ML20116M536

Rv Closure Head Penetration Tube Id Weld Overlay Repair, Westinghouse Owners Group Program Rept

ML20116M536
Person / Time
Site:	North Anna
Issue date:	11/22/1995
From:	WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP., WESTINGHOUSE OPERATING PLANTS OWNERS GROUP
To:
Shared Package
ML19317C138	List: ML20094P991 ML20116M536 ML20117B678
References
WCAP-14519, NUDOCS 9608200194
Download: ML20116M536 (93)

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WESTINGliOUSE NON-PROPRIET RY CL' ASS 3 WCAP-14519 - RV Closum Head Penetration Tube ID Weld Oveday Repair A Westinghouse Owners Group Program Report J l i

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l i-t i WESTINGHOUSE ELEC'IRIC CORPORATION Nuclear Technology Division P.O. Box 355 i Pittsburgh, Pennsylvania 15230 01995 Westinghouse Electric Corporation All Rights Reserved 'I 4 mA2506er.wyf:Ib-ll1095 i

f

TABLE OF CONTENTS j

4-Section Page 1

Table of Contents i

List of Illustrations ill { List of Tables v - Executive Summary ' vi 1.0.- _ Introduction-1-1 2.0 - Program Description 2-1 [ 2.1 Objectives 2-1 2.2 Weld Repair Program Outline 2-2 ' 310 Approach for Development of Penetration Tube Weld Repair and 3 Overlay Designs 3.1 Local Weld Repair - 3-1 3.2 - _360* Weld Overlay 3-2 3.3 General Program Goal 3-2 4.0 Penetration hbe Sample & Reactor Vessel Head / Penetration 4-1 hbe Mock-Up Fabrication 4.1 Preparation of Penetration hbe Samples 4-1 4.2 Fabrication of Reactor Vessel Closme Head /' 4-1 Penetration hbe Mock-Up 5.0 Weld Process Specification 5-1 5.1 Selection of Welding Equipment 51 5.2 Quali6 cation of the Welding Parameters 5-1 5.3 Welding of Penetration hbe samples 5-3 5.4 Welding Reactor Vessel Closure Head / Penetration 5-4 hbe Mock-Up 6.0 Evaluation of Welded Penetration hbe Samples 6-1 6.1 Discussion of Diametral Measurements 6-1 7.0 Residual Stress Measmements on Reactor Vessel Head / 7-1 Penetration hbe Mock Up 7.1 Approach to Residual Stress Measurement 7-1 7.2 Hole Drilling Method. 71 7.2.1 Installation of Strain Gage Rosettes 7-2 7.2.2 Drilling Holes 7-2 -7.3 Test Results 7-2 7.4 ' Comparison of Test Results to Analysis 7-3 m:5506w.wp0lb-111095 - 1

l TABLE OF CONTENTS (Continued) Section Page i 8.0 Discussion of Post Weld Surface Treatment 8-1 8.1 General Discussion of Shot Peening 8-1 8.2 Shot Peen Parameters 8-2 8.3 Conclusions Regarding Post Weld Surface Treatment 8-3 l 9.0 Discussion of Weld Overlay Repairs 9-1 9.1 Penetration Tube Repair Parameters 0-1 9.1.1 Excavation Depths and Weld Thickness 9-1 9.1.2 Repair Geometry 9-2 9.1.3 Weld Surface Finish 9-3 9.1.4 ASME Code Approach to Weld Repair 9-4 9.1.5 Post-Weld laspection Requirements 9-4 i 9.2 Conclusions 9-5 10.0 References 10-1 i Appendix A Welding Process Specification A-1 Appendix B Weld Repair Drawing B-1 Appendix C Data Package for the Penetration Mock-Up & C-1 Penetration Mock-Up Sketches Appendix D Penetration Tube Dimensional Data D-1 4 J i m:u506w.wpf:1b-111095 11

LIST OF ILLUSTRATIONS figure Title Page Figure 3.01 Reactor Vessel Closure Head to Penetration hbe Geometry 3-4 Figure 4.1-1 Excavation Geometry for the 10 Inch Penetration Tube Sample 4-3 1 Figure 4.1-2 Full Size Mock-up Sketch Depicting "J" Preparation Excavation 44 i Geometry Figure 5.1-1 Weld Head used for Weld Repair Program 5-5 Figure 5.12 Weld Power Supply / Controller Used for Weld Repair Program 5-6 Figure 5.2-1 Joint Geometry for Qualification Samples 5-7 . Figure 5.3-1 Penetration hbe Sample No. 8 Cross-Section Showing Weld Repair 5-9 Over a Circumferential EDM Notch Figure 5.3-2 Penetration hbe Sample No. 8 Cross-Section Showing Weld Repair 5-10 Over the Longitudinal EDM Notches Figure 5.3-3 Penetration Abe Sample No. 7 Cross-Section Showing Weld Repair Over the 5-11 Circumferential (Bottom) and Longitudmal (Top) EDM Notches j l Figure 5.41 Photograph Depicting Weld Tooling Set-Up In Full Size Penetration 5-12 Tube Mock-Up Figure'6.1-1 Deformation in Penetration Tube Sample #1 [ ]**#, 6-3 Angle 90* Figure 6.1-2 Deformation in Penetration hbe Sample #2 [ ]**#, 6-4 Angle 360* i Figure 6.1-3 Deformauon in Penetrkdon hbe Sample #3 [ ]**#, 65 Angle 90' l Figure 6.1-4 Deformation in Penetration Tube Sample #4 [ ]**#, 6-6 Angle 360' Figure 6.1-5 Deformation in Penetration hbe Sample #5. [ ]**#, 6-7 Angle 45' i Figure 6.1-6 Deformation in Penetration Tube Sample #6 [ ]**#, 6-8 Angle 90' I Figure 6.1-7 Deformation in Penetration hbe Sample #7 [ ]**#, 6-9 Angle 90* l t l m:u506w.wpf:Ib.111095 iij 1

l - LIST OF ILLUSTRATIONS (Continued) Figare Title Page Figure 6.1.8 Deformation in Penetration hbe Sample #8 [ ]*##, 6-l0 Angle 360* l Figure 7.5-1 Overall Dimensions of Head Penetration Model and Air Abrasive Drill 7-6 Positioning Fixture Figure 7.2-1 Location Map of Residual Stress Measurements for Step 1 - The 7-8 As-Received Condition i Figure 7.2 Location Map of Residual Stress Measurements for Step 2 - After 7-9 Machining Weld Repair Areas l Figure 7.2-3 Location Map of Residual Stress Measurements for Step 3 - After 7-10 Welding Repair Areas Figure 7.2-4 Test Setup for Residual Stress Measurements 7-11 Figure 7.2-5 Adjusting Hole Drilling Fixture 7-12 Figure 7.3-1 Hole Drilling Rosette Strain Gage Data 7-14 4 Figure 7.3-2 Relationship of Principal Stress Directions to Rosette Gages 7-15 i Figure 7.3-3 Residual Stress Versus Distance From End of Tube for Step 1 at 7-16 180* Location j Figure 7.3-4 Residual Stress Versus Distance From End of hbe for Step 1 at 7-17. t 0* Location Figure 's.+1 Resioom hoop Stress As-Measured Compared to Analytical Estimates 7-18 of Hoop Stress for Center Side of Penetration Figure 7.4-2 Residual Hoop Stress As-Measured Compared to Analytical Estimates 7-19 4 j of Hoop Stress for Hill Side of Penetration Figure 7.4-3 Residual Axial Stress As-Measured Compared to Analytical Estimates 7-20 of Hoop Stress for Center Side of Penetration Figure 7.4 Residual Axial Stress As-Measured Compared to Analytical Estimates 7-21 of Hoop Stress for Hill Side of Penetration L t m:\\2$o6w.wpf:1b.111095 jy j

9 LIST OF TABLES Tame Title Page Table 53-1 TEST MATRIX FOR [ ]'## PENETRATION TUBE SAMPLES 5-8 Table 7.2-1 ROSETTE LOCAT10NS ON THE ID OF THE TUBE 7-7 Tabte 73-1 RESIDUAL STRESS MEASUREMENTS IN REACTOR VESSEL 7-13 HEAD / PENETRATION TUBE MOCK-UP i i i I 1 4 2 l l sw - f m:u506w.wpf:1h111095 y

-___.-._ __.. _. _.... _. ~. _.. _. } 4 I t ' REVISION RECORD i 11 10 05 - Proprietary infonnanon marked in preparation of Class 3 i Report No.14519 : D. Boyle i i I

i i

t t ? r i i i l t t I t l a e t-i i t J 4 i ] r i l .r i i 1 i 4 1 a 4 s 'l 1 l I m:\\2506w.wpf:1b-Ii1095 - vi i- 't ,,e e~

