ML071520329

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Request for Alternatives for Application of Structural Weld Overlays to Pressurizer Dissimilar Metal Nozzle Welds for Third 10-Year Inservice Inspection Program Interval
ML071520329
Person / Time
Site: Callaway Ameren icon.png
Issue date: 07/10/2007
From: Hiltz T
NRC/NRR/ADRO/DORL/LPLIV
To: Naslund C
Union Electric Co
Donohew J N, NRR/DORL/LP4, 415-1307
References
TAC MD2815
Download: ML071520329 (22)
v • d • e


Text

July 10, 2007 Mr. Charles D. Naslund Senior Vice President and Chief Nuclear Officer Union Electric Company Post Office Box 620 Fulton, MO 65251

SUBJECT:

CALLAWAY PLANT, UNIT 1 - ALTERNATIVES FOR APPLICATION OF STRUCTURAL WELD OVERLAYS TO PRESSURIZER DISSIMILAR METAL NOZZLE WELDS (TAC NO. MD2815)

Dear Mr. Naslund:

By letter dated August 14, 2006, as supplemented by letters dated March 26 and April 5, 2007 (ULNRC-05292, -05385, and -05395, respectively), the Union Electric Company (the licensee) requested relief from certain Section XI requirements in the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) at its Callaway Plant, Unit 1 (Callaway). The licensee requested relief from the ASME Code,Section XI, installation, repair, and examination requirements for full structural weld overlays in (1) Subsections IWA-4410, IWA-4430, IWA-4520(a), IWA-4530, IWA-4600, and Table IWB-2500-1 (Examination Categories B-F and B-J) and (2) Appendix VIII, Supplement 11, Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds, to the 1998 Edition through the 2000 Addenda of the ASME Code,Section XI. The licensee incorporated its alternatives to the requirements in the IWA subsections and Table IWB-2500-1 in the proposed modifications to ASME Code Case N-504-2, Alternative Rules for Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping,Section XI, Division 1 (N-504-2), and Code Case N-638-1, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW [Gas Tungsten Arc Weld] Temper Bead Technique (N-638-1). The requested relief would be used to perform preemptive full structural weld overlays on nozzle-to-safe-end dissimilar metal and safe-end-to-piping stainless steel butt welds associated with pressurizer and connected piping at Callaway.

The relief request was verbally authorized in a conference call on April 5, 2007, and the structural weld overlays were performed during the refueling outage conducted during the spring of 2007.

Based on the enclosed safety evaluation, the NRC staff concludes that the alternatives to the ASME Code requirements in (1) the modified Code Cases N-504-2 and N-638-1, and (2) Appendix VIII, Supplement 11, in the relief request for the preemptive full structural overlay or weld repair at Callaway for the welds listed in the August 14, 2006, letter, 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 alternatives to Code Cases N-504-2 and N-638-1 for the remaining service life of the subject welds. Secondly, pursuant also to 10 CFR 50.55a(a)(3)(i),

the NRC staff authorizes the proposed alternatives to Appendix VIII, Supplement 11, for the remainder of the third 10-year inservice inspection interval, which began on December 19,

C. D. Naslund 2004, and ends on December 18, 2014. 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.

Sincerely,

/RA/

Thomas G. Hiltz, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-483

Enclosure:

Safety Evaluation cc w/encl: See next page

ML071520329 NRR-028 OFFICE NRR/LPL4/PM NRR/LPL4/LA CNPB/BC OGC - NLO w/edit NRR/LPL4/BC NAME JDonohew:sp JBurkhardt TChan/JTsao for JBiggins THiltz DATE 6/26/07 6/26/07 6/14/07 6/25/07 7/2/07 Callaway Plant, Unit 1 cc:

John ONeill, Esq. Technical Services Branch Chief Pillsbury Winthrop Shaw Pittman LLP FEMA Region VII 2300 N. Street, N.W. 2323 Grand Boulevard, Suite 900 Washington, D.C. 20037 Kansas City, MO 64108-2670 Mr. Keith A. Mills, Supervising Engineer Mr. Dan I. Bolef, President Regional Regulatory Affairs/Safety Analysis Kay Drey, Representative AmerenUE Board of Directors Coalition for the P.O. Box 620 Environment Fulton, MO 65251 6267 Delmar Boulevard University City, MO 63130 U.S. Nuclear Regulatory Commission Resident Inspector Office Mr. Lee Fritz, Presiding Commissioner 8201 NRC Road Callaway County Courthouse Steedman, MO 65077-1302 10 East Fifth Street Fulton, MO 65251 Mr. Les H. Kanuckel Manager, Quality Assurance Mr. David E. Shafer AmerenUE Superintendent, Licensing P.O. Box 620 Regulatory Affairs Fulton, MO 65251 AmerenUE P.O. Box 620 Missouri Public Service Commission Fulton, MO 65251 Governor Office Building 200 Madison Street Manager, Regulatory Affairs P.O. Box 360 AmerenUE Jefferson City, MO 65102-0360 P.O. Box 620 Fulton, MO 65251 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission Mr. Keith G. Henke, Planner 611 Ryan Plaza Drive, Suite 400 Division of Community and Public Health Arlington, TX 76011-4005 Office of Emergency Coordination 930 Wildwood P.O. Box 570 Mr. H. Floyd Gilzow Jefferson City, MO 65102 Deputy Director for Policy Department of Natural Resources Director, Missouri State Emergency P.O. Box 176 Management Agency Jefferson City, MO 65102-0176 P.O. Box 116 Jefferson City, MO 65102-0116 Mr. Rick A. Muench President and Chief Executive Officer Mr. Scott Clardy, Director Wolf Creek Nuclear Operating Corporation Section for Environmental Public Health P.O. Box 411 P.O. Box 570 Burlington, KA 66839 Jefferson City, MO 65102-0570 Certrec Corporation 4200 South Hulen, Suite 422 Fort Worth, TX 76109 June 2007

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

1.0 INTRODUCTION

By its application dated August 14, 2006, as supplemented by letters dated March 26 and April 5, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML062350116, ML070990115, and ML071020041, respectively), Union Electric Company (the licensee) requested relief from the requirements in Section XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) for the Callaway Plant, Unit 1 (Callaway). The relief from the ASME Code was requested pursuant to paragraph 55a(a)(3)(i) of Part 50, Domestic Licensing of Production and Utilization Facilities, of Title 10, Energy, of the Code of Federal Regulations (i.e., 10 CFR 50.55a(a)(3)(i)) in that the alternatives to the ASME Code requirements will provide an acceptable level of quality and safety.

