ML110120540

Relief Request RI-36 for Alternative Weld Overlay Repairs for the Fourth 10-Year Inservice Inspection Interval

ML110120540
Person / Time
Site:	Cooper
Issue date:	02/18/2011
From:	Markley M Plant Licensing Branch IV
To:	O'Grady B Nebraska Public Power District (NPPD)
Wilkins, L E, NRR/DORL/LPL4, 415-1377
References
TAC ME3321
Download: ML110120540 (18)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 February 18, 2011 Mr. Brian J. O'Grady Vice President-Nuclear and CNO Nebraska Public Power District 72676 648A Avenue Brownville, NE 68321

SUBJECT:

COOPER NUCLEAR STATION - RELIEF REQUEST NO. RI-36, REVISION 0, FOR FOURTH 10-YEAR INSERVICE INSPECTION INTERVAL REGARDING WELD OVERLAY REPAIR (TAC NO. ME3321)

Dear Mr. O'Grady:

By letter dated February 5,2010 (Agencywide Documents Access and Management System (ADAMS) Accession No ML100480038), as supplemented by letter dated August 17, 2010 (ADAMS Accession No. ML102350161), Nebraska Public Power District (the licensee),

submitted request for relief No. RI-36, Revision 0, from certain inservice inspection (lSI) requirements of Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code) for Cooper Nuclear Station (CNS). Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) paragraph 50.55a(a}(3}(i}, the licensee requested U.S. Nuclear Regulatory Commission (NRC) approval to perform alternatives to the dissimilar metal weld repair requirements of Section XI for certain nozzle-to-control rod drive end-cap weld joints for the fourth 1O-year inservice inspection (lSI) interval at CNS.

The proposed alternative would implement a weld overlay repair in accordance with ASME Code Cases N-638-1, "Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW [Gas Tungsten Arc Welding] Temper Bead Technique,Section XI, Division 1,""

and N-504-3, "Alternative Rules for Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping,Section XI, Division 1," as modified by the licensee in its submittal letters. Relief Request No. RI-36, Revision 0, is based upon restoring the structural integrity of the RCA-BF-1, 5-inch Control Rod Drive Return Cap-to-Nozzle 9A Weld by applying a full structural weld overlay over the weld joint.

The NRC staff has reviewed the licensee's submittal, as supplemented, and concludes that the proposed alternatives in relief request RI-36 provides an acceptable level of quality and safety.

Therefore, the proposed alternative is authorized in accordance with 10 CFR 50.55a(a}(3}(i} for the fourth 10-year lSI interval, which commenced on March 1, 2006, and ends on January 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.

B. O'Grady -2 The detailed results of the NRC staff review are provided in the enclosed safety evaluation. If you have any questions concerning this matter, please contact Ms. L. Wilkins of my staff at (301) 415-1377 or via e-mail at Lynnea.Wilkins@nrc.gov.

Sincerely, Michael T. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-298

Enclosure:

As stated cc w/encl: Distribution via Listserv

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION FOURTH 10-YEAR INSERVICE INSPECTION INTERVAL REQUEST FOR RELIEF NO. RI-36, REVISION 0 NEBRASKA PUBLIC POWER DISTRICT COOPER NUCLEAR STATION DOCKET NO. 50-298

1.0 INTRODUCTION

By letter dated February 5, 2010 (Agencywide Documents Access and Management System (ADAMS) Accession No ML100480038), as supplemented by letter dated August 17, 2010 (ADAMS Accession No. ML102350161), Nebraska Public Power District (the licensee),

submitted request for relief No. RI-36 for the fourth 10-year inservice inspection (lSI) for Cooper Nuclear Station (CNS). The fourth 1O-year lSI interval at CNS began on March 1, 2006, and ends on January 18, 2014. Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) paragraph 50.55a(a)(3)(i), the licensee requested U.S. Nuclear Regulatory Commission (NRC) approval to use an alternative to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI inspection requirements regarding dissimilar metal welding involving nickel alloys. The proposed alternative would implement a weld overlay repair in accordance with ASME Code Cases N-638, "Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW [Gas Tungsten Arc Welding] Temper Bead Technique,Section XI, Division 1," and N--504-3, "Alternative Rules for Repair of Class 1,2, and 3 Austenitic Stainless Steel Piping,Section XI, Division 1." Relief Request No. RI-36, Revision 0, is based upon restoring the structural integrity of the RCA-BF-1, 5-inch Control Rod Drive Return Cap-to-Nozzle 9A Weld by applying a full structural weld overlay over the weld joint.

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 (lSI) 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.

