ML063110575

Relief Request 06-GO-001 Commitments

ML063110575
Person / Time
Site:	Mcguire
Issue date:	10/26/2006
From:	Gordon Peterson Duke Energy Carolinas, Duke Energy Corp, Duke Power Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML063110575 (19)

Text

GARY R. PETERSON Vice President PoEnergy. McGuire Nuclear Station Duke Energy Corporation MG01 VP /-J2,,700 Hagers Ferry Rd.

Huntersville,I.C 28078 704 875 5333 704 875 4809 fax grpeters@duke-energy.com October 26, 2006 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

SUBJECT:

Duke Power Company LLC d/b/a Duke Energy Carolinas, LLC (Duke)

McGuire Nuclear Station, Unit 2 Docket Number 50-370 Relief Request 06-GO-001 Commitments On July 27, 2006, Duke submitted Relief Request 06-GO-001 pursuant to 10 CFR 50.55a(a)(3)(i), requesting NRC approval to use alternatives to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), Section Xl Inservice inspection (ISI) requirements for the McGuire and Catawba Nuclear Stations, Units 1 & 2. This proposed alternative approach is to support application of full structural weld overlays on various pressurizer nozzle-to-safe end welds and will provide an acceptable level of quality and safety.

On August 30, 2006, the NRC Staff electronically requested additional information regarding several issues contained within the relief request. Duke submitted a response to this request on September 11, 2006.

The NRC requested further clarification to the relief request during a conference call on September 20, 2006. This information included further technical clarification as well as a request to incorporate all changes into one document and resubmit the entire relief request. This relief request was resubmitted on September 27, 2006 for McGuire Unit 2 and Catawba Unit 1.

www. duke-energy. corn

U. S. Nuclear Regulatory Commission October 26, 2006 Page 2 The September 27, 2006 contained two commitments.

1. The following information will be submitted to the NRC within fourteen days of completion of the final UT on each unit included in this relief request. Also included in the results will be a discussion of any repairs to the overlay material and/or base metal and the reason for the repair.

• a listing of flaw indications detected

• the disposition of all indications using the standards of ASME Section XI, IWB-3514-2 and/or IWB-3514-3 criteria and, if possible,

" the type and nature of the indications The information required by the commitment above is included as Attachment 1.

The inspections were performed using the EPRI Performance Demonstration Initiative (PDI) qualified ultrasonic inspection procedure. No flaw indications were detected in the overlays.

2. Prior to entry into Mode 4 from the McGuire Unit 2 outage in the fall of 2006, a summary of the results of the stress analyses demonstrating that the preemptive full structural weld overlay will not hinder the components from performing their design function will be submitted to the NRC.

The information required by the commitment above is included as Attachment 2.

If you have any questions or require additional information, please contact Kay Crane at (704) 875-4306.

Gary R. Peterson Attachments

U. S. Nuclear Regulatory Commission October 26, 2006 Page 3 W. D. Travers, Region II Administrator U.S. Nuclear Regulatory Commission Sam Nunn Atlanta Federal Center, 23 T85 61 Forsyth St., SW Atlanta, GA 30303-8931 J. F. Stang, Jr., Senior Project Manager (CNS & MNS)

U. S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop 0-8 H 4A Rockville, MD 20852-2738 J. B. Brady NRC Senior Resident Inspector McGuire Nuclear Station

Attachment I Summary of Ultrasonic Examinations of Preemptive Weld Overlays for Pressurizer Nozzle Locations Containing Alloy 600 Materials V kmWa INtrIly Amctes, Inc Attachment to SIR-06-409, Rev. 0 I I of 4 PCR-06-011

Ultrasonic Examination Procedure SI-UT-126, Revision 0, Procedurefor the PhasedArray Ultrasonic Examination of Weld Overlaid Similarand DissimilarMetal Welds, was used during the examinations. This procedure, and the examiners who applied the procedure, are qualified through the PDI Program at the EPRI NDE Center.

