NMP1L3513, Submittal of Emergency Relief Request I5R-11 Concerning the Installation of a Weld Overlay on Reactor Pressure Vessel Recirculation Inlet Nozzle N2E Safe End-to-Nozzle Dissimilar Metal Weld (32-WD-208)

Submittal of Emergency Relief Request I5R-11 Concerning the Installation of a Weld Overlay on Reactor Pressure Vessel Recirculation Inlet Nozzle N2E Safe End-to-Nozzle Dissimilar Metal Weld (32-WD-208)

ML23083B991
Person / Time
Site:	Nine Mile Point
Issue date:	03/24/2023
From:	David Gudger Constellation Energy Generation
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
NMP1L3513
Download: ML23083B991 (1)

Text

200 Exelon Way Kennett Square, PA 19348

www.constellation.com

10 CFR 50.55a

NMP1L3513

March 24, 2023

U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 -0001

Nine Mile Point Nuclear Station, Unit 1 Renewed Facility Operating License No. DPR -63 NRC Docket No. 50-220

Subject:

Submittal of Emergency Relief Request I5R-11 Concerning the Installation of a Weld Overlay on Reactor Pressure Vessel Recirculation Inlet Nozzle N2E Safe End-to-Nozzle Dissimilar Metal Weld (32 -WD-208)

In accordance with 10 CFR 50.55a, Codes and standards, paragraph (z)(1), Constellation Energy Generation, LLC (CEG) requests emergency approval of the attached proposed alternative associated with the repair of the recirculation inlet nozzle N2E safe end-to-nozzle dissimilar metal (DM) weld. This proposed alternative (Attachment 2) applies to one operating cycle for the fifth 10-year Inservice Inspection (ISI) Interval. The fifth 10-year ISI interval for Nine Mile Point Nuclear Station, Unit 1 (NMP1) began on August 23, 2019, and will concluded on August 22, 2029. The fifth 10-year ISI interval complies with the American Society of Mechanical Engineers (ASME) Boiler and Pressure V essel Code,Section XI, 2013 Edition.

During the current refueling outage (N1R27) NMP 1 identified an unacceptable flaw indicative of Intergranular Stress Corrosion Cracking (IGSCC) in the N2E safe end -to-nozzle DM weld. CEG intends to repair the DM weld by installing a weld overlay using an alternative based on the requirements of ASME Code Case N-740-2 and Nonmandatory Appendix Q (2013 Edition).

CEG requests approval of the proposed alternative to support the return to service from the current NMP1 refueling outage. CEG requests approval of this relief request by March 28, 2023.

Relief is requested for the duration of the NMP1 Cycle 28 which is currently expected to conclude in the Spring of 2025.

A summary of the regulatory commitments contained in this submittal is provided in Attachment 1. contains Relief Request I5R-11.

If you have any questions concerning this letter, please contact Tom Loomis at Thomas.Loomis@constellation.com.

Respectfully,

David T. Gudger Senior Manager - Licensing & Regulatory Affairs Constellation Energy Generation, LLC

Emergency Relief Request I5R-11 March 24, 2023 Page 2

Attachment:

1) Summary of Commitments

2) Relief Request I5R-11

3) Review of Code Case N-740-2 against the Proposed Alternative Weld Overlay

4) Ambient Temperature Temper Bead - Elimination of 48-Hour Hold Time from N-888 When using Austenitic Filler Material - White Paper

cc: Regional Administrator, Region I, NRC NRC Senior Resident Inspector, NMP Project Manager NRC, NMP A. L. Peterson, NYSERDA

ATTACHMENT 1

Summary of Commitments

ATTACHMENT 1

SUMMARY

OF COMMITMENTS

COMMITTED COMMITMENT TYPE COMMITMENT DATE OR ONE-TIME Programmatic OUTAGE ACTION (Yes/No)

(Yes/No)

Constellation Energy Generation, LLC (CEG) Within 60 days Yes No commits to providing the following information to following the the NRC: end of the

1. A listing of indications detected in the overlaid current weld. refueling outage.

2. A description of any repairs to the overlay material and/or base metal and the reason for the repair.

3. The disposition of all indications using the acceptance standards of ASME Code,Section XI, IWB-3514.

4. The final one cycle flaw evaluation documenting the structural integrity of the weld, assuming the flaw has grown through the full thickness of the DM weld.

ATTACHMENT 2

Nine Mile Point Nuclear Station, Unit 1

Proposed Alternative Associated with N2E Safe End-to-Nozzle Dissimilar Metal Weld Repair by Weld Overlay

RELIEF REQUEST I5R-11

10 CFR 50.55a Proposed Alternative I5R-11 Revision 0 (Page 1 of 47)

Proposed Alternative for Installation of a Weld Overlay on Recirculation Inlet Nozzle N2E Safe End-to-Nozzle Dissimilar Metal Weld In Accordance with 10 CFR 50.55a(z)(1)

1.0 ASME CODE COMPONENT(S) AFFECTED Code Class: 1

Reference:

Code Case N-716-1 & BWRVIP-75A, Category D Examination Category: R-A Item Number: R1.16, Welds Subject to IGSCC

Description:

Reactor Pressure Vessel (RPV) Recirculation Inlet Nozzle N2E Safe End-to-Nozzle DM Weld Materials: Nozzle - SA-336 with buttering Weld Material - INCONEL 82/182 Safe End - SA-182 F316 Size: Nominal 29 Inches (Outer Diameter)

Component Number(s): Weld No. 32-WD-208 Drawing Numbers: ISI-NOZ-002

2.0 APPLICABLE CODE EDITION AND ADDENDA

The fifth interval of the Nine Mile Point Nuclear Station, Unit 1 Inservice Inspection (ISI) Program is based on the American Society of Mechanical Engineers (ASME)

Boiler and Pressure Vessel (B&PV) Code,Section XI, 2013 Edition. The fifth ISI interval began on August 23, 2019, and is scheduled to conclude on August 22, 2029.

3.0 APPLICABLE CODE REQUIREMENT S

IWA-4411 of the ASME Code,Section XI states that Welding, brazing and installation shall be performed in accordance with the Owners Requirements and, except as modified below, in accordance with the original Construction Code of the item.

IWA-4411(a) of the ASME Code,Section XI states in part, that Later Editions and Addenda of the Construction Code, or a later different Construction Code, either in its entirety or portions thereof, and Code Cases may be used, provided the substitution is as listed in IWA-4221(c).

