ML063110322

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Request for Relief (RR ISI-3-18) from the Requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code - Third 10-Year ISI Interval
ML063110322
Person / Time
Site: San Onofre Southern California Edison icon.png
Issue date: 12/14/2006
From: Terao D
NRC/NRR/ADRO/DORL/LPLIV
To: Rosenblum R
Southern California Edison Co
Kalynanam N, NRR/DORL/LP4, 415-1480
References
TAC MD0191
Download: ML063110322 (23)


Text

December 14, 2006 Mr. Richard M. Rosenblum Senior Vice President and Chief Nuclear Officer Southern California Edison Company San Onofre Nuclear Generating Station P.O. Box 128 San Clemente, CA 92674-0128

SUBJECT:

SAN ONOFRE NUCLEAR GENERATING STATION, UNIT 2 - RE: REQUEST FOR RELIEF FROM THE REQUIREMENTS OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS BOILER AND PRESSURE VESSEL CODE (TAC NO. MD0191)

Dear Mr. Rosenblum:

By letter dated February 22, 2006, as supplemented by letters dated March 17 and May 10, 2006, Southern California Edison (SCE, the licensee) submitted a request for the use of alternatives to certain American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, requirements at San Onofre Nuclear Generating Station, Unit 2 (SONGS 2). Specifically, Relief Request (RR) ISI-3-18 requests approval to use alternatives to the requirements of the ASME Code, Section Xl, 1995 Edition through 1996 Addenda, IWA-4000, for repair/replacement activities related to the performance of structural weld-overlay repairs at SONGS 2 for the third 10-year inservice inspection (ISI) interval.

The U.S. Nuclear Regulatory Commission (NRC) staff authorizes the alternatives proposed by SCE in accordance with paragraph 50.55a(a)(3)(i) of Title 10 of the Code of Federal Regulations (10 CFR), which states that the proposed alternatives may be used when authorized by the Director of the Office of Nuclear Reactor Regulation if the applicant demonstrates that the proposed alternatives would provide an acceptable level of quality and safety. Therefore, RR ISI-3-18 is authorized for the remaining third 10-year ISI interval for SONGS 2, which ends on August 17, 2013. Due to the immediate need of this relief request, verbal authorization for the use of this relief request was granted on March 23, 2006, for SONGS 2.

R. Rosenblum The NRC staff is providing the safety evaluation (SE) to you at this time, for review, to assure that any information that Westinghouse Electric Company claims to be proprietary would not be inadvertently released to the general public. The NRC staff will delay placing the SE in the public document room for a period of 10 working days from the date of this letter to provide you with the opportunity to comment on the proprietary aspects. If you believe that any information in the enclosure is proprietary, please identify such information line-by-line and define the basis for such a determination pursuant to the criteria of 10 CFR 2.390. After 10 working days, the SE will be made publicly available. The NRC staffs conclusions concerning the proprietary nature of your February 22 and March 17, 2006, submittals, are contained in the letters to Mr. P.C. Riccardella, Structural Integrity Associates, Inc., dated March 13 and April 13, 2006.

The staff's SE is enclosed.

Sincerely,

/RA/

David Terao, Branch Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-361

Enclosure:

Safety Evaluation cc w/encl: See next page

ML063110322 *Editorial changes made in Staff provided SE OFFICE NRR/LPL4/PM NRR/LPL4/LA DCI/CFEB* OGC -NLO Subj to edits NRR/LPL4/BC NAME NKalyanam LFeizollahi KGruss TCampbell DTerao DATE 12/11/06 12/13/06 11/3/06 12/13/06 12/14/06 San Onofre Nuclear Generating Station Units 2 and 3 cc:

Mr. Daniel P. Breig Director, Radiologic Health Branch Southern California Edison Company State Department of Health Services San Onofre Nuclear Generating Station P.O. Box 997414, MS 7610 P.O. Box 128 Sacramento, CA 95899-7414 San Clemente, CA 92674-0128 Resident Inspector/San Onofre NPS Mr. Douglas K. Porter, Esquire c/o U.S. Nuclear Regulatory Commission Southern California Edison Company Post Office Box 4329 2244 Walnut Grove Avenue San Clemente, CA 92674 Rosemead, CA 91770 Mayor Mr. David Spath, Chief City of San Clemente Division of Drinking Water and 100 Avenida Presidio Environmental Management San Clemente, CA 92672 P.O. Box 942732 Sacramento, CA 94234-7320 Mr. James T. Reilly Southern California Edison Company Chairman, Board of Supervisors San Onofre Nuclear Generating Station County of San Diego P.O. Box 128 1600 Pacific Highway, Room 335 San Clemente, CA 92674-0128 San Diego, CA 92101 Mr. James D. Boyd, Commissioner Mark L. Parsons California Energy Commission Deputy City Attorney 1516 Ninth Street (MS 31)

City of Riverside Sacramento, CA 95814 3900 Main Street Riverside, CA 92522 Mr. Ray Waldo, Vice President Southern California Edison Company Mr. Gary L. Nolff San Onofre Nuclear Generating Station Assistant Director - Resources P.O. Box 128 City of Riverside San Clemente, CA 92764-0128 3900 Main Street Riverside, CA 92522 Mr. Brian Katz Southern California Edison Company Regional Administrator, Region IV San Onofre Nuclear Generating Station U.S. Nuclear Regulatory Commission P.O. Box 128 611 Ryan Plaza Drive, Suite 400 San Clemente, CA 92764-0128 Arlington, TX 76011-8064 Mr. Steve Hsu Mr. Michael R. Olson Department of Health Services San Diego Gas & Electric Company Radiologic Health Branch 8315 Century Park Ct. CP21G MS 7610, P.O. Box 997414 San Diego, CA 92123-1548 Sacramento, CA 95899 March 2006

San Onofre Nuclear Generating Station Units 2 and 3 cc:

Mr. A. Edward Scherer Southern California Edison Company San Onofre Nuclear Generating Station P.O. Box 128 San Clemente, CA 92674-0128 March 2006

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION WELD OVERLAY REPAIR OF PRESSURIZER SAFETY AND SPRAY NOZZLES THIRD 10-YEAR INSERVICE INSPECTION INTERVAL RELIEF REQUEST ISI-3-18 SAN ONOFRE NUCLEAR GENERATING STATION, UNIT 2 SOUTHERN CALIFORNIA EDISON DOCKET NUMBER 50-361