Enclosure

- 2 Pursuant to 10 CFR 50.55a(a)(3), alternatives to requirements may be authorized by the NRC if the licensee demonstrates that: (i) the proposed alternatives provide an acceptable level of quality and safety, or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. The licensee submitted the subject relief request, pursuant to 10 CFR 50.55a(a)(3)(i), which proposed an alternative to the implementation of the ASME Code,Section XI requirements based on ASME Code Cases N-638-1 and N-504-3, as modified by the licensee, for the deposition of weld overlays for the remaining service life of the components.

3.0 TECHNICAL EVALUATION

3.1 Applicable ASME Code Components Affected (as stated by the licensee)

Code Class: 1 Examination Category: 8-F Item Numbers: 85.10 Component Number: RCA-8F-1, 5 inch Control Rod Drive Return Cap-to Nozzle 9A Weld 3.2 Applicable Code Edition and Addenda (as stated by the licensee)

American Society of Mechanical Engineers (ASME) Code Section XI, 2001 Edition, 2003 Addenda.

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

The licensee requested to use ASME Code,Section XI, Code Cases N-638-1 and N-504-3 with modifications. ASME Code Cases N-638-1 and N-504-3 have been conditionally approved by the NRC in Regulatory Guide (RG) 1.147, Revision 15, "Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1" (ADAMS Accession No. ML072070419). The licensee requested to use ASME Code Cases N-638-1 and N-504-3, as modified by the proposed alternatives identified in Section 3.4 below.

3.4 Reason for Request (as stated by the licensee)

Pursuant to 10 CFR 50.55a, "Codes and Standards," Paragraph (a){3), relief is requested from the requirements of ASME Code Section XI requirements. The request is based upon restoring the structural integrity of the nozzle to control rod drive end cap weld joint by applying a full structural weld overlay over the weld joint using technically sound welding practices and nondestructive examination (NDE), while limiting repair personnel exposure to the maximum extent practical.

Currently, there exist no generically accepted Code approved criteria for a

-3 licensee to apply a full structural weld overlay to dissimilar metal welds involving nickel alloys such as Alloy 600, 82 and 182 at ambient temperature.

The following cited ASME Section XI articles identify the actions that would be required if a repair is performed in accordance with the Code without exception:

IWA-4421 (a) and IWA-4611.1 (a) require removal of the detected flaw. The repair cavity would extend through-wall since outer diameter (00) removal would be required. Internal diameter (10) removal of the indication and subsequent weld repair would be impractical due to the need to drain the vessel to perform the repair, and the resultant radiation levels would present unacceptable exposure burden.

IWA-4610(a) requires that the area to be welded shall be pre-heated to 300"F minimum for GTAW. Since the nozzle will remain full of water, establishing the 300"F minimum pre-heat temperature cannot be achieved.

IWA-4610(a) also requires the use of thermocouples to monitor process temperature. Due to the personnel exposure associated with the installation and removal of the thermocouples, the nozzle configuration, and because the nozzle will be full of water, a contact pyrometer will be used, in lieu of thermocouples, to provide equivalent temperature monitoring capabilities.

IWA-4631 (b) specifies the surface of the completed weld on the ferritic steel shall not exceed 100 square inches. Restoring the structural integrity with the weld overlay of the end cap-nozzle weld may require welding on more than 100 square inches of surface on the low alloy steel base material.

IWA-4633.2(c) specifies the first three layers of the weld shall be deposited with heat inputs within +/-10% of that used in the procedure qualification test.

Subsequent layers shall be deposited using heat input equal to or less than that used for layers beyond the third in the procedure qualification. Code Case N-638-1!1] allows for layers beyond the third to exceed the heat input, provided it is in accordance with the procedure qualification records (PQRs).

IWA-4633.2(c) also specifies that at least one layer of weld reinforcement shall be deposited and then this reinforcement shall be removed to be substantially flush with the surface surrounding the weld. The weld reinforcement will not be removed flush to the surface.

Appendix VIII provides requirements for performance demonstration for ultrasonic examination systems. Supplement 11 provides qualification requirements for full structural overlaid wrought austenitic piping welds.

Appendix VIII, Supplement 11 cannot be implemented as written for ultrasonic examination of structural weld overlay repair.

ASME Code Case N-638-1, "Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique,Section XI, Division 1."

- 4 Code Case N-504-3

• Code Case N-504-3 was prepared specifically to apply a weld overlay to austenitic stainless steel material. An alternative was required to implement the N-504-3 weld overlay methodology due to the specific materials and configuration of the eXisting nickel-based alloy weld and buttering (Alloy 82 and Alloy 182) and Alloy 600 cap.

• Code Case N-504-3, Requirement (b), requires that the weld overlay shall be low carbon (0.035 percent maximum) austenitic stainless steel. An alternative was required since a nickel-based filler (Alloy 52M) has been selected to be used.

