ML071560008

Relief Request Nos. 36 and 37 Alternatives to Weld Overlay Requirements for Inservice Inspection

ML071560008
Person / Time
Site:	Palo Verde
Issue date:	06/21/2007
From:	Hiltz T NRC/NRR/ADRO/DORL/LPLIV
To:	Edington R Arizona Public Service Co
Markley, M T, NRR/DORL/LP4, 301-415-5723
References
TAC MD4272, TAC MD4273, TAC MD4274, TAC MD5579, TAC MD5580, TAC MD5581
Download: ML071560008 (25)

Text

June 21, 2007 Mr. Randall K. Edington Senior Vice President, Nuclear Mail Station 7602 Arizona Public Service Company P. O. Box 52034 Phoenix, AZ 85072-2034

SUBJECT:

PALO VERDE NUCLEAR GENERATING STATION, UNITS 1, 2, AND 3 -

RELIEF REQUEST NOS. 36 AND 37 RE: ALTERNATIVES TO WELD OVERLAY REQUIREMENTS FOR INSERVICE INSPECTION (TAC NOS.

MD4272, MD4273, MD4274, MD5579, MD5580, AND MD5581)

Dear Mr. Edington:

By letters dated February 8, May 16, and June 18, 2007, Arizona Public Service Company (APS) submitted Relief Requests Nos. 36 and 37, respectively, requesting relief from certain American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code) requirements at Palo Verde Nuclear Generating Station (Palo Verde), Units 1, 2 and 3. APS proposes to use these relief requests, in part, to satisfy commitments related to the U.S.

Nuclear Regulatory Commission (NRC) Confirmatory Action Letter dated March 15, 2007.

NRC approval of Relief Request No. 36 would authorize preemptive full structural weld overlays of dissimilar metal welds on pressurizer spray, safety, and surge nozzles-to-safe-ends and hot-leg shutdown cooling and surge nozzles-to-safe-ends and their adjoining welds. The relief request would authorize alternatives to ASME Code,Section XI, Articles IWA-4000 and IWA-4300 which requires that defects be removed or reduced to an acceptable size. Relief Request No. 36 would also authorize the use of ASME Code,Section XI, 2001 Edition and Addenda through 2003 pursuant to 10 CFR 50.55a(g)(4)(iv), and in accordance with the guidance provided in NRC Regulatory Issue Summary 2004-16, "Use of Later Editions and Addenda to ASME Code Section XI for Repair and Replacement Activities" dated October 19, 2004. Use of the 2001 Edition and Addenda through 2003 will be subject to the limitations and modifications listed in 10 CFR 50.55a(b)(2) for the repair/replacement activities on Class 1, 2, and 3 components at Palo Verde, Units 1 and 3. The proposed alternative for Relief Request No. 36 would be applicable for the remainder of the second 10-year inservice inspection (ISI) interval for Units 1 and 3 and the remainder of the third 10-year ISI interval for Unit 2.

NRC approval of Relief Request No. 37 would authorize an alternative to ASME Code Case N-638-1, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW

[Gas Tungsten Arc Welding] Temperbead Technique, for Palo Verde, Units 1, 2, and 3. The relief request authorizes the 48-hour hold time to begin following the completion of the third layer of the weld overlay. The proposed alternative for Relief Request No. 37 would be applicable for the second and third 10-year ISI intervals for Units 1 and 3 and the remainder of the third 10-year ISI interval for Unit 2.

R. K. Edington Based on the information provided in the licensees submittals, the NRC staff concludes that the licensee has provided acceptable alternatives to the requirements of the ASME Code in Relief Request Nos. 36 and 37. The NRC staff concludes that the alternatives proposed by the licensee provide an acceptable level of quality and safety. Therefore, pursuant to Title 10 of the Code of Federal Regulations (10 CFR), paragraph 50.55a(a)(3)(i), the alternatives are authorized for the Palo Verde units, for the remainder of the 10-year ISI intervals stipulated above.

A copy of the related Safety Evaluation is enclosed. All other ASME Code,Section XI, requirements for which relief has not been specifically requested and approved remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

Sincerely,

/RA/

Thomas G. Hiltz, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. STN 50-528, STN 50-529, and STN 50-530

Enclosure:

Safety Evaluation cc w/encl: See next page

ML071560008 *No Legal Objection OFFICE NRR/LPL4/PM NRR/LPL4/LA NRR/LPL4/PM DCI/CPNB/BC OGC* NRR/LPL4/BC NAME MMarkley JBurkhardt MFields JTsoa for TChan JBonanno THiltz DATE 6/4/07 6/18/07 6/18/07 6/15/07 6/20/07 6/21/07 Palo Verde Nuclear Generating Station cc:

Mr. Steve Olea Mr. John Taylor Arizona Corporation Commission Public Service Company of New Mexico 1200 W. Washington Street 2401 Aztec NE, MS Z110 Phoenix, AZ 85007 Albuquerque, NM 87107-4224 Mr. Douglas Kent Porter Mr. Geoffrey M. Cook Senior Counsel Southern California Edison Company Southern California Edison Company 5000 Pacific Coast Hwy Bldg N50 Law Department, Generation Resources San Clemente, CA 92672 P.O. Box 800 Rosemead, CA 91770 Mr. Robert Henry Salt River Project Senior Resident Inspector 6504 East Thomas Road U.S. Nuclear Regulatory Commission Scottsdale, AZ 85251 P.O. Box 40 Buckeye, AZ 85326 Mr. Jeffrey T. Weikert Assistant General Counsel Regional Administrator, Region IV El Paso Electric Company U.S. Nuclear Regulatory Commission Mail Location 167 Harris Tower & Pavillion 123 W. Mills 611 Ryan Plaza Drive, Suite 400 El Paso, TX 79901 Arlington, TX 76011-8064 Mr. John Schumann Chairman Los Angeles Department of Water & Power Maricopa County Board of Supervisors Southern California Public Power Authority 301 W. Jefferson, 10th Floor P.O. Box 51111, Room 1255-C Phoenix, AZ 85003 Los Angeles, CA 90051-0100 Mr. Aubrey V. Godwin, Director Mr. Brian Almon Arizona Radiation Regulatory Agency Public Utility Commission 4814 South 40 Street William B. Travis Building Phoenix, AZ 85040 P.O. Box 13326 1701 North Congress Avenue Mr. Scott Bauer, Acting General Manager Austin, TX 78701-3326 Regulatory Affairs and Performance Improvement Ms. Karen O'Regan Palo Verde Nuclear Generating Station Environmental Program Manager Mail Station 7636 City of Phoenix P.O. Box 52034 Office of Environmental Programs Phoenix, AZ 85072-2034 200 West Washington Street Phoenix AZ 85003 Mr. Matthew Benac Assistant Vice President Nuclear & Generation Services El Paso Electric Company 340 East Palm Lane, Suite 310 Phoenix, AZ 85004 January 2007

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION INSERVICE INSPECTION PROGRAM RELIEF REQUEST NOS. 36 AND 37 ARIZONA PUBLIC SERVICE COMPANY, ET AL.