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IWA-4411(b) of the ASME Code,Section XI states that Revised Owners Requirements may be used, provided they are reconciled in accordance with IWA-4222.

IWA-4412 states Defect removal shall be accomplished in accordance with the requirements of IWA-4420.

IWA-4611 specifies requirements for defect removal and examination following defect removal.

4.0 REASON FOR REQUEST

Dissimilar metal (DM) welds containing nickel welding alloys 82 and 182 have experienced Intergranular Stress Corrosion Cracking (IGSCC) in components operating at boiling water reactor temperatures.

On March 18, 2023, during automated encoded UT examination of the N2E safe end-to-nozzle DM weld (32-WD-208) one relevant indication was recorded. The indication is axially oriented and is located in the DM weld and adjacent safe end material. The indication is located approximately 14 inches clockwise from top of center. The indication is inner diameter connected with attributes that are indicative of Intergranular Stress Corrosion Cracking (IGSCC). The indication parameters are as follows:

Thickness at Flaw: 1.83 Axial Length: 1.65 Flaw Depth: 1.52 Remaining Ligament: 0.313 Location: Weld/Adjacent Safe End Material

This flaw does not meet the acceptance standards of IWB-3500 and cannot be accepted by analytical evaluation in accordance with IWB-3600; therefore, a repair/replacement activity is required in accordance with IWA-4000.

Constellation Energy Generation, LLC (CEG) proposes to perform an emergent repair of the Nine Mile Point, Unit 1 (NMP1) Reactor Recirculation Inlet Nozzle N2E Safe-End-to-Nozzle DM weld by installing a weld overlay using the guidance of ASME XI Code Case N-740-2 and Nonmandatory Appendix Q (2013 Edition). This alternative is proposed in lieu of replacement of the component or installation of a permanent full structural weld overlay (FSWOL), to ensure the leak-tight integrity of this weld until a permanent repair can be performed during refueling outage N1R28.

The Edition of ASME Code,Section XI applicable to NMP1 (2013 Edition) does not contain requirements for nickel alloy weld overlays; however, nickel alloy overlay repairs have been applied to other RPV nozzle DM welds in boiling water reactors (BWRs) using alternative requirements. This request proposes to use the guidance

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in ASME Code Case N-740-2 and Nonmandatory Appendix Q for application of a weld overlay to the N2E Safe End-to-Nozzle DM weld at NMP1. Because Code Case N-740-2 has not been approved by the NRC in the latest revision of Regulatory Guide (RG) 1.147, an alternative is required. This proposed alternative describes the requirements that CEG proposes to use to design and install a weld overlay on the N2E Safe End-to-Nozzle DM weld.

The welding will be performed utilizing a machine Gas Tungsten Arc Welding (GTAW) process and the ambient temperature temper bead method with ERNiCrFe-7A (referred to as Alloy 52M in subsequent discussion in this document) weld metal.

Alloy 82 will be used for the bridge beads over the original weld material. When temper bead welding is not required, manual GTAW with Alloy 52M is an acceptable alternative to the machine GTAW and may be used if local repairs of weld defects are necessary or if additional weld metal is required locally to form the final weld overlay contour. Shielded metal arc welding (SMAW) using Alloy 152M (ENiCrFe-7), or GTAW using Alloy 52M, would only be used to repair indications in the existing DM weld prior to weld overlay initiation. ER309L will be used for a small segment for the sulfur mitigation on the stainless steel safe end.

5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE

Pursuant to 10 CFR 50.55a(z)(1), CEG proposes an alternative to the ASME Code requirements stated in Section 3.0 to allow the installation of a weld overlay that will ensure the continued leak-tightness of this weld until a permanent repair can be performed during refueling outage N1R28. The details of the proposed alternative are described below.

CEG plans to apply a design (leakage barrier), Alloy 52M/152M weld overlay over the dissimilar metal Alloy 82/182 weld identified in Section 1.0. The weld overlay will be a minimum of 3 layers per the temper bead rules in Code Case N-638-10.

Although the leakage barrier overlay is not classified as a Full Structural Weld Overlay per N-740-2, there is reasonable assurance of structural integrity due to the geometry of the weld overlay and the flaw orientation. Axial flaws do not pose a structural concern in areas of high fracture toughness. Given the location of the flaw and materials of the weld and base material, theres no concern for catastrophic failure. The subsequent flaw evaluation will show there is adequate margin in the overlay design for one cycle of operation.

5.1 Description of Weld Overlay

5.1.1. Overview

CEG proposes the following detailed requirements for the design, analysis, fabrication, examination, and pressure testing of the NMP1 Reactor Recirculation Inlet Nozzle N2E dissimilar metal weld overlay. These requirements, which are derived from applicable portions of ASME Code Case N-740-2 and Nonmandatory

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Appendix Q, provide an acceptable methodology for providing a temporary repair that will eliminate the risk of through-wall leakage that could result from continued growth of the IGSCC initiated flaw identified in Section 4.0 of this request.

The weld overlay will be applied by deposition of weld reinforcement (i.e., weld overlay) on the outside surface of the nozzle, safe end, and associated dissimilar metal weld, in accordance with the following requirem ents:

5.1.2 GENERAL REQUIREMENTS (Correlated to N -740-2, paragraph 1)

5.1.2.1 Definitions

(a) SCC susceptible materials - For this proposed alternative, the stress-corrosion-cracking (SCC) susceptible materials are Unified Numbering System (UNS) N06600, W86182, or austenitic stainless steels in boiling water reactor environments.

(b) Design Overlay - A weld overlay used to address weldments with a total length of circumferential cracking less than approximately 10% of the circumference, with no more than four axial cracks, as defined in NUREG -0313.

5.1.2.2 General Overlay Requirements

(a) A design weld overlay, that will function as a leakage barrier, will be applied by deposition of weld reinforcement (i.e., weld overlay) on the outside surface of the circumferential weld. This proposed method applies to austenitic nickel alloy and austenitic stainless steel welds between the following:

P-No. 8 or P-No. 43 and P-Nos. 1, 3, 12A, 12B, or 12C P-No. 8 and P-No. 43 Between P-Nos. 1, 3, 12A, 12B, and 12C materials

(b) The weld overlay on any of the material combinations in 5.1.2.2(a) shall not obstruct a required examination of an adjacent P -No. 8 to P-No. 8 weld.

(c) Weld overlay filler metal will be austenitic nickel alloy (i.e., 28 percent chromium minimum, ERNiCrFe-7/7A) meeting the requirements of 5.1.2.2(e)(1) or (2), as applicable, applied 360 degrees around the circumference of the item and deposited using a Welding Procedure Specification (WPS) for groove welding, qualified in accordance with the Construction Code and Owners Requirements identified in the Repair/Replacement Plan.

