RA-18-0073, Application of Dissimilar Metal Weld Full Structural Overlay - Reactor Pressure Vessel Nozzles N4A and N4D

Application of Dissimilar Metal Weld Full Structural Overlay - Reactor Pressure Vessel Nozzles N4A and N4D

ML18179A455
Person / Time
Site:	Brunswick
Issue date:	06/28/2018
From:	Wooten B Duke Energy Progress
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RA-18-0073
Download: ML18179A455 (27)

Text

Brunswick Nuclear Plant P.O. Box 10429 Southport, NC 28461 June 28, 2018 Serial: RA-18-0073 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

Subject:

Brunswick Steam Electric Plant, Unit No. 1 Renewed Facility Operating License No. DPR-71 Docket No. 50-325 Application of Dissimilar Metal Weld Full Structural Overlay - Reactor Pressure Vessel Nozzles N4A and N4D

Reference:

Letter from William R. Gideon (Duke Energy) to the U.S. Nuclear Regulatory Commission Document Control Desk, Proposed In-service Inspection Alternative for Application of Dissimilar Metal Weld Full Structural Overlay - Nozzles N4A and N4D, dated March 19, 2018, ADAMS Accession Number ML18078A804 Ladies and Gentlemen:

By letter dated March 19, 2018 (i.e., Reference), Duke Energy Progress, LLC (Duke Energy),

proposed a 10 CFR 50.55a(z)(1) alternative to apply dissimilar metal weld full structural weld overlays (FSWOLs) to the reactor pressure vessel (RPV) nozzles N4A and N4D for the Brunswick Steam Electric Plant (BSEP), Unit No. 1.

Within 90 days of completion of the BSEP Refueling Outage B1R22, Duke Energy committed to perform the following for the N4A and N4D nozzles.

1. Nozzle specific stress analyses will be performed to establish a residual stress profile in the N4 nozzle. Inside diameter (ID) weld repairs will be assumed in these analyses to effectively bound any actual weld repairs that may have occurred in the nozzle. The analysis shall then simulate application of the FSWOL to determine the final residual stress profile. Post weld overlay residual stresses at normal operating conditions will be shown to result in an improved stress state at the ID of the N4 nozzle weld region that reduces the probability for further crack propagation due to stress corrosion cracking (SCC).

2. The analyses will demonstrate that the application of the FSWOL satisfies all ASME Code,Section III stress and fatigue criteria.

3. Fracture mechanics analyses will be performed to predict crack growth. Crack growth due to SCC and fatigue crack growth in the original dissimilar metal weld (DMW) shall be evaluated. These crack growth analyses will consider all design loads and transients,

U.S. Nuclear Regulatory Commission Page 2 of 3 plus the post weld overlay through-wall residual stress distributions and will demonstrate that the assumed cracks will not grow beyond the design bases for the weld overlay.

4. The total added weight on the piping system due to the overlay will be evaluated for the potential impact on reactor pressure vessel nozzle stresses and dynamic characteristics.

The enclosed Structural Integrity Associates, Inc. Report No. 1800500.402.R0, Summary of Design and Analysis for Initial Full Structural Weld Overlay Repair of Brunswick Nuclear Plant, Unit 1, Feedwater Nozzle N4A and N4D Dissimilar Metal Welds (N4A ID No: 1B21N4A-2-SW1-

2) and (N4D ID No: 1B21N4D-5-SW1-2), provides the committed analyses, in accordance with Items 1 through 4 above.

No regulatory commitments are contained in this letter.

Please refer any questions regarding this submittal to Mr. Lee Grzeck, Manager - Regulatory Affairs, at (910) 832-2487.

Sincerely, Bryan B. Wooten Director - Organizational Effectiveness Brunswick Steam Electric Plant MAT/mat

Enclosure:

Structural Integrity Associates, Inc. Report No. 1800500.402.R0, Summary of Design and Analysis for Initial Full Structural Weld Overlay Repair of Brunswick Nuclear Plant, Unit 1, Feedwater Nozzle N4A and N4D Dissimilar Metal Welds (N4A ID No: 1B21N4A-2-SW1-2) and (N4D ID No: 1B21N4D-5-SW1-2)

U.S. Nuclear Regulatory Commission Page 3 of 3 cc:

