ML061090834

American Society of Mechanical Engineers Code, Section Xi Repair Requirements Preemptive Weld Overlay - Stress Summaries

ML061090834
Person / Time
Site:	Cook
Issue date:	04/11/2006
From:	Jensen J N Indiana Michigan Power Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
AEP:NRC:6055-05, TAC MC9305
Download: ML061090834 (11)

Text

INDI Indiana Michigan Power IN ANA Cook Nuclear Plant MICHIGAN One Cook Place* Bridgman, MI 49106 F40WR*AEP~com A unit of American Electric Power April 11, 2006 AEP:NRC:6055-05 Docket No.: 50-316 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Stop O-P1-17 Washington, DC 20555-0001 Donald C. Cook Nuclear Plant Unit 2 AMERICAN SOCIETY OF MECHANICAL ENGINEERS CODE, SECTION XI REPAIR REQUIREMENTS PREEMPTIVE WELD OVERLAY -STRESS SUMMARIES (TAC NO. MC9305)

Reference:

1. Letter from Daniel P. Fadel, Indiana Michigan Power Company (I&M), to U. S. Nuclear Regulatory Commission (NRC) Document Control Desk,"Donald C. Cook Nuclear Plant Unit 2, Proposed Alternative to the American Society of Mechanical Engineers Code,Section XI Repair Requirements," AEP:NRC:5055-13, Accession Number ML053570112, dated December 21, 2005.2. "Cook Unit 2: Draft Request for Additional Information on Relief Request, Re: Preemptive Weld Overlay (TAC MC9305)," Accession Number ML060340609, dated February 15, 2006.3. Letter from Joseph N. Jensen, I&M, to NRC Document Control Desk,"Donald C. Cook Nuclear Plant Unit 2, Proposed Alternative to the American Society of Mechanical Engineers Code,Section XI Repair Requirements," AEP:NRC:6055, Accession Number ML060620063, dated March 1, 2006.By Reference 1, I&M proposed an alternative to the American Society of Mechanical Engineers Code,Section XI (ASME Section XI) repair requirements.

I&M proposed the use of preemptive weld overlays (PWOLs) using Code Cases N-504-2 and N-638-1, with modifications, to address dissimilar metal weld concerns for piping connected to the Unit 2 pressurizer.

Reference 2 documented an NRC request for additional information regarding the proposed alternative.

Reference 3 provided I&M's response to the additional information requested by the NRC.Reference 3 included a commitment by I&M to provide stress analysis summaries for the piping that is to be repaired using PWOLs, i.e., the pressurizer safety/relief lines, spray line, and surge line.Additionally, the NRC has requested a summary of the PWOL fatigue crack growth analysis for the piping.-0'o7 U. S. Nuclear Regulatory Commission Page 2 AEP:NRC:6055-05 Attachment 1 to this letter provides the stress analysis summary. Attachment 2 provides the fatigue crack growth analysis summary.This letter contains no new commitments.

Should you have any questions, please contact Mr. Michael K. Scarpello, Regulatory Affairs Supervisor, at (269) 466-2649.Sincerely N. Jensen Site Vice President RV/dmb Attachments:

1. D. C. Cook Pressurizer

-Safety/Relief, Spray, and Surge Nozzles Weld Overlay Stress Analysis Summary -ASME Section III Criteria 2. D. C. Cook Pressurizer

-Safety/Relief, Spray, and Surge Nozzles Weld Overlay Fatigue Crack Growth Analysis Summary c: R. Aben -Department of Labor and Economic Growth J. L. Caldwell -NRC Region III K. D. Curry -AEP Ft. Wayne J. T. King -MPSC MDEQ -WHMD/RPMWS NRC Resident Inspector P.S. Tam -NRC Washington, DC Attachment 1 to AEP:NRC:6055-05 D. C. Cook Pressurizer-Safety/Relief, Spray and Surge Nozzles Weld Overlay Stress Analysis Summary -ASME Section III Criteria Abbreviations Used in this Attachment ASME American Society of Mechanical Engineers B&PV Boiler and Pressure Vessel Code ksi thousand pounds per square inch OBE operating basis earthquake Attachment 1 to AEP:NRC:6055-05 Page 2 D.C. COOK PRESSURIZER-SAFETY/RELIEF.

