predicted rate of corrosion was such that 1 RN-883 would not remain functional. until the next refueling outage. Based on data from 7/21/2016: 1) a localized pit below the thickness for hoop stress values as soon as 18 weeks and 2) average wall thinning below structural stress values in 47 weeks. Data continues to be collected at this location weekly to ensure any changes in corrosion rates are quickly identified. ·

4.3 Based on the observed thinning behavior to date, it is desirable to perform repairs at both of these locations at the earliest opportunity commensurate with plant maintenance system rotation windows. Performing these activities during a '1 B' Train week allows the plant to be in the safest configuration to perform maintenance. The next desirable '1 B' work window . begins 9/12/2016.

4.4 This request is submitted to allow the installation of pressure retaining parts that will be temporarily used to encapsulate locally thinned areas of the 3 inch RN piping.

4.5 Duke Energy believes that requiring removal of defective portions of this piping prior to performing temporary repair/replacement activities represents a hardship or unusual difficulty without a compensating increase in the level of quality and safety for reasons identified in this request.

Page 3of11

Enclosure 1 5 Proposed Alternative and Basis for Use

5.1 In lieu of the requirement of IWA-4400 to remove the defective portion of the component prior to performing repair/replacement activities by welding, Code Case N-786-2 will be utilized as an alternative, utilizing the "Type B" sleeve design (See Attachment 3). Additional clarifications and any exceptions are specifically noted below:

5.1.1 The defective area shall be encapsulated with a section of split section of carbon steel (SA-106 Grade B) pipe to form a sleeve similar to a Type B configuration in Code Case N-786-2. The sleeve material shall comply with the Construction Code and Owner's requirements. The lengthwise cut shall be symmetrical along the long axis to provide two pieces for clam-shell type installation. The design shall conform to the details in Attachment 3.

5.1.2 . The piping system will no longer rely on the encapsulated parts for structural integrity or leak tightness.

5.1.3 The sleeve's inner diameter shall closely match the outside diameter of the carrier piping.

5.1.4 The longitudinal welds shall be full penetration on both sides and shall be performed prior to performing circumferential welds.

5.1.5 Backing strips may be utilized along the longitudinal welds to prevent burn through. If required, sleeves will be machined to allow for backing material as shown in Code Case N-786-2.

5.1.6 Appropriate gasket material or sealant may be used between sleeve and base piping to prevent welding on wet surfaces. Any residual moisture shall then be removed by heating prior to welding.

5.1. 7 Prior to installation of a sleeve, an ultrasonic examination shall be performed to characterize the defective and locally thinned area(s) and to confirm the continued absence of cracks or crack-like indications.

5.1.B Encapsulation of the defective or locally thinned area(s) at each location shall be performed only once. ·

5.1.9 Welds of carbon steel to carbon steel components shall be performed with ER70S-2/E7018-H4R.

5.1.1 O Welds between carbon steel and stainless steel components shall be performed with ER309UE309L-16.

5.1.11 Manual welding of reinforcing sleeves on water-b!:!cked piping shall use the Shielded Metal Arc Welding (SMAW) process and low- hydrogen electrodes.

5.1.12 A coupling shall be shop welded to one side of the sleeve to allow for purging of any weld gasses and leak testing in accordance with IWA-4540.

5 .. 1.13 Following completion of leak testing, appropriate sealant compatible for use with raw water shall be injected. Upon completion of sealant injection, a cap shall be installed in the coupling and shall be seal welded.

5.1.14 All welds shall receive a surface examination in accordance with N-786-2, Section 6. The longitudinal welds in the sleeve shall be ultrasonically examined in accordance with the ASME Code, Section Ill, Subsection ND, 1971 Edition with Winter 71 Addenda.

Page 4of11

J

Enclosure 1 5.1.15 The sleeve shall be monitored visually for evidence of leakage at least monthly.

Injection of a sealant will prevent corrosion issues that might arise in the sleeve ensuring its adequacy for the projected life of the temporary repair. The sleeve shall also be ultrasonically inspected at monthly intervals until the next refueling outage, when the sleeve is removed for permanent repair activities.