U.S. Nuclear Regulatory Commission, Region II ATTN: Ms. Catherine Haney, Regional Administrator 245 Peachtree Center Ave, NE, Suite 1200 Atlanta, GA 30303-1257 U. S. Nuclear Regulatory Commission ATTN: Mr. Dennis J. Galvin 11555 Rockville Pike Rockville, MD 20852-2738 U.S. Nuclear Regulatory Commission ATTN: Mr. Gale Smith, NRC Senior Resident Inspector 8470 River Road Southport, NC 28461-8869 Chair - North Carolina Utilities Commission (Electronic Copy Only) 4325 Mail Service Center Raleigh, NC 27699-4300 swatson@ncuc.net Mr. Cliff Dautrich, Bureau Chief North Carolina Department of Labor Boiler Safety Bureau 1101 Mail Service Center Raleigh, NC 27699-1101

RA-18-0073 Enclosure Structural Integrity Associates, Inc.

Report No. 1800500.402.R0 Summary of Design and Analysis for Initial Full Structural Weld Overlay Repair of Brunswick Nuclear Plant, Unit 1, Feedwater Nozzle N4A and N4D Dissimilar Metal Welds (N4A ID No: 1B21N4A-2-SW1-2) and (N4D ID No: 1B21N4D-5-SW1-2)

5215 Hellyer Avenue, Suite 210, San Jose, CA 95138 l [14088337292]

rbax@structint.com June 27, 2018 Report No. 1800500.402.R0 Quality Program: Nuclear Commercial Mr. John Goelz Brunswick Nuclear Plant - Duke Energy PO Box 10429 Southport, NC, 28461-0429

Subject:

Summary of Design and Analysis for Initial Full Structural Weld Overlay Repair of Brunswick Nuclear Plant, Unit 1, Feedwater Nozzles N4A and N4D Inboard Dissimilar Metal Welds

Reference:

Duke Energy Letter No. BSEP 18-0039, Brunswick Steam Electric Plant, Unit No. 1, Renewed Facility Operating License No. DPR-71, Docket No. 50-325, Proposed In-service Inspection Alternative for Application of Dissimilar Metal Weld Full Structural Overlay, March 19, 2018, ADAMS Accession No. ML18078A804.

Dear Mr. Goelz:

This letter report is being provided in support of Brunswicks response to a commitment in the above-referenced proposed alternative:

Commitment:

Brunswick will submit to the NRC a stress analysis summary demonstrating that the repaired dissimilar metal welds (DMW) for feedwater nozzles N4A and N4D will perform their intended design function after weld overlay installation. This information will be submitted to the NRC within 90 days of completing Brunswicks Unit 1 Refueling Outage 22.

The body of the referenced Duke letter states the stress analysis report will include results showing that the requirements of NB-3200 and/or NB-3600 of the ASME Code,Section III are satisfied. The stress analysis will also include results showing that the requirements of IWB-3000 of the ASME Code,Section XI, are satisfied. The results will show that the as-found defects, including their growth, will not adversely affect the integrity of the overlaid weld.

Attachment A to this letter report provides the stress analysis summary to satisfy this commitment.

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 If you have any questions or comments regarding this summary, please contact one of the undersigned.

Prepared by: Verified by:

6/27/18 6/27/18 Richard L. Bax Jr. Date James W. Axline, P.E. Date Associate Associate Approved by:

6/27/18 James W. Axline, P.E. Date Associate Attachment cc: Project File No 1800500.402.R0 PAGE l 2

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 Attachment A Summary of Design and Analysis for Initial Full Structural Weld Overlay Repair of Brunswick Nuclear Plant, Unit 1, Feedwater Nozzle N4A and N4D Dissimilar Metal Welds (N4A ID No: 1B21N4A-2-SW1-2) and (N4D ID No: 1B21N4D-5-SW1-2)

PAGE l A1

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0

1.0 INTRODUCTION

Brunswick Nuclear Plant, Unit 1 (Brunswick-1) applied an Initial full structural weld overlay (FSWOL) on dissimilar metal welds (DMWs) 1B21N4A-2-SW1-2 and 1B21N4D-5-SW1-2 between the reactor pressure vessel (RPV) feedwater nozzle (N4) inboard safe end extension and the safe end for nozzles N4A and N4D.

The purpose of this overlay is to repair the as-found flaws and to mitigate any potential future intergranular stress corrosion cracking (IGSCC) in these welds. The overlays were installed using an IGSCC resistant weld filler material; Alloy 52M [3].