1.0 INTRODUCTION

By letter dated February 22, 2006 (available in the Agencywide Documents Access and Management System (ADAMS) Accession Number ML060550423), Southern California Edison (the licensee) submitted for U.S. Nuclear Regulatory Commission (NRC) staff approval alternatives to the requirements of the American Society of Mechanical Engineers (ASME)

Code,Section XI, 1995 Edition through 1996 Addenda, for repair/replacement activities related to structural weld-overlay repairs of pressurizer safety and spray nozzles at San Onofre Nuclear Generating Station, Unit 2 (SONGS 2). Specifically, the licensee requested modifications to selected criteria in Code Case N-504-2, Alternative Rules for Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping Section XI, Division 1, Code Case N-638-1, Similar and Dissimilar Metal Welding Using Ambient Temperature Machines GTAW [Gas Tungsten Arc Welding] Temper Bead Technique Section XI, Division 1, and alternatives to Appendix VIII, Supplement 11 of the ASME Code,Section XI. The weld-overlay repairs are described in Relief Request (RR) ISI-3-18. The request is applicable for the remainder of the third 10-year inservice inspection (ISI) interval which ends on August 17, 2013.

On March 7 and 14, 2006, the NRC staff requested that the licensee provide additional information. By letter dated March 17, 2006 (ADAMS Accession Number ML060800401, Non-Publicly Available), the licensee responded to the staffs requests for additional information. By letter dated May 10, 2006 (ADAMS Accession Number ML061350412), the licensee submitted a summary report of the weld-overlay design and analysis which it had committed to provide to the NRC in the February 22, 2006, letter.

During the Cycle 14 refueling outage in April 2006, the licensee performed ultrasonic testing (UT) examinations of pressurizer nozzles at SONGS 2 in accordance with the following guidance and programs: SONGS Risk-Informed Inservice Inspection (RI-ISI) program, SONGS response to NRC Bulletin 2004-01, Material Reliability Program, Primary System Piping Butt Weld Inspection and Evaluation Guideline (MRP-139), and ASME Section XI Code. These examinations included four high-safety significant (HSS) pressurizer nozzle-to-safe-end-welds.

These welds are ISI Designation Numbers 02-005-027, 02-005-028, 02-005-029, and 02-005-030, which are three safety-valve line nozzles and the pressurizer spray line nozzle, respectively.

The licensee detected axial indications in welds 02-005-027 and 02-005-028 and concluded that the indications were not caused by primary water stress-corrosion cracking (PWSCC).

Nevertheless, the licensee has decided to perform a structural weld overlay on all four welds to eliminate dependence on the Alloy 82/182 welds as a pressure-boundary weld and to mitigate any potential PWSCC in the future.

2.0 REGULATORY EVALUATION

The ISI of the ASME Code Class 1, Class 2, and Class 3 components is to be performed in accordance with the ASME Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, and applicable edition and addenda as required by paragraph 50.55a(g) of Title 10 of the Code of Federal Regulations (10 CFR 50.55a(g)), except where specific relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). Paragraph 10 CFR 50.55a(g)(6)(i) states that ...[t]he Commission will evaluate determinations... that

[ASME] code requirements are impractical. The Commission may grant such relief and may impose such alternative requirements as it determines is authorized by law and will not endanger life or property or the common defense and security, and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility...

Pursuant to paragraph 50.55a(a)(3), alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if the applicant 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.

Pursuant to paragraph 50.55a(g)(4) of 10 CFR, 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, to the extent practical within the limitations of design, geometry, and materials of construction of the components. Paragraph 50.55a(g)(4) of 10 CFR requires that inservice examination of components and system pressure tests conducted during the first 10-year inspection interval and subsequent inspection intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in paragraph 50.55a(b),

12 months prior to the start of the 10-year inspection interval.

The ISI code of record for the third 10-year interval at SONGS 2 is the 1995 Edition through 1996 Addenda of the ASME Code, Section Xl.

3.0 RELIEF REQUEST ISI-3-18 3.1 Components for which Relief is Requested

1. Pressurizer S21201ME087 safety nozzle-to-safe-end HSS dissimilar metal weld (ISI Designation Number 02-005-027) with Alloy 82/182 weld material. This weld contains five axial flaw indications that were confirmed by supplemental eddy current testing (ET) examination to not be surface connecting.
2. Pressurizer S21201ME087 safety nozzle-to-safe-end HSS dissimilar metal weld (ISI Designation Number 02-005-028) with Alloy 82/182 weld material. This weld contains one axial flaw indication that was confirmed by supplemental ET and visual examination to not be surface connecting.
3. Pressurizer S21201ME087 safety nozzle-to-safe-end HSS dissimilar metal weld (ISI Designation Number 02-005-029) with Alloy 82/182 weld material. This weld contains no reportable indications.
4. Pressurizer S21201ME087 spray nozzle-to-safe-end HSS dissimilar metal weld (ISI Designation Number 02-005-030) with Alloy 82/182 weld material. This weld contains no reportable indications.

The size of the weld-overlay repair on each of the four welds is limited to cover only the designated weld. The adjacent welds were UT examined per the RI-ISI program, with no reportable indications.

ASME Code Class: These welds are all ASME Code Class 1 welds located within the reactor coolant pressure boundary and subject to the steam space environment of the pressurizer.

System: Reactor Coolant System ASME Code Category: Examination Category B-F, Risk-Informed Piping Examinations ASME Code Item No. B5.40: Welds subject to PWSCC (ISI Designation Numbers 02-005-027, 02-005-028, 02-005-029, and 02-005-030), and Welds subject to Thermal Fatigue (ISI Designation Numbers 02-005-027, 02-005-028, 02-005-029, and 02-005-030) 3.2 Applicable ASME Code Edition and Addenda The licensee stated that the applicable ASME Code edition and addenda for RR ISI-3-18 are as follows: 1995 Edition through the 1996 Addenda of the ASME Code Section XI, IWA-4610(a);

1995 Edition with the 1996 Addenda, of the ASME Code,Section XI, Appendix VIII, Supplement 11; Modification to the NRC-approved Code Case N-504-2 with the 2005 Addenda, Nonmandatory Appendix Q; and Code Case N-638-1.

3.3 Licensees Proposed Alternative The licensee proposed a structural weld-overlay to repair four dissimilar metal welds between the nozzles and safe ends for the pressurizer spray and safety valve lines. The material of the above four nozzles is ferritic steel (P3). The pipe safe ends are austenitic stainless steel (P8).