SPRAY. & SURGE NOZZLES WELD OVERLAY STRESS ANALYSIS

SUMMARY

-ASME SECTION III CRITERIA 1 Introduction ASME B&PV Code Section HII stress analyses were performed for D.C. Cook Unit 2 pressurizer nozzles repaired with weld overlays (Safety/Relief, Spray, and Surge nozzles) in compliance with ASME Code Case N-504-2, Paragraph (g)(1). 3-D ANSYS finite element models for the three nozzles with weld overlays were developed, and detailed finite element analyses (thermal and structural) were conducted.

The purpose of these calculations is to qualify the weld overlay design to the requirements of the 1998 ASME B&PV Code,Section III criteria.

The weld overlay size (thickness and length) was calculated per ASME B&PV Code,Section XI, Division I, and ASME Code Case N-504-2.Thermal stresses were determined for the appropriate design transients and a fatigue analysis was performed.

The design conditions, as well as the thermal transients, were investigated with the finite element models. The results of the thermal analysis were reviewed by examining the magnitude of the temperature difference between critical locations in the models at all time points of interest (i.e., when the maximum thermal stresses may develop).

The stresses due to the nozzle external loads were conservatively calculated and added to the stresses resulting from internal pressure and thermal gradients.

The applicable criteria of the 1998 ASME B&PV Code,Section III requirements were met.It should be noted that the results of the weld overlay stress analysis summarized below are based on conservative inputs. The external loads are derived from allowable stresses and the operating design transients were developed on conservative basis.2. Results 2.1 Primary Stress Intensity Criteria for Design Conditions and All Service Level Loadings The weld overlay applied on the outside surface relieves the nozzle primary stress burden resulting from the applied internal pressure and external loads. Therefore, ASME B&PV Code Section III primary stress requirements for design conditions and all service level loadings as specified in NB-3221, NB-3222, NB-3223, NB-3224, and NB-3225 have been satisfied for the nozzles, welds with overlays, safe ends, and piping elbows under investigation.

Therefore, the primary stress intensity criteria for design conditions and all service level loadings are bounded by the original design.

Attachment 1 to AEP:NRC:6055-05 Page 3 2.2 Minimum Required Pressure Thickness and Reinforcement Area Criteria Adding weld overlay will increase the nozzle wall thickness.

As a result, the ASME B&PV Code Section III requirements contained in NB-3324 and NB-3330 are satisfied.

2.3 Primary

+ Secondary Stress Intensity (NB-3222.2)

The final stress intensity range is obtained by conservatively adding the maximum membrane plus bending stress intensity (SI) range during transients to that due to the applied external loads (thermal + OBE). Although the final SI range at most locations under investigation is below the 3Sm limit, there are several locations where the limit is exceeded.

The highest SI range in each nozzle is listed as follows: Safety/Relief Nozzle = 55.1 ksi > 3Sm= 48.0 ksi Spray Nozzle = 70.9 ksi > 3 m= 51.6 ksi Surge Nozzle = 129.4 ksi > 3Sm= 48.4 ksi Per NB-3228.5 of the ASME B&PV Code Section III, the 3Sm limit on the primary plus secondary SI range may be exceeded provided that the following six requirements are met.2.3.1 l" Requirement (NB-3228.5(a)):

Primary plus secondary membrane plus bending SI range, excluding thermal bending stresses, shall be less than 3Sm.Safety/Relief and Spray Nozzles: the requirement has been satisfied for all the locations where the SI range is above the 3Sm limit.Surge Nozzle: the 3Sm limit is still exceeded at two locations (79.9 ksi, 82.6 ksi > 3Sm = 56.1 ksi). Therefore the ASME code requirement is not met at these locations and as a result a detailed evaluation based on the elastic-plastic approach for the Heat-up Cool-down (HUCD)transients with insurges of 320°F AT was performed.

Elastic -Plastic Analysis of the Surge Nozzle Weld Overlay for HUCD Transients:

the elastic-plastic analysis was performed in accordance with NB-3228.4-Shakedown analysis.