5.1.16 UT examination of the 3" piping near the 8" header has been performed, demonstrating that the existing pipe wall thickness is both sufficient for welding and will retain sufficient thickness for the predicted life of the repair. This wall thickness determination is calculated in accordance with section 3.2(k) of Code Case N-786-2. UT data shows the area of accelerated degradation is only directly adjacent to the valve ..

5.1.17 The sleeve repair will be performed at 1 RN-883 prior to performing the repair at 1 RN-884, unless the conditions at 1 RN-884 accelerate to the point of requiring installation first. Since the pipe is more robust at 1 RN-883 it will allow for verification of installation procedures and processes to ensure the efficacy of the repair at 1 RN-884 is maximized.

5.1.18 The modification shall be designed as a Type B "full structural sleeve in accordance with Code Case N-786-2 except as noted specifically below:

1. General Design Requirements for Type A and Type B Sleeves, section 3.2{c) requires a sleeve length to be at least 4" long. This requirement is impossible to meet due to the physical configuration of the pipe branch being only 3.6875 inches long as shown in Attachment 2. The proposed length of sleeve and welding configuration, as shown in Attachment 3, is acceptable since the sleeve and piping analyses have been reviewed with stresses being significantly below required maximum allowable values. ·

2. In lieu of the requirement for type B to utilize partial penetration welds, the sleeve shall be secured circumferentially by appropriately sized fillet welds at the ends. The ends shall be cut at 90 degrees to the long axis to provide the appropriate fillet weld geometry.

3. The configuration of the piping as shown in Attachment 2 and the proposed· alternative as shown in Attachment 3 does not allow room for a partial penetration weld between the end of the sleeve and the pipe being encapsulated as indicated in section 3.4(e) of Code Case N-786-2. Fillet welds that are designed for the loading conditions of the encapsulated pipe will be utilized in lieu of the partial penetration welds. Analysis shows the loading conditions at this location are low such that fillet welds provide sufficient structural integrity to withstand full internal design pressure and design piping loads.

4. The sleeve meets the valve body such that a fillet weld is possible at this location. The location is on structurally sound valve body material. Duke Energy believes the use of a partial penetration weld as indicated in section 3.4( e) of Code Case N-786-2 might add significant heat to the area that might d.amage the integrity of the valve and seal material. Damage to the valve and seal might challenge system drain down isolation required at a later date for full repair. Analysis shows the loading conditions at this location are extremely low such that fillet welds provide sufficient structural integrity to withstand full internal design pressure and design piping loads.

Page 5of11

Enclosure 1 5.2 The basis for the proposed alternative is as follows:

5.2.1 Removal of defective portions of this piping would require isolatior:i of the Supply and Return RN Essential Headers which would remove a complete train of safety related equipment from service (including its associated emergency diesel generator), resulting in a high probabilistic risk configuration affecting multiple accident scenarios. Compensatory measures required for the mitigation of all of the impacted scenarios would be a significant burden.

5.2.2 Duke Energy believes that it would be a challenge to isolate the Supply and Return '1 B' Essential Headers, complete the required repairs, and return the affected train to service wit~in the limits of Technical Specification 3.7.7, Condition A.

5.2.3 Installation of a mechanical line stop in the 3 inch piping to isolate the affected components is not possible since there is only approximately 3 inches of pipe length ,between the 8" pipe and the valves in both configurations.

5.2.4 . Installation of mechanical line stops in the 8 inch piping is not practical due to various interferences with various other structures and components. This is also not desirable because this activity could result in metal shavings or the removed portion of the pipe wall dislodging, entering the system, and becoming debris that could hinder syst13m operation and make it difficult to retrieve the loose material.

5.2.5 Installation of mechanical line stops in the 30 and 36 inch piping to isolate the affected components might be possible. However, Duke Energy believes that it would be a challenge to perform these modifications, perform the temporary repair, and return the affected train to service within the limits of Technical Specification 3.7.7, Condition A. Additionally, it is not desirable because this activity could result in metal shavings or the removed portion of the pipe wall dislodging, e·ntering the system, and becoming debris that could hinder system operation and make it difficult to retrieve the loose material.

