ML071370352

Stress Analysis Summary Report, Pressurizer and Reactor Coolant Hot Leg Weld Overlays

ML071370352
Person / Time
Site:	Arkansas Nuclear
Issue date:	05/08/2007
From:	Scheide R Entergy Operations
To:	Document Control Desk, NRC/NRR/ADRO
References
1CAN050703
Download: ML071370352 (19)

Text

~, I vuEntervgy Entergy Operations, Inc.

1448l R. 333 Russellville, AR 72802 Tel 479-858-4619 Dale E. James Manager, Licensing 1 CAN050703 May 8, 2007 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555

REFERENCES:

Stress Analysis Summary Report Pressurizer and Reactor Coolant Hot Leg Weld Overlays Arkansas Nuclear One, Unit 1 Docket No. 50-313 License No. DPR-51

1.

Entergy supplemental letter to the NRC dated March 22, 2007, Request for Alternative ANO I-R&R-O 10, Proposed Alternative to ASME Code Requirements for Weld Overlay Repairs (CNRO-2007-00014)

2.

Entergy revised letter to the NRC dated March 6, 2007, Request for Alternative ANOI-R&R-010, Proposed Alternative to ASME Code Requirements for Weld Overlay Repairs (CNRO-2007-0001 0)

3.

Entergy letter to the NRC dated January 12, 2007, Request for Alternative ANOI-R&R-010, Proposed Alternative to ASME Code Requirements for Weld Overlay Repairs (CNRO-2007-00001)

Dear Sir or Madam:

On March 22, 2007, Entergy Operations, Inc. (Entergy) submitted a supplemental letter to the NRC (Reference 1) concerning a proposed alternative to ASME Code requirements for weld overlay repairs associated with the reactor coolant pressurizer and hot leg piping nozzles (References 2 and 3). In the revised letter, Entergy committed to submitting a stress analysis summary report relating to the results of the aforementioned weld overlays performed during the Arkansas Nuclear One, Unit 1 (ANO-1) refueling outage, 1 R-20. The commitment required submittal of the report prior to initial entry into plant operating Mode 4 following 1 R-20.

The required stress analysis report is included in Attachment 1 of this letter. All reactor coolant pressurizer and hot leg piping nozzle weld overlays installed during 1 R-20 were found to be satisfactory and meet all requirements for ANO-1 Cycle 21 operation.

There are no new commitments proposed in this letter.

4&iY7

1 CAN050703 Page 2 of 2 if you have any questions or require additional information, please contact David Bice at 479-858-5338.

1 declare under penalty of perjury that the foregoing is true and correct. Executed on May 8, 2007.

Sincerely, DEJ/dbb Attachments:

1. Summary of Design and Analyses of Weld Overlays for Pressurizer and Hot Leg Nozzle Large Bore Dissimilar Metal Welds for Alloy 600 Mitigation cc:

Dr. Bruce S. Mallett Regional Administrator U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 NRC Senior Resident Inspector Arkansas Nuclear One P. 0. Box 310 London, AR 72847 U. S. Nuclear Regulatory Commission Attn: Ms. Farideh E. Saba MS 0-8 B1 Washington, DC 20555-0001 Mr. Bernard R. Bevill Director Division of Radiation Control and Emergency Management Arkansas Department of Health & Human Services P.O. Box 1437 Slot H-30 Little Rock, AR 72203-1437 1 CAN050703 Summary of Design and Analyses of Weld Overlays for Pressurizer and Hot Leg Nozzle Large Bore Dissimilar Metal Welds for Alloy 600 Mitigation to 1 CAN050703 Page 1 of 16 Summary of Design and Analyses of Weld Overlays for Pressurizer and Hot Leg Nozzle Large Bore Dissimilar Metal Welds for Alloy 600 Mitigation 1.0 Introduction Entergy will preemptively apply full structural weld overlays (WOLs) on dissimilar metal welds (DMWs) of two 3" safety valve nozzles, one 2-1/2" relief valve nozzle, one 4" spray nozzle (including one nozzle-to-safe end weld and one safe end-to-pipe weld), and one 10" surge nozzle in the pressurizer and one 10" surge nozzle in the hot leg. The purpose of these overlays is to eliminate dependence on the primary water stress corrosion cracking (PWSCC) susceptible Alloy 82/182 welds as pressure boundary welds and to mitigate any potential future PWSCC in these welds. The overlays will be installed using a PWSCC resistant weld filler material, Alloy 52M [1].

