ML090340017

Safety Evaluation for Request to Use Weld Overlay Repairs as Alternative to ASME Code,Section XI Repair Requirements

ML090340017
Person / Time
Site:	Hatch
Issue date:	06/24/2009
From:	Melanie Wong Plant Licensing Branch II
To:	Madison D Southern Nuclear Operating Co
Martin R, NRR/DORL, 415-1493
References
TAC MD8948, TAC MD8949
Download: ML090340017 (13)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 June 24, 2009 Mr. Dennis R. Madison Vice President - Hatch Edwin I. Hatch Nuclear Plant 11028 Hatch Parkway North Baxley, GA 31513

SUBJECT:

EDWIN I. HATCH NUCLEAR PLANT, UNIT NO.1, SAFETY EVALUATION FOR REQUEST TO USE WELD OVERLAY REPAIRS AS ALTERNATIVE TO ASME CODE, SECTION XI, REPAIR REQUIREMENTS (TAC NOS. MD8948, MD8949)

Dear Mr. Madison:

By letters to the Nuclear Regulatory Commission (NRC) dated June 11 and October 8,2008, Southern Nuclear Operating Company, Inc., submitted a request for relief from certain American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, requirements for the Edwin I. Hatch Nuclear Plant, Unit 1 and Unit 2 (HNP). As an alternative to the ASME Code requirements, the licensee proposed to implement a full structural weld overlay (FSWOL) repair for listed reactor pressure vessel (RPV) nozzle-to-safe-end dissimilar metal welds.

Based on the enclosed safety evaluation, the NRC staff concludes that the proposed relief request (RR) to perform a FSWOL for the HNP RPV nozzle-to-safe-end dissimilar metal welds listed in the June 11, 2008 submittal, will provide an acceptable level of quality and safety.

Therefore, pursuant to Title 10 of the Code of Federal Regulations, Part 50, Section 55a(a)(3)(i),

the proposed RR, for the installation of a FSWOL over the identified welds is authorized for the HNP fourth 10-year lSI interval which began January 1, 2006, and will end on December 31, 2015. All other requirements of ASME Code,Section XI, for which relief has not been specifically requested and approved, remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

Please contact Robert Martin at 301-415-1493 with any questions.

Sincerely,

~~:j(

Plant Licensing Branch 11-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-321,50-366

Enclosure:

Safety Evaluation cc w/encl: Distribution via ListServ

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION INSERVICE INSPECTION PROGRAM REQUEST FOR ALTERNATIVE FOR EDWIN I. HATCH NUCLEAR PLANT, UNIT NOS. 1 AND 2 SOUTHERN NUCLEAR OPERATING COMPANY, INC.

DOCKET NOS. 50-321, 50-366

1.0 INTRODUCTION

By letter dated June 11, 2008 (Agencywide Document Access and Management System (ADAMS) Accession No. ML090260295), to the U.S. Nuclear Regulatory Commission (NRC), as supplemented by letter dated October 8, 2008 (ADAMS Accession No. ML082820363),

Southern Nuclear Operating Company Inc. (SNC, the licensee), requested relief under the provisions of Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.55a(a)(3)(i), from certain American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) requirements for the Edwin I. Hatch Nuclear Plant, Unit 1 and Unit 2 (HNP). In lieu of using the existing repair procedures in the ASME Code,Section XI, Article IWA-4000, "Repair/Replacement Activities," SNC proposes an alternative for the design, fabrication, pressure testing, and examination of the weld overlays. The alternative will reduce a defect in austenitic nickel alloy welds to an acceptable size by increasing the wall thickness through deposition of a weld overlay. The subject welds were fabricated using Alloy 82/182.

The licensee described its alternative in the enclosure to its June 11, 2008, submittal. In Appendices 4 and 5 to its submittal, SNC also compared its proposed alternative to the requirements of ASME Code Cases (CCs) N-504-3, "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 Temper Bead Technique,Section XI, Division 1." Section 50.55(a) of 10 CFR Part 50 states the requirements governing the use of CCs and Regulatory Guide (RG)1.147, "Inservice Inspection [lSI] Code Case Acceptability, ASME Section XI, Division1 ," Revision 15, October 2007, which has been incorporated into 10 CFR 50.55(a)(b) by reference, lists all the CCs accepted by the NRC. For this (RR), the NRC staff reviewed the proposed alternatives by comparing them to alternatives approved by the staff in CCs N-504-2 and N-638-1, which have been incorporated by reference in 10 CFR 50.55a.