• Code Case N-504-3, Requirement (e), requires that the first two layers of the weld overlay shall have a ferrite content of at least 7.5 FN (Ferrite Number). Cooper Nuclear Station (CNS) does not intend to perform these measurements for this type of overlay on the basis that the nickel based alloy filler is a fully austenitic material.

• Code Case N-504-3, Requirement (h), specifies that a system hydrostatic test shall be performed in accordance with ASME Section XI, IWA-5000 if the flaw penetrates the original pressure boundary. In the event a flaw becomes through-wall, leak testing in accordance with IWA-5000 will be performed.

Code Case N-638-1

• Code Case N-638-1, paragraph 1.0(a), specifies that the maximum weld area on the finished low alloy steel surface shall be 100 square inches.

Restoring the structural integrity of the nozzle to end cap weld will require application of the weld overlay on more than 100 square inches of surface on the low alloy steel base material.

• Code Case N-638-1, paragraph 4.0(b), specifies that the final weld surface and the band around the area (to a width of 1.5 times the thickness of the weld (1.5T) or 5 inches, whichever is less) shall be examined using surface and ultrasonic test (UT) 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 shall be in accordance with ASME Section XI, Appendix I. Full UT examination of the 1.5T band will not be performed.

• Code Case N-638-1, paragraph 4.0(c), specifies that the area from which weld-attached thermocouples have been removed shall be ground and examined using a surface examination method. Thermocouples will not be used. Instead, calibrated pyrometers will be utilized to monitor preheat and interpass temperatures.

- 5 3.5 Proposed Alternative and Basis for Use (as stated by the licensee)

The component for which a full structural weld overlay repair may be needed is identified in the following Table 1. The overlay would entirely replace the original pressure boundary of the dissimilar metal welds identified in Table 1.

Table 1 Component Component Material 1 Material 2 Maximum Surface ID Description Area of Weld Overlay (Ferritic side, in 2)

RCA-BF-1 5 inch Control Rod Nozzle: SB-166 260 Drive Return Cap to A508 Class Nozzle N9 Weld 2 The full structural weld overlay will be designed consistent with the requirements of the following:

1. NUREG-0313, Revision 2[2] implemented by Nuclear Regulatory Commission (NRC) Generic Letter 88-01[31.

2. Code Case N-504-3[21, "Alternative Rules for Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping,Section XI, Division 1." Regulatory Guide 1.147, Revision 15 requires the following condition to be met when using Code Case N-504-3:

'The provisions of Section XI, Non-Mandatory Appendix Q, "Weld Overlay Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping Weldments tt, must also be met. It CNS will meet the associated requirements contained in Non-mandatory Appendix Q, 2007 Edition[41.

2 NUREG-0313 Revision 2, Date Published: January 1988 ["Technical Report on Material Selection and Processing Guidelines for BWR Coolant Pressure Boundary Piping," ADAMS Accession No. ML031470422].

3 NRC Generic Letter 88-01, "NRC Position on IGSCC [Intergranular Stress Corrosion Cracking] in BWR [Boiling-Water Reactor] Austenitic Stainless Steel Piping," January 25, 1988, and Supplement 1, February 4, 1992 [ADAMS Accession No. ML031130463].

4 ASME Section XI, Nonmandatory Appendix Q, "Weld Overlay Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping Weldments," 2007.

- 6

3. Code Case N-638-1, "Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique,Section XI, Division 1,,(5], listed in Regulatory Guide 1.147, Revision 15, requires the following condition to be met when using Code Case N-638-1:

"UT volumetric examinations shall be performed with personnel and procedures qualified for the repaired volume and qualified by demonstration using representative samples which contain construction type flaws. The acceptance criteria of NB-5330 in the 1998 Edition through 2000 Addenda of Section III apply to all flaws identified in the repair volume. "

CNS will implement this limitation.

4. IWB-3640, ASME Section XI 2001, Edition including Addenda through 2003 with Appendix C.

The use of an overlay filler material that provides excellent resistance to stress corrosion cracking (SCC) creates an effective barrier to flaw extension. Also, temper bead welding techniques produce excellent toughness and ductility in the weld heat-affected zone (HAZ) of low alloy steel materials and, in this case, results in compressive residual stresses on the inside surface that help to inhibit further SCC of the original weldment. The design of the overlay for the nozzle to end cap weldment uses methods that are standard in the industry. There are no new or different approaches in this overlay design which would be considered either a first-of-a-kind or inconsistent with previous approaches.

The overlay will be designed as a full structural weld overlay in accordance with Code Case N-504-3. The temper bead welding technique that will be implemented in accordance with Code Case N-638-1 will produce a tough, ductile, corrosion-resistant overlay.