EXECUTIVE

SUMMARY

A technical approach to address the issue of primary water stress corrosion cracking (PWSCC) on the ID surface of reactor vessel closure head penetration tubes has been outlined by the Westinghouse Owners Group (WOG). In addition, the WOG has supported NUMARC at the jadustry level in taking a proactive role in resolution of this issue. In structuring an approach the WOG has supported root l cause evaluations, investigated how WOG plants are impacted, submitted a generic safety evaluation, developed plant inspection criteria, and solicited volunteers to perform pi mt inspections. Also, via the weld overlay program authorization (MUHP-5017), the subject of this report, the WOG is providing generic guidelines applicable for penetration tube repair and potentially a methodology to mitigate PWSCC in the penetration tube ID. This part of the program provides a weld design package which can be applied to repair reactor vessel closure head penetration tube ID initiated PWSCC. The weld design package provides the criteria for the repair of the penetration tube ID either through the application o local weld repair or via the application of a 360' weld overlay. The local w' ld repair process is targeted at restoring the minimum e required design thickness of the penetration tube wall. The 360* weld overlay is intended to provide a remedial measure to mitigate PWSCC in the Alloy 600 penetration tube ID by eliminating exposure of the highly stressed regions of the tube wall to the primary water environment. If an.' :dividual utility decides tg perform volumetric inspections of vessel head penetrations indications could possibly be encountered which wou:d require disposition in oruer to permit plant l start-up. Indications detected via penetration tube volueetric inspections need not necessarily immediately be repaired. Each p-netration tube indication weds to be evaluated against the established industry acceptance criteria. Dependent on indicatico position, depth, and orientation it is quite possible no immediate corrective action is required. In fact no corrective measure may be required for the remaining design life of the plant. If however corrective action is required the first course of action would require removal of the defect by excavation. Excavation by itselfis an acceptable corrective measure as long as the minimum required design thickness of the penetration tube wall is not violated, approximately 0.3 inch. If the minimum required design thickness is violated the integrity of the penetration tube wall needs to be re-established, i.e. via the local weld repair. m:\\2506w.wpf:ttw111095 vii

In support of the weld repair processes the following has been investigated; 1) Excavation geometries and various depths as related to flaw geometry, 2) Limitation of the weld repair with respect to crack length, 3) 'Ihe definition of welding process parameters,4) The definition of allowable weld filler metals,5) Weld surface finish, 6) Requirements relative to the surface profile of the penetration inside diameter,7) Industry suggested parameters for shot peening, and 8) Weld inedan requirements. Shot peening was examined as a post weld surface treatment to mitigate the residual stresses induced by welding. In addition to support the repair process, Westinghouse performed a i generic 50.59 Safety Evaluation such that a utility could license such a repair on an as needed basis. 'Ihe definition of the above items along with the safety evaluation provides a comprehensive package sudi that the utilities can independently implement and or contract such services, i.e. local weld repair or 360* weld overlay. Conclusions of the program are: An acceptable weld overlay process has been developed and qualified to Section IX of the ASME Code. i The welding promss specification developed as a result of the quali6 cation is applicable for I both locel weld repairs and 360* weld overlays in the reactor vessel closure head penetration tubes. Multiple repair geometries exist, each repair required should be individually specified. An individual utility needs to specify repair requirements based on the technical merits and economic impacts of each repair situation. i An excavation only repair is suggested up to a depth of [ ]*##. 1 It is suggested that if excavation to.a depth of [ ]**# doen not remove the entire defect, excavation should continue until the defect is removed or until [ ]*## inch of the penetration tube wall remains. A weld overlay repair needs to restore the minimum required penetration tube wall design thickness. ' cA2506w.wpf:1b.111095 viii m

[ f Repair weldistg pro /M an overall increase in the surface principle stresces in the penetration l tube. Dependent on weld thickness and circumferential extent the principle stresses will vary. These residual principle stresses for any of the geometries considered are comparable in magnitude to the residual plus operating stresses estimmed via the' clastic / plastic analysis for the l f outermost m.iion tubes. Areas af the penetration tube adjacent to the weld may be more susceptible to PWSCC than the i alloy o00 base material not impacted by the welding process. However the susceptibility of adjacent material quickly dissipates due to the drop off of residual stresses as you move away from the weld. I i The extent to which a utility wishes to pursue post weld surface treatment (s), such as shot f peening needs to be an individual utility decision based on the technical merits and economic l impacts. The Westinghouse owner's group may consider such a program in the future. j t The final geometry and surface finish of the repaired area needs to be such to facilitate base, [ and potential future volumetric inspections. [ i Weld design depths, geometry, location, and circumferential extent can be varied in an attempt I to minimize the impacts of the associated welding residual stresses. 'Ihese variations are f outlined on the associated design drawings provided in Appendix B. The WCAP report which I follows is intended to provide the in depth information required to uudctstand these impacts. j l. I l 1 4 l ad25%w.wpf:Ib111095 ix

1.0 INTRODUCTION

Previously, leakage has been reported from an Alloy 600 reactor vessel closure head penetration tube in a French plant during hydro testing at elevated pressure. Subsequent inspections of the leaking penetration indicate the presence of axial cracks on the inside diameter of the penetration tube. Cracks extend above and below the penetration tube to reactor vessel head attachment weld. The leakage has been determined to result from an axially oriented through-wall crack in the penetration tube wall. The cause of the axially oriented cracks has been attributed to primary water stress corrosion cracking (PWSCC), driven by both steady state operating and residual stress. 'Ihe residual stresses have been attributed to the ovality in the penetration tube which is a ducct result of benchng introduced in the - penetration tube due to the offset geometry of the attachment weld. Reported data from inspecuons of head penetrations at additional plants (Both French plants and plants of Westinghouse design) has estabbshed the presence of axially oriented cracking in additional nenetrations. The plants of Westinghouse design with reported reactor vessel head penetration tube inside diameter PWSCC are [ ]*". A review of available inspection data would I indicate that flaws have been detected in approximately 2% to 3% of the penetrations inWM A review of the reported inspection results also indicates that the majority of flaws were detected in penetration tubes located at the periphery of the reactor vessel closure head. This finding is consistent with estimate that residual stresses are greatest in the peripheral [w.isons because the offset in the (or angle of) attachment weld is greatest at these locations. Reactor vessel closure head penetrations on all Westinghouse supplied plants are of similar construction as that of the French plants and Westinghouse designed plants that have experienced cracking. Thus, based on the character of the cracking and the known potential of the Alloy 600 matenal for susceptibility to PWSCC this phenomenon may be possible on all WMaghause plants. Currently the WOG has undertaken an extensive program to examine and manage the phenomena of PWSCC initiated from the inside diameter of the reactor vessel Alloy 600 penetration tubes. The WOG's position has been that U.S. industry should take a proactive but logical approach to addressing the issue. Thus the WOG has initiated various project authorizations, outlined below, which are intended to address the various aspects of this issue such that the issue can be technically and economically managed to a successful resolution. mN!506w.wpf:115111095 j.} i i 4 ,,. ~, -

Understand the cause and extent of cracking experienced by the French in their plants. From this phase of the work the WOG concluded that the issue could impact selected US plants, j however the extent and/or time frame could not be immediately quantified. i a Assess the safety impacts of the issue. Detailed engineering analyses were conducted to - understand the extent and safety impacts of cracking. A generic safety evaluation was I performed and presented to the NRC. The conclusions were that the issue does not represent an immediate safety issue. The significar.cc of cracking is that it can result in leakage which could d result in wastage of the carbon steel vessel head. The WOG estimated wastage corrosion rates based on analysis performed by Westinghouse and experimental data provided by the i Combustion Engineering Owners Group. The conclusion was that wastage could alter the reactor vessel head however the ASME Code Allowable stresses would be naintained for a minimum of 6 years. i The experimental data used to estimate crack propagation for the thick walled Alloy 600 l 4 l penetration tubes, which was used in the flaw tolerance evaluation portion of the safety l t evaluation, was based on thin-walled Alloy 600 tubing. The WOG chose to investigate crack propagation rates in thick-walled Alloy 600 tubing to verify that the crack propagation model for thin-walled tubing was valid for use. Thus the WOG initiated a crack propagation tes:ing program to investigate this phenomenon. This work is scheduled to be completed in the fourth \\ quarter of 1994. I I l 1he WOG had the opportunity to confirm the mechanism of cracking in t" penetration tim. The [ ]*## plant, a Westinghouse supplied plant, has also experienced cracking l and has undettaken a program to investigate the cracking. As part of the Ringhals program q boat samples were removed from the ID of a penetration which has experienced cracking. The WOG was offered the opportunity to perform a failure evaluation on one of tiese boat samples. s Westinghouse performed this work under authorization [ ]"##. This work further confirrned the French findings that the cause of cracking was PWSCC. i The WOG has authorized a report outlining a Flaw Evaluation Procedure which is intended to identify the techniques required to estimate the propagation of any flaws detected by an inspection. i f m:uso6w.wpr;tM it095 12 i $r S t--

The WOG has supported an industry initiative coordinated by NUMARC to develop acceptance criteria for flaws detected along the inside diameter of reactor vessel closure head penetration tubes. These accepiance standards have been provided as the standard for acceptance of any flaws Wed during an in-plant inspection. Additionally, EPRI has applied these acceptance standards in developing a qualification program and standards for utilities to use in the qualification of vendors offering inspection services. The WOG has also solicited utility volunteers to perform pilot volumelde inspections of their reactor vessel closure head penetrations. The WOG intends to evaluate inspection results and assess the impact on the pilot and other W plants. i l