The spray nozzle material is SA-508, Class 2, and the safe-end material is SA-182F, Type 316.

The safety nozzle material is SA-508, Class 2, and the safe-end material is SA-351, CF8M.

The existing weld filler material is Alloy 82/182 (F43 equivalent to P43). The overlay will be designed as a structural weld overlay in accordance with Code Case N-504-2 and Nonmandatory Appendix Q of the ASME Code,Section XI. The temper bead welding technique will be implemented in accordance with Code Case N-638-1 for that portion of the overlay applied over the ferritic base material for which the Construction Code requires post-weld heat treatment. Temperature monitoring requirements contained within Code Case N-638-1 will be performed using contact pyrometers in lieu of thermocouples as required by IWA-4610(a) of the ASME Code,Section XI, 1995 Edition through 1996 Addenda.

The licensee stated that the structural weld-overlay is sized to satisfy the requirements of the ASME Code,Section III, without crediting the existing pipe. The structural weld-overlay will completely cover the existing Alloy 82/182 weld metal and will extend onto the ferritic and austenitic stainless steel material on each end of the weld. The thickness of the overlay is determined by the requirement of the ASME Code,Section XI, that no flaw of depth greater than 75 percent through-wall is acceptable, along with the consideration of applied loading.

The length of the structural weld-overlay must be sufficient for inspection of an area that is 1/2 inch beyond the required repair length and the outer 25 percent of the original wall thickness. The length of the structural weld-overlay was extended and blended into the low-alloy steel nozzle outer diameter taper to permit UT inspection of the weld and to minimize stress concentration on the nozzle outer diameter. Since the outside diameter of the nozzle is larger than that of the safe end, the structural weld-overlay thickness on the safe end is increased to allow a smooth transition surface for UT inspection. Therefore, the final structural weld overlay length and thickness after taking into consideration the UT inspection requirements will exceed the length required for a structural weld-overlay repair in accordance with the Code Case N-504-2 and Section XI, Appendix Q.

The licensee stated further that the structural weld-overlay repair of a piping weld with Alloy 82/182 weld material will be performed as a repair/replacement activity in accordance with IWA-4000 of the 1995 Edition, through 1996 Addenda, of ASME Code,Section XI, with the exception of the requirements in IWA-4610(a). The UT examination of the completed structural weld-overlay will be accomplished in accordance with Supplement 11 of Appendix VIII to the ASME Code,Section XI, 1995 Edition with the 1996 Addenda with the alternatives used to comply with the Performance Demonstration Initiative (PDI) program. The temper bead weld technique requirements in accordance with Code Case N-638-1 will be applied to the ferritic nozzle base material with the modifications.

3.4 Duration of Proposed Alternative The licensee stated that RR ISI-3-18 is applicable for the remainder of the current (third) 10-year ISI interval that started on August 18, 2003, and will end on August 17, 2013. Once these structural weld-overlays are installed, they will remain in place for the design life of the

repair, which is defined by the evaluation required in paragraph (g) of Code Case N-504-2 and corresponding requirements in Nonmandatory Appendix Q. The structural weld-overlays are also subject to the satisfactory examination requirements of Article Q-4000 for ISI. Those requirements include adding any installed structural weld-overlay repairs into the SONGS 2 ISI plan per Subarticle Q-4300 for at least one inservice examination to be completed within the next two refueling cycles.

3.5 Staff Evaluation As discussed above, the licensee proposed to repair three safety valve nozzles and one pressurizer spray valve nozzle. All four nozzles are made of low-alloy steel (SA-508) material.

The safe-end material for the spray line is SA-182F 316 stainless steel forging. The safe-end material for the three safety valve lines is SA-351 CF8M cast stainless steel (CSST). The weld material between the four nozzles and safe ends is Alloy 82/182. The licensee found flaws in two Alloy 82/182 butt welds (weld numbers 02-005-027 and 02-005-028) in the pressurizer safety-valve piping. The flaws were oriented in the axial direction, planar in shape, and within the inner one-third wall thickness of the weldment. This weld material has a history of developing PWSCC. However, the flaws could only be interrogated from the ferritic (nozzle) side of the weld. The inspection of dissimilar metal welds (DMWs) must be examined from both sides. UT examination from the CSST side of the DMW was not possible because the industry has been unable to qualify personnel and procedures for UT examinations of CSST piping.

To assist with the disposition of the flaws, the licensee performed ET examinations on the inside surface of the nozzle-to-safe-end weld. The ET did not detect any surface-breaking flaws, which would suggest that the flaws may not be PWSCC but a by-product of the weld fabrication process. Fabrication flaws are less likely to propagate than flaws generated during plant operations, such as PWSCC. Examination of construction radiographs for evidence of existing flaws were inconclusive. The licensee elected to conservatively disposition the flaws as PWSCC.

The licensee considered the options of redesigning and replacing the affected welds with a configuration and material that is inspectable using UT techniques or of applying a full structural weld-overlay in a configuration that permits access for UT examinations. Small fabrication flaws are normally innocuous and stress-corrosion cracks are normally repaired with weld overlays. The licensee selected full structural weld-overlays as the method of repair.

The proposed weld-overlay repair will be designed, installed, and inspected in accordance with Code Cases N-504-2 and N-638-1 and Appendix VIII, Supplement 11, with certain modifications and alternatives. The staff evaluated the modifications to Code Cases N-504-2 and N-638-1, and alternatives to Appendix VIII, Supplement 11, as follows.

3.5.1 Modifications To Code Case N-504-2 Code Case N-504-2 states that defects in austenitic stainless steel piping may be reduced to a flaw of acceptable size by deposition of weld reinforcement (weld overlay) on the outside surface of the original weld. The licensee proposed to use the methodology under N-504-2 to install a full structural weld-overlay on ferritic base material (P3) and nickel-alloy base material (F43/P43), in addition to austenitic stainless steel (P8) base material. Industry operational

experience has shown that PWSCC cracks in Alloy 82/182 will blunt at the interface with stainless steel base metal, ferritic base metal, or Alloy 52/52M weld metal. SONGS 2 plans to apply a 360-degree structural weld-overlay to minimize growth in any PWSCC crack and maintain weld integrity. The weld-overlay will induce compressive stress in the original weld, thus impeding growth of any exisitng cracks. Furthermore, the overlay will be sized to meet all structural requirements independent of the existing weld. The staff finds that the application of Code Case N-504-2 weld repair to ferritic base material (P3) and nickel-alloy weld material (F43/P43) is acceptable because applying the weld-overlay to ferritic and nickel-alloy base metal would be as effective as applying the weld-overlay to austenitic stainless steel base metal.