The requirements for design of weld overlay repairs are defined in the Relief Request [2],

which is based on ASME Code Case N-740 [3]. Weld overlay repairs are considered to be acceptable long-term repairs for PWSCC susceptible weldments if they meet a conservative set of design assumptions which qualify them as "full structural" weld overlays. The design basis flaw assumption for full structural weld overlays is a circumferentially oriented flaw that extends 3600 around the component; that is, completely through the original component wall thickness. A combination of internal pressure, deadweight, seismic and other dynamic stresses is applied to the overlaid nozzles containing this assumed design basis flaw, and they must meet the requirements of ASME Code,Section XI, IWB 3641 [4].

ASME Code,Section III stress and fatigue usage evaluations are also performed that supplement existing piping, safe end, and nozzle stress reports, to demonstrate that the overlaid components continue to meet ASME Code,Section III requirements. The original construction Code for the pressurizer was ASME,Section III, 1965 Edition, Summer 1967 Addenda, and for the Hot Leg was USAS, B31.7, 1968 Edition, June 1968 Errata. However, as allowed by ASME Section XI, Code Editions and Addenda later than the original construction Code may be used. ASME Code,Section III, 2001 Edition with Addenda through 2003 [5] was used for these analyses.

In addition to providing structural reinforcement to the PWSCC susceptible locations with a resistant material, weld overlays have also been shown to produce beneficial residual stresses that mitigate PWSCC in the underlying DMWs. The weld overlay approach has been used to repair stress corrosion cracking in U.S. nuclear plants on hundreds of welds, and there have been no reports of subsequent crack extension after application of weld overlays. Thus, the compressive stresses caused by the weld overlay have been effective in mitigating new crack initiation and/or growth of existing cracks.

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

to 1 CAN050703 Page 2 of 16 2.0 Analysis Summary and Results 2.1 Weld Overlay Structural Sizing Calculations Detailed sizing calculations for weld overlay thickness were performed using the "Codes and Standards" module of the pc-CRACK computer program [6], which incorporates ASME Code,Section XI, IWB-3640 evaluation methodology. Loads and stress combinations were provided by Entergy. Both normal operating/upset (Level A/B) and emergency/faulted (Level C/D) load combinations were considered in this evaluation, and the design was based on the more limiting results. The resulting minimum required overlay thicknesses are summarized in Table 2-1.

The weld overlay length must consider: (1) length required for structural reinforcement, (2) length required for access for preservice and inservice examinations of the overlaid weld, and (3) residual stress improvement. In accordance with the Relief Request [2] and ASME Code Case N-740 [3], the minimum weld overlay length required for structural reinforcement was established by evaluating the axial-radial shear stress due to transfer of primary axial loads from the pipe into the overlay and back into the nozzle, on either side of the weld(s) being overlaid. Axial weld overlay lengths were established such that this stress is less than the ASME Section III limit for pure shear stress. Because of the Alloy 600 safe end on the pressurizer spray nozzle and the DMW between the safe end and stainless steel piping, it is necessary to extend the overlay over both the nozzle-to-safe end weld and the safe end-to-pipe weld for the spray nozzle. The resulting minimum length requirements are summarized in Table 2-1.

