ML050830265
| ML050830265 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 03/16/2005 |
| From: | Bethay S Entergy Nuclear Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| TAC MC2496 | |
| Download: ML050830265 (9) | |
Text
'Entergy Entergy Nuclear Operations, Inc.
Pilgrim Station 600 Rocky Hill Road Plymouth, MA 02360 Stephen J. Bethay Drector, Nuclear Assessment March 16, 2005 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555-0001
SUBJECT:
Entergy Nuclear Operations, Inc.
Pilgrim Nuclear Power Station Docket No. 50-293 License No. DPR-35 Pilgrim Relief Request, PRR-39, Revision 2 (TAC NO. MC2496)
REFERENCE:
- 1. Entergy Letter No. 2.04.091, Response to NRC Request for Additional Information and PRR-39, Rev. 1, Alternative Contingency Repair Plan for Reactor Pressure Vessel Nozzle Safe-End and Dissimilar Metal Piping Welds Using ASME Code Cases N-638 and N-504-2 with Exceptions, dated, October 12, 2004.
LETTER NUMBER: 2.05.024
Dear Sir or Madam:
This letter provides Pilgrim revised PRR-39, Revision 2 (Attachment 1). Revision 2 to PRR-39 limits the maximum weld overlay repair area to 300 sq. in.
There are no commitments contained in this letter.
If you have any questions or require additional information, please contact Mr. Bryan Ford, Licensing Manager, at (508) 830-8403.
WGUdm Attachment 1: Pilgrim Relief Request, (PRR)-39, Revision 2 (7 pages) 2.05.024 XIn
Entergy Nuclear Operations, Inc. Letter Number: 2.05.024 Pilgrim Nuclear Power Station Page 2 CC: Mr. John P. Boska, Project Manager U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Region 1 Mail Stop: 0-8B-1 475 Allendale Road U.S. Nuclear Regulatory Commission King of Prussia, PA 19406 1 White Flint North 11555 Rockville Pike Senior Resident Inspector Rockville, MD 20852 Pilgrim Nuclear Power Station 2.05.024
ATTACHMENT 1 PILGRIM RELIEF REQUEST (PRR) NO. - 39, Rev. 2 Alternative Repair Plan for Reactor Pressure Vessel Nozzle Safe-End and Dissimilar Metal (DM) Piping Welds A. COMPONENT IDENTIFICATION A full structural weld overlay repair is proposed for the weldment associated with the following austenitic reactor pressure vessel nozzle safe-end and dissimilar metal (DM) piping welds. This is a contingency repair plan to be used if needed during the upcoming refueling outage-1 5.
WELD ID DESCRIPTION SYSTEM DRAWING 14-A-1 SAFE END TO NOZZLE Cs ISI-1-14-1 14-B-1 SAFE END TO NOZZLE CS ISI-1-14-1 2R-N1B-1 SAFE END TO NOZZLE RECIRC ISI-+-2R-A 2R-N2D-1 SAFE END TO NOZZLE RECIRC ISI-1-2R-A 2R-N2E-1 SAFE END TO NOZZLE RECIRC ISI-1-2R-A 2R-N2F-1 SAFE END TO NOZZLE RECIRC ISI-1-2R-B 2R-N2G-1 SAFE END TO NOZZLE RECIRC ISI-1-2R-B 2R-N2J-1 SAFE END TO NOZZLE RECIRC ISI-1-2R-B 14-A-3 PIPE TO REDUCER CS ISI-1-14-1 14-B-3 PIPE TO REDUCER CS ISI-1-14-1 14-A-10A VALVE TO PIPE CS ISI-1-14-1 14-B-10A VALVE TO PIPE CS ISI-1-14-1 These welds fall within the scope of GL 88-01 and BWRVIP-75.
The weld overlay material for the proposed repair is as follows:
- For machine gas tungsten arc welding (GTAW), the weld material is ASME Section 11,Part C, SFA 5-14 Filler Wire ER NiCrFe-7 UNS N06052 F-No. 43 known commercially as Alloy 52.
- For manual shielded metal arc weld (SMAW) welding, the weld material is ASME Section II, Part C, SFA 5-11 Weld Electrode E NiCrFe-7 UNS W86152 known commercially as Alloy 152.
B. EXAMINATION AND REPAIR REQUIREMENTS Weld overlay will be designed consistent with the requirements of NUREG-0313, (which was implemented by Generic Letter 88-01), ASME Code Cases N-504-2, N-638, and ASME,Section XI, Paragraph IWB-3640.
Welder Qualification and Welding Procedures All welders and welding procedures will be qualified in accordance with ASME Section Xl and any special requirements from Section Xl or applicable code cases.