PALO VERDE NUCLEAR GENERATING STATION, UNITS 1, 2, AND 3 DOCKET NOS. STN 50-528, STN 50-529, AND STN 50-530

1.0 INTRODUCTION

By letters dated February 8, May 16, and June 18, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML070470525, ML071420036, and ML071710422, respectively), Arizona Public Service Company (APS or the licensee) submitted Relief Requests Nos. 36 and 37, respectively, requesting relief from certain American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code) requirements at Palo Verde Nuclear Generating Station (Palo Verde), Units 1, 2 and 3.

NRC approval of Relief Request No. 36 would authorize alternatives to the requirements of ASME Code, 2001 Edition, 2003 Addenda,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, for Palo Verde Units 1, 2, and 3. Relief Request No. 36 would authorize alternatives to Section IWA-4110, which stipulates that weld repairs be performed in accordance with Section IWA-4000 and IWA-4300 which requires that defects be removed or reduced to an acceptable size. This relief request would authorize preemptive full structural weld overlays (FSWOL) of dissimilar metal welds (DMW) on pressurizer spray, safety, and surge nozzles-to-safe-ends and hot-leg shutdown cooling and surge nozzles-to-safe-ends and their adjoining welds.

Pursuant to 10 CFR 50.55a(g)(4)(iv), and guidance in U.S. Nuclear Regulatory Commission (NRC) Regulatory Issue Summary (RIS) 2004-16, "Use of Later Editions and Addenda to ASME Code Section XI for Repair/Replacement Activities" dated October 19, 2004, Relief Request would also authorize the use of ASME, IWA-4000, Repair/Replacement Activities, of the 2001 Edition and Addenda through 2003. This relief request authorizes the use of the 2001 Edition and Addenda through 2003 subject to the limitations and modifications listed in 10 CFR 50.55a(b)(2) for the repair/replacement activities on Class 1, 2, and 3 components at Palo Verde, Units 1 and 3. APS intends to use this later edition and addenda for the duration of the current Palo Verde, Units 1 and 3, second 10-year inservice inspection (ISI) intervals in support of the FSWOL commitments in APS Letter No. 102-05640, dated January 31, 2007, and the associated NRC Confirmatory Action Letter dated March 15, 2007 (ADAMS Accession No. ML070660298). APS will be implementing the 2001 Edition through the 2003 Addenda of the ASME Code for Palo Verde, Unit 2's third 10-year ISI interval starting on March 18, 2007.

Therefore, APS requested approval to transition Units 1 and 3 to the same Edition and Addenda of the Code at the same time. Palo Verde, Units 1 and 3, will be entering the third

10-year ISI intervals on July 18 and January 11, 2008, respectively. The proposed alternative for Relief Request No. 36 would be applicable for the remainder of the second 10-year ISI interval for Units 1 and 3 and the remainder of the third 10-year ISI interval for Unit 2.

NRC approval of Relief Request No. 37 would authorize an alternative to ASME Code Case N-638-1, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW

[Gas Tungsten Arc Welding] Temperbead Technique, for Palo Verde, Units 1, 2, and 3.

Specifically, the relief request would authorize the 48-hour hold time to begin following the completion of the third layer of the weld overlay. The proposed alternative for Relief Request No. 37 would be applicable for the second and third 10-year ISI intervals for Units 1 and 3 and the remainder of the third 10-year ISI interval for Unit 2.

2.0 RELIEF REQUEST NO. 36 2.1 Regulatory Evaluation Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) will 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 ISI 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.

In accordance with 10 CFR 50.55a(g)(6)(ii)(C)(1), the implementation of Supplements 1 through 8, 10, and 11 of Appendix VIII to Section XI, 1995 Edition with the 1996 Addenda of the ASME Code, was required on a phased schedule which ended on November 22, 2002.

Supplement 11 was required to be implemented by November 22, 2001. Additionally, 10 CFR 50.55a(g)(6)(ii)(C)(2) requires licensees to implement the 1995 Edition with the 1996 Addenda of Appendix VIII and supplements to Appendix VIII of Section XI of the ASME Code.

Pursuant to 10 CFR 50.55a(g)(4)(iv), ISI items may meet the requirements set forth in subsequent editions and addenda of the ASME Code that are incorporated by reference in 10 CFR 50.55a(b), subject to the limitations and modifications listed therein, and subject to Commission approval. Portions of editions and addenda may be used provided that related requirements of the respective editions and addenda are met.

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 alternative provides 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. The licensee submitted the subject relief request, pursuant to 10 CFR 50.55a(a)(3)(i), which proposed alternatives to the implementation of the ASME Code,Section XI, Appendix VIII, Supplement 11, and modifications to N-504-2 and N-638-1, for the deposition of preemptive FSWOLs.

2.2 Technical Evaluation 2.2.1 ASME Code, Class 1 Component(s) Affected The request for relief is applicable to the nozzle-to-safe-end welds for the nine ASME Code Class 1 pressurizer spray, relief, safety, and surge nozzles in each Palo Verde unit, as specified in Section 1.0 of Enclosure 1 of the licensees February 8, 2007, submittal.

A DMW is defined as a weld that joins two pieces of different type of metals. In the proposed alternative, the DMW joins the ferritic (i.e., low-alloy steel) pressurizer nozzle to the austenitic stainless steel safe end or piping. The DMW itself is made of nickel-based Alloy 82/182. The proposed weld overlay repair is a process by which weld filler metal that is resistant to stress-corrosion cracking is deposited on the outside surface of the pipe including the original pipe weld.

2.2.2 Applicable Code Edition and Addenda The Code of record for the second 10-year ISI interval for Palo Verde, Units 1 and 3, is the ASME Code,Section XI, 1992 Edition, 1992 Addenda. The Code of record for the third 10-year ISI interval for Palo Verde, Units 1, 2, and 3, will be the ASME Code,Section XI, 2001 Edition and Addenda through 2003. Palo Verde, Unit 2, entered its third 10-year ISI interval on March 18, 2007.