Relief Nozzle Weld Overlay Examination Component Identification: PORV 2PZR-W3SE Examination Date: 10/14/06 Examination Time: 01:45 through 03:00 Examination Regions: Weld Overlay Material, Outer 25% Dissimilar Metal Weld & Adjacent Base Material and Outer 25% Safe End-to-Elbow Weld & Adjacent Base Material Axial Examination Angles: 0' through 83' - Circumferential Examination Angles: 0' through 660 Examination Summary: No suspected flaw indications were observed during the examinations.

The examination gain was adjusted to maintain the procedure-specified baseline noise level from 5% to 20% of full screen height. The lower range of examination angles detected responses from the inside surface of the component which were useful for monitoring search unit contact /

coupling effectiveness during the examination.

Safety Nozzle NC1 Weld Overlay Examination Component Identification: 2NC I 2PZR-W4ASE Examination Date: 10/12/06 Examination Time: 02:45 through 03:45 Examination Regions: Weld Overlay Material, Outer 25% Dissimilar Metal Weld & Adjacent Base Material and Outer 25% Safe End-to-Elbow Weld & Adjacent Base Material Axial Examination Angles: 0' through 830 - Circumferential Examination Angles: 00 through 660 Examination Summary: No suspected flaw indications were observed during the examinations.

The examination gain was adjusted to maintain the procedure-specified baseline noise level from 5% to 20% of full screen height. The lower range of examination angles detected responses from the inside surface of the component which were useful for monitoring search unit contact /

coupling effectiveness during the examination.

Attachment to SIR-06-409, Rev. 0/ 2 of 4 SfwtuW iftgrityAssociates, Inc.

PCR-06-011

Safety Nozzle NC2 Weld Overlay Examination Component Identification: 2NC2 2PZR-W4BSE Examination Date: 10/14/06 Examination Time: 01:45 through 03:00 Examination Regions: Weld Overlay Material, Outer 25% Dissimilar Metal Weld & Adjacent Base Material and Outer 25% Safe End-to-Elbow Weld & Adjacent Base Material Axial Examination Angles: 0' through 830 - Circumferential Examination Angles: 0' through 660 Examination Summary: No suspected flaw indications were observed during the examinations.

The examination gain was adjusted to maintain the procedure-specified baseline noise level from 5% to 20% of full screen height. The lower range of examination angles detected responses from the inside surface of the component which were useful for monitoring search unit contact /

coupling effectiveness during the examination.

Safety Nozzle NC3 Weld Overlay Examination Component Identification: 2NC3 2PZR-W4CSE Examination Date: 10/12/06 Examination Time: 03:45 through 04:45 Examination Regions: Weld Overlay Material, Outer 25% Dissimilar Metal Weld & Adjacent Base Material and Outer 25% Safe End-to-Elbow Weld & Adjacent Base Material Axial Examination Angles: 00 through 83' - Circumferential Examination Angles: 0' through 660 Examination Summary: No suspected flaw indications were observed during the examinations.

The examination gain was adjusted to maintain the procedure-specified baseline noise level from 5% to 20% of full screen height. The lower range of examination angles detected responses from the inside surface of the component which were useful for monitoring search unit contact /

coupling effectiveness during the examination.

Spray Nozzle Weld Overlay Examination Component Identification: 2PZR-W2SE Examination Date: 10/13/06 Examination Time: 23:02 through 00:31 Examination Regions: Weld Overlay Material, Outer 25% Dissimilar Metal Weld & Adjacent Base Material and Outer 25% Safe End-to-Elbow Weld & Adjacent Base Material Axial Examination Angles: 00 through 830 - Circumferential Examination Angles: 0' through 650 Examination Summary: No suspected flaw indications were observed during the examinations.

The examination gain was adjusted to maintain the procedure-specified baseline noise level from 5% to 20% of full screen height. The lower range of examination angles detected responses from the inside surface of the component which were useful for monitoring search unit contact /

coupling effectiveness during the examination.

Attachment to SIR-06-409, Rev. 0/ 3 of 4 SftnWf kfti Associates, Inc.