• Ihrough thw programs the WOG has attempted to deternune cause, address the safety significance of this issue, develop inspection and @ criteria, provide a mechanism to qualify vendors offering inspection services such that interpretation of results across the industry is consistent, and make l

available pilot inspection results ssch that the future actions / requirements with respect to this issue relative to the U.S. nuclear industry can be formulated. Lastly, the WOG authorized a program to develop a weld repair methodology for penetrations which have experienced cracking. The followmg 1 \\ document outlines the program and reports on the results of the weld repair program. 4 i 1 m:u506w.wpf;lb-111095 13 r. . + m

2.0 PROGRAM DESCRIPITON 4 2.1 Objectives l The objective of the program was to provide a weld design package which can be applied to repair - reactor vessel closure head penetration tube ID initimi PWSCC. The weld design study has investigated repair of partial through-wall and full tiecugh-wall cracks. The objective was to investigate'2 local weld repair prccs and a 360* weld overlay process as part of the weld design package. In addition to the weld repair process,infonnation regarding excavation geomen;es and post weld surface treatment was investigated.~ Excavation serves two purposes; 1) It provides access for application of the weld, and 2) It serves to remove any existing defects. For the purposes of this project authorization the post weld surface treatment investigated was shot peening. The objective of a ' post weld surface treatment such as shot peening is to negate / mitigate residual stresses la&wwi by welding. l In support of the weld repair processes Westinghouse investigated; 1) Excavation geometries and various depths as related to flaw geometry, 2) Limitation of the weld repair with respect to crack length, 3) 1he dermition of welding process parameters,4) 1he definition of allowable weld filler metals,5) Identification of the weld surface finish, 6) Requirements relative to the surface profile of l the penetration inside &mnwter,7) Industry suggested parameters for shot peening, and 8) Weld inspection requirements. *Ihc definition of these items provides a comprehensive definition of the process such that the utilities can irdpendently implement such a repair. In support of the repair process, Westinghouse performed a generic 50.59 Safety Evaluation such that a utility could license such a repair on an as needed basis. Also, this program provided engineering justification of the process through the preparation of a full size penetration mock-up to provide j !~ engineering data to enable evaluation of effects on penetration residual stress and deformation due to the weld overlay. 'Ihe change in stress was measured using a Hole Drilling Strain Gage Method in 3 1 . accordance with ASTM E837. Mock-up testing was also used to inveqigate the extent of weld shrinkage associated with the weld overlay process and the extent that the weld overlay process j impacts the shrink fit between the penetration tube and reactor vessel head. 1 J m:\\2506w.wp(:lkl11095 2-1

3 1 i 2.2. Weld Repair Program Outline i The development of a weld repair design package was structured to investigate specific weld process par n s and provide engineering justification for the various associated technical issues. In order to investigate the weld process parameters and technical issues several major program tasks were defined. { Each of these tasks along with a brief description follows: i Task 1 Development of Weld Overlay Repair Process Spcification: i 'Ihe Westinghouse weld repair process specification defines: A weld thickness of [ ]*## o [ - ]*## inches, defines critical welding process parameters, defines i t i allowable weld filler metals [ i l' '

• and identifiu weld surface finish requirements and inspection requirements.

Also, shot peening as a post weld surface treatment available for mitigation of post weld l residual stresses will be discussed. The documentation also defines target shot peening process parameters. Target shot peen process parameters were provided as a result of recon.mendations solicited from a commercial shot peen vendor and work performed by l Westinghouse, independent of this program authorization. Task 2 Define Penetration E cavation Geometry: K A drawing is supplied to compliment the penetration repair process to define such items the excavation geometry and depths for both an excavation only repair and excavation as: followed by a weld repair, the required ID profile of the penetration ID after the application of the weld overlay, and any limitations with respect to positioning the weld overlay relative to projected stress profiles in the penetrations. In addressing excavation of the penetration two aspects were addressed: 1) It was imperative that the structural adequacy of the penetration was not compromised, this was investigated via a review of available ASME code stress reports on the reactor vessel closure head, and 2) 'Ihe excavation geometry was defined such that adequate . m:U506w.wpf:1b-111095 2-2

l I penetration material was removed such that, application of the weld does not restrict the flow area in the penetration or thermal sleeve movement is not impacted. i Task 3 Provide Evaluation of Applying Weld Overlay Over Existing Cracks: } The effect of applying weld material over existing partial through wall and full through- [ wall cracks was investigated. The applicable ASME Code paragraphs were investigated, which discuss leaving cracks in the pressure boundary were nyiewed. Also EDM notches { were placed in mock-ups to assess impacts on the welding process. Task 4 Penetration Mock-up Tests: t A full size penetration mock-up was fabricate,i The mock-up was fabricated using an f i alloy 600 penetration tube welded in a plate of low alloy carbon steel using the partial j "J"-groove geometry for the attachment weld. The mock penetration tube was skewed to f i the surface of the plate to simulate the weld offset of actual penetration tube assembled in the reactor vessel closure head. The mock-up was used to investigate the application of weld material in a similar geometry to the penetration tube, and to quantify the addition of f any residual stresses on the ID adjacent to the weld repair. I Several mock penetration tubes were also fabricated to investigate the application of various weld thicknesses and geometries. The various weld thicknesses were evaluated for claddag integrity via a cross-section taken through the weld thickness. Task 5. Generic Safety Evaluation: A generic 50.59 safety evaluation was performed to aid WOG members in implementing a weld overlay repair at their specific plant sites. The Safety Evaluation is provided as a stand alone document. In completing the above tasks the stated goal was to identify engineermg justification and appropriate specifications for implementation of a local weld repair and a 360' weld overlay. Both weld repairs involve an appropriate amount of excavation from the penetration inside diameter followed by mA2506w.wpf:lkil1095 2-3

application of filler metal in the cravated area. In the case of the local weld repair the repair is i targeted at restoring the minimum required penetration tube wall to maintain the pressure boundary. For the 360* weld overlay the intent is to provide a remedial measure for mitigation of PWSCC. 'Ihe l 360* weld overlay would cover the entire inside surface of the penetration tube most susceptible to i PWSCC over some given length. f i e i I i r l l 1 i i .i 1 i I 1 i I i f m:US06w.ipf:1b 111095 2-4 9

3.0 APPROACH FOR DEVELOPMENT OF PENETRATION TUBE WELD REPAIR AND DVERLAY DESIGNS in developing the weld application options for the reactor vessel closure head penetration tubes, two basic designs were targeted; 1) A local weld repair process and 2) A 360* weld overlay process. 'Ihe l local weld repair prowss is targeted to restore the minimum required design thickness of the penetration tube wall. De 360* weld overlay repair is intended to provide a remedial measure to mitigate PWSCC in the Alloy 600 penetration tube ID. Refer to Figure 3.0-1 for an oveniew of the reactor vessel closure head to penetration tube geometry. 3.1 Local Weld Repair in designing a local weld repair several considerations were taken into account: De weld repair has to restore the minimum required design thickness. The governing design requirement with respect to the penetration tube is design pressure. An exammation of a typical 4-loop vessel head indicates that the required penetration tube thickness to meet design pressure requirements is approximately 0.29 inch. Slots were examined in [ ]'" Reference 6, as a potential repair for the reduction of residual surface stresses in the penetration tube ID. De maximum slot depth examined was [ ]'" inch. De industry flaw acceptar.cc criteria developed for penetration tubes identifies the depth of an allowable flaw to be 75% of the tube wall thickness or [ ]* " = { ]"" inch. Dus a weld overlay repair in a penetration excavated to a depth of [ ]"'*# inch may be required. in specifying the circumferential extent of the local weld repair designs, the stress analysis ' results reported in WCAP-13525, Reference 5, were taken into account as well as the slot widths examined in [ )*" Reference 6. For the purpose of the local weld repair the intent was to position the toe of the weld in an area of the penetration tube ID having relatively low hoop stresses. Dus circumferential extents of 45* and 90* were selected, such i I mM506w.wpf:Ib-ll1095 3-1 I li i

i i that the toe of the weld could be approximately located on the 45* axis of tim penetration tubes l where the hoop stresses were estimated to be low. I l -Additionally, lengths of'4 and 6 inches were ulected to investigate the variations which might occur due to changing the overall weld length. i ' Based on the above considerations local weld repelt design geometries with varying weld thicknesses { of[ }"## inch. overall lengths of 4 to 6 inches, and having circumferential extents of 45' through 90* were considered for investigation. 3.2 360' Weld Overlay i ' In performing a 360' weld overlay repair the two items taken into concideration were; 1) The weld i overlay depth should be thick enough to provide a boundary which prohibits exposure of the Alloy I 1 600 base material to the primary waer over the applied length of the repaar, and 2) The depth should be minimized such that any associated weld shrinkage minimizes the residual stress in the base material and does not negatively impact the interference fit on the OD of the penetration tube between the reactor vessel closure head and penetration tube. Based on the above a [ ]*## inch weld thickness was judged as appropriate to meet the above two t criteria. A thickness of[ ]*## inch is approximately [ ]*## weld passes. However, an overlay need not be Umited to [ ]*## inch. Weld overlay thickness of [ ]*## inch were investigated for lengths varying from 4 to 6 inches. i 'Ihe perceived advantages of the weld overlay are; 1) Application of the weld overlay can be a continuous process using a sparaling application, and 2) both ends of the weld overlay can be readily i positioned in lower stress regions of the penetration tube ID. 3.3 General Program Goal i In order to evaluate the above defined design geometries a series of tests and measurements were identified for investigation of a weld process which could be qualified to the ASME Section IX Code l requirements, Reference 2. Additionally, these test and measurements were used to assess technical l l m:\\2506w.wpf lb 111095 3-2 I r