Palo Verde, Units 1 and 3, will be entering the third 10-year ISI interval on July 18 and January 11, 2008, respectively. APS has requested, as part of this submittal, that the NRC approve use of ASME Code,Section XI, IWA-4000, Repair/Replacement Activities, of the 2001 Edition and Addenda through 2003 starting on March 18, 2007, for repair/replacement activities in Units 1 and 3. In addition, 10 CFR 50.55a, ASME Code,Section XI, 2001 Edition will be used for Appendix VIII, Performance Demonstration for Ultrasonic Examinations.

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

Appendix 2 to Enclosure 1 of the licensees submittal dated February 8, 2007, provides a comparison of APS proposed alternative versus Code Cases N-504-2 and N-638-1 (Regulatory Guide 1.147, Revision 14, Table 2, identifies these Code Cases as conditionally acceptable).

Currently, pressurizer nozzle and hot-leg DMW examinations are required to be performed at Palo Verde in accordance with Electric Power Research Institute's (EPRI) Materials Reliability Program (MRP)-139. The examinations are the same as the volumetric examinations specified in Section XI, Table IWB2500-1, Category B-J and B-F.

2.2.4 Reason for Request Primary water stress-corrosion cracking (PWSCC) has been identified as a degradation mechanism for Alloy 82/182 welds and weld buttering. While no PWSCC flaws have been detected in Palo Verde pressurizer and hot leg piping, there are geometric limitations such that the required examination volume cannot be met with qualified ultrasonic (UT) techniques. APS has concluded that the application of an FSWOL over the pressurizer and hot leg Alloy 82/182 welds is the most appropriate course of action to ensure the integrity of the reactor coolant pressure boundary. In addition, the overlays will be designed to improve the configurations for future examinations.

The 2001 Edition and Addenda through 2003 of the Code does not provide rules for the design of weld overlays or for repairs without removal of flaws. In addition, Code Case N-504-2, which has been approved with conditions by the NRC for use, does not provide the methodology for overlaying nickel-alloy welds joining austenitic and ferritic base materials; therefore, APS proposes the following alternative.

2.2.5 Licensees Proposed Alternative and Licensees Basis for Use of Proposed Alternative A preemptive full structural Alloy 52 overlay will be applied to each of the pressurizer and hot-leg Alloy 82/182 DMWs identified in this request. For a preemptive FSWOL, a flaw will be assumed. If through-wall leakage is detected by visual examination on any of the Palo Verde pressurizer or hot-leg Alloy 82/182 safe-end welds, a contingency FSWOL will be applied.

For all nine welds identified in Section 1.0 of Enclosure 1 of APS February 8, 2007, submittal, in lieu of performing UT examinations, the flaw will be assumed to be 100 percent through the original wall thickness for the entire circumference for preemptive as well as contingency FSWOL.

Due to the proximity of the adjacent similar metal piping welds, preemptive or contingency overlay of the DMWs may preclude the examination of the adjacent similar metal piping welds; therefore, the overlay will be extended over the adjacent similar metal piping welds, if required.

However, which similar metal welds will be overlaid will be determined after designing the dimensions of the DMW overlay.

These similar metal welds will not be inspected prior to installing the overlay. The selection and examination of the similar metal weld population is currently performed using an NRC-approved risk-informed program described in Relief Request 32, dated November 3, 2006 (ADAMS Accession No. ML062930208). The risk-informed application uses failure probability analysis, probabilistic risk assessment, and an expert panel evaluation to identify the piping components that require examination. The piping components selected for examination are only a small portion of the total population of similar metal welds; however, the basic intent of identifying and repairing flaws before piping integrity is challenged is maintained by the risk-informed application. As a final step in the selection process, a statistical model was used to assure that a sufficient number of welds are being examined. The welds adjacent to the DMWs were not selected for examination in the risk-informed application for PWSCC degradation mechanism, and the licensee concluded that these adjacent similar metal welds do not need to be examined

to maintain an acceptable level of quality and safety. After the overlay is applied, the licensee plans to examine these welds in accordance with the proposed alternative.

In lieu of using the existing IWA-4000 Repair Procedures in the 2001 Edition and Addenda through 2003 Section XI Code, APS proposes to use the following alternative for the design, fabrication, pressure testing, and examination of the weld overlays. This will provide an acceptable methodology for reducing a defect in austenitic nickel-alloy welds to an acceptable size by increasing the wall thickness through deposition of a weld overlay. ASME Code references in this alternative are the 2001 Edition and Addenda through 2003 for Section III and 2001 Edition and Addenda through 2003 for Section XI as modified by 10 CFR 50.55a. This methodology is based upon ASME Code Case N-740 and the only applicable requirements of the Code Case are presented below as alternatives.

The use of weld overlay materials resistant to PWSCC (e.g., Alloy 52) that create low tensile or compressive residual-stress profiles in the original weld provide increased assurance of structural integrity. The weld overlay will be of sufficient thickness and length to meet the applicable stress limits from ASME Code,Section III, NB-3200. Crack-growth evaluations for PWSCC and fatigue of any as-found flaws or any conservatively postulated flaws will ensure that structural integrity will be maintained.

As a part of the design of the weld overlay, the weld length, surface finish, and flatness are specified in order to allow qualified ASME Code,Section XI, Appendix VIII, UT examinations, as implemented through the EPRI Performance Demonstration Initiative (PDI) program, of the weld overlay and the required volume of the base material and original weld. The examinations specified in this proposed alternative, versus those limited examinations performed on the original DMWs, will provide improved assurance of structural integrity. Based on the EPRI PDI program, the licensee states that, if no flaws are found in the outer 25 percent of the original wall thickness by the preservice UT examinations, the postulated 75 percent through-wall flaw for the preemptive overlays is conservative for crack-growth evaluations. If flaws are found during the preservice examination 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) would be used for the crack-growth analysis. The size of all flaws will be projected to the end of the design life of the overlay or until the next scheduled ISI. 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 shall consider the most limiting of the two materials.

The implementation of the alternative reduces the likelihood for PWSCC in the identified welds and improves piping geometries to permit Appendix VIII UT examinations as implemented through the EPRI PDI program. Weld overlay repairs of DMWs have been installed and performed successfully for many years in both pressurized-water reactor (PWR) and boiling-water reactor (BWR) applications. The alternative provides improved structural integrity and reduced likelihood of leakage for the primary system. Accordingly, the use of the alternative provides an acceptable level of quality and safety in accordance with 10 CFR 50.55a(a)(3)(i).