PCR-06-011

Surge Nozzle Weld Overlay Examination Component Identification: 2PZR-W ISE Examination Date: 10/11/06 Examination Time: 14: 25 through 16:25 Examination Regions: Weld Overlay Material, Outer 25% Dissimilar Metal Weld & Adjacent Base Material and Outer 25% Safe End-to-Pipe Weld & Adjacent Base Material Axial Examination Angles: 00 through 830 - Circumferential Examination Angles: 00 through 700 Examination Summary: No suspected flaw indications were observed during the examinations.

The examination gain was adjusted to maintain the procedure-specified baseline noise level from 5% to 20% of full screen height. The lower range of examination angles detected responses from the inside surface of the component which were useful for monitoring search unit contact /

coupling effectiveness during the examination.

SVntcrial Inegrity Associates, Inc.

Attachment to SIR-06-409, Rev. 0 I "~of4 PCR-06-011

Attachment 2 Summary of Design and Analyses of Preemptive Weld Overlays for Pressurizer Nozzle Locations Containing Alloy 600 Materials VM~bIbtft lAssociafes, Inc.

Attachment to SIR-06-409, Rev. 0 I I of 12 PCR-06-011

1.0 Introduction Duke Energy has applied full structural weld overlays (WOLs) on dissimilar metal welds (DMWs) of four 6" pressurizer safety/relief nozzles, one 4" pressurizer spray line nozzle, and one 14" pressurizer surge line nozzle at the McGuire Nuclear Station, Unit 2. The purpose of these overlays is to eliminate dependence on the primary water stress corrosion cracking (PWSCC) susceptible Alloy 82/182 welds as pressure boundary welds and to mitigate any potential future PWSCC in these welds. The overlays were installed using a PWSCC resistant weld filler material, Alloy 52M [1].

The requirements for design of weld overlay repairs are defined in ASME Code Case N-504-2

[2], supplemented for this application by the Relief Request [3]. Weld overlay repairs are considered to be acceptable long-term repairs for PWSCC susceptible weldments if they meet a conservative set of design assumptions which qualify them as "full structural" weld overlays.

The design basis flaw assumption for full structural weld overlays is a circumferentially oriented flaw that extends 360' around the component, completely through the original component wall.

A combination of internal pressure, deadweight and seismic stresses is applied to the overlaid nozzles containing this assumed design basis flaw, and they must meet the requirements of ASME Code,Section XI, IWB 3641 [4].

ASME Section III stress and fatigue usage evaluations are also performed that supplement existing piping, safe end, and nozzle stress reports, to demonstrate that the overlaid components continue to meet ASME Code,Section III. The original construction Code for the pressurizer was ASME Section III, 1971 Edition through Summer and Winter 1971 Addenda. However, as allowed by ASME Section XI, Code Editions and Addenda later than the original construction Code may be used. ASME Section III, 2001 Edition with Addenda through 2003 [5] was used for these analyses.

In addition to providing structural reinforcement to the PWSCC susceptible locations with a resistant material, weld overlays have also been shown to produce beneficial residual stresses that mitigate PWSCC 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. In addition, the weld residual stresses from the overlays act as compressive mean stresses in fatigue crack growth assessments.

Finally, evaluations are performed, based on as-built measurements taken after the overlays are applied, to demonstrate that the overlays meet their design basis requirements, and that they will not have an adverse effect on the balance of the piping systems. These include comparison of overlay dimensions to design dimensions, evaluations of shrinkage stresses and added weight effects on the piping systems.

Attachment to SIR-06-409, Rev. 0/ 2 of 12 SbudnIh*urf

• Associates, Inc.

PCR-06-011

2.0 Analysis Summary and Results 2.1 Weld Overlay Structural Sizing Calculations Detailed sizing calculations for weld overlay thickness were performed using the "Codes and Standards" module of the pc-CRACK computer program [6], which incorporates ASME Code,Section XI, IWB-3640 evaluation methodology. Loads and stress combinations were provided by Duke Energy. Both normal operating/upset (Level A/B) and emergency/faulted (Level C/D) load combinations were considered in this evaluation, and the design was based on the more limiting results. The resulting minimum required overlay thicknesses are summarized in Table 2-1. Because of weld metal dilution concerns over the low alloy steel nozzle, a dilution weld layer is specified, in addition to the thickness required for structural reinforcement, to allow for the possibility that the minimum required chromium content for PWSCC resistance (24%) may not be achieved in the first layer.