Code Case N-504-2(b) requires that reinforcement weld metal be low-carbon (0.035 percent maximum) austenitic stainless steel applied 360 degrees around the circumference of the pipe, and that it be deposited in accordance with a qualified welding procedure specification identified in the owners Repair Program. The licensee proposed to use a nickel-based alloy for the reinforcement filler metal in lieu of austenitic stainless steel filler material.

The licensee explained that the weld metal that will be used is either ERNiCrFe-7A (Alloy 52M, UNS N06054) or ERNiCrFe-7 (Alloy 52 UNS N06052). This weld metal is assigned the designation F43 by Code Case 2142-2 of the ASME Code,Section III. The requirements of ASME Code, Section Ill, NB-2400, will be applied to all filler material. The chromium content of Alloy 52M is 28 percent to 31.5 percent, which is identical to that of Alloy 52 and imparts excellent corrosion resistance. The main difference between Alloy 52 and Alloy 52M is a higher niobium content (0.5 percent to 1 percent). Alloy 52/52M improves the weldability of the material and pins the grain boundaries thus preventing separation between the grains and hot tearing during weld-puddle solidification. These filler materials were selected for their improved resistance to PWSCC. The existing Alloy 82/182 weld and the Alloy 52/52M overlay are nickel based and have ductile properties and toughness similar to austenitic stainless steel piping welds at pressurized-water reactor operating temperature. These filler materials are suitable for welding over the Alloy 82/182 weld of the ferritic nozzle or pipe and the austenitic stainless steel pipe or safe ends.

By letters dated March 7 and 14, 2006, the staff asked the licensee to (1) discuss any adverse impact of the Alloy 52M weld-overlay on cast austenitic stainless steel (the safe end) and low-alloy carbon steel (the pressurizer nozzle) in terms of the microstructure interactions between the base metal and Alloy 52M weld metal, and (2) provide any crack-growth rate data of Alloy 52M. If not available, the staff asked the licensee to discuss whether the crack-growth rate of Alloy 52M is similar to that of Alloy 52.

By letter dated March 17, 2006, the licensee stated that the weld-overlay material is deposited using a welding process and as such a heat-affected zone (HAZ) will necessarily be produced in the material immediately below the weld deposit. Because a portion of the HAZ of the low-alloy steel will be heated above the critical transformation temperature, brittle-transformation products will be generated on cooling that need to be tempered to restore the fracture toughness of the low-alloy steel material. This restoration is accomplished through the use of the temper bead welding technique and verified by welding-procedure qualification testing. There is no evidence to suggest that this material would be any more vulnerable to PWSCC than material outside the HAZ. The licensee stated further that there is no reason to

expect any detrimental micro-structural effects of the weldment on the underlying cast austenitic stainless steel (the safe end). The ASME Code permits welding of nickel-based alloys on cast austenitic stainless steel, as would occur in this overlay, with no requirement for post-weld heat treatment.

As previously stated, the licensee indicated that Alloy 52M is a filler material having an inherently high resistance to PWSCC. There is a well-established correlation between PWSCC propensity in nickel-based alloys and the chromium content of the alloy; the higher the chromium content of the alloy, the greater its resistance is to PWSCC (References 1 and 2).

An evaluation of field and laboratory data was performed in Reference 3, which established a significant factor of improvement between the PWSCC resistance of the reference nickel-based Alloy 600 and its weld metals Alloys 82 and 182 (which have experienced PWSCC in the field) and the higher chromium replacement nickel-based Alloy 690 and its weld metals Alloys 52 and 152. Although PWSCC crack-growth data are not currently available for Alloy 52M, it is strongly expected that it will perform in a manner similar to Alloy 52, and will thus exhibit a similar improvement in PWSCC resistance with respect to the more susceptible Alloy 600 and its weld metals Alloys 82 and 182.

On the basis of the above referenced studies, and noting the properties of Alloys 52/52M, the staff finds that Alloy 52 or 52M may be used in lieu of austenitic stainless steel filler material.

Code Case N-504-2(e) requires that the weld reinforcement consist of a minimum of two weld layers having as-deposited delta ferrite content of at least 7.5 FN [ferrite number]. The first layer of weld metal with delta ferrite content of at least 7.5 FN shall constitute the first layer of the weld reinforcement design thickness. Alternatively, first layers of at least 5 FN may be acceptable based on a metallurgical evaluation of the weld material. The licensee proposed that delta ferrite measurements will not be performed for weld-overlay repairs made of Alloy 52/52M weld metal because welds of Alloy 52/52M are 100 percent austenitic and contain no delta ferrite due to the high-nickel composition (approximately 60 percent nickel). The staff agrees with the licensees conclusion that the delta ferrite content requirement in Code Case N-504-2 does not apply to the proposed weld overlay design because the weld metal is a nickel-based alloy which contains no delta ferrite.

3.5.2 Modifications To Code Case N-638-1 Paragraph 4.0(b) of Code Case N-638-1 requires that the final weld surface and a band around the area defined in paragraph 1.0(d) shall be examined using surface and ultrasonic methods when the completed weld has been at ambient temperature for at least 48 hours2 days <br />0.286 weeks <br />0.0658 months <br />. The UT examination shall be in accordance with Appendix I to the 1989 Edition with the 1989 Addenda and later Editions and Addenda of the ASME Code. Paragraph 1.0(d) of Code Case N-638-1 requires that prior to welding, the area to be welded and a band around the area of at least 1.5 times the component thickness or 5 inches, whichever is less, shall be at least 50 degrees Fahrenheit.

The licensees proposed modification states that in lieu of the required base material ultrasonic examination, only the required liquid penetrant examination of the base material will be performed. The ultrasonic examination of the weld overlay will still be performed in accordance with N-504-2 and Appendix Q to the ASME Code,Section XI. The licensee stated that for the

application of the weld-overlay repair addressed in this request, it is not possible to perform a meaningful UT examination of the required band of base material because of the existing nozzle configuration. 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. However, for this type of repair, any major base-material cracking would take place in the HAZ directly below the weld overlay or in the underlying lnconel 82/182 weld deposit and not in the required band of material out beyond the overlay. Therefore, the licensee assumed that if this cracking were to occur it would be identified by the UT examination of the weld-overlay and that not performing the required base material UT examination should be considered acceptable.

