L-PI-08-090, Stress Analysis Summary Report of Preemptive Structural Weld Overlay for the Unit 2 Pressurizer Surge Nozzle

Stress Analysis Summary Report of Preemptive Structural Weld Overlay for the Unit 2 Pressurizer Surge Nozzle

ML082900808
Person / Time
Site:	Prairie Island
Issue date:	10/16/2008
From:	Wadley M Northern States Power Co, Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-PI-08-090, TAC MD5868
Download: ML082900808 (20)

Text

@

/ Xcel Energye L-PI-08-090 10 CFR 50.55a U S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie lsland Nuclear Generating Plant Unit 2 Docket 50-306 License No. DPR-60 Stress Analvsis Summary Report of Preemptive Structural Weld Overlav for the Unit 2 Pressurizer Surge Nozzle (TAC No. MD5868)

References:

1) Letter from NMC to NRC Document Control Desk, L-PI-07-054, "10 CFR 50.55a Request: Proposed Alternatives for Application of Structural Weld Overlay to the Prairie lsland Nuclear Generating Plant Unit 2 Pressurizer Surge Nozzle Weld (2-RR-4-8)," dated June 25,2007 (ML071760332)

2) Letter from NMC to NRC Document Control Desk, L-PI-08-003, "Response to Request for Additional Information Regarding 10 CFR 50.55a Request for Relief from ASME Section XI Repair and Replacement Requirements: Proposed Alternatives for Application of Structural Weld Overlay to the Prairie lsland Nuclear Generating Plant Unit 2 Pressurizer Surge Nozzle Weld (2-RR-4-8)

(TAC MD5868),19dated January 15,2008 (ML081510906)

3) Letter from NMC to NRC Document Control Desk, L-PI-08-041, "Additional Commitment Regarding 10 CFR 50.55a Request:

Proposed Alternatives for Application of Structural Weld Overlay to the Prairie lsland Nuclear Generating Plant Unit 2 Pressurizer Surge Nozzle Weld (2-RR-4-8) (TAC MD5868),11dated May 7, 2008 (ML081280890)

4) Letter from NRC to NMC, "Prairie lsland Nuclear Generating Plant, Unit 2 - Alternative to ASME Code,Section XI, Structural Weld Overlay of Pressurizer Surge Nozzle Weld, Alternative Request No.

2-RR-4-8, Revision 1 (TAC NO. MD5868)j1dated June 15, 2008 (MLO81360646) 1717 Wakonade Drive East Welch, Minnesota 55089-9642 Telephone: 651.388.1121

Document Control Desk Page 2 By letter dated June 25, 2007 (Reference I ) , and pursuant to 10 CFR 50.55a(a)(3), Nuclear Management Company, LLC, (NMC) requested U.S. Nuclear Regulatory (NRC) approval of 10 CFR 50.55a Request 2-RR-4-8, Revision 0, for the Prairie Island Nuclear Generating Plant (PINGP). Relief was requested to support the PINGP's installation of a preemptive full structural weld overlay on the pressurizer surge line nozzle-to-safe end dissimilar metal and safe end-to-reducer stainless steel butt welds during the Unit 2 refueling outage (2R25). The original 10 CFR 50.55a request was revised (2-RR-4-8, Revision 1) and supplemented with responses to NRC requests for additional information (RAI) on January 15, 2008 (Reference 2). An additional commitment regarding the inservice inspection requirements in the 10 CFR 50.55a request was submitted May 7, 2008 (Reference 3). The NRC authorized the use of 2-RR-4-8, Revision 1 on June 15, 2008 (Reference 4).

As part of the 10 CFR 50.55a request, NMC committed to submitting a stress analysis summary demonstrating that the pressurizer nozzle will perform its intended design functions after the preemptive full structural weld overlay installation. The stress analysis report will include results showing that the requirements of NB-3200 and NB-3600 of the ASME code Section Ill are satisfied. The results will show that the postulated crack including its growth in the nozzle will not adversely affect the integrity of the overlaid welds. This commitment required submittal of the stress analysis summary report prior to Mode 4 start-up.