In its application, the licensee requested relief from the ASME Code,Section XI, installation, repair, and examination requirements for full structural weld overlays in (1) Subsections IWA-4410 (and its referenced original Construction Code for the pressurizer and attached piping),

IWA-4430, IWA-4520(a), IWA-4530, IWA-4600, and Table IWB-2500-1 (Examination Categories B-F and B-J) and (2) Appendix VIII, Supplement 11, Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds, to the 1998 Edition through the 2000 Addenda of the ASME Code,Section XI. The licensee incorporated its alternatives to the requirements in the IWA subsections and Table IWB-2500-1 in the proposed modifications to ASME Code Case N-504-2, Alternative Rules for Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping,Section XI, Division 1, and Code Case N-638-1, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW [Gas Tungsten Arc Weld] Temper Bead Technique. The requested relief would be used to perform preemptive full structural weld overlays on nozzle-to-safe-end dissimilar metal and safe-end-to-piping stainless steel butt welds associated with pressurizer and connected piping at Callaway.

2.0 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 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 ISI Code of record for Callaway for the third 10-year ISI interval, which began on December 19, 2004, and ends on December 18, 2014, is the 1998 Edition of the ASME Code through the 2000 Addenda.

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 ending on November 22, 2002. Supplement 11 was required to be implemented by November 22, 2001. Additionally, 10 CFR 50.55a(b)(2)(xv),

Appendix VIII specimens set and qualification requirements, requires that licensees implementing the 1995 Edition through the 2001 Edition shall apply the provisions under Paragraph 50.55a(b)(2)(xv) except for those in provision (F), which are optional.

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 Nuclear Regulatory Commission (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), and proposed alternatives to the implementation of (1) certain ASME Code,Section XI requirements by the use of modified ASME Code Cases N-504-3 and N-638-1, and (2) ASME Code,Section XI, Appendix VIII, Supplement 11, for preemptive or repair full structural weld overlays on the pressurizer and connected piping at Callaway.

Regulatory Guide (RG) 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, lists the code cases that are acceptable to the NRC for application in licenseesSection XI ISI programs. A licensee may use a code case specified in the RG without prior approval by the NRC if it meets the conditions specified in the code case.

3.0 TECHNICAL EVALUATION

3.1 ASME Code Components Affected

The licensee listed the following welds in its application as the welds affected by its relief request:

Description:

Nozzle-to-safe-end dissimilar metal (DM) Alloy 82/182 butt welds and safe-end-to-piping stainless steel butt welds on

the safety, relief, spray, and surge line connections to the pressurizer.

ASME Code Class: Class 1 Examination Categories: R-A (risk-informed designation for B-F and B-J categories)

Weld Numbers: 2-TBB-03-1-W (14" surge nozzle-to-safe-end weld) 2-TBB-03-2-W (4" spray nozzle-to-safe-end weld) 2-TBB-03-3-A-W (6" safety A nozzle-to-safe-end weld)*

2-TBB-03-3-B-W (6" safety B nozzle-to-safe-end weld) 2-TBB-03-3-C-W (6" safety C nozzle-to-safe-end weld) 2-TBB-03-4-W (6" relief nozzle-to-safe-end weld) 2-BB-01-F004B (14" surge nozzle safe-end-to-piping weld) 2-BB-02-F001 (6" safety nozzle safe-end-to-piping weld)*

2-BB-02-F005 (6" safety nozzle safe-end-to-piping weld) 2-BB-02-F006 (6" safety nozzle safe-end-to-piping weld) 2-BB-02-F008 (6" relief nozzle safe-end-to-piping weld)*

2-BB-04-F001 (4" spray nozzle safe-end-to-piping weld)

The above welds that are designated with an asterisk (*) are welds that the licensee stated were selected under the risk-informed program.

3.2 Applicable ASME Code Edition and Addenda In its application, the licensee stated that the following editions and addenda of the ASME Code, Sections III and XI, are applicable to Callaway:

  • Section XI, 1998 Edition through the 2000 Addenda.
  • Section III, 1974 Edition through Summer 1974 Addenda, is the original Code of Construction for the pressurizer.
  • Section III, 1974 Edition through Winter 1974 Addenda, is the original Construction Code for top head pressurizer piping.
  • Section III, 1974 Edition through Winter 1975 Addenda is the original Construction Code for bottom head pressurizer piping.

3.3 Applicable ASME Code Requirements for Which Relief Is Requested Under the requirements of IWA-4610(a), the area to be welded plus a band around the area of at least one and one-half times the component thickness or 5 inches, whichever is less, shall be preheated and maintained at a minimum temperature of 350 degrees Fahrenheit (EF) for the shielded metal arc welding (SMAW) process and 300 EF for the GTAW process.

ASME Code Cases N-638-1 and N-504-2, which are approved with the conditions specified for the code cases in RG 1.147, Revision 14, dated August 2005, are applicable to this relief

request. ASME Code,Section XI, 1998 Edition through the 2000 Addenda, Appendix VIII, Supplement 11, is required to be implemented in accordance with 10 CFR 50.55a(b)(2)(xv).

The specific requirements are addressed in this safety evaluation (SE) below.

3.4 Licensees Proposed Modifications to Code Case N-504-2 As described in its letters, the licensee proposed to use a modified Code Case N-504-2 for the full structural weld overlays and provide the following with the following statements about the proposed modifications to the code case:

1. The use of a nickel-based alloy weld material, Alloy 52M/152, rather than the low-carbon (0.035 percent maximum) austenitic stainless steel.
2. The relaxation from the requirement to perform delta ferrite measurements to meet the 7.5 Ferrite Number (FN) requirement of Code Case N-504-2. The FN requirement cannot be met because the Alloy 52M/152 weld material is 100 percent austenitic and contains no delta ferrite.
3. The modification to the provisions of Appendix Q-3000(b) to be published in the 2006 Addenda of ASME Code,Section XI, which deletes the requirement that the overlay meet the Construction Code.
4. The modification to the provisions of Appendix Q-3000(b)(3) to be published in the 2006 Addenda of ASME Code,Section XI, which inserts the wording overlay design thickness.
5. The performance of a system leakage test, instead of a hydrostatic test, in accordance with ASME Code,Section XI, IWA-5000 in the 2000 Addenda.

