ML080580291

Safety Evaluation of Proposed Alternative to Apply Weld Overlay to Dissimilar Metal Welds

ML080580291
Person / Time
Site:	Vogtle, Farley
Issue date:	03/10/2008
From:	Cotton K NRC/NRR/ADRO/DORL/LPLII-1
To:	Jerrica Johnson Southern Nuclear Operating Co
Cotton, Karen -301-415-1438 NRR/DORL
References
TAC MD6307, TAC MD6308
Download: ML080580291 (18)

Text

March 10, 2008 Mr. J. Randy Johnson Vice President - Farley Joseph M. Farley Nuclear Plant 7388 North State Highway 95 Columbia, AL 36319

SUBJECT:

FARLEY UNIT 2 AND VOGTLE UNIT 1 RE: SAFETY EVALUATION OF PROPOSED ALTERNATIVE TO APPLY WELD OVERLAY TO DISSIMILAR METAL WELDS OF PRESSURIZER NOZZLES (TAC NOS. MD6307 AND MD6308)

Dear Mr. Johnson:

By letter dated July 24, 2007, as supplemented by letter dated December 26, 2007, Southern Nuclear Operating Company proposed alternative ISI-GEN-ALT-07-01, Version 2.0, to repair dissimilar metal welds of the pressurizer nozzles at Farley Nuclear Plant Unit 2 and Vogtle Electric Generating Plant Unit 1. Alternative ISI-GEN-ALT-07-01, Version 2.0, uses a full structural weld overlay to repair dissimilar metal welds on a contingency and preemptive basis.

The proposed approach is an alternative to the requirements of American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI.

Based on the information submitted, the U.S. Nuclear Regulatory Commission (NRC) staff concludes that the proposed alternative provides an acceptable level of quality and safety.

Therefore, pursuant to Title 10 of the Code of Federal Regulation 50.55a(a)(3)(i), the NRC staff authorizes alternative ISI-GEN-ALT-07-01, Version 2.0, for the repair of the dissimilar metal welds for the pressurizers at Farley Nuclear Plant Unit 2 and Vogtle Electric Generating Plant Unit 1. The effective period of the proposed alternative for Farley Unit 2 is the fourth ISI interval which ends on November 30, 2017. The effective period of the proposed alternative for Vogtle Unit 1 is the third ISI interval which ends on May 30, 2017.

Sincerely,

/RA/

Melanie C. Wong, Branch Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-364 and 50-424

Enclosure:

Safety Evaluation cc w/encl: See next page

March 10, 2008 Mr. J. Randy Johnson Vice President - Farley Joseph M. Farley Nuclear Plant 7388 North State Highway 95 Columbia, AL 36319

SUBJECT:

FARLEY UNIT 2 AND VOGTLE UNIT 1 RE: SAFETY EVALUATION OF PROPOSED ALTERNATIVE TO APPLY WELD OVERLAY TO DISSIMILAR METAL WELDS OF PRESSURIZER NOZZLES (TAC NOS. MD6307 AND MD6308)

Dear Mr. Johnson:

By letter dated July 24, 2007, as supplemented by letter dated December 26, 2007, Southern Nuclear Operating Company proposed alternative ISI-GEN-ALT-07-01, Version 2.0, to repair dissimilar metal welds of the pressurizer nozzles at Farley Nuclear Plant Unit 2 and Vogtle Electric Generating Plant Unit 1. Alternative ISI-GEN-ALT-07-01, Version 2.0, uses a full structural weld overlay to repair dissimilar metal welds on a contingency and preemptive basis.

The proposed approach is an alternative to the requirements of American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI.

Based on the information submitted, the U.S. Nuclear Regulatory Commission (NRC) staff concludes that the proposed alternative provides an acceptable level of quality and safety.

Therefore, pursuant to Title 10 of the Code of Federal Regulation 50.55a(a)(3)(i), the NRC staff authorizes alternative ISI-GEN-ALT-07-01, Version 2.0, for the repair of the dissimilar metal welds for the pressurizers at Farley Nuclear Plant Unit 2 and Vogtle Electric Generating Plant Unit 1. The effective period of the proposed alternative for Farley Unit 2 is the fourth ISI interval which ends on November 30, 2017. The effective period of the proposed alternative for Vogtle Unit 1 is the third ISI interval which ends on May 30, 2017.

Sincerely,

/RA/

Melanie C. Wong, Branch Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-364 and 50-424

Enclosure:

Safety Evaluation cc w/encl: See next page Distribution:

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SAFETY EVALUATION REPORT BY THE OFFICE OF NUCLEAR REACTOR REGULATION PROPOSED ALTERNATIVE ISI-GEN-ALT-07-01, VERSION 2.0 WELD OVERLAY OF PRESSURIZER NOZZLES JOSEPH M. FARLEY NUCLEAR PLANT, UNIT 2 VOGTLE ELECTRIC GENERATING PLANT, UNIT 1 SOUTHERN NUCLEAR OPERATING COMPANY DOCKET NUMBERS 50-364 and 50-424

1.0 INTRODUCTION

By letter dated July 24, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML072060283), Southern Nuclear Operating Company (the licensee) proposed alternative ISI-GEN-ALT-07-01, Version 1.0, to repair dissimilar metal welds associated with the pressurizer nozzles at Farley Nuclear Plant Unit 2 (FNP-2) and Vogtle Electric Generating Plant Unit 1 (VEGP-1). Alternative ISI-GEN-ALT-07-01, Version 1.0, uses a full structural weld overlay to repair dissimilar metal welds on a contingency and preemptive basis. The proposed approach is an alternative to the requirements of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI.