The weld filler metal to be used in the weld overlay is ERNiCrFe-7A (Alloy 52M).

(d) Prior to deposition of the weld overlay, the surface to be weld overlaid will be examined using the liquid penetrant method. Indications with major dimensions greater than 1/16 inch (i.e., 1.5 millimeters) will be removed, reduced in size, or weld repaired in accordance with the following requirements:

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(1) One or more layers of weld meta l will be applied to seal unacceptable indications in the area to be repaired with or without excavation. The thickness of these layers will not be used in meeting weld reinforcement design thickness requirements. Peening the unacceptable indication prior to welding is permitted.

(2) If weld repair of indications is required, the area where the weld overlay is to be deposited, including any local weld repairs or initial weld overlay layer, will be examined by the liquid penetrant method. The area shall contain no indications with major dimensions greater than 1/16 inch (i.e.,

1.5 millimeters) prior to application of the structural layers of the weld overlay.

(3) To reduce the potential of hot cracking when applying an austenitic nickel alloy over P-No. 8 base metal, a layer or multiple layers of austenitic stainless steel filler material will be applied over the austenitic stainless steel base metal. The stainless steel filler metal shall have a delta ferrite content of 5 to 15 Ferrite Numb er (FN), as reported on the Certified Material Test Report. The thickness of these buffer layers will not be used in meeting weld reinforcement design thickness requirements.

A minimum of one layer of ER309L stainless steel filler metal will be applied to the stainless-steel safe end to prevent the potential of hot cracking.

Weld material shall be deposited using the machine GTAW welding process.

(e) Weld overlay deposits will meet the following requirements:

(1) The austenitic stainless steel weld overlay shall consist of at least two weld layers having as-deposited delta ferrite content of at least 7.5 FN. The first layer of weld metal with delta ferrite content of at least 7.5 FN shall constitute the first layer of the weld reinforcement that may be credited toward the required thickness. Alternatively, layers of at least 5 FN are acceptable, provided the carbon content of the deposited weld metal is determined by chemical analysis to be less than 0.02%.

Since an Alloy 52M weld overlay will be used, this stipulation of ASME Code Case N-740-2 does not apply.

(2) The austenitic nickel alloy weld overlay shall consist of at least two weld layers deposited using a filler material with a Cr content of at least 28%.

The first layer of weld metal deposited may not be credited toward the required thickness. A dilution layer may be credited toward the required thickness, provided the portion of the layer over the austenitic base

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material, austenitic filler material weld, and the associated dilution zone from an adjacent ferritic base material contain at least 20% Cr, and the Cr content of the deposited weld metal is determined by chemical analysis of the production weld or of a representative coupon taken from a mockup prepared in accordance with the WPS for the production weld.

Welding shall comply with the requirements of ASME Code Case N -638-10, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique,Section XI, Division 1, except as follows:

An alternative is proposed to the requirement of N-638-10, 4(a)(2) that requires that When austenitic materials are used, the completed weld shall be nondestructively examined after the three tempering layers (i.e., layers 1, 2, and 3) have been in place for at least 48 hr. Examination of the welded region shall include both volumetric and surface examination methods.

In lieu of the above requirement, nondestructive examinations may be performed after completing the weld overlay. This is consistent with requirements of ASME Code Case N-888-1 and is supported by the White Paper that was developed for the proposed change in Code Case N -888-1.

Although this ASME Code Case has not yet been approved in Regulatory Guide 1.147, the supporting White Paper (Attac hment 4) provides a technical basis for eliminating this requirement.

(f) This case is only for welding in applications predicted not to have exceeded thermal neutron (E < 0.5 eV) fluence of 1 x 1017 neutrons per cm2 prior to welding.

The N2E nozzle is located in the lower head of the reactor vessel, well below the beltline region (high fluence region). The current accumulated Effective Full Power Years (EFPY) for NMP1 is 40.3. For the N1 nozzles, which are above the N2E nozzle and also below the beltl ine region, the fast neutron fluence value (E>1.0 MeV) projected at 46 EFPY at the inside diameter (0T) of the vessel is 7.39 E+16 neutron/cm2 for the N1 nozzle closest in azimuth to the N2E nozzle.

This value is below the threshold level of 1E+17 neutron/cm2 (E > 1.0 MeV) and as such the material in the area of this repair is not expected to have decreased fracture toughness and ductility associated with damage of low alloy steels in the beltline region. In the lower head region of the reactor vessel, the thermal neutron fluence (E < 0.5 eV) is predicted to be below the threshold of concern for weldability based upon the findings in BWRVIP A, which shows that vessel internals components below the core plate are all considered within the generic weldability boundary. This weld overlay will be installed external to the reactor vessel below the core plate elevation; therefore there is not a weldability concern for the repair.

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(g) A new weld overlay is not being installed over the top of an existing weld overlay that has been in service.

5.1.3 CRACK GROWTH AND DESIGN (Correlated to N -740-2, paragraph 2)

(a) Crack Growth Calculation of Flaws in the Original Weld or Base Metal. The size of the flaw detected in the base metal will be used to define the life of each overlay. The inspection interval will not be longer than the shorter of the life of the overlay or the period specified in 5.1.4(c). Crack growth due to both stress corrosion and fatigue, will be evaluated. Flaw characterization and evaluation will be based on the examination result or postulated flaw, as described below. If the flaw is at or near the boundary of two different materials, evaluation of flaw growth in both materials is required.

Alloy 52M material is used in the weld overlay. A stress corrosion crack growth analysis has been performed assuming the axial flaw is 100% through-wall.

(1) For the repair overlay, a pre-overlay examination has been performed and the initial flaw size for crack growth in the base metal will be based on the as-found flaw.

(2) The initial flaw size for crack growth in the original weld or base metal shall be based on the as-found flaw size.

The initial flaw size for crack growth was sized based on the as-found size, but the design of the weld overlay assumes that the flaw grows 100 percent through-wall to the O.D. of the existing weld.

(3) If an ASME Section XI, Appendix VIII, Supplement 10, or Supplement 2, as applicable, ultrasonic examination is performed prior to application of the overlay, and no inside-surface-connected planar flaws are discovered, initial flaws originated from the inside surface of the weldment equal to 10 percent of the original wall thickness will be assumed in both the axial and circumferential directions, and the overlay shall be considered mitigative.

