ML061180496

Third 10-Year Inservice Inspection Interval, Relief Request I3R-08, Structural Weld Overlays on Pressurizer Spray, Relief, Safety and Surge Nozzle Safe-ends and Associated Alternative Repair Techniques

ML061180496
Person / Time
Site:	Byron
Issue date:	04/28/2006
From:	Hoots D Exelon Generation Co, Exelon Nuclear
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
1.10.0101, Byron 2006-0050
Download: ML061180496 (31)

Text

Ee~n.

10 CFR 50.55a April 28, 2006 LTR: Byron 2006-0050 File: 1.10.0101 United States Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Byron Station, Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. SIN 50-454 and STN 50-455

Subject:

Third 10-Year Inservice Inspection Interval, Relief Request 13R-08, Structural Weld Overlays on Pressurizer Spray, Relief, Safety and Surge Nozzle Safe-ends and Associated Alternative Repair Techniques Pursuant to 10 CFR 50.55a(a)(3)(i), Exelon Generation Company, LLC (EGC), is proposing an alternative to the repair/replacement requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), Section Xl, 2001 Edition, through 2003 Addenda, IWA-4000, for the structural weld overlays on pressurizer spray, relief, safety and surge nozzle safe-ends.

During the next Byron Station Unit 1 refueling outage (B1R14) and Byron Station Unit 2 refueling outage (B2R13), EGC will be performing full structural weld overlays (SWOLs) on all pressurizer nozzle safe-end to nozzle welds where Alloy 182 was originally used to butter the nozzle face and used to weld the stainless steel safe-ends to nozzles.

The alternative is proposed under the provisions of 10 CFR 50.55a(a)(3)(i), an alternative that provides an acceptable level of quality and safety.

EGO requests that the review of this relief request be completed by September 11, 2006. If you have any questions regarding this letter, please contact William Grundmann at (815) 406-2800.

Respectfully, David M. Hoots Site Vice President Byron Nuclear Generating Station DMH/JL/rah

Enclosure:

Byron Station Relief Request l3R-08

IS! Program Plan Units I & 2, Third Intenial 10 CFR 50.55a RELIEF REQUEST 13R-08 Revision 0 Page 1 of 30 Request for Relief for Alternative Requirements of Structural Weld Overlays (SWOLs) of the Pressurizer Surge, Spray, Safety and Relief Nozzles, Dissimilar Welds including the SWOLs of the Safe-End to Pipe, Reducer and Elbow Welds on Pressurizer Surge, Spray, Safety and Relief Nozzles In Accordance with 10 CFR 50.55a(a)(3)(i) 1.0 ASME CODE COMPONENT(S) AFFECTED Code Class: 1

Reference:

IWA-4000, Repair/Replacement Activities Examination Category: R-A Item Number: See Table 1 for listing

Description:

Alternative Structural Weld Overlays (SWOL5) of the Pressurizer Surge, Spray, Safety and Relief Nozzles, Dissimilar Welds and also including the SWOLs of the Safe-End to Pipe, Reducer and Elbow Welds on Pressurizer Surge, Spray, Safety and Relief Nozzles Component Number(s): See Table 1 for listing Drawing Number(s): Unit 1: 1PZR-1-lSl (Pressurizer), 1RC-1-lSl SheetS (Surge Line), 1RC-l-ISI Sheet 16 (Spray Line), 1RC lSl Sheet 32 (Relief Lines), and 1RC-1-lSl Sheet 35 (Safety Line)

Unit 2: 2PZR-1 -ISI (Pressurizer), 2RC-1-lSl Sheet 5 (Surge Line), 2RC-1-lSl Sheet 16 (Spray Line), 2RC-l-ISI Sheet 32 (Relief Lines), and 2RC-1-lSl Sheet 35 (Safety Line) 2.0 APPLICABLE CODE EDITION AND ADDENDA The Inservice Inspection program is based on the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code, Section Xl, 2001 Edition through the 2003 Addenda.

3.0 APPLICABLE CODE REQUIREMENT ASME Section Xl, 2001 Edition, through 2003 Addenda, IWA-4000 requires that repairs be performed in accordance with the owners original construction Code of the component or system, or later editions and addenda of the Code. The pressurizer Code of Construction is ASME Section III, 1971 Edition through Summer 1973 Addenda, with Code Case NB-4643, 1493-1. The proposed alternative activities are supported by the requirements presented in:

ASME Code Case N-638-1 Similar and Dissimilar Metal Welding Using Ambient Temperature Machine ClAW Temper Bead Technique conditionally approved in Exe/on Byron Station

IS! Program Plan ____________ ____________________ Unitsl&  ?~Third In ten/al 10 CFR 50.55a RELIEF REQUEST 13R-08 Revision 0 (Page 2 of 30)

Nuclear Regulatory Commission (NRC) Regulatory Guide (RG) 1.147 Revision 14.

ASME Code Case N-504-2 Alternative Rules for Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping conditionally approved in RG 1.147 Revision 14.

In addition, ASME Code, Section Xl, 1995 Edition including Addenda through 1996, Appendix VIII Supplement 11 is used for examination qualification requirements of the final welded overlays.

4.0 REASON FOR THE REQUEST Dissimilar metal welds (DMWs), typically consisting ofAlloy 182 weld are frequently used in pressurized water reactors (PWR) construction to connect stainless steel pipe and safe ends to vessel nozzles, generally constructed of carbon or low alloy ferritic steel. These welds have shown a propensity for primary water stress corrosion cracking (PWSCC) degradation, especially in components subjected to higher operating temperatures, such as the pressurizer (PZR).

Exelon Generating Company, LLC (EGO), Byron Station Units 1 and 2 is proposing to take a proactive approach on the Byron Station Unit 1 and 2 Pressurizer and apply a preemptive Structural Weld Overlay (SWOL) on the Pressurizer Nozzle Safe-end to Nozzle Dissimilar Metal Welds to mitigate the occurrence of PWSCC prior to detectable evidence of PWSCC. Structural Weld Overlays (SWOL) have been used for several years on both boiling water reactors (BWR) and pressurized water reactors (PWR) to arrest existing flaws from propagating while establishing a new structural pressure boundary. In some cases, SWOLs have been used to reestablish structural integrity of the DMW containing through wall leaking flaws.

The SWOLs will also facilitate ultrasonic examination of the DMWs by providing a more consistent outer surface configuration from which scanning can be performed.

The welding will be performed using a remote mechanized Gas Tungsten-Arc Welding (GTAW) process and using the ambient temperature temper bead method with AWS Classification ERNiCrFe-7 (Alloy 52 or Alloy 52M*) weld metal. Manual GTAW, using Alloy 52 or Alloy 52M, will only be permitted subsequent to the SWOLs being essentially completed or to repair indications detected in base materials prior to overlay initiation. Also, Manual GTAW may be used if local repairs of weld defects are necessary or additional weld metal is required locally to form the final SWOL contour. Shielded Metal Arc Welds (SMAW), using AWS Classification ERNiCrFe-7 (Alloy 152), will be used only as needed to repair indications in base materials prior to overlay initiation.

• The material suppliers weld wire designation may be either 52M or 52MS. The S designates the process route that converts the hot-rolled billet into finished cold-drawn wire. The material properties are not Exe/on Byron Station

IS! Program Plan ________________ Units 1 &2, Third Interval 10 CFR 50.55a RELIEF REQUEST l3R-08 Revision 0 (Page 3 of 30) affected. For this reason, references herein to 52M are considered to encompass S2MS filler material as well.

As discussed herein, there is no comprehensive criterion for a licensee to apply a SWOL repair to a DMW that is constructed ofAlloy 82/182 weld material and is believed to be susceptible to or contain PWSCC degradation. Although the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), Section Xl, 2001 Edition, through 2003 Addenda, IWA-4000, is used for the Byron Unit 1 and 2 Section Xl Repair/Replacement Program, it does not contain the needed requirements for this type of weld overlay repair. Repair/replacement activities associated with weld overlays of this type are required to address the materials, welding parameters, personnel radiation exposure concerns, operational constraints, examination techniques and procedure requirements.

5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE EGO proposes using SWOLs designed in accordance with Code Cases N-504-2 (Reference 1) with the modifications proposed in Table 2. Code Case N-504-2, currently approved for use in RG 1.147 with additional requirements of ASME Section Xl, 2005 Addenda Appendix Q being required, allows a flaw to be reduced to an acceptable size by deposition of weld reinforcement on the outside surface of the pipe without flaw removal. The SWOLs will extend around the full circumference of the applicable DMWs as required by Code Case N-504-2. The specific thickness and length will be determined according to the guidance provided in Code Case N-504-2, The overlay will completely cover the DMWs and the adjacent stainless steel safe-end to pipe welds with Alloy 52 or Alloy 52M material that is highly resistant to PWSCC. A typical SWOL configuration is shown in Figure 1.

The temper bead welding technique for the specified nozzles adjacent to DMWs will be implemented in accordance with ASME Code Case N-638-1 (Reference 2) with the modifications proposed in Table 3.

The ultrasonic examination (UT) of the completed SWOL will be accomplished in accordance with ASME Section Xl, 1995 Edition with the 1996 Addenda, Appendix VIII Supplement 11 with the modifications described in Table 4. These modifications were developed by the EPRI Performance Demonstration Initiative (PDI) program to implement the requirements of Appendix VIII. These EPRI Supplement 11 modifications have previously been approved for use (see Reference 6).

6.0 DURATION OF THE PROPOSED ALTERNATIVE This relief request will be implemented during the remainder of Byron Station, Units 1 and 2 third ten-year inservice inspection interval.

ExeIon Byron Station

IS! Program Plan _______ ____ ____ Units 1 & 2, Third Interval 10 CFR 50.55a RELIEF REQUEST l3R-08 Revision 0 (Page 4 of 30) 7.0 PRECEDENT Similar relief requests have been previously approved for AmerGen Energy Company for its Three Mile Island Nuclear Station, Unit 1 in July, 2004, at Constellation Energys Calvert Cliffs Nuclear Power Plant, Unit 2 in July, 2005 and at Dominion Nuclear Connecticuts Millstone Power Station Unit 3 in October 2005.

These requests were associated with welding over detected flaws outside the acceptance criteria of Section Xl.

8.0 REFERENCES

1. ASME Code Case N-504-2, Alternative Rules for Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping, dated March 12, 1997.