2.2.6 Duration of Proposed Alternative The proposed alternative for Relief Request No. 36 would be applicable for the remainder of the second 10-year ISI interval for Units 1 and 3 and the remainder of the third 10-year ISI interval for Unit 2.

2.3 Staff Evaluation The licensee provided details concerning requirements for the design and non-destructive examination (NDE) of the weld overlay in Enclosure 1 to Relief Request No. 36, entitled Proposed Alternative: Use of Full-Structural Weld Overlay in the Repair of Dissimilar Metal Welds. Appendix 1 to Relief Request No. 36 includes the requirements for the ambient temperature temper-bead welding technique. Appendix 2 to Relief Request No. 36 provides a comparison between the APS proposed alternative and Code Cases N-504-2 and N-638-1.

The licensee also provided details of the proposed alternative to Code Case N-638-1 in to Relief Request No. 37 entitled, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temperbead Technique.

The proposed methodology and associated requirements for the weld overlay 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 in 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 Temperbead Technique Section XI, Division 1. The staff has endorsed Code Cases N-504-2 and N-638-1, but not Code Case N-740. Therefore, the staff evaluated the acceptance of Relief Request No. 36 based on the requirements of Code Cases N-504-2 and N-638-1.

The Joseph M. Farley Nuclear Plant and Vogtle Electric Generating Plant proposed similar alternatives that were approved by the NRC (ADAMS Accession No. ML070600246).

Attachments 1 and 2 of Enclosure 3 to the licensees submittal dated February 8, 2007, provide the APS response to the NRC requests for additional information that were provided previously to the Farley and Vogtle nuclear stations.

2.3.1 General Requirements (as stated by the Licensee)

(a) A[n] [FSWOL] will be applied by deposition of Alloy 52 weld reinforcement (weld overlay) on the outside surface of the carbon steel pressurizer and hot-leg nozzle (P-No. 1 or P-No. 3) to the stainless steel safe end (P-No. 8), inclusive of the Alloy 82/182 weld that joins the two items. In addition, the overlay will be extended (when required) to include the adjacent wrought stainless steel to stainless steel welds (P-No. 8 to P-No. 8).

There are no requirements specified in this proposed alternative for these stainless steel to stainless steel welds (such as flaw growth calculations) because they are not susceptible to stress corrosion cracking in a PWR water environment. Specific dimensions of the overlay thickness will be in the design package.

(b) The Alloy 52 weld overlay filler metal is an austenitic nickel-alloy having a chromium (Cr) content of at least 28 percent. The weld overlay is applied 360 degrees around the circumference of the item, e.g., safe end to nozzle weld, and will be deposited using a Welding Procedure Specification (WPS) for groove welding, qualified in accordance with the Construction Code and Owner's requirements and identified in the Repair/Replacement Plan. As an alternative to the post-weld heat treatment requirements of the Construction Code and Owner's requirements, the provisions for Ambient Temperature Temper Bead Welding will be used on the ferritic nozzles. The maximum area of an individual weld overlay on the finished surface of the ferritic material shall be no greater than 300 square inches.

(c) Prior to deposition of the weld overlay, the surface will be examined by the liquid penetrant method. Indications larger than 1/16 inches shall be removed, reduced in size, or corrected. 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.

(d) Weld overlay deposits shall meet the following requirements:

The austenitic nickel-alloy weld overlay shall consist of at least two weld layers deposited using a filler material identified in (b) above. The first layer of weld metal deposited will not be credited toward the required thickness because of chemical dilution.

Alternatively, the first layer may be credited toward the required thickness, provided the portion of the layer over the austenitic base material, austenitic filler material weld and the associated dilution zone from an adjacent ferritic base material contains at least 24 percent Cr. The Cr content of the deposited weld metal as determined by chemical analysis of the production weld or of a representative coupon taken from a mockup prepared in accordance with the Welding Procedure Specification (WPS) for the production weld shall contain at least 24 percent Cr.

(e) Welding will only be performed for applications predicted not to have exceeded a thermal neutron fluence of 1 x 1017 (E< 0.5 eV) neutrons per cm2 prior to welding.

The NRC staff finds the proposed general requirements acceptable because the preemptive weld overlay materials are resistant to PWSCC (Alloy 52) and because the weld overlay will create low tensile or compressive residual stress profiles in the original weld which provide increased resistance to PWSCC. Further, the weld overlay is of sufficient thickness and length to meet the applicable stress limits from ASME Code,Section III, NB-3200.

2.3.2 Crack Growth Considerations and Design (as stated by the Licensee)

(a) Crack Growth Considerations Crack growth calculations will be performed as part of a design package. Flaw characterization and evaluation requirements shall be based on the as-found flaw in the case of a contingency overlay. For a preemptive overlay, a flaw in the original DMW with a depth of 75 percent and a circumference of 360 degrees that originates from the inside of the pipe is postulated for crack-growth purposes. A 75 percent through-wall depth flaw is the largest flaw that could remain undetected during the FSWOL preservice examination. This preservice examination will verify there is no cracking in the upper 25 percent of the original weld wall thickness, and thus verify that the assumption of a 75 percent through-wall crack is conservative. However, if any crack-like flaws are found during the preservice examination 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) would be used for the crack-growth analysis. The size of all flaws will be projected to the end of the design life of the overlay or until the next scheduled ISI. 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 shall consider the most limiting of the two materials.

The NRC staff finds the crack-growth consideration proposed by the licensee acceptable because the licensee is postulating in its analysis the existence of a 75 percent through-wall flaw. A 75 percent through-wall depth flaw is the largest flaw that could remain undetected during the FSWOL preservice examination. This proposed preservice examination will verify that there is no cracking in the upper 25 percent of the original weld wall thickness, and thus verify that the assumption of a 75 percent through-wall crack is conservative.

(b) Design of the FSWOL (as stated by the Licensee)

The design of the weld overlay shall satisfy the following, using the assumptions and flaw characterization restrictions in (a) above. The following design analysis shall be completed in accordance with IWA-4311.

(1) The axial length and end slope of the weld overlay shall cover the weld and the heat affected zones on each side of the weld, and shall provide for load redistribution from the item into the weld overlay and back into the item without violating applicable stress limits of ASME Code,Section III, NB-3200. Any laminar flaws in the weld overlay shall be evaluated in the analysis to ensure that load redistribution complies with the above. These requirements will usually be satisfied if the weld overlay full thickness length extends axially beyond the projected flaw by at least 0.75/Rt, where R is the outer radius of the item and t is the nominal wall thickness of the item.