By letter dated December 26, 2007 (ADAMS Accession No. ML073610061), the licensee submitted revised alternative, ISI-GEN-ALT-07-01, Version 2.0, based on its response to the staffs request for additional information.

By letter dated August 10, 2006 (ADAMS Accession No. ML062220586), as supplemented by letters dated October 20, 2006 (ADAMS Accession No. ML062960237), January 3, 2007 (ADAMS Accession No. ML070040355), and February 21, 2007 (ADAMS Accession No. ML070540416), the licensee submitted proposed alternative ISI-GEN-ALT-06-03 to use a full-structural weld overlay to mitigate or repair dissimilar metal welds on a contingency and preemptive basis and to overlay adjacent similar metal welds when necessary.

By letter dated March 8, 2007, the U.S. Nuclear Regulatory Commission (NRC) staff authorized the use of Alternative ISI-GEN-ALT-06-03, Revision 2 (ADAMS Accession No. ML070600246).

Subsequently, by letter dated March 15, 2007 (ADAMS Accession No. ML070750077), the licensee requested relief from the requirements of the NRC-approved ISI-GEN-ALT-06-03, Revision 2, to change the frequency of interpass temperature measurements.

By letter dated April 3, 2007, the NRC authorized the alternate frequency for interpass temperature monitoring in ISI-GEN-ALT-06-03, Revision 2 (ADAMS Accession No. ML070790240).

The NRC-approved alternative ISI-GEN-ALT-06-03, Revision 2, has expired. Therefore, the licensee submitted alternative ISI-GEN-ALT-07-01, Version 2.0 to complete the weld overlay campaigns in FNP-2 and VEGP-1. The proposed alternative ISI-GEN-ALT-07-01, Version 2.0, is based on the technical requirements of NRC-approved alternative ISI-GEN-ALT-06-03, Revision 2.0.

The dissimilar metal butt weld joins the ferritic (i.e., carbon steel) pressurizer nozzle to the austenitic stainless steel safe end and is made of nickel-based Alloy 82/182. The industry has experienced degradation of the Alloy 82/182 weld material which is susceptible to primary water stress corrosion cracking (PWSCC) in the pressurized water reactor environment. The weld overlay repair is a process by which a PWSCC-resistant weld metal (such as Alloy 52 or 52M) is deposited on the outside surface of the degraded dissimilar metal weld as a new pressure boundary.

2.0 REGULATORY EVALUATION

Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) must meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, Rules for Inservice Inspection (ISI) of Nuclear Power Plant Components, to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examination of components and system pressure tests conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein.

Pursuant to 10 CFR 50.55a(a)(3), alternatives to requirements may be authorized by the NRC if the licensee demonstrates that: (i) the proposed alternatives provide an acceptable level of quality and safety, or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Farley Unit 2 is in the fourth ISI interval. Vogtle unit 1 is in the third ISI interval. The Code of record for FNP-2 and VEGP-1 is the ASME Section XI, 2001 edition through 2003 addenda. In addition, as required by 10 CFR 50.55a, performance demonstration examination of the welds will be based on Appendix VIII to the ASME Section XI, 2001 edition.

3.0 PROPOSED ALTERNATIVE ISI-GEN-ALT-07-01, Version 2.0

3.1 ASME Code Components Affected

Vogtle Unit 1 Dissimilar Metal Welds Similar Metal Welds 11201-V6-002-W17 (Relief) 11201-059-1 (Relief) 11201-V6-002-W18 (Safety) 11201-056-1 (Safety) 11201-V6-002-W19 (Safety) 11201-057-1 (Safety) 11201-V6-002-W20 (Safety) 11201-058-1 (Safety) 11201-V6-002-W21 (Spray) 11201-030-45 (Spray) 11201-V6-002-W22 (Surge) 11201-053-6 (Surge)

Farley Unit 2 Dissimilar Metal Welds Similar Metal Welds APR1-4205-49DM (Spray)

APR1-4205-48 (Spray)

APR1-4501-1DM (Safety)

APR1-4501-2 (Safety)

APR1-4502-1DM (Safety)

APR1-4502-2 (Safety)

APR1-4503-1DM (Safety)

APR1-4503-2 (Safety)

APR1-4504-1DM (Relief)

APR1-4504-2&3 (Relief) 3.2

Applicable Code Edition and Addenda

The current code of record for Farley Unit 2 and Vogtle Unit 1 is ASME Code,Section XI, 2001 edition through 2003 addenda. In addition, as required by 10 CFR 50.55a, ASME Code,Section XI, 2001 edition, is used for Appendix VIII, Performance Demonstration for Ultrasonic Examinations.

3.3 Applicable Code Requirements Subarticle IWA-4110 of the ASME Code,Section XI requires that repairs of welds shall be performed in accordance with Article IWA-4000. Subarticle IWA-4300 requires that defects be removed or reduced to an acceptable size.