This stipulation is not applicable because ultrasonic examinations have determined the identified flaw to be ID connected.

(4) If an ASME Section XI, Appendix VIII, Supplement 10, or Supplement 2, as applicable, ultrasonic examination is not performed prior to application of the overlay, initial inside-surface-connected planar flaws equal to at least 75 percent through the original wall thickness shall be assumed, in both the axial and circumferential directions, and the overlay shall be considered a repair. For cast austenitic stainless steel (CASS) items, a 100 percent through-wall flaw shall be assumed unless the subsequent inservice inspection schedule is modified.

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This stipulation is not applicable because ultrasonic examinations have been performed prior to application of an overlay.

(5) There may be circumstances in which an overlay examination is performed using an ultrasonic examination procedure qualified in accordance with Appendix VIII, Supplement 11 for depths greater than the outer 25 percent of the original wall thickness (i.e., see Figure 5.1-2 below). For such cases, the initial flaw depths are assumed to be the detected depth found by the Appendix VIII, Supplement 11 qualified examination, plus the postul ated worst-case flaw in the region not covered by the Appendix VIII ultrasonic examination.

This stipulation is not applicable because ultrasonic examinations have been performed in accordance with Appendix VIII, Supplement 10.

(6) In determining the life of each overlay, any inside-surface-connected planar flaw found by the overlay preservice inspection that exceeds the depth of (3), (4), or (5) above shall be used as part of the initial flaw depth. The initial flaw depth assumed is the detected flaw depth plus the postulated worst-case flaw depth in the region of the pipe wall thickness that was not examined using an ultrasonic examination procedure meeting Appendix VIII for that region.

Since the overlay will meet this condition, it is considered a repair, rather than mitigation. Note that the life of the overlay is limited to the end of the next refueling outage (N1R28) in 2025.

(b) Structural Design and Sizing of the Overlay. The design of the weld overlay will satisfy the following, using the assumptions and flaw characterization requirements. The following design analysis will be completed in accordance with IWA-4311:

(1) The axial length and end slope of the weld overlay will cover the weld and heat-affected zones on each side of the weld, as well as any stress corrosion cracking susceptible base material adjacent to the weld and provide for load redistribution from the item into the weld overlay and back into the item without violating applicable stress limits of NB-3200. Any laminar flaws in the weld overlay will be evaluated in the analysis to ensure that load redistribution complies with the above. These requirements are usually satisfied if the weld overlay full thickness length extends axially beyond the SCC susceptible material or projected flaw by at least 0.75 (Rt), where R is the outer radius of the item and t is the nominal wall thickness of the item at the applicable side of the overlay (i.e., R and t of the nozzle on the nozzle side and R and t of the safe-end on the safe-end side).

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(2) The end transition slope of the overlay shall not exceed 30 deg., unless specifically analyzed.

CEG proposes to use a transition slope no larger than 45 deg., in accordance with Nonmandatory Appendix Q, Q -3000(b)(2).

(3) The assumed flaw in the underlying base material or weld will be based on the limiting case which results in the larger required overlay thickness.

(a) 100 percent through-wall circumferential flaw for the entire circumference.

(b) 100 percent through-wall flaw with length of 1.5 inches (i.e., 38 millimeters), or the combined width of the weld plus buttering plus any SCC-susceptible material, whichever is greater, in the axial direction.

The thickness of the overlay will be designed using Nonmandatory Appendix Q, Q-3000(a)(5), using the measured flaw length of 1.65 inches.

Using a flaw length of 1.65 inches is justified for the following reasons:

1. Nonmandatory Appendix Q, Q-3000(a)(5) allows a weld overlay to be designed with only weld reinforcement satisfying the requirements of Q-2000(d) if the weldment contains four or fewer axial flaws, each shorter than 1.5 inches (and no circumferential flaws). A weldment with four axial flaws of just under 1.5 inches in length (that could be closely spaced) is considered to be more significant than a single axial flaw of 1.65 inches. The weld overlay is designed to bound the 1.65 inches axial flaw and projected flaw growth for the operating cycle.

2. NUREG-0313, 4.4.2 requires that Weldments with a total length of circumferential cracking less than approximately 10% of the circumference, with no more than four axial cracks, are considered appropriate for repair by a designed overlay. There is no specified limit on the size and number of axial flaws that may be overlayed.

(4) The overlay design thickness will be verified, using only the weld overlay thickness conforming to the deposit analysis requirements. The combined wall thickness at the weld overlay, any postulated worst -case planar flaws under the laminar flaws in the weld overlay, and the effects of any discontinuity within a distance of 2.5 (Rt), from the toes of the weld overlay, including the flaw size assumptions, will be evaluated and shall meet the requirements of IWB -3640, IWC-3640, or IWD-3640, as applicable.

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Only those flaws within the weld overlay will be evaluated and shall meet the requirements of IWB-3640. The design of the weld overlay assumes that the flaw grows 100 percent through -wall to the OD of the existing weld.

(5) The effects of any changes in applied loads, as a result of weld shrinkage from the entire overlay, on other items in the piping system (e.g., support loads and clearances, nozzle loads, and changes in system flexibility and weight due to the weld overlay) will be evaluated.

5.1.4 EXAMINATION (Correlated to N -740-2, paragraph 3)

The following requirements will be implemented as part of the weld overlay repair.

In lieu of all other examination requirements, the following examination requirements shall apply.

1. Nondestructive examination methods will be in accordance with IWA -2200, except as specified herein.

2. Nondestructive examination personnel shall be qualified in accordance with IWA-2300.

3. Ultrasonic examination procedures will be qualified in accordance with the requirements of ASME Code Case N-653-2.

4. Ultrasonic examination will be performed, to the maximum extent practicable, for axial and circumferential flaws. If 100 percent coverage of the required volume for axial flaws cannot be achieved, but essentially 100 percent coverage for circumferential flaws (i.e., 100 percent of the susceptible volume) can be achieved, the examination for axial flaws will be performed to achieve the maximum coverage practicable, with limitations noted in the examination report. The examination coverage requirements will be considered to be met.

(a) Acceptance Examination

(1) The weld overlay will have a surface finish of 250 micro-inches (-in),

RMS or better and contour that permits ultrasonic examination in accordance with procedures qualified in accordance with ASME Code,Section XI, Appendix VIII. The weld overlay will be inspected to verify acceptable configuration.

This requirement will be met, except that ultrasonic examination procedures will be qualified in accordance with ASME Code Case N-653-2 in lieu of Appendix VIII, Supplement 11.