The ASME Code criteria NB-3228.4 are met.2.3.2 2Id -6th Requirements (NB-3228.5(b-f)):

These requirements are met for the Safety/Relief and Spray Nozzles at all locations where the 3Sm limit is exceeded.

Attachment 1 to AEP:NRC:6055-05 Page 4 2.4 Fatigue Analysis The fatigue usage factor of the three nozzles is conservatively calculated for 60 years of operation (40 design life plus 20 years life extension).

Below is a summary: SafetyiRelief Nozzle: the highest cumulative fatigue usage factor = 0.157 < 1.0 (ASME Criteria)Spray Nozzle: the highest cumulative fatigue usage factor = 0.738 < X .0 (ASME Corteri)Surge Nozzle: the highest cumulative fatigue usage factor = 0.9 < 1.0 (ASME Criteria)3. Conclusion Based on the above results, the requirements of Paragraph (g)(1) of ASME Coop Case N-5"4-2 are met, and the repair has been shown to be acceptable for the remaining service life of D.C. Cook Unit 2.

Attachment 2 to AEP:NRC:6055-05 D. C. Cook Pressurizer

-Safety/Relief, Spray, and Surge Nozzles Weld Overlay Fatigue Crack Growth Analysis Summary Abbreviations Used in this Attachment ASME American Society of Mechanical Engineers FCG flaw crack growth m. inches psi pounds per square inch WOL Weld overlay Attachment 2 to AEP:NRC:6055-05 Page 2 DC COOK PRESSURIZER

-SAFETY/RELIEF.

SPRAY. & SURGE NOZZLES WELD OVERLAY FATIGUE CRACK GROWTH ANALYSIS

SUMMARY

1. Introduction Due to the susceptibility of Alloy 600 and its associated weldments Alloy 82/182 to primary water stress corrosion cracking (PWSCC), American Electric Power (AEP) plans to install full structural weld overlays at the safety, relief, spray and surge nozzles of the pressurizer at DC Cook Unit 2 (CNP-2). A repair procedure has been developed where the dissimilar metal (DM) Alloy 82/182 weld and butter and stainless steel (SS) safe end and weld, and a portion of both the nozzle and attached pipe are overlaid with PWSCC resistant Alloy 52 material.The overlays were analyzed for potential growth of a worst case flaw in the nozzle/pipe welds. It was postulated that a 3600 circumferential flaw would propagate by PWSCC through the thickness of the Alloy 82/182 weld and butter, to the interface with the Alloy 52 overlay material.

Although PWSCC would not continue to occur in the Alloy 52 overlay, it was further conservatively postulated that a small fatigue initiated flaw forms in the Alloy 52 overlay and combines with the PWSCC crack in the Alloy 82/182 weld to form a large part through-wall full circumferential flaw that would propagate into the Alloy 52 overlay by fatigue crack growth under cyclic loading conditions.

Fracture mechanics analyses were performed to evaluate this worst case flaw in the repair configuration in compliance with ASME Code Case N-504-2, Paragraph (g)(2). These evaluations considered welding residual, steady state and normal/upset condition transient stresses with the associated number of transient cycles to predict the final flaw size at the end of license extension at DC Cook Unit, which equates to a 32 year service life. These evaluations demonstrated that the postulated circumferential flaw met the 1989 ASME Code Section XI, Appendix C acceptance criteria.

An additional check was made on the primary membrane stresses in the remaining ligament under normal operating conditions.

These analyses were performed for both the Alloy 82/182 weld as well as the stainless steel weld joining the safe end to the piping.

Attachment 2 to AEP:NRC:6055-05 Page 3 2. Results 2.1 Safety/Relief Nozzles 2.1.1 Flaw Growth Results Min WOL thickness, in.Additional WOL thickness for FCG, in.Initial flaw size, in.Final flaw size after 32 years, in.Flaw growth, in.Final crack depth to thickness ratio, twoI=At.0 1 =a 1 =Ef =Aa =at =DM WELD OVERLAY 0.4720 in.0.0070 in.1.4150 in.1.4201 in.0.0051 in.0.7498 SS WELD OVERLAY 0.2150 in.0.0030 in.0.6450 in.0.6470 in.0.0020 in.0.7498 2.1.2 Limit Load Analysis Results At the final crack depth, the plastic collapse stress calculated according to ASME Code Section XI, Appendix C is compared to the failure bending stress in the pipe, accounting for safety factors for normal/upset and emergency/faulted conditions.