The weld overlay length must consider: (1) length required for structural reinforcement, (2) length required for access for preservice and inservice examinations of the overlaid weld, and (3) residual stress improvement. In accordance with ASME Code Case N-504-2, the minimum weld overlay length required for structural reinforcement was established by evaluating the axial-radial shear stress due to transfer of primary axial loads from the pipe into the overlay and back into the nozzle, on either side of the weld(s) being overlaid. Axial weld overlay lengths were established such that this stress is less than the ASME Section III limit for pure shear stress. The resulting minimum length requirements are summarized in Table 2-1.

The overlay length and profile must also be such that the required post-WOL examination volume can be inspected using Performance Demonstration Initiative (PDI) qualified nondestructive examination (NDE) techniques. This requirement can cause required overlay lengths to be longer than the minimums for structural reinforcement. A typical weld overlay design for the McGuire Unit 2 pressurizer nozzles is illustrated in Figure 2-1. Because of the relatively short lengths of the original safe-ends, it was necessary to extend the overlay over both the DMW and the adjacent stainless steel (SS) welds, to ensure sufficient overlay length for inspectability and residual stress improvement. The designs were reviewed by qualified NDE personnel to ensure that they meet inspectability requirements for both welds, and the overlays were designed to satisfy full structural requirements for both the DMWs and the SS welds.

Table 2-1: Weld Overlay Structural Thickness and Length Requirements Safety/Relief Spray Nozzle Surge Nozzle Nozzle Minimum* Nozzle Side 0.397 0.292 0.427 Thickness (in.) Safe End Side 0.365 0.242 0.469 Minimum** Nozzle Side 0.932 0.590 1.175 Length (in.) Safe End Side 1.503 0.917 1.683

• - Weld dilution layer (0.08") must be added

- Additional length requirements apply for inspectability Attachment to SIR-06-409, Rev. 0/ 3 of 12 Wldmi IntgWAssocates, Inc.

PCR-06-011

2.2 Section III Stress Analyses Stress intensities for the weld overlaid Safety/Relief, Spray and Surge nozzles were determined from finite element analyses for the various specified load combinations and transients using the ANSYS software package [8]. Linearized stresses were evaluated at a total of nine stress locations - three paths as shown in Figure 2-2, each evaluated at the intrados, extrados and cheek locations for 3-dimensional models. (3-dimensional models were used for the safety/relief and spray nozzles because of the adjacent elbows. The surge nozzle was deemed to be adequately modeled by a 2-dimensional, axisymmetric model.) The stress intensities at these locations were evaluated in accordance with ASME Code,Section III, Sub-articles NB-3200 and NB-3600 [5],

and compared to applicable Code limits. A summary of the stress aind fatigue usage comparisons for the most limiting locations is provided in Table 2-2. The stresses and fatigue usage in the weld overlaid nozzles are within the applicable Code limits. Figure 2-2 illustrates a typical stress model and stress paths evaluated. In general, the limiting location for the Section III stress analyses was found to be the section of the original pipe at the end of the overlay (Path I in Figure 2-2).

Table 2-2: Limiting Stress Results for Weld Overlaid Nozzles Nozzle Load Combination Type Calculated Allowable Eqn. 10: Primary + Secondary (P +Q) (ksi)* 67.58** 47.88 Safety/ Level A/B Eqn.12/13: Simplified Elastic-Plastic Anal 42.25** 47.88 Relief (P +Q) (ksi)

Fatigue Cumulative Usage Factor 0.051 1.000 Eqn. 10: Primary + Secondary (P +Q) (ksi)* 149.09** 48.53 Spray Level A/B Eqn. 12/13: Simplified Elastic-Plastic Anal 45.72** 48.53 (P +Q) (ksi)

Fatigue Cumulative Usage Factor 0.986 1.000 Surge Level A/B Eqn. 10: Primary + Secondary (P +Q) (ksi)* 48.28 48.34 Fatigue Cumulative Usage Factor 0.994 1.000

• Primary stress acceptance criteria are met via the sizing calculations discussed in Section 2.1.