This report, which satisfies one of the Brunswick-1 commitments of the Relief Request [1],

summarizes the results of the component specific residual stress analyses and the fracture mechanics evaluations, and documents that all ASME Code,Section III stress and fatigue criteria are met. This information is to be submitted within 90 days of completing the refueling outage.

The requirements for design of the weld overlay repair are defined in the Relief Request [1],

which is based upon ASME Code Case N-740-2 [2], and ASME Code,Section XI, Nonmandatory Appendix Q [4]. The analytical basis for the design of the repair is in accordance with the requirements of ASME Code,Section XI [5], IWB-3640. Weld overlay repairs are acceptable long-term repairs for IGSCC flawed weldments if they meet a conservative set of design assumptions, which qualify them as full structural weld overlays. The three principal design requirements that qualify a weld overlay as full structural are as follows:

1. The design basis for the repair is a circumferentially oriented flaw that extends 360º around the component and is 100% through the original component wall. This conservative assumption eliminates concerns about IGSCC susceptibility of the original Alloy 82/182 DMW. In addition, potential concerns about the integrity of the original butt weld material are not applicable, since no credit is taken for the load carrying capability of this weld.

2. As required by ASME Code,Section XI [5], Appendix C, a combination of internal pressure, deadweight, seismic, and other dynamic stresses is used in the design of a weld overlay repair. Thermal and other secondary stresses are not required to be included for structural sizing calculations (since the repairs are applied using a GTAW process that produces a high toughness weld deposit), but they are addressed later in subsequent stress, fatigue, and stress corrosion cracking evaluations.

3. Following the repair, the surface finish of the overlay must be sufficiently smooth to allow preservice and future inservice ultrasonic examinations through the overlay material and into a portion of the original base metal. The purpose of these examinations is to demonstrate that the overlay design basis does not degrade with time due to flaw propagation.

ASME Code,Section III stress and fatigue usage evaluations are also performed to demonstrate that the overlaid components continue to meet ASME Code,Section III requirements. The applicable Code-of-Record for design of the Unit 1 RPV feedwater (N4) nozzle thermal sleeve modification is ASME Code,Section III, 1974 Edition including the Summer 1974 Addenda and PAGE l A2

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 Code Case 1661 [7] as specified in the General Electric Installation Specification 22A3897 [8].

However, the original Construction Code has been reconciled to the ASME Code,Section III editions applicable to the stress and fatigue usage analyses, and as allowed by ASME Code,Section XI [5], Subsection IWA-4222, Code Editions and Addenda later than the original construction Code may be used. ASME Code,Section III, 2001 Edition with Addenda through 2003 [6] was used for these analyses.

In addition to providing structural reinforcement to the IGSCC susceptible locations with a resistant material, weld overlays have also been shown to produce beneficial residual stresses that mitigate IGSCC in the underlying DMWs. The weld overlay approach has been used to repair stress corrosion cracking in U.S. nuclear plants on hundreds of welds, and there have been no reports of subsequent crack extension after application of weld overlays. Thus, the compressive stresses caused by the weld overlay have been effective in mitigating new crack initiation and/or growth of existing cracks.

Finally, evaluations were performed, conservatively based on the on the bounding minimum or maximum Initial FSWOL design dimensions (thickness and length), to demonstrate that the overlay meets their design basis requirements, and that they will not have an adverse effect on the balance of the piping systems. These include the comparison of as-built N4A and N4D weld overlay dimensions to Initial FSWOL design dimensions, evaluations of weld shrinkage and the added weight/stiffness of the overlays effects on the piping systems.

2.0 ANALYSIS

SUMMARY

AND RESULTS 2.1 Weld Overlay Structural Sizing Calculations ASME Code Case N-740-2 [2], which incorporates ASME Code,Section XI [5], IWB-3640 evaluation methodology, was used to determine the thickness of the overlay. Equations from ASME Code,Section XI [5], Appendix C, and the maximum stresses at the DMW that bound the various Service Levels, were used to determine the design FSWOL thickness.

The weld overlay length must consider: (1) sufficient distance on either side of the defect location to provide for effective load transfer across the defect location, (2) length required for access for preservice and inservice examinations of the overlaid weld, and (3) limitation on the area of the component that can be overlaid.