2.0 REGULATORY EVALUATION

Pursuant to 10 CFR 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 preservice examination requirements, set forth in the ASME Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," to the extent practical within the limitations of

- 2 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 lSI 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. The fourth 10-year lSI interval for HNP began January 1, 2006, and will end on December 31,2015. The lSI code of record for HNP for the fourth 10-year lSI interval is the 2001 Edition of the ASME Code,Section XI, including Addenda, through 2003, with an exception. The exception, in accordance with 10 CFR 50.55a(b)(2)(xxiv), is that for ASME Code,Section XI, Appendix VIII, the 2001 Edition of the ASME Code will be used.

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 would 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.

3.0 TECHNICAL EVALUATION

3.1.1 HNP-1 Components Affected As Identified by the Licensee There are 14 Category B-F, reactor pressure vessel (RPV) nozzle-to-safe end dissimilar metal (OM) welds. The nozzles are fabricated from SA-508, CL. 2 (P No.3), the safe ends are fabricated from SA-182, F-304 (P No.8), and the weld material is Alloy 82/182 (F No. 43).

These 14 welds are described below:

- Two 4-inch Jet Pump Instrument RPV Nozzle-to-Safe End Welds

- Two 10-inch Core Spray Nozzle Safe End Welds

- Eight 12-inch" Recirculation Inlet Nozzle-to-Safe End Welds

- Two 28-inch Recirculation Outlet Nozzle-to-Safe End Welds There are four small diameter Category B-F, RPV nozzle-to-safe end OM welds. The RPV nozzles are fabricated from Inconel SB-166 (P No. 43), the safe ends are fabricated from SA 182, F304 (P No.8), and the weld material is Alloy 82/182 (F No. 43). These four welds are described below:

- Three 2-inch Instrument Nozzle-to-Safe End Welds

- One 2-inch Standby Liquid Control Nozzle-to-Safe End Weld There is one Category B-J 24-inch residual heat removal carbon steel valve body to stainless steel extension piece OM weld. The valve body is fabricated from A-352-LCB (P No.1), the extension piece is fabricated from F304 stainless steel (P No.8) and the weld material is INCO WELD A (F No. 43).

3.1.2 HNP-2 Components Affected As Identified by the Licensee There are 16 Category B-F, RPV nozzle-to-safe end OM welds. The nozzles are fabricated from SA-508. CL. 2 (P No.3), the safe-ends are fabricated from SA-182, F-304 (P No.8), and the weld material is Alloy 82/182 (F No. 43). These 16 welds are described below:

- 3

- Two 4-inch Jet Pump Instrument RPV Nozzle-to-Safe End Welds

- Two 10-inch Core Spray Nozzle Safe End Welds

- Ten 12-inch Recirculation Inlet Nozzle-to-Safe End Welds

- Two 28-inch Recirculation Outlet Nozzle-to-Safe End Welds There is one Category 8-F, RPV nozzle-to-cap (5.375 inch nominal outside diameter) OM weld.

The control rod drive return nozzle is fabricated from SA-508, CL. 2 (P No.3). The cap is fabricated from S8-166 (P No. 43), and the weld material is Alloy 82/182 (F No. 43).

There are 4 small diameter Category 8-F, RPV nozzle-to-safe end OM welds. The nozzles are fabricated from Inconel S8-166 (P No. 43), the safe ends are fabricated from SA-182, F304 (P No.8), and the weld material is Alloy 82/182 (F No. 43). These four welds are described below:

- Three 2-inch Instrument Nozzle-to-Safe End Welds

- One 2-inch Standby Liquid Control Nozzle-to-Safe End Weld There are 8 Category 8-F Feedwater 12-inch Alloy 600 safe end (P No. 43)-to-carbon steel (P No.1) OM welds. The weld material is Alloy 82/182 (F No. 43).

There are 4 Category 8-F Feedwater 12-inch carbon steel transition piece (P No. 1)-to-Alloy 600 safe end (P No. 43) OM welds. The weld material is Alloy 82/182 (F No. 43).