i r i impacts such that the specification of weld repair would not negadvely impact the penetration tube geometry. 'these tests and measurements involved the fabrication of penetradon tube samples and a full size reactor vessel closure head / penetration tube mock-up as well as the investigation of methodologies for performing weld overlay repahs The following sections provide the details and results of these investigations. l i I i i i i ] 5 A t i f i i i i l ) ) mA25%w.wpf:1b 111095 33 l

i -~ R/V i Head l Penetration Tube b ) b s\\ A N s A Hill Side Confer Side 45* Axis Attachment ,- s/ [ Weld '[ \\ Outline e-4 See- \\ / \\ / / b _' 90* SECTION A-A Figure 3.01 Reactor Vessel casure Head to Penetration Tube Geometry 3-4

4.0 PENETRATION TUBE SAMPLE & REACTOR VESSEL HEAD / PENETRATION TUBE MOCK UP FABRICATION i 4.1 Preparation'of Penetration Tube Saniples Figure 4.1-1 depicts the geometry of the grooves machined in the 10 inch penetration tube samples. 1 '!he grooves were machined using electric discharge machming (EDM). As shown in Figure 4.1-1 the - 1 tube wall wt : machined to the defia cd depth and made use of a [ ]*## taper to blend the excavation l depth into the original tube inside diameter (2.75 inch). 'Ihe [ ]*## taper was applied both circumferentially and axially. For the groove depths of [ ]*## inch and [ ]*## inch the [ ]*## l t taper resulted in an acceptable geometry. However, for those samples with a groove depth of [ ]**# inch the taper was reduced to a ratio of [ J'##. The taper was reduced because the . ]"## aper was impractical from the standpoint that it extended two far around the penetration [ t circumference, requiring too much weld filler metal to fill in the taper transition area. After t performing weld repairs on the [ ' ]*## aper geometry process time was still too long and too much t weld filler metal was still required, thus an alternative transition design was identified for blending from the excavation depth to the inside surface of the penetration tube. The alternative transition is a typical weld "J" preparation applied in the industry and is depicted in Figure 4.1-2. 1 4.2 Fabrication of Reactor Vessel Closure Head / Penetration Tube Mock-Up A full scale mock-up of the reactor vessel closure head and penetration tube was fabricated to depict j . the most peripheral penetration in a 4-loop reactor vessel head, thus indicative of a penetration tube i with the greatest offset in the attachment weld, i.e. therefore the maximum residual stress. Fabrication sketches of the mockup are provided in Appendix C, Fabrication Data Package for the Penetration Mock-Up & Penetration Mock-Up Sketches. 'Ihe fabrication data package includes as-built dimensional data. -To validate the applicability of the mock up, measurements were taken of the penetration tube inside - diameter to measure the ovality which occurred as a result of performing the mock-up attachment weld. As in the actual reactor vessel head geometry, a "J" groove weld prep was used for the attachment weld between the penetration tube and low carbon steel plate. The maximum ovality t b sa:\\2506w.wpf:tb 't1995 4-1 4

(major diameter less minor diameter) which occurred in the mock-up was I J'" mils ([ J'## inch) as compared to the maximum approximated ovality of [ ]*## mils ([ j'## inch) estimated from the linear regression equation for ovality which was developed based on actual plant ovality measurements. Reference 1. ~ 4 i m:\\2506w.wpf:lti Il1095 42 1

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5.0 WELD PROCESS SPECIFICATION

A welding process specification, which can be used for either the local repair or application of the 360* weld overlay in the reactor vessel closure head penetration tubes was ;-.Ed and is attached in Appendix A of this WCAP report. The welding process specification is written to provide guirlance for the qualificadon of welding procedures to be used for the performance of welding in Westinghouse PWR reactor vessel closure head penetration tubes. The parameters recommended in the speci6 cation were based on the welding operations performed for this feasibility study. 'Iherefore, the parameters

' were quali6ed for the intended applications to the extent as disc'2sse * !n the following paragraphs. 5.1 Selection of Welding Equipment - An automated pulsed gas tungsten arc welding (GTAW) system designed and manufactured by The [ ]**# (power supply model 215, Figure 5.1-1, and model 94 ID claddmg and welding head, Figure 5.12), was. selected.

c. program. The model 94 weld head is designed for spiral cladding and groove welding inside eaueters as small as 2 inches. The model 94 provides arc rotation, axial (linear) travel, filler wire feed and arc voltage control (AVC) for are gap control. The combination of axial travel and are rotation provides a spiralling effect duectly applicable for use in a 360 degree weld metal overlay process.

To demonstrate the capabilities of the selected automated welding system and identify target welding parameters a pipe ID weld ov' rlay was performed on a 2 inch nickel base alloy pipe with inconel e 82 filler metal. The current design of the model 94 weld head feeds a 0.030 inch diameter weld wire. The filler metal of choice for this program, [ j'*# was not available in 0.030 inch diameter at the time of the demonstration. A 20 lb. spool of 0.035 in. diameter [ ]**# filler metal was obtained and reduced to the required 0.030 inch diameter. 5.2 Qualification of the Welding Parameters The intent of qualifying the parameters at the beginning of the program was to ensure that the starting parameters were appropriate for use wi h the [ ]**# filler metal. The staning parameters t were based on the parameters used with the [ ]" *# filler metal during the demonstration of the welding system. This approach was taken due to the limited supply of the [ ]'*# filler m:us06w.wpf;Ih.111095 5-1

s wire at the beginning of the program, and the long lead time required to reduce the diameter of the f . available weld wire to 0.030 inth. 'Ihe weld wire situation prevented any practice welding to establish welding parameters in advance with the [ ]"#. i i Two alloy 600 pipe assemblies were welded using [ }# filier metal to qualify the parameters to the ASME Section IX mechanical test requirements. Four 5-inch long pipe samples { were machined with' 37.5* grooves as shown in Figure 5.2-1. The 37.5' groove was' machined starting ~ from the ID of the pipe and finishing the groove at the OD of the pipe so that the groove could be welded from the pipe ID.' Starting process parameters for welding the pipe assemblies with the [ }"# filler metal were those. process parameters used in the demonstration with [ }"#. 'Ihe parameters were adjusted as . welding progressed. Some difficulties were epaaod in welding the first assembly, during the la' ltial two layers burn-through and stuck wire in the weld puddle occurred. Once the parameters were adjusted based on the difficulties, there was no problem with the subsequent layers of the first j assembly or the second assembly. Upon completion of welding the two pipe assemblies, mechanical i test coupons, i.e., tensile and bend (face and root) specimens, were machined from each assembi) in accordanz with ASME Section IX requirements. All bend specimens were free of cracks with the exception of the root bend specimen of the first matemhly. 'Ihe failure of the root bend was attributed j to the difficulties experienced as explained above. i . During welding of the qualificatfon p pe assemblies it was observed that inconel 52 filler metal has a very sluggish characteristic, even worse than [. )**#. "Ihis may be due to higher contents of Cr, Fe and deoxidizers such as Al and Ti in [ }"# compared to [ ]"#. The [. }"# filler metal mixed well with the alloy 600 penetration tube producing a relatively smooth surface, as was observed in the first layers of the pipe assemblies. 'Ihe subsequent layers, however, started showing the sluggish characteristics which produced a relatively rough surface in comparison. . In g'eneral the surface condition of a weld is controlled by grinding or machining operations after welding.' However, considering the actual field applications of this proceu it was desirable to improve the surface ccadition through weld process controls such that no grinding operation would be required after repair welding. ' As an attempt to improve the surface finish a [ ]"# n f m:\\2506w.wpf:ll>111095 .52 .i - -. J.