Currently, pressurizer weld examinations are performed at the Vogtle and Farley nuclear plants using a Risk-Informed Program (Category R-A) that has been approved by the NRC. The examinations performed are the same as those volumetric examinations specified in Section XI, Table IWB-2500-1, Category B-J and B-F. After the installation of the weld overlays, the similar and dissimilar metal welds will no longer be included in the Risk-Informed ISI population, but will be examined in accordance with this proposed alternative.

3.4 Proposed Alternative and Basis In lieu of using IWA-4000 of the ASME Code,Section XI, the licensee proposes to use the alternative for the design, fabrication, pressure testing, and examination of the weld overlays.

VEGP-1 is scheduled to have preemptive full-structural weld overlays (FSWOLs) applied during the spring 2008 refueling outage. The licensee does not plan to perform ultrasonic examinations of the similar or dissimilar metal welds prior to the installation of the preemptive FSWOLs. Four of the six dissimilar welds on VEGP-1 have coverage less than 50 percent and for the other two dissimilar metal welds that are examinable, it is estimated about 0.6 Rem would be required to perform the examinations.

FNP-2 is scheduled for preemptive FSWOLs of the remaining welds during the spring 2010 refueling outage. The licensee does not plan to perform ultrasonic examinations of the similar or dissimilar metal welds prior to the installation of the preemptive FSWOLs. The licensee performed ultrasonic examinations on each of the six FNP-2 dissimilar metal butt welds during the spring 2007 refueling outage. As a result of ultrasonic indications detected in the surge nozzle dissimilar metal weld, the weld was overlaid per alternative ISI-GEN-ALT-06-03. In addition, the licensee examined two pressurizer dissimilar metal butt welds at FNP-2 during the fall 2005 outage with no evidence of PWSCC. For the remaining five dissimilar metal welds, it is estimated that about 0.5 Rem would be required to perform the examinations.

If through-wall leakage is detected by visual examination on any of the Farley or Vogtle pressurizer Alloy 82/182 safe-end welds, a contingency FSWOL will be applied. In lieu of performing ultrasonic examinations, the flaw will be assumed to be 100 percent through the original wall thickness for the entire circumference. Flaw characterization will be based on the as-found flaw size as discussed in section 2(a) of Alternative ISI-GEN-ALT-07-01, Version 2.0.

Due to the proximity of the adjacent similar metal piping welds, preemptive or contingency overlay of the safe-end welds may preclude the examination of the adjacent similar metal piping weld(s); therefore, the overlay will be extended over the adjacent similar metal piping welds, as necessary. This is expected to include all adjacent similar metal welds with the possible exception of those on the surge lines, where there may be sufficient separation between the dissimilar metal weld and the similar metal weld to allow examination of the similar metal weld after the dissimilar metal weld is overlaid. FNP-2 similar metal welds APR1-4504-2 and APR1-4504-3 are only a few inches apart; therefore, both welds may be overlaid along with the dissimilar metal weld.

This proposed alternative meets the technical requirements previously set forth in the April 3, 2007, NRC safety evaluation (SE) for alternative ISI-GEN-ALT-06-03, Revision 2.0 (as supplemented by letter dated March 15, 2007) with the single exception that the start of the 48-hour clock prior to performing examinations has been revised. This change to the start of the 48-hour clock has previously been approved by the NRC for Arkansas Nuclear One-Unit 1; therefore, this proposed alternative does not contain any technical content that has not already been approved by the NRC.

3.5 Duration of the Alternative The proposed alternative is applicable to VEGP-1 from May 31, 2007, through May 30, 2017, and applicable to FNP-2 from December 1, 2007, through November 30, 2017.

4.0 STAFF EVALUATION The methodology and associated requirements for the weld overlay design in proposed alternative ISI-GEN-ALT-07-01, Version 2.0, are similar to Code Case N-740, Dissimilar Metal Weld Overlay for Repair of Class 1, 2, and 3 ItemsSection XI, Division 1 of the ASME Code,Section XI. Code Case N-740 combines the requirements of Code Case N-504-2, Alternative Rules for Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping Section XI, Division 1, and N-638-1, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW [gas tungsten arc welding] Temper Bead Technique Section XI, Division 1.

The NRC staff has not yet adopted Code Case N-740. The NRC staff evaluated the proposed alternative based on the requirements of Code Case N-504-3 and N-638-1 which the NRC has endorsed in Regulatory Guide (RG) 1.147, Revision 15 which is incorporated by reference in 10 CFR 50.55a. In RG 1.147, Revision 15, the NRC staff imposed a condition on the use of Code Case N-504-3 that the requirements of Appendix Q to the ASME Code,Section XI, shall also be applied.

Although weld overlay of similar metal butt welds will be performed as part of weld overlay of the Alloy 82/182 welds, the licensee did not ask relief from the ASME requirements for weld overlay of the similar metal welds. Therefore, similar metal welds will not be discussed extensively and will not be part of the NRCs safety evaluation.

As the licensee stated above, proposed alternative ISI-GEN-ALT-07-01, Version 2.0, meets the proposed alternative ISI-GEN-ALT-06-03, Revision 2.0 (as supplemented by licensees letter dated March 15, 2007) with the single exception that the start of the 48-hour clock prior to performing examinations of the weld overlay has been revised. Although the weld overlay issues have been resolved in the review of ISI-GEN-ALT-06-03, Revision 2.0, some of the issues will be discussed in this SE for the purpose of updating the issue and providing regulatory traceability.