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If necessary, a manual SMAW procedure will be qualified to facilitate localized repairs and to provide a seal weld, prior to the overlay. This procedure uses UNS W86152 SMAW electrodes consistent with ASME Section Xl requirements. Personnel qualified in accordance with the Welding Procedure Specification for welding Alloy 52/152 will perform the repair activities.
Welding Wire Material A consumable welding wire highly resistant to intergranular stress corrosion cracking (IGSCC) will be used for the overlay material. This material, designated UNS N06052, is a nickel-based weld filler material (commonly referred to as Alloy 52), and will be applied using the GTAW process. Alloy 52 is identified as F-No. 43 Grouping for Ni-Cr-Fe, classification UNS N06052 Filler Metal. Alloy 52 contains about 30% chromium, which imparts excellent corrosion resistance to this material. Alloy 152 welding wire will be used for manual (SMAW) seal welding activities.
Weld Overlay Design The weld overlay will extend around the full circumference of the weldment location in accordance with NUREG-0313, Code Case N-504-2, Generic Letter 88-01, and BWRVIP-
- 75. The overlay will be performed using a standard overlay design as described in NUREG-0313, Section 4.4.1. This design assumes a crack completely through the wall for 360'.
The calculation methods for design of the overlay will be in accordance with NUREG-0313, Section 4.1.
The specific thickness and length will be computed using the guidance provided in ASME Section Xl, Code Case N-504-2, and ASME Section Xl, Paragraph IWB-3640,1989 Edition.
The overlay will completely cover any flaw location and the existing Inconel 182 weld deposit butter with the highly corrosion resistant Alloy 52 material. Inorder to accomplish this objective, it is necessary to weld on the low alloy steel (LAS) material. A temper bead welding approach will be used for this purpose according to the provisions of ASME Code Case N-638. This code case provides for machine GTAW temper bead weld repairs to P No.3 nozzle materials (SA 508 Cl.2) at ambient temperature. The temper bead approach was selected because temper bead welding supplants the requirement for post weld heat treatment (PWHT) of heat-affected zones in welded LAS material.
The Code case N-638, General Requirements, 1(a) limits the maximum finished surface area of the weld overlay repair to 100 sq. in. The overlay repair (design and fabrication) on large diameter (13 and 29-inch OD) recirculation nozzle safe-end welds would exceed the 100 sq. in. limit and requires NRC approval for a maximum finished weld repair surface area up to 300 sq. in. on the basis of analysis in EPRI Technical Report 1003616, "Additional Evaluations to Extend Repair Limits for Pressure Vessels and Nozzles", dated March 2004.
Susquehanna Station has used the EPRI Report as justification for recent nozzle weld overlay repairs. If the weld overlay necessary for a nozzle exceeds 300 sq. in., additional relief will be requested.
Examination Requirements The repair, pre-service inspection (PSI), and in-service inspection (ISI) examinations of the weld overlay repair will be performed in accordance with the ISI Program and Plan along with NUREG-0313, Generic Letter 88-01,and approved plant procedures as specified bythe ISI Repair/Replacement Program.
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The weld overlay will be examined using the industry developed PDI procedure, as approved in PRR-38 (Relief from ASME Code Section Xi, Appendix VIII, Supplement 11, Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds, TAC No.
MC0961, dated February 26, 2004).
System leakage testing will be performed as allowed by Code Case N-416-2 with the additional condition that hold times specified in IWA-5213 (d) be observed, in lieu of the system hydrostatic test required by Code Case N-504-2. This complies with Regulatory Guide 1.147, Revision 13, relative to the NRC's conditional acceptance of Code Case N-416-2. The VT-2 inspections will be performed with the insulation removed from the locations where the proposed weld overlays are performed. This will allow a 10 minute hold before the VT-2 is performed.
The examinations and acceptance criteria, as identified below, will be in accordance with ASME Code,Section III, 1992 Edition, Subsection NB for Class 1Components, ASME Code Section Xl, 1989 Edition, and Code Cases N-504-2 and N-638.
A description of the required examinations for the weld overlay is provided in the following table.
Examination Description Method Technique Reference Weld Overlay Surface Area PT Visible Dye N-504-2 Preparation Exam First Two Weld Overlay Layers PT Visible Dye N-504-2 Surface Exam First Two Weld Overlay Layers UT or 00 Long. UT or N-504-2 Thickness Measurements Mechanical Mechanical Height Measurement Completed Overlay UT or 00 Long. UT or N-504-2 Thickness Measurements Mechanical Mechanical Height Measurement Surface Exam of Final Overlay PT Visible Dye NB-5350 Surface and Adjacent Band within IWB-3514 1.5t (7/8" Band) of Weld Overlay. N-638 This also serves as Preservice N-504-2 Surface Examination of completed overlay.