? s mixture of shielding gas was tried during the welding of the second pipe assembly. The [ ]*## mixture gas was tried because it was readily available for a similar application on a nickel base alloy. The change in the shielding gas did not imprnve the surface finish of the as-welded l condition. Thus the shielding gas was changed back to [ ]* *# gas. Welding process f parameters were adjusted during welding of the subsequent test tube samples to maximize the quality of the final surface finish. 5.3 Welding of Penetration Tube Samples i Table 5.31 shows the matrix of the eight [ ]*# penetration tube samples and their respective [ geometries. Repair welding of the tube samples started with sample number 4, which had a 360 degree groove of [ ]*# inches deep. Although the welding system was capable of welding f the groove in one spiral operation the operation was stopped every one (1) inch or so to maintain the 'nterpass temperature below [ ]*## maximum. The [ ]*# interpass temperature was selected because this is typical industry practice for minimizing distonion in stainless and nickel base alloys. Those samples with a partial groove, [ ]*##, required a similar interpass temperature control. It should be pointed out that the samples with a partial groove took a much longer time to weld due to the setup required for every pass. Each weld pass was performed circumferentially for this program. The necessity of a setup for evm/ pass could impose some difficulties on actual field applications for repair welding and special attention should be given in development of field tooling to minimize this impact. l As explained in the previous section during welding of the [ ]*## tube samples the parameters were adjusted to improve the weld surface finish, such that the surface smoothness could be maximized. Although surface finish appeared to be adequate, more improvement would appear to be possible. Welding of additional samples for funher adjustment of parameters would be beneficial as ' well as investigating the use of other shielding gases. Another possible shield' ing gas would be a helium / argon mixture. Other options, such as a combination of [ ]*## with [ ]**# and/or [ ]*## on the last layer should be considered. As *ndicated in the Table 5.3-1 tube sample number 7 and 8 included EDM notches in the repair area. This was to study repair welding over [ ]*##. Figures 5.3-1 through 5.3 3 depict the cross sections of repair welds over the EDM notches. The notches were i i t mA2506w.m;L11095 5-3 4 r

4 1 approximately [- ]"# inches deep and [ ]**# inch wide. L'Ihe metallography samples of the i n$ches showed no cracks or indications generated in the surrounding area due to the welding. j Considering [ t 1**#. i 1 ' 5.4. Welding Ranctor Vessel Oosure Head / Penetration Tube Mock-Up i i Two EDM grooves, Figure 4.12, were machined in the penetration mockup to simulate weld repairs i in the plant. It was learned from the [ }**# penetration tube samples that a 360* groove would - l be much easier to weld repar as opposed to the partial groove with the welding system available. Thus, partial grooves were selected for the mockup to investigate the potential difficulties which might i t 4 be experienmd in a field application. The [ }# inch groove depth was selected for the partial s i grooves as the most probable thickness of weld overlay to be used is a field application. 1 ' Repair welding the excavation areas in the mockup were performed very much the'same as in the f penetration tube samples. Since the mockup, Figure 5.4-1, had more mass to transfer the heat during j welding it was not necessary to stop the welding operation as often as in the [ J'*# inch penetration l tube' samples, to meet the [ ]A*# interpass temperature requirement. It is estimated that the interpass temperature control may not be a concern with the field application due to the mass of the penetration tube and surrounding reactor vessel closure head. J I i j 4 i \\ l t 5 3 4 1 mA2506w.wpf;1t>111095 .54 i i 1

...._~ _..... ~ _.. a.c.e ) 1 l ARC MACHINES, INC. i h E k J t 1 h j 4 4 4 I s 1 4 Figure 5.1 1 Weld Head Used for Weld Repair Program i ( E ? m:u$06w.wpf:Ib-111095 55

h A.C,e j i I i l ARC MACHINES, INC.- i t 1 I i i t I e ~ Figure 5.12 Weld Power Supply / Controller Used for Weld Repair Program m:U506w.wyt:1b.I11095 5-6

w b f i PIPE ON 1 - PlPE ID 0.050 in. --- /-37.5 dog. 0.030 in. land extension %. N 3/32l" R S in. 4 1 .4 4 'l } i t 1 f Figure 5.2-1 Joint Geometry for Qualification Samples 4 m:\\25%w.wpf:1t>l11095 5-7 ^

Table 5.3-1 TEST MATRIX FOR [ ]*## PENETRATION TUBE SAMPI.ES i R.C,C i i 1 l 1 eug.u 9 1 1 I m:uso6w.wpt: kitio95 5-8

l t - i i a,c.e t I l 6 I t i i I i, s i i t i I i 4 I i p i ? i ? I d i I 1 l Figure 5.31 Penetration Tube Sample No. 8 Cross-Section Showing Weld Repair 1 I [ ]*'** I 4 . m:250tm.wpf:lb 111095. 59 e 4 i

LA. A-l t - l i a,c.e f I ) i t f i I i ? i ? r f L a t d I l r J 4 I J v 1 i - 1 i' Figure 5.3 2 Penetration Tube Sample No. 8 Cross Section Showing [ - ]** . m:uso6w.wyt:1M11095 5-10 i l j

1 l .l a,c.e t h -1 4 S A .l t 5 1 I 4 '4 i i a i I 3 t i T !r j. s t i I L t t I t I l ( t i i Figure 5 3-3 Penetration Tube Sample No. 7 Cross-Section [ Iw* f 'mA2506w wys:1b-111495 5-11 I s i b m.

-. _ - ~.. i .1 1 i l 4 1,C,C i d nun naswes IHLARC 4 I ~ I {c p t l _L L g w ::- 1 /~9 l 7 'u g l .g- .I Jos n. f 7 \\ '- f. 1 j p, .e d ' ~ M l l w r 4 V } w l l-se K d,. . s'..:e iss.:::fr.;2m,,mm . r'f i ^ ,a l l l l 4 l 1 j Figure 5.4-1 Photograph Depicting Weld Tooling Set-Up In Full Size Penetration i I Tube Mock Up l i l I i mA2506w.wpf:Ib lll495 5-12 4 4 e .,-,,,,-,,--,---,-----,--------m--

~-... - -.. _ -. ~.. - - - } l &0 EVALUATION OF WELDED PENETRATION TUBE SAMPLES l The penetration tube' samples were used to evaluate the feasibility of welding within the 2.75 inch i i diameter of the penetration tube and to evaluate the impacts of the various selected geometries. - As i de6aed in Table 5.3-1, eight penetration tube samples were seMcted to explore the various weld repair geometries. The overall weld length, circumferential extent ard depth were varied. l 01 Discussion of Diametral Meraure.nents i To evaluate the penetration tube samples each sample had pre and post weld dimensional data taken. 'Ihe measurements were taken across both the inside and outside diameter in 0.5 inch increments over ) the entire length. ' 1he outside diameter measurements were used as the primary mechanism for l comparison as opposed to inside diameter mammwements in order to acid variations resulting from the weld surface finish and the weld applied thickness. Figures 6.1-1 through 6.18 provide plots of the dimensional data. The dimensional data as-measured pre and post welding is provided in Appendix D, Penetration Tube Dimensional Esta. l 1he penetration tubes were acribed to retain the orientation of the axis, i.e. 0*,45',90', and 135*. i lhe outside diameter measurements taken across each of these axis were very consistent and on the average were 4.000 +/- 0.001 inch. The pre-weld diametral measurements were averaged and plotted as a single line on Figures 61-1 through 6.1-8. Pcet weld measurements were taken across the same i axis and are pioned individually on each of their respective figures. i Basc! upon a review of Figures 6.1-1 through 6.1-8 the following observations were mn&- Regardless of the weld length (4 or 6 inches) the diametral dimensions are impaM over a length approximately 1 inch greater than the weld repair length. Recall the weld repair lengths do not include the taper length which is also filled with weld material. This would indicate that an approximately 0.5 inch transition zone exists from the end of the repair depth where weld shrinkage impacts the diametral meamwements. This transition zone appears to independent of weld depth or taper length. i l l mA2506w.wpf:lb.111095 6-1 b

- +- .+. u-an-i i A 360* weld repair results in deformation across each axis. The deformation is approximately [ uniform for each axis, Refer to Figures 6.1-2,6.1-4, and 6.1-8. i The deformation associated with a 90* weld repair also impacts each axis, particularly those j axis 45' from the weld centerline (i.e. primary axis). The 45' axis experiences deformation approximmely 30% to 40% of the primary axis. The axis 90* from the primary amb appears to be the least impacted See Mgure 6.1-3 and 6.15. In all penetration tube samples the deformation, resulting from weld shrmkage, appeared to l result in a decrease of the outside diameter except over a very few number oflocal positions, See Mgures 6.1-1, 6.1-5, and 6.1-7. i t On the average the deformations resulting from the various weld depths are: i Weld Depth - Average Deformation Maximum Deformation (inch) (inch) (inch) g ju.= g ju.e [ jue I i"# I 1"# [ 1"# { g jue g ju.e g ju.e These deformations are based orr the measurements taken in the []"# penetration tube samples. It is judged that deformation in the actual plant penetration tubes would be less because of the available mass to dissipate the welding heat input. l l mA2506w.wpf:1h111095 6-2 i