4.1 General Requirements The licensee stated that when components subject to being overlaid contain levels of trace chemicals (e.g., sulfur) that could cause unacceptable indications in the Alloy 52/152 weld, an initial layer of low carbon (maximum 0.035 percent) austenitic stainless steel may be applied as a buffer between the base metal and the Alloy 52/152 overlay. This buffer will be considered as a non-credited layer, i.e., the thickness of the buffer layer will not be considered as part of the total weld overlay thickness. The buffer layer will provide an acceptable chemical composition to apply the FSWOL. Depending on the chemical composition of the base materials where the weld overlay is to be applied, there may be different ways to apply the first layer of weld material. The licensee considered the effects of the buffer layer on the requirements previously set forth in this alternative. Significant points are:

1. The licensee stated that Code Case N-740, from which this alternative is derived, provides a methodology for the application of low carbon austenitic stainless and austenitic nickel alloys.

2. The licensee will not include this non-credited buffer layer in [weld overlay thickness]

calculations required by this alternative. This means that the actual weld overlay will be thicker than the design thickness and therefore is conservative.

3. Because the FSWOL over the Alloy 82/182 dissimilar metal weld will continue to consist of Alloy 52/152, there will be no effect on the ability of the overlay to stop the progress of PWSCC. The Alloy 52/152 weld overlay will continue to provide resistance to PWSCC considering the buffer layer.

4. The licensee and Electric Power Research Institute (EPRI) nondestructive examination (NDE) personnel reviewed the geometry of the weld overlay design and indicated that there will be no appreciable effect on the performance of ultrasonic examinations.

5. The licensee stated that no effects detrimental to the structure will be introduced by addition of the non-credited buffer layer.

6. Prior to deposition of the non-credited buffer layer, the surface will be examined by the liquid penetrant method. The licensee stated that indications larger than 1/16-inch shall be removed, reduced in size, or corrected in accordance with the following requirements:

(a) The licensee stated that one or more layers of weld metal shall be applied to seal unacceptable indications in the area to be repaired, with or without excavation. The thickness of these layers shall not be used in meeting weld reinforcement design thickness requirements. Peening the unacceptable indication prior to welding is permitted (b) If correction of indications is required, the area where the weld overlay is to be deposited, including any local repairs or initial weld overlay layer, shall be examined by the liquid penetrant method. The area shall contain no indications greater than 1/16-inch prior to the application of the structural layers of the weld overlay.

The NRC staff notes that many licensees have successfully applied the buffer layers to the stainless steel base metal prior to applying weld overlay as a means of preventing cracking in the Alloy 52/152 weld filler metal when applied to stainless steel base metal.

The staff finds that the installation of the non-credited buffer layer on the base metal is acceptable because the buffer layer prevents cracking of alloy 52/152 on austenitic stainless steel base metal, does not affect the ability of the Alloy 52/152 weld overlay to mitigate potential PWSCC in the base metal, and does not affect ultrasonic examination of the weld overlay.

4.2 Crack Growth Considerations and Design Section 2, Crack Growth Considerations and Design, of the proposed alternative provides the requirements for overlay design and the crack growth calculation. For a contingency weld overlay repair, the proposed alternative requires that flaw characterization and growth calculations be based on the as-found flaw(s) in the original weld. For the preemptive weld overlay, the crack growth calculation will be based on an initial flaw with a depth of 75 percent and a circumference of 360 degrees in length because the 75 percent through wall depth flaw is the largest flaw that could remain undetected during the FSWOL preservice examination.

The licensee will perform a preservice volumetric examination after application of the overlay using an ASME Code,Section XI, Appendix VIII [as implemented through the performance demonstration initiative (PDI)] examination procedure. This examination will verify that there is no cracking in the upper 25 percent of the original weld and base material. The PDI procedure is not qualified to examine the lower 75 percent of the pipe wall thickness. Therefore, a conservative approach is that a 75 percent through-wall crack is assumed to exist in the lower 75 percent of the pipe wall thickness. If no flaws were identified in the upper 25 percent of the original weld during preservice examination, the flaw depth for crack growth calculation would be 75 percent through-wall in the original weld. If any crack-like flaws are found during the preservice examination in the upper 25 percent of the original weld or base metal, the licensee will use an analyzed flaw (the postulated 75 percent through wall flaw plus the portion of the as-found flaw in the upper 25 percent) for the crack growth calculation. The NRC staff finds that after weld overlay installation, the licensee provided a conservative assumption of a 75 percent though-wall crack in the weld region where PDI is not qualified. The NRC staff also finds the assumption of the as-found flaw site plus the postulated 75 percent through-wall flaw is a conservative crack growth calculation.

With respect to the design of the FSWOL, the thickness of the overlay will be the same for preemptive and contingency FSWOLs and is calculated based on the assumption of a 100 percent through-wall flaw, with a length of 360 degrees in the underlying pipe. The overlay is applied so that the criteria of IWB-3640 of the ASME Code,Section XI, are met after the overlay is applied.

The proposed alternative requires that effects of any changes in applied loads, as a result of weld shrinkage from the entire overlay, on other items in the piping system (e.g., support loads and clearances, nozzle loads, changes in system flexibility and weight due to the weld overlay) shall be evaluated. The licensee is required to perform a stress analysis to demonstrate that the pressurizer nozzles will perform their intended design function with the FSWOL installed.