(2) Unless specifically analyzed in accordance with (b)(1) above, the end transition slope of the overlay shall not exceed 45 degrees.

(3) The thickness of the FSWOL shall be determined based on the assumption of a through-wall flaw, with a length of 360 degrees in the underlying pipe. The overlay will be applied, so that the criteria of IWB-3640 are met for the assumed flaw after the overlay is applied.

(4) 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 (e.g., support loads and clearances, nozzle loads, changes in system flexibility and weight due to the weld overlay) shall be evaluated. (There are no preexisting flaws previously accepted by analytical evaluation in the Palo Verde welds to be considered in this evaluation.)

The NRC staff finds the proposed design of the weld overlay acceptable because the overlay satisfy the design analysis specified in ASME Code,Section XI, IWA-4311.

2.3.3 Examination and Inspection Requirements (as stated by the Licensee)

[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 EPRI [PDI].

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 by 10 CFR 50.55a, Final Rule dated October 1, 2004.

Ultrasonic examination will be performed to the maximum extent achievable.

Pre-Overlay Examinations Palo Verde, Units 1, 2 and 3, are scheduled for full structural overlays during the upcoming refueling outages. APS does not plan to perform UT of the pressurizer and hot-leg nozzles [DMWs] or the adjacent similar metal welds on these units prior to the installation of the overlays. Since APS intends to apply full structural overlays designed for a worst case through-wall flaw that is 360 degrees in circumference, the dose received from the examination of these welds would result in a hardship without a compensating increase in the level of quality and safety.

Post-Overlay Examinations There are two examinations to be performed after the overlay is installed, the Acceptance Examination of the Overlay and the Preservice Examination. The purpose of the Acceptance Examination is to assure a quality overlay was installed. The purpose of the Preservice Examination is to provide a baseline for future examinations and to locate and size any cracks that might have propagated into the upper 25 percent of the original wall thickness and to evaluate them accordingly. While listed below as two

separate examinations they will be performed during the same time period. An identification of the examination coverage of each overlay will be developed and available for NRC review prior to plant startup. [Note: In its February 8, 2007, submittal (Item 19, Enclosure 3, Page 14), the licensee stated that APS will inform the NRC project manager for Palo Verde of the examination results of weld overlays, including any repair to the overlay material and/or base metal and the reason for any repairs, within 14 days after completion of the ultrasonic examination of the weld overlay installations. APS Letter No. 102-05640, dated January 31, 2007, and the associated NRC Confirmatory Action Letter dated March 15, 2007 (ADAMS Accession No. ML070660298), identify the prior APS commitment to notify NRC of the inspection results in writing within 60 days of unit restart.]

The NDE requirements listed below cover the area that will be affected by the application of the overlay. Any PWSCC degradation would be in the alloy 82/182 weld or the adjacent heat-affected zone [HAZ]. Further, the original weld and adjacent base materials have received a radiographic examination (RT) during installation. 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 will be identified.

(a) Acceptance Examination (as stated by the Licensee)

(1) The weld overlay shall have a surface finish of 250 micro-inches RMS or better and a flatness sufficient to allow for adequate examination in accordance with procedures qualified per Appendix VIII. The weld overlay shall be examined to verify acceptable configuration.

(2) The weld overlay and the adjacent base material for at least one-half inch from each side of the weld shall be examined using the liquid penetrant method. The weld overlay shall satisfy the surface examination acceptance criteria for welds of the Construction Code or ASME Code,Section III, NB-5300. The adjacent base metal shall satisfy the surface examination acceptance criteria for base material of the Construction Code or ASME Code,Section III, NB-2500. If ambient temperature temper-bead welding is used, the liquid penetrant examination shall be conducted at least 48 hours2 days <br />0.286 weeks <br />0.0658 months <br /> after the completed overlay has returned to ambient temperature. [Note: The licensee proposed an alternative to the 48-hour hold time in Relief Request No. 37 which is discussed in Section 3.0 of this safety evaluation.]

(3) The examination volume A-B-C-D in Figure 1 below shall be ultrasonically examined to assure adequate fusion (i.e., adequate bond) with the base metal and to detect welding flaws, such as interbead lack of fusion, inclusions, or cracks [Note: Figure 1 is in the February 8, 2007, submittal, but is not included in this safety evaluation report]. The interface C-D shown between the overlay and the weld includes the bond and the heat affected zone from the overlay. If ambient temperature temper-bead welding is used, the UT shall be conducted at least 48 hours2 days <br />0.286 weeks <br />0.0658 months <br /> after the

completed overlay has returned to ambient temperature. [See note for (a)(2) above regarding 48-hour hold time.]

(4) Planar flaws shall meet the preservice examination standards of Table IWB-3514-2. In applying the acceptance standards, wall thickness "tw" shall be the thickness of the weld overlay. For weld overlay examination volumes with unacceptable indications, the unacceptable indications will be removed and the volume will be re-welded. Re-examination per IWB-2420 is not required because unacceptable indications will be removed and the volume will be re-welded.

(5) Laminar flaws shall meet the acceptance standards of Table IWB-3514-3 with the additional limitation that the total laminar flaw shall not exceed 10 percent of the weld surface area and that no linear dimension of the laminar flaw area exceeds 3.0 inches.

(6) After completion of all welding activities, affected restraints, supports, and snubbers shall be VT-3 examined to verify that design tolerances are met.

(b) Preservice Inspection (1) The examination volume A-B-C-D in Figure 2 provided below shall be ultrasonically examined [Note: Figure 2 is in the February 8, 2007, submittal, but is not included in this safety evaluation report]. The angle beam shall be directed perpendicular and parallel to the piping axis, with scanning performed in four directions, to locate and size any cracks that might have propagated into the upper 25 percent of the base material or into the weld overlay.

Note 1 [Figure 2] For axial or circumferential flaws, the axial extent of the examination volume shall extend at least 1/2 inches beyond the toes of the original weld, including weld end butter, where applied.

(2) The preservice examination acceptance standards of Table IWB-3514-2 shall 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 3(c) will be followed. In applying the acceptance standards, 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 is not required because unacceptable indications will be removed and the volume will be re-welded.

(3) Cracks in the outer 25 percent of the original wall thickness shall meet the design analysis requirements as addressed in Section 2, Crack Growth Considerations and Design, of this proposed alternative.