• • - Elastic analysis exceeds the allowable value of 3Sm, however, criteria for simplified elastic-plastic analysis and thermal ratchet are met.

2.3 Residual Stress and Section XI Crack Growth Analyses Weld residual stresses for the McGuire Unit 2 pressurizer nozzle weld overlays were determined by detailed elastic-plastic finite element analyses. The analysis approach has been previously documented to provide predictions of weld residual stresses that are in reasonable agreement with experimental measurements [7]. Two-dimensional, axisymmetric finite element models were developed for each of the nozzles. Modeling of weld nuggets used in the analysis to lump the combined effects of several weld beads is illustrated in Figure 2-3. The models simulated an inside surface (ID) repair at the DMW location with a depth of approximately 50% of the original wall thickness. This assumption is considered to conservatively bound any weld repairs that may have been performed during plant construction from the standpoint of producing tensile residual stresses on the ID of the weld. The models also simulated the SS pipe to safe-end weld.

.*; StructuralInto"i Associates, Inc.

-:0: Attachment to SIR-06-409, Rev. 0 / 4 of 12 PCR-06-011

The residual stress analysis approach consists of a thermal pass to determine the temperature response of the model to each individual lumped weld nugget as it is added in sequence, followed by an elastic-plastic stress pass to calculate the residual stress due to the temperature cycling from the application of each nugget. Since residual stress is a function of welding history, the stress passes for each nugget are performed sequentially, over the residual stress fields induced from all previously applied weld nuggets. The resulting residual stresses were evaluated on the inside surface of the original welds and safe-end components, as well as on several paths through the DMW and SS welds (Figures 2-4 and 2-5).

The residual stress calculations were then utilized, along with stresses due to applied loadings and thermal transients, to demonstrate that assumed cracks that could be missed by inspections will not exceed the overlay design basis during the ASME Section XI inservice inspection interval due to fatigue or PWSCC. In the fatigue crack growth analyses, 25% of the original 40 year design quantity of each applied transient was assumed to be applied in the 10 year interval.

Initial flaw sizes for the crack growth assessments were assumed consistent with the post-overlay UT inspections performed. Fatigue crack growth results are summarized in Table 2-3 for initial flaw sizes of 25%, 50% and 75% of the original pipe wall thickness. In all cases, the maximum crack depth at the end of the ten-year inspection interval is less than the weld overlay design basis flaw (the original wall thickness plus dilution layer for the DMW or just the original wall thickness for the SS welds, since no dilution layer was specified). Since the exam volume for the PDI qualified post-overlay UT inspections includes the weld overlay plus the outer 25% of the original wall thickness, a 75% through wall crack is the largest flaw that could escape detection by this examination.

For crack growth due to PWSCC, the total sustained stress intensity factor during normal plant operation was determined as a function of assumed crack depth, considering internal pressure stresses, residual stresses, steady state thermal stresses, and stresses due to sustained piping loads (including deadweight). Zero PWSCC growth is predicted for assumed crack depths at which the combined stress intensity factor due to sustained steady state operating conditions is less than zero. For all nozzles, considering the worst case paths in the DMWs, the sustained stress intensity factors remained negative for crack depths up to and beyond 75% of the original wall thickness. Therefore, no crack propagation due to PWSCC is predicted in the overlaid nozzles.

Attachment to SIR-06-409, Rev. 0/ 5 of 12  ! ShV aI hlafyAssoctS,Inc PCR-06-011

Table 2-3: IImitin~

Tahle 2-3: Fatigue

_____________-c - ---- C-- Crack Growth Results for Weld Overlaid Nozzles DMW Safety/Relief Spray Nozzle Surge Nozzle Nozzles Initial Flaw Size Flaw Size (in.) Flaw Size (in.) Flaw Size (in.)