(2) The weld overlay and the adjacent base material for at least 1/2 inch (i.e.,

13 millimeters) from each side of the overlay will be examined using the liquid penetrant method. The weld overlay will satisfy the surface

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examination acceptance criteria for welds of the Construction Code or NB-5300. The adjacent base material will satisfy the surface examination acceptance criteria for base material of the Construction Code or NB-2500.

If ambient temperature temper bead welding is performed, the liquid penetrant examination of the completed weld overlay will be conducted no sooner than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> following completion of the three tempering layers over the ferritic steel.

This requirement will be met, except that the liquid penetrant examination may be performed prior to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> following completion of the weld overlay. The justification for this exception is documented in 5.1.2.2(e)(2).

(3) The examination volume A-B-C-D in Figure 5.1-1(a), shown below, will be ultrasonically examined to assure adequate fusion (i.e., adequate bond) with the base material and to detect welding flaws, such as interbead lack of fusion, inclusions, or cracks. The interface C-D shown between the overlay and weld includes the bond and heat -affected zone from the overlay. If ambient temperature temper bead welding is performed, the ultrasonic examination will be conducted no sooner than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> following completion of the three tempering layers over the ferritic steel. Planar flaws detected in the weld overlay acceptance examination will meet the preservice examination standards of IWB-3514. In applying the acceptance standards to planar indications, the thickness, t1 or t2 defined in Figure 5.1-1(b) will be used as the nominal wall thickness in IWB-3514, provided the base material beneath the flaw (i.e., safe end, nozzle, or piping material) is not susceptible to stress corrosion cracking. For susceptible material, t1 will be used. If a flaw in the overlay crosses the boundary between the two regions, the more conservative of the two dimensions (t 1 or t2) will be used.

Laminar flaws in the weld overlay will meet the following requirements:

(a) The acceptance standards of IWB -3514 will be met, with the additional limitation that the total laminar flaw area will not exceed 10 percent of the weld surface area and that no linear dimension of the laminar flaw area shall exceed the greater of 3 inches (i.e., 76 millimeters) or 10 percent of the pipe circumference.

(b) For examination volume A -B-C-D in Figure 5.1-1(a), shown below, the reduction in coverage due to laminar flaws will be less than 10 percent. The uninspectable volume is the volume in the weld overlay underneath the laminar flaws for which coverage cannot be achieved with the angle beam examination method.

(c) Any uninspectable volume in the weld overlay will be assumed to contain the largest radial planar flaw that could exist within that volume. This assumed flaw will meet the preservice examination acceptance standards of IWB-3514, with nominal wall thickness as defined above the planar flaws. Alternatively, the assumed flaw will be

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evaluated and meet the requirements of IWB-3640, IWC-3640, and IWD-3640, as applicable. Both axial and circumferential planar flaws will be assumed.

The requirements of 5.1.4(a)(3) shall be met, except as follows:

1. Ultrasonic examination may be performed at any time following completion of the weld overlay. The justification for this exception is documented in 5.1.2.2(e)(2).

2. The examination volume identified in Code Case N -740-2, Figure 1 will not be examined. In lieu of this requirement, the examination volume A-B-C-D in Figure Q-4100-1 of Nonmandatory Appendix Q shall be examined. ASME Section XI, Non-Mandatory Appendix Q, Figure Q-4100-1 has been accepted by the NRC for defining the acceptance examination volume for weld overlay repairs. Figure Q -

4100-1 is equivalent to Code Case N -740-2, Figure 1(a).

Because the proposed alternative does not take structural credit for the weld overlay, Figure 1(b) of N-740-2 is not required for defining the acceptance standards for the weld overlay.

(4) After completion of all welding activities, VT-3 visual examination shall be performed on all affected restraints, supports, and snubbers, to verify that design tolerances are met.

(b) Preservice Inspection

(1) The examination volume in Figure 5.1-2 will be ultrasonically examined.

The angle beam will be directed perpendicular and parallel to the piping axis, with scanning performed in four directions, to locate and size any planar flaw that have propagated into the outer 25 percent of the base metal thickness or into the weld overlay.

The examination volume specified in Figure 5.1 -2 is identical to that in Nonmandatory Appendix Q, Figure Q -4300-1.

(2) The preservice examination acceptance standard s of IWB-3514 will be met for the weld overlay. In applying the acceptance standards to planar indications, the thickness, t1 or t2, defined in N-740-2, Figure 1(b) will be used as the nominal wall thickness in IWB -3514, provided the base material beneath the flaw (i.e., safe end, nozzle, or piping material) is not susceptible to SCC. For susceptible material, t1 will be used. Planar flaws in the outer 25 percent of the base metal thickness will meet the design analysis requirements of 5.1.3(b).

When performing the preservice examination, only those planar flaws in the weld overlay shall be evaluated in accordance with IWB -3514. The design

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of the weld overlay assumes that the flaw grows 100 percent through-wall to the O.D. of the existing weld. Since the proposed alternative does not take structural credit for the weld overlay, Figure 1(b) of N-740-2 is not required for defining the examination volume for preservice examinations of the weld overlay.

(3) The flaw evaluation requirements of IWB-3640, IWC-3640, or IWD-3640 will not be applied to planar flaws, identified during preservice examination, that exceed the preservice examination acceptance standards of IWB -

3514.

This will be applied only to the weld overlay volume.

Figure 5.1-2 Preservice and Inservice Examination Volume Examination Volume A-B-C-D (from N-740-2)

Notes:

1. The weld includes the nozzle or safe end butter, where applied.

2. For axial or circumferential flaws, the axial extent of the examination volume shall extend at least 1/2 inch (i.e., 13 millimeters) beyond the as-found flaw and at least 1/2 inch (i.e., 13 millimeters) beyond the toes of the original weld, including weld end butter, where applied.

(c) Inservice Inspection

There are no inservice examinations proposed for the weld overlay because the life of the weld overlay is limited to the end of the next refueling outage (N1R28) in 2025.

5.1.5 PRESSURE TESTING

A system leakage test and VT-2 visual examination shall be performed on the weld overlay in accordance with IWA -5000 following completion of the weld overlay and acceptance examinations.

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5.1.6 DOCUMENTATION

Use of this proposed method will be documented on Form NIS-2A.