The stress analysis report will include results showing that the requirements of Subarticles NB-3200 and NB-3600 of the ASME Code,Section III are satisfied. The stress analysis will also include results showing that the requirements of IWB-3000 of the ASME Code,Section XI, are satisfied. The results will show that the postulated crack including its growth in the nozzles will not adversely affect the integrity of the overlaid welds. This analysis will be provided to the NRC prior to entering Mode 4. The licensee will also confirm that the original leak-before-break analyses are valid after the weld overlay installation, the amount of shrinkage is determined, and the shrinkage stresses are calculated.

The staff finds that the proposed weld overlay design, crack growth calculations, and stress analyses are acceptable because they are consistent with Code Case N-504-3 and NRC staffs position.

4.3 Examination and Inspection Section 3, Examination and Inspection, of the proposed alternative provides the requirements for acceptance, preservice and inservice examinations after the weld overlays are installed.

The proposed requirements are consistent with Code Case N-504-3 with the following exceptions. The NRC staff notes that the licensee addressed the exceptions and many issues that the NRC staff raised in the review of alternative ISI-GEN-ALT-06-03, Revision 2. The discussion and disposition of the issues are provided in the NRCs safety evaluation in the March 3, 2007 letter to the licensee.

The licensee stated that NDE methods shall be in accordance with IWA-2200, except as specified herein. NDE personnel shall be qualified in accordance with IWA-2300. Ultrasonic examination procedures and personnel shall be qualified in accordance with Appendix VIII,Section XI, as implemented through the PDI. The licensee will use Appendix VIII of the 2001 Edition of the ASME Code,Section XI, for the ultrasonic examination of the weld overlays. The licensee noted that the PDI Program Status for Code Compliance and Applicability developed in June 2005 indicates that the PDI Program is in compliance with Appendix VIII, 2001 Edition of Section XI as amended and mandated by 10 CFR 50.55a, Final Rule dated October 1, 2004 (69 FR 58804). The staff finds that the proposed alternatives requirements regarding ultrasonic examination under the PDI program is consistent with 10 CFR 50.55a and, therefore, is acceptable.

4.3.1 Acceptance Examination Section 3(a), Acceptance Examination of the Overlay, of the proposed alternative, requires surface and ultrasonic examinations of an installed weld overlay and use the acceptance criteria of NB-5300 of the ASME Code,Section III. The ultrasonic examinations of the installed weld overlay will be performed to assure adequate fusion and to detect fabrication defects. The required examination surface and volume are defined in Figure 1 of the proposed alternative.

The acceptance criteria for the ultrasonic examination will be based on IWB-3514-2 of the ASME Code,Section XI. Any planar indication found in the FSWOL that is rejected by IWB-3514-2 will be removed. The NRC staff finds that the licensees alternative is acceptable because removal of unacceptable indication(s) in accordance with IWB-3514-2 is consistent with the staff position.

Paragraph 3(a)3 of the proposed alternative requires that if ambient temperature temperbead welding is used, the ultrasonic examination be conducted at least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the third layer of the weld overlay has been completed. However, Code Case N-638-1 requires that the 48-hour clock starts after the overlay is cooled to ambient temperature. The proposed 48-hour requirement is not as stringent as Code Case N-638-1 because the licensee could perform the surface and ultrasonic examinations earlier than the code case requirement. The 48-hour delay in N-638-1 was provided to allow sufficient time for hydrogen cracking to occur (if it is to occur) in the heat affected zone (HAZ) of ferritic materials prior to performing examinations, to ensure detection by NDE.

The licensee stated that based on research and industry experience, EPRI has provided a technical basis for starting the 48-hour hold after completion of the third temperbead weld layer rather than waiting for the weld overlay to cool to ambient temperature. Weld layers beyond the third layer are not designed to provide tempering to the ferritic HAZ during ambient temperature temperbead welding. EPRI has documented their technical basis in Technical Update report 1013558, Repair and Replacement Applications Center: Temperbead Welding Applications 48-Hour Hold Requirements for Ambient Temperature Temperbead Welding (ADAMS Accession No. ML070670060). The technical data provided by EPRI in their report is based on testing performed on SA-508, Class 2 low-alloy steels, which is the material of the FNP and VEGP pressurizer nozzles. After evaluating all of the issues relevant to hydrogen cracking such as microstructure of susceptible materials, availability of hydrogen, applied stresses, temperature, and diffusivity and solubility of hydrogen in steels, EPRI concluded that:...[t]here appears to be no technical basis for waiting the 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after cooling to ambient temperature before beginning the NDE of the completed weld. There should be no hydrogen present, and even if it were present, the temperbead welded component should be very tolerant of the moisture... EPRI also notes that over 20 weld overlays and 100 repairs have been performed using temperbead techniques on low alloy steel components over the last 20 years. During this time, there has never been an indication of hydrogen cracking by the NDE performed after the 48-hour hold or by subsequent ISI examinations.

In addition, the ASME Technical Basis Paper (ADAMS Accession No. ML070790679) points out that the introduction of hydrogen to the ferritic HAZ is limited to the first weld layer since this is the only weld layer that makes contact with the ferritic base material. While the potential for the introduction of hydrogen to the ferritic HAZ is negligible during subsequent weld layers, these layers provide a heat source that accelerates the dissipation of hydrogen from the [ferritic] HAZ in non-water backed applications. The Technical Basis Paper concludes that there is sufficient delay time to facilitate the detection of potential hydrogen cracking when NDE is performed 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after completion of the third weld layer.