Subsection NB-3600 of the ASME Section Ill code applies to the piping attached to the nozzle. An evaluation of the attached piping was performed to verify that the full structural weld overlay would not adversely affect the surge line. This evaluation analyzed the effects of weld shrinkage, additional nozzle weight, and increased stiffness at the joint. The full structural weld overlay was found to not have any significant impact on the attached piping or supports. Therefore, subsection NB-3600 of the ASME Section Ill code does not apply to this full structural weld overlay.

The enclosures to this letter contain the required weld overlay stress analysis summary report and the crack growth analysis summary report. With the completion of the scheduled full structural weld overlay on the pressurizer nozzle and submittal of the enclosed summaries by Northern States Power Company -

Minnesota, commitment number 2 of the Reference 1 letter has been fulfilled.

Any reference to NMC in the enclosed summaries also refers to Northern States Power Company - Minnesota.

Document Control Desk Page 3 Summary of Commitments This letter contains no new commitments. This letter closes out one commitment (commitment 2) made to support the 2-RR-4-8, Revision 1. This commitment was:

2. NMC will submit to the NRC a stress analysis summary demonstrating that the pressurizer nozzle will perform its intended design functions after the full structural weld overlay installation. The stress analysis report will include results showing that the requirements of NB-3200 and NB-3600 of the ASME code, Section Ill are satisfied. The results will show that the postulated crack including its growth in the nozzle will not adversely affect the integrity of the overlaid welds. This information will be submitted prior to Mode 4 start-up.

Michael D. Wadley Site Vice president Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota Enclosures (2) cc: Administrator, Region Ill, USNRC Project Manager, Prairie Island Nuclear Generating Plant, USNRC Resident Inspector, Prairie Island Nuclear Generating Plant, USNRC Chief Boiler Inspector, State of Minnesota

Enclosure 1 to L-PI-08-090 Prairie Island Unit 2 Pressurizer Surge Nozzle Weld Overlay Stress Analysis Summary

9 0402-01-F01 (20687) (Rev. 012,04/04/2008)

CALCULATION

SUMMARY

SHEET (CSS)

Title Prairie Island Unit 2 Pressurizer Surge Nozzle Weld Overlay Stress Analysis Summary The purpose of this document is to summarize the pressurizer surge nozzle weld overlay stress analysis based on the calculation 32-9044661-002 (Reference 1).

Summary Of Results:

The calculation 32-9044661-002 (Reference 1) demonstrates that the Prairie Island Unit 2 pressurizer nozzle weld overlay meets the applicable stress and fatigue requirements of the 1998 with Addenda through 2000 ASME B&PV Code, Section Ill (Reference 3) for all deflned operating load conditions.

The results of the conservative fatigue analysis Indicates that the maximum fatigue usage factor for the nozzle with weld overlay is 0.665 for 40 year design life or 60 year extended operation, which Is below the ASME acceptance criteria of 1.0, THE DOCUMENT CONTAINS ASSUMPTIONS THAT MUST BE THE FOLLOWING COMPUTER CODES HAVE BEEN USED IN THIS DOCUMENT: VERIFIED PRIOR TO USE ON SAFETY-RELATED WORK CODENERSIONIREV CODENERSlONlREV YES IXI No AREVA NP Inc., an AREVA and Slernens company Page 1 of 10

0402-01.F01 (20697) (Rev. 012, 04/04/2008)

AREVA AREVA NP Inc.. Document No. 86-9092967-000 an AREVA and Slsmens coinpnpany Pralrie island Unit 2 Pressurizer Surge Nozzle Weld Overlay Stress Analysls Summary Signature Block Pages/Sectlons Name PlRlA PreparedlRevlewedlApproved (printed or typed) and and and Title Signature LPILR Date CommentslRevlew Method Amy Chen P All Principal Engineer 1 0/ ~ / O ~ S T .