The overlay length and profile must also be such that the required post-WOL examination volume can be inspected using Performance Demonstration Initiative (PDI) qualified nondestructive examination (NDE) techniques. This requirement can cause required overlay lengths to be longer than the minimums for structural reinforcement. Typical weld overlay designs for the ANO-1 pressurizer and hot leg nozzles are illustrated in Figures 2-1 through 2-3. The designs were reviewed by qualified NDE personnel to ensure that they meet inspectability requirements, and the overlays were designed to satisfy full structural requirements for the DMWs. The design thickness and length specified on the design drawings bound the calculated minimum values, and may be greater to facilitate desired geometry for examination.

to 1 CAN050703 Page 3 of 16 Table 2-1: Weld Overlay Structural Thickness and Length Requirements 2-1/2" 3Se SprayN Spray**

Hot Leg Pressurizer Location Relief Safety Nozzle-Safe End-Surge Surge Valve Valve Safe End Pipe Weld Nozzle Nozzle Nozzle Nozzle Weld Minimum Nozzle Side 0.271 0.387 0.188 0.135 0.417 0.375 Thickness Flange/Pipe/

0.333 0.417 0.250 0.145 0.333 0.354 (in.)

Safe End Side Nozzle Side 0.543 1.258 0.454 NA 0.975 1.136 Minimum*

Length (in.)

Elbow/Safe 0.582 1.349 NA 0.471 1.010 1.234 End Side

• Length shown is the minimum required for structural acceptance and does not include additional lengths necessary to meet inspectability.

• • For spray nozzle, both the nozzle-to-safe end weld and the safe end-to-pipe weld are dissimilar metal welds. For the safe end-to-pipe weld, the nozzle side is the safe end side.

to 1 CAN050703 Page 4 of 16 2.2 Section III Stress Analyses Stress intensities for the weld overlaid pressurizer safety valves, relief valve, spray and surge nozzles and the hot leg surge nozzle were determined from finite element analyses for the various specified load combinations and transients using the ANSYS software package [7].

Linearized stresses were evaluated at various stress locations using 2-dimensional, axisymmetric and 3-dimensional solid models. A typical finite element model showing stress path locations is provided in Figure 2-4. The stress intensities at these locations were evaluated in accordance with ASME Code,Section III, Sub-articles NB-3200 and NB-3600 [5], and compared to applicable Code limits. A summary of the stress and fatigue usage comparisons for the most limiting locations is provided in Table 2-2. The stresses and fatigue usage in the weld overlaid nozzles are within the applicable Code limits. In general, the limiting location for the Section III stress analyses was found to be the section of the original pipe at the end of the overlay (Path 1 in Figure 2-4).

Table 2-2: Limiting Stress Results for Weld Overlaid Nozzles Load Nozzle Combination Type Calculated Allowable Level A/B Primary + Secondary (P +Q) (ksi)*

41.28 49.33 3" Safety Fatigue Cumulative Usage Factor 0.0084 1.000 2-1/2" Level A/B Primary + Secondary (P +Q) (ksi)*

29.95 49.33 Relief Fatigue Cumulative Usage Factor 0.0039 1.000 Primary + Secondary (P +Q) (ksi)*

65.3**

59.03 Level A/B Simplified Elastic-Plastic Analysis 31.8**

59.03 Spray (P +Q) (ksi)

Fatigue Cumulative Usage Factor 0.006**

1.000 Primary + Secondary (P +Q) (ksi)*

65.613**

49.94 Hot Leg Level A/B Simplified Elastic-Plastic Analysis 30.52**

54.82 Surge (P +Q) (ksi)

Fatigue Cumulative Usage Factor 0.811 1.000 Primary + Secondary (P +Q) (ksi)*

56.21**

49.8 PZR Level A/B Simplified Elastic-Plastic Analysis 27.37**

49.8 Surge (P +Q) (ksi)

Fatigue Cumulative Usage Factor 0.365 1.000

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

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

to 1 CAN050703 Page 5 of 16 2.3 Residual Stress and Section XI Crack Growth Analyses Weld residual stresses for the ANO-1 pressurizer and hot leg nozzle weld overlays were determined by detailed elastic-plastic finite element analyses. The analysis approach has been previously documented to provide predictions of weld residual stresses that are in reasonable agreement with experimental measurements. Two-dimensional, axisymmetric finite element models were developed for each of the nozzles. Modeling of weld nuggets used in the analysis to lump the combined effects of several weld beads is illustrated in Figure 2-5. The models simulated an inside surface (ID) repair at the DMW location with a depth of approximately 50% of the original wall thickness. This assumption is considered to conservatively bound any weld repairs that may have been performed during plant construction from the standpoint of producing tensile residual stresses on the ID of the weld.