The staff asked the licensee to explain why its repair design does not require UT examination of the base metal after the overlay is applied per paragraph 4.0(b) of Code Case N-638-1. In the March 17, 2006, letter, the licensee responded that Code Case N-638-1 addresses the use of the temper bead welding technique. In the case of weld overlays applied at SONGS 2, this technique was used on the P3 ferritic nozzle base material adjacent to the Inconel 82/182 weld.

This entire area was then overlaid with Alloy 52M weld material and is now part of the weld-overlay examination volume and will be examined with the PDI-qualified UT procedures.

The purpose of these examinations is to assure that no hydrogen-delayed cracking is present, which may be caused by the temper bead welding process. In the unlikely event this type of cracking does occur, it would be initiated on the surface on which the welding was performed which, in this case, is the outside surface. The most appropriate technique to detect this type of cracking is a surface examination technique. The licensee will perform a surface examination of the weld-overlay and the adjacent base material on the nozzle side of the weld adjacent to where the temper bead welding was performed, and on the safe-end base material side of the weld even though this area was not exposed to the temper bead welding technique.

The licensee stated that for UT scanning on the nozzle side, the pressurizer spray and safety nozzles have limited access, due to the weld-overlay and transition slope required by Code Case N-504-2 and Appendix Q. The susceptible area will be examined during the weld-overlay examination and will be supplemented with the additional surface examination of the adjacent base material.

The licensee stated that the temper bead welding process will only be applied on the nozzle side of the welds, thus there is no reason to believe that there is a possibility of hydrogen delay cracking on the safe-end side of the weld because hydrogen-delayed cracking is unique to ferritic steel material (P3). The licensee will, therefore, perform a surface examination of this area.

The licensee concluded that the nozzle side of the weld, which contains ferritic steel (P-3) material is subject to Code Case N-638-1. The safe-end side material is austenitic stainless steel (P-8) material and does not require post-weld-heat treatment. Therefore, paragraph 4(b) of Code Case N-638-1 is not applicable to the safe-end side.

Based on the licensees explanation, the staff finds that the proposed modification to paragraph 4.0(b) of Code Case N-638-1 is acceptable.

Paragraph 4.0(c) of Code Case N-638-1 requires temperature monitoring by welded thermocouples per IWA-4610(a) of the ASME Code,Section XI. The licensee proposed to

measure preheat and interpass temperatures for the weld pad using a contact pyrometer.

Interpass temperature will be monitored for the first three layers at each repair location. On the first repair location, the interpass temperature measurements will be taken every three to five passes. After the first three layers, interpass temperature measurements will be taken every six to ten passes. The heat input from layers applied after the third layer will not have a metallurgical affect on the low-alloy steel HAZ. The licensee stated that due to the location of the repair and area radiation dose rate, the placement of welded thermocouples for monitoring weld-interpass temperature is determined to be not beneficial based on dose savings.

Therefore, welded thermocouples are not planned for use to monitor interpass temperature during welding. The staff finds the use of contact pyrometer acceptable because it will provide equivalent temperature monitoring.

3.5.3 Nondestructive Examination 3.5.3.1 Proposed Alternatives 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 methods for qualifying equipment, procedures, and personnel for examinations of weld-overlays in accordance with the UT criteria of Appendix VIII, Supplement 11. Prior to the Supplement 11 program, the Electric Power Research Institute (EPRI) maintained a performance demonstration program for weld-overlay qualification under the Tri-party Agreement (Reference 4). Instead of having two programs with similar objectives, the NRC staff recognized the PDI program for weld-overlay qualifications as an acceptable alternative to the Tri-party Agreement (Reference 5).

The PDI program does not fully comport with the existing requirements of Supplement 11.

PDI presented the differences at public meetings in which the NRC participated (References 6 and 7). 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 intergranular stress-corrosion cracking.

The licensee proposed using the PDI program in lieu of Supplement 11 of Appendix VIII to the ASME Code,Section XI. The PDI requirements that deviate from Supplement 11 are considered as alternatives and evaluated below.

Paragraph 1.1(b) of Supplement 11 limits the maximum thickness for which a procedure may be qualified. The Code states that [t]he specimen set must include at least one specimen with overlay thickness within minus 0.10-inch to plus 0.25-inch of the maximum nominal overlay thickness for which the procedure is applicable. The Code requirement addresses the specimen-thickness tolerance for a single specimen in a test set, but is confusing when multiple specimens are part of the set. The PDI proposed alternative provides criteria for determining a weld-overlay thickness range for procedure qualification. The thickness criteria are that the specimen set shall include specimens with overlays not thicker than 0.10-inch more than the minimum thickness, nor thinner than 0.25-inch 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 specimens in a set that are being used to demonstrate an overlay-thickness range. The proposed wording eliminates confusion while maintaining the intent of the overlay-thickness tolerance. Therefore, the staff finds this PDI Program alternative acceptable.

Paragraph 1.1(d)(1) requires that all base-metal flaws be cracks. PDI determined that certain Supplement 11 requirements pertaining to location and size of cracks in test specimens 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, PDI 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 PDI alternative also states that [t]he use of Alternative flaws shall be limited to when the implantation of cracks produces spurious reflectors that are uncharacteristic of actual flaws.

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

Paragraph 1.1(e)(1) requires that at least 20 percent but less than 40 percent of the flaws shall be oriented within +/-20 degrees of the pipe axial direction. Flaws contained in the original base metal HAZ beneath the weld-overlay satisfy this requirement. However, PDI excludes axial fabrication flaws in the weld-overlay material. PDI 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. The NRC finds this approach to implantation of fabrication flaws to be reasonable. Therefore, PDIs application of flaws oriented in the axial direction is acceptable.

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. PDI treats each flaw as an individual flaw and not as part of a system of closely-spaced flaws. PDI controls the flaws going into a test specimen set so that the flaws are free of interfering reflections from adjacent flaws.

In some cases, this permits flaws to be spaced closer than is allowed for classification as a multiple set by IWA-3300, thus potentially making the performance demonstration more challenging. Hence, PDIs application for closely-spaced flaws is acceptable.

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 to denote the overlay process 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 and associated with the appropriate material. Therefore, the staff finds the PDI alternative to the Supplement 11 requirements is acceptable.

