RA-18-007, Brunswick, Unit 1, Application of Dissimilar Metal Weld Full Structural Overlay - Reactor Pressure Vessel Nozzles N4A and N4D

Brunswick, Unit 1, Application of Dissimilar Metal Weld Full Structural Overlay - Reactor Pressure Vessel Nozzles N4A and N4D

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

Text

Proposed In-service Inspection Alternative for Application of Dissimilar Metal Weld Full Structural Overlay - Nozzles N4A and N4D 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)

5215HellyerAvenue,Suite210,SanJose,CA95138l[1 408 833 7292]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 Alternativ e 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 Brunswick's response to a commitment in the above-referenced propos ed 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 Brunswick's 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. Th e 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, 2018Report No. 1800500.402.R0 PAGEl2 If you have any questions or comments regard ing this summary, please contact one of the undersigned.

Prepared b y: Verified b y: 6/27/18 6/27/18Richard L. Bax Jr. DateJames W. Axline, P.E. DateAssociate Associate

Approved b y: 6/27/18James W. Axline, P.E. DateAssociate

Attachment

cc: Project File No 1800500.402.R0

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 1

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)

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 2

1.0 INTRODUCTION

Brunswick Nuclear Plant, Unit 1 (Brunswick-1) applied an "Initial" full st ructural weld overlay (FSWOL) on dissimilar metal welds (DMWs) 1B21N4A-2-SW1-2 and 1B21N4D-5-SW1-2 between the reactor pressure ve ssel (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 circumfere ntially 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 Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 3 Code Case 1661 [7] as specified in the General Electric Installation Specification 22A3897 [8]. However, the original Construction Code has been reconciled to the AS ME 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 Edit ions 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 pl ants 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 dime nsions, evaluations of weld shrinkage and the added weight/stiffness of the overlay's 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 Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 4 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 Item Location (From DMW Toe)

Structural Thickness or Length Design Minimum Thickness or Length Design Maximum Thickness or Length Thickness (in.) Safe End Side0.310.35 0.60Safe End Extension Side0.310.35 0.60 Length (in.) Safe End Side0.692.32 3.32Safe End Extension Side0.802.32 3.32

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 5 Table 2-2. Initial FSWOL Design - As-Built Dimensions for Nozzle N4A Item Location (From DMW Toe)

As-Built Thickness or Length (1) Thickness (in.) Safe End Side0.476 Safe End Extension Side0.461 Length (in.) Safe End Side3.028 Safe End Extension Side3.016 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 Item Location (From DMW Toe)

As-Built Thickness or Length (1) Thickness (in.) Safe End Side0.461 Safe End Extension Side0.503 Length (in.) Safe End Side2.981 Safe End Extension Side2.948 Notes: 1) The as-built dimensions shown are the average of the four measured azimuthal measurements taken for each location.

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 6 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, T 1, was calculated. The through-wall temperature difference (T) was calculated for each path and compared to the allowable. The bounding location re sults 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 Path (1) P m (psi) Allowable (psi) Accept P L (psi) Allowable (psi) Accept P L+P b (2) (psi) Allowable (psi) Accept4 6,033 18,700Yes 13,24028,050Yes15,466 28,050Yes9 6,033 18,700Yes 13,00428,050Yes17,047 28,050Yes11 8,753 18,700Yes 15,26028,050Yes16,756 28,050Yes12 8,753 23,300Yes 11,05134,950Yes12,529 34,950Yes13 8,753 18,700Yes 14,96428,050Yes17,891 28,050Yes14 8,753 23,300Yes 11,09434,950Yes13,756 34,950YesNotes: 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 Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 7 Load Combination Path (3) and Type Calculated (psi) Allowable (psi) Service Level A/B/Test Path 4 Primar y + Secondar y (P + Q)24,017 59,208Path 9 Primar y + Secondar y (P + Q)24,741 59,208Path 11 Primar y + Secondar y (P + Q)28,944 58,862 Path 12 (1) Primar y + Secondar y (P + Q)96,582 69,900Path 13 Primar y + Secondar y (P + Q)29,075 58,862 Path 14 (1) Primar y + Secondar y (P + Q)96,408 69,900Simplified Elastic Plastic Path 12 (1) Equation 123,331 69,900Equation 1367,971 69,900 Path 14 (1) Equation 123,044 69,900Equation 1368,807 69,900 Calculated AllowableThermal Ratchetin g Path 12 T 1 194°F 620°F Fatigue Path 12 Cumulative Usage Factor (60 y ears)0.1617 1.000 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.

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 8 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 re sidual stress fluctuations due to stress distribution caused by normal operating load

s. 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.

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 9 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 Flaw Type Path (2) Material Time for Initial 75% Flaw Depth to Reach Overlay (years) Initial Overlay Circumferential P1 Allo y 182 > 60 P2 Allo y 182 > 60 P3 Allo y 182 > 60 P4 Ferritic > 60 P5 Ferritic N/A(1) P6 Allo y 182 > 60 P7 Allo y 182 > 60 P8 Allo y 182 > 60 P9 Ferritic > 60 P10 Ferritic N/A(1) Axial P1 Allo y 182 > 60 P2 Allo y 182 > 60 P3 Allo y 182 > 60 P4 Ferritic > 60 P5 Ferritic N/A(1) P6 Allo y 182 > 60 P7 Allo y 182 > 60 P8 Allo y 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

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 10 2.5 Evaluation of As-Built Conditions

The Relief Request [1] and Code Case N-740-2 [2] require evalua tion 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 2S m , which is 2(20) = 40 ksi at 70°F.

For the feedwater sparger piping, the highest stress caused by th e 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 2S m, 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.

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 11

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 require ment to meet NDE inspection requirements.

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 12 Figure 2-2: Finite Element Model of the Initial FSWOL Design for Operat ing Stress Evaluations

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 13 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)

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 14 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 th e welding processes involved. The RPV N4 nozzle is on the right and the safe end is on the left.

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 15 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, Path s 1 through 5 also correspond to Paths 8 through 10 in Figure 2-7, respectively.

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 16 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, Path s 1 through 5 also correspond to Paths 8 through 10 in Figure 2-7, respectively.

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 17 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)

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 18 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")

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 19

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 Ca se 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 AS ME Code,Section XI, IWB-3640 based on an assumed circumferential flaw 100% thr ough-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 we ld 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% thr ough 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 th at 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.

Mr. John Goelz June 27, 2018Report No. 1800500.402.R0 PAGElA 20

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 edit ion, 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.

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