Volumetric Exam of Final Overlay UT PDI procedure ASME 1995, and Adjacent Band within 1.5t Section Xl (7/8" Band) of Weld Overlay. Appendix VIII; This also serves as Preservice ASME 1989 Volumetric Examination of Section Xl completed overlay.
Preservice Baseline Exam of UT PDI Procedure N-504-2 Final Overlay Outer 25% of the Underlying Pipe Wall to Identify the Original Flaws.
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The acceptance criteria for the volumetric examinations shall be ASME Code Section XI, Paragraph IWB-3514, "Standards for Examination Category B-F, Pressure Retaining Dissimilar Metal Welds, and Examination Category B-J, Pressure Retaining Welds in Piping".
It is noted that the curvatures of reactor nozzles require an exception to the ultrasonic inspection requirement for a 1.5t adjacent band volumetric examination at the end of the overlay on the nozzle end. The PT examination of this surface will constitute the acceptance testing for the overlay deposit.
Thickness will be characterized at four (4) azimuths representing each of the four (4) pipe quadrants. Thickness measurements will be determined using UT techniques or by mechanical measurement. Liquid penetrant examinations will be performed at the same stages of the overlay application as the thickness measurements identified above.
The alternative, as described below, provides an acceptable level of quality and safety while neither draining the reactor vessel nor applying preheat and post weld heat treatments.
C. ALTERNATIVE TO REPAIR REQUIREMENTS The repair will utilize ASME Code Case N-504-2, "Alternative Rules for Repair of Class 1,2, and 3 Austenitic Stainless Steel Piping," and Code Case N-638, "Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique," with the following exceptions and clarifications.
Clarification of Code Case N-504-2 for Applicability to Nickel-Based Austenitic Alloy Code Case N-504-2 was prepared specifically for austenitic stainless steel material. An alternate application to use nickel-based austenitic materials (i.e., Alloy 52) is requested due to the specific configuration of the nickel-based austenitic weldment.
Exception from Code Case N-504-2 Paragraph (b)
Code Case N-504-2 paragraph (b) requires that the reinforcement weld metal shall be low carbon (0.035 % maximum) austenitic stainless steel. In this application, a nickel-based filler is required and Alloy 52 has been selected in place of low carbon austenitic stainless steel.
Exception from Code Case N-504-2 Paraaraoh (e)
Code Case N-504-2 paragraph (e) requires as-deposited delta ferrite measurements of at least 7.5% for the weld reinforcement. These measurements have no meaning for nickel-based materials and will not be performed for this overlay.
Exception from Code Case N-504-2 Paragraph (h)
Code Case N-504-2 paragraph (h) requires a system hydrostatic test of completed repairs if the repaired flaw penetrated the original pressure boundary or if there is any observed indication of the flaw penetrating the pressure boundary during repairs. A system leak test of completed repairs will be used in lieu of a hydrostatic test.
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Use of Code Case N-638 Applicability Code Case N-638 shall be applied to the nozzle material.
Exception from Code Case N-638 Paragraph 1 (a)
The Code case N-638, General Requirements, 1(a) limits the maximum finished surface area of the weld overlay repair to 100 sq. in. Relief is requested to extend the size of the repairs up to 300 sq. in. finished area to accommodate overlay repair on large diameter (13 and 29 -inch OD) recirculation nozzle safe-end welds.
D. BASIS FOR THE ALTERNATIVE Clarification of Code Case N-504-2 for Applicability to Nickel-Based Austenitic Steel The weldment being addressed is austenitic material having a mechanical behavior similar to austenitic stainless steel. The weldment is designed to be highly resistant to IGSCC and is compatible with the existing weldment and base metal materials. Accordingly, this alternative provides an acceptable level of quality and safety. Therefore, Code Case N-504-2 should be interpreted to apply equally to both materials.
Exception from Code Case N-504-2 Paragraph (b)
A consumable welding wire highly resistant to IGSCC was selected for the overlay material.
This material, designated UNS N06052, is a nickel-based alloy weld filler material, commonly referred to as Alloy 52, and will be applied using the GTAW process. Alloy 52 contains about 30% chromium, which imparts excellent stress corrosion cracking resistance to this material. By comparison, Alloy 82 is identified as an IGSCC resistant material in NUREG 0313 and contains about 18 to 22% chromium while Alloy 182 has a nominal chromium composition of 13 to 17%. Alloy 52 with its high chromium content provides a high level of resistance to IGSCC consistent with the requirements of the code case.
Therefore, this alternative provides an acceptable level of quality and safety.