2. ASME Code Case N-638-1, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique, dated February 13, 2003.

3. Letter from Richard Laufer, NRC to Christopher M. Crane, AmerGen, Three Mile Island Nuclear Station, Unit 1 (TMI-1) Request for Relief From Flaw, Heat Treatment, and Nondestructive Examination Requirements for the Third 10 year lnservice Inspection (ISI) Interval (TAC No. MC1O1), Accession Number ML041670510, dated July 21, 2004.

4. Letter from Richard J. Laufer, NRC to George Vanderheyden, Calvert Cliffs, Calvert Cliffs Nuclear Power Plant, Unit No. 2 Relief Request For Use Weld Overlay and Associated Alternative Inspection Techniques (TAO Nos. MC6219 and MC6220), Accession Number ML051930316, dated July 20, 2005.

5. Letter from L. Raghavan, NRC to Mano K. Nazar, l&M, Donald C. Cook Nuclear Plant, Unit 1 (DOCNP-1) Alternatives Regarding Repair of Weld 1 -PZR-23 on Pressurizer Nozzle to Valve Inlet Line (TAO No. MC6704), Accession Number ML053220019, dated December 1, 2005.

6. Letter from L. Raghavan, NRC, to Mano K. Nazar, l&M, Donald C. Cook Nuclear Plant, Unit 1 Alternative to Repair Requirements of Section Xl of the American Society of Mechanical Engineers Code (TAC No. MC06751), Accession Number ML051720006, dated June 27, 2005.

7. Letter from Leslie N. Hartz, Dominion Nuclear Connecticut, to NRC Document Control Desk, Dominion Nuclear Connecticut, Inc., Millstone Power Station Unit 3, Second 10-year Inservice Inspection Interval, Revision 1 to Relief Request IR-2-39, Use of Weld overlay and Associated Alternative Repair Techniques, Accession Number ML052930108, dated October 19, 2005.

8. Letter from Richard J. Laufer, NRC, to Bryce L. Shriver, PPL Susquehanna, Susquehanna Steam Electric Station, Unit 1 Relief from American Society of Mechanical Engineers, Boiler and Pressure Vessel Code (ASME Code), Section Xl Appendix VIII, Supplement 11, Requirements and Oases N-504-2 and N-638 Exe/on Byron Station

IS! Program Plan ______ Unitsl& 2, Third_Interval 10 CFR 50.55a RELIEF REQUEST 13R-08 Revision 0 (Page 5 of 30)

Requirements (TAO Nos. MC2450 and MC2594), Accession Number ML051220568, dated June 22, 2005.

9.0 ATTACHMENTS

1. RRA 05-08, BCO6-134, Technical Basis Paper N-638-x, Ambient Temperature Temperbead Welding: Begin 48 Hour Hold After 3~Layer Completion, authored by Bruce Newton, PCI Energy Services.

2. RRM-02-05, BCO4-1 003, Develop New Code Case to Address Inconel Weld Overlay on Various Materials, SIR-05-030, Rev. 0, Effect of Chromium Content on Nickel-base Alloy SOC Resistance Exelon Byron Station

IS! Program Plan _____ ___________ Unitsl& 2, Third Intenial 10 CFR 50.55a RELIEF REQUEST 13R-08 Revision 0 (Page 6 of 30)

TABLE I COMPONENT IDENTIFICATION For Unit I Pressurizer IRYOIS PIPING WELD SAFE-END IDENTIFICATION ITEM # SIZE CONFIGURATION ITEM #

(Line,_Weld)

Surge PN-01 Fl R1.11 14 1RY11AA-14, Safe-end to Pipe R1.11 R1.15 J1A Spray PN-02 F2 R1.11 4 1RYO1C-4, J1 6x4 Reducerto R1.11 R1.15 Safe-end Relief PN-03 F3 R1.15 6 IRYO2A-6, J1 Safe-end to Out 45° R1.20 Elbow Safety PN-04 F4 R1.1S 6 1RYO3AA-6, J1 Safe-end to Cut 90° R1.20 A Elbow Safety PN-05 ES R1.15 6 1RYO3AB-6, J1 Safe-end to Cut 90° R1.20 B Elbow Safety PN-06 E6 R1.15 6 1RYO3AC-6, J1 Safe-end to Cut 90° R1.20 C Elbow For Unit 2 Pressurizer 2RYOIS SAFE-END IDENTIFICATION ITEM # SIZE PIPING WELD CONFIGURATION ITEM #

(Line,_Weld)

Surge PN-01 El Rl.11 14 2RY11AA-l4, Safe-endto Pipe R1.1l R1.15 J1 Spray PN-02 E2 R1.1l 4 2RYO1C-4, Jl 6x4 Reducer to Rl.ll Rl.15 Safe-end Relief PN-03 E3 Rl.lS 6 2RYO2A-6, J1 Safe-end to Cut 45° Rl.20 Elbow Safety PN-04 E4 Rl.15 6 2RYO3AA-6, J1 Safe-end to Cut 90° Rl.20 A Elbow Safety PN-05 ES R1.l5 6 2RYO3AB-6, Jl Safe-end to Cut 90° Rl.20 B Elbow Safety PN-06 E6 R1.15 6 2RYO3AC-6, Jl Safe-end to Cut 90° R1.20 0 Elbow Note: Item numbers reflect Risk-Informed classification per ASME Code Case N-578-1.

Ri. ii: Elements Subject to Thermal Fatigue.

Ri.iS: Elements Subject to Primary Water Stress Corrosion Cracking.

Ri20: Elements not Subject to a Damage Mechanism.

Exelon Byron Station

ISI Program Plan Units I & 2, Third Interval 10 CFR 50.55a RELIEF REQUEST I3R-08 Revision 0 (Page 7 of 30)

Figure 1 Typical SWOL Configuration SS Eli (SA-182 F316L)

SWOL (A52~

EJNozzle Weld Class 2)

Exelon Byron Station

IS! Program Plan Units 1 & 2, Third Interval IOCFR 50.55a RELIEF REQUEST 13R-08 Revision 0 (Page 8 of 30)

TABLE 2 DESIGN I MATERIAL I NONDESTRUCTIVE EXAMINATION Modifications to Code Case N-504-2 and ASME Section Xl, Appendix Q CODE CASE N-504-2 AND ASME SECTION XI APPENDIX Q Reply: It is the opinion of the Committee that, Modification: Oode Oase N-504-2 and Appendix in lieu of the requirements of IWA-4120 in Q will be used for the weld overlay of the ferritic Editions and Addenda up to and including the (P3) nozzle material, nickel alloy (F43/P43) 1989 Edition with the 1990 Addenda, in IWA- weld material, and austenitic stainless steel 4170(b) in the 1989 Edition with the 1991 base (P8, safe end and pipe) and weld Addenda up to and including the 1995 Edition, materials.

and in IWA-4410 in the 1995 Edition with the Basis: Oode Oase N-504-2 is accepted for use 1995 Addenda and later Editions and in the current NRC Regulatory Guide 1.147 Addenda, defect in austenitic stainless steel Rev. 14, and has been used extensively in piping may be reduced to a flaw of acceptable BWR primary system piping. More recently, N-size in accordance with IWB-3640 from the 504-2 has been applied to PWR applications, 1983 Edition with the Winter 1985 Addenda, or with modifications, for the weld overlay repair of later Editions and Addenda, by deposition of dissimilar metal welds with known flaws.

weld reinforcement (weld overlay) on the Industry operating experience in the area has outside surface of the pipe, provided the shown that PWSOO in Alloy 82/182 will arrest at following requirements are met. the interface with stainless steel base metal, ferritic base metal, or Alloy 52/52M/1 52 weld metal. The 360°full structural weld overlay will control growth in any PWSCC crack and maintain weld integrity. The weld overlay will also induce compressive stress in the weld, thus potentially impeding growth of any reasonably shallow cracks. Furthermore, the overlay will be sized to meet all structural requirements without considering the existing 82/1 82 weld.

Exe/on Byron Station

Ee~n.

10 CFR 50.55a April 28, 2006 LTR: Byron 2006-0050 File: 1.10.0101 United States Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Byron Station, Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. SIN 50-454 and STN 50-455

Subject:

Third 10-Year Inservice Inspection Interval, Relief Request 13R-08, Structural Weld Overlays on Pressurizer Spray, Relief, Safety and Surge Nozzle Safe-ends and Associated Alternative Repair Techniques Pursuant to 10 CFR 50.55a(a)(3)(i), Exelon Generation Company, LLC (EGC), is proposing an alternative to the repair/replacement requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), Section Xl, 2001 Edition, through 2003 Addenda, IWA-4000, for the structural weld overlays on pressurizer spray, relief, safety and surge nozzle safe-ends.

During the next Byron Station Unit 1 refueling outage (B1R14) and Byron Station Unit 2 refueling outage (B2R13), EGC will be performing full structural weld overlays (SWOLs) on all pressurizer nozzle safe-end to nozzle welds where Alloy 182 was originally used to butter the nozzle face and used to weld the stainless steel safe-ends to nozzles.

The alternative is proposed under the provisions of 10 CFR 50.55a(a)(3)(i), an alternative that provides an acceptable level of quality and safety.

EGO requests that the review of this relief request be completed by September 11, 2006. If you have any questions regarding this letter, please contact William Grundmann at (815) 406-2800.