Furthermore, the solubility of hydrogen in austenitic materials such as Alloy 52M is much higher than that of ferritic materials while the diffusivity of hydrogen in austenitic materials is lower than that of ferritic materials. As a result, hydrogen in the ferritic HAZ tends to diffuse into the austenitic weld metal, which has a much higher solubility for hydrogen. This diffusion process is enhanced by heat supplied in subsequent weld layers.

On the basis of information submitted, the staff finds that it is not necessary to wait 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the completed overlay has reached ambient temperature to perform NDE because any delayed hydrogen cracking, were it to occur, is expected to occur within the 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> following completion of the third temper bead weld layer. Therefore, the staff concludes that NDE of the weld overlay 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after completion of the third temper bead weld layer is acceptable.

Paragraph 3(a)2 of the proposed alternative requires that the weld overlay and the adjacent base material for at least 0.5 inch from each side of the weld shall be examined using the liquid penetrant method. This requirement is not consistent with Section 4.0(b) of Code Case N-638-1, which requires surface and ultrasonic examination of a band on either side of the overlay with an axial length of at least 1.5 times the component thickness or 5 inches whichever is greater.

In its letter dated October 20, 2006, the licensee stated that the examination requirements of N-638-1 are applicable to cavity type repairs and have been utilized for overlay repairs with NRC approval. The NDE requirements in the relief request are only applicable to the area that would be affected by application of the overlay. Any PWSCC degradation would be in the alloy 82/182 weld or the adjacent HAZ. Further, the original weld and adjacent base materials have received a radiographic examination prior to initial acceptance during the plant construction. The proposed surface and volumetric examinations provide adequate assurance that any defects produced by welding of the overlay or by extension of pre-existing defects would be identified.

The staff finds that the alternative provides sufficient surface examination and ultrasonic examination of the weld overlay to detect potential defects and is acceptable.

4.3.2 Preservice Examination Section 3(b), Preservice Inspection, of the proposed alternative requires a preservice ultrasonic examination of the installed weld overlay and the upper (outer) 25 percent of the original pipe wall thickness. The required examination volume is defined in Figure 2 of the proposed alternative.

Paragraph 3(b)2 of the proposed alternative requires that the preservice examination acceptance standards of Table IWB-3514-2 of the ASME Code,Section XI, be applied to planar indications in the weld overlay material. If the indication is found acceptable per Table IWB-3514-2, the weld overlay will be placed in service and the inservice schedule and acceptance criteria of Paragraph 3(c) of the proposed alternative will be followed. In applying the acceptance standards of Table IWB-3514-2, wall thickness, tw, shall be the thickness of the weld overlay. Planar flaws not meeting the preservice acceptance standards of Table IWB-3514-2 shall be repaired. Re-examination per IWB-2420 of the ASME Code,Section XI, is not required because unacceptable indications will be removed.

In RG 1.147, Revision 15, the NRC staff imposed a condition on Code Case N-638-1 regarding ultrasonic examination and associated acceptance criteria based on NB-5330 of the ASME Code,Section III. As stated in paragraph 3(b)2 of the proposed alternative, the licensee will be using acceptance criteria of ASME Code,Section XI in lieu of Section III. In the October 20, 2006 letter (ADAMS Accession No. ML062960237), the licensee stated that Code Case N-638-1 (and the temper bead welding techniques in IWA-4600) was written to address repair welds where a defect in piping is excavated and the resulting cavity is filled using a temper bead technique. However, an excavated cavity configuration differs significantly from the weld overlay configuration. The licensee has concluded that the proposed alternative was written to specifically address weld overlays, and not only does it adequately examine the weld overlays, but it provides more appropriate examinations and acceptance criteria than the NRC-imposed position. Conversely, the imposition of ASME Section III acceptance standards to weld overlays is inconsistent with years of NRC precedence and without justification given the evidence of past NRC approvals and operating experience.

The licensees conclusion is based on the following:

1. Weld overlays have been used for repair and mitigation of cracking in Boiling Water Reactors since the early 1980s. In Generic Letter 88-01, the NRC approved the use of Section XI acceptance standards for determining the acceptability of installed weld overlays.

2. Weld overlays for repair of cracks in piping are not addressed by ASME Section III.

ASME Section III, utilizes nondestructive examination procedures and techniques with flaw detection capabilities that are well within the practical limits of workmanship standards for welds. These standards are most applicable to volumetric examinations conducted by radiographic examination. Radiography (RT) of weld overlays is not appropriate because of presence of radioactive material in the Reactor Coolant system and water in the pipes. The acceptance standards are written for a range of fabrication flaws including lack of fusion, incomplete penetration, cracking, slag inclusions, porosity, and concavity. However, experience and fracture mechanics have demonstrated that many of the flaws that are rejected using ASME Section III acceptance standards do not have a significant effect on the structural integrity of the component.

3. The ultrasonic test (UT) examinations performed in accordance with the proposed alternative are in accordance with ASME Section XI, Appendix VIII, Supplement 11 as implemented through the PDI. These examinations are considered more sensitive for detection of defects, either from fabrication or service-induced, than either ASME Section III RT or UT methods. Further, construction type flaws have been included in the PDI qualification sample sets for evaluating procedures and personnel.