Exception from Code Case N-504-2 Paragraph (e)
The composition of nickel-based Alloy 52 is such that delta ferrite is not formed during welding. Ferrite measurement requirements were developed for welding of 300 series stainless steels that required delta ferrite to develop corrosion resistance. Weld using Alloy 52 is 100% austenitic and contains no delta ferrite due to the high nickel composition (approximately 60% Ni and low iron content). Alloy 52 with its high chromium content provides a high level of resistance to hot cracking and IGSCC consistent with the purpose for the delta ferrite requirements for stainless steels of the code case. Therefore, this alternative provides an acceptable level of quality and safety.
Exception from Code Case N-504-2 Paragraph (Wi In lieu of the hydrostatic pressure test requirements defined in Code Case N-504-2, the required pressure test shall be performed in accordance with the Third Interval ISI Page 5 of 7
Program and Plan and Code Case N-416-2 with the exception that the volumetric examination performed shall be an ultrasonic examination of the weld overlay. These alternative requirements are sufficient to demonstrate that the overlay is of adequate quality to ensure the pressure boundary integrity. Accordingly, this alternative provides an acceptable level of quality and safety.
Use of Code Case N-638 Applicabilitv Code Case N-638 was developed for temper bead applications for similar and dissimilar metals. It permits the use of machine GTAW process at ambient temperature without the use of preheat or PWHT on Class 1, 2, and 3 components.
Temper bead welding methodology is not new. Numerous applications over the past decade have demonstrated the acceptability of temper bead technology in nuclear environments. Temper bead welding achieves heat affected zone (HAZ) tempering and grain refinement without subsequent PWHT. Excellent HAZ toughness and ductility are produced. Use of Code Case N-638 has been accepted in Regulatory Guide 1.147 Revision 13 as providing an acceptable level of quality and safety.
The overlay repair on large diameter (13 and 29-inch OD) recirculation nozzle safe-end welds would exceed the 100 sq. in. limit specified in Code Case N-638, paragraph 1(a).
EPRI Technical Report 1003616, "Additional Evaluations to Extend Repair Limits for Pressure Vessels and Nozzles", dated March 2004, justifies extending the size of the temper bead repair finished area. The ASME Code Committees have recognized that the 100 sq.
in. restriction on the overlay surface area is excessive and a draft code case, RRM-04, is currently being progressed within ASME Section Xl to increase the area limit. Furthermore, Three Mile Island and V. C. Summer have completed weld overlay repairs involving approximately 200 and 300 sq. inches respectively. Susquehanna Station in its Relief Request No.31 has used the EPRI Report, ASME proposed draft code case, V. C. Summer and Three Mile Island expanded repairs as justifications for recent expanded nozzle weld overlay repairs. As discussed in the EPRI Report, increasing the allowed areas for ambient temper bead repairs did not detrimentally change the residual stresses, thereby providing an acceptable level of quality and safety.
E. CONCLUSION Weld overlays involve the application of weld metal circumferentially over and in the vicinity of the flawed weld to restore ASME Section Xl margins as required by ASME Code Case N-504-2. Weld overlays have been used in the nuclear industry as an acceptable method to repair flawed weld. The use of overlay filler material that provides excellent resistance to IGSCC provides an effective barrier to crack extension.
The design of the overlay uses methods that are standard in the industry for size determination of pipe-to-pipe overlays. There are no new or different approaches used in these overlay designs that would be considered first of a kind or inconsistent with previous approaches. The overlay is designed as a full structural overlay in accordance with the recommendation of NUREG-0313, which was forwarded by Generic Letter 88-01, and Code Case N-504-2 and ASME Section Xl Paragraph IWB-3640.
Temper bead techniques, as defined by Code Case N-638, will produce a tough corrosion resistant overlay deposit that meets or exceeds all code requirements for the weld overlay.
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Pilgrim concludes that the contingency repair plan presents an acceptable level of quality and safety to satisfy the requirements of 10CFR50.55a(a)(3)(i). Similar proposed alternatives to the requirements of 10CFR50.55a(c)(3) have been previously approved by the NRC for James A Fitzpatrick (TAC No. MB0252, dated October 26, 2000), Duane Arnold Energy Center (NRC Staff's letter dated November 19, 1999), Nine Mile Point Unit 2 plant (NRC Staff's letter dated March 30,2000) and for Pilgrim to repair the RPV N10 nozzle to safe-end weld (PRR-36 and 38).
F. DURATION OF THE PROPOSED ALTERNATIVE The proposed alternative applies to the repairs of RPV nozzle safe-end and piping welds for the scheduled outage and for the remaining service life of this weld. Re-inspection will be per BWRVIP-75 Guidelines.
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