The residual stress analysis approach consists of a thermal pass to determine the temperature response of the model to each individual lumped weld nugget as it is added in sequence, followed by an elastic-plastic stress pass to calculate the residual stresses due to the temperature cycling from the application of each nugget. Since residual stresses are a function of welding history, the stress passes for each nugget are performed sequentially, over the residual stress fields induced from all previously applied weld nuggets. The resulting residual stresses were evaluated on the inside surface of the original welds and safe-end components, as well as on several paths through the DMWs (Figures 2-6 and 2-7). Note that PWSCC susceptible regions are marked by dashed lines in Figure 2-7.

The residual stress calculations were then utilized, along with stresses due to applied loadings and thermal transients, to demonstrate that assumed cracks that could be missed by inspections will not exceed the overlay design basis during the ASME Section XI inservice inspection interval due to fatigue or PWSCC. In the fatigue crack growth analyses, the 60 year design quantity of each applied transient was assumed to be applied. Initial flaw sizes for the crack growth assessments were assumed consistent with the post-overlay UT inspections performed. Fatigue crack growth results are summarized in Table 2-3 for initial flaw sizes of 25%, 50% and 75% of the original weld thickness. In all cases, the maximum crack depth at the end of the 60-year design life is less than the weld overlay design basis flaw, except for the pressurizer surge nozzle and the hot leg surge nozzle. In these cases, the maximum crack growth life is specified and it is greater than the 10-year inspection period. The design basis flaw for crack growth purposes is the original weld thickness for all the nozzle welds except for the hot leg surge nozzle weld. The design basis flaw for the hot leg surge nozzle weld includes excess weld overlay thickness specified on the design drawing beyond that required for structural reinforcement per Table 2-1. Since the exam volume for the PDI qualified post-overlay UT inspections includes the weld overlay plus the outer 25% of the original wall thickness, a 75% through wall crack is the largest flaw that could escape detection by this examination.

For crack growth due to PWSCC, the total sustained stress intensity factor during normal plant operation was determined as a function of assumed crack depth, considering internal pressure stresses, residual stresses, steady state thermal stresses, and stresses due to sustained piping loads (including deadweight). Zero PWSCC growth is predicted for assumed crack depths at which the combined stress intensity factor due to sustained steady state operating conditions is less than zero. For all nozzles, considering the worst case paths in the DMWs, the sustained stress intensity factors remained negative for crack depths up to to 1 CAN050703 Page 6 of 16 and beyond 75% of the original wall thickness, except for circumferential flaws in the hot leg surge nozzle. Therefore, no crack propagation due to PWSCC is predicted in the overlaid nozzles, except for the hot leg surge nozzle. The crack growth results provided in Table 2-3 for circumferential and axial flaws in the pressurizer and hot leg surge nozzle include both PWSCC and fatigue crack growth.

2.4 Evaluation of As-Built Conditions The Relief Request [2] and Code Case N-740 [3] require evaluation of the as-built weld overlays to determine the effects of any changes in applied loads, as a result of weld shrinkage from the entire overlay, on other items in the piping system. These evaluations will be performed and documented separately from this report and will include the effects of the disposition of any non-conformances that occurred during weld overlay installation. In anticipation of the required as-built evaluations, calculations were performed based on design dimensions to confirm that the overlays would not adversely affect critical piping components.

Specifically, the predicted axial and radial shrinkage effects of the overlays on the thermal sleeves attached to the pressurizer spray and surge nozzles, based on design dimensions and welded mockups, were evaluated and found to be acceptable. Also, the effect of the added weight of the overlays on the adjacent piping systems, based on design dimensions, was evaluated and found to be insignificant.