(c) Inservice Inspection (1) The weld overlay examination volume A-B-C-D in Figure 2 shall be added to the applicable inspection plans and shall be ultrasonically examined during the first or second refueling outage following application.

(2) The weld overlay examination volume in Figure 2 shall be ultrasonically examined to determine if any new or existing cracks have propagated into the upper 25 percent of the base material or into the overlay. The angle beam shall be directed perpendicular and parallel to the piping axis, with scanning performed in four directions.

(3) The inservice examination acceptance standards of Table IWB-3514-2 shall be applied to planar indications detected in the weld overlay material. If the planar indication is found acceptable per Table IWB-3514-2, the weld overlay will be re-examined in accordance with 3(c)5 below. If the inservice acceptance criteria of Table IWB-3514-2 are not met, the planar flaw may be evaluated in accordance with IWB-3640, provided that the flaw is not caused by PWSCC. If accepted for continued service, the weld overlay will be re-examined in accordance with 3(c)5. If the flaw is not acceptable for continued service per IWB-3640, then it shall be repaired. [Note: By letter dated June 18, 2007, APS modified their February 8, 2007, submittal (Section 3.0(c)3.,

Enclosure 1, page 11) to clarify the above language concerning the Code and PWSCC (ADAMS Accession No. ML071710422)]

(4) Cracks in the outer 25 percent of the base metal shall meet the design analysis requirements as addressed in Section 2, Crack Growth Considerations and Design, of this proposed alternative. Weld overlay examination volumes that show indication of crack growth or new cracking will be reexamined in accordance with 3(c)5. Weld overlay examination volumes that show no indication of crack growth or new cracking shall be placed into a population group for each unit to be examined on a sample basis. Twenty-five percent of this population shall be examined once every ten years.

(5) Successive Examinations - The weld overlay examination volume shall be reexamined during the first or second refueling outage following discovery of:

• Growth of indications in the overlay material or the presence of new indications in the overlay material.

• Crack growth or new cracking in the outer 25 percent of the base metal.

(d) Scope Expansion If inservice examinations reveal an unacceptable indication, crack growth into the weld overlay design thickness, or axial crack growth beyond the specified examination volume, additional weld overlay examination volumes, equal to the number scheduled for the current inspection period, shall be examined prior to return to service. If additional unacceptable indications are found in the second sample, a total of 50 percent of the total population of weld overlay examination volumes shall be examined prior to operation. If additional unacceptable indications are found, the entire remaining population of weld overlay examination volumes shall be examined prior to return to service.

The NRC staff finds the examination and inspection requirements specified by the licensee acceptable because the licensee is proposing to perform a pre-weld overlay surface examination and post-weld NDE, followed by preservice examination of the weld overlay. In addition an inservice examination will be performed during the first or second refueling outage.

Further, the proposed NDE methods shall be in accordance with ASME Code,Section XI, IWA-2200 and the NDE personnel shall be qualified in accordance with IWA-2300. Ultrasonic examination procedures and personnel shall be qualified in accordance with Appendix VIII, 2001 Edition of Section XI as amended by 10 CFR 50.55a, Final Rule dated October 1, 2004.

2.3.4 Staff Evaluation of Code Case N-740 As previously noted in Section 2.3 of this safety evaluation, the proposed methodology and associated requirements for the weld overlay proposed by the licensee are similar to Code Case N-740, of the ASME Code,Section XI. Code Case N-740 combines the requirements in Code Cases N-504-2 and N-638-1. The staff has endorsed Code Cases N-504-2 and N-638-1, but not Code Case N-740. Therefore, the staff also evaluated the acceptance of Relief Request No. 36 based on the requirements of Code Cases N-504-2 and N-638-1, and did not evaluate the acceptance of Code Case N-740.

2.3.5 Staff Evaluation of Code Case N-504-2 The review of Appendix 2 to Relief Request No. 36 revealed that the licensee is following the methodology of Code Case N-504-2 with the following modifications for the proposed preemptive FSWOLs:

• Use of a nickel-based alloy weld material, Alloy 52/52M rather than the low-carbon (0.035 percent maximum) austenitic stainless steel.

• Relaxation from the requirement to perform delta ferrite measurements to meet the 7.5 Ferrite Number (FN) requirement of N-504-2. The FN requirement cannot be met because the Alloy 52/52M weld material is 100 percent austenitic and contains no delta ferrite.

The first proposed modification to the N-504-2 provisions involves the use of a nickel-based alloy weld material, rather than the low-carbon austenitic stainless steel. In lieu of the stainless steel weld material, Alloy 52 welding metal highly resistant to PWSCC, was proposed for the overlay weld material. The NRC staff notes that the use of Alloy 52 material is consistent with weld filler material used to perform similar weld overlays at other operating nuclear power plants. For material compatibility in welding, the NRC staff considers Alloy 52 a better choice of filler material than austenitic stainless steel material for this weld joint configuration. Alloy 52 material contains about 28-30 percent chromium which would provide excellent resistance to PWSCC in the reactor coolant environment. This material is identified as F-No. 43 Grouping for Ni-Cr-Fe, classification UNS N06052 Filler Metal and has been previously approved by the NRC staff for similar applications. Therefore, the licensees proposed use of Alloy 52 for the weld overlays as a modification to the requirements of N-504-2, paragraph (b) and is acceptable as it will provide an acceptable level of quality and safety.

The second proposed modification to the N-504-2 provisions involved Paragraph (e) of N-504-2 which requires as-deposited delta ferrite measurements of at least 7.5 FN for the weld reinforcement. The delta ferrite measurements cannot be performed for this overlay because the deposited Alloy 52 material is 100 percent austenitic and contains no delta ferrite due to the high nickel composition (approximately 60 percent nickel). N-504-2 allows the use of weld overlay repair by deposition of weld reinforcement on the outside surface of the pipe in lieu of mechanically reducing the defect to an acceptable flaw size. However, N-504-2 is only applicable to weld overlay repair of austenitic stainless steel piping. Therefore, the material requirements regarding the carbon content limitation (0.035 percent maximum) and the delta ferrite content of at least 7.5 FN, as delineated in N-504-2, paragraphs (b) and (e), apply to austenitic stainless steel weld overlay materials. These requirements are not applicable to Alloy 52, a nickel-based material which the licensee will use for the weld overlays. Based on the discussion above, the staff concludes that the modifications to N-504-2 paragraph (e) will provide an acceptable level of quality and safety, and are therefore, acceptable.