Respectfully, David M. Hoots Site Vice President Byron Nuclear Generating Station DMH/JL/rah

Enclosure:

Byron Station Relief Request l3R-08

IS! Program Plan Units I & 2, Third Intenial 10 CFR 50.55a RELIEF REQUEST 13R-08 Revision 0 Page 1 of 30 Request for Relief for Alternative Requirements of Structural Weld Overlays (SWOLs) of the Pressurizer Surge, Spray, Safety and Relief Nozzles, Dissimilar Welds including the SWOLs of the Safe-End to Pipe, Reducer and Elbow Welds on Pressurizer Surge, Spray, Safety and Relief Nozzles In Accordance with 10 CFR 50.55a(a)(3)(i) 1.0 ASME CODE COMPONENT(S) AFFECTED Code Class: 1

Reference:

IWA-4000, Repair/Replacement Activities Examination Category: R-A Item Number: See Table 1 for listing

Description:

Alternative Structural Weld Overlays (SWOL5) of the Pressurizer Surge, Spray, Safety and Relief Nozzles, Dissimilar Welds and also including the SWOLs of the Safe-End to Pipe, Reducer and Elbow Welds on Pressurizer Surge, Spray, Safety and Relief Nozzles Component Number(s): See Table 1 for listing Drawing Number(s): Unit 1: 1PZR-1-lSl (Pressurizer), 1RC-1-lSl SheetS (Surge Line), 1RC-l-ISI Sheet 16 (Spray Line), 1RC lSl Sheet 32 (Relief Lines), and 1RC-1-lSl Sheet 35 (Safety Line)

Unit 2: 2PZR-1 -ISI (Pressurizer), 2RC-1-lSl Sheet 5 (Surge Line), 2RC-1-lSl Sheet 16 (Spray Line), 2RC-l-ISI Sheet 32 (Relief Lines), and 2RC-1-lSl Sheet 35 (Safety Line) 2.0 APPLICABLE CODE EDITION AND ADDENDA The Inservice Inspection program is based on the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code, Section Xl, 2001 Edition through the 2003 Addenda.

3.0 APPLICABLE CODE REQUIREMENT ASME Section Xl, 2001 Edition, through 2003 Addenda, IWA-4000 requires that repairs be performed in accordance with the owners original construction Code of the component or system, or later editions and addenda of the Code. The pressurizer Code of Construction is ASME Section III, 1971 Edition through Summer 1973 Addenda, with Code Case NB-4643, 1493-1. The proposed alternative activities are supported by the requirements presented in:

ASME Code Case N-638-1 Similar and Dissimilar Metal Welding Using Ambient Temperature Machine ClAW Temper Bead Technique conditionally approved in Exe/on Byron Station

IS! Program Plan ____________ ____________________ Unitsl&  ?~Third In ten/al 10 CFR 50.55a RELIEF REQUEST 13R-08 Revision 0 (Page 2 of 30)

Nuclear Regulatory Commission (NRC) Regulatory Guide (RG) 1.147 Revision 14.

ASME Code Case N-504-2 Alternative Rules for Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping conditionally approved in RG 1.147 Revision 14.

In addition, ASME Code, Section Xl, 1995 Edition including Addenda through 1996, Appendix VIII Supplement 11 is used for examination qualification requirements of the final welded overlays.

4.0 REASON FOR THE REQUEST Dissimilar metal welds (DMWs), typically consisting ofAlloy 182 weld are frequently used in pressurized water reactors (PWR) construction to connect stainless steel pipe and safe ends to vessel nozzles, generally constructed of carbon or low alloy ferritic steel. These welds have shown a propensity for primary water stress corrosion cracking (PWSCC) degradation, especially in components subjected to higher operating temperatures, such as the pressurizer (PZR).

Exelon Generating Company, LLC (EGO), Byron Station Units 1 and 2 is proposing to take a proactive approach on the Byron Station Unit 1 and 2 Pressurizer and apply a preemptive Structural Weld Overlay (SWOL) on the Pressurizer Nozzle Safe-end to Nozzle Dissimilar Metal Welds to mitigate the occurrence of PWSCC prior to detectable evidence of PWSCC. Structural Weld Overlays (SWOL) have been used for several years on both boiling water reactors (BWR) and pressurized water reactors (PWR) to arrest existing flaws from propagating while establishing a new structural pressure boundary. In some cases, SWOLs have been used to reestablish structural integrity of the DMW containing through wall leaking flaws.

The SWOLs will also facilitate ultrasonic examination of the DMWs by providing a more consistent outer surface configuration from which scanning can be performed.

The welding will be performed using a remote mechanized Gas Tungsten-Arc Welding (GTAW) process and using the ambient temperature temper bead method with AWS Classification ERNiCrFe-7 (Alloy 52 or Alloy 52M*) weld metal. Manual GTAW, using Alloy 52 or Alloy 52M, will only be permitted subsequent to the SWOLs being essentially completed or to repair indications detected in base materials prior to overlay initiation. Also, Manual GTAW may be used if local repairs of weld defects are necessary or additional weld metal is required locally to form the final SWOL contour. Shielded Metal Arc Welds (SMAW), using AWS Classification ERNiCrFe-7 (Alloy 152), will be used only as needed to repair indications in base materials prior to overlay initiation.

• The material suppliers weld wire designation may be either 52M or 52MS. The S designates the process route that converts the hot-rolled billet into finished cold-drawn wire. The material properties are not Exe/on Byron Station

IS! Program Plan ________________ Units 1 &2, Third Interval 10 CFR 50.55a RELIEF REQUEST l3R-08 Revision 0 (Page 3 of 30) affected. For this reason, references herein to 52M are considered to encompass S2MS filler material as well.

As discussed herein, there is no comprehensive criterion for a licensee to apply a SWOL repair to a DMW that is constructed ofAlloy 82/182 weld material and is believed to be susceptible to or contain PWSCC degradation. Although the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), Section Xl, 2001 Edition, through 2003 Addenda, IWA-4000, is used for the Byron Unit 1 and 2 Section Xl Repair/Replacement Program, it does not contain the needed requirements for this type of weld overlay repair. Repair/replacement activities associated with weld overlays of this type are required to address the materials, welding parameters, personnel radiation exposure concerns, operational constraints, examination techniques and procedure requirements.

5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE EGO proposes using SWOLs designed in accordance with Code Cases N-504-2 (Reference 1) with the modifications proposed in Table 2. Code Case N-504-2, currently approved for use in RG 1.147 with additional requirements of ASME Section Xl, 2005 Addenda Appendix Q being required, allows a flaw to be reduced to an acceptable size by deposition of weld reinforcement on the outside surface of the pipe without flaw removal. The SWOLs will extend around the full circumference of the applicable DMWs as required by Code Case N-504-2. The specific thickness and length will be determined according to the guidance provided in Code Case N-504-2, The overlay will completely cover the DMWs and the adjacent stainless steel safe-end to pipe welds with Alloy 52 or Alloy 52M material that is highly resistant to PWSCC. A typical SWOL configuration is shown in Figure 1.

The temper bead welding technique for the specified nozzles adjacent to DMWs will be implemented in accordance with ASME Code Case N-638-1 (Reference 2) with the modifications proposed in Table 3.

The ultrasonic examination (UT) of the completed SWOL will be accomplished in accordance with ASME Section Xl, 1995 Edition with the 1996 Addenda, Appendix VIII Supplement 11 with the modifications described in Table 4. These modifications were developed by the EPRI Performance Demonstration Initiative (PDI) program to implement the requirements of Appendix VIII. These EPRI Supplement 11 modifications have previously been approved for use (see Reference 6).

6.0 DURATION OF THE PROPOSED ALTERNATIVE This relief request will be implemented during the remainder of Byron Station, Units 1 and 2 third ten-year inservice inspection interval.

ExeIon Byron Station

IS! Program Plan _______ ____ ____ Units 1 & 2, Third Interval 10 CFR 50.55a RELIEF REQUEST l3R-08 Revision 0 (Page 4 of 30) 7.0 PRECEDENT Similar relief requests have been previously approved for AmerGen Energy Company for its Three Mile Island Nuclear Station, Unit 1 in July, 2004, at Constellation Energys Calvert Cliffs Nuclear Power Plant, Unit 2 in July, 2005 and at Dominion Nuclear Connecticuts Millstone Power Station Unit 3 in October 2005.

These requests were associated with welding over detected flaws outside the acceptance criteria of Section Xl.

8.0 REFERENCES

1. ASME Code Case N-504-2, Alternative Rules for Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping, dated March 12, 1997.

2. ASME Code Case N-638-1, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique, dated February 13, 2003.

3. Letter from Richard Laufer, NRC to Christopher M. Crane, AmerGen, Three Mile Island Nuclear Station, Unit 1 (TMI-1) Request for Relief From Flaw, Heat Treatment, and Nondestructive Examination Requirements for the Third 10 year lnservice Inspection (ISI) Interval (TAC No. MC1O1), Accession Number ML041670510, dated July 21, 2004.

4. Letter from Richard J. Laufer, NRC to George Vanderheyden, Calvert Cliffs, Calvert Cliffs Nuclear Power Plant, Unit No. 2 Relief Request For Use Weld Overlay and Associated Alternative Inspection Techniques (TAO Nos. MC6219 and MC6220), Accession Number ML051930316, dated July 20, 2005.

5. Letter from L. Raghavan, NRC to Mano K. Nazar, l&M, Donald C. Cook Nuclear Plant, Unit 1 (DOCNP-1) Alternatives Regarding Repair of Weld 1 -PZR-23 on Pressurizer Nozzle to Valve Inlet Line (TAO No. MC6704), Accession Number ML053220019, dated December 1, 2005.

6. Letter from L. Raghavan, NRC, to Mano K. Nazar, l&M, Donald C. Cook Nuclear Plant, Unit 1 Alternative to Repair Requirements of Section Xl of the American Society of Mechanical Engineers Code (TAC No. MC06751), Accession Number ML051720006, dated June 27, 2005.

7. Letter from Leslie N. Hartz, Dominion Nuclear Connecticut, to NRC Document Control Desk, Dominion Nuclear Connecticut, Inc., Millstone Power Station Unit 3, Second 10-year Inservice Inspection Interval, Revision 1 to Relief Request IR-2-39, Use of Weld overlay and Associated Alternative Repair Techniques, Accession Number ML052930108, dated October 19, 2005.

8. Letter from Richard J. Laufer, NRC, to Bryce L. Shriver, PPL Susquehanna, Susquehanna Steam Electric Station, Unit 1 Relief from American Society of Mechanical Engineers, Boiler and Pressure Vessel Code (ASME Code), Section Xl Appendix VIII, Supplement 11, Requirements and Oases N-504-2 and N-638 Exe/on Byron Station

IS! Program Plan ______ Unitsl& 2, Third_Interval 10 CFR 50.55a RELIEF REQUEST 13R-08 Revision 0 (Page 5 of 30)

Requirements (TAO Nos. MC2450 and MC2594), Accession Number ML051220568, dated June 22, 2005.

9.0 ATTACHMENTS

1. RRA 05-08, BCO6-134, Technical Basis Paper N-638-x, Ambient Temperature Temperbead Welding: Begin 48 Hour Hold After 3~Layer Completion, authored by Bruce Newton, PCI Energy Services.