(% of Orig. Thick.) Initial Final* Initial Final* Initial Final*

Circumferential Flaws 25% 0.2975 0.2986 0.2188 0.2196 0.377 0.487 50% 0.5950 0.5961 0.4375 0.4375 0.754 0.873 75% 0.8925 0.8946 0.6563 0.6563 1.131 1.183 Axial Flaws 25% 0.2975 0.2975 0.2188 0.2191 0.377 0.378 50% 0.5950 0.5950 0.4375 0.4376 0.754 0.755 75% 0.8925 0.8927 0.6563 0.6574 1.131 1.132 Original thickness 1.27 1 0.955 1.588

+ dilution layer* II SS Welds Safety/Relief Spray Nozzle Surge Nozzle Nozzles Initial Flaw Size Flaw Size (in.) Flaw Size (in.) Flaw Size (in.)

(% of Orig. Thick.) Initial Final* Initial Final* Initial Final*

Circumferential Flaws 25% 0.1950 0.2038 0.1475 0.2230 0.360 0.434 50% 0.3900 0.4078 0.2951 0.3770 0.721 0.843 75% 0.5850 0.6105 0.4426 0.5139 1.081 1.404 Axial Flaws 25% 0.1950 0.1992 0.1475 0.2140 0.360 0.452 50% 0.3900 0.4375 0.2951 0.4783 0.721 0.883 75% 0.5850 0.6528 0.4426 0.5728 1.081 1.224 Original thickness* 0.78 1 0.590 1.441

• - Allowable crack depth at end of ten year inspection interval.

2.4 As-Built Measurements and Reconciliations The measured as-built thicknesses and lengths of the McGuire Unit 2 overlays, after final machining, were determined in order to demonstrate the adequacy of the installed repairs. For each critical dimension listed in Table 2-1, the as-built measurements exceeded the minimum required structural design dimension. Thus, the as-built configurations of the overlays satisfied all established design requirements.

V St wtural Int4fy Associates, Inc.

Attachment to SIR-06-409, Rev. 0/ 6 of 12 PCR-06-011

Figure 2- 1: Illustration of Typical Weld Overlay Design for McGuire Unit 2 Pressurizer Nozzles StructurW Integrity Assocra*inc.

Attachment to SIR-06-409, Rev. 0/ 7 of 12 PCR-06-011

AN EXTRADOS LOCA'ION Pah7 Safety/Relief Nozzle Figure 2-2: Typical Finite Element Model for Section III Stress Evaluation showing Stress Paths Figure 2-3: Typical Finite Element Model for Residual Stress Analysis showing Nuggets used for Welding Simulations Attachment to SIR-06-409, Rev. 0/ 8 of 12 V*Mhw&I lmfteril Assd~, ft PCR-06-011

Finite Figure Model 2-4" for idual Stress Analysis or O ResE v a lu atio n showing s Paths used in Crack Attachm

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ent to5SR 06S2 0- 9 ReV.

pCR-06-0Ol 0f 9M-06-409 of 240Oa, Inc.

Post-Repair McGuire/Catawba Pressurizer Spray Nozzle -- e-- Post-ButtWead IDSurface Axial Stress Post-WOLl

-Post-WOL4-70F

--- Post-WOL4-650F L=

as 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 1.2 -1.4 -1.6 -1.8 -2 Distance from ID Weld Repair Centerline (in)

---

Post-Repair McGuire/Catawba Pressurizer Spray Nozzle --- Post-ButtWeld ID Surface Hoop Stress Post-WOLl Post-WOL4-70F X---Post-WOL4-650F 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 1.2 -1.4 -1.6 -1.8 -2 Distance from ID Weld Repair Centerline (in)

Figure 2-5: Typical Residual Stress Results along Inside Surface of Original Butt Welds and Safe-End Attachment to SIR-06-409, Rev. 0/ 10 of 12 V StI b Aftpf Associates, Inc.

PCR-06-011

3.0 Conclusions The design of the McGuire Unit 2 weld overlays was performed taking guidance from the requirements of ASME Code Case N-504-2 [2], amended in accordance with the Relief Request

[3]. The weld overlays are demonstrated to be long-term mitigation of PWSCC in these welds based on the following:

0 In accordance with ASME Code Case N-504-2, structural design of the overlays was performed to meet the requirements of ASME Section XI, IWB-3640 based on an assumed flaw 100% through and 360' around the original welds. The resulting full structural overlays thus restore the original safety margins of the nozzles, with no credit taken for the underlying, PWSCC-susceptible material.