Paragraph 1.1(e)(2)(a)(1) states: [A] base grading unit shall include at least 3 inches of the length of the overlaid weld. The base grading unit includes the outer 25% 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 that 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 redirection 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. By reducing the flaw-free distance from 3 inches to 1 inch, the candidate has an increased probability of receiving signals back from a different flaw making the demonstration more challenging than the Code. Therefore, PDIs use of the 1-inch length of the overlaid weld-base grading unit and the elimination from the grading unit the need to include both sides of the weld, as described in the revised PDI program alternative, is acceptable.

Paragraph 1.1(e)(2)(a)(2) states: [W]hen base metal cracking penetrates into the overlay material, the base grading unit shall include the overlay metal within 1 inch of the crack location.

This portion of the overlay material shall not be used as part of any overlay grading unit. The PDI reworded this requirement and removed the criterion for 1-inch-side-spacing parallel to the weld to permit flaws on both sides of the welds. The staff finds that the PDI program adjusts for the changes in paragraph 1.1(e)(2)(a)(2) and, conservatively stated that when base metal flaws penetrate into the overlay material, the base metal grading unit shall not be used as part of any fabrication grading unit, thus preventing double-counting of a single flaw. The staff finds that the PDI program also provided clarification using the terms flaws (described in paragraph 1.1(d)(1) above) instead of cracks and fabrication instead of overlay grading unit. The staff concludes that the PDI program alternative provides clarification and conservatism and, therefore, is acceptable.

Paragraph 1.1(e)(2)(a)(3) states: [W]hen a base grading unit is designed to be unflawed, at least 1 in. of unflawed overlaid weld and base metal shall exist on either side of the base grading unit. This weld overlay is designed to minimize the number of false identifications of extraneous reflectors. The PDI program stipulates that unflawed overlaid weld and base metal must exist on all sides of the grading unit and that flawed grading units must be free of interfering reflections from adjacent flaws. These requirements address the same concerns as the Code and permit utilization of existing specimens from the Tri-Party Agreement. Hence, PDIs application of the variable flaw-free area adjacent to the grading unit is acceptable.

Paragraph 1.1(e)(2)(b)(1) states: [A]n overlay grading unit shall include the overlay material and the base metal-to-overlay interface of at least 6 square inches. The overlay grading unit shall be rectangular, with minimum dimensions of 2 inches. The PDI program reduces the base metal-to-overlay interface to a minimum of 1 inch (in lieu of a minimum of 2 inches) and eliminates the minimum rectangular dimension. This criterion is necessary to allow the use of existing examination specimens that were fabricated with flaws on both side of the weld which were used for performance testing to meet NRC Generic Letter 88-01 (Tri-party Agreement in

Reference 1). This criterion is more conservative than the Code because of the variability associated with different-shaped grading units. Hence, PDIs application of the grading unit is acceptable.

Paragraph 1.1(e)(2)(b)(2) states: [A]n overlay grading unit designed to be unflawed 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. This permits using existing specimens from the Tri-Party Agreement which has flaws spaced closer than 1 inch. The 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 of closer flaw spacing. Therefore, the staff concludes that the PDIs application is an acceptable alternative to the Supplement 11 requirements.

Paragraph 1.1(e)(2)(b)(3) requirements are retained in the PDI program. The PDI program increases the number of flaws for the initial procedure qualification to the equivalent of three times the number of flaws required for a personal qualification. To qualify new values of essential variables, the equivalent of at least one personal qualification set is required. The staff concludes that PDIs additions enhance the ASME Code requirements and, therefore, are acceptable because they provide for more stringent qualification criteria.

Paragraph 1.1(f)(1) requirements are retained in the PDI program, with the substitution of the term flaws for cracks. In addition, the PDI program includes the requirement 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 personal qualification. To qualify new values of essential variables, the equivalent of at least one personal qualification set is required. The staff concludes that PDIs additions enhance the ASME Code requirements and, therefore, are acceptable because they provide more stringent qualification criteria.

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 the use of alternative flaws would provide representative responses that are not achievable with implanted cracks. The staff concludes that this clarification in the PDI program meets the intent of the ASME Code requirements, and is acceptable.

Paragraph 2.0 requirements are retained in the PDI program alternative. In addition, the PDI program provides clarification that the overlay fabrication flaw test and the base metal flaw test may be performed separately. The ASME Code is nonspecific on this issue. Since flaw specific criteria exist for the overlay fabrication process, separating the base metal test should produce the same results as the combined test. Therefore, the staff concludes that this clarification in the PDI program meets the intent of the ASME Code requirements, and is acceptable.

Paragraph 2.1 and 2.2(d) requirements are clarified by the PDI program by the addition of the terms metal and fabrication. The change provides consistency with the terms normally used

for these applications in the manufacturing sector. The change is editorial in nature. The staff determined that the clarifications provide acceptable classification of the terms. Therefore, the staff concludes that the PDI program meets the intent of the ASME Code requirements, and is acceptable.

Paragraph 2.3 requires 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 conducted separately. PDI revised the weld-overlay program to allow sizing to be conducted either in conjunction with, or separately from, the flaw detection test. If depth sizing is performed in conjunction with detection, the depth sizing is more difficult because the candidate does not have prior knowledge of flaw locations. If additional specimens are needed to complete the depth sizing demonstration, they will be presented to the candidate with the regions containing flaws identified. Each candidate will be required to determine the maximum depth of flaws 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, PDI 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. The above clarification provides a basis for implementing sizing tests in a systematic, consistent manner that meets the intent of Supplement 11. When performed in conjunction with the detection test, the sizing is more conservative because of the absence of prior knowledge of the flaw locations. Therefore, this method is acceptable to the staff.

Paragraph 3.1 requires examination procedures, equipment, and personnel (as a complete ultrasonic system) to be 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 demonstration 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) than required by Supplement 11. 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. The staff concludes that the PDI program criteria is acceptable.

Paragraph 3.2(a) requirements are clarified by the PDI program by replacing the term cracking with flaws because of the use of alternative flaw mechanisms. The staff concludes that this clarification in the PDI program maintains the intent of the ASME Code requirement and is acceptable.

Paragraph 3.2(b) requires that all extensions of base metal cracking into the overlay material by at least 0.10-inch be reported as being intrusions into the overlay material. The PDI program eliminates 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 flaws be depth-sized to the tolerance specified in the ASME Code, which is 0.125 inches. Since the ASME Code tolerance is close to the 0.10-inch

value of paragraph 3.2(b), any flaws extending beyond 0.10-inch into the overlay material would be identified as such from the characterized dimensions. Flaws less than 0.10 inch may not be sized because of the tolerance for depth sizing. The staff determined that reporting of an extension in the overlay material is non-productive because of the flaw-sizing tolerance.

