ML063530335

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

ML063530335
Person / Time
Site:	Cook
Issue date:	12/07/2006
From:	Jensen J Indiana Michigan Power Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
AEP:NRC:6055-19
Download: ML063530335 (10)

Text

Indiana Michigan Power INDIANA Cook Nuclear Plant MICHIGAN One Cook Place Bridgman, MI 49106 POWERO AEPcom A unit of American Electric Power December 7, 2006 AEP:NRC:6055-19 10 CFR 50.55a Docket No.: 50-315 U. S. Nuclear Regulatory Commission ATTN: Documnent Control Desk Mail Stop O-P1-17

.Washington, DC 20555-0001 Donald C. Cook Nuclear Plant Unit 1 AMERICAN SOCIETY OF MECHANICAL ENGINEERS CODE,.

SECTION XI REPAIR REQUIREMENTS PREEMPTIVE WELD OVERLAY - STRESS SUMMARIES

Reference:

Letter firom Mark A. Peifer, Indiana Michigan Power Company, to Nuclear Regulatory Conmmission Document Control Desk, "Donald C. Cook Nuclear Plant Unit 1, Supplement to Proposed Alternative to the American Society Of Mechanical Engineers Code,Section XI Repair Requirements," AEP:NRC:6055-17, Accession Number ML062780203, dated September 26, 2006.

In the referenced letter, Indiana Michigan Power Company (I&M), the licensee for Donald C. Cook Nuclear Plant Unit 1, proposed an alternative to the repair requirements of the American Society of Mechanical Engineers Code,Section XI. .Approval of the proposed alternative was requested to allow I&M to apply full structural preemptive weld overlays (PWOLs) on pressurizer nozzle safe end to nozzle welds where NiCrFe Alloy 82/182 was originally used to weld the safe ends thereto.

In requesting approval of the proposed alternative, I&M committed to providing the Nuclear Regulatory Commission with the stress summaries for the PWOLs. The attachment to this letter provides the PWOL stress summaries and the associated flaw growth evaluation, which has been conservatively calculated by assuming that a 360 degree circumferential flaw would propagate by primary water stress corrosion cracking through the thickness of the Alloy 82/182 weld, to the interface with the Alloy 52/52M overlay material.

This letter contains no new commitments. Should you have any questions, please contact Ms. Susan D. Simpson, Regulatory Affairs Manager, at (269) 466-2428.

Vice President Site Support Services RGV/rdw Aoq7

U. S. Nuclear Regulatory Commission AEP:NRC:6055-19 Page 2

Attachment:

Donald C. Cook Unit 1, Preemptive Weld Overlay Structural Evaluation Summnary c: R. Aben - Department of Labor and Economic Growth J. L. Caldwell - NRC Region III K. D. Curry - AEP Ft. Wayne, w/o attachment J. T. King - MPSC, w/o attachment MDEQ - WHMD/RPMWS, w/o attachment NRC Resident Inspector P. S. Tarn - NRC Washington DC

ATTACHMENT TO AEPiNRC:6055-19 Donald C. Cook Unit 1 PREEMPTIVE WELD OVERLAY STRUCTURAL EVALUATION

SUMMARY

Abbreviations and Symbols Used in this Attachment ASME American Society of Mechanical Engineers B&PV Boiler and Pressure Vessel Code CNP Donald C. Cook Nuclear Plant DM Dissimilar Metal FCG Flaw Crack Growth HUCD Heatup Cooldown in. inches ksi thousand pounds per square inch OBE Operating Basis Earthquake psi pounds per square inch PWSCC Primary Water Stress Corrosion Cracking SI Stress Intensity SS Stainless Steel

'Equal to

< Less than

> Greater than

Attachment to AEP:NRC:6055-19 Page 2 PRESSURIZER PIPING WELD OVERLAY STRESS ANALYSIS

SUMMARY

ASME SECTION III CRITERIA 1.0 Introduction Due to the susceptibility of Alloy 600 and its associated weldments, Alloy 82/182, to PWSCC, Indiana Michigan Power Company applied full structural weld overlays to the safety, relief, spray, and surge nozzles of the CNP Unit 1 pressurizer. A repair procedure was developed where the DM Alloy 82/182 weld and butter, the SS safe end and weld, and a portion of both the nozzle and attached pipe were overlaid with PWSCC resistant Alloy 52/52M material.