3.5.1 Alternative to Code Case N-504-3, Requirement (b) (as stated by the licensee)

Alternative to Code Case N-504-3, Requirement (b), requires the weld overlay shall be low carbon (0.035% maximum) austenitic stainless steel. A consumable welding wire highly resistant to SCC [stress corrosion cracking] was selected for the overlay material. This material, designated as UNS N06054, FN 43, is a nickel based alloy weld filler material, commonly referred to as Alloy 52M, and will be deposited using the machine GTAW process with cold wire feed. Alloy 52M contains about 30 wt% [weight percent] chromium, which imparts excellent corrosion resistance to the material. By comparison, Alloy 82 is identified as a 5

ASME Code Case N-638-1. "Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique,Section XI, Division 1."

-7 SCC-resistant material in NUREG-0313, Rev. 2[6J implemented, Revision 2, and contains nominally 20 wt% chromium, while Alloy 182 has a nominal chromium content of 1S wt%. With its significantly higher chromium content than Alloy 82, Alloy S2M provides an even higher level of resistance to SCC consistent with the requirements of the Code Case. Therefore, this alternative provides an acceptable level of quality and safety.

3.S.2 Alternative to ASME Code Case N-S04-3, Requirement (e) (as stated by the licensee)

Code Case N-S04-3, Requirement (e), requires the first two layers of the weld overlay to have a ferrite content of at least 7.S FN. The composition of nickel based Alloy S2M is such that delta ferrite does not form during welding, because Alloy S2M welds are 100% austenitic and contain no delta ferrite due to the high nickel composition (approximately 60 wt% nickel).

Consequently, delta ferrite measurements will not be performed for this overlay.

Therefore, this alternative provides an acceptable level of quality and safety.

3.S.3 Alternative to ASME Code Case N-S04-3, Requirement (h) (as stated by the licensee)

Code Case N-S04-3, Requirement (h), specifies that a system hydrostatic test shall be performed in accordance with IWA-SOOO if the flaw penetrates the pressure boundary. Leak testing in accordance with ASME Section XI (2001 Edition with the 2003 Addenda), IWA-SOOO and IWB-2S00-1, Category B-P, will be performed. Therefore, this alternative provides an acceptable level of quality and safety.

3.S.4 Alternative to ASME Code Case N-638-1, Paragraph 1.0(a) (as stated by the licensee)

Code Case N-638-1, paragraph 1.0(a), specifies that the maximum weld area on the finished surface shall be 100 square inches. Restoring the structural integrity with the weld overlay of the nozzle to end-cap weld will require welding on more than 100 square inches of surface on the low alloy steel base material. The weld overlays could, if needed, cover up to 260 square inches. The maximum surface area is a conservative estimate. The actual surface area is expected to be less, depending on the location of a detected flaw. The NRC has accepted the increase on surface area to SOO square inches for Millstone Power Station Unit 3[7].

6 NUREG-0313 Revision 2, Date Published: January 1988 ["Technical Report on Material Selection and Processing Guidelines for BWR Coolant Pressure Boundary Piping," ADAMS Accession No. ML031470422].

7 Letter from Harold K. Chernoff, NRC, to David A. Christian, Dominion Nuclear, dated May 3,2007. for the Millstone Power Station Unit 3 (ADAMS Accession No. ML071210024).

- 8 Code Case N-432-1, "Repair Welding Using Automatic or Machine Gas Tungsten-Arc Welding (GTAW) Temper Bead Technique,Section XI, Division 1,"

allows temper bead welding on low alloy steel nozzles, without limiting the temper bead weld surface area. The two additional conditions required by N-432-1 that are not required by Code Case N-638-1 are (1) that temper bead welds have preheat applied, and (2) that the procedure qualification be performed on the same specification, type, grade, and class of material.

Elevated preheat necessitates draining of the reactor pressure vessel. By removing the water in the nozzle area, and (in vessel) inlet riser, a large amount of shielding is removed. The radiation dose rates at the weld overlay location would increase, thereby significantly increasing personnel dose.

The ASME Code committees have recognized that the 100 square inches restriction on the surface area is unnecessarily limiting and Code Case N-638-3 has been issued to increase the surface area limit to 500 square inches. The code case attempts to combine the features of Code Cases N-432 and N-638 into a single code case. The supporting analysis for the code case is documented in Electric Power Research Institute (EPRI) Technical Report 1008454, "Expansion of Temper Bead Repair: Proposed Code Case," which concluded that the residual stresses are not detrimentally changed by increasing the surface area of the repair. The technical basis that justifies exceeding 100 square inches of surface area for repair welds is found in EPRI Technical Report 1003616, "Additional Evaluations to Expand Repair limits for Pressure Vessels and Nozzles" [8l. This technical report describes an ANSYS Finite Element Analysis conducted on the Nine Mile Point Unit 2 feedwater nozzle weld overlay repair. The analysis consisted of modeling the welding processes for both thermal and mechanical aspects. Two overlays were modeled: one was 100 square inches, the other was extended to blend into the nozzle radius to achieve greater than the 100 square inches surface area repair currently permitted by the ASME Code requirements. Comparison of the residual stresses of the two overlays showed that the effect of extending the overlay to the nozzle radius minimally impacted the residual stress profile and, in some cases, slightly increased the beneficial compressive stresses on the nozzle inner diameter.