2. RRM-02-05, BCO4-1 003, Develop New Code Case to Address Inconel Weld Overlay on Various Materials, SIR-05-030, Rev. 0, Effect of Chromium Content on Nickel-base Alloy SOC Resistance Exelon Byron Station

IS! Program Plan _____ ___________ Unitsl& 2, Third Intenial 10 CFR 50.55a RELIEF REQUEST 13R-08 Revision 0 (Page 6 of 30)

TABLE I COMPONENT IDENTIFICATION For Unit I Pressurizer IRYOIS PIPING WELD SAFE-END IDENTIFICATION ITEM # SIZE CONFIGURATION ITEM #

(Line,_Weld)

Surge PN-01 Fl R1.11 14 1RY11AA-14, Safe-end to Pipe R1.11 R1.15 J1A Spray PN-02 F2 R1.11 4 1RYO1C-4, J1 6x4 Reducerto R1.11 R1.15 Safe-end Relief PN-03 F3 R1.15 6 IRYO2A-6, J1 Safe-end to Out 45° R1.20 Elbow Safety PN-04 F4 R1.1S 6 1RYO3AA-6, J1 Safe-end to Cut 90° R1.20 A Elbow Safety PN-05 ES R1.15 6 1RYO3AB-6, J1 Safe-end to Cut 90° R1.20 B Elbow Safety PN-06 E6 R1.15 6 1RYO3AC-6, J1 Safe-end to Cut 90° R1.20 C Elbow For Unit 2 Pressurizer 2RYOIS SAFE-END IDENTIFICATION ITEM # SIZE PIPING WELD CONFIGURATION ITEM #

(Line,_Weld)

Surge PN-01 El Rl.11 14 2RY11AA-l4, Safe-endto Pipe R1.1l R1.15 J1 Spray PN-02 E2 R1.1l 4 2RYO1C-4, Jl 6x4 Reducer to Rl.ll Rl.15 Safe-end Relief PN-03 E3 Rl.lS 6 2RYO2A-6, J1 Safe-end to Cut 45° Rl.20 Elbow Safety PN-04 E4 Rl.15 6 2RYO3AA-6, J1 Safe-end to Cut 90° Rl.20 A Elbow Safety PN-05 ES R1.l5 6 2RYO3AB-6, Jl Safe-end to Cut 90° Rl.20 B Elbow Safety PN-06 E6 R1.15 6 2RYO3AC-6, Jl Safe-end to Cut 90° R1.20 0 Elbow Note: Item numbers reflect Risk-Informed classification per ASME Code Case N-578-1.

Ri. ii: Elements Subject to Thermal Fatigue.

Ri.iS: Elements Subject to Primary Water Stress Corrosion Cracking.

Ri20: Elements not Subject to a Damage Mechanism.

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Figure 1 Typical SWOL Configuration SS Eli (SA-182 F316L)

SWOL (A52~

EJNozzle Weld Class 2)

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TABLE 2 DESIGN I MATERIAL I NONDESTRUCTIVE EXAMINATION Modifications to Code Case N-504-2 and ASME Section Xl, Appendix Q CODE CASE N-504-2 AND ASME SECTION XI APPENDIX Q Reply: It is the opinion of the Committee that, Modification: Oode Oase N-504-2 and Appendix in lieu of the requirements of IWA-4120 in Q will be used for the weld overlay of the ferritic Editions and Addenda up to and including the (P3) nozzle material, nickel alloy (F43/P43) 1989 Edition with the 1990 Addenda, in IWA- weld material, and austenitic stainless steel 4170(b) in the 1989 Edition with the 1991 base (P8, safe end and pipe) and weld Addenda up to and including the 1995 Edition, materials.

and in IWA-4410 in the 1995 Edition with the Basis: Oode Oase N-504-2 is accepted for use 1995 Addenda and later Editions and in the current NRC Regulatory Guide 1.147 Addenda, defect in austenitic stainless steel Rev. 14, and has been used extensively in piping may be reduced to a flaw of acceptable BWR primary system piping. More recently, N-size in accordance with IWB-3640 from the 504-2 has been applied to PWR applications, 1983 Edition with the Winter 1985 Addenda, or with modifications, for the weld overlay repair of later Editions and Addenda, by deposition of dissimilar metal welds with known flaws.

weld reinforcement (weld overlay) on the Industry operating experience in the area has outside surface of the pipe, provided the shown that PWSOO in Alloy 82/182 will arrest at following requirements are met. the interface with stainless steel base metal, ferritic base metal, or Alloy 52/52M/1 52 weld metal. The 360°full structural weld overlay will control growth in any PWSCC crack and maintain weld integrity. The weld overlay will also induce compressive stress in the weld, thus potentially impeding growth of any reasonably shallow cracks. Furthermore, the overlay will be sized to meet all structural requirements without considering the existing 82/1 82 weld.

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TABLE 2 DESIGN / MATERIAL I NONDESTRUCTIVE EXAMINATION Modifications to Code Case N-504-2 and ASME Section Xl, Appendix Q CODE CASE N-504-2 AND ASME PROPOSED MODIFICATIONS SECTION XI APPENDIX Q b) Reinforcement weld metal shall be low Modification: Weld overlay filler metal shall be carbon (0.035% maximum) austenitic stainless an austenitic nickel alloy (28% Or mm.) applied steel applied 360°around the circumference of 360°around the circumference of the item, and the pipe, and shall be deposited in accordance shall be deposited using a Welding Procedure with a qualified welding procedure specification Specification for groove welding, qualified in identified in the Repair Program [essentially accordance with the Repair/Replacement Code same as Q-2000(a)}. and Owners requirements and identified in the Repair /replacement Plan.

Basis: Industry operational experience has shown that PWSOO in Alloy 82/1 82 will blunt at the interface with stainless steel base metal, ferritic base metal, or Alloy 52/52M/152 weld metal.

e) The weld reinforcement shall consist of a Modification: Delta ferrite measurements will minimum of two weld layers having as not be performed for this overlay.

deposited delta ferrite content of at least 7.5N. The first two layers will be credited as part of The first layer of weld metal with delta ferrite the required weld overlay thickness and will not content of at least 7.5N shall constitute the first be considered as sacrificial layers.

layer of the weld reinforcement design Basis: The deposited Alloy 52 or Alloy 52M is thickness. Alternatively, first layers of at least 100% austenitic and contains no delta ferrite 5FN may be acceptable based on evaluation due to the high nickel composition

[essentially the same as Q2000(d) except if the (approximately 60% nickel) The austenitic nickel deposited weld metal has a carbon content of alloy weld overlay shall consist of at least two

<0.02% the first layers of at least 5FN are weld layers deposited using a filler material with acceptable]. a Or content of at least 28%. For applications addressed by this request, when welding over, a diluted first layer of at least 24% Or is considered acceptable, provided the Or content of the deposited weld metal is determined by chemical analysis of a representative coupon.

[ (Refer to Attachment 1 for details).

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TABLE 2 DESIGN I MATERIAL I NONDESTRUCTIVE EXAMINATION Modifications to Code Case N-504-2 and ASME Section Xl, Appendix Q CODE CASE N-504-2 AND ASME PROPOSED MODIFI SECTION Xl APPENDIX Q h) The completed repair shall be pressure Modification: In lieu of hydrostatic testing, a tested in accordance with IWA-5000. If the system leakage test and an ultrasonic flaw penetrated the original pressure boundary examination (UT) of the weld overlay shall be prior to welding, or if any evidence of the flaw performed in accordance with the Byron Station penetrating the pressure boundary is observed Third Interval ISI Program.

during welding operation, a system hydrostatic Basis: Byron Station Third Interval ISI Program test shall be performed in accordance with is to the ASME 2001 Edition, through 2003 IWA-5000. If the system pressure boundary Addendum, which does not require a hydrostatic has not been penetrated, a system leakage, test. The combination of the system leakage inservice, or functional test shall be performed test and the ultrasonic examination of the weld in accordance with IWA-5000. overlay are sufficient to demonstrate that the overlay is of adequate quality to ensure pressure boundary integrity.

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TABLE 3 AMBIENT TEMPERATURE TEMPER BEAD WELDING Modifications to Code Case N-638-1 CODE CASE N-638-1 PROPOSED MODIFICATIONS (a) The maximum area of an individual weld Modification: The maximum area of an based on the finished surface shall be 100 sq. individual weld based on the finished surface in., and the depth of the weld shall not be over the ferritic material will exceed 100 sq. in.

greater than one-half of the ferritic base metal and will be on the order of 300 sq. in. The one thickness. half base metal thickness limitation applies only to excavation and repair and is not applicable to this application.

Basis: The SWOL will require welding on more than 100 sq. in. of surface on the low alloy steel base material. The SWOL will extend to the transition taper of the low alloy steel nozzle so that qualified UT of the required volume can be performed.

There have been a number of temper bead WOL repairs applied to safe-end to nozzle welds in the nuclear industry, and a SWOL repair having a 300 sq. in. surface was recently approved for the Susquehanna Steam Electric Station (Reference 9).

ASME Code Case N-432-1, which is approved for use in RG 1.147, allows temper bead welding on low alloy steel nozzles without limiting the temper bead weld surface area.

The two additional conditions required by Oode Oase N-432-1 that are not required by Code Case N-638-1 are that temper bead welds have preheat applied and that the procedure qualification be performed on the same specification, type, grade and class of material.

The elevated preheat would present a radiation exposure burden when performing the repair.

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TABLE 3 AMBIENT TEMPERATURE TEMPER BEAD WELDING Modifications to Code Case N-638-1 CODE CASE N-638-I PROPOSED MODIFICATIONS 4M EXAMINATION _________________________

(b) The final weld surface and the band around Modification: For the SWOLs, full UT of the the area defined in para. 1.0(d) shall be 1 .5T band will not be performed. UT will be examined using surface and ultrasonic methods performed on the actual weld overlay, meeting when the completed weld has been at ambient the requirements of ASME Section Xl, NMA temperature for at least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. The Appendix Q-4100.

ultrasonic examination shall be in accordance When austenitic filler materials are used, the with Appendix I. weld overlay will be examined using a surface and ultrasonic methods when the three tempering weld layers (i.e., layers 1, 2, and 3) are completed and have been in place for at least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />.