Tomas Straka R All, detailed design review Principal Engineer . /o/t/o 8 Tim Wiger -d&&~--- A /0/7/08 &

• . M y . $

Note: PIRIA designates Preparer (P), Reviewer (R), Approver (A);

LPILR designates Lead Preparer (LP), Lead Reviewer (LR)

Page 2

0402-01-F01 (20697) (Rev. 012, 04/04/2008)

AREVA ARBVA NP Inc., Document No. 86-9092967-000 an ARBVA and Slemonr company Prairie Island Unit 2 Pressurizer Surge Nozzle Weld Overlay Stress Analysls Summary Record of Revlslon Revision PageslSectlonsl No. Date Paragraphs Changed Brief Descrlptlon I Change Authorlzatlon 000 10/2008 All lnltlal Release Page 3

AREVA .

Document No 66-9092967-000 AREVA NP Inc.,

an AREVA and Slemens company Prairie Island Unlt 2 Pressurizer Surge Nozzle Weld Overlay Stress Analysis Summary Table of Contents Page SIGNATURE BLOCK.............. . . ................................................................................................... 2 RECORD OF REVISION ....................................................................................................................... 3

1.0 INTRODUCTION

............ .......................................................................................................... 5 1.1 Purpose .....................

5 1.2 Analytical Methodology........ . . .....................................................................................................

5 2.0 ASSUMPTIONS ........................................................................................................................ 5 3.0 RESULTS.................................................................................................................................. 6 3.1 Primary Stress Intensity Criteria for Design and Service Level Conditions......................................6 3.2 Minimum Pressure Thickness and Reinforcement Area Criteria ...................................... 6 3.3 Primary Plus Secondary Stress Intensity (NB-3222.2).................................................................... 6 3.4 Simplified Elastic-Plastic Analysis (NB-3228.5) ...............................................................................6 3.4.1 Primary Plus Secondary SI Range Excluding Thermal Bending Stresses NB-3228.5(a)6 -

3.4.2 Factor Ke - NB-3228.5(b)................................................................................................... 7 3.4.3 -

Fatigue Usage Factor NB-3228.5(c) and NB-3222.4 .................... . . . . ................7 3.4.4 Thermal Stress Ratchet - NB-3228.5(d) and NB-3222.5 ................................................. 7 3.4.5 -

Temperature Limits NB-3228.5(e) ...................... . . ..... . .............................................7 3.4.6 Minimum Strength Ratio - NB-3228.5(f) ............................................................................7 3.5 Elastic-Plastic Analysis (NB-3228.4) ................................................................................................ 8

4.0 CONCLUSION

........................................................................................................................ 9

5.0 REFERENCES

........................................... .... .................... . ........................................... 10 Page 4

A Document No. 88-9092987-000 AREVA AREVA NP Inc..

an AREVA end Slemenr company Prairie Island Unlt 2 Pressurizer Surge Nozzle Weld Overlay Stress Analysis Summary

1.0 INTRODUCTION

1.1 Purpose The purpose of this document is to summarize the pressurizer nozzle weld overlay stress analysis based on Reference 1.

1.2 Analytical Methodology Stress analyses were performed for Prairie Island Unit 2 pressurizer nozzle weld overlay In compliance with Reference 3, 1998 through Addenda 2000 ASME B&PV Code, Sectlon Ill, Subsection NB-3000 criteria for the defined operating load conditions.

2-D and 3-D finite element models with thermal and structural elements were developed for the nozzle weld overlay stress analyses.

The results of the thermal analysis are evaluated to identify the maximum temperature gradients and temperature distribution throughout the structure. Stress analyses are performed under mechanical (internal pressure) and thermal (temperature gradients) loads at all time points of interest, at which the maximum thermal stresses may develop. The overall and localized stress is reviewed at the path lines through the model at locations where stresses are maximal. All locations where the 3Smlimit is exceeded are evaluated by the simplified elastic-plastic analysis. The critical paths TS and PPI, where the stress limit 3Smcannot be met by simplified elastic-plastic analysis, were evaluated by elastic-plastic analysis. The stresses for all loading conditions and fatigue usage factors are compared to the ASME code criteria. ANSYS and ANSYS Workbench version 11.0 were used for finite element analysis and stress intensity range calculation.