5.1.7 AMBIENT-TEMPERATURE TEMPER BEAD WELDING (CORRELATED TO N-740-2, MANDATORY APPENDIX I)

Ambient temperature temper bead welding shall be performed in accordance with ASME Code Case N-638-10, which has been approved for use in Table 1 of Regulatory Guide 1.147, Revision 20. The only exception to use of this case is discussed is removal of the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold time discussed later in this alternative.

5.1.8 WELD OVERLAY DESIGN INFORMATION (NON -ITALICIZED)

Schematic Configuration for the Weld Overlay

A representation of the weld overlay configuration for the N2E nozzle weld 32-WD-208 is presented schematically in Figure 5-1, below.

RPV Recirculation Inlet Nozzle N2E Safe End-to-Nozzle Dissimilar Metal Weld

The RPV Recirculation Inlet Nozzle N2E is fabricated from SA-336 low alloy steel.

The nozzle-to-safe end weld is made using buttering with Alloy 82/182 weld material, and the safe end material is SA-182, F316.

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Figure 5-1 Schematic Configuration for the N2E Nozzle with Weld Overlay

Suitability of Proposed Post Overlay Nondestructive Examination (NDE)

As part of the design of the weld overlay, the length, surface finish, and end transition specified will allow for post-installation, UT examinations qualified in accordance with ASME Code Case N-653-2 to be performed. These examinations include the weld overlay and the required volume of the base material and original weld underneath the overlay. Nondestructive examinations may be performed at any time following completion of the weld overlay, as documented in this alternative.

The examinations specified in this proposed alternative provide adequate assurance that the overlay was installed correctly and can ensure the leak-tight integrity of the nozzle-to-safe end weld for the following reasons:

• The UT examinations will be performed with the proposed alternative ASME Code Case N-653-2 in lieu of the requirements of Appendix VIII, Supplement

11. Examinations performed using these requirements can be used to assess service-induced and fabrication-induced flaws. It is applicable for wrought austenitic, ferritic, or dissimilar metal welds, overlaid with austenitic weld material. ASME Code,Section XI has specific acceptance criteria and evaluation methodology. The criteria considers the materials in which the flaw indications are detected, the orientation and size of the indications, and ultimately their potential structural effects on the component. The acceptance criteria include allowable flaw indication tables for planar flaws (i.e., Table IWB-3514-1) and for laminar flaws (i.e., Table IWB -3514-3).

• A laminar flaw is defined in (IWA-3360) as a flaw oriented within 10 degrees of a plane parallel to the surface of the component. This definition is applicable to welds, weld overlays, and base materials. The ASME Code,Section XI

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laminar flaw standards are contained in Table IWB-3514-3 of the ASME Code,Section XI, and are supplemented by requirements in the proposed alternative. These criteria require that the sum of laminar flaw lengths in any direction must be less than 10 percent of the overlay length, with a total reduction in area equal to or less than Table IWB-3514-3. For weld overlay areas where examination is precluded by the presence of a Laminar flaw, the areas must be postulated to be cracked.

• Any planar flaws found during the weld overlay acceptance and preservice examinations of the weld overlay (excluding base metal and existing weld) are required to meet the preservice standards of ASME Code,Section XI, IWB -

3514.

• Weld overlays for repair of cracks in piping are not addressed by ASME Code,Section III. ASME Code,Section III utilizes NDE procedures and techniques with flaw detection capabilities that are within the practical limits of workmanship standards for welds. These standards are most applicable to volumetric examinations conducted by radiographic examination. Radiogr aphy (RT) of weld overlays is not practical because of the presence of radioactive material in the reactor coolant system and water in the pipes. The ASME Code,Section III acceptance standards are written for a range of fabrication flaws including lack of fusion, incomplete penetration, cracking, slag inclusions, porosity, and concavity.

The ASME Code,Section XI acceptance standards are the logical choice for evaluation of potential flaw indications in post-overlay examinations, in which unnecessary repairs to the overlays would result in additional personnel radiation exposure and could potentially degrade the effectiveness of the overlays by affecting the favorable residual stress field that they produce. The criteria are consistent with previous criteria approved by the NRC for weld overlay installations. Weld overlays have been used for repair and mitigation of cracking in BWRs for many years. In NRC Generic Letter 88-01, NRC Position on IGSCC in BWR Austenitic Stainless Steel Piping, the NRC approved the use of ASME Code,Section XI inspection procedures for determining the acceptab ility of installed weld overlays in BWR reactor coolant pressure boundary piping. Nonmandatory Appendix Q incorporates the requirements of ASME Code Case N-504-4, which was developed to codify the BWR weld overlay experience. Code Case N -740-2 has since been developed for use on DM welds, but the NRC has not yet approved use of this case in Regulatory Guide 1.147.

ASME Code Case N-653-2 specifies alternative requirements to Appendix VIII, Supplement 11 and will be used for qualification requirements for detection and length and depth sizing of flaws in the overlay. This case is approved for use in Regulatory Guide 1.147 and is documented in the NMP1 Inservice Inspection Program Plan, as required by IWA-2441.

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Weld Overlay Design and Evaluation

The following list of evaluations will be performed subject to the specific design, analysis, and inspection requirements that have been defined in this proposed alternative.

1. The as-built dimensions of the weld overlay will be measured and evaluated to demonstrate that they equal or exceed the minimum design dimensions of the overlay design.

2. CEG is proposing to apply a design (NUREG-0313, Revision 2) weld overlay using guidance from ASME Code,Section XI, Nonmandatory Appendix Q, Weld Overlay Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping Weldments. The sizing requirements for a design weld overlay will be developed taking guidance from Appendix Q, Q-3000(a)(5) of ASME Code,Section XI and ASME Code Case N-740-2.

ASME Code Case N-740-2 is being used because the Alloy 52M weld overlay material will be deposited over an existing Alloy 82/182 weldment.

3. Alloy 52M material is used for the weld overlay. A stress corrosion crack growth analysis has been performed assuming the axial flaw is 100% through -

wall.

4. The total added weight on the piping system due to the overlay will be evaluated for potential impact on RPV nozzle stresses and dynamic characteristics.

The following information will be submitted to the NRC within 60 days following the end of the current refueling outage:

1. A listing of indications detected in the overlaid weld.

2. A description of any repairs to the overlay material and/or base metal and the reason for the repair.

3. The disposition of all indications using the acceptance criteria of ASME Code,Section XI, IWB-3514.

4. The final one cycle flaw evaluation documenting the structural integrity of the weld, assuming the flaw has grown through the full thickness of the DM weld.