There are 2 Category 8-J 24-inch and one 20-inch residual heat removal A-106 Gr 8 carbon steel piping (P No. 1)-to-F-316 Nuclear Grade stainless steel piping OM welds (P No.8). The weld material is Alloy 82/182 (F No. 43).

There are 3 Category 8-J Feedwater 12-inch Alloy 600 safe end extension (P No. 43)-to-Alloy 600 safe end (P No. 43) similar metal welds. The weld material is Alloy 82/182 (F No. 43).

ASME Section XI, defines these welds as similar metal welds; however, since the weld material is Alloy 82/182, the same type of cracking may occur that occurs in the OM welds. (There were originally four similar metal welds; however, the fourth weld was previously overlaid due to an unacceptable indication).

3.2 ASME Code Requirements for which Relief is Requested The lSI code of record for HNP-1 for the fourth 10-year lSI interval is the ASME Code,Section XI,2001 Edition, including Addenda 2003, with an exception. The exception is that for ASME Code,Section XI, Appendix VIII, the 2001 Edition of ASME Code will be used.

Under the rules of IWA-4220, repairs shall be performed in accordance with the licensee's design specification and the original Construction Code. Later editions and addenda of the Construction Code or of ASME Code Section III, either in their entirety or portions thereof, and ASME CCs, may be used.

3.3 Duration of Relief This relief for HNP is applicable to its fourth 10-year lSI interval which began January 1, 2006, and will end on December 31, 2015.

-4 3.4 Licensee's Proposed Alternatives for ASME CC N-504-3 3.4.1 Requirement (b) of CC N-504-3 requires that the FSWOL be low carbon (0.035 percent maximum) austenitic stainless steel. An alternative was required since a nickel-based filler (Alloy 52/52M/152) has been selected to be used. The licensee proposed to use a consumable welding wire highly resistant to stress-corrosion cracking (SCC) for the overlay material. This alternative material, designated as UNS N06052, F-No. 43, is a nickel-based alloy weld filler material, commonly referred to as Alloys 52152M, and will be deposited using the machine gas tungsten arc welding (GTAW) process with cold wire feed. As stated by the Licensee, "The Alloy 52/152 weld overlay filler metal is an austenitic nickel-based alloy having a chromium (Cr) content of at least 28%. 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 for groove welding, qualified in accordance with the Construction Code and Owner's requirements and identified in the Repair/Replacement Plan."

3.4.2 Requirement (e) of CC N-504-3 requires the first two layers of the FSWOL to have a ferrite content of at least 7.5 FN (Ferrite Number). These measurements will not be performed for this overlay since the nickel alloy filler is a fully austenitic material and does not contain ferrite. The composition of nickel-based Alloy 52/52M is such that delta ferrite does not form during welding because Alloy 52/52M welds are 100 percent austenitic and contain no delta ferrite due to the high nickel composition (approximately 60 wt% nickel). Consequently, delta ferrite measurements will not be performed for this overlay.

3.4.3 Requirement (h) of CC N-504-3 specifies that a system hydrostatic test be performed in accordance with ASME Code,Section XI, IWA-5000 if the flaw penetrates the original pressure boundary. As an alternative, leak testing in accordance with IWA-5000 will be performed.

3.4.4 The acceptance of CC N-504-3 in RG 1.147, was conditioned on meeting the provisions of ASME Section XI, Nonmandatory Appendix 0, "Weld Overlay Repair of Class 1,2, and 3 Austenitic Stainless Steel Piping Weldments." Paragraph 3(c) of the proposed alternative states that lSI of overlays would be in accord with Appendix 0, subparts Q 4300 and 0-4310, modified by the licensee in Appendix 8 of its submittal.

. 3.5 Staff Evaluation of Alternatives to N-504-3 Under the rules of ASME Code,Section XI, IWA-4220, repairs shall be performed in accordance with the licensee's design specification and the original Construction Code.

Later editions and addenda of the Construction Code or of ASME Code,Section III, either in their entirety or portions thereof, and ASME CCs may be used. In addition to the above, defects shall be removed or reduced in size in accordance with ASME Code,Section XI, IWA-4400. ASME Code Case N-504-3 will be used by the licensee to perform a FSWOL on the previously listed welds. ASME CC N-504-3 was conditionally approved by the staff for use under RG 1.147, Revision 15. Therefore, the use of N 504-3 as an alternative to the mandatory ASME Code repair provisions is acceptable to

- 5 NRC staff, provided that all conditions and provisions specified in RG 1.147, Revision 15 are complied with.