ASME B&PV Code,Section III stress analyses were performed for the CNP Unit 1 pressurizer nozzles repaired with weld overlays in compliance with ASME Code Case N-504-2, Paragraph g (1). Three dimensional ANSYS computer code finite element models for the three nozzles with weld overlays were developed, and detailed finite element analyses (thermal and structural) were performed. The purpose of these calculations was to qualify the weld overlay design to the requirements of the 1998 ASME B&PV Code, including Addenda through 2000, Section 11 criteria. The weld overlay size (thickness and length) was calculated per ASME B&PV Code, Section Xl, Division 1 and ASME Code Case N-504-2.

Thermal stresses were deternmined for the appropriate design transients and a fatigue analysis was performed. The design conditions as well as the thermal transients were evaluated 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 times when the maximum thermal stresses would develop. The stresses due to the nozzle external loads were 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.

2.0 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 Paragraphs 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 that were evaluated.

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

Attachment to AEP:NRC:6055-19 Page 3 2.2 Minimum Required Pressure Thickness and Reinforcement Area Criteria Adding the weld overlay will increase the nozzle wall thickness. As a result the ASME B&PV Code Section III requirements contained in Paragraphs NB-3324 and NB-3330 are satisfied.

2.3 Primary Plus Secondary Stress Intensity The final SI range is obtained by adding the. maximum membrane plus bending SI range during transients to that due to the applied external loads (thermal plus OBE). Per ASME B&PV Code,

Section III, Subparagraph NB-3222.2, the SI range limit is 3Sin, Although the final SI range at most locations evaluated is below the 3S.. limit, there are several locations where the limit is exceeded. When~the 3 S..limit is exceeded, the shear bending SI range was subtracted flom the total menmbrane plus bending SI range. The highest SI range in each nozzle is listed as follows:

Safety/Relief Nozzle 69.66 ksi <.3S,,= 69.90 ksi Spray Nozzle 97.57 ksi > 'S,..= 49.38 ksi Surge Nozzle 121.30 ksi > 3S= 56.10 ksi As can be seen, the spray nozzle and the surge nozzle have locations that exceed the 3S,, limiit.

Per the ASME B&PV Code, Section II1, the 3S,, limit on the prilnary plus secondary SI range may be exceeded provided that the requirements of Subparagraph NB-3228.5 (a) through (f) are met: The evaluations of the spray and surge nozzles are provided in the following paragraphs..

2.3.1 Spray Nozzle The spray nozzle meets all criteria at all locations where the 3Sin limit is exceeded.

2.3.2 Surge Nozzle The surge nozzle did not meet the requirement (a) criterion that the primary plus secondary membrane plus bending SI range, excluding thermal bending stresses, shall be less than 3 SM.

The 3S.. limit is still exceeded at the thermal sleeve, 87.6 ksi > 3S.. = 56.1 ksi. Therefore, the ASME B&PV Code,Section III requirement is not met at this location and a detailed evaluation based on the elastic-plastic approach was performed for the HUCD transients with an insurge-outsurge fluid temperature difference of 320 degrees Fahrenheit.

Elastic - Plastic Analysis of the Surge Nozzle Weld Overlay for HUCD Transients: The elastic-plastic analysis was performed in accordance with ASME B&PV Code, Section lII, Subparagraph NB-3228.4, "Shakedown Analysis." The Subparagraph NB-3228.4 criteria are met.

Attachment to AEP:NRC:6055-19 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:

Safety/Relief Nozzle: the highest cumulative fatigue usage factor = 0.025 < 1.0 (ASME Criteria)

Spray Nozzle: the highest cumulative fatigue:usage factor = 0.890 < 1.0 (ASME Criteria)

Surge:Nozzle: the highest cumulative fatigue usage. factor = 0.214 < 1.0 (ASME Criteria) 3.0 Conclusion Based on the above results, the requirements of Paragraph (g)(1) of ASME Code Case N-504-2 are met, and the repair has been shown to be acceptable for the remaining service life of CNP Unit 1.

Attachment to AEP:NRC:6055-19 Page 5 PRESSURIZER PIPING WELD OVERLAY FATIGUE CRACK GROWTH ANALYSIS

SUMMARY

1.0 Introduction The overlays applied to the pressurizer piping were analyzed for potential growth of a worst case flaw in the nozzle/pipe welds. It was postulated that a 360 degree circumferential flaw would propagate by PWSCC through the thickness of the Alloy 82/182 weld, to the interface with the Alloy 52/52M overlay material. Although PWSCC would not continue to Occur in the Alloy 52/52M overlay, it was postulated that a small fatigue initiated flaw forms in the Alloy 52/52M 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 52/52M 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 the residual welding, 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 CNP Unit 1, which equates to a 29 year service life. These evaluations demonstrated that the postulated circumferential flaw met the 1989 ASME B&PV Code,Section XI, Appendix C acceptance criteria. An additional check was made on the applied 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 SS weld joining the safe end to the piping.