Additional Information

CEG notes that the adjacent low alloy steel nozzle-to-vessel weld is inaccessible for examination from the nozzle side of the weld due to the configuration of the weld joint. Installation of the proposed weld overlay will not affect the ultrasonic

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examination coverage of this weld that can be obtained from the vessel side of the weld.

A comparison of the proposed alternative to the requirements of Code Case N -740-2, is provided in Attachment 3.

The proposed alternative provides an acceptable methodology for mitigation of the IGSCC initiated defect in Weld 32-WD-208. The use of weld overlay filler metals that are resistant to IGSCC (e.g., Alloy 52M), and post overlay examination requirements provide assurance that the leak-tight integrity will be maintained for the duration of the life of the weld overlay.

The use of this alternative is requested on the basis that the proposed requirements will provide an acceptable level of quality and safety.

6.0 DURATION OF THE PROPOSED ALTERNATIVE

This alternative is proposed for use until the end of Unit 1 refueling outage N1R28 in 2025 during which a full structural weld overlay repair shall be performed on the N2E safe end-to-nozzle weld.

7.0 PRECEDENTS

A similar relief request to use the guidance of Code Case N-740-2 was previously approved via a verbal authorization on May 15, 2018, for the Duke Energy Progress Brunswick Steam Electric Plant Unit 1. The NRC Safety Evaluation was subsequently issued on May 15, 2018 (ML18124A308).

8.0 REFERENCES

1. ASME Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," 2013 Edition.

2. ASME Code Case N-740-2, Full Structural Dissimilar Metal Weld Overlay for Repair or Mitigation of Class 1, 2, and 3 Items,Section XI, Division 1, dated November 10, 2008.

3. ASME Code Case N-653-2, Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds,Section XI, Division 1, dated June 23, 2015.

4. ASME Code Case N-638-10, Similar and Dissimilar Metal Wel ding Using Ambient Temperature Machine GTAW Temper Bead Technique,Section XI, Division 1, dated May 6, 2019.

5. ASME Code Case N-716-1, Alternative Classification and Examination Requirements,Section XI, Division 1, dated January 27, 2013.

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6. NUREG-0313, Revision 2, Technical Report on Material Selection and Processing Guidelines for BWR Coolant Pressure Boundary Piping.

7. Generic Letter 88-01, NRC Position on IGSCC in BWR Austenitic Stainless Steel Piping, January 25, 1988.

8. BWRVIP-75-A: BWR Vessel and Internals Project, Technical Basis for Revisions to Generic Letter 88-01 Inspection Schedules, dated October 2005.

9. BWRVIP-97-A: BWR Vessel and Internals Project, Guidelines for Performing Weld Repairs to Irradiated BWR Internals, dated June 2009.

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ATTACHMENT 3

Review of Code Case N-740-2 against the Proposed Alternative Weld Overlay

Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative

1. GENERAL REQUIREMENTS 1.1 DEFINITION

(a) Full Structural Weld Overlay. Deposition of weld No Definition does not apply to proposed N/A reinforcement on the outside diameter of the piping, alternative component, or associated weld, such that the weld reinforcement is capable of supporting the design loads, without consideration of the piping, component, or associated weld beneath the weld reinforcement. Full structural weld overlay can be either mitigative or repair weld overlay as defined in (b) and (c).

(b) Mitigative Weld Overlay. Weld overlay that is ap-plied No Definition does not apply to proposed N/A over material with no inside surface connected flaws found alternative during an examination performed in accordance with 2(a)(3), prior to the weld overlay being applied.

(c) Repair Weld Overlay. Weld overlay that is applied over No Definition does not apply to propose N/A material with an inside surface connected flaw or subsurface alternative defect, or where a pre-weld overlay examination is not performed.

(d) SCC Susceptible Materials. For this Case, the stress-Yes The referenced BWR materials, UNS N/A corrosion-cracking (SCC) susceptible materials are UNS N06600 and W86182, are also recognized as N06600, N06082, or W86182 in PWR environment; or UNS susceptible materials in ASME Section XI, N06600, W86182, or austenitic stainless steels and 2013 Edition.

associated welds in BWR environments.

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative 1.2 GENERAL OVERLAY REQUIREMENTS

(a) A full-structural weld overlay shall be applied by Yes 32-WD-208 is a dissimilar metal weld The proposed alternative deposition of weld reinforcement (weld overlay) on the between the SA-336 (P-No. 3) N2E nozzle is not a full-structural outside surface of circumferential welds. This Case applies and the SA-182 F316 (P-No.8) safe end weld overlay as defined in to austenitic nickel alloy and austenitic stainless-steel made with Alloy 82/182 filler metal which Code Case N-740-2.

welds between the following: meets the configuration of Code Case N-740-2. The Case was specifically written to (1) P-No. 8 or P-No. 43 and P-Nos. 1, 3, 12A, 12B, or address the applicable of weld overlays over 12C1 dissimilar metal welds and austenitic (2) P-No. 8 and P-No. 43 stainless-steel welds.

(3) Between P-Nos. 1, 3, 12A, 12B, and 12C 1 materials

(b) If a weld overlay on any of the material combinations in No The adjacent safe end-to-pipe weld (32-WD-The weld overlay is not (a) obstructs a required examination of an adjacent P-No. 8 207) is a Category R-A, Item No. R1.20 (no being extended to include to P-No. 8 weld, the overlay may be extended to include degradation mechanism) component in the the adjacent weld.

overlaying the adjacent weld. RI-ISI program. There is no requirement in the RI-ISI program that this component be examined, and it is not currently included in the RI-ISI program examination scope.

Therefore, the weld overlay will not be extended to include the adjacent weld.

Additionally, the adjacent low alloy steel nozzle-to-vessel (P-No. 3 to P-No. 3) weld is inaccessible for examination from the nozzle side of the weld due to the configuration of the weld joint. Although we perform a supplemental exam from the nozzle side, we do not credit the coverage to our exam. This is a limited exam, and the Installation of the proposed weld overlay will not affect the ultrasonic examination coverage of this weld that can be obtained from the vessel side of the weld.

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative (c) Weld overlay filler metal shall be austenitic nickel alloy Yes The weld filler metal and procedure Ambient-temperature (28% Cr min., ERNiCrFe-7/7A) meeting the requirements of requirements of N-740-2 are equivalent to temper bead welding will (e)(1) or (e)(2), as applicable, applied 360 deg around the ASME Section XI, Appendix Q, which is be performe d in circumference of the item and deposited using a Welding accepted for use by the NRC. accordance with Code Procedure Specification (WPS) for groove welding, qualified Case N-638-10 amended in accordance with the Construction Code and Owner's as discussed below.