Table 2-3:

Limiting Fatigue Crack Growth Results for Weld Overlaid Nozzles 2-112" Relief PZR Surge DMW 3" Safety Nozzle Nzl oze Nozzle Nozzle*

Initial Flaw Size Flaw Size (in.)

Flaw Size (in.)

Flaw Size (in.)

(% of Orig. Thick.)

Initial Final Initial Final Initial Final Circumferential Flaws 25%

0.2813 0.2818 0.25 0.25 50%

0.5625 0.5625 0.50 0.50 75%

0.8438 0.8438 0.75 0.75 0.855**

1. 1406**

Axial Flaws 25%

0.2813 0.2813 0.25 0.25 50%

0.5625 0.5625 0.50 0.50 75%

0.8438 0.8438 0.75 0.75 0.855**

1.1406**

Overlay design 1.125 1.0 1.1406 basis flaw Includes PWSCC and fatigue crack growth for the pressurizer and hot leg surge nozzle circumferential and axial flaws only.

Time to reach overlay design basis flaw is 25.7 years for circumferential flaw and 36.3 years for axial flaw. 25% and 50% initial flaw sizes were not evaluated.

to 1 CAN050703 Page 7 of 16 Hot Leg Surge Spray Nozzle-Safe Spray Safe End-Nozzle*

End Weld to-Pipe Weld Initial Flaw Size Flaw Size (in.)

Flaw Size (in.)

Flaw Size (in.)

(% of Orig. Thick.)

Initial Final Initial Final Initial Final Circumferential Flaws 25%

0.1875 0.1875 0.1050 0.1053 50%

0.3750 0.3750 0.2100 0.2104 75%

0.711**

1.2075**

0.5625 0.5625 0.3150 0.3160 Axial Flaws 25%

0.1875 0.1875 0.1050 0.1050 50%

0.3750 0.3750 0.2100 0.2100 75%

0.711 1.2075 0.5625 0.5625 0.3150 0.3150 Overlay design 1.2075***

0.75 0.42 basis flaw I

Includes PWSCC and fatigue crack growth for the pressurizer and hot leg surge nozzle circumferential and axial flaws only.

Time to reach overlay design basis flaw is 18.1 years for circumferential flaw and greater than 60 years for axial flaw. 25% and 50% initial flaw sizes were not evaluated.

Original weld thickness 0.9475" plus 0.26" of overlay thickness.

to 1CAN050703 Page 8 of 16 ANO-1 Pressurizer Spray Nozzle Structural Overlay Alloy 52M Overlay UI L

Alty18 Alloy 82/182 Ss Weld I

Pipe 4" PZR Spray Nozzle A508 Class 1 Carbon Steel It Figure 2-1: Illustration of Typical Weld Overlay Design for ANO-1 Pressurizer Spray Nozzle to 1 CAN050703 Page 9 of 16 ANO-1 Pressurizer Safety and ERV Nozzle Structural Overlay 4-.---.-f SSAlloy 182 Cld Butter I

I 3" PZR Safety Nozzles (typ), A508 Class 1 2.5" PZR ERV Nozzle, A508 Class 1 Carbon Steel Alloy 82/182 Weld SS Flanges (typ)

SA-182 TP 316 Figure 2-2: Illustration of Typical Weld Overlay Design for ANO-1 Valve Nozzle Pressurizer Safety/Relief

Attachment I to 1 CAN050703 Page 10 of 16 ANO-1 Pressurizer and Hot Leg Surge Nozzle Structural Overlay (typ)

SAllay SM Overlay Figure 2-3: Illustration of Typical Weld Overlay Design for ANO-1 Pressurizer and Hot Leg Surge Nozzle to 1 CAN050703 Page 11 of 16 ANSYS