3.5.1 The first proposed modification to the ASME CC N-504-3 provisions involves the use of a nickel-based alloy weld material rather than the low carbon austenitic stainless steel.

The licensee stated that Paragraph (b) of N-504-3 requires that the reinforcement weld material shall be low carbon (0.035 percent maximum) austenitic stainless steel. In lieu of the stainless steel weld material, Alloy 52/52M, a consumable welding wire, and Alloy 152, a covered electrode, which are highly resistant to SCC, were proposed for the overlay weld material. The NRC staff notes that the use of 52/52M/152 materials are consistent with, weld materials used to perform similar FSWOLs at other operating boiling-water reactor facilities. The NRC staff also notes that the licensee is performing the subject FSWOL on dissimilar metal welds made of Alloy 82/182 material. For material compatibility in welding, the staff considers that Alloy 52/52M is a better choice of filler material than austenitic stainless steel material for this weld joint configuration.

Alloy 52/52M/152 contains about 30 percent Cr which would provide excellent resistance to SCC if exposed to 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 staff for similar applications. Therefore, the licensee's proposed use of Alloy 52/52M/152 for the FSWOL, as a modification to the requirements of N-504-3, Paragraphs (b) and (e), is acceptable as it will provide an acceptable level of quality and safety.

3.5.2 Requirement (e) of N-504-3 requires as-deposited delta ferrite measurements of at least 7.5 FN for the weld reinforcement. The licensee proposed that delta ferrite measurements will not be performed for this overlay because the deposited Alloy 52/52M/152 material is 100 percent austenitic and contains no delta ferrite due to the high nickel composition (approximately 60 percent nickel). N-504-3 allows the use of FSWOL 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-504-3 is designed for FSWOL 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-504-3, Paragraphs (b) and (e),

apply only to austenitic stainless steel FSWOL materials to ensure its resistance to sec.

These requirements are not applicable to Alloy 52/52M/152, a nickel-based material which would be used for the FSWOL. Therefore, the NRC staff finds that the requested alternative will provide an acceptable level of quality and safety.

3.5.3 Requirement (h) of CC N-504-3 is modified by the licensee to perform leak testing in accordance with ASME Code,Section XI, (2001 Edition with the 2003 Addenda), IWA 5000. Use of a leak test at normal operating temperature and pressure in lieu of a hydrostatic test has been incorporated in ASME Code,Section XI, beginning in the 1998 Edition with the 1999 Addenda. HNP-1 is currently in its fourth 10-year lSI interval and the lSI Code of record for the fourth 10-year lSI interval is the ASME Code,Section XI, 2001 Edition, including Addenda through 2003. As the licensee's alternative is consistent with the Code requirement, the NRC staff accepts the licensee's basis for this alternative.

-6 3.5.4 Inservice Examination Paragraph 3(c) of the proposed alternative in the SNC submittal dated June 11,2008, requires that inservice examinations of the FSWOLs be performed in accordance with subarticles 0-4300 and 4310 of Appendix 0 to the 2004 Edition of Section XI with Addenda through 2005 with modifications. Appendix 8 of the SNC submittal provides SNC's modifications to subarticles 0-4300 and 4310, as shown in italics. The proposed lSI requirements are discussed below.

Modified 0-4300 Inservice Flaw Evaluation Requirements, paraqraphs (at (b) and (c) in Appendix 8 require that:

(a) Flaws characterized as SCC in the Alloy 52/152 weld overlay are unacceptable and the use of IWB-3514-2 and IWB-3640 for SCC evaluation in the Class 1 overlay material is prohibited. .

(b) For non-SCC flaws in the Alloy 52/152 overlay, Table IWB-3514-2 must be used to evaluate recordable indications prior to the use of the acceptance criteria of IWB 3600. If the requirements of Table IWB-3514-2 cannot be satisfied, the acceptance criteria of IWB-3600 shall be satisfied. For unacceptable indications, the weld overlay (or the portion of the weld overlay containing the unacceptable indication) shall be removed and corrected by a repair/replacement activity in accordance with IWA-4000.