2.0 ASSUMPTIONS There are no major assumptions used in the summarized document, Reference 1.

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AREVA Document No. 86-9092067-000 AREVA NP Inc.,

an AREVA and Slomona company Prairie island Unlt 2 Pressurizer Surge Nozzle Weld Overlay Stress Analysls Summary 3.0 RESULTS 3.1 Primary Stress lntenslty Criteria for Design and Servlce Level Condltlons The weld overlay reinforces the nozzle and relieves the prlmary stress under the internal pressure and external loads. This primary stress intensity criteria has been met as addressed by the original deslgn.

Therefore, primary stress requirements of Reference 3 for design and all service level conditions are met for the surge nozzle with weld overlay.

3.2 Minimum Pressure Thickness and Reinforcement Area Crlterla Adding weld overlay will increase the nozzle wail thickness. As a result, the Reference 3 requirements of minimum thickness and reinforcement area in NB-3324 and 1\18-3330 are met.

3.3 Primary Plus Secondary Stress lntenslty (NB-3222.2)

The maximum primary plus secondary stress intensity range is obtained by conservatlvely adding the maximum membrane plus bending stress intensity (SI) range under operating transients and the nozzle external (OBE+ thermal) loads. Reference 1, Table 9-3 gives maximal primary plus secondary (M+B)

SI range at predetermined paths along the weld overlay. The maximum primary plus secondary stress Intensity criteria is not met for some of the path lines. Therefore, the paths with stresses exceed the 3Smlimit are listed for further qualification.

The highest SI range in the weld overlay is 99.847 ksi > 3Sm=46.08 ksi at the inside node of path TS.

3.4 Simplified Elastic-Plastic Analysis (NB-3228.5)

Per NB-3228.5 of the Reference 3, the primary plus secondary stress intensity range in the model may exceed 3Smif the requirements of the simplified elastic-plastic analysis are met.

3.4.1 Primary Plus Secondary SI Range Excluding Thermal Bending Stresses NB-3228.5(a) -

The range of Primary plus secondary membrane plus bending stress intensity, excluding thermal bending stress intensity shall be less than 3S,.

The requirement has been satisfied for all the locations (except the path TS) where the SI range is above the 3Smlimit by the simplified elastic-plastic analysis.

The maximum primary plus secondary membrane plus bending stress intensity, excluding thermal bending stress intensity range (Tables 9-4 and 9-5, Reference 1) is 44.78 ksi c 38, = 44.88 ksi.

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A Document No. 86-9092867-000 AREVA AREVA NP Inc.,

an AREVA and Slamanr company Prairie Island Unit 2 Pressurizer Surge Nozzle Weld Overlay Stress Analysis Summary 3.4.2 Factor Ke NB-3228.6(b)

The Ke factors are applied to values of Saltused in the calculation of the fatigue usage factor.

3.4.3 Fatigue Usage Factor NB-3228.6(c) and NB-3222.4 i

The fatigue usage factor of the nozzle weld overlay is calculated for 40 year design life per Reference 2 where plan life extension to 60 years is based on the original number of operating cycles.

For consideration of fatigue usage, the Peak Stress Intensity (SI) Ranges are calculated. At a geometric discontinuity, an unrealistic peak stress may result from the modeling approach, element type and mesh sizes. The total stress obtained from the finite element analysis may not be able to capture the actual stress condition. To account for the possible modeling inaccuracies, a Fatigue Strength Reduction Factor (FSRF) is usually applied to the M+B stress intensity range for location experiencing the discontinuity. The maximum stress intensity ranges due to OBE and thermal loads are conservatively added to the stress ranges of the transients.

The highest cumulative fatigue usage factor is 0.665 < 1.0; therefore, the ASME Code requirement is met for these locations.