In accordance with the Relief Request [1], which is based on ASME Code Cases N-740-2 [2],

the minimum weld overlay length required for structural reinforcement is the length which will provide adequate load transfer from one side of the flaw to the other. Per Reference [2], this criterion is generally satisfied if the overlay full thickness length extends axially at least 0.75Rt on each side of susceptible material where R and t are the outer radius and nominal wall thickness of the overlaid components, prior to depositing the weld overlay.

However, in order to assure compliance with the stress limits of ASME Code,Section III, NB-3200 [6], the minimum overlay length is determined explicitly from shear stress calculations.

A length was determined to achieve adequate load transfer and ensure all ASME Code pure PAGE l A3

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 shear allowable values are met. Figure 2-1 provides a general illustration of the analyzed configuration of the FSWOL and lists the structural minimum FSWOL thickness and length requirements.

The overlay length and profile must also be such that the required post-FSWOL examination volume can be inspected using Performance Demonstration Initiative (PDI) qualified nondestructive examination (NDE) techniques. The final configuration was reviewed by qualified NDE personnel to ensure that it meets inspectability requirements and the Relief Request [1].

ASME Code Case N-740-2 [2] limits the area of the ferritic material for which temper bead welding would be required to below 500 square inches. As the Initial FSWOL design does not result in the deposition of weld material onto the low alloy nozzle, this requirement is not applicable.

The as-built weld overlay thickness and lengths for nozzles N4A and N4D are provided in Table 2-2 and Table 2-3, respectively. These measurements fall within the minimum and maximum design dimensions in Table 2-1, thereby demonstrating the adequacy of the as-installed repair.

Table 2-1. Weld Overlay Structural Thickness and Length Requirements for Initial FSWOL Design Design Design Structural Location Minimum Maximum Item Thickness or (From DMW Toe) Thickness or Thickness or Length Length Length Thickness Safe End Side 0.31 0.35 0.60 (in.) Safe End Extension Side 0.31 0.35 0.60 Length Safe End Side 0.69 2.32 3.32 (in.) Safe End Extension Side 0.80 2.32 3.32 PAGE l A4

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 Table 2-2. Initial FSWOL Design - As-Built Dimensions for Nozzle N4A As-Built Location Item Thickness or (From DMW Toe)

Length (1)

Thickness Safe End Side 0.476 (in.) Safe End Extension Side 0.461 Length Safe End Side 3.028 (in.) Safe End Extension Side 3.016 Notes:

1) The as-built dimensions shown are the average of the four measured azimuthal measurements taken for each location.

Table 2-3. Initial FSWOL Design - As-Built Dimensions for Nozzle N4D As-Built Location Item Thickness or (From DMW Toe)

Length (1)

Thickness Safe End Side 0.461 (in.) Safe End Extension Side 0.503 Length Safe End Side 2.981 (in.) Safe End Extension Side 2.948 Notes:

1) The as-built dimensions shown are the average of the four measured azimuthal measurements taken for each location.

PAGE l A5

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 2.2 ASME Code,Section III Stress Analyses Stress intensities for the Initial FSWOL design for the Brunswick-1 RPV feedwater nozzle (N4) inboard DMW were determined from finite element analyses for the various specified load combinations and transients using the ANSYS software package [9]. Linearized stresses were evaluated at various stress locations using three-dimensional solid models. The finite element model is provided in Figure 2-2, with the stress path locations shown in Figure 2-3.

The stress intensities at these locations were evaluated in accordance with ASME Code,Section III [6], Subarticles NB-3200 and NB-3600, and compared to applicable Code limits.

Bounding primary loads (pressure, deadweight and seismic) from all Service Levels were conservatively combined and the resulting stress compared to the Design primary stress acceptance criteria. The acceptable results are shown in Table 2-4.

A summary of the primary-plus-secondary stress and fatigue usage comparisons for the most limiting locations is provided in Table 2-5. Some paths did not meet the primary-plus-secondary stress range criteria check. However, the limit on the range of primary-plus-secondary stress intensity may be exceeded provided that the requirements of NB-3653.6 are met [6], as the failing paths occurred on a piping component. The results of this check are shown in Table 2-5.

Several evaluated paths are located on piping components, and thus need to meet the thermal stress ratcheting requirements described in Subparagraph NB-3653.7 [6]. A conservatively determined limiting range of through-wall temperature gradient, T1, was calculated. The through-wall temperature difference (T) was calculated for each path and compared to the allowable. The bounding location results are shown in Table 2-5.