The NRC staff finds that the proposed alternative provides acceptable acceptance criteria for the ultrasonic examination based on the requirements of ASME Code,Section XI. The NRC staff agrees with the licensee that the condition imposed on Code Case N-638-1 in RG 1.147, Revision 14 is not applicable.

4.3.3 Inservice Examination Paragraph 3(c) of the proposed alternative requires that inservice examinations of the FSWOLs be performed in accordance with subarticles Q-4300 and 4310 of Appendix Q to the 2004 Edition of Section XI with Addenda through 2005 with modifications. Appendix 8, Enclosure 1, of the proposed alternative provides the licensees modifications to subarticles Q-4300 and 4310. The proposed ISI requirements are discussed below.

Paragraph (a) under Modified Q-4300 Inservice Flaw Evaluation Requirements in Appendix 8,, of the proposed alternative, requires that flaws characterized as PWSCC in the Alloy 52/152 weld overlay are unacceptable and the use of IWB-3514-2 and IWB-3640 for PWSCC evaluation in the Class 1 overlay material is prohibited. The NRC staff finds that it is conservative to prohibit any PWSCC flaws to remain in service because PWSCC growth rate can be aggressive and unpredictable. Therefore, this requirement is acceptable.

Paragraph (c) under Modified Q-4300 Inservice Flaw Evaluation Requirements in Appendix 8,, of the proposed alternative, requires that if examinations reveal crack growth or new cracking in the upper 25 percent of the original weld or base materials, the as-found flaw (postulated 75 percent through wall plus the portion of the flaw in the upper 25 percent) will be used to re-evaluate the crack growth analysis. The size of all flaws will be projected to the end of the design life of the overlay. Crack growth, including both stress corrosion and fatigue crack growth, shall be evaluated in the materials in accordance with IWB-3640. If the flaw is at or near the boundary of two different materials, evaluation of flaw growth in both materials is required. For unacceptable indications, the weld overlay shall be removed, including the original defective piping weldment, and corrected by a repair/replacement activity in accordance with IWA-4000. The NRC staff finds that these requirements are consistent with the NRC position on disposition of flaws detected in the weld overlays and, therefore, are acceptable.

Paragraph (b) under Modified Q-4300 Re-Examination Requirements in Appendix 8, Enclosure 1, of the proposed alternative requires that if inservice examinations reveal acceptable crack growth or new cracking in the upper 25 percent of the original weld or base materials, the weld overlay examination volume shall be reexamined during the first or second refueling outage following discovery of the growth or new cracking. Weld overlay examination volumes that show no additional indication of crack growth or new cracking shall be placed into a population to be examined on a sample basis. Twenty-five percent of this population shall be examined once every ten years. The NRC staff notes that this requirement is specifically applied to flaws detected in the original weld or base metal. The proposed requirement is consistent with Appendix Q-4300 of the ASME Code,Section XI and, therefore, is acceptable.

Paragraph (c) under Modified Q-4300 Re-Examination Requirements in Appendix 8,, of the proposed alternative requires that if inservice examinations reveal acceptable non-PWSCC flaws in the overlay material, the weld overlay examination volume shall be reexamined during the first or second refueling outage following discovery of the growth or new cracking. Weld overlay examination volumes that show no additional indication of crack growth or new cracking shall be placed into a population to be examined on a sample basis.

Twenty-five percent of this population shall be examined once every ten years. The NRC staff notes that this requirement is specifically applied to flaws detected in the weld overlays (as opposed to the original weld or base metal). The proposed requirement is consistent with Appendix Q-4300 of the ASME Code,Section XI, and the staffs position. The NRC staff finds this requirement acceptable.

4.3.4 Pressure Testing Section 4 of the proposed alternative requires that a system leakage test be performed in accordance with IWA-5000. The NRC staff finds that this requirement is consists with Code Case N-504-3 and, therefore, is acceptable.

4.4 Appendix 1-- Ambient Temperature Temper Bead Welding Appendix 1, Enclosure 1, of the proposed alternative ISI-GEN-ALT-07-01, Version 2.0, specifies requirements for the ambient temperature temper bead welding, which are consistent with requirements of Code Case N-638-1 except for the following significant exceptions.

Paragraph 1.0(a) of Appendix 1 to the proposed alternative ISI-GEN-ALT-07-01, Version 2.0, does not limit the thickness of the weld overlay not to exceed the 50 percent of the ferritic base metal thickness.

Paragraph 2(g) of Appendix 1 to the proposed alternative ISI-GEN-ALT-07-01, Version 2.0, provides requirements for the case when the average lateral expansion value of the heat affected zone (HAZ) of Charpy V-notch specimens is less than the average value for the unaffected base metal.

Paragraph 3.0(c) of Appendix 1 to the proposed alternative ISI-GEN-ALT-07-01, Version 2.0, requires the heat input of the first three layers not to exceed 45,000 Joule/inch under any conditions.