3.4.4 Thermal Stress Ratchet NB-3228,5(d) and NB-3222.5 The requirements NB-3228.5(d) and NB3222.5 are met at all locations (except the path PPI), where the 3S, limit is exceeded, using the simplified elastic-plastic or plastic analyses.

The maximum allowable range of thermal stress is determined per NB3222.5.

The maximum range of thermal stress is 108.64 ksi at path TS; this is less than allowable stress 115.35 ksi, therefore the requirements is met at these locations.

3.4.5 Temperature Limits NB-3228.5(e) -

The maximum temperature of the weld overlay is 680 OF. The maximum allowable temperature for the Alloy 52M (690) material is 800F (Table NB-3228.5(b)-1).

Therefore, the ASME Code requirement is met.

3.4.6 Minimum Strength Ratio NB-3228.5(f) -

The material shall have a ratio of specified minimum yield strength S, to minimum tensile strength S, less the 0.80; the maximum allowable ratio of S, / S, = 0.8 (NB-3228.5(f)),

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h Document No. 86-9092967-000 AREVA AREVA NP Inc.,

m AREVA and Slomen~company Prairie Island Unlt 2 Pressurizer Surge Nozzle Weld Overlay Stress Analysis Summary Ratios of S, to Sy are 0.38, 0.40, 0.41 < 0.8 All Minimum Strength Ratios are less than 0.8; therefore, this Reference 3 requirement is met, 3.6 Elastic-Plastic Analysls (NB-3228.4)

The critical path lines TS and PPI, where the stress limit 3S, cannot be met and simplified elastlc-plastic analysis methodology Is not permitted, were evaluated in accordance with NB-3228.4 -

Shakedown Analysis.

3-D finite element model was built using elastic-plastic materials defined by stress-strain curves.

Multilinear kinematic hardening material model was used, The maximum strain and stress were produced by the elastic-plastic analysis under the specified thermal and structural loads, including external loads (Dead Weight and thermal loads), and Insurge/Outsurge transients. The calculated maximum stress intensity ranges are used to get the fatigue usage for nozzle with weld overlay under Insurge/Outsurgetransients.

The total fatigue usages at the path lines evaluated using elastic plastic methodology are composed of partial usage factors based on the elastic approach results and the elastic plastic approach results, Note that the Insurge/outsurge events were analyzed on elastic-plastic bases.

The highest total cumulative fatigue usage factor compounded from the elastic and elastic-plastic calculations is 0.07473 c 1.O; therefore, the Reference 3 requirement is met for these critical locations.

Page 8

AREVA Document No. 86-9092967-000 AREVA NP Inc.,

an AREVA and Slemona company Prairie Island Unit 2 Pressurizer Surge Nozzle Weld Overlay Stress Analysis Summary

4.0 CONCLUSION

The maximum stress and fatigue usage for nozzle with weld overlay are summarized as follows:

Limits of NB-3222.2, NB-3228.5(d) and NB-3222.5 exceeded based on elastic calculations were justified and quallfled by using the elastic-plastic approach.

The calculation Reference 1 demonstrates that the Prairie Island Unit 2 pressurizer nozzle weld overlay meets the applicable stress and fatigue requirements of the Reference 3 for all defined operating load conditions.

The results of the conservative fatigue analysis indicates that the maximum fatigue usage factor for the nozzle with weld overlay is 0.665 for 40 year design life or 60 year extended operation (Reference 2),

which is below the ASME (Reference 3) acceptance criteria of I.Om Page 9

A Document No. 86-9092967-000 AREVA AREVA N P Inc.,

an AREVA and Slomana company Prairie Island Unit 2 Pressurizer Surge Nozzle Weld Overlay Stress Analysis Summary

5.0 REFERENCES

1. AREVA NP Inc. Document No: 32-9044661-002, "Pralrie Island Unit 2 Pressurizer Surge Noule Weld Overlay Analysis", 2008.