(c) If examinations reveal crack growth or new cracking in the upper 25% of the original weld or base materials, the as-found flaw (postulated 75% through wall, plus the portion of the flaw in the upper 25%) 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.

For paragraph (a) the NRC staff finds that it is conservative to prohibit any SCC flaws to remain in service and that paragraphs (b) and (c) are consistent with the NRC staff position on disposition of flaws detected in the weld overlays. Therefore, these modifications are acceptable.

Modified 0-4300 Re-Examination Requirements, paraqraphs (a), (b) and (c) in Appendix 8 require that:

(a) Paragraph (a) is unchanged from 0-4300.

(b) If inservice examinations reveal acceptable crack growth or new cracking in the upper 25% 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

-7 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.

(c) If inservice examinations reveal acceptable non-SCC 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.

For paragraph (b), 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.

For paragraph (c) 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 NRC staff's position. The NRC staff finds this requirement acceptable.

3.5.5 The sections of the licensee's submittal pertaining to ASME CC N-504-3, requirements (c) and (d) concerning weld non-destructive examination (NDE) disposition of indications and surface preparation prior to application of the overlay, requirement (f) which concerns design considerations, requirement (g) which concerns evaluation of the repaired weldment, requirement (i) which concerns nondestructive examination (NDE) including preservice inspection, inservice inspection and additional examinations of the repair area, U) which concerns the NDE volume and requirement (k) which addresses post-repair visual examinations, (k) visual examinations, (I) applicability of IWA-4000, and (m) documentation of CC used, meet or exceed the pertinent sections of ASME CC N-504-3.

Aside from the requirements of ASME Code Case N-504-3, these paragraphs in the licensee's submittal also contain additional requirements imposed by Non-Mandatory Appendix Q, "Weld Overlay Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping Weldments." On these bases, the licensee's modified CC N-504-3, requirements (c), (d),

(f), (g), (i), U), (k), (I), and (m) are acceptable to the NRC staff.

3.6 Licensee's Proposed Alternatives to ASME CC N-638-1 3.6.1 Paragraph 1.0(a) of CC N-638-1, specifies that the maximum area of finished surface of the weld shall be limited to 100 square inches and one-half of the ferritic base metal thickness. As an alternative, the maximum area of finished surface of the weld shall be limited to 300 square inches over the ferritic material. SNC notes that CC N-638-3 has been approved by the ASME. SNC also notes that residual stress analyses performed in support of Code Case N-638-3 shows that stresses for 100 square inch through 500 square inch surface area overlays are very similar.

3.6.2 Paragraph 2.1 U) of CC N-638-1 requires that the average Charpy V notch values of heat affected zone (HAZ) test coupon shall be equal to or greater than the average value of the base metal test coupon. If this criterion is not met, as an alternative, the licensee

-8 would use the provisions that are specified in paragraph NB-4335.3 of the ASME Code,Section III, 2001 Edition with 2002 Addenda which would allow adjustment to Charpy V notch test temperature at which the aforementioned criterion is met. The licensee proposed to use the provisions that were approved by the ASME Code Committee and were subsequently incorporated in the ASME Code Case N-638-2. These provisions include an adjustment temperature for the procedure qualification which shall be determined in accordance with NB-4335.3 of ASME Code,Section III, 2001 Edition with 2002 Addenda. Reference nil ductility temperature or lowest service temperature of the materials for which the welding procedure will be used will be increased by a temperature equivalent to that of the adjustment temperature.

3.6.3 Section 4.0, "Examination" of CC 638-1, specifies the requirements for examination of welds. Section 4.0 of Appendix 5 to the licensee's June 11, 2008, submittal indicates that SNC's alternative to Section 4.0 of CC 638-1 is provided in Section 3 of the enclosure to its June 11, 2008 submittal.

ASME CC N-638-1, Paragraph 4.0 (b) specifies that the final weld surface shall be examined using surface and UT testing examinations no sooner than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the weld reaches ambient temperature. As an alternative, the licensee would perform surface and volumetric examinations 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the third layer is installed. Based on research and industry experience, Electric Power Research Institute (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 during ambient temperature temper bead welding. EPRI has documented their technical basis in Technical Update report 1013558, "Repair and Replacement Applications Center: Temper bead Welding Applications 48-Hour Hold Requirements for Ambient Temperature Temper bead 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 nozzle material. 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 temper bead welded component should be very tolerant of the moisture..."