It should be noted that the licensee will not be adopting the 2006 Addenda of the ASME Code,Section XI. The NRC staffs evaluation of Appendices Q-3000(b) and Q3000(b)(3) is in Section 3.4.2 of this SE.

3.4.1 Licensees Basis for Relief From Code Case N-504-2 Pursuant to 10 CFR 50.55a(a)(3)(i), the licensee stated in its letters that the weld overlay has been designed consistent with the requirements of Code Case N-504-2 with the specific thickness and length computed according to the guidance provided in the code case. The licensee stated that Alloy 52M/152 material is highly resistant to primary water stress-corrosion cracking (PWSCC) and that industry operational experience has shown that PWSCC in Alloy 82/182 will blunt at the interface with stainless steel base metal, ferritic base metal, or Alloy 52M/152 weld metal. The 360 degree structural weld overlay will control growth in any PWSCC crack and maintain weld integrity. The weld overlay will induce compressive stress in the weld, thus impeding growth of any reasonably shallow cracks.

The weld metal used will be Alloy 52M/152, which is an austenitic nickel alloy. These filler materials were selected for their improved resistance to PWSCC. Alloys 52M and 152 contain about 30 percent chromium, which imparts excellent corrosion resistance. The existing

Alloy 82/182 weld and the Alloy 52M/152 overlay are nickel-based, and have ductile properties and toughness similar to austenitic stainless steel piping welds at pressurized-water reactor (PWR) operating temperatures. These filler materials are suitable for welding over the ferritic nozzle, Alloy 82/182 weld and the austenitic stainless steel pipe or safe-end materials.

Paragraph (e) of Code Case N-504-2 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 52M/152 is 100 percent austenitic and contains no delta ferrite due to the high-nickel composition (i.e., approximately 60 percent nickel).

The licensee stated further that ASME Code approved a revision to Appendix Q, which will be published in the 2006 Addenda of ASME Code,Section XI. This revised paragraph is intended to correct the wording in nonmandatory Appendix Q, which was first published in the 2005 Addenda and is a condition in RG 1.147 for licensees to use Code Case N-504-2. The first revision addresses a problem with Appendix Q-3000(b) and deletes the requirement that the design of the overlay satisfy the requirements of the construction code and owners requirements. This revision is necessary because there is no similar wording in the approved Code Case N-504-2. The licensee stated that the wording in the codified version was inappropriate because meeting the requirements of the Construction Code required the absence of cracks, and the primary purposes of the code case and nonmandatory Appendix Q is to repair cracks with the external overlay.

The licensee also stated that a system hydrostatic test at 1.02 times Class 1 reactor coolant system operating pressure at normal operating temperature is of no value and provides no more assurance about the structural condition of the weld overlay than the system leakage test.

For the application of weld overlays, extensive surface and volumetric examinations of the weld overlay are required by Code Case N-504-2 and nonmandatory Appendix Q, which provide equivalent assurance of the quality of the overlay.

3.4.2 NRC Staff Evaluation of Proposed Modifications to Code Case N-504-2 Under the rules of IWA-4420, in editions and addenda up to and including the 1998 Edition with the 2000 Addenda, repairs shall be performed in accordance with the Owners Design Specification and the original Construction Code of the component or system. Later editions and addenda of the Construction Code, or of ASME Code,Section III, either in their entirety or portions thereof, and ASME Code cases may be used. Defects shall be removed or reduced in size. Alternatively, the component may be evaluated and accepted in accordance with the design rules of either the Construction Code, or Section III, when the Construction Code was not Section III.

Code Case N-504-2 will be used by the licensee to perform full structural weld overlays on the pressurizer welds listed in Section 3.1 of this SE, which is Table 1 of the licensees August 14, 2006, application. The overlays will be installed as a preemptive measure against cracking due to PWSCC.

Code Case N-504-2 was conditionally approved by the NRC staff for use by licensees in RG 1.147, Revision 14. The condition required the use of nonmandatory Appendix Q, which

provides the nondestructive examination (NDE) methods, volume, and acceptance criteria for the weld overlay. Therefore, the use of Code Case N-504-2 as an alternative to the ASME Code repair provisions is acceptable to the NRC staff, but it should be noted that using the code case requires that all conditions and provisions of Code Case N-504-2 are complied with by the licensee. The licensee, however, has proposed modifications to the code case. These are listed at the beginning of Section 3.4 of this SE.

The first proposed modification to the Code Case N-504-2 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 the code case requires that the reinforcement weld material shall be low-carbon (0.035 percent maximum) austenitic stainless steel. Instead of the stainless steel weld material, Alloy 52M/152, a consumable welding wire highly resistant to PWSCC, was proposed for the overlay weld material. The NRC staff notes that the licensee is performing a full structural overlay on dissimilar metal welds made of Alloy 182 material and, for material compatibility in welding, considers Alloy 52M/152 a better choice of filler material than austenitic stainless steel material for this weld-joint configuration. Because Alloy 52M/152 contains about 28 to 30 percent chromium, which would provide excellent resistance to PWSCC in the reactor coolant environment, and is identified as F-No. 43 Grouping for Ni-Cr-Fe, classification UNS N06054 and W86152 filler metal, which has been approved by the NRC staff for similar applications, the NRC staff concludes that the licensees proposed use of Alloy 52M/152 for the weld overlays as a modification to the requirements of Code Case N-504-2, paragraph (b), provides an acceptable level of quality and safety.

The second proposed modification to the code case involves paragraph (e), which requires as-deposited delta ferrite measurements of at least 7.5 FN for the weld reinforcement. The licensee proposed not to perform delta ferrite measurements for this overlay because the deposited Alloy 52M/152 material is 100 percent austenitic and contains no delta ferrite due to the high-nickel composition (approximately 60 percent nickel). Code Case 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, the code case is only applicable to weld overlay repairs 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 paragraphs (b) and (e), apply to austenitic stainless steel weld overlay materials and these requirements are not applicable to Alloy 52M/152, a nickel-based material, which the licensee will use for the weld overlays.

Based on this, the NRC staff concludes that the modifications to N-504-2, paragraph (e), will provide an acceptable level of quality and safety.

The third and fourth modifications to the code case involve the licensees use of two corrections to nonmandatory Appendix Q-3000, which had not been published in the 2006 Addenda of ASME Code,Section XI, at the time of the licensees application. The first correction involves the deletion of the phrase the requirement for the design of the overlay to satisfy the requirements of the Construction Code and Owners requirements from Appendix Q-3000(b).