The stresses, thermal ratcheting and fatigue usage in the weld overlaid DMW are within the applicable Code limits.

Table 2-4. Bounding Primary Stress Intensity Results for RPV Feedwater (N4) Nozzle Inboard DMW with Initial FSWOL Design Pm Allowable PL Allowable PL+Pb (2) Allowable Path (1) Accept Accept Accept (psi) (psi) (psi) (psi) (psi) (psi) 4 6,033 18,700 Yes 13,240 28,050 Yes 15,466 28,050 Yes 9 6,033 18,700 Yes 13,004 28,050 Yes 17,047 28,050 Yes 11 8,753 18,700 Yes 15,260 28,050 Yes 16,756 28,050 Yes 12 8,753 23,300 Yes 11,051 34,950 Yes 12,529 34,950 Yes 13 8,753 18,700 Yes 14,964 28,050 Yes 17,891 28,050 Yes 14 8,753 23,300 Yes 11,094 34,950 Yes 13,756 34,950 Yes Notes:

1) Paths are defined in Figure 2-3.

2) The bending stress due to pressure is conservatively included.

Table 2-5. Limiting Service Level A/B/Test Stress Results for Initial FSWOL Design PAGE l A6

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 Load Calculated Allowable Path (3) and Type Combination (psi) (psi)

Path 4 Primary + Secondary (P + Q) 24,017 59,208 Path 9 Primary + Secondary (P + Q) 24,741 59,208 Service Level Path 11 Primary + Secondary (P + Q) 28,944 58,862 A/B/Test Path 12 (1) Primary + Secondary (P + Q) 96,582 69,900 Path 13 Primary + Secondary (P + Q) 29,075 58,862 Path 14 (1) Primary + Secondary (P + Q) 96,408 69,900 Equation 12 3,331 69,900 Path 12 (1)

Simplified Elastic Equation 13 67,971 69,900 Plastic Equation 12 3,044 69,900 Path 14 (1)

Equation 13 68,807 69,900 Calculated Allowable Thermal Path 12 T1 194°F 620°F Ratcheting Cumulative Usage Factor Fatigue Path 12 0.1617 1.000 (60 years)

Notes:

1) Elastic analysis result exceeds the allowable value of 3Sm; however, criteria for simplified elastic-plastic analysis are met.

2) The limiting fatigue usage location is on the inside surface at the nose of the weld overlay on the SB-166 safe end. The calculated Cumulative Usage Factor accounts for a 60-year design life for the weld overlaid configuration.

3) Paths are defined in Figure 2-3.

PAGE l A7

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 2.3 Residual Stress Analyses Weld residual stresses for the Initial FSWOL design for the Brunswick-1 RPV feedwater nozzle (N4) inboard DMW the were determined by detailed elastic-plastic finite element analyses. The approach used in the analysis has been benchmarked and validated through multiple 2-dimensional and 3-dimensional ANSYS finite element analyses following the guidelines discussed in MRP-316 [10] and MRP-317 [11], and using the information provided in the problem statements for mock-up specimens [10, 12, 13] and experimental measurements [10].

A two-dimensional, axisymmetric finite element model was developed for the overlay configuration. The modeling of weld nuggets used in the analysis is illustrated in Figure 2-4. The model simulated an inside surface (ID) repair at the DMW location with a depth of approximately 50% of the original wall thickness. This ID weld repair is intended to meet the guidelines of the MRP-169 Safety Evaluation Report, Section 3.2.2, paragraph three [14], which

states, The residual stress analysis assumes a highly unfavorable, pre-overlay residual stress condition which would result from an inside diameter surface weld repair during construction.

An analysis is performed to simulate the welding process of the adjacent welds, the 50% ID weld repair of the DMW, and the Initial FSWOL welding process. The analysis consists of a thermal pass to determine the temperature response of the model to each individual weld nugget as it is added in sequence, followed by a non-linear elastic-plastic stress pass to calculate the residual stress due to the temperature cycling from the application of each nugget weld pass. Since residual stress is a function of the welding history, the stress pass for each nugget is applied to the residual stress field induced from all previously applied weld nuggets.