3.5.5 Alternative to ASME Code Case N-638-1, Paragraph 4.0(b) (as stated by the licensee)

Code Case N-638-1, Paragraph 4.0(b), specifies that the final weld surface and band area [1.5T width or 5 inches, whichever is less, per 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 />. Code Case N-638-1 requires that the final post-weld examinations be performed after completion of welding. The alternative is to begin the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold period following the completion of the third temper bead weld layer on the ferritic base metal. The 48-hour hold period is invoked specifically to permit delayed hydrogen cracking 8

EPRI Technical Report 1003616, "Additional Evaluations to Expand Repair Limits for Pressure Vessels and Nozzles," March 2004.

-9 to occur prior to the final NDE. Extensive industry experience has identified no evidence of delayed hydrogen cracking in nuclear applications involving ambient temperature temper bead welding. Absence of cracking is attributed to use of the GTAW machine welding process, and to the extensive process and quality controls present in nuclear welding applications. Revising the start time for the 48-hour period reduces adverse cost and scheduling impacts, while retaining effective assurance that delayed hydrogen cracking has not occurred.

The UT shall be in accordance with ASME Section XI, Appendix I. Surface exams will be performed. IWA-4634 requires UT of the area to be welded only.

Any laminar flaws in the weld overlay will be evaluated in accordance with ASME Section XI, Non-mandatory Appendix 0, Paragraph 0-4100 (2007 Edition),

except, as allowed by IWB-3132.3 (2001 Ed., 2003 Add.), any flaws that exceed the acceptance standards of Table IWB-3510-1 (2001 Ed., 2003 Add.) are acceptable for continued service, without repair, if an analytical evaluation, performed in accordance with IWB-3600 (2001 Ed., 2003 Add.), meets the acceptance criteria of IWB-3600.

Full UT of the 1.5T band will not be performed. Full ultrasonic examination of the 1.5T band will not be possible due to geometric interferences. The ultrasonic examination may not extend up to the very edge of the overlay. The weld overlay will extend into the blend radius of the nozzle beyond the length required by Code Case N-504-3 for structural reinforcement. This extension into the blend radius eliminates a stress riser on the nozzle and may provide additional surface area for ultrasonic examination of the defect area in the original weld.

UT examination on the nozzle beyond the overlay will not provide any information regarding the area of the defect that required repair. Additionally, such UT would likely be unsatisfactory when applied to the nozzle blend radius, where the toe of the weld overlay resides. The UT return signal would be difficult to obtain and to interpret. Figures 1 and 2 [of the licensee's letter dated February 5, 2010]

identify the extent of coverage expected for scans in the circumferential and axial directions. The full weld overlay surface will be scanned. See Table 2 [of the licensee's letter dated February 5, 2010] for the examination summary.

Because this is a surface application of a temperbead welding process (specifically performed to minimize heat input into the ferritic steel nozzle), there is minimal impact to the volume of the ferritic shell nozzle material in the area surrounding the weld overlay. Also, no additional useful information can be gained by a volumetric examination of the area beyond the physical boundaries of the weld overlay. The weld and heat affected zone beneath the weld overlay will be volumetrically examined after welding to ensure that sound weld metal has been deposited and that the process did not introduce flaws into the base material. Surface examinations of the weld overlay surface will be performed (See Figure 3 [of the licensee's letter dated February 5, 2010] for the examination area). This is sufficient to verify that defects were not introduced in either the ferritic steel nozzle or Alloy 600 (SB-166) end cap due to welding.

- 10 Later editions of Section XI, as well as Code Case N-638-2, have deleted the requirement for the 1.ST examination band for both ultrasonic examination and surface examination. This is consistent with the less restrictive requirements for ultrasonic examination of the ferritic nozzle because hydrogen cracking away from the temper bead weld is not considered a concern. The NDE requirements in these documents apply to any type of welding where a temperbead technique is to be employed (which includes weld repairs of excavated flaws) and is not specifically written for weld overlay. For the weld overlay type of repair, any ferritic steel base material cracking would occur in the HAZ directly below or adjacent to the weld overlay and not in the 1.ST examination band of ferritic material beyond the edges of the weld overlay. If this type of cracking occurs it will be detected by the NDE of the weld overlay and adjacent ferritic steel surfaces as described in the relief request and non-mandatory Appendix Q.

Therefore, this alternative provides an acceptable level of quality and safety.