Construction Code NB-5300 acceptance criteria does not allow the presence of cracks, regardless of size. Both preemptive weld overlay and full structural overlay repairs may require welding over existing cracks, which is considered a mitigation technique for crack growth. The second correction in Appendix Q-3000(b)(3) consisted of changing the words pressure design

to overlay design thickness. The licensee stated that pressure design is incorrect and is not used in Code Case N-504-2, and overlay design thickness is considered a more appropriate description.

The NRC staffs review of the modifications confirm that the licensee is complying with the version of Appendix Q identified in the condition to Code Case N-504-2 in RG 1.147, Revision 14, and that the corrections are primarily editorial in nature. Based on its review, the NRC staff concludes that the third and fourth modification to use the corrections to nonmandatory Appendix Q, as discussed above, will provide reasonable assurance of the integrity of the weld overlays and, therefore, provides an acceptable level of quality and safety.

The fifth modification requested by the licensee is to use a system leakage test in accordance with ASME Code,Section XI, IWA-5000 in the 2000 Addenda. The licensees proposed modification, to perform a system leakage test instead of a hydrostatic test, is supported by the NRC staffs position with respect to Code Case N-416-3, Alternative Pressure Test Requirement for Welded or Brazed Repairs, Fabrication Welds or Brazed Joints for Replacement Parts and Piping Subassemblies, or Installation of Replacement Items by Welding or Brazing, Classes 1, 2, and 3,Section XI, Division 1 (N-416-3). Code Case N-416-3 is unconditionally approved for use by licensees in RG 1.147, Revision 14, and states that:

... a system leakage test may be used provided the following requirements are met:

(a) NDE shall be performed on welded repairs, fabrication and installation joints in accordance with the methods, and acceptance criteria of the applicable Subsection of the 1992 Edition of Section III.

The above acceptance criteria in Section III do not allow the presence of cracks, regardless of length, and is geared more towards construction-type welds. The licensee stated that it will conduct a system pressure test and post-repair NDE examinations which are required by Code Case N-504-2, utilizing the appropriate Electric Power Research Institute (EPRI) Performance Demonstration Initiative (PDI) procedures, as discussed later in this SE. The post-repair examination volume includes the full thickness of the weld overlay plus 25 percent of the underlying base metal thickness. The specimen sets for PDI qualification for weld overlay examinations include construction-type flaws. Therefore, use of PDI qualified personnel and procedures for the examination of the weld overlay will result in the reliable detection of construction-type flaws and meets the intent of compliance with the applicable subsection of the 1992 Edition of Section III. Based on this, the NRC staff concludes that the fifth modification to the code case will provide an acceptable level of quality and safety.

As discussed above, the NRC staff has reviewed the licensees proposed modifications to Code Case N-504-2 and concludes that all its concerns have been addressed by the licensee in its letters. Therefore, based on the discussion above, the NRC staff concludes that the modifications to the code case, as an alternative to the mandatory ASME Code repair provisions, is acceptable because the alternative will provide an acceptable level of quality and safety.

3.5 Licensees Proposed Modifications to Code Case N-638-1 In its application, the licensee proposed to use Code Case N-638-1 with the following modifications to the code case for the full structural weld overlays:

1. The maximum area of an individual weld based on the finished surface over the ferritic material will be approximately 500 square inches (in2). This was reduced to 300 in2 in the supplemental letter dated March 26, 2007.
2. Instead of the 48-hour hold time from ambient temperature for the start of postweld NDE, the NDE may start following completion of the third temper-bead layer.
3. Full ultrasonic testing (UT) of the 1.5T band on the ferritic side of the overlay(s) will not be performed. The UT will be performed on the actual weld overlay, meeting the requirements of Code Case N-504-2 and nonmandatory Appendix Q.

3.5.1 Licensees Basis for Relief For the first modification, the licensee proposed the minimum area of an individual weld overlay over the ferritic nozzle material to be 300 in2 in place of the 100 in2 specified in Code Case N-638-1. The licensee stated that the one-half base metal thickness limitation, which also includes the 100 in2 surface area limitation under paragraph 1.0(a) of Code Case N-638-1, apply only to excavations and repairs, and are not applicable to the weld overlays that are the subject of this relief request and, therefore, the 100 in 2 surface area limitation is not applicable to this configuration, which consists of an overlay rather than an excavation of ferritic material.

For the second modification, the licensee stated that EPRI Report 1013558, 48-Hour Hold Requirement for Ambient Temperature Temperbead Welding, provides justification for deviation from the 48-hour hold requirement of Code Case N-638-1. It also stated that the ferritic nozzle base material region is the only area susceptible to delayed heat-affected zone (HAZ) cracking, and the area and volume is tested under the requirements of Code Case N-504-2 and Appendix Q. This testing requires liquid penetrant examination prior to installation of the full structural weld overlay, which requires a clean surface that would not leave surface contamination necessary to start hydrogen cracking. Finally, the use of Alloy 52M/152 weld material, with its high affinity for hydrogen, will protect the ferritic portion of the base material, which is covered by the structural weld overlay, from cracking.

For the third modification, the licensee stated that instead of the requirement to perform a UT examination of the 1.5T band next to the overlay, the post overlay NDE will be performed in accordance with the requirements of Code Case N-504-2. The licensee further stated that Code Case N-638-1 applies to any type of welding where a temper-bead technique is to be employed and is not specifically written for a weld overlay repair. The licensee stated that if the cracking were to occur, it would be beneath the HAZ of the weld overlay instead of the 1.5T band that is not covered by the overlay. Finally, a UT of the 1.5T band is not feasible because of the nozzle configuration, therefore, meaningful information cannot be obtained from the UT of the 1.5T band.

3.5.2 NRC Staff Evaluation of Modification to Code Case N-638-1 Under the requirements of IWA-4610(a), the area to be welded plus a band around the area of at least one and one-half times the component thickness or 5 inches, whichever is less, shall be preheated and maintained at a minimum temperature of 350 EF for the SMAW welding process and 300 EF for the GTAW welding process. Code Case N-638-1 allows the use of machine GTAW with ambient temperature preheat and no postweld heat treatment when draining the vessel is impractical. To eliminate the need for preheat and postweld heat treatment under the Construction Code, the industry developed a temper-bead welding technique, which was published as Code Case N-638-1 and NRC recently endorsed the code case in RG 1.147, Revision 14. 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 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 postweld heat treatment specified by the ASME Construction Code is not necessary to produce a sound weld using the temper-bead process in the code case.