2. AREVA NP Inc. Document No. 51-8017248-003, "Prairie Island Unit 2 Surge Nozzle Weld Overlay Technical Requirements", 2008.

3. ASME Boiler and Pressure Vessel Code, Section Ill, Division I,Subsection NB, 1998 edition with addenda through 2000.

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Enclosure 2 to L-PI-08-090 Summary of Prairie Island Unit 2 Pressurizer Surge Nozzle Weld Overlay Crack Growth Analysis

0402-01-F01(20697) (Rev. 012,04/04/2008)

CALCULATION

SUMMARY

SHEET (CSS)

Document No.

he purpose of this 86-document is to summarize the results of crack growth analysis for Prairie Island Unit 2 ressurizer surge nozzle weld overlay in calculation document 32-9044663-003 [I].

he results from the fracture mechanics analysis performed to evaluate the worst case flaws in the repair '

onfiguration show that for the minimum SWOL design with 0.15 inch additional SWOL thickness requirement (from the results of current crack growth analysis) for path lines FR1, FR2, and FR3 and 0.080 inch additional thickness requirement for path line FR4, the final flaw depth after 27 years of service is less than the allowable flaw depth per Section XI acceptance criteria (21.

THE DOCUMENT CONTAINS ASSUMPTIONS THAT MUST BE THE FOLLOWING COMPUTER CODES HAVE BEEN USED IN THIS DOCUMENT. VERIFIED PRIOR TO USE ON SAFETY-RELATEDWORK CODWERSIONIREV CODENERSIONIREV YES W No v

AREVA NP Inc., an AREVA and Siemens company Page 1 of 5

A AREVA 0402-01-F01 (20697) (Rev. 012,04/04/2008)

AREVA NP Inc., Document No. 86-9093154-000 sn AREVA end Simmen8 company Summary of Prairie Island Unit 2 Pressurizer Surge Nozzle Weld Overlay Crack Growth Analysls Signature Block PageslSections PreparedlReviewe dlApproved Name PIRIA and (printed or typed) and and CommenWRevie Title Signature LPlLR Date w Method Heqin Xu P All Engineer IV S. J. Noronha Engineer IV T. M. Wiger

• - R A

lo /6 /o8 IO~~(DB All (Detailed Check)

All Engineering Manager I d - 0 w

1/48 Note: PIRIA designates Preparer (P), Reviewer (R), Approver (A);

LPILR designates Lead Preparer (LP), Lead Reviewer (LR)

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0402-01-F01 (20697) (Rev. 012,0410412008)

AREVA A R N A NP Inc., Document No. 86-9093154-000 an A R N A and Shnmn. company Summary of Prairie Island Unit 2 Pressurizer Surge Nozzle Weld Overlay Crack Growth Analysis Record of Revision Revision PageslSectlonsl No. Date Paragraphs Changed Brief Description IChange AuthorIration 000 1012008 All Original Release Page 3

A Document No. 86-90931 54-000 AREVA AREVA NP Inc..

an AREVA end Sl.m*no compury Summary of Prairie lsland Unit 2 Pressurizer Surge Noule Weld Overlay Crack Growth Analysis

1.0 INTRODUCTION

Due to the susceptibility of Alloy 600 and its associated weldments Alloy 821182 to primary water stress corrosion cracking (PWSCC), Nuclear Management Company (NMC) plans to install full structural weld overlays (SWOL) at Prairie Island Unit 2 Pressurizer Surge Noule. A repair procedure has been developed where the dissimilar metal (DM)Alloy 821182 weld, the safe end, the stainless steel weld, a portion of the nozzle and a portion of the stainless steel reducer are overlaid with PWSCC-resistant Alloy 52M material.