Basis: Later additions of the ASME Section Xl code and the next revision to code case N-638(-

2) removed the requirement for the 1 .5T requirement. This is in line with the less restrictive requirements for UT of the ferritic nozzle due to hydrogen cracking that is not considered an issue in later additions of the ASME Section XI code and code case N-638.

The code case applies to any type of welding where a temper bead technique is to be employed and is not specifically written for a SWOL repair. However, it is believed that for this type of repair, any major base material cracking would take place in the heat-affected zone directly below the weld overlay or in the underlying Alloy 82/1 82 weld deposit and not in the required band of material out beyond the overlay. Therefore, it is assumed that if this cracking were to occur, it would be identified by the UT of the SWOL.

A white paper in support of a proposed revision to Code Case N-638-x, enabling 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold initiation after layer 3 installation is provided as Attachment 2.

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TABLE 4 MODIFICATIONS TO APPENDIX VIII, SUPPLEMENT II Appendix VIII, Supplement II PDI Modification 1.0 SPECIMEN REQUIREMENTS (b) The specimen set shall consist of at least (b) The specimen set shall consist of at least three specimens having different nominal pipe three specimens having different nominal pipe diameters and overlay thick nesses. They shall diameters and overlay thick nesses. They shall include the minimum and maximum nominal include the minimum and maximum nominal pipe diameters for which the examination pipe diameters for which the examination procedure is applicable. Pipe diameters within procedure is applicable. Pipe diameters within a range of 0.9 to 1.5 times a nominal diameter a range of 0.9 to 1.5 times a nominal diameter shall be considered equivalent. If the procedure shall be considered equivalent. If the procedure is applicable to pipe diameters of 24 inches or is applicable to pipe diameters of 24inches or larger, the specimen set must include at least larger, the specimen set must include at least one specimen 24 inches or larger but need not one specimen 24 inches or larger but need not include the maximum diameter. The specimen include the maximum diameter.

set must include at least one specimen with The specimen set shall include specimens with overlay thickness within 0.1 inches to +0.25 overlays not thicker than 0.1 inches more than inches of the maximum nominal overlay the minimum thickness, nor thinner than 0.25 thickness for which the procedure is applicable. inches of the maximum nominal overlay thickness for which the procedure is applicable.

(d) Flaw Conditions (1) Base metal flaws. All flaws must be cracks (1) Base metal flaws. All flaws must be cracks in or near the butt weld heat-affected zone, in or near the butt weld heat-affected zone, open to the inside surface, and extending at open to the inside surface, and extending at least 75 percent through the base metal wall. least 75 percent through the base metal wall.

Flaws may extend 100 percent through the Intentional overlay fabrication flaws shall not base metal and the overlay; in this case, interfere with ultrasonic detection or intentional overlay fabrication flaws shall not characterization of the base metal flaws.

interfere with ultrasonic detection or Specimens containing IGSCC shall be used characterization of the cracking. Specimens when available. At least 70 percent of the flaws containing IGSOC (intergranular stress in the detection and sizing tests shall be cracks corrosion cracking) shall be used when and the remainder shall be alternative flaws.

available. Alternative flaw mechanisms, if used, shall provide crack-like reflective characteristics and shall be limited by the following:

(a) The use of Alternative flaws shall be limited to when the implantation of cracks produces spurious reflectors that are uncharacteristic of actual flaws.

(b) Flaws shall be semi elliptical with a tip width of less than or equal to 0.002 inches.

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TABLE 4 MODIFICATIONS TO APPENDIX VIII, SUPPLEMENT 11 Appendix VIII, Supplement 11 PDI Modification (e) Detection Specimens (1) At least 20 percent but less than 40 percent (1) At least 20- percent but less than 40 percent of the flaws shall be oriented within +/- 20 of the base metal flaws shall be oriented within degrees of the pipe axial direction. The +/- 20 degrees of the pipe axial direction. The remainder shall be oriented circumferentially. remainder shall be oriented circumferentially.

Flaws shall not be open to any surface to which Flaws shall not be open to any surface to which the candidate has physical or visual access. the candidate has physical or visual access.

The rules of IWA-3300 shall be used to determine whether closely spaced flaws should be treated as single or multiple flaws.

(2) Specimens shall be divided into base and (2) Specimens shall be divided into base metal over-lay grading units. Each specimen shall and overlay fabrication grading units. Each contain one or both types of grading units. specimen shall contain one or both types of grading units. Flaws shall not interfere with ultrasonic detection or characterization of other flaws.

(a)(1) A base grading unit shall include at least (a)(1) A base metal grading unit includes the 3 inches of the length of the overlaid weld. The overlay material and outer 25 percent of the base grading unit includes the outer 25 percent original overlaid weld. The base metal grading of the overlaid weld and base metal on both unit shall extend circumferentially for at least 1 sides. The base grading unit shall not include inch and shall start at the centerline and be the inner 75 percent of the overlaid weld and wide enough in the axial direction to encompass base metal overlay material, or base metal-to- one half of the original weld crown and a overlay interface, minimum of 0.50 inch of the adjacent base material.

(a)(2) When base metal cracking penetrates (a)(2) When base metal flaws penetrate into the into the overlay material, the base grading unit overlay material, the base metal grading unit shall include the overlay metal within 1 inch of shall not be used as part of any overlay the crack location. This portion of the overlay fabrication grading unit.

material shall not be used as part of any overlay grading unit.

(a)(3) When a base grading unit is designed to (a)(3) Sufficient unflawed overlaid weld and be unflawed, at least 1 inch of unflawed overlaid base shall exist on all sides of the grading unit weld and base metal shall exist on either side of to preclude interfering reflections from adjacent the base grading unit. The segment of weld flaws.

length used in one base grading unit shall not be used in another base grading unit. Base grading units need not be uniformly spaced around the specimen.

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TABLE 4 MODIFICATIONS TO APPENDIX VIII, SUPPLEMENT 11 Appendix VIII, Supplement 11 PDI Modification (b)(1) An overlay grading unit shall include the (b)(1) An overlay fabrication grading unit shall overlay material and the base metal-to-overlay include the overlay material and the base metal-interface of at least 6 square inches. The to-overlay interface for a length of at least 1 overlay grading unit shall be rectangular, with inch.

minimum dimensions of 2 inches.

(b)(2) An overlay grading unit designed to be (b)(2) Overlay fabrication grading units unflawed shall be surrounded by unflawed designed to be unflawed shall be separated by overlay material and unflawed base metal-to- unflawed overlay material and unflawed base overlay interface for at least 1 inch around its metal-to-overlay interface for at least 1 inch at entire perimeter. The specific area used in one both ends. Sufficient unflawed overlaid weld overlay grading unit shall not be used in another and base metal shall exist on both sides of the overlay grading unit. Overlay grading units overlay fabrication grading unit to prelude need not be spaced uniformly about the interfering reflections from adjacent flaws. The specimen. specific area used in one overlay fabrication grading unit shall not be used in another overlay fabrication grading unit. Overlay fabrication grading units need not be spaced uniformly about specimen.

(b)(3) Detection sets shall be selected from (b)(3) Detection sets shall be selected from Table VIII-S2-1. The minimum detection Table Vlll-S2-1. The minimum detection sample set is five flawed base grading units, ten sample set is five flawed base metal grading unflawed base grading units, five flawed overlay units, ten unflawed base metal grading units, grading units and ten unflawed grading units. five flawed overlay fabrication grading units, and For each type of grading unit, the set shall ten unflawed overlay fabrication grading units.

contain at least twice as many unflawed as For each type of grading unit, the set shall flawed grading units. contain at least twice as many unflawed grading units. For initial procedure qualification, detection sets shall include the equivalent of three personnel qualification sets. To qualify new values of essential variables, at least one personnel qualification set is required.

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TABLE 4 MODIFICATIONS TO APPENDIX VIII, SUPPLEMENT 11 Appendi x VIII, Supplement II PDI Modification (f) Sizing Specimen (1) The minimum number of flaws shall be ten. (1) The minimum number of flaws shall be ten.

At least 30 perce nt of the flaws shall be overlay At least 30 percent of the flaws shall be overlay fabrication flaws. At least 40 percent of the fabrication flaws. At least 40 percent of the flaws shall be cracks open to the inside surface. flaws shall be open to the inside surface. Sizing sets shall contain a distribution of flaw dimensions to assess sizing capabilities. For initial procedure qualification, sizing sets shall include the equivalent of three personnel qualification sets. To qualify new values of essential variables, at least one personnel qualification set is required.

(3) Base metal cracking used for length sizing (3) Base metal flaws used for length sizing demonstrations shall be oriented demonstrations shall be oriented circumferentially. circumferentially.

(4) Depth sizing s pecimens sets shall include at (4) Depth sizing specimen sets shall include at least two distinct locations where cracking in the least two distinct locations where a base metal base metal exten ds into the overlay material by flaw extends into the overlay material by at least at least 0.1 inch i n the through-wall direction. 0.1 inch in the through-wall direction.

2.0 CONDUCT OF PERFORMANCE DEMONSTRATION The specimen ins ide surface and identificatkn The spec~meninside surface and identification shall be conceale d form the candidate. All shall be concealed from the candidate. All examinations sha II be completed prior to examinations shall be completed prior to grading the results and presenting the results to grading the results and presenting the results to the candidate. Divulgence of particular the candidate. Divulgence of particular specimen results or candidate review of specimen results or candidate viewing of unmasked specimens after the performance unmasked specimens after the performance demonstration is prohibited. demonstration is prohibited. The overlay fabrication flaw test and the base metal flaw test may be performed separately.

2.1 Detection Test Flawed and unflawed grading units shall be Flawed and unflawed grading units shall be randomly mixed. Although the boundaries of randomly mixed. Although the boundaries of specific grading units shall not be revealed to specific grading units shall not be revealed to the candidate, the candidate shall be made the candidate, the candidate shall be made aware of the type or types of grading units aware of the type or types of grading units (base or overlay) that are present for each (base metal or overlay fabrication) that are specimen. present for each specimen.

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TABLE 4 MODIFICATIONS TO APPENDIX VIII, SUPPLEMENT II Appendix VIII, Supplement 11 PDI Modification 2.2 Length Sizing Test (d) For flaws in base grading units, the (d) For flaws in base metal grading units, the candidate shall estimate the length of that part candidate shall estimate the length of that part of the flaw that is in the outer 25 percent of the of the flaw that is in the outer 25 percent of the base wall thickness. base metal wall thickness.