The NRC staff evaluated the above three exceptions as part of its review of alternative ISI-GEN-ALT-06-03, Revision 2.0, and found the above exceptions acceptable as documented in the NRC letter dated April 3, 2007 (ADAMS Accession ML070790240). The staffs conclusions remain valid for ISI-GEN-ALT-07-01, Version 2.0. Paragraph 3(e) of Appendix 1 to the proposed alternative ISI-GEN-ALT-07-01, Version 2.0, requires that the interpass temperature be determined by direct temperature measurement. If it is impossible to measure the weld interpass temperature in this manner, the licensee will use heat flow calculations and mock-up testing in combination as identified in paragraphs 3.0(e)(2) and 3.0(e)(3). In addition, the licensee will measure the interpass temperature with certain weld pass/bead deposition frequency. The staff finds the requirements of paragraph 3(e) provide more temperature monitoring than Code Case N-638-1 and, therefore, are acceptable.

4.4.1. Licensees Commitments

1. The licensee will provide to the NRC, prior to entering Mode 4, the stress analysis report which will include results showing that the requirements of Subarticles NB-3200 and NB-3600 of the ASME Code,Section III are satisfied. The stress analysis will also include results showing that the requirements of IWB-3000 of the ASME Code,Section XI, are satisfied. The results will show that the postulated crack including its growth in the nozzles do not adversely affect the integrity of the overlaid welds.

The licensee will provide to the NRC, within 14 days after the completion of the ultrasonic examination of the weld overlay installations, (a) the examination results of the weld overlays, and (b) a discussion of any repairs to the overlay material and/or base metal and the reason for repair.

2. The licensee will provide to the NRC, within 90 calendar days of the completion of the refueling outage, the IWB-3640 evaluation performed for any assumed flaw in any uninspectable volume in the weld overlay beneath a laminar flaw, if that assumed flaw failed to meet the preservice acceptance criteria of Table IWB-3514-2.

The staff finds that the licensees commitments are acceptable because they will provide timely information regarding the weld overlay examination for the staff to monitor the quality of the weld overlay installation.

5.0 CONCLUSION

The NRC staff has reviewed the licensees submittal and determined that the proposed alternatives will provide an acceptable level of quality and safety. Pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff authorizes the use of the proposed alternative ISI-GEN-ALT-07-01, Version 2.0, for the full structural weld overlay of the dissimilar metal welds of the pressurizer nozzles at Farley Unit 2 and Vogtle Unit 1. The effective period of the proposed alternative for Farley Unit 2 is through November 30, 2017. The effective period of the proposed alternative for Vogtle Unit 1 is through May 30, 2017.

All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in this relief request remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

Principal Contibutor: John Tsao, NRR Date: March 10, 2008

Joseph M. Farley Nuclear Plant, Units 1 & 2 cc:

Mr. J. Randy Johnson Vice President - Farley Joseph M. Farley Nuclear Plant 7388 North State Highway 95 Columbia, AL 36319 Mr. B. D. McKinney, Licensing Manager Southern Nuclear Operating Company, Inc.

P.O. Box 1295 Birmingham, AL 35201-1295 Mr. M. Stanford Blanton Balch and Bingham Law Firm P.O. Box 306 1710 Sixth Avenue North Birmingham, AL 35201 Mr. J. Gasser Executive Vice President Southern Nuclear Operating Company, Inc.

P.O. Box 1295 Birmingham, AL 35201 State Health Officer Alabama Department of Public Health 434 Monroe St.

Montgomery, AL 36130-1701 Chairman Houston County Commission P.O. Box 6406 Dothan, AL 36302 Resident Inspector U.S. Nuclear Regulatory Commission 7388 N. State Highway 95 Columbia, AL 36319 William D. Oldfield SAER Supervisor Southern Nuclear Operating Company, Inc.

P.O. Box 470 Ashford, AL 36312

Vogtle Electric Generating Plant, Units 1 & 2 cc:

Mr. Tom E. Tynan Vice President - Vogtle Vogtle Electric Generating Plant 7821 River Road Waynesboro, GA 30830 Mr. N. J. Stringfellow Manager, Licensing Southern Nuclear Operating Company, Inc.

P.O. Box 1295 Birmingham, AL 35201-1295 Mr. Jeffrey T. Gasser Executive Vice President Southern Nuclear Operating Company, Inc.

P.O. Box 1295 Birmingham, AL 35201-1295 Mr. Steven M. Jackson Senior Engineer - Power Supply Municipal Electric Authority of Georgia 1470 Riveredge Parkway, NW Atlanta, GA 30328-4684 Mr. Reece McAlister Executive Secretary Georgia Public Service Commission 244 Washington St., SW Atlanta, GA 30334 Mr. Harold Reheis, Director Department of Natural Resources 205 Butler Street, SE, Suite 1252 Atlanta, GA 30334 Attorney General Law Department 132 Judicial Building Atlanta, GA 30334 Mr. Laurence Bergen Oglethorpe Power Corporation 2100 East Exchange Place P.O. Box 1349 Tucker, GA 30085-1349 Arthur H. Domby, Esquire Troutman Sanders Nations Bank Plaza 600 Peachtree Street, NE Suite 5200 Atlanta, GA 30308-2216 Resident Inspector Vogtle Plant 8805 River Road Waynesboro, GA 30830 Office of the County Commissioner Burke County Commission Waynesboro, GA 30830 Mr. Bob Masse Resident Manager Oglethorpe Power Corporation Vogtle Electric Generating Plant 7821 River Road Waynesboro, GA 30830