5.2.6 · Use of a freeze seal to isolate the 3 inch pipe is not possible due to the short length of drain piping, and use of a freeze seal to isolate the 8 inch is not practical due to the pipe location where significant quantities of gas storage cylinders would be required to be maintained. ·

5.2. 7 Duke Energy believes that the proposed alternative to IWA-4400 and utilization of Code Case N-786-2 with the exceptions noted will· provide reasonable assurance of continued structural integrity of the component until permanent repairs are made in compliance with the Construction Code and Owner's requirements during the next refueling outage.

5.2.8 For the reasons stated above, Duke Energy.believes that complying with IWA-4400 requirements to remove defective portions of this piping prior to performing a repair/replacement activity represents a hardship or unusual difficulty without a compensating increase in the level of quality and safety.

6 Duration of Proposed Alternative

The proposed alternative is requested until the next Unit 1 refueling outage in Fall 2017, (designated as 1 EOC2p).

Page 6of11

Enclosure 1 7 Precedents

7 .1 Letter dated July 31, 2014 to Exelon Generation Company, LLC; "Braidwood, Units 1 And 2; Byron Station, Unit Nos. 1 And 2; Calvert Cliffs Nuclear Power Plant, Units 1 And 2; Clinton Power Station, Unit No. 1; Dresden Nuclear Power Station, Units 2 And 3; R.E. Ginna Nuclear Power Plant. Lasalle County Station, Units 1 And 2; Limerick Generating Station, Units 1 And 2; Nine Mile Point Nuclear Station, Units 1 And 2; Oyster Creek Nuclear Generating Station; Peach Bottom Atomic Power Station, Units 2, And 3; Quad Cities Nuclear Power Station, Units 1 And 2; And Three Mile Island Nuclear Station, Unit 1 - Proposed Alternative To Utilize Code Case N-786, "Alternative Requirements For Sleeve Reinforcement Of Class 2 And 3 Moderate-Energy Carbon Steel Piping Section XI, Division 1", ML 141758593.

8 Refer~nces

8.1 ASME Code Case N-786-2, "Alternative Requirements for Sleeve Reinforcement of Class 2 and 3 Moderate-Energy Carbon Steel Piping Section XI, Division 1"

9 Attachments

9.1 Attachment 1,MCFD-1574-03.00, Rev 37, "Flow Diagram of Nuclear Service Water System (RN)"

9.2 Attachment 2, "Details of Pipe Layout for valves 1RN-883 and 1RN-884", MC-1418-14.41-02, Revision 53

9.3 Attachment 3, "Temporary Sleeve Repair for 1 RN883 and 1 RN884"

Page 7of11

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Attachment 2 "Details of Pipe Layout for valves lRN-883 and lRN-884"

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Page 10 of 11

Attachment 3 Temporary Sleeve Repair for lRN-883 and lRN-884

NOTE 1: Weld size may be revised if required by Weld Technical Support with Engineering approval.

NOTE 2: Minor dimensional changes fo r sleeve or fltup are acceptable to allow proper fitup and welding with Engineering approval.

I Existing 8" RN (service water) Header SA-106 Gr B Carbon Steel Schedule 40 Design Pressure - 135 psig Design Temperature --150 F

(1/4) Note 1

NOTE 3: Appropriate gasket material or sealant may be used between sleeve and base piping to eliminate welding I water interface concerns if necessarv.

Existing 3" Pipe Stub SA-106 Gr B, C.S. Sch. 40, 3-1/2" O.D.

I 3-1/2" Diameter, Nominal Pipe Size Sleeve, SA-106 Gr B, CS Sch. 40 x 2.5" Long, ( .. 3.5" ID after machining). Split along axis. Field to locate for welding. Notes 2,3,4

( Typical Far Side, Use Note 1 backing strip as needed.

Valve lRN-883 / lRN-884 Ball­~--- Type Isolation Drain Valves, 300#

Class

Existing 150# Class Drain Flanges

NOTE 4: Install 1/4" threaded carbon steel 3000# half-coupling on sleeve for testing and venting. Field to locate. Install threaded carbon steel plug and seal weld after testing.

Page 11 of 11