8. Ii Path 3 Path 2 Path 1 Node 1736 l

Figure 2-4: Typical Finite Element Model for Section III Stress Evaluation showing Stress Paths to 1CAN050703 Page 12 of 16 AM3 SPRAY JNDZZLE-FEM 1M-[EL Figure 2-5: Typical Finite Element Model for Residual Stress Analysis showing Nuggets used for Welding Simulations to 1 CAN050703 Page 13 of 16 ANSYS 8. IA1 (ode 267 Node 298 Node 300 ANsYs 8. IAI S3 ANSYS 8. IAI Nod 470 Node 1064 I

Node 66 Node 553 Figure 2-6: Finite Element Model for Residual Stress Analysis showing Paths used in Crack Growth Evaluations to 1 CAN050703 Page 14 of 16 ID Surface Axial Residual Stress Post ID weld repair 70°F Post weld overlay 6500F Post weld overlay 70°F

--=- Post butt weld 70OF 80 60 40 20 0

-20

-40

-60

-4

-2 0

2 4

6 8

Distance from ID Weld Repair Centerline (in) 10 ID Surface Hoop Residual Stress Post ID weld repair 70°F

-A-Post weld overlay 70°F Post weld overlay 650°F Post butt weld 70°F 80 60 Nozzle sio

• Ppe side 40 T 0 A

-40

-60

-80 I

I

-4

-2 0

2 4

6 8

10 Distance from ID Weld Repair Centerline (in)

Figure 2-7: Residual Stress Results along Inside Surface of Original Butt Welds and Safe-End for Spray Nozzle (General profile typical for other nozzle welds) to 1CAN050703 Page 15 of 16 3.0 Conclusions The design of the ANO-1 weld overlays was performed in accordance with the requirements of the Relief Request [2], which is based on ASME Code Case N-740 [3]. The weld overlays are demonstrated to provide long-term mitigation of PWSCC in these welds based on the following:

" In accordance with the Relief Request [2], structural design of the overlays was performed to meet the requirements of ASME Section Xl, IWB-3640 based on an assumed flaw 100% through and 3600 around the original welds. The resulting full structural overlays thus restore the original safety margins of the nozzles, with no credit taken for the underlying, PWSCC-susceptible material.

The weld metal used for the overlay is Alloy 52M, which has been shown to be resistant to PWSCC [1], thus providing a PWSCC resistant barrier. Therefore, no PWSCC crack growth is expected into the overlay except for the hot leg surge nozzle circumferential flaw.

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

Nozzle specific residual stress analyses were performed, after first simulating severe ID weld repairs in the nozzle-to-safe-end welds, prior to applying the weld overlays.

The post weld overlay residual stresses were shown to result in beneficial compressive stresses on the inside surface of the components, and well into the thickness of the original DMWs, except in certain limited cases, assuring that future PWSCC initiation or crack growth into the overlay is highly unlikely or at worst for certain cases, limited.

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

Both fatigue and PWSCC crack growth were considered, and found to be acceptable.

Based on the above observations and the fact that similar nozzle-to-safe end weld overlays have been applied to other plants since 1986 with no subsequent problems identified, it is concluded that the Arkansas Nuclear One, Unit 1 pressurizer surge, safety, relief and spray nozzle, and hot leg surge nozzle dissimilar metal welds have received long term mitigation against PWSCC.

to 1 CAN050703 Page 16 of 16 4.0 References

1. "Materials Reliability Program (MRP): Resistance to Primary Water Stress Corrosion Cracking of Alloys 690, 52, and 152 in Pressurized Water Reactors (MRP-111)," EPRI, Palo Alto, CA: 2004. 1009801

2. Request for Alternative ANO1-R&R-010, "Proposed Alternative to ASME Code Requirements for Weld Overlay Repairs."

3. ASME Boiler and Pressure Vessel Code, Code Case N-740, "Dissimilar Metal Weld Overlay for Repair of Class 1, 2, and 3 Items,Section XI, Division 1."

4. ASME Boiler and Pressure Vessel Code, Section Xl, 1992 Edition.

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

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

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