Therefore, the staff concludes that PDIs elimination of highlighting a crack extending beyond 0.10 inch into the overlay material is acceptable.

Based on the above evaluation, the staff has determined that the licensees proposed alternative to use the PDI qualification program for the UT examination of overlay repaired piping welds is acceptable, because it will provide an acceptable level of quality and safety.

3.5.3.2 Inspection of Cast Stainless Steel The UT examinations required by N-504-2 were not achievable for the CSST material used in the fabrication of the components. The UT examination volume consists of the weld-overlay and the upper 25 percent of the base metal beneath the overlay. The UT examination must be performed with qualified Section XI, Appendix VIII, Supplement 11, personnel and procedures.

Supplement 11 qualification requires blind performance demonstrations on representative mock-ups containing representative construction flaws. The licensee performed the required examination of the weld-overlay, ferritic nozzle base material, and weld base material in accordance with Code Case N-504-2, but could not take credit for the CSST safe-end base material because the procedures and personnel have not yet been demonstrated on CSST. In lieu of the Code-required examination of the CSST base material, the licensee performed a best-effort UT examination using the existing qualified Supplement 11 personnel and procedures.

At the time of the repair, the licensee did not have access to representative mock-ups containing representative construction flaws of overlaid CSST piping for blind performance demonstrations. Thus, the licensee could not qualify personnel and procedures. The licensee is working with the industry to obtain the necessary mock-ups, qualified personnel, and procedures. The licensee has committed to subjecting the UT procedures that were used for the best-effort examination of the subject welds to a Supplement 11 performance demonstration containing CSST mock-ups by the end of the next two refueling cycles (about 2010). Because this issue is not resolved at this time, the staff limits the approval of performing a best-effort examination to pressurizer safety-valve-nozzle welds 02-005-027 and 02-005-028 only.

The staff finds that this after-the-fact demonstration is an appropriate approach because (1) the weld-overlay is a full structural overlay that does not take any credit for the original weld, (2) the material used in the weld-overlay is Alloy 52M, which is resistant to PWSCC due to its composition, especially its chromium content, (3) the flaws detected in nozzles 27 and 28 are in the lower one-third of the base material near the inside diameter and well within the favorable compressive stress field induced by the weld-overlay that limits their growth, and (4) the flaws detected in these nozzles were confirmed by eddy current examination to be not surface-connecting.

3.5.4 Issues Related to Relief Request ISI-3-18 In Chapter 8 of the EPRI report in the February 22, 2006, submittal, EPRI discussed the UT examination of the safe end, but not the pressurizer nozzle. The staff asked the licensee to clarify whether the pressurizer nozzle will be examined ultrasonically as part of the weld-overlay repair and whether the ultrasonic technique is qualified to examine the pressurizer nozzle. By letter dated March 17, 2006, the licensee responded that the pressurizer nozzle will be ultrasonically examined with PDI-qualified techniques as part of the weld-overlay repair. These UT examination techniques are fully qualified to examine the nozzle, except for the small portion of base material within the examination volume which is cast austenitic stainless steel.

The staff finds that the pressurizer nozzle will be inspected and, therefore, this issue is resolved.

The staff asked the licensee to address the scenario of the indications in the safety nozzles growing to through-wall, becoming a leakage path, and propagating into the overlay. By letter dated March 17, 2006, the licensee responded that the weld-overlays were designed as full structural overlays, under the assumption that active PWSCC flaws do exist in the nozzles.

Existing flaws, if any, or potential future cracking is mitigated by the favorable residual stress reversal from tensile to compressive in the PWSCC-susceptible inner portion of the original pipe. The overlays are structural reinforcement made with PWSCC resistant material (Alloy 52M) to meet ASME Code,Section XI, margins with no credit for any of the underlying butt weld. In addition, the weld-overlays are examined with qualified UT techniques based on the PDI program as part of examination volume specified in figure Q-4300-1, thus leading to early detection of the unlikely occurrence of flaw propagation.

The staff finds the likelihood of existing safety nozzle indications propagating into the weld-overlay is small and, therfore, this issue is resolved.

In the February 22, 2006, letter, the licensee stated that as a result of the weld-overlay, the resulting stresses in the piping material will be decreased. However, the staff believes that some stresses such as tensile stresses or residual stresses may be increased. Also, stresses may be changed depending on the location of the pipe wall thickness (e.g., the inside diameter region versus the outside diameter region). The staff asked the licensee to discuss the stress distribution along the thickness and length of the pipe/weld wall. By letter dated March 17, 2006, the licensee responded that the weld-overlay will result in a reversal of residual stress at the inside diameter of the overlaid joint from tensile to PWSCC-resistant-compressive stress.

The overlaid weld layer will enhance the joint compatibility with the surrounding metal and, therefore, result in lower thermal gradient stress at the critical section of the nozzle. The primary stress will be reduced due to the added material. The effect of weld-overlay will be considered in the stress report in accordance with ASME Code,Section III, paragraph NB-3200.

In the letter dated March 17, 2006, the licensee provided typical residual stress distributions before and after the application of the weld-overlay computed for the SONGS pressurizer spray nozzle. The plots present axial and hoop residual stresses on the inside surface of the nozzle in the vicinity of the PWSCC-susceptible material. Prior to application of the overlay, the nozzle exhibits high tensile stresses in the susceptible material, attributable to a simulated inside-diameter surface repair during plant construction. Subsequent to the application of the

weld overlay, the stresses are reduced and in fact reversed to a compressive state at operating temperature, overcoming the detrimental effects of the assumed repair. Similar results were obtained for residual stresses in the SONGS safety nozzles.

In its letter dated May 10, 2006, the licensee provided a final stress analysis of the weld-overlay. The licensee revised the stress analysis in accordance with ASME Code,Section III, Paragraph NB-3200 for the overlaid joint and adjacent material of the nozzle on both sides of the joint. The evaluation took into account the new geometry of the weld overlaid joint, and the original design loads as shown in the existing design report. All stress checks required by the ASME Code were considered including primary stress, primary plus secondary, fatigue, and thermal ratchet. Crack growth analyses were also performed, considering the residual stresses, demonstrating that any flaws smaller than the detection capability of the inspection technique would not grow to an unacceptable size during the post-overlay inspection intervals.

The staff finds that the licensee has demonstrated by analysis the acceptability of the residual stresses after the weld-overlay repair.