ASME CC N-638-1, Paragraph 4.0(c), specifies that the area from which weld-attached thermocouples have been removed shall be ground and examined using a surface examination method. Thermocouples will not be used. Instead, preheat and interpass temperatures will be monitored by calibrated pyrometers or temperature indicating crayons. As an alternative, if it is not possible to measure temperature by the aforementioned tools, heat flow calculations in conjunction with a measurement of maximum interpass temperature on a test coupon will be used to determine the interpass temperature. The test coupon will be made using maximum heat input of the welding procedure to be used in production and the thickness of the test coupon will be equal to or greater than the thickness of the item to be welded.

- 9 3.7 Staff Evaluation of Modifications to N-638-1 The licensee is applying a 360 degree, full structural weld overlay to maintain weld integrity. The full structural weld overlay will fulfill all structural requirements, independent of the existing weld. Operational experience has also shown that SCC in Alloy 82/182 will blunt at the interface with stainless steel base metal, carbon steel base metal, or Alloy 52/152 weld metal.

To eliminate the need for preheat and post-weld heat treatment under the Construction Code, the industry developed requirements for implementation of a temper bead welding technique which were published in CC N-638-1. The NRC endorsed CC N-638-1 in RG 1.147, Revision 15. The temper bead technique carefully controls heat input and bead placement which allows subsequent welding passes to stress relieve and temper the HAZ of the low alloy or carbon steel base material and preceding weld passes. The welding is performed with low hydrogen electrodes under a blanket of inert gas. The inert gas shields the molten metal from moisture and hydrogen. Therefore, the need for the preheat and post-weld heat treatment specified by the ASME Construction Code is not necessary to produce a sound weld using a temper bead welding process which meets the requirements of Code Case N-638-1.

3.7.1 Paragraph 1.0(a) of CC N-638-1 requires that the maximum area of an individual weld, based on the finished surface, shall be limited to 100 square inches and the depth of the weld shall not exceed one-half of the ferritic base metal thickness. This condition will not be met because the design for the weld overlay covers an area up to approximately 300 square inches on some of the ferritic components, which exceeds the limitations of Code Case N-638-1. EPRI Technical Report 1003616 provides technical justification for exceeding the size of the temper bead repairs up to a finished area of 500 square inches over the ferritic material. Results of industry analyses and testing performed to date have indicated that there is no direct correlation between the amount of surface area repaired and residual stresses generated using temper bead welding. Residual stresses associated with larger area repairs (>100 square inches) remain compressive at an acceptable level. Based on the preceding discussions, the NRC staff concludes that the modification to increase the weld overlay to as much as 300 square inches provides an acceptable level of quality and safety and is, therefore, acceptable.

3.7.2 Paragraph 2.1 G) of CC N-638-1 requires that the average Charpy V notch values of the HAZ test coupon shall be equal to or greater than the average value of the base metal test coupon. If this criterion was not met, either the weld procedure would be re-qualified or the licensee would implement the existing requirements in NB-4335.2 of ASME Code,Section III which allows the use of an adjustment temperature for weld procedure qualifications at which the average HAZ Charpy V notch value exceeds the average value of the base metal test coupon. The lowest service temperature is increased by a temperature equivalent to that of the adjustment temperature. The NRC staff finds the licensee's proposal acceptable because either successful re-qualification of the welding procedure or implementation of the ASME Code,Section III, provisions for the adjustment of lowest service temperature would ensure that the notch toughness of the HAZ of the ferritic component is not compromised due to temper bead welding.

Therefore, the alternate provides an acceptable level of quality and safety.

- 10 3.7.3 Section 4.0, "Examination" of CC 638-1, specifies the requirements for examination of welds. Section 4.0 of Appendix 5, to the licensee's June 11, 2008, submittal indicates that SNC's alternative to Section 4.0 of CC 638-1 is provided in Section 3 of the enclosure to its June 11,2008 submittal.