3.S.6 Alternative to ASME Code Case N-638-1, Paragraph 4.0(c}

In its letter dated February S, 2010, the licensee stated:

Code Case N-638-1, paragraph 4.0(c), specifies that the area from which weld attached thermocouples have been removed shall be ground and examined using a surface examination method. Due to the personnel exposure associated with the installation and removal of the thermocouples, the nozzle configuration, and because the nozzle will be full of water, thermocouples will not be used to verify that the pre-heat and interpass temperature limits are met. In lieu of thermocouples, a contact pyrometer will be used to verify pre-heat temperature and interpass temperature compliance with the WPS [welding procedure surveillance] requirements. Therefore, this alternative provides an acceptable level of quality and safety.

The use of overlay filler material that provides excellent resistance to SCC develops an effective barrier to flaw extension. Also, temper bead welding techniques produce excellent toughness and ductility in the weld HAZ low alloy steel materials, and in this case, results in compressive residual stresses on the inside surface that help to inhibit further SCC. The design of the overlay for the control rod drive end cap to nozzle weldment uses methods that are standard in the industry. There are no new or different approaches in this overlay design which would be considered either first-of-a-kind or inconsistent with previous approaches. The overlay will be designed as a full structural overlay in accordance with Code Case N-S04-3, except as noted above. The temper bead welding technique that will be implemented in accordance with Code Case N-638-1 will produce a tough, ductile, corrosion-resistant overlay.

In its letter dated August 17, 2010, the licensee stated:

The interpass temperatures will be measured every three (3) to five (S) beads for the first three (3) layers and every six (6) to ten (10) beads for the remaining layers. This action will be implemented as part of implementing RI-36,

- 11 Revision 0, which is a contingency 10 CFR 50.55a request for Cooper Nuclear Station Refueling Outage 26.

3.6 NRC Staff Technical Evaluation 3.6.1 Alternatives to N-504-3 The licensee has requested to use ASME Code Cases N-638-1 and N-504-3 with modifications.

Relief Request No. RI-36, Revision 0, is based upon restoring the structural integrity of the RCA-BF-1, 5 inch Control Rod Drive Return Cap-to-Nozzle 9A weld by applying a full structural weld overlay over the weld joint. ASME Code Case N-504-3 has been conditionally approved by the NRC in Regulatory Guide (RG) 1.147, Revision 15. Therefore, the use of ASME Code Case N-504-3 as an alternative to the mandatory ASME Code repair provisions is acceptable to the NRC staff, provided that the licensee complies with all of conditions and provisions specified in RG 1.147, Revision 15. Under the rules of ASME Code,Section XI, IWA-4220, repairs shall be performed in accordance with the licensee's design specification and the original Construction Code. Later editions and addenda of the Construction Code or of ASME Code,Section III, either in their entirety or portions thereof, and Code Cases may be used. In addition to the above, defects shall be removed or reduced in size in accordance with ASME Code,Section XI, IWA-4400.

3.6.1.1 Alternative to Code Case N-504-3, Requirement (b)

As addressed in Sections 3.4 and 3.5.1 of this safety evaluation (SE), the licensee proposes to modify the ASME Code Case N-504-3 provisions for the use of a nickel-based alloy weld material rather than a low carbon austenitic stainless steel weld material. The licensee states that Requirement (b) of ASME Code Case N-504-3 requires that the reinforcement weld material shall be low carbon (0.035% maximum) austenitic stainless steel. In lieu of stainless steel weld material, Alloy 52M, a consumable welding wire highly resistant to SCC, is proposed for the overlay weld material. The NRC staff concludes that the use of 52M material is consistent with weld filler material used to perform similar weld overlays at other operating boiling water reactor facilities. For material compatibility in welding, the NRC staff considers that Alloy 52M is a better choice of filler material than austenitic stainless steel material for a weld overlay. Alloy 52M contains about 30 percent chromium which provides excellent resistance to SCC if exposed to the reactor coolant environment. This material is identified as F-No. 43 Grouping for the ERNiCrFe-7A, classification UNS N06054 Filler Metal and has been previously approved by the NRC staff for similar applications. Therefore, the NRC staff concludes that the licensee's proposed use of Alloy 52M for the weld overlays as a modification to the requirements of ASME Code Case N-504-3, Requirement (b) is acceptable as it will provide an acceptable level of quality and safety.