With respect the first modification by the license to the code case, Code Case N-638-1, paragraph 1(a), limits the size of the repair to 100 in2 maximum and a depth of weld not greater than one-half of the ferritic base metal thickness, or 3/8 inch. Some of the reasons for these limits are distortion of weld and base metal, cracking in the weld and base metal, and high residual stresses when a large repair excavation is being performed in the ferritic material of a dissimilar metal weld. In its supplemental letter dated March 26, 2007, the licensee reduced the maximum area of an individual weld from its original request of 500 in2 to an area not to exceed 300 in2, because of the diameter of the components. In the application for this relief request or repair of an existing service related flaw, there is no large excavation in the ferritic portion of the material, therefore, the 100 in2 limitation does not significantly contribute to cracking when the ferritic material is overlaid rather than excavated. The overlay of tough, nickel-based alloy material results in the deposition of compressive stresses in the original Alloy 82/182 weld materials thereby providing reasonable assurance of the continued structural integrity of the component.

Also, in Code Case N-504-2, paragraphs (g)(2) and (g)(3) require the consideration of the residual stresses produced by the weld overlay with other applied loads on the system. The evaluation of other welds and components in the system is necessary to consider potential increases in loading, including shrinkage effects, due to all the weld overlays in the reactor coolant system. These welds and components must meet the applicable stress limits of the plant construction code. The NRC staff considers this evaluation important in assuring that the reactor coolant system will not be adversely effected after preemptive weld overlays are deposited.

In its response to an NRC question, in its letter dated March 26, 2007, the licensee stated it would measure and evaluate the axial weld shrinkage after the overlays are completed in accordance with Code Case N-504-2 and made this a regulatory commitment. As required by the code case, the evaluation would be completed before the weld overlays are placed in service, which will be prior to plant startup from the refueling outage conducted during the spring of 2007. The licensee informed the NRC staff that this evaluation was done in the spring

2007 refueling outage when the weld overlays were performed prior to plant startup and putting the subject welds into service.

Based on the preceding discussions and the licensees commitment to complete the analyses required under N-504-2, paragraphs g(2) and (3), prior to startup, the NRC staff concludes that the modification to increase the preemptive weld overlays beyond the 100 in2 maximum to 300 in2, will provide an acceptable level of quality and safety and is, therefore, acceptable.

The licensees second modification changed the start of the 48-hour hold time from the completion of the entire full structural weld overlay to the completion of the third temper-bead layer over the ferritic base material. The NRC staff has reviewed EPRI Report 1013558 and finds the assumptions drawn in the report to be reasonable for the purposes of the commencement of the 48-hour hold time. The NRC staff agrees that the temper-bead welding process in combination with the 350 EF interpass temperature provide an effective combination to ensure high HAZ toughness and protection against sensitization. In addition to the above, postweld Hydrogen delayed cracking is most susceptible in the ferritic materials, but the use of Alloy 52M/152 weld material, with its high affinity for mon-atomic hydrogen will protect the ferritic material from cracking. Finally, the postweld liquid penetrant examination will provide reasonable assurance that if the cracking were to occur, it would be detected. The acceptance criteria in Appendix Q does not allow for the presence of any cracking, therefore, if discovered, it would be removed and repaired prior to placing the material in service. Based on the above discussion, the staff concludes that the information provided by the licensee provides reasonable assurance of the structural integrity and is considered acceptable.

The third modification requested by the licensee is that the full UT examination of the 1.5T band will not be performed, which is required under paragraph 4.0(b) of the code case. The NRC staff notes that the postweld overlay area, as defined under Appendix Q, is one-half inch on either side of the overlay for surface examination and the completed overlay for UT examination. The licensee specifically stated in its letters that it will comply with Appendix Q, a condition to the use of Code Case N-504-2. The issue of cracking and/or distortion of the weld and base metal were not specifically addressed in the code case development work. Since the weld overlays are fabricated from austenitic materials with inherent toughness, no cracking in the overlays is expected to occur due to the shrinkage associated with the weld overlay. With respect to the ferritic portion of the overlays, many temper-bead weld overlays have been applied in the nuclear industry to these nozzle-to-safe-end locations. In no instance has there been any reported cracking due to the weld overlay application. The stiffness and high toughness inherent in the low-alloy steel material is expected to protect against any cracking and limit any distortion that might occur in the low-alloy steel material.

In addition to the above, any cracking which might occur should be detected by the final NDE of the weld overlay required under Appendix Q, which provides additional assurance of the deposition of a defect-free, structurally sound overlay. The assessment of the shrinkage stresses on the piping, plus postweld NDE volumes under Appendix Q, provide reasonable assurance that defect-free welds will result in maintaining the structural integrity of the piping.

The NRC staff concludes that the modifications to the 1.5T band ultrasonic examination requirement under paragraph 4.0(b) will provide an acceptable level of quality and safety and is, therefore, acceptable.

The weld overlays in this relief request are to mitigate PWSCC in dissimilar metal welds at Callaway, which is an operating nuclear power plant. The application of Code Case N-504-2 is for applying austenitic Alloy 52/52M weld metal on austenitic base material. The application of Code Case N-638-1 is to apply austenitic weld metal on ferritic base material using a controlled heat input that relieves welding stresses and prevents crack sensitive microstructures in the ferritic material. The purpose of Code Case N-638-1 is to establish an austenitic surface for the application of Code Case N-504-2 to complete the structural weld overlay. The N-638-1-applied weld metal is sandwiched between base metal and N-504-2 weld metal. Locating a flaw in Code Case N-638-1 weld metal using Section III radiography would be extremely difficult.

Many flaws that are not detected or accurately sized with radiography have a high likelihood of being detected and sized with UT, depending on orientation. These flaws are normally detected with UT during the Section XI, pre-service inspection. Also, the pre-service UT is used to characterize flaws detected during the Section III radiography examination. The flaws of concern are the ones that cause failure immediately or grow to failure in the future. The Section Xl pre-service acceptable flaw standards were developed to consider the materials in which the flaw indications are detected, the orientation and size of the indications, and ultimately their potential structural impact of the flaw on the component. The flaws detected during pre-service inspections are subjected to periodic ISIs as established in Appendix Q, Q-4300. This includes inspection frequencies for monitoring existing crack growth and identifying new cracks. Thus, the established pre-service NDE acceptance criteria in Code Case N-504-2 for weld overlays made with Alloy 52M/152 weld metal also applies to the portion of the weld overlay made during the application of Code Case N-638-1, as modified by this section of the SE. The NRC staff, therefore, concludes that the NDE acceptance criteria proposed by the licensee are appropriate for this application and will provide an acceptable level of quality and safety, and are acceptable.