In the March 17, 2006, letter, the licensee provided additional information on the original welds.

The outside diameter of each of the three safety relief nozzles is approximately 7.957 inches and the average thickness of these welds is approximately 1.40 inches. The spray nozzle is a tapered design, and has a diameter ranging from 6.68 inches on the nozzle side near the weld to 4.47 inches on the safe-end-side of the weld. The thickness of the weld ranges from 1.040 inches on the nozzle-side of the weld to 0.565 inches on the safe-end side. The width (in the axial direction) of the welds on the outside diameter for the pressurizer safety nozzles varies from about 1.5 inches to about 1.75 inches including the butter. The width (in the axial direction) of the welds on the outside diameter for the pressurizer spray nozzle is 1.5 inches including the butter. All four overlay welds are designed to be within the area and thickness limits of Code Case N-638-1.

The staff asked the licensee whether the thickness of the weld-overlay satisfies the required thickness per Code Cases N-504-2 and N-638-1. By letter dated March 17, 2006, the licensee responded that the thickness of the overlay is determined by the ASME Code,Section XI, requirement that no flaw of depth greater than 75 percent through-wall is acceptable, along with the consideration of applied loading. The design process of the weld-overlay basically followed the procedures of IWB-3640, Table IWB-3641-1 (for normal and upset conditions) and Table IWB-3641-2 (for emergency and faulted conditions) for evaluation and acceptance criteria. The sizing calculation is an iterative process, in which the overlay is applied, the stress ratio adjusted based on the new overlaid nozzle-wall thickness, and the allowable flaw size determined for the new primary stress ratio and wall thickness. The process is repeated until the overlay thickness converges to an overlay thickness and allowable flaw size that exactly equals the design flaw assumption (completely through the original pipe wall thickness and 360 degrees). The results indicate that the acceptance criterion for the maximum allowable flaw size of a/t = 0.75 (a is the depth and t is the thickness of the pipe) governed the sizing for both the safety nozzles and spray nozzle, which resulted in an overlay thickness of t original wall /3.

This meets the requirement of Code Case N-504-2 and does not exceed the t/2 limitation of Code Case N-638-1.

The staff finds that the thickness of the weld overlay satisfies Code Cases N-504-2 and N-638-1 and, therefore, is acceptable.

The staff asked the licensee to discuss the inspection schedule for the four weld-overlay repairs during the third 10-year ISI inspection interval and any conflict between the inspections required by Examination Category B-F, and Articles Q-4000 and Q-4300 in Appendix Q to the ASME Code,Section XI. In the March 17, 2006, letter, the licensee responded that as specified in Subarticle Q-4300 Inservice Inspection, it will perform weld-overlay examinations of the volumes specified in Figure Q-4300-1. These welds will be added to the inspection plan and UT examined during the first or second refueling outage following application. Weld-overlay examination volumes that show no indication of crack growth or new cracking will be placed in the population to be examined on a sampling basis. Twenty-five percent of this population will be examined once every 10 years. If the weld-overlay examinations do not meet the acceptance standard as specified in Q-4300(b) and (c), then the inservice examination of the weld overlay will comply with the requirements of the Q-4300(e), Q-4300(f), and Q-4310.

The licensee stated further that the existing welds are classified as RI-ISI, Code Category B-F.

RI-ISI is a living program and requires the program to be updated based on changes in the plant. After the weld-overlay, the licensee will perform qualified UT examinations per the PDI program as specified in Article Q-4200, Preservice Examination, and Q-4300, ISI. The design of the weld configuration has changed after the structural weld-overlay installation. Code Case N-504-2 and Section XI, Appendix Q, examination rules govern the future inservice examination. Therefore, there is no conflict.

The staff finds that the inspection schedule of the four weld-overlay repairs follows the appropriate ASME Code requirement and, therefore, is acceptable.

4.0 CONCLUSION

The staff has determined that (1) the licensees proposed alternative to use the PDI program for weld-overlay qualifications as described in the submittal, in lieu of Supplement 11 to Appendix VIII of Section XI of the ASME Code, and (2) modifications to Code Cases N-504-2 and N-638-1, will provide an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the proposed RR ISI-3-18 is authorized for the remaining third 10-year ISI interval at SONGS 2.

The licensee has not qualified nondestructive examination (NDE) personnel and procedures to the requirements of Supplement 11 for the examination of CSST base material. However, the licensee is working toward completing that goal by approximately 2010. Because this issue is not resolved at this time, the staff limits approval of performing a best-effort examination to pressurizer-safety valve nozzle welds 02-005-027 and 02-005-028 only.

All other requirements of the ASME Code, Sections III and XI, for which relief has not been specifically requested and approved remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

5.0 REFERENCES

1. "Materials Reliability Program: Crack Growth Rates for Evaluating Primary Water Stress Corrosion Cracking of Alloy 82, 182, and 132 Welds (MRP-115)," EPRI, Palo Alto, CA; 2004, 1006696.
2. "Materials Reliability Program (MRP) Crack Growth Rates for Evaluating Primary Water Stress Corrosion Cracking (PWSCC) of Thick-Wall Alloy 600 Materials (MRP-55),"

Revision 1, EPRI, Palo Alto, CA; 2004, 1006695.

3. "Materials Reliability Program: Resistance to Primary Water Stress Corrosion Cracking of Alloys 690, 52 and 152 in Pressurized Water Reactors (MRP-111)," EPRI, Palo Alto, CA; 2004, 1009801.
4. The Tri-Party Agreement is between NRC, EPRI, and the Boiling Water Reactor Owners Group (BWROG), Coordination Plan for NRC/EPRI/BWROG Training and Qualification Activities of NDE Personnel, dated July 3, 1984.
5. US NRC Letter from William H. Bateman to Michael Bratton, "Weld Overlay Performance Demonstration Administered by PDI as an Alternative for Generic Letter 88-01 Recommendations," dated January 15, 2002 (ML020160532).
6. US NRC Memorandum from Donald G. Naujock to Terence Chan, "Summary of Public Meeting Held January 31 - February 2, 2001, with PDI Representatives," dated March 22, 2001 (ML010940402).
7. US NRC Memorandum from Donald G. Naujock to Terence Chan, "Summary of Public Meeting Held June 12 through June 14, 2001, with PDI Representatives," dated November 29, 2001 (ML013330156).

Principal Contributors: J. Tsao D. Naujock Date: December 14, 2006