After completion of the weld overlay simulation, the model was then allowed to cool to a uniform steady state temperature of 70°F, and then five cycles of shake down with normal operating temperature and pressure were applied to stabilize the residual stress fluctuations due to stress distribution caused by normal operating loads. These shakedown cycles are consistent with MRP-317, Volume 1, pages 5-8, Shakedown Evaluation [11].

The resulting residual stresses were evaluated on three paths through the DMW and one path through the inboard adjacent ferritic weld and will be used in the crack growth evaluation. These path definitions are shown in Figure 2-5. The resulting through wall residual stresses along these paths are shown in Figure 2-6.

2.4 ASME Code,Section XI Crack Growth Analyses The residual stress calculations were then utilized (see Figure 2-5 and 2-6), along with stresses due to applied loadings and thermal transients (see Figure 2-7), to demonstrate that assumed cracks that could be missed by inspections or the as-found cracks in the weld will not exceed the overlay design basis during the ASME Code,Section XI inservice inspection interval due to fatigue or IGSCC. In the fatigue crack growth analysis, the 60-year projected cycles for each applied transient was applied.

PAGE l A8

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 The crack growth results for an initial flaw of 75% of the original base metal thickness (which bounds the as-found flaw) are shown in Table 2-6. For both the DMW and inboard adjacent ferritic weld, it takes greater than 60 years for an initial flaw of 75% of the original base metal thickness at the analyzed section to reach the overlay for both the circumferential flaw and axial flaw.

IGSCC is not active in the original base metal at the DMW for both the 75% through-wall circumferential and axial flaws, since Ks at steady state normal operating conditions are negative for all flaw depths. Figure 2-8 shows an example of through-wall Ks at steady normal operating condition.

Table 2-6. Crack Growth Results Time for Initial 75% Flaw Depth to Reach Overlay (years)

Flaw Type Path (2) Material Initial Overlay P1 Alloy 182 > 60 P2 Alloy 182 > 60 P3 Alloy 182 > 60 P4 Ferritic > 60 P5 Ferritic N/A (1)

Circumferential P6 Alloy 182 > 60 P7 Alloy 182 > 60 P8 Alloy 182 > 60 P9 Ferritic > 60 P10 Ferritic N/A (1)

P1 Alloy 182 > 60 P2 Alloy 182 > 60 P3 Alloy 182 > 60 P4 Ferritic > 60 P5 Ferritic N/A (1)

Axial P6 Alloy 182 > 60 P7 Alloy 182 > 60 P8 Alloy 182 > 60 P9 Ferritic > 60 P10 Ferritic N/A (1)

Notes:

1) Not evaluated as this weld is not covered by the FSWOL.

2) See Figure 2-7 for the paths extracted from the Initial FSWOL design.

3) Initial flaw depth = 75% of original base metal thickness at the sections analyzed

= 0.65625 inches PAGE l A9

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 2.5 Evaluation of As-Built Conditions The Relief Request [1] and Code Case N-740-2 [2] require evaluation of the weld overlays to determine the effects of any changes in applied loads, as a result of weld shrinkage from the entire overlay on other items in the piping system, and to address the added weight/stiffness effect of the weld overlay on the adjacent piping systems.

Evaluation of Weld Overlay Shrinkage Stresses due to an assumed shrinkage were evaluated via two piping models, the feedwater Loop-A piping system and the feedwater Loop-A sparger piping. The assumed axial shrinkage was modeled as 0.1 inch. This value for axial shrinkage is a conservative estimate based on previous industry experience.

For the feedwater piping system, the highest stress caused by the weld shrinkage was found to be 0.703 ksi. This stress occurs at the first elbow from the feedwater nozzle. This weld shrinkage stress is acceptable, since this stress is less than the cold springing allowable stress of 2Sm, which is 2(20) = 40 ksi at 70°F.

For the feedwater sparger piping, the highest stress caused by the weld shrinkage was found to be 25.12 ksi. This stress occurs in the forged tee. This weld shrinkage stress is acceptable, since this stress is less than the cold springing allowable stress of 2Sm, which is 2(20) = 40 ksi at 70°F.

The maximum measured as-built shrinkage due the installation of the Initial FSWOL, after final surface contouring for nozzle N4A was found to be 0.06 inch (average was 0.03 inch), while the maximum shrinkage in nozzle N4D was found to be 0.09 inch (average was 0.053 inch). Given that the evaluated shrinkage assumed 0.1 inches of shrinkage the resulting stresses from the assumed shrinkage of 0.1 inch bound the as-built.