As discussed in Section 3(a), "Acceptance Examination of the Overlay," of the June 11, 2008, submittal, the licensee will perform a surface examination of an installed weld overlay and use the acceptance criteria of NB-5300 of ASME Code,Section III. The UT examinations of the installed weld overlay will be performed to assure adequate fusion and to detect fabrication defects. The required examination volume is defined in Appendix 2, Figure 1, of the RR. The acceptance criteria for the UT examination will be based on IWB-3514-2 of ASME Code,Section XI. Any unacceptable planar indication found in the FSWOL that does not meet IWB-3514-2 will be removed. The staff finds that the licensee's alternative is acceptable because removal of an unacceptable indication as determined by IWB-3514-2 is consistent with the staffs position.

ASME CC N-638-1, Paragraph 4.0(b), specifies that the final weld surface shall be examined using surface and UT methods no sooner than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the weld reaches ambient temperature. EPRI Technical Report 1013558, Temper bead Welding Applications - 48 Hour Hold Requirement for Ambient Temperature Temper bead Welding, has shown that it is not necessary to wait until ambient temperature is reached before initiating the 48-hour hold in order to assure adequate hydrogen removal. No further tempering or potential hydrogen absorption effects will occur after deposition of the third overlay layer. The described approach has previously been reviewed and approved by the staff (Safety Evaluation By the Office of Nuclear Reactor Regulation Related To ASME Code,Section XI, Alternatives for Union Electric Company Callaway Plant, Unit 1, Docket No. 50-483, July 10, 2007)," (ADAMS Accession No. ML071520329). Therefore, the licensee's proposed alternative to perform the surface and UT examinations no sooner than 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 is installed provides an acceptable level of quality and safety.

ASME CC N-638-1, Paragraph 4.0(c) of CC N-638-1 specifies that the area from which weld-attached thermocouples have been removed shall be ground and examined using a surface examination method. Thermocouples will not be used. Instead, preheat and interpass temperatures will be monitored by calibrated pyrometers or temperature indicating crayons. These temperature sensing devices will be used to verify preheat temperature and interpass temperature of every weld pass of the first three layers. If it is not possible to measure temperature by the aforementioned tools, heat flow calculations in conjunction with a measurement of maximum interpass temperature on a test coupon will be used to determine the interpass temperature. The test coupon will be made using maximum heat input of the welding procedure to be used in production and the thickness of the test coupon shall be equal to or greater than the thickness of the item to be welded. The staff determined that the large mass of the weldment relative to the weld bead size, coupled with the low heat input GTAW process helps to ensure that the maximum interpass temperature will not be exceeded. Additionally, the alternate heat flow calculations which take into account weld heat input, thickness of the weld joint, and thermal conductivity of the materials will provide a good estimation of the interpass

- 11 temperature. Therefore, the NRC staff concludes that this type of monitoring of the interpass temperature provides an acceptable level of quality and safety.

3.7.4 The sections of the licensee's submittal pertaining to ASME CC N-638-1, requirements 1.b, 1.c, 1.d, 1.e, and 1.f concerning general requirements; 2.0 concerning welding qualifications; 2.1.a, 2.1.c, 2.1.d, 2.1.e, 2.1.f, 2.1.g, and 2.1.i concerning procedure qualification; 2.2 concerning performance qualification; 3.a, 3.b, 3.c, 3.d and 3.e concerning welding procedure requirements; 4.a, 4.d and 4.e concerning examination, meet or exceed the pertinent sections of ASME CC N-638-1. Therefore, these licensee modified CC N-638-1 requirements are acceptable to the NRC staff.

4.0 CONCLUSION

Based on the discussion above, the NRC staff concludes that the modifications proposed in the RR ISI-ALT-08-02, Version 1.0, to perform a FSWOL on the listed welds will provide an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff authorizes the proposed RR ISI-ALT-08-02, Version 1.0, for the installation of a FSWOL over the welds identified in the subject RR. This RR is authorized for the HNP fourth 10-year lSI interval which began January 1,2006, and will end on December 31, 2015.

Principal Contributors: E. Andruszkiewicz R. Martin Date of Issuance: June 24, 2009

ML090340017 NRR-106 OFFICE NRRlLPL2-1/PM NRRlLPL2-1/LA NRRlCVIB/BC OGC NLO NRRlLPL2-1/BC NAME RMartin SRohrer MMitchell LBS MWonq DATE 06/11/09 06/22/09 06/11/09 06/19/09 06/24/09