3.6 Appendix VIII, Supplement 11, Requirements From Which Relief Is Requested Pursuant to 10 CFR 50.55a(a)(3)(i), the licensee requested relief from the weld overlay requirements in the ASME Code,Section XI, Appendix VIII, Supplement 11. In lieu of the requirements of ASME Code,Section XI, 1998 Edition, 2000 Addenda, Appendix VIII, Supplement 11, the licensee proposed that the PDI program as described in its application be used as an alternative to certain requirement in Supplement 11. The duration of the relief is for the remainder of the third 10-year ISI interval for Callaway. The 20 specific Supplement 11 paragraphs that the licensee proposed alternatives in its relief request are the following Supplement 11 paragraphs: 1.1(b), 1.1(d)(1), 1.1(e)(1), 1.1(e)(2), 1.1(e)(2)(a)(1),

1.1(e)(2)(a)(2), 1.1(e)(2)(a)(3), 1.1(e)(2)(b)(1), 1.1(e)(2)(b)(2), 1.1(e)(2)(b)(3), 1.1(f)(1), 1.1(f)(3),

1.1(f)(4), 2.0, 2.1, 2.2(d), 2.3, 3.1, 3.2(a), and 3.2(b).

3.6.1 Licensees Basis for Relief The licensee stated that these modifications were developed by the EPRI PDI program to implement the requirements of Appendix VIII and have previously been approved by the NRC staff for use by licensees.

3.6.2 NRC Staff Evaluation of Proposed Modifications to Appendix VIII, Supplement 11 The U.S. nuclear utilities created the PDI program to implement performance demonstration requirements contained in Appendix VIII of Section XI of the ASME Code. To this end, the PDI program has developed a program for qualifying equipment, procedures, and personnel in accordance with the UT criteria of Appendix VIII, Supplement 11. Prior to the Supplement 11 program, EPRI was maintaining a performance demonstration program (the precursor to the PDI program) for weld overlay qualification under the Tri-party Agreement with NRC in the NRC letter dated July 3, 1984 (ADAMS Accession No. 8407090122). This NRC letter to EPRI defined a coordination plan for training and qualification activities of NDE personnel employed in performance of ultrasonic examination of piping weldments during ISI of boiling-water reactor (BWR) power plants. Instead of having two programs with similar objectives, the NRC staff recognized the EPRI PDI program for weld overlay qualifications as an acceptable alternative to the Tri-party Agreement in its letter dated January 15, 2002, to the PDI Chairman (ADAMS Accession No. ML020160532). As stated in the January 15, 2002, letter issued by the NRC, the purpose of the letter was to inform the PDI program that the PDIs performance demonstration program for weld overlays was an acceptable alternative to the performance demonstration recommendations of NRC Generic Letter (GL) 88-01, NRC Position on IGSCC

[Intergranular Stress-Corrosion Cracking] in BWR Austenitic Stainless Steel Piping, dated January 25, 1988.

Although the PDI program was developed during ISIs at BWR plants, it is applicable to weld overlay qualification for PWR plants, like Callaway, because the weld overlays for BWRs are the same as weld overlays for PWRs.

The PDI program does not fully comply with the existing requirements in Supplement 11. The differences are in flaw location within test specimens and fabricated flaw tolerances. The changes in flaw location permitted using test specimens from the Tri-party Agreement, and the changes in fabricated flaw tolerances provide UT acoustic responses similar to the responses associated with IGSCC. The 20 differences to Appendix VIII, Supplement 11, in this relief request are addressed below:

1. Paragraph 1.1(b) states that limitations to the maximum thickness for which a procedure may be qualified.

The ASME Code states that The specimen set must include at least one specimen with overlay thickness within minus 0.10 inches to plus 0.25 inches of the maximum nominal overlay thickness for which the procedure is applicable. The ASME Code requirement addresses the specimen thickness tolerance for a single specimen set, but is confusing when multiple specimen sets are used. The PDI-proposed alternative states that the specimen set shall include specimens with overlay not thicker than 0.10 inches more than the minimum thickness, nor thinner than 0.25 inches of the maximum nominal overlay thickness for which the examination procedure is applicable. The proposed alternative provides clarification on the application of the tolerance. The tolerance is unchanged for a single specimen set; however, it clarifies the tolerance for multiple specimen sets by providing tolerances for both the minimum and maximum thicknesses. Because the proposed wording eliminates confusion while maintaining the intent of the overlay thickness tolerance, the NRC staff finds that this PDI program revision is acceptable.

2. Paragraph 1.1(d)(1) requires that all base metal flaws be cracks.

The PDI program determined that certain Supplement 11 requirements pertaining to location and size of cracks would be extremely difficult to achieve. For example, flaw implantation requires excavating a volume of base material to allow a pre-cracked coupon to be welded into this area. This process would add weld material to an area of the specimens that typically consists of only base material, and could potentially make UT examination more difficult and not representative of actual field conditions. In an effort to satisfy the requirements, the PDI program developed a process for fabricating flaws that exhibit crack-like reflective characteristics. Instead of all flaws being cracks as required by paragraph 1.1(d)(1), the PDI weld overlay performance demonstrations contain at least 70 percent cracks with the remainder being fabricated flaws exhibiting crack-like reflective characteristics. The fabricated flaws are semi-elliptical with tip widths of less than 0.002 inches. The licensee provided further information describing a revision to the PDI program alternative to clarify when real cracks, as opposed to fabricated flaws, will be used: [f]laws shall be limited to the cases where implantation of cracks produces spurious reflectors that are uncharacteristic of actual flaws.

The NRC has reviewed the PDI flaw fabrication process, compared the reflective characteristics between actual cracks and PDI-fabricated flaws, and found the fabricated flaws acceptable for this application.

3. Paragraph 1.1(e)(1) requires that at least 20 percent but less than 40 percent of the flaws be oriented within +/-20 degrees of the axial direction [of the piping test specimen].