2.3 Depth Sizing Test For the depth sizing test, 80 percent of the flaws (a) The depth sizing test may be conducted shall be sized at a specific location on the separately or in conjunction with the detection surface of the specimen identified to the test.

candidate. For the remaining flaws, the regions (b) When the depth sizing test is conducted in of each specimen containing a flaw to be sized conjunction with the detection test and the shall be identified to the candidate. The detected flaws do not satisfy the requirements candidate shall determine the maximum depth of 1.1(f), additional specimens shall be provided of the flaw in each region. to the candidate. The regions containing a flaw to be sized shall be identified to the candidate.

The candidate shall determine the maximum depth of the flaw in each region.

(c) For each separate depth sizing test, the regions of each specimen containing a flaw to be sized shall be identified to the candidate.

The candidate shall determine the maximum depth of the flaw in each region.

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TABLE 4 MODIFICATIONS TO APPENDIX VIII, SUPPLEMENT 11 Appendix VIII, Supplement II P01 Modification 3.0 ACCEPTANCE CRITERIA 3.1 Detection Acceptance Criteria Examination procedures, equipment, and a) Examination procedures are qualified for personnel are qualified for detection when the detection when; results of the performance demonstration satisfy 1) All flaws within the scope of the procedure the acceptance criteria of Table Vll-S2-1 for are detected and the results of the performance both detection and false calls. The criteria shall demonstration satisfy the acceptance criteria of be satisfied separately by the demonstration Table VIl-S2-1 for false calls.

results for base grading units and for overlay (a) At least one successful personnel gradIng unlts. demonstration has been performed meeting the acceptance criteria defined in (b).

(b) Examination equipment and personnel are qualified for detection when the results of the performance satisfy the acceptance criteria of Table Vll-S2-1 for both detection and false calls.

(c) The criteria in (a), (b) shall be satisfied separately by the demonstration results for base metal grading units and for overlay fabrication grading units.

3.2 Sizing Acceptance Criteria (a) The RMS error of the flaw length (a) The RMS error of the flaw length measurements, as compared to the true flaw measurements, as compared to the true flaw length, is less than or equal to 0.75 inch. The lengths, is less than or equal 0.75 inch. The length of base metal cracking is measured at length of base metal flaws is measured at the the 75 percent through-base-metal position. 75 percent through-base-metal position.

(b) All extensions of base metal cracking into This requirement is omitted.

the overlay material by at least 0.1 inch are reported as being intrusions into the overlay material.

(c) The RMS error of the flaw depth (c) The RMS error of the flaw depth measurements, as compared to the true flaw measurements, as compared to the true flaw depths, is less than or equal to 0.125 inch. depths, is less than or equal to 0.125 inch Exelon Byron Station

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ATTACHMENT I RRM-02-05, BCO4-1 003, Develop New Code Case to Address Inconel Weld Overlay on Various Materials, SIR-05-030, Rev. 0, Effect of Chromium Content on Nickel-base Alloy SCC Resistance Note: Attachment 1 is referenced on page 9, Table 2: Design / Material / Nondestructive Examination, Modifications to Code Case N-504-2 and ASME Section Xl, Appendix Q.

1. Introduction This evaluation provides a technical basis to establish a minimum chromium content for an overlay layer to be considered resistant to Inter Granular Stress Corrosion Cracking (IGSCC) in boiling water reactors (BWR) environment as well as resistant to Primary Water Stress Corrosion Cracking (PWSCC) in the pressurized water reactors (PWR) environment. Experimental work was performed in the 1980s to study crack initiation in BWR environments for creviced Alloy 600 and its filler alloys, 82 and 182. In addition, field experience on the use of this family of alloys has been good, absent a crevice, in BWR service. More recently work has been done by the Japanese to develop a stress corrosion resistivity index (SCRI) [8].

The only well established correlation between primary water stress corrosion cracking (PWSCC) propensities and nickel-based alloys and weld metal composition is the chromium content of the alloy [1]. However, there have been very few systematic studies to determine the minimum chromium content for PWSCC mitigation in either wrought materials or weld metals. Most studies have involved a straightforward comparison of Alloy 600 with 14-17% chromium and Alloy 690 with 28-31% chromium with no testing of custom nickel-chromium-iron alloys whose chromium content falls in between these two alloys.

This absence creates a chromium composition gap between the susceptible Alloy 600/182/82 and very resistant Alloy 690/152/52.

Table 1-1 presents the nominal chemical compositions of nickel-base weld metals plus reference wrought Alloys 690 and 600 for each weld metal, i.e., Alloys 52, 152 and 72 for Alloy 690 and Alloys 82, 182, and 132 for Alloy 600 [2-5]. Based on chromium content, it would be anticipated that weld metals Alloys 52, 152 and 72 would be the most PWSOO resistant and this hypothesis has been verified by experiment. It is noted that Alloy 52M has the same chromium content as Alloy 52 and should be considered equivalent. Alloy 52M is a variant of Alloy 52 having increased Niobium (Nb) to improve weldability.

2. Discussion 2.1. Investigations of IGSCC in a BWR Environment The relative susceptibilities of wrought Alloys 600 and 690 and weld metals Alloys 52 (R-127), 152 (R-135), 82 and 182 to IGSOC in pure or simulated resin intrusion BWR environments at 550°F have been investigated [6, 7]. Constant Extension Rate Test Exe/on Byron Station

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ATTACHMENT 1 RRM-02-05, BCO4-1 003, Develop New Code Case to Address Inconel Weld Overlay on Various Materials, SIR-05-030, Rev. 0, Effect of Chromium Content on Nickel-base Alloy SCC Resistance (CERTs) for IGSCC initiation evaluations were conducted in high purity water containing 200 ppb or 8 ppm dissolved oxygen for uncreviced specimens and 16 ppm dissolved oxygen for graphite wool/nickel foil creviced specimens. Uncreviced Alloys 600, 690, 82 and 182 demonstrated resistance to IGSCC in oxygenated environments (no cracking).

Creviced Alloys 600 and 182 did suffer IGSCC and Inter Dendritic Stress Corrosion Cracking (IDSOC), respectively, while creviced Alloy 82 suffered Inter Granular Attack (IGA). Creviced Alloy 690 exhibited no susceptibility to IGSCC initiation in this CERT study. Types 316 NG and 308L stainless steel and Alloys 72, 52 (R-127) and 152 (R-l35) were also found to resist IGSCC in this investigation.

Similar to the CERT studies described above, twenty constant load specimens of the same materials were tested at 1.25 and 1.5 times the 550 °Fyield stress in high purity water containing 200 ppb or 8 ppm dissolved oxygen for uncreviced specimens and 16 ppm dissolved oxygen for graphite wool/nickel foil creviced specimens. Although no IGSCC was detected during the 8200-hour exposure, post-test examination of the specimens revealed grooving of machining marks on the specimens surface. The grooves seemed to be the result of localized attack of machining marks and resembled linear crevices. A number of cracks <1 mil deep were associated with the grooving. Since the cracking was only identified with the grooves and not the smooth surface, it appeared that IGSCC susceptibility was related only to the presence of the crevice. Surface grooves accompanied by small cracks were present on all Alloy 600 or 182 specimens. No IGSCC of Alloy 690 or 82 was identified. Furthermore, neither cracks nor grooves were identified underneath the graphite crevice on the Alloy 690 specimens.

2.2. Stress Corrosion Resistivity Index (SCRI)

The SCRI was developed based on the results of creviced bent beam (OBB) tests where the beneficial effect of chromium content on IGSCC resistance is indeed factored into the materials resistance ranking [8]:

SORI = %Cr + 5[%Nb] + l0[%Ti] 1 16.S[%C]

Cr, Nb, Ti and 0 are individual weight percentages of these alloying elements.

To assure strong resistance to IGSCC in the BWR environment, a criterion of SCRI >34 is used.

If one calculates the SCRI for Alloy 82 and Alloy 182, the respective values are 32.85 versus 22.85. This is further evidence of the superior resistance to IGSOC for Alloy 82.

Alloy 52 and Alloy 152 produce even higher values. The Alloy 52M variant of Alloy 52 has higher Nb with the same Or level and thus results in even higher SCRI ranking.

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ATTACHMENT I RRM-02-05, BCO4-1 003, Develop New Code Case to Address Inconel Weld Overlay on Various Materials. SIR-05-030, Rev. 0, Effect of Chromium Content on Nickel-base Alloy SCC Resistance Chromium Content Threshold for PWSCC Resistance To determine the threshold chromium content of a nickel-base weld metal to mitigate PWSCC, it is necessary to review the limited test results obtained in PWR environments and also examine the results from tests on wrought nickel alloys. Note that some information was obtained in oxygenated environments. However, these data are also largely characterized by Alloy 600 versus Alloy 690 investigations.

The PWSCC resistance of nickel-based weld metals with various chromium contents ranging from approximately 15% to 30% chromium has been evaluated [1,9]. Testing was performed on U-bend specimens exposed to impurity doped steam and primary water.

Alloy 182, with approximately 14.5% chromium, was the most susceptible to PWSCC while Alloy 82 with 1820% chromium took three or four times longer to initiate PWSCC. For example, PWSCC appeared in one of the Alloy 182 specimens at the first test interruption after 500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br /> of exposure and the second specimen cracked after 1,500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br />. The first Alloy 82 specimen cracked after 2,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> and all were cracked at 6,500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br />. For chromium contents between 21 and 22%, no PWSCO initiation was observed for tests lasting between 18,000 and 27,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />. This was also the case for Alloys 52 and 152 that have approximately 30% chromium. These results indicated that weld metals having 30% chromium were very resistant to PWSCC. Thus a threshold for PWSCC resistance appears to exist somewhere between 21% and 30% chromium.

The above PWSCC behavior for nickel base alloys is consistent with test results on solution annealed wrought Ni-Cr-Fe base alloys (i.e., higher chromium content provides more PWSCC resistance) [1, 101. Constant load tests were used to evaluate the effect of chromium content on the PWSCC susceptibility of wrought Ni-Cr-Fe alloys in 680°F (360°C)water. The constant load specimens were loaded at an applied stress 2.4 times the 0.2% proof stress. Figure 1-1 clearly demonstrates that the PWSCC initiation susceptibility decreased as the chromium content increased from approximately 1% to over 15% [1,10]. Unfortunately, this study did not evaluate higher chromium alloys (e.g., 18-22% Cr).