3.6.1.2 Alternative to ASME Code Case N-504-3, Requirement (e)

As addressed in Sections 3.4 and 3.5.2 of this SE, the licensee proposes to modify the ASME Code Case N-504-3 provisions in Requirement (e) which requires as-deposited delta ferrite measurements of at least 7.5 FN for the weld reinforcement. The licensee proposes that delta ferrite measurements will not be performed for this overlay because the deposited Alloy 52M material is 100 percent austenitic and contains no delta ferrite due to the high nickel

- 12 composition (approximately 60 percent nickel). ASME Code Case N-S04-3 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, ASME Code Case N-S04-3 is designed for weld overlay repair of austenitic stainless steel piping. Therefore, the material requirements regarding the delta ferrite content of at least 7.S FN, as delineated in ASME Code Case N-S04-3, Requirement (e), apply only to austenitic stainless steel weld overlay materials to ensure its resistance to SCC. These requirements are not applicable to Alloy S2M, a nickel-based material which the licensee will use for the weld overlay. Since the filler is a fully austenitic material, the NRC staff concludes this alternative acceptable in that it provides an acceptable level of quality and safety.

3.6.1.2 Alternative to ASME Code Case N-S04-3. Requirement (h)

As addressed in Sections 3.4 and 3.S.3 of this SE, the licensee proposes to modify Requirement (h) of ASME Code Case N-S04-3 to perform leak testing in accordance with ASME Code,Section XI (2001 Edition with the 2003 Addenda), IWA-SOOO. Precedence for use of a leak test at normal operating temperature and pressure in lieu of a hydrostatic test has been set with ASME Code Case N-416-1, "Alternative Pressure Test Requirements for Welded Repairs or Installation of Replacement Items by Welding, Class 1,2, and 3,Section XI, Division 1,"

which has been incorporated in ASME Code,Section XI beginning in the 1998 Edition with the 1999 Addenda. The provisions to substitute leak testing for hydrostatic testing have been accepted by the NRC by its endorsement of the ASME Code, Sections XI Editions and Addenda since the 1998 Edition and 1999 Addenda in 10 CFR SO.SSa. CNS is currently in its fourth 10-year lSI interval, which began March 1,2006, and ends January 18, 2014. The lSI Code of record for CNS for the second 10-year lSI interval is the ASME Code,Section XI, 2001 Edition, including Addenda through 2003. Therefore, the NRC staff concludes this alternative acceptable in that it provides an acceptable level of quality and safety.

3.6.2 Alternatives to N-638-1 To eliminate the need for preheat and post-weld heat treatment under the Construction Code, the industry developed requirements for implementation of a temper bead welding technique which were published in ASME Code Case N-638-1. ASME Code Case N-638-1 has been conditionally approved by the NRC in RG 1.147, Revision 1S. Therefore, the NRC staff concludes that the use of ASME Code Case N-638-1 as an alternative to the mandatory ASME Code repair provisions is acceptable, provided that the licensee complies with all conditions and provisions specified in RG 1.147, Revision 1S.

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 post-weld heat treatment specified by the ASME Construction Code is not necessary to produce a sound weld using a temper bead welding process which meets the requirements of ASME Code Case N-638-1.

- 13 The licensee will meet the requirements of ASME Code Case N-638-1, with the exception of the following paragraphs in ASME Code Case N-638-1 as stated in Sections 3,6,2,1 through 3.6.2,3 of this SE.

3.6.2.1 Alternative to ASME Code Case N-638-1, Paragraph 1,0(a)

As addressed in Sections 3.4 and 3.5.4 of this SE, ASME Code Case N-638-1, Paragraph 1.0(a), requires the maximum area of an individual weld, based on the finished surface, be limited to 100 square inches and the depth of the weld not to exceed one-half of the ferritic base metal thickness, This condition is not being met because the design for the weld overlay could cover an area up to 260 square inches which exceeds the limitations of ASME Code Case N-638-1. The licensee states that it will perform an evaluation to determine the effect of exceeding the 100-square-inch area limitation for temper bead welding onto a low alloy steel nozzle. This evaluation will be conducted under the guidance of ASME Code Case N-504-3. Paragraphs (g)(2) and (g)(3) of ASME Code Case N-504-3 require consideration of the effects of residual stresses produced by the weld overlay, when coupled with other applied loads on other welds and components throughout the system, The evaluation of other welds and components in the system considers potential increases in loading, including shrinkage effects, due to all weld overlays in the reactor coolant system. These welds and components are to meet the applicable stress limits of the Construction Code. The NRC staff considers this evaluation important in assuring that the reactor coolant system will not be adversely affected after the weld overlay is deposited, EPRI Technical Report 1003616 provides technical justification for exceeding the size of the temper bead repairs up to a finished area of 500 square inches over the ferritic material. The total area of coverage over the P3 (ferritic) material could be up to 260 square inches of overlay surface area. Results of industry analyses and testing performed to date have indicated that there is no direct correlation of amount of surface area repaired when comparing residual stresses using temper bead welding. Residual stresses associated with larger area repairs

(>100 square iriches) remain compressive at an acceptable level. Based on the above, the NRC staff concludes that the modification to increase the weld overlay to approximately 260 square inches provides an acceptable level of quality and safety and is, therefore, acceptable.