2.0 Results 2.1 Safety/Relief Nozzles 2.1.1 Flaw Growth Results DM Weld SS Weld Minimum Weld Overlay Thickness, in. 0.5370 0.4850 Additional Weld Overlay Thickness for FCG, in. 0.0300 0.0000 Initial Flaw Size, in. 1.4800 0.7150 Final Flaw Size after 29 Years, in. 1.4858 0.7150 Flaw Growth, in. 0.0058 0.0000 Final Crack Depth to Thickness Ratio 0.7497 0.5958

Attachment to AEP:NRC:6055-19 Page 6 2.1.2 Limit Load Analysis Results At the final crack depth, the plastic collapse stress calculated in accordance with ASMIE B&PV 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 requirement that the plastic collapse stress exceed the failure bending stress is met.

NormallUpset Emergency/Faulted Plastic collapse stress at DM weld, psi 30,473 30,349 Failure bending stress at DM weld, psi 9,347 8,980 Plastic collapse stress at SS weld, psi 45,788 45,602 Failure bending stress at SS weld, psi 15,761 15,828 2.1.3 Applied Membrane Stress Considerations The applied niemnbrane stress in the remaining ligament is less than the operating temperature yield stress:.

• Yield stress at DM weld, psi 27,500 Memibt~ane stress at DM weld, psi 10,588 Yield stress at SS weld, psi 27,500 Menibrane stress at SS weld, psi 9,057 2.2 Spray Nozzle 2.2.1 Flaw Growth Results DM Weld SS Weld Minimum Weld Overlay Thickness, in. 0.397000 0.35140 Additional Weld Overlay Thickness for FCG, in. 0.023000 0.00000 Initial Flaw Size, in. 1.060000 0.44000 Final Flaw Size after 29 Years, in. 1.060004 0.44003 Flaw Growth, in. 0.000004 0.00003 Final Crack Depth to Thickness Ratio 0.7491 0.5560 2.2.2 Limit Load Analysis Results At the final crack depth, the plastic collapse stress calculated according to ASME B&PV 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

Attachment to AEP:NRC:6055-19 Page 7 (the DM and SS welds), the requirement that the plastic collapse stress exceed the failure bending stress is met.

Normal/Upset Emergency/Faulted Plastic collapse stress at DM weld, psi 30,300 30,091 Failure bending stress at DM weld, psi 12,959 10,064 Plastic collapse stress at SS weld, psi 49,474 49,123 Failure bending stress at SS weld, psi 23,369 18,557 2.2.3 Applied Membrane Stress Consideration The applied membrane stress in the remaining ligament is less than the operating temnperature yield stress.

Yield stress at DM weld, psi 27,500 Membrane stress at DM weld, psi 11,169 Yield stress at SS weld, psi 27,500 Membrane stress at SS weld, psi 8,732 2.3 Surge Nozzle 2.3.1 Flaw Growth Results DM Weld SS Weld Minimum Weld Overlay Thickness, in. 0.5200 0.7600 Additional Weld Overlay Thickness for FCG, in. 0.0120 0.0000 Initial Flaw Size, in. 1.5600 1.3900 Final Flaw Size after 29 Years, in. 1.5678 1.3900 Flaw Growth, in. 0.0078 0.0000 Final Crack Depth to Thickness Ratio 0.7494 0.6465 2.3.2 Limit Load Analysis Results At the final crack depth, the plastic collapse stress calculated according to ASME B&PV 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

Attachment to AEP:NRC:6055-19 Page 8 (the DM and SS welds), the requirement that the plastic collapse stress exceed the failure bending stress is met.

Normal/Upset Emergency/Faulted Plastic collapse stress at DM Weld, psi 27,490 27,130 Failure bending stress at DM weld, psi 11,165 20,808 Plastic collapse stress at SS weld, psi 39,800 39,493 Failure bending stress at SS weld, psi 10,724 20,157 2.3.3 Applied Membrane Stress Consideration The applied membrane stress in the remaining ligament is less than the operating temperature yield stress.

Yield stress at DM weld, psi 27,500 Membrane stress at DM weld, psi 17,844 Yield stress at SS weld, psi 27,500 Membrane stress at SS weld, psi 11,633 3.0 Conclusion Based on the above results, the requirements of Paragraph (g)(2) of ASME Code Case N-504-2 are met, and the repair has been shown to be acceptable for the remaining service life of CNP Unit 1.