To possibly identify a chromium content threshold for PWSOC mitigation, it is necessary to discuss a more fundamental mechanistic experiment. Alloy 600 obtained from a vessel head penetration containing 16.05% chromium and Alloy 690 obtained from a steam generator tube plug containing 29.14% chromium were tested in simulated PWR primary water (1200 ppm B and 2 ppm Li) at 680 °F(360 °O)under electrochemical conditions corresponding to Ni/NiO equilibrium potential. The Ni/NiO equilibrium potential corresponds to a maximum susceptibility of Alloy 600 to the initiation of PWSCC [11]. The resulting oxidized structures (corrosion scale and underlying metal) were examined by Exe/on Byron Station

IS! Program Plan Units I & 2, Third Interval 10 CFR 50.55a RELIEF REQUEST 13R-08 Revision 0 (Page 22 of 30)

ATTACHMENT I RRM-02-05, BCO4-1 003, Develop New Code Case to Address Inconel Weld Overlay on Various Materials, SIR-05-030, Rev. 0, Effect of Chromium Content on Nickel-base Alloy SCC Resistance transmission electron microscopy (TEM) using cross section specimens. The oxide on Alloy 600 consisted of small 50 nm Ni(Cr,Fe)204 and large 200 nm NiFe2O4 crystallite oxides, while the oxide on Alloy 690 consisted of small 30 nm Ni(Cr,Fe)2O4 and large 100 nm NiFe2O4 crystallite oxides. Alloy 690s oxide film was 50% thinner than Alloy 600s oxide film, which is characteristic of a more rupture resistant and protective oxide film.

For both alloys, energy dispersive X-ray spectroscopy (EDX) analysis revealed a chromium rich oxide layer where the underlying metal was chromium depleted. In both alloys a non-compact external oxide scale was identified, and a thin continuous inner layer rich in chromium was observed. Consequently, a chromium depleted zone just in the underlying alloy was observed. For Alloy 600, the particular importance of the depletion was found to be also associated with the presence of oxygen. Chromium oxide was even found in a triple grain boundary as far as 3 pm from the metal-oxide interface.

These test results tend to support the crack initiation mechanism induced by intergranular oxidation of the chromium-depleted zones [123. Assuming that this mechanism is operative in these exposure conditions, it is then possible to explain, at least in terms of local reactivity, the effect of the carbide precipitation sites (transgranular- intergranular) on the crack initiation resistance of Alloy 600 exposed to PWR experimental conditions. Most importantly for this evaluation, when considering Alloy 690, despite its chromium depletion from 29% to 17% in the underlying alloy, the chromium content remains sufficiently high that an intergranular oxidation mechanism cannot be operative because the chromium content is greater than the 10% chromium needed to mitigate intergranular oxidation [13].

Thus, the excellent resistance of Alloy 690 to PWSCC can be explained. In contrast, Alloy 600 suffers PWSCC because its chromium content is also reduced by approximately 11 to 12% from a starting level of 16%. This reduces the chromium level to 5% a level that is below the 10% chromium threshold for internal oxidation.

The oxide mechanistic study results suggest that a chromium depletion of 11 to 12%

occurs in nickel-base wrought alloys exposed to PWR environments under environmental conditions that clearly support and promote PWSCC. Since the internal oxidation threshold for these alloys is approximately 10% chromium, then an additional 11 to 12%

chromium should be present in the starting material to mitigate PWSCC. This suggests that an initial concentration of 21 to 22% chromium should be sufficient to mitigate PWSCO.

This threshold value is consistent with the U-bend test results that indicated weld metals having 22 and 30% chromium were very resistant to PWSCC. The results from the above Alloy 82 studies suggest that 18 to 20% chromium is insufficient to mitigate cracking.

However, since the required chromium content to mitigate cracking must exceed 22%, and Exe/on Byron Station

ISI Program Plan Units I & 2, Third Interval 10 CFR 50.55a RELIEF REQUEST l3R-08 Revision 0 (Page 23 of 30)

ATTACHMENT I RRM-02-05, BCO4-1 003, Develop New Code Case to Address Inconel Weld Overlay on Various Materials, SIR-05-030, Rev. 0, Effect of Chromium Content on Nickel-base Alloy SCC Resistance the Alloy 82 specification permits up to 22% chromium [1], then the required chromium required to mitigate cracking must exceed 22%.

3. Conclusion 3.1. BWR Applications Testing and field service has shown that Alloy 600, Alloy 82 and 182 are all reasonably resistant to IGSCC. In the creviced condition test results and field service have shown that Alloy 600 and Alloy 182 have cracked where Alloy 82 has remained uncracked. The SCRI has shown that Alloy 82 is more resistant than Alloy 182 or Alloy 600. To provide some IGSCC margin, it is recommended that a minimum of 20% chromium be present in the first overlay layer considered resistant to IGSCC.

3.2. PWR Applications Considering the paucity of data and fragmentary nature of the available data on the effects of chromium on PWSCC, the relevant available test data plus a mechanistic analysis has been combined to suggest that the threshold chromium content for PWSCC mitigation will be somewhere greater than 22% chromium. Therefore a conservative estimate of the chromium threshold to mitigate PWSCO is 24%. This level of chromium would be considered as a minimum in the first overlay layer to be considered resistant to PWSCC.

Exe/on Byron Station

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ATTACHMENT I RRM-02-05, BCO4-1 003, Develop New Code Case to Address Inconel Weld Overlay on Various Materials, SIR-05-030, Rev. 0, Effect of Chromium Content on Nickel-base Alloy SCC Resistance Table 1-1 Compositions of Nickel-base Alloys and Weld Metals Alloy 52 Alloy 152 Alloy 72 Alloy 132II-Alloying Alloy 690 Alloy 82 Alloy 182 electrode filler metal electrode) filler metal Alloy 600 [5]

Element (Nuclear) [2] filler metal [3} electrode [3]

[3] [3] (nominal) [4] 3]

Ni + Co 58.0 mm. Balance Balance 55 72.0 mm. 67.0 mm. 59.0 mm. 62.0 mm C 0.04 max. 0.04 max, 0.05 max. 0.05 0.15 max. 0.10 max. 0.10 max. 0.08 max Mn 0.Smax. l.Omax. 5.Omax. 0.1 l.O0max. 2.5-3.5 5.0-9.5 3.Smax Fe 7.0-11.0 7.0-11.0 7.0-12.0 0.2 6.00-11.00 3.Omax. l0.Omax. ll.Omax S 0.OlSmax. 0.OlSmax. 0.OlSmax. 0.008 0.Ol5max. 0.OlSmax. 0.OlSmax. 0.O2max Si 0.50 max. 0.50 max. 0.75 max. 0.1 0.50 max. 0.50 max. 1.0 max. 0.75 max Mo 0.S0max. 0.S0max.

Cu 0.50 max. 0.30 max. 0.50 max. 0.20 0.50 max. 0.50 max. 0.50 max. 0.50 max Cr 28.0-31.0 28.0-31.5 28.0-31.5 44.0 14.0-17.0 18.0-22.0 13.0-17.0 13.0-17.0 Ti l.Omax. 0.50 max. 0.6 0.75 max. 1.Omax.

Al 1.l0max. 0.S0max.

P 0.020 max. 0.030 max. 0.030 max. 0.030 max. 0.03 max Nb + Ta 0.10 max. 1.0-2.5 2.0-3.0 1.0-2.5 1.5-4.0 Al+Ti 1.Smax.

Others 0.50 max. 0.50 max. 0.50 max. 0.50 max. 0.50 niax Exe/on Byron Station

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ATTACHMENT I RRM-02-05, BCO4-I 003, Develop New Code Case to Address Inconel Weld Overlay on Various Materials, SIR-05-030, Rev. 0, Effect of Chromium Content on Nickel-base Alloy SCC Resistance 5,000 1,000

.~

500 100 50 0 5 10 15 Cr Content,  %

Figure 1-1. Effect of Chromium Content on the Stress Corrosion Cracking Resistance of Solution Annealed Ni-Cr-Fe Alloys [71 Exe/on Byron Station

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ATTACHMENT I RRM-02-05, BCO4-I 003, Develop New Code Case to Address Inconel Weld Overlay on Various Materials, SIR-05-030, Rev. 0, Effect of Chromium Content on Nickel-base Alloy SCC Resistance

4. References

1. Materials Reliability Program: Crack Growth Rates for Evaluating Primary Water Stress Corrosion Cracking ofAlloy 82, 182, and 132 Welds (MRP-115), EPRI, Palo Alto, CA:

2004. 1006696.

2. Special Metals Corporation, SMC-079, October 3, 2003.

3. Inco Alloy International, IAI-27-3/7M, 1993.

4. S. Kiser fax to B. M. Gordon, Inconel Filler metal 72, May 2, 2000.

5. Special Metals Corporation, SMC-027, September 2, 2002.

6. R. A. Page and A. McMinn, Stress Corrosion Cracking Resistance of Alloys 600 and 690 and Compatible Weld Metals in BWRs, EPRI, NP-5882M, Palo Alto, CA, July 1988.

7. R. A. Page and A. McMinn, Stress Corrosion Cracking Resistance of Alloys 600 and 690 and Compatible Weld Metals in BWRs, EPRI, NP-5882S, Palo Alto, CA, July 1988. M.

8. Akashi, Effects of Cr and Nb Contents on the Susceptibility of Alloy 600 Type Ni-base Alloys to Stress Corrosion Cracking in a Simulated BWR Environment, paper 407 presented at Corrosion 95, NACE, Orlando, FL, March 1995.

9. D. Buisine, et al., PWSCC Resistance of Nickel Based Weld Metals with Various Chromium Contents, Proceedings: 1994 EPRI Workshop on PWSCC of Alloy 600 in PWRs, EPRI, Palo Alto, CA: 1995. TR-l05406, Paper D5.

10. T. Yonezawa, N. Sasaguri, and K. Onimura, Effects of Metallurgical Factors on Stress Corrosion Cracking ofNi-base Alloys in High Temperature Water, Proceedings of the 1988 JAIF International Conference on Water Chemistry in Nuclear Power Plants, 1988, pp. 490 495.