Flaws contained in the original base metal HAZ satisfy this requirement; however, the PDI program excludes axial fabrication flaws in the weld overlay material. The PDI program has concluded that axial flaws in the overlay material are improbable because the overlay filler material is applied in the circumferential direction (parallel to the girth weld); therefore, fabrication anomalies would also be expected to have major dimensions in the circumferential direction. Based upon its engineering judgement, the NRC finds that this approach to implantation of fabrication flaws to be reasonable for meeting the intent of the Supplement 11 requirement and, therefore, the PDI programs application of flaws oriented in the axial direction is acceptable.

4. Paragraph 1.1(e)(1) also requires that the rules of IWA-3300 be used to determine whether closely spaced flaws should be treated as single or multiple flaws.

The PDI program treats each flaw as an individual flaw and not as part of a system of closely spaced flaws and controls the flaws going into a test specimen set such that the flaws are free of interfering reflections from adjacent flaws. In some cases, this permits flaws to be spaced closer than what is allowed for classification as a multiple set of flaws by IWA-3300 and, thus, potentially making the performance demonstration more challenging. Based on this criteria in the PDI program, the NRC staff concludes that the PDI programs application for closely spaced flaws is acceptable.

5. Paragraph 1.1(e)(2) requires that specimens be divided into base metal and overlay grading units.

The PDI program adds clarification with the addition of the word fabrication and ensures flaw identification by ensuring all flaws will not be masked by other flaws with the addition of Flaws shall not interfere with ultrasonic detection or characterization of other flaws. PDIs alternative provides clarification and assurance that the flaws are identified. Therefore, the staff finds the PDI alternative to the Supplement 11 requirements is acceptable.

6. Paragraph 1.1(e)(2)(a)(1) requires that a base grading unit include at least 3 inches of the length of the overlaid weld, and the base grading unit includes the outer 25 percent of the overlaid weld and base metal on both sides.

The PDI program reduced the criteria to 1 inch of the length of the overlaid weld and eliminated from the grading unit the need to include both sides of the weld. The proposed change permits the PDI program to continue using test specimens from the existing weld overlay program, which have flaws on both sides of the welds. These test specimens have been used successfully for testing the proficiency of personnel for over 16 years. The weld overlay qualification is designed to be a near-side (relative to the weld) examination, and it is improbable that a candidate would detect a flaw on the opposite side of the weld due to the sound attenuation and re-direction caused by the weld microstructure. However, the presence of flaws on both sides of the original weld (outside the PDI grading unit) may actually provide a more challenging examination, as candidates must determine the relevancy of these flaws, if detected. Therefore, the NRC staff concludes that the PDI programs use of the 1-inch length of the overlaid weld base grading unit and elimination, from the grading unit, the need to include both sides of the weld, as described in the revised PDI program alternative, is acceptable.

7. Paragraph 1.1(e)(2)(a)(2) requires, when base metal cracking penetrates into the overlay material, that a portion of the base grading unit shall not be used as part of the overlay grading unit.

The NRC staff finds that the PDI program adjusts for the changes in Paragraph 1.1(e)(2)(a)(2) and conservatively states that when base metal flaws penetrate into the overlay material, no portion of it shall be used as part of the overlay fabrication grading unit. The NRC staff also finds that the PDI program also provided clarification by the addition of the term flaws for cracks and the addition of fabrication to overlay grading unit. Based on this, the NRC staff concludes that the PDI program alternative to this paragraph provides clarification and conservatism and, therefore, is acceptable.

8. Paragraph 1.1(e)(2)(a)(3) requires that for unflawed base grading units, at least 1 inch of unflawed overlaid weld and base metal shall exist on either side of the base grading unit.

This requirement is to minimize the number of false identifications of extraneous reflectors.

The PDI program stipulates that unflawed overlaid weld and base metal exists on all sides of the grading unit and that flawed grading units must be free of interfering reflections from adjacent flaws, which addresses the same concerns as the ASME Code. Based on this

requirement, the NRC staff concludes that the PDI programs application of the variable flaw-free area adjacent to the grading unit is acceptable.

9. Paragraph 1.1(e)(2)(b)(1) requires that an overlay grading unit include the overlay material and a base metal-to-overlay interface of at least 6 in2. The overlay grading unit shall be rectangular, with minimum dimensions of 2 inches.

The PDI program reduces the base metal-to-overlay interface to at least 1 inch (instead of a minimum of 2 inches) and eliminates the minimum rectangular dimension. This PDI program criterion is necessary to allow the licensee to use existing examination specimens that were fabricated in order to meet GL 88-01. This criterion may be more challenging than the ASME Code criterion in Supplement 11 because of the variability associated with the shape of the grading unit. Based on its engineering judgement, the NRC staff concludes that the PDI programs application of the grading unit is an acceptable alternative to the Supplement 11 requirement and is, therefore, acceptable.

10. Paragraph 1.1(e)(2)(b)(2) requires that unflawed overlay grading units shall be surrounded by unflawed overlay material and unflawed base metal-to-overlay interface for at least 1 inch around its entire perimeter.

The PDI program redefines the area by noting unflawed overlay fabrication grading units shall be separated by at least 1 inch of unflawed material at both ends and sufficient area on both sides to preclude interfering reflections from adjacent flaws. The NRC staff determined that the relaxation in the required area on the sides of the specimens, while still ensuring no interfering reflections, may provide a more challenging demonstration than required by the ASME Code because of the possibility for having a parallel flaw on the opposite side of the weld. Therefore, based on engineering judgement, the NRC staff concludes that the PDIs application is an acceptable alternative to the Supplement 11 requirements.

11. Paragraph 1.1(e)(2)(b)(3) requirements are retained in the PDI program.

In addition to the Paragraph 1.1(e)(2)(b)(3) requirements being retained in the PDI program, the PDI program requires that initial procedure qualification contain three times the number of flaws required for a personnel qualification. To qualify new values of essential variables, the equivalent of at least one personnel qualification set is required. Based on this, the NRC staff concludes that PDIs additions enhance the ASME Code requirements and are, therefore, acceptable because it provides for a more stringent qualification criteria.

12. Paragraph 1.1(f)(1) requirements are retained in the PDI program, with the clarification change of the term flaws for cracks.

In addition to the Paragraph 1.1(f)(1) requirements being retained in the PDI program, the PDI program includes the requirements that sizing sets shall contain a distribution of flaw dimensions to verify sizing capabilities. The PDI program also requires that initial procedure qualification contain three times the number of flaws required for a personnel qualification. To qualify new values of essential variables, the equivalent of at least one personnel qualification set is required. Based on this, the NRC staff concludes that PDIs additions enhance the ASME

Code requirements and are, therefore, acceptable because it provides a more stringent qualification criteria.