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7.0 RESIDUAL STRESS MEASUREMENTS ON REACTOR VESSEL HEAD / PENETRATION TUBE MOCK-UP 7.1 Approach to Residual Stress Measurement To determine the residual stresses buildup from welding the reactor vessel closure head and penetration tube full scale mock-up fabricated for this program was used. 'Ihe fabrication of the mockup was described in a previous section of this report. 'Ihe hole drilling med.ad of residual stress measurement was used for these measurements. A # S of the head penetration model and test fixture is shown in Figure 7,1-1. All of the. at m measurements were made on the ID of 4 4 L 71.e residual stress measurement program was divioed into three steps: l ja c.e 7.2 Hole Drilling Method This method involves mounting a three strain gage rosette at the location the measurement is required. J A small hole is drilled at the center of the rosette and the relieved strain is measured by the three gages of the rosette. The relieved strain and elastic constants of the material and constants for the rosette are used to calculate the residual stress. The rosette constants are obtained by calibration, either by the rosette manufacturer, or using the ASTM standard practices. The rosettes used were procured from Micro Measurements, gage model [ ]* *#. This is a special three element 45' rosette in a circular pattem The hole drilling method measures a near surface residual stress and is described in ASTM standard E-837-92. Stress is assumed to be uniform, or at worst, varying uniformly through the thickness of the object measured. For a unifonn stress field the accuracy is estimated within [ ]*##, m:u506w.wpf:1b.111095 71 i 1 4

7.2.1 Installation of Strain Gage Rosettes Rosette locations for each step are shown in Figures 7.2-1, 7.2-2, and 7.2-3. These figures depict i maps of the inside surface of the penetration tube and show the angular position and dimance from the inside end of the penetration tube. De rosette locations are also tabulated in Table 7.2-1. Rosettes were oriented with the number one gage in the axial direction of the mbe. The ID surface of the tube was prepared for installation of the strain gages by first cleaning with a chlorothen degrenser. The surfacc over which the stram gage rosettes were installed was dusted with micro sand blasters to give a mat finish for better adhesion of the stram gages. For mounting strain gage rosettes in the EDM unchined areas, in Step 2, the surface was first smoothed [ i ]*##. The welds i'. the weld repair area, in step 3, were ground to a flat surface suitable for strain gage installation. [ ]*## adhesive was used to bond the gages, i 7.2.2 Drilling Holes The setup for the residual stress measurements on the model is shown in Figures 7.2-4 and 7.2-5. Air i L abrasive machining was used to machine the holes. A special fixture (shown in Figure 7.1-1) was made to position the drill to target the center of the rosette. The rosettes are masked before drilling to i protect them from the abrasive. Strain readings are taken before and after drilling. Hole depth is determined by air pressure, abrasive size, nozzle diameter and time. [ jax.e 7.3 Test Results t The principal stresses and directions were calculated using the relieved strains and equations in { ASTM E 837. [ l )** # The relieved strains were corrected for transverse sensitivity and gage factor r variations. These factors are provided by the strain gage manufacturer (see Figure 7.3-1). The i equations for the calculation of residual stresses are: [ [ m:\\2506w.wpf:1b 111095 - 7-2 l I

i i ~ 1 i a,c.e i 2 i i i i i 1 'the equation for calculating the angle C from gage 1 of the rosette tc the nearer principal stress is: a.c4 i i. t . The relationslup of principal stress directions to the rosette is shown in Figure 7.3-2. s t i The results of the residual stress measurementc are given in Table 7.3-1. Residual stress versus i i distance from the end of the tube is shown in F gures 7.3-3 and 7.3-4. 4 7.4 Comparison of Test Results to ArJysis J { Elastic / Plastic analysis of the reactor w ssel closure head / penetration tube geometry has been l_ performed and documented in WCAP43525, Reference 5, also several repair geometries have been f i analyzed and documented in [ }"'*#, Reference 6. The elastic / plastic analysis are of 1-particular interest for mmparison with residual stress measurements taken in the reactor vessel closure head / penetration tube mock-up, because the measurements serve to validate both the analysis and i measurements. Also, the repair geometries examined local grooves (i.e. slots) as measures to reduce penetration tube residual stresees. { i i i .m:u506w.wpt:Iblito95 : 7-3 i

~.. While the hole drilling technique is a fairly accurate means for the measurement of residual stresses it should be noted that the measured elues represent an average stress over the depth of the hole, [- }***# loch in this case. Thus the measured stress value is slightly below the actual surface stress -l i on the order of magnitude of 10% The finite element analysis provides a calculation of the surface t stress. Figures ~7.4-1 through 7.4-4 provide plots of the penetration tube residual stress as calculated after welding (as-opposed to the residual + operating stress) as compared with the measured stress values. Figures 7.4-1 and 7.4-2 plot hoop stresses while Figures 7.4-3 and 7.4-4 provide plots of the j . axial stresses. Also, the plots distinguish between the penetration tube center side (180* orientation on l Figures 7.2-1,7.2-2, and 7.2-3) and hill side (0*/360' orientation). The plots depict in general the i same trends (peaks and valleys) between the measurements and the finite element calculations, also j fairly good quantitative agreement exists, particularly for the hoop stress values. I k Several other observations / comparisons were drawn from the hole drilling residual stress measurements i and finite element calculations (It should be noted that the residual stress measurement locations in i l i Table 7.3-1 identified with the same numerical value are approximately positioned with the same [ coordinates): j l 'Ihe machining of the grooves generally appeared to loweir stresses at the location measured. Hoop stresses were decreased at locations 4a, 8a, 9a,12a,14a and increased only at locations 3a. Axial stresses were decreased at locations 3a, 8a,9a,12a,14 and increased only I at location 4a. This generally supports the conclusions made in the analytical study of repair configurations, Reference 6. i Weld repair areas have fairly high residual stresses, the greatest measured value being a principal stress of [ l'*# ksi, see location lib on Figure 7.2-3. Although fairly high this value is comparable with the calculated surface stresses. Tensile stresses adjacent to the weld as indicated are fairly high but dissipate rather quickly, see locations lib and 16b on Figure 7.2 3. Adjacent to the weld the axial / hoop stresses are [ ]"*# ksi respectively, but drop to [ J' *# ksi less that 1 inch away, i l mA2506w.wpf:lb.111095 74

i I The j~a.iion tube stresses approaching the 45* axis are expected by analysis to be low approaching compression. A review of these stresses after welding, see location 12B and 14b, i in fact have compressive axlS stresses of[ ]*## and [ ]*## ksi with low hoop stresses i of[ ]*## and [ ]*## ksi. Axial and hoop stresses in the alloy 690 weld repair are higher than their corresponding values T j before welding, hoop stresses increasing by approximately [ ]*## ksi with the largest increase 4 being in the axial stress components [ ]*## ksi to [ ]*## ksi and [ ]*## ksi to i [ ]*## ksi, see locations 3/3b and 9/9b. i A review of measured principal stress in the penetration tube weld region prior to and after welding indicate an overall increase in surface stresses. F Although the individual measured stress components (axial and hoop) prior to and after welding indicate an overall increasein surface stresses the after welding values are comparable to I calculated values. Again, Figures 7.4.1 through 7.4.4 provide the calculated and measured stress component values prior to welding. 1 4 i ) m:uso6w.wpf:th:Hoa 75

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Figure 7.1 1 Overall Dimensions of Head Penetration Model 1

I and Air Abrasive Drill Positioning Fixture \\

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Table 7.3-1 RESIDUAL STRESS MEASUREMENTS IN REACTOR VESSEL HEAD / PENETRATION TUBE MOCK-LP a,c.e I 1 l 1 m:\\2506w wpf:1b.1I1095 7 13

i 1 a,c.e i i P k 1 I l I ] Figure 73-1 Hole Drilling Rosette Strain Gage Data J 1 1 m:usosw.wpcib 111095 7-M -l 1 u,.-

g J t a,c.e i > 4 l 1 e i i l i 1 t b t s 1 r d 4 i t i 1 4 i .f P E 4 4 a Figure 7.3 2 Relationship of Principal Stress Directions to Rosette Gages - mM506w.wpf:Ib 11to95 7-15 4 V r

i l = a,c.e 1 l r t i } v i t i i i i i f 9 i i t ~' Figure 7.3-3 ' Residual Stress Versus Distance From End of Tube for Step 1 at 180'. Location m:uso6w.wyr: M 11ons 7-16

.. ~ i 'I I i l a.c.e 4 t b i 1 ? i i i '1 4 i i i t I Figure 7.3 4 Residual Stress Versus Distance From End of Tube ) i for Step 1 at O' Location + m:u506w.wpf:lb-ll1095 7 17 't L t i

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R l-I 4-2 I = 3 Y G I l 8 1 I Figure 7.4-2 Residual Hoop Stres As-Measured Compared to Analytical Estirnate of Hoop Stress for Hill Side of h

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m. ~.... _,. _ E I I I= N t 6 U C ? I i I I I Figure 7.4-3 Residual Axial Stress As-Measured Compared to Analytical Estimates of Hoop Stress for Center Side of e as 1