0 The weld metal used for the overlay is Alloy 52M, which has been shown to be resistant to PWSCC [(1], thus providing a PWSCC resistant barrier. Therefore, no PWSCC crack growth is expected into the overlay.

• Because of the short safe-end lengths in the original nozzle designs, the overlays were extended to cover the adjacent stainless steel pipe to safe-end welds. Although not susceptible to PWSCC, covering them with the overlays was necessary to ensure inspectability and effective residual stress improvement of the DMWs. The overlays were also designed as full structural over the stainless steel welds, thereby providing additional structural margin.

0 No credit was taken in the overlay designs for the first overlay layer, which could have been diluted by the base metal during the welding process.

• Application of the weld overlays was shown to not impact the conclusions of the existing nozzle Stress Reports. Following application of the overlay, all ASME Code,Section III stress and fatigue criteria are met.

• Nozzle specific residual stress analyses were performed, after first simulating severe ID weld repairs in the nozzle to safe-end welds, prior to applying the weld overlays. The post weld overlay residual stresses were shown to result in beneficial compressive stresses on the inside surface of the components, and well into the thickness of the original DMWs, assuring that future PWSCC initiation or crack growth into the overlay is highly unlikely.

• Fracture mechanics analyses were performed to determine the amount of future crack growth which would be predicted in the nozzles, assuming that cracks exist that are equal to or greater than the thresholds of the NDE techniques used on the nozzles. Both fatigue and PWSCC crack growth were considered, and found to be acceptable.

• Axial shrinkage was measured following the overlay applications and was found to be small. Therefore shrinkage stresses at other locations in the piping systems arising from the weld overlays are not expected to have an adverse effect on the systems.

• All hanger set points and pipe whip restraint clearances were checked after the overlay repair, and were found to be within the design ranges.

• The total added weight on the piping systems due to any individual overlay is insignificant compared to the weight of the piping systems and therefore does not impact the piping system stresses nor their dynamic characteristics.

Attachment to SIR-06-409, Rev. 0 / SlnWtvi Ihftegrify Associates, Ioc.

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• The as-built dimensions of the overlays exceeded the minimum design dimensions, thus demonstrating that the as-applied overlays satisfied the design requirements.

Based on the above observations and the fact that similar nozzle-to-safe end weld overlays have been applied to other plants since 1986 with no subsequent problems identified, it is concluded that the McGuire Nuclear Station Unit 2 pressurizer surge, safety/relief and spray nozzle dissimilar metal welds have received long term mitigation against PWSCC. Detailed calculations supporting the above conclusions are documented in the design report [9].

4.0 References

t. "Materials Reliability Program (MRP): Resistance to Primary Water Stress Corrosion Cracking of Alloys 690, 52, and 152 in Pressurized Water Reactors (MRP-I 11)," EPRI, Palo Alto, CA: 2004. 1009801

2. ASME Code, Code Case N-504-2, "Alternative Rules for Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping,Section XI, Division I."

3. Request No. 06-GO-001, Duke Energy Corporation, McGuire Unit 2 and Catawba Nuclear Station Unit [, Request for Alternative 06-GO-01.

4. ASME Boiler and Pressure Vessel Code,Section XI, 1998 Edition (with Addenda up to 2000).

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

6. pc-CRACK for Windows, Version 3.1-98348, Structural Integrity Associates, 1998.

7. Materials Reliability Program Report MRP-169, "Technical Basis for Preemptive Weld Overlays for Alloy 82/182 Butt Welds in PWRs," August 2005.

8. ANSYS/Mechanical, Release 8.1 (w/Service Pack 1), ANSYS Inc., June 2004.

9. Report SIR-06-399, Revision 0, "Design Report for the Weld Overlay Repair of Pressurizer Locations Containing Alloy 600 Materials McGuire Nuclear Station, Unit 2", DUKE-42Q-401, October, 2006.

Attachment to S[R-06-409, Rev. 0/ 12 of 12 Sb hW tegfilty Associates, Inc.

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