11. J. Panter, et al., Surface Layers on Alloys 600 and 690 in PWR Primary Water: Possible Influence on Stress Corrosion Crack Initiation, paper 02519 presented at Corrosion 2002, Houston, TX, April 7-11, 2002, NACE, Houston, TX.

12. P. M. Scott, An Overview of Internal Oxidation as a Possible Explanation of Intergranular Stress Corrosion Cracking of Alloy 600 in PWRs, paper presented at the 9th International Symposium on Environmental Degradation of Materials in Nuclear Power Systems Water Reactors, Newport Beach, CA, August 1-5, 1999, published in proceedings of same, TMS.

Warrendale, PA, p. 387.

13. C. S. Giggins and F. S. Petit. Oxidation of Ni-Cr Alloys between 800 and 1200 °C, Transaction of the Metallurgical Society of AIME, 245, 1969.

Exe/on Byron Station

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ATTACHMENT 2 RRA 05-08, BCO6-I34 Technical Basis Paper N-638-x, Ambient Temperature Temperbead Welding:

Begin 48 Hour Hold After 3rd Layer Completion Note: Attachment 2 is referenced on page 12, Table 3: Ambient Temperature Temp Bead Welding, Modifications to Code Case N-638-1

Background:

Ambient temperature temperbead welding eliminates elevated-temperature preheat and post-soak when conventional temperbead welding is impractical. Extensive nuclear industry experience continues to demonstrate its viability, safety, and effectiveness.

Historically, temperbead welding rules impose a 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> delay between welding completion and final Non-Destructive Examination (NED). The 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> delay serves solely to provide time for delayed hydrogen cracking before final NDE is performed. Early temperbead welding employed welding processes that were primarily flux-based and were, therefore, known to be susceptible to hydrogen pick-up. The 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> delay provided an effective measure of weld safety; necessary because of the moisture inherent in welding fluxes.

N-638 retains the conventional 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> NDE delay. N-638, however, excludes flux-based processes; it relies solely on the Gas Tungsten Arc Welding (GTAW) machine welding process. This process has been proven, through extensive laboratory testing, to consistently deliver low-hydrogen weld deposits. Testing includes welds deposited in fog chambers (~95% humidity) using high-moisture argon shield gas, wherein deposits consistently meet very low hydrogen criteria (i.e., <1.0 mI/bOg H2). These worst case conditions are far more severe than will be encountered in field applications. Still, test samples demonstrated that the most severe environments achievable yielded hydrogen levels too low to support delayed hydrogen cracking (Ref. EPRI Report GO-i 11050). Filler wire is another potential hydrogen source; however, the solid bare wire used for GTAW is not considered susceptible to moisture absorption. Test results prove, therefore, that the GTAW environment is essentially impervious to hydrogen from both internal and external sources. The inherently low hydrogen contents of GTAW machine weld deposits, coupled with extensive crack-free industry experience in their application, enables limited relaxation of the mandatory 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> NDE delay period.

Description of Change:

This action retains the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> NDE hold, but revises the time at which the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold time is initiated. Current rules require hold initiation after weld completion, and after the weldment has cooled to ambient temperature. The proposed change revises hold initiation time such that the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold begins immediately after completion of the third weld layer.

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ATTACHMENT 2 RRA 05-08, BCO6-134 Technical Basis Paper N-638-x, Ambient Temperature Temperbead Welding:

Begin 48 Hour Hold After 3d Layer Completion Justification for Change:

Industry experts generally accept the inherent low-hydrogen characteristics of GTAW machine welding. These inherently low hydrogen characteristics enable consistently low-hydrogen deposits even when external sources of hydrogen are present during welding.

Still, external contaminants may be present during welding, and laboratory conditions cannot effectively simulate every potential hydrogen source. The 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> NDE hold is a conservative means of hydrogen assessment, since it evaluates hydrogens effects, rather than its presence. In so doing, the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> NDE hold evaluates hydrogen introduced through any number of sources, including surface oxides, residues, and other base metal contaminants.

While the potential for external contaminants during temperbead welding cannot be completely ruled out, the extent of these contaminants can be minimized. Regarding surface cleanliness prior to welding, N-638 requires a liquid penetrant examination before weld initiation. As a result, the weld area and adjacent base materials are cleaned to bright, shiny metal. This cleaning removes potential hydrogen sources, and demonstrates substrate soundness, which ensures that external sources of hydrogen are effectively minimized. N-638 further minimizes HAZ exposure to external contaminants by stipulating that only the first weld layer contacts the base material(s). The initial weld layer, therefore, constitutes the only weld layer in which unknown surface contaminants may be encountered. All subsequent layers contact only clean, newly deposited weld material.

Since the initial weld layer constitutes the primary opportunity for hydrogen ingress to the crack-susceptible coarse-grained heat affected zone, it is reasonable to tie initiation of the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold to completion of this layer, instead of to overall weld completion.

Contaminant exposure is one concern; another is weldings proximity to the HAZ. Only welding performed in contact with, or in close proximity to the HAZ has the potential to introduce hydrogen into the hardened HAZ. In temperbead welding, each successive layer provides a progressively decreasing opportunity for HAZ hydrogen introduction, because of each successive layers decreasing proximity to the HAZ. Only the first weld layer contacts base material, and the second and third layers extend along the full length of this first layer.

When these three layers are installed, the HAZ is considered to be effectively tempered.

Existing N-638 methodology, therefore, identifies these three layers as an effective, protective barrier between subsequent weld layers and the HAZ. This protective barrier not only insulates the HAZ from additional tempering, but also effectively protects the HAZ from additional hydrogen introduction.

Exelon Byron Station

IS! Program Plan ______ _______________________ Units 1 & 2, Third Interval 10 CFR 50.55a RELIEF REQUEST l3R-08 Revision 0 (Page 29 of 30)

ATTACHMENT 2 RRA 05-08, BCO6-I34 Technical Basis Paper N-638-x, Ambient Temperature Temperbead Welding:

Begin 48 Hour Hold After 3rd Layer Completion Test data clearly demonstrates that GTAW machine welds installed using N-638 methodology are likely to free of damaging levels of hydrogen be completely free of hydrogen. Nevertheless, let us assume that some external contaminant was not removed from the base metal surface and serves as a hydrogen source. Further, let us assume that the GTAW processes inherent propensity to protect the weld pool from free hydrogen somehow fails, and hydrogen is introduced into the weld deposit. In this situation, HAZ hydrogen exposure would occur during installation of the first weld layer. This layer, because it is the only layer in direct contact with the base metal contaminants and since it is the only layer that directly contacts the HAZ, is considered to have the greatest potential contribution to hydrogen cracking. For the second and third (tempering) weld layers, the likelihood of additional hydrogen introduction is negligible. For the fourth through final weld layers, the likelihood of introducing additional HAZ hydrogen is virtually nonexistent.

Because the proposed change to N-638 is limited to austenitic filler materials, and because austenitic filler materials have a much greater affinity for hydrogen than carbon steel base metals, hydrogen can be assumed to move rapidly away from the HAZ through the austenitic material matrix, further reducing chances of HAZ cracking.

Weidment Temperatures During Ambient Temperature Temperbead Welding:

When conventional GTAW temperbead welding is employed, HAZ hydrogen is mitigated either by imposing a 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> NDE delay, or by performing a 450°Fto 550 °Fpost-soak for two hours. Ambient temperature temperbead welding effectively simulates these alternatives during installation of the fourth and subsequent weld layers, as follows:

Water Backed Applications: Ambient temperature temperbead welding is often performed with water backing, wherein the base metal acts as an infinite heat sink during welding.

This heat sink contributes to a moderate HAZ temperature, particularly as the fourth and subsequent weld layers are installed. This reduced HAZ temperature effectively enables time at ambient temperature to occur while the fourth and subsequent weld layers are installed. The proposed change enables credit to be taken for this time at ambient temperature, even though it occurs while welding is in process.

Non-Water Backed Applications: As ambient temperature temperbead methodology has matured, changes in conventional temperbead welding have occurred. These changes recognize that an elevated temperature post-soak (typically 450°Fto 550 °Ffor 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />) accelerates hydrogen dissipation. Current Code rules recognize, therefore, that an elevated temperature post-soak is an effective alternative to the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> NDE delay period (Ref. IWA-4624, 2004 Edition). Ambient temperature temperbead welding may, in some instances, be performed without water backing. In these instances, the 350°Finterpass Exelon Byron Station

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ATTACHMENT 2 RRA 05-08, BCO6-I34 Technical Basis Paper N-638-x, Ambient Temperature Temperbead Welding:

Begin 48 Hour Hold After 3rd Layer Completion temperature imposed by N-638, combined with the effective heat sink provided by the vessel or nozzle to be welded, typically contributes to low HAZ temperatures during welding. In some instances, however, smaller weldments may experience temperature increases. In these applications, moderate HAZ temperature increases serve to accelerate hydrogen dissipation, reducing the risk of delayed hydrogen cracking. Since hydrogen sources are essentially nonexistent for the second and subsequent layers, this accelerated dissipation effectively mitigates the risk of hydrogen cracking. Hydrogen dissipation is improved when austenitic filler materials are used, as is the case for all welding within the scope of this proposed Action. Hydrogen dissipates much more easily through the austenitic matrix of these filler materials, further reducing the propensity for high hydrogen levels in the hardened carbon steel HAZ.

Both with and without water backing, therefore, ambient temperature temperbead welding contains process controls that effectively moderate adverse hydrogen effects during weld installation. These factors, when considered in light of the inherent low-hydrogen characteristics of GTAW machine weld deposits, help to explain why not a single instance of delayed hydrogen cracking has been identified in any ambient temperature temperbead repair performed to date.

Summary:

This action recognizes that welding occurs in a variety of locations, and that sources of external contamination cannot always be completely quantified and/or eliminated.

Acknowledging these variables, this action retains the existing 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> NDE hold, but enables it to start immediately upon completion of the third weld layer. The proposed change thereby provides an effective method that delays final NDE sufficiently to detect any delayed hydrogen cracking. Concurrently, this action acknowledges the inherently low susceptibility of ambient temperature temperbead welding to delayed hydrogen cracking.

The result is an effective compromise that maintains safety, yet enables application of recognized science to reduce unwarranted costs and schedule delays associated with the existing 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> requirement.

Exe/on Byron Station