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i 8.0 DISCUSSION OF POST WELD SURFACE TREATMENT I Post weld surface treatment of welds is typically performed to serve one or all of the following i functions: i '1) Improve the surface finish such that an acceptable surface is provided for performing post. weld inspections and/or future penetration tube inspections. i 2) Provide an acceptable geometry such that the funcdon of the component b not negatively f impacted. In the case of the penetration tube inside diameter, the inside diameter can not be reduced such that it impacts the thermal sleeve or reduces the flow path in the penetration tube ID to thermal sleeve OD annulus [ )"#. 3) Mitigate the residual stresses in the weld metal and adjacent base material which occur as a result of the welding process. In developing process requirements for welding, regardless ifit is to be used as a mitigative measure for PWSCC (360* overlay) or a repair to restore the penetration tube pressure boundary (local repair), i - ~._ items (1) and (2) above are intended to be addressed via process controls. 'Ihe post wdd surface ~ finish, item 1, and the post weld geometry, item 2, are intended to te controlled via weld process and inspections requirements. In order to address item 3 the WOG requested via the program authorization that shot peening be examined as the remedial measure for the mitigation of residu J stresses induced by weldinP. 8.1 General Discussion of Shot Peening Shot peening is a cold working process in which the surface of the material is bombarded with small spherical media called shot. Each piece of shot striking the material acts as a tiny peening hammer, imparting to the surface a small indentation or dimple. In order for the dimple to be created, the I surface fibers of the material must be yielded. The cold working process results in the application of beneficial compressive stresses being applied at or just below the material surface. Compressive stresses are beneficial in increasing resistance to fatigue failures and stress corrosion cracking. Benefits obtained due to cold working include hardening, intergrannular corrosion resistance and m:uso6w.wpf:lts1:1095 g.1 (i' _ r

~ ' surface texturing. Westinghouse has investigated shot peening as a mitigative technique for-application to the Alloy 600 penetration tube to increase the materials margin against primary water . stress corrosion cracking (PWSCC). 1 The maximum value of the residual compressive stress is often called the magnitude of the residual stress induced. Variations in the shot peening process have little effect on the magnitude of the compressive stress induced as long as the shot used is at least as hard as or harder than the material 4 being peened. The magnitude of the compcssive stress is pnmarily a function of'the base material p mechanical properties. As a general rule the magnitude of compressive stress induced has a value of at least one half the yield strength to a maximum of approximately 60% of the ultimate tensile strength.' For the minimum allowable mechanical propertiec listed for alloy 600 SB-166 & 167 this relates to a compressive stress range of [ 1"##. The energy of the shot is a function of the media size, material, hardness, velocity and impingement + angle. In order to specify, measure *and calibrate peening energy a method utilizing SAE1070 spong steel specimens, called Almen strips, was developed. There are three stamlard Almen scales currendy in use, each based on a different Almen strip thicirec. The three scales are the "N", "A", and "C" scale in increasing order ofintensity. The depth of the compressive layer is proportional to the Almen intensity. It should be noted that the magnitude of the compressive stress induced is independent of the compressive layer depth. Peening depth needs to be examined from two aspects; 1) The greater the depth the larger the impact on surface or subsurface material imperfections, and 2) The stress . distribution through the component has to be balanced, thus for the case of the penetration tube wal! an increase of compressive stress on the ID results in an increase in tensile stress on the OD. The maximum benefit of shot peening is realized when the surface is uniformly peened to a saturation energy level. Satu ation is defined as the earliest point where doubling the exposure time produces no more than a 10% increase in Almen intensity. 8.2 Shot Peen Parameters Westinghouse performed a feasibility study to investigated shot peening for the reactor vessel closure ' head penetration geometry. The two primary objectives of the feasibility were: i l , as:u506w.wpf:1k111095 82 _.i

I Show that tensile stresses on the inside diameter of the test chamber (;:: etration tube mock up) ] before shot peening were [ ]^ *#. i l 'Confhm that shot peening reduces these inside diameter tensile stresses to [ ]**#. The intent of these two objectives were to produce stresses in the penetration tube above the estimated threshold to PWSCC such that the penetration tube test chambers were susceptible to PWSCC. The shot peen process investigated did successfully reduce the su:ceptibility of the test chamber sample material to stress corrosion cracking in a series of laboratory tests. l 1hrough the speci6 cation of process control parameters an Almen intensides of [ ]"*# on the "N" scale were developed in the test chambers resulting in a compression layer depth of approxunately [ ]**#. It was estimated that the magnhude of compressive stress l induced was [ J'##, approximately [ J'*# of the ultimate tensile strength of the i material used in the test. Subsequent discussions with commercial shot peen vendors have indica.ed that it should be feasible to i develop Almen latensities of approximately 8 on the "C" scale resuidag in approximate compressive depth layers of[ ]* *#. Although the Almen inte'aity scales can not be directly related the approximate relationship between the two scales is: N = 0.lC or 10N = C. i 8.3 Conclusions Regarding Post Weld Surface Treatment f i A properly controlled shot peening process should a reliable remedial measure for the mitigation of i residual tensile stresses associated with'a weld overlay repair. It appears feasible that a shot peen process can be developed which would apply a compressive stress to the surface of the base material on the order of [ J# ksi or greater dependent on the base material properties to a depth [ ]*##, Such a process should increase the margin against PWSCC in the alloy 600 base material both in the heat affected zone adjacent to the weld and generally throughaut the penetration tube ID. l Much investigation has been given to the development of approaches to provide margin against cracking in the weld toe profile. One common methodology is to grind the weld toe profile such that ' m:\\2506w.wpf;lt8111095 83 )

1 l 4 l i l the geometric aiscontinuities are removed from this area. This practice could also prove beneficial to the penetration tube ID, either performed by itself or in combination with shot peening. "Ihe extent to which a utility wishes to pursue post weld surface treatment needs to be an individual utility decision i based on the technical merits and economic impacts. Clearly all post weld surface treatments add margin to weld life, each having its individual implementation costs and radiological impacts i r i I 3 t t ) l I ^ l l t l l L I h m:U$06w.wpf;1ts 111095 84 .k

i 9.0 DISCUSSION OF WELD OVERLAY REPAIRS 9.1 Penetration Tube Repair Parameters Generally, prior to the implementation of a weld overlay repair, any detected flaws will be evaluated against the industry acceptance standard using flaw evaluation techniques to determine if the flaws can be accepted as-is or need to be repaired. If repair is required or the utility chooses to implement a j repair, the next appropriate repair would be the removal of the defect. Ifit is either determined by volumetric inspecdon or during the course of defect removal that the minimum required penetration i tube wall tidekness is violated a repair of that penetration location would be required. As investigated via this WCAP report a weld overlay repair is viable option for that repair. 9.1.1 Eacavation Depths and Weld 'Ihickness As defined, the minimum required penetration tube wall thickness is approximately 0.3 inch. Excavation depths which leave a remaining wall ligament ofless than the required design thickness, -0.3 inch, would require a build up of the penetration tube wall. Additionally, another factor should be consider in specifying excavation depths. Excavation of the penetration tube wall and subsequent repair weld' e could result in a heat affected zone in the reactor vessel closure head base material. To avoid having to perform a post weld heat treatment of the weld repaired area and adjacent reactor vessel closure head base material it is suggested that some minimum ligament be maintained in the penetration tube wall. [ ] It is judged that this thickness could be directly applied for use in repair of the penetration tube wall. Thus during excavation it is suggested that a minimum penetration tube wall thickness (ligament) of [ ] inch be m'aintained. Based on the above discussion the following' criteria are suggested for repair of reactor vessel closure head penetration tubes: Any defects detected in the penetration tube wall surface should first be repaired by excavation. No additional repair is required if the excavation depth does not violate the minimum required design basis thickness, approximately 0.3 inch. 4 mA1506w.wpf:ltw111095 91

If excavation to a depth of 1 )*## inch does not remove the entire defect, excavation should continue until the defect is removed or until l }*## inch' of the penetration tube wall remains. A weld repair to restore the minimum required design thickness needs to take into consideration. the remaining rcysle penetration tube wall thickness such that the acceptable tube wall after repair welding is 0.3 inch or greater. For example; if the flaw were through wall, no remaining v=/tsie penetration tube wall thickness would exist and the minimum required weld overlay thickness would be 0.3 inch. Conversely, if the remaining Ecapesle tube wall thickness were [ ]*## inch, the minimum required weld overlay thickness would be [ }*## inch, such that the total thickness was 0.3 bch. 9.1.2 Repair Geometry 1 As reponed welding does provide an overall increase in the surface principle stresses of the penetration tube. 'Ihese residual stresses are comparable in magnitude to the maximum residual plus operating stresses estimated via the clastic / plastic analysis for the outermost penetration tubes. It is difficult to quantify the impacts this increase in stress would have on the susceptibility of the alloy 600 base material to PWSCC. However,it would seem appropriate to estimm Lt the areas of the penetration tube adjacent to the weld would be more susceptible to PWSCC than the alloy 600 base material not impacted by the welding process. Of course, the alloy 690 weld filler metal should not be susceptible to PWSCC as compared wihn the base material. As discussed previously, the toe of the weld could potentially be positioned, by design,in areas of the penetration tube estimated to initially have relatively low stresses by comparison. 'Ihe intent being that the increase in stress due to welding will result in final stresses of lower magnitude than if the toe of the weld were positioned in a high stress region initially. l These considerations directly impact the selection of weld repair circumferential extent. I ms506w.wpr:1b.111095 92 l

8 As investigated in this WCAP, if it is desirable to locate the toe of the weld outside the ' omparably c high stress zones in the penetration tube ID, the circumferential extent of the weld should be selected ^ I sudt that it falls along the [ ).*## Or as discussed in Section 8.0, post weld . surface tramemene(s) could be used as a means to possibly mitigate the residual stresses inthwd by . welding. t

'The specific local weld repair geometry a utility' wishes to pursue needs to be an individual utility i

decision based on the technical merits and economic impacts Westinghouse drawing [ ],*## attached in Appendix B, depicts the various weld repair geometry requirements and suggesse'd repair l ,ronies. j Drawing '[ ' }'## also depicts the geometries naarrimeart with a 360* weld overlay. As stated . carlier a 360* weld' overlay repair was investigated to offer a remedial repair which could generally be implemented to mitigate PWSCC in the highly susceptible region of the penetration tube ID. 9.1.3 Weld Surface Finish

• Ihe surface finish achieved in the application of a local weld repair or 360' weld overlay in the reactor vessel closse head penetration tubes is important from two aspects; l) An acceptable weld surface finish is desirable m permit inspection of the weld and penetration tube base material, and

2) ' Die smoother the weld surface finish the less susceptible the weld filler metal is to the initiation of surface cracks.