2.3.6 Staff Evaluation of Code Case N-638-1 The licensee is, in general, following the methodology of Code Case N-638-1, with the exception that the maximum area of an individual weld based on the finished surface over the ferritic material will be approximately 300 square inches (in2).

Paragraph 1.0(a) of Code Case N-638-1 limits the maximum area of an individual weld to 100 square inches on the ferritic base material using temper-bead welding. However, the proposed alternative allows the weld surface area up to 300 square inches on the ferritic base material.

The technical justification for allowing weld overlays on ferritic materials with surface areas up to 500 square inches is provided in the white paper supporting the changes in ASME Code Case N-638-3 and EPRI Report 1011898, "Justification for the Removal of the 100 Square Inch Temper bead Weld Repair Limitation" (Reference 1). The EPRI report cites evaluations of a 12-inch diameter nozzle weld overlay to demonstrate adequate tempering of the weld HAZ, residual stress evaluations demonstrating acceptable residual stresses in weld overlays ranging from 100 to 500 square inches, and service history in which weld repairs exceeding 100 square inches were NRC approved and applied to DMW nozzles in several BWR and PWR applications. Some of the cited repairs are greater than 15 years old, and have been inspected several times with no evidence of any continued degradation. The above theoretical arguments

and empirical data have been verified in practice by extensive field experience with temper-bead weld overlays, with ferritic material coverage ranging from less than 10 square inches up to and including 325 square inches.

The staff finds that the proposed 300-square-inch weld area on the ferritic material is acceptable because the stress analysis presented in EPRI report 1012898 shows that the structural integrity of ferritic material is not adversely affected by a 300-square inch weld overlay area. Also, the staff has previously approved 300-square-inch weld area for the Susquehanna Nuclear Plant (ADAMS Accession No. ML051220568).

2.3.7 Staff Evaluation of 2001 Edition and Addenda through 2003 The licensee also requested that the NRC approve use of the ASME Code,Section XI, 2001 Edition and Addenda through 2003 pursuant to 10 CFR 50.55a(g)(4)(iv) and in accordance with the guidance provided in NRC RIS 2004-16, "Use of Later Editions and Addenda to ASME Code Section XI for Repair and Replacement Activities" dated October 19, 2004. Use of the 2001 Edition and Addenda through 2003 will be subject to the limitations and modifications listed in 10 CFR 50.55a(b)(2) for the repair/replacement activities on Class 1, 2, and 3 components at Palo Verde, Units 1 and 3.

APS intends to use this later edition and addenda for the duration of the current Palo Verde, Units 1 and 3, second 10-year inservice inspection (ISI) intervals in support of the FSWOL commitments in APS Letter No. 102-05640, dated January 31, 2007, and the associated NRC Confirmatory Action Letter dated March 15, 2007 (ADAMS Accession No. ML070660298). APS will be implementing the 2001 Edition through the 2003 Addenda of the ASME Code for Palo Verde, Unit 2's third 10-year ISI interval starting on March 18, 2007. Therefore, APS requested approval to transition Units 1 and 3 to the same edition and addenda of the Code at the same time. Palo Verde, Units 1 and 3, will be entering the third 10-year ISI intervals on July 18 and January 11, 2008, respectively.

The NRC staff finds the licensee request to use later ASME Code Edition for its Palo Verde, Units 1 and 3, acceptable pursuant to 10 CFR 50.55a(g)(4)(iv) because the licensee has committed to follow all modifications and limitations placed on the 2001 Edition through the 2003 Addenda as stated in 10 CFR 50.55a.

3.0 RELIEF REQUEST NO. 37 3.1 Regulatory Evaluation 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 alternative provides 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. The licensee submitted the subject relief request, pursuant to 10 CFR 50.55a(a)(3)(i), which allows proposed alternatives to the requirements of paragraphs (c), (d), (e), (f), (g), and (h), providing that the licensee demonstrates that the proposed alternative would provide an acceptable level of quality and safety.

Pursuant to 10 CFR 50.55a(a)(3)(i), the licensee submitted the proposed alternative to modify the requirements of N-638-1, for acceptance examination.

3.2 Technical Evaluation 3.2.1 Code Requirements for which Relief is Requested The request is applicable to the nozzle-to-safe-end welds for the nine ASME Code Class 1 pressurizer spray, relief, safety, and surge nozzles and hot leg nozzles in each Palo Verde unit, as specified in Section 1.0 of Enclosure 1 of the licensees May 16, 2007, submittal.

3.2.2 Applicable Code Edition and Addenda The Code edition and addenda described in Section 2.2.2 of this safety evaluation applies to Section 3.2.2 concerning Relief Request No. 37.

3.2.3 Applicable Code Requirements Relief Request No. 37 excerpts Subsections (2) and (3) of Enclosure 1, Section 3.0(a),

Acceptance Examination, of Relief Request No. 36 in citing applicable Code requirements related to conducting liquid penetrant and ultrasonic examination after the completed weld overlay has returned to ambient temperature. Sections 2.3.3(a)(2) and (3) of this safety evaluation provides the staff evaluation of Relief Request No. 36 concerning the applicable Code requirements and is applicable to Relief Request No. 37.

3.2.4 Reason for Request Currently, the applicable Code requirements state that if ambient temperature temperbead welding is used, the liquid penetrant and ultrasonic examinations shall be conducted at least 48 hours2 days <br />0.286 weeks <br />0.0658 months <br /> after the completed overlay has returned to ambient temperature.

Two documents support an alternative to starting the 48-hour hold after the completed overlay has returned to ambient temperature, which is to start the 48-hour hold at the completion of the third layer of the weld overlay. They are the Electric Power Research Institute (EPRI) Technical Document 1013558 (White Paper), 48-Hour Hold Requirements for Ambient Temperature Temperbead Welding, (ADAMS Accession No. ML070670060) and the ASME Section XI Committee published Technical basis Paper, RRA 05-08, N638-x, Ambient Temperature Temperbead Welding: Begin 48- Hour Hold After 3rd Layer Completion, (ADAMS Accession No. ML070790679).

As stated in the ASME paper, there is no effect on safety (reduction), yet the change enables substantial cost reductions by reducing the schedule impacts; reducing the complexity of plant operation, specifically with regard to plant operation during outage periods and has some potential to directly reduce facility down time and radiation exposure. Without this relief request, preliminary NDE would be performed during the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold time, then final NDE upon expiration of the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> window. This change will minimize or eliminate the need for preliminary NDE, which will directly reduce radiation exposure.