3,6.2.2 Alternative to ASME Code Case N-638-1, Paragraph 4.0(b)

As addressed in Sections 3.4 and 3.5.5 of this SE, the licensee proposes to modify the requirements under ASME Code Case N-638-1, Paragraph 4.0(b), stating that full UT of the 1.5T band would not be performed. Using ASME Code Case N-638-1, the temper bead weld is for filling a cavity in the base metal. The licensee's application, however, is for a structural weld overlay above the base metal, which results in a contour that is UT inspectable except for the edge taper where the overlay transitions to the nozzle surface. The proposed weld edge configuration has the same UT examination difficulties as are considered under ASME Code,Section XI, Appendix Q. Appendix Q only requires a surface examination of the tapered area of the weld overlay, In addition to verifying the soundness of the weld, a purpose of the UT is to assure that delayed cracking due to hydrogen introduced during the temper bead welding process or cracking in the ferritic material does not occur, In the unlikely event cracking does occur, it would initiate on the surface on which the welding is actually performed or in the HAZ

- 14 immediately adjacent to the weld. The most appropriate technique to detect surface cracking is a surface examination technique. Therefore, the NRC staff concludes that the use of a surface examination in the area of the weld overlay taper and band beyond the toe of the overlay on the ferritic material is acceptable in that it provides an acceptable level of safety and quality.

3.6.2.3 Alternative to ASME Code Case N-638-1! Paragraph 4.0(c)

As addressed in Sections 3.4 and 3.5.6 of this SE, ASME Code Case N-638-1, Paragraph 4.0(c), specifies that the area from which weld-attached thermocouples have been removed shall be ground and examined using a surface examination method. The licensee has stated that, due to the personnel exposure associated with the installation and removal of the thermocouples, the nozzle configuration, and because the nozzle will be full of water, thermocouples will not be used to verify that the preheat and interpass temperature limits were met. In lieu of thermocouples, the licensee states that a contact pyrometer will be used to verify preheat temperature and interpass temperature compliance with the WPS requirements. The preheat temperature required for this welding is 50 OF. The maximum interpass temperatures required for this welding are 150 OF for the first three layers and 350 OF for the balance of the welding. A contact pyrometer will be used to adequately monitor these preheat and interpass temperatures. Also, the large mass of the nozzle coupled with the low heat input GTAW process helps ensure that the maximum interpass temperatures will not be exceeded. The alternate temperature measurement method ensures that a close control is maintained on these temperatures. The NRC staff concludes that this type of temperature measurement provides an acceptable level of quality and safety and, therefore, is acceptable.

3.7 NRC Staff Conclusion

Based on the discussion above, the NRC staff concludes that the proposed alternatives to ASME Code Cases N-504-3 and N-638-1 will allow the licensee to perform a full structural weld overlay on the RCA-BF-1, 5-inch Control Rod Drive Return Cap-to-Nozzle 9A weld at CNS with an acceptable level of quality and safety. Therefore, the licensee's Relief Request RI-36, Revision 0, to implement a weld overlay repair at CNS in accordance with ASME Code Cases N-638-1 and N-504-3, as modified by the licensee's requested alternatives and compliance with the limitations specified in RG 1.147, Revision 15 for the use of the aforementioned code cases, is acceptable.

4.0 COMMITMENT In its August 17, 2010, letter, the licensee made the following regulatory commitment:

A contact pyrometer will be used to measure the preheat temperature prior to welding. The interpass temperatures will be measured every three (3) to five (5) beads for the first three (3) layers and every six (6) to ten (10) beads for the remaining layers.

The licensee stated that this commitment will be completed by Refueling Outage 26, contingent upon the need to implement RI-36.

The NRC staff concludes this commitment is acceptable.

- 15

5.0 CONCLUSION

On the basis of review and evaluation of the licensee's submittals, the NRC staff concludes that the proposed alternatives would provide an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the staff authorizes the use of Relief Request RI-36, Revision 0, related to the installation of a full structural weld overlay of the subject welds. The relief is authorized for the remainder of the fourth 10-year lSI interval, which ends on January 18, 2014, at CNS.

All other ASME Code,Section XI, requirements for which relief was not specifically requested and authorized herein by the NRC staff remain applicable, including the third-party review by the Authorized Nuclear Inservice Inspector.

Principal Contributor: E. Andruszkiewicz Date: February 18, 2011

ML110120540 *memo dated OFFICE NRR/LPL4/PM NRR/LPL4/LA NRR/DCI/CVIB NRR/LPL4/BC NRR/LPL4/PM NAME LWilkins JBurkhardt MMitchell* MMarkley LWilkins l2,ATE 1/14/11 1/14/11 12/13/10 2/18111 2/18/11