The overlays were analyzed for potential growth of a worst case flaw in the noulelpipe welds. It is postulated that inside surface-connected, partial through-wall, 360" circumferential flaw(s) and semi-elliptical axial flaw@) would propagate by PWSCC and fatigue through the thickness of the DM weld, to the interface with the Alloy 52 overlay material. The initial flaw depths for the circumferential and axial flaws are taken to be 75% of the thickness of the original welds from the inside surface. If the postulated flaws grow through the original DM and SS weld, fatigue crack growth analysis will be performed to determine the amount of crack growth into the PWSCC-resistant Alloy 52 overlay. Since the Alloy 52M overlay is resistant to PWSCC, extensions of the postulated flaws into the SWOL would only be due to fatigue crack growth under cyclic loading conditions.

Fracture mechanics analyses were performed to evaluate this worst case flaw in the repair configuration. These evaluations considered welding residual, steady state and normallupset condition transient stresses with the associated number of transient cycles to predict the final flaw size at the end of license extension at Prairie Island Unit 2, which equates to a 27 year service life. This analysis is performed for the Alloy 821182 DM weld, the stainless steel weld, and the SWOL. These evaluations demonstrated that the postulated circumferential and axial flaws met the 1998 ASME Code Section XI, Appendix C [2] acceptance criteria.

2.0 FLAW GROWTH RESULTS 2.1 Circumferential Flaws The circumferential flaws with an initial depth of 75% of the thickness of the original welds from the inside surface were evaluated in Reference [I], and are summarized in the table below:

DM WELD OVERLAY SS WELD OVERLAY FR1 FR2 FR3 FR4 Min WOL thickness, in. L= 0.525 0.525 0.525 0.784 Additional WOL thickness, in. At,,,,= 0.150 0.150 0.150 0.080 WOL thickness evaluated, in. At = 0.675 0.675 0.675 0.864 Total wall thickness, in. 1.f = 2.280 2.280 2.280 2.011 Initial flaw depth, in. ai= 1.1550 1.1550 1.1550 0.8605 Flaw growth, in. Aa = 0.5534 0.5404 0.5276 0.6163 Final flaw size after 27 years, in. af = 1.7084 1.6954 1.6826 1.4768 Allowable Flaw depth, in. aalb, = 1.710 1.710 1.710 1.508 Final crack depth to thickness ratio a& = 0.749 0.744 0.738 0.734 Page 4

AREVA Document No. 86-9093154-000 AREVA NP Inc..

an A R N A and S l e w s company Summary of Prairie Island Unit 2 Pressurizer Surge Noule Weld Overlay Crack Growth Analysis 2 2.2 Axial Flaws The axial flaws with an initial depth of 75% of the thickness of the original welds from the Inside surface I were evaluated in Reference [I], and are summarized In the table below:

i i

DM WELD OVERLAY 88 WELD OVERLAY FRI FR2 FR3 FR4 Min WOL thickness, in. f,~ 0.525 0.525 0.525 0.784 Additional WOL thickness, in. A& 0.150 0.150 0.1 50 0.080 WOL thickness evaluated, in. At = 0.675 0.675 0.675 0.864 Total wall thickness, in. k r = 2.280 2.280 2.280 2.011 Initial flaw depth, in. alP 1.1550 1.1550 1.I 550 0.8605 Flaw growth, in. Aa 0.4580 0.4500 0.4550 0.0023 Final flaw size after 27 years, in. a(= 1.6130 1.6060 1.6100 0.8628 Allowable Flaw depth, in. aak = 1.710 1.710 1.710 1.SO8 Final crack depth to thickness ratio a# a 0.707 0.704 0.706 0.429

3.0 CONCLUSION

The results from the fracture mechanics analysis performed to evaluate the worst case flaws in the repair configuration show that for the minimum SWOL design with 0.15 inch additional SWOL thickness requirement for path lines FR1, FR2, and FR3 and 0.080 inch additional thickness requirement for path line FR4, the final flaw depth after 27 years of service is less than the allowable flaw depth per Section XI [2] acceptance criteria.

4.0 REFERENCE

1. AREVA NP Document 32-9044663-003, "Prairie Island Unit 2 Pressurizer Surge Noule Weld Overlay Crack Growth Analysis."

2. ASME Boiler and Pressure Vessel Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, 1998 Edition including Addenda through 2000.

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