Evaluation of the Effect of FSWOL Weight The conservatively calculated weight added from the FSWOL (using maximum design dimensions) for the feedwater system piping is insignificant (i.e., less than 4.37% of the affected piping weight) when compared to the weight of the affected piping up to the first snubber. Thus, the added weight of the Initial FSWOL design will not be adverse.

As the as-built dimensions for nozzle N4A (see Table 2-2) and nozzle N4D (see Table 2-3) fall between the minimum and maximum required design dimensions shown in Table 2-1, the bounding weight evaluation remains valid. Therefore, the as-built N4A and N4D Initial FSWOLs do not impact the dynamic response characteristics of the feedwater system piping or the systems overall weight behavior.

Relative to stiffness, the Initial FSWOL was applied to the N4A and N4D nozzle/inboard safe end region. Thus, the location of the FSWOL installations are significantly stiffer than the attached piping and the FSWOLs only makes them stiffer. Thus, the dynamic characteristic of a flexible piping system attached to a significantly stiffer nozzle is not altered, and therefore, the stiffness impact of the FSWOL is not adverse.

PAGE l A10

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 Figure 2-1: General Illustration of Initial Weld Overlay Design Note: Minimum structural FSWOL thickness and length dimensions shown. The dimensions do not include the added thickness or length requirement to meet NDE inspection requirements.

PAGE l A11

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 Figure 2-2: Finite Element Model of the Initial FSWOL Design for Operating Stress Evaluations PAGE l A12

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 Figure 2-3: Paths Locations Evaluated for ASME Code,Section III Stress Analyses of the Initial FSWOL Design (Note: The two cross-sectional planes shown are 90 degrees apart, P4, P11, P12 @ Top Dead Center (TDC)

P9, P13, P14 @ horizontal side of nozzle)

PAGE l A13

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 Figure 2-4: Finite Element Model for Initial FSWOL Design Residual Stress Analysis showing Nuggets used for Welding Simulation Note: The plot represents the nuggets for all the welding processes involved. The RPV N4 nozzle is on the right and the safe end is on the left.

PAGE l A14

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 Figure 2-5: Path Locations for Through-Wall Stress Extractions for Initial FSWOL Weld Residual Stress Analysis Note: Paths 1 through 5 corresponds to Paths 1 through 5 in Figure 2-7, respectively. As the analysis was a 2-D axisymmetric model, Paths 1 through 5 also correspond to Paths 8 through 10 in Figure 2-7, respectively.

PAGE l A15

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 Safe End Extension-to-Safe End DMW Old Safe End Stub-to-Safe End Extension Nozzle-to-Old Safe End Stub Ferritic Weld Ferritic Weld Figure 2-6: Weld Residual Stress Results along Stress Paths Note: Paths 1 through 5 corresponds to Paths 1 through 5 in Figure 2-7, respectively. As the analysis was a 2-D axisymmetric model, Paths 1 through 5 also correspond to Paths 8 through 10 in Figure 2-7, respectively.

PAGE l A16

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 Figure 2-7: Paths Locations Evaluated for Crack Growth Analyses (Note: The two cross-sectional planes shown are 90 degrees apart, P1 through P5 @ Top Dead Center (TDC)

P6 through P10 @ horizontal side of nozzle)

PAGE l A17

Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0 Circumferential Flaw Axial Flaw Figure 2-8: K Distributions at Steady State Normal Operating Conditions Note: (75% Flaw Depth @ 0.656, FSWOL interface @ 0.875)

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Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0

3.0 CONCLUSION

S The design of the Brunswick-1 Initial weld overlay for the N4A and N4D feedwater nozzle inboard dissimilar metal welds was performed in accordance to the requirements of the Relief Request [1], which is based on ASME Code Case N-740-2 [2], and ASME Code,Section XI, Nonmandatory Appendix Q [4]. The weld overlay design is demonstrated to be a long-term repair and provide mitigation of IGSCC in the welds based on the following:

In accordance with ASME Code Case N-740-2, structural design of the overlay was performed to meet the requirements of ASME Code,Section XI, IWB-3640 based on an assumed circumferential flaw 100% through-wall, and 360° around the original weld.