The intent as discussed in development of the weld process perms was to refine the parameters such that the best possible surface finish could be achieved. The goal was to achieve a surface finish that would permit the volumetric inspection (ECT and/or UT) of the weld filler metal and base metal without having to rework the weld surface finish by some post weld machining operation. While rework of the surface is permissible the intent was to avoid the time and cost associated with rework of the surface.. A realistic target surface finish judged to be achievable via the weld process and yet-permissible for volumenic inspection was [ )."## in the development work performed a[ . J'## was achieved over limited lengths'of applied weld, but over the full 6 inch length weld applied in the penetration tube samples the [ ]*## surface finish was . not maintained, m:uso6w.wpt:Ib.1i1095 93-

4 It is suggested that the final check / qualification of the applied welding process should be verification that the final weld geometry / surface finish could be volumetrically lap d, using ECT as a l minimum. 9.I.4 ASME Code Approach to Weld Repair Repair welding is inwadad to be performed to the guidelines established in Section XI of the ASME Code. However, Section XI does not specifically define guidelines for what depdi of flaws must be t repaired in the reactor vessel closure head penetration tube ID. In applying weld repair to re-establish j the minimum required design thickness of tie penetration tube wall no code ambiguities seem to exist for the case where the defects have been totally removed.. ( pc.e a,c.e i 4 i i 9.1.5 Post Weld Inspection Requirements ASME Code Section XI Subsection IWA-4500 outlines the guidelines for inspections of repair welds made to pressure boundary components. 'Ihe code requires that a baseline volumetric inspection be performed of the weld repair for future reference, this is also consistent with the general guidelines m:u5h.wpf;IkiI1095 94

4 t outlined for repair welds made to base metal by the cornponent fabricator, ASME Section III l . Subsection NB-4130. 9.2 Conclusions - .l In summary the following conclusions are made: q ue i i 4 e i t f t P L I i m:u506w.wpf:Ib111095' 95 f' ? I {

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10.0 REFERENCES

a,c.e j 2. ASME Boiler and Pressure Vessel Code, Section IX, " Welding and Brazing Qualifications," 1989 Edition, ASME, New York, New York, July 1,1989 3. ASME Boiler and Pressure Vessel Code, Section XI, " Rules for Inservice Inspection of Nuclear l Power Plant Connponents," 1989 Edition, ASME, New York, New York, July 1,1989 r a,c.e i 1 i l 1 l i i m:u$06w.wpf:Ib-ll1095 10-1 i

APPENDIX A WELDING PROCESS SPECIFICATION 1 1 1 m:\\2506w.wpf:1k111095 A-1

t i REPAIR WELDING OF REACTOR VESSEL CLOSURE HEAD PENETRATIONS I [ l'" l ' SAFETY REQUIREMENTS: Personnel responsible for welding application shall have a safety and industrial hygiene program for handling hazardous materials and arc welding equipment (ANSI B7.1, ZA3 and Z49.1) I i 1.0 }.CQEg a,c.e I 4 1.2 This process specification is applicable to the Safety related ASME Code items. The applicable code issue'and/or other requirements will be specified in the equipment specification or procurement document. ] 1.3 This promas speci6 cation is intended as a guide for the qualification of welding procedures and for the performance of welding on Westinghouse Nuclear Steam Supply System Components. Any exceptions to or deviations from the requirements s of this specification must be documented in writing and submitted to _WNTD l (Westinghouse Nuclear Technology Division), Materials and Engineering Mechanics, l at the time the welding procedure is submitted for approval. 2.0 REFERENCE DOCUMENTS d 2.1 ASME Boiler and Pressure Vessel Code Section IX " Welding and Brazing Qualifications". I 2.2 ASME Code Case 2142. 6 au.506w.wpf:lkil1095 - A-2

f a,c.e - 3 2.4 Additional documents that may be referenced in design specification, drawings and/or procurement documents. b 3.0 MATERIALS 3.1 Base Materials 3.1.1 Nickel-Chromium-iron Alloy base material in the solution annealed condition, ASME Section IX classification P-43. 32 Filler Materials a,c.e 3.3 Electrode a,c.e 3.4 Shieldine Gas 3.4.1 The shielding gas shall be welding grade [ ]*. I m:uso6w.wpt:1b.1 1095 A-3

4.0 PROCEDURE REOUIREMENTS j 4.1 Oualification i ' All weld procedure specifications and welding personnel shall be qualified to the requirements of Section XI of the ASME Code. Exceptions to this regarement will only be permitted by written approval ofE, NTD, prior to any welding being performed on components. 4.2 Eauipment a,c.e i 4.3 Joint Geometry & Preparadon 4.3.1 Weld joint geometry shall be in accordance with the drawing number [ )*C# attached in Appendix C. 4.3.2 The joint geometry shall be prepared by [ ]" *#. 1,c.e m:\\2506w.wpf:Ib.ll1095 A.4

} 4.4 ' Electrical Charactetistics a,c.e A 4.5 Waw-- Pa= Mon - All welding shan oc done in the horizontal (2G) position where possible. 4.6 Preheat and laearnans Tamaarature 7 a,c,e 4.7 Postweld Heat T'raatmaat Postweld Heat Treatment (PWHT) is not required, nor permitted, unless specified in design specification, design drawings or other contractual documents. 4.8 Techniaue 4.8.1 Filler metal diameter shall be suitable for the base material thickness and weld joint configuration used in the component. [ ]*## diameter is required for the parameters in table 1. a,c.e 4 d 4.8.2 Deposition Method 4.8.2.1 All welds must be deposited with stringer beads. m:uso6w.wpt:Ib.111095 A.5

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i 4.8.3 lateroass Cleaning l a,c.e l a,c,c I i 4.9 .T._oline & Fixturine

• o 4.9.1 Discretion shall be used in the selection of material for tooling and fixturing for parts being welded such that there will be no detrimental effects to the weldment due to contaralantion as a result of heating, rubbing, smearing or excessive clamping pressure.

a,C,e 5.0 OUALITY ASSURANCE 5.1 Fabricators Quality System Quality Release Requirements, Data Packages, and i witness and notification points, when required, shall be as specified in the procurement documents. 5.1.1 Weld procedures shall be submitted to W NTD, or its designee, for review and approval. Any deviation from the requirements of this speciScation shall be I muso6w.wpfab.111095 .A-6

resolved by W NTD, Materials and Engineering Mechanics, as specified in Paragraph 1.3 of this specification. 5.1.2 All nondestructive examination procedures shall be submitted to W NID, or its designee for review and approval. Any procedure requirements not in q compliance with Code or procurement document requirements shall be resolved by W NTD, as specified in paragraph 1.3 of this specification. 5.2 All welding inspections shall be in accordance with applicable code requirements i and/or design speci6 cations and drawings. i 9 m:\\2506w.wpf:115111095 A-7

~... 4 t Table 1 - MACHINE WELDING PARAMETERS l, i 2 i ~ '. I W Funcdon e 4 } Tinte-3 ~8,c.c j 4 k 2 1 r i i d i i t l t l 5 I ? .t 5 t t i L F E t m:\\2506w.wpf:Ib-111095 - A-8 t

9 8 9 1 APPENDIX B WELD REPAIR DRAWING a J A d d m:u506w.wpf:Ib Il1095 B.1

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APPENDIX C i DATA PACKAGE FOR THE PENETRATION MOCK-UP PENETRATION MOCK-UP SKETCHES b All of this section is proprietary "## I This Appendix C, pages C-1 thru C-31, contains danil dimemional data on the penetration mock-up test piece and material certifications that apply to the components within the mock-ups. Also contained are proprietary Wda@2=a sub vendor informanan i l mM506w 1.wpf:1b-111795 C1

s. i 1 I I 1 i 1 v j 2 i ) i j APPENDIX D j PENETRATION TUBE DIMENSIONAL DATA 4 4 All of this section is proprietary **#8 This Appendix D, pages D-1 thru D-33, contains detail diametrical measurement data on the l penetralian mock-up tube camplee before and after weld repar. Also contaimi are propnetary Westinghouse sub vendor informatica 4, 3 e 1 4 i l 4 i i m:\\2506w-1.wpf:Ib 111795 D-1 i .}}