13. Paragraphs 1.1(f)(3) and 1.1(f)(4) requirements are clarified by the PDI program by replacing the term cracking with flaws because of the use of alternative flaw mechanisms.

The NRC staff concludes that this clarification in the PDI program meets the intent of the ASME Code requirements and is acceptable.

14. Paragraph 2.0, Conduct of Performance Demonstration, in Supplement 11 is clarified in PDI by the addition of the sentence, [T]he overlay fabrication flaw test and the base metal flaw test may be performed separately.

With the addition of the sentence given above, the NRC staff concludes that the PDI program did not change the intent of the ASME Code but provided additional clarification. Therefore, this alternative in PDI is acceptable.

15. Paragraph 2.1, Detection Test, in Supplement 11 states, in part, ... the candidate shall be made aware of the types of grading units (base or overlay) that are present for each specimen.

In the PDI program, this sentence is changed to ... the candidate shall be made aware of the types of grading units (base metal or overlay fabrication) that are present for each specimen.

Based on engineering judgement, the NRC staff concludes that the PDI program did not change the intent of the ASME Code, but provided additional clarification, and, therefore, this alternative in the PDI program is acceptable.

16. Paragraph 2.2(d) requirements are clarified by the PDI program by the addition of the terms metal and fabrication.

Based on its review of the change to Supplement 11, the NRC staff determined that the clarifications provide acceptable classification of the terms they are enhancing. Therefore, based on this determination, the NRC staff concludes that the PDI program meets the intent of the ASME Code requirements and is, therefore, acceptable.

17. Paragraph 2.3 states that, for depth sizing tests, 80 percent of the flaws shall be sized at a specific location on the surface of the specimen identified to the candidate. This requires detection and sizing tests to be separate.

The PDI program revised the weld overlay program to allow sizing to be conducted either in conjunction with, or separately from, the flaw detection test. If performed in conjunction with detection, and the detected flaws do not meet the Supplement 11 range criteria, additional specimens will be presented to the candidate with the regions containing flaws identified. Each candidate will be required to determine the maximum depth of flaw in each region. For separate sizing tests, the regions of interest will also be identified and the maximum depth and length of each flaw in the region will similarly be determined. In addition, the PDI program stated that grading units are not applicable to sizing tests, and that each sizing region will be

large enough to contain the target flaw, but small enough that candidates will not attempt to size a different flaw. Because the above clarification provides a basis for implementing sizing tests in a systematic, consistent manner that meets the intent of Supplement 11, the NRC staff concludes that this method is acceptable.

18. Paragraph 3.1 requires that examination procedures, equipment and personnel (as a complete ultrasonic system) are qualified for detection or sizing of flaws, as applicable, when certain criteria are met.

The PDI program allows procedure qualification to be performed separately from personnel and equipment qualification. Historical data indicate that, if ultrasonic detection or sizing procedures are thoroughly tested, personnel and equipment using those procedures have a higher probability of successfully passing a qualification test. In an effort to increase this passing rate, PDI has elected to perform procedure qualifications separately in order to assess and modify essential variables that may affect overall system capabilities. For a procedure to be qualified, the PDI program requires three times as many flaws to be detected (or sized) as shown in Supplement 11 for the entire ultrasonic system. The personnel and equipment are still required to meet the Supplement 11 requirement. Therefore, the PDI program criteria exceeds the ASME Code requirements for personnel, procedures, and equipment qualification. Based on this, the NRC staff concludes that the PDI program criteria is acceptable.

19. Paragraph 3.2(a), in Supplement 11 states, ... The length of base metal cracking is measured at the 75% through-base-metal position.

In PDI, this is changed to ... The length of base metal flaws is measured at the 75%

through-base-metal position. Based on its engineering judgement, the NRC staff concludes that the PDI program did not change the intent of the ASME Code, but provided additional clarification, and, therefore, this alternative in the PDI program is acceptable.

20. Paragraph 3.2(b) requires that all extensions of base metal cracking into the overlay material by at least 0.10 inches be reported as being intrusions into the overlay material.

The PDI program omits this criterion because of the difficulty in actually fabricating a flaw with a 0.10-inch minimum extension into the overlay, while still knowing the true state of the flaw dimensions; however, the PDI program requires that cracks be depth-sized to the tolerance of 0.125 inches as specified in the ASME Code. Since the ASME Code tolerance is close to the 0.10-inch value of paragraph 3.2(b) of Supplement 11, any crack extending beyond 0.10 inches into the overlay material would be identified as such from the characterized dimensions. The reporting of an extension in the overlay material is redundant for performance demonstration testing because of the flaw sizing tolerance. Based on this redundancy, the NRC staff concludes that the PDI programs omission of highlighting a crack extending beyond 0.10 inches into the overlay material is acceptable.

3.6.3 Conclusion on Alternatives to Supplement 11 Based on the above evaluation of the alternatives in the PDI program to the requirements in Supplement 11, the NRC staff concludes that the alternatives provide an acceptable level of

quality and safety and, therefore, the PDI program alternatives to Supplement 11 are acceptable.

3.7 CONCLUSION

Based on the evaluations in Sections 3.4 and 3.5 of this SE, the NRC staff concludes that the Code Case N-504-2 and N-638-1 modifications proposed for the preemptive full structural overlay of the welds listed by the licensee in its August 14, 2006, application, as supplemented by its letters dated March 26 and April 5, 2007, 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 modifications for the remaining service life of the subject welds.

Secondly, based on the evaluation in Section 3.6 of this SE, the NRC staff also concludes that the alternatives to ASME Appendix VIII, Supplement 11, 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 alternatives for the remainder of the third 10-year ISI interval at Callaway.

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.

3.8 REGULATORY COMMITMENTS In Attachment 2 to its letter dated March 26, 2007, the licensee stated that it would (1) submit to NRC a summary report of the UT results of the structural welds overlay performed in its spring 2007 refueling outage and (2) complete the analyses required under Code Case N-504-2, paragraphs (g)(2) and (g)(3), prior to placing the subject welds into service. This report was submitted by letter dated May 4, 2007 (ULNRC-05413, ADAMS Accession No. ML071300382),

and the licensee informed the NRC staff that it had completed this evaluation required by the code case in the spring 2007 refueling outage when the weld overlays were performed prior to plant startup and putting the subject welds into service.

Principal Contributor: Timothy K. Steingass Jack N. Donohew Date: July 10, 2007

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