3.2.5 Licensees Proposed Alternatives to N-638-1 APS proposes to start the 48-hour hold at the completion of the third layer of the weld overlay.

3.2.6 Licensees Basis for Relief Based on Code Case N-638-1, the 48-hour hold for performing NDE starts after the weld overlay cools to ambient temperature when performing ambient temperature temperbead welding. This 48-hour hold is specified to allow sufficient time for hydrogen cracking to occur (if it is to occur) in the HAZ of ferritic materials prior to performing final NDE. Based on extensive research and industry experience, EPRI has provided a technical basis for starting the 48-hour hold after completing the third layer of the weld overlay rather than waiting for the completed weld overlay to cool to ambient temperature. Weld layers beyond the third layer are not designed to provide tempering to the ferritic HAZ when performing ambient temperature temperbead welding. EPRI documented their basis in Technical Report 1013558. Although the technical data provided by EPRI is based on testing performed on SA-508, Class 2 alloy steels and other P-Number 3, Group 3 materials, the conclusions are bounding and applicable to pressurizer nozzles (P3, Group 3) as well as hot leg nozzles (P1, Group 1). After evaluating 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 the following on page 5-2 of the report: "There appears to be no technical basis for waiting 48 hours2 days <br />0.286 weeks <br />0.0658 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." Page 5-2 of the report 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 nondestructive examination performed after the 48-hour hold or by subsequent inservice inspection.

In addition to the EPRI report, the ASME Code,Section XI Committee approved Revision 4 to ASME Code Case N-638 (N-638-4) in October 2006 to allow the 48-hour hold time to begin after completing the third weld layer when using austenitic filler metals. Paragraph 4(a)(2) of the code case states in part: When austenitic materials are used, the weld shall be nondestructively examined after the three tempering layers (i.e., layers 1, 2, and 3) have been in place for at least 48 hours2 days <br />0.286 weeks <br />0.0658 months <br />. The ASME Code,Section XI, technical basis for this change is documented in an ASME White Paper (ADAMS Accession No. ML070790679). The ASME white paper points out that introducing 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 introducing 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 nonwater-backed applications. 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. Like the EPRI report, the ASME white paper concludes that there is sufficient delay time to facilitate detecting potential hydrogen cracking when NDE is performed 48 hours2 days <br />0.286 weeks <br />0.0658 months <br /> after completing the third weld layer.

3.2.7 Duration of Proposed Alternative The proposed alternative for Relief Request No. 37 would be applicable for the second and third 10-year ISI intervals for Units 1 and 3 and the remainder of the third 10-year ISI interval for Unit 2.

3.3 Staff Evaluation Relief Request 37 would require that when ambient temperature temper-bead welding is performed on ferritic materials, the liquid penetrant and UT examinations will not be performed until at least 48 hours2 days <br />0.286 weeks <br />0.0658 months <br /> after completing of the third layer of the weld overlay. This requirement deviates from Code Case N-638-1 which requires that the liquid penetrant and UT examinations not be performed until at least 48 hours2 days <br />0.286 weeks <br />0.0658 months <br /> after the finished weld reaches the ambient temperature.

This 48-hour hold time is specified to allow sufficient time for hydrogen cracking to occur (if it is to occur) in the HAZ of ferritic materials prior to performing NDE so that if hydrogen cracking does occur, NDE would be able to detect it. However, based on research and industry experience, the EPRI has provided a technical basis for starting the 48-hour hold after completion of the third temper-bead 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 when performing ambient temperature temper-bead welding.)

EPRI has documented their technical basis and conclusions on pages 5-1 and 5-2 of the White Paper.

In addition, the ASME Code,Section XI Committee published a White Paper to support the 48-hour hold time alternative. The ASME White Paper 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 nonwater-backed applications. 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. The ASME White Paper concludes that there is sufficient delay time to facilitate the detection of potential hydrogen cracking when NDE is performed 48 hours2 days <br />0.286 weeks <br />0.0658 months <br /> after completion of the third weld layer.

The staff finds that 48-hour hold time after the third weld layer is acceptable because the licensee has provided sufficient technical justification to show that hydrogen cracking in the weld overlay would not likely to occur under the proposed alternative. The NRC has approved a similar relief request concerning the 48-hour hold time for Arkansas Nuclear One, Unit 1 (ADAMS Accession No. ML070850915), and Sequoyah Nuclear Plants, Units 1 and 2 (ADAMS Accession No. ML070800361).

4.0 CONCLUSION

The staff has reviewed the licensees submittal and determined that Relief Request No. 36 for Palo Verde, Units 1, 2 and 3, will provide an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the staff authorizes the use of Relief Request No. 36, for the installation of FSWOL on the DMWs of the pressurizer and hot leg nozzles at Palo Verde, Units 1, 2, and 3. The effective period of Relief Request No. 36 is for the remainder of the second ISI interval for Palo Verde, Units 1 and 3, and the remainder of the third 10-year ISI interval for Palo Verde, Unit 2. Further, the NRC staff finds the licensee request to use later ASME Code Edition for its Palo Verde, Units 1 and 3, acceptable pursuant to 10 CFR 50.55a(g)(4)(iv) because the licensee has committed to follow all modifications and limitations placed on the 2001 Edition through the 2003 Addenda as stated in 10 CFR 50.55a.

The staff has reviewed the licensees submittal and determined that Relief Request No. 37 for Palo Verde, Units 1, 2 and 3, will provide an acceptable level of quality and safety. Therefore, Pursuant to 10 CFR 50.55a(a)(3)(i), the staff authorizes the use of Relief Request No. 37 for the second and third 10-year ISI intervals for Units 1 and 3 and the remainder of the third 10-year ISI interval for Unit 2.

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.

5.0 REFERENCES

1. Justification for the Removal of the 100 Square Inch Temper Bead Weld Repair Limitation, Electric Power Research Institute Report, 1011898.

2. Electric Power Research Institute (EPRI) Technical Document 1013558, 48-Hour Hold Requirements for Ambient Temperature Temperbead Welding, December 2006 (ADAMS Accession No. ML070670060).

3. ASME Section XI Committee Technical Basis Paper, RRA 05-08, N-638-x, Ambient Temperature Temperbead Welding: Begin 48 Hour Hold After 3rd Layer Completion (ADAMS Accession No. ML070790679).

Principal Contributor: G. Georgiev Date: June 21, 2007