The resulting full structural weld overlay thus restores the original safety margins of the original weld, with no credit taken for the underlying IGSCC-susceptible material.

The weld metal used for the overlay is Alloy 52M, which has been shown to be resistant to IGSCC [3], thus providing an IGSCC resistant barrier. Therefore, little if any IGSCC crack growth is expected to occur in the overlay.

Application of the weld overlay does not impact the conclusions of the existing system Stress Report. Following application of the overlay, all ASME Code,Section III stress and fatigue criteria are met.

A conservative weld specific residual stress analysis was performed by simulating the weld out of the DMW and the adjacent ferritic welds and included a severe ID weld repair in the DMW, prior to applying the weld overlay. The post weld overlay residual stresses were shown to result in significant compressive stresses throughout the original DMW thickness.

A fracture mechanics analysis was performed to determine the amount of future crack growth which would be predicted following the installation of the FSWOL, assuming an initial flaw depth of 75% through the wall of the original base material. Both fatigue and IGSCC crack growth were considered and found to be acceptable. The time for the crack depth to reach the overlay interface, for both the DMW and the adjacent ferritic weld, is a duration greater than 60 years.

Based on the above observations and the fact that weld overlays have been applied to other plants since 1986 with no subsequent problems identified, it is concluded that the installation of the Initial FSWOL design to the Brunswick-1 N4A and N4D feedwater nozzle inboard DMWs have received long term resistance to IGSCC.

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Mr. John Goelz June 27, 2018 Report No. 1800500.402.R0

4.0 REFERENCES

1. Duke Energy Letter No. BSEP 18-0039, Brunswick Steam Electric Plant, Unit No. 1, Renewed Facility Operating License No. DPR-71, Docket No. 50-325, Proposed In-service Inspection Alternative for Application of Dissimilar Metal Weld Full Structural Overlay, dated March 19, 2018, ADAMS Accession No. ML18078A804.

2. ASME Boiler and Pressure Vessel Code, Code Case N-740-2, Full Structural Dissimilar Metal Weld Overlay for Repair or Mitigation of Class 1, 2 and 3 Items,Section XI, Division 1.

3. Peter L. Andresen, et al., GE Global Research Center, SCC of High Cr Alloys in BWR Environments, 15th International Conference on Environmental Degradation, TMS (The Minerals, Metals & Materials Society), 2011.

4. ASME Code,Section XI, 2007 Edition with Addenda through 2008, Nonmandatory Appendix Q, Weld Overlay Repairs of Classes 1, 2, and 3 Austenitic Stainless Steel Piping Weldments.

5. ASME Boiler and Pressure Vessel Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, 2001 Edition with Addenda through 2003.

6. ASME Boiler and Pressure Vessel Code,Section III, 2001 Edition with Addenda through 2003.

7. ASME Code,Section III. Nuclear Power Plant Components, 1974 edition, including the Summer 1974 Addenda and Code Case 1661.

8. General Electric Document No. 22A3897, Rev. 0, Installation Specification, Nozzle, Feedwater, Safe End Removal and Replacement and the Welded-In Feedwater Sparger.

9. ANSYS Mechanical APDL, Release 14.5 (w/ Service Pack 1 UP20120918), ANSYS, Inc.,

September 2012.

10. Materials Reliability Program: Finite-Element Model Validation for Dissimilar Metal Butt-Welds (MRP-316, Revision 1): Volumes 1 and 2, EPRI, Palo Alto, CA, 3002005498.

11. Materials Reliability Program: Welding Residual Stress Dissimilar Metal Butt-Weld Finite Element Modeling Handbook (MRP-317, Revision 1), EPRI, Palo Alto, CA, 3002005499.

12. U.S. NRC, International Weld Residual Stress Round Robin Problem Statement, Version 1.0, U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research, Division of Engineering, Component Integrity Branch, December 2009.

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13. U.S. NRC, International Weld Residual Stress Round Robin Problem Statement: Phase 2b of the NRC/EPRI WRS Validation Program, Version 3.0, U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research, Division of Engineering, Component Integrity Branch, December 2013

14. Material Reliability Program: Technical Basis for Preemptive Weld Overlays for Alloy 82/182 Butt Welds in Pressurized Water Reactors (PWRs) (MRP-169), Revision 1-A, EPRI, Palo Alto, CA: 2010. 1021014 (includes NRC SER ML101660468).

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