At both overlaid locations (the DM and SS welds), the plastic collapse stress exceeds the failure bending stress, precluding failure by net section collapse.Overlay at DM Weld Normal/Upset Plastic collapse stress (psi) 30,467 Failure bending stress (psi) 8,214 Emergency/Faulted 30,188 9,761 Overlay at SS Weld NormaVUpset Emergency/Faulted Plastic collapse stress (psi) 26,609 25,873 Failure bending stress (psi) 19,142 22,884 2.1.3 Primary Membrane Stress Considerations The applied primary membrane stress in the remaining ligament is less than the operating temperature yield stress.

Attachment 2 to AEP:NRC:6055-05 Page 4 Overlay at DM Weld Yield stress (psi) 27,500 Membrane stress (psi) 10,925 Overlay at SS Weld Yield stress (psi) 27,500 Membrane stress (psi) 21,151 2.2 Spray Nozzle 2.2.1 Flaw Growth Results Min WOL thickness, in.Additional WOL thickness for FCG, in.Initial flaw size, in.Final flaw size after 32 years, in.Flaw growth, in.Final crack depth to thickness ratio, t.1 =Atwo =a =Of =Aa =aft =DM WELD OVERLAY 0.3320 in.0.0010 in.0.9950 in.0.9952 in.0.0002 in.0.7494 SS WELD OVERLAY 0.1810 in.0.0130 in.0.4050 in.0.4171 in.0.0121 in.0.6963 2.2.2 Limit Load Analysis Results At the final crack depth, the plastic collapse stress calculated according to ASME Code Section XI, Appendix C is compared to the failure bending stress in the pipe, accounting for safety factors for normal/upset and emergency/faulted conditions.

At both overlaid locations (the DM and SS welds), the plastic collapse stress exceeds the failure bending stress, precluding failure by net section collapse.Overlay at DM Weld Normal/Upset Emergency/Faulted Plastic collapse stress (psi) 30,055 29,828 Failure bending stress (psi) 14,404 11,225 Overlay at SS Weld Normal/Upset Plastic collapse stress (psi) 32,581 Failure bending stress (psi) 32,133 Emergency/Faulted 31,963 25,413 2.2.3 Primary Membrane Stress Consideration The applied primary membrane stress in the remaining ligament is less than the operating temperature yield stress.

Attachment 2 to AEP:NRC:6055-05-Page 5 Overlay at DM Weld Yield stress (psi) 27,500 Membrane stress (psi) 11,734 Overlay at SS Weld Yield stress (psi) 27,500 Membrane stress (psi) 17,544 2.3 Surge Nozzle 2.3.1 Flaw Growth Results Min WOL thickness, in.Additional WOL thickness for FCG, in.Initial flaw size, in.Final flaw size after 32 years, in.Flaw growth, in.Final crack depth to thickness ratio, tMo 1 =At.,o =a =af =Aa =aft =DM WELD OVERLAY 0.5270 in.0.0790 in.1.5800 in.1.6389 in.0.0589 in.0.7497 SS WELD OVERLAY 0.5440 in.0.0040 in.1.6310 in.1.6338 in.0.0028 in.0.7498 2.3.2 Limit Load Analysis Results At the final crack depth, the plastic collapse stress calculated according to ASME Code Section XI, Appendix C is compared to the failure bending stress in the pipe, accounting for safety factors for normal/upset and emergency/faulted conditions.

At both overlaid locations (the DM and SS welds), the plastic collapse stress exceeds the failure bending stress, precluding failure by net section collapse.Overlay at DM Weld Normal/Upset Emergency/Faulted Plastic collapse stress (psi) 27,636 27,401 Failure bending stress (psi) 19,296 19,826 Overlay at SS Weld Normal/Upset Emergency/Faulted Plastic collapse stress (psi) 27,765 27,524 Failure bending stress (psi) 19,309 20,162