Requirements identified in the Repair/Replacement Plan. As The weld overlay shall be deposited with an alternative to the post weld heat treatment (PWHT) ERNiCrFe-7A (Alloy 52M) filler metal which requirements of the Construction Code and Owner's has excellent resistance to stress corrosion requirements, the provisions of Mandat ory Appendix I cracking as documented in EPRI Technical may be used for ambient -temperature temper bead Report MRP-115, Section 2.2[5]. The WPS welding. used for depositing the weld overlay is qualified as a groove welding procedure to ensure that mechanical properties of the WPS are appropriately established. Where welding is performed on the ferritic nozzle material, an ambient temperature temper bead WPS shall be used.

(1) For P-No. 1 base materials, the Construction No Ambient-temperature temper bead welding N/A Code PWHT exemptions permitted for circumferential will be performed in accordance with Code butt welds may be applied to exempt the weld overlay Case N-638-10 amended as discussed from PWHT, with the following clarifications: below.

(-a) The nominal weld thickness is defined as the maximum overlay thickness applied over the ferritic base material.

(-b) The base material thickness is defined as the maximum thickness of the ferritic material where the overlay is applied.

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative (2) If ambient-temperature temper bead welding is No Ambient-temperature temper bead welding N/A used, Mandatory Appendix I shall be used. will be performed in accordance with Code Case N-638-10 amended as discussed below.

(d) Prior to deposition of the weld overlay, the surface Yes The requirements for examination prior to N/A to be weld overlaid shall be examined using the liquid deposition of the weld overlay in N-740-2 are penetrant method. Indications with major dimensions equivalent to ASME Section XI, Non-greater than 1/16 in. (1.5 mm) shall be removed, reduced Mandatory Appendix Q, Q-2000 which has in size, or weld repaired in accordance with the been accepted for use by the NRC.

following requirements:

(1) One or more layers of weld metal shall be Yes The requirements for examination prior to N/A applied to seal unacceptable indications in the area to deposition of the weld overlay in N-740-2 are be repaired with or without excavation. The thickness of equivalent to ASME Section XI, Non-these layers shall not be used in meeting weld Mandatory Appendix Q, Q-2000 which has reinforcement design thickness requirements. Peening been accepted for use by the NRC.

the unacceptable indication prior to welding is permitted.

(2) If weld repair of indications identified in (d) is re-Yes The requirements for examination prior to N/A quired, the area where the weld overlay is to be deposition of the weld overlay in N-740-2 are deposited, including any local weld repairs or initial equivalent to ASME Section XI, Non-weld overlay layer, shall be examined by the liquid Mandatory Appendix Q, Q-2000 which has penetrant method. The area shall contain no indications been accepted for use by the NRC.

with major dimensions greater than 1/16 in. (1.5 mm) prior to application of the structural layers of the weld overlay.

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative (3) To reduce the potential of hot cracking when Yes A minimum of one layer of ER309L stainless N/A applying an austenitic nickel alloy over P-No. 8 base steel filler metal will be applied the stainless-metal, it is permissible to apply a layer or multiple layers steel safe end to prevent the potential of hot of austenitic stainless steel filler material over the cracking.

austenitic stainless steel base metal. The thickness of these layers shall not be used in meeting weld reinforcement design thickness requirements. The filler material used shall meet the minimum requirements for delta ferrite.

(e) Weld overlay deposits shall meet the following No The requirements of N-740-2(e)(1) are not N/A requirements: applicable based on the use of Alloy 52M.

(1) The austenitic stainless steel weld overlay shall consist of at least two weld layers having as-deposited delta ferrite content of at least 7.5 FN. The first layer of weld metal with delta ferrite content of at least 7.5 FN shall constitute the first layer of the weld reinforcement that may be credited toward the required thickness. Alternatively, layers of at least 5 FN are acceptable, provided the carbon content of the deposited weld metal is determined by chemical analysis to be less than 0.02%.

(2) The austenitic nickel alloy weld overlay shall consist of Yes Welding shall comply with the requirements Alternative requirements at least two weld layers deposited using a filler material with of ASME Code Case N-638-10, Similar and for crediting the dilution a Cr content of at least 28%. The first layer of weld metal Dissimilar Metal Welding Using Ambient layer for PWRs will not be deposited may not be credited toward the required thickness. Temperature Machine GTAW Temper Bead used.

Alternatively, for PWR applications, a first diluted layer Technique,Section XI, Division 1, except as may be credited toward the required thickness, provided follows:

the portion of the layer over the austenitic base material, austenitic filler material weld, and the associated dilution An alternative is proposed to the requirement zone from an adjacent ferritic base material contain at of N-638-10, 4(a)(2) that requires that When least 24% Cr, and the Cr content of the deposited weld austenitic materials are used, the completed metal is determined by chemical analysis of the weld shall be nondestructively examined production weld or of a representative coupon taken after the three tempering layers (i.e., layers from a mockup prepared in accordance with the WPS 1, 2, and 3) have been in place for at least 48

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative for the production weld. Alternatively, for BWR hr. Examination of the welded region shall applications, a diluted layer may be credited toward the include both volumetric and surface required thickness, provided the portion of the layer over the examination methods. N-638-10 is approved austenitic base material, austenitic filler material weld, and for use in Regulatory Guide 1.147.

the associated dilution zone from an adjacent ferritic base material contain at least 20% Cr, and the Cr content of the In lieu of the above requirement, deposited weld metal is determined by chemical analysis of nondestructive examinations may be the production weld or of a representative coupon taken from performed after completing the weld overlay.

a mockup prepared in accordance with the WPS for the This is consistent with requirements of ASME production weld. Code Case N-888-1, and is supported by the White Paper that was developed for the proposed change in Code Case N-888-1.

(f) This Case is only for welding in applications Yes The N2E nozzle is located in the lower head N/A predicted not to have exceeded thermal neutron (E < of the reactor vessel well below the beltline 0.5 eV) fluence of 1 x 1017 neutrons per cm2 prior to region (high fluence region). The current welding. accumulated EFPY for NMP1 is 40.3. For the N1 nozzles, which are above the N2E nozzle and also below the beltline region, the fast neutron fluence value (E>1.0 MeV) projected at 46 EFPY at the inside diameter (0T) of the vessel is 7.39 E+16 neutron/cm2 for the N1 nozzle closest in azimuth to the N2E nozzle. This value is below the threshold level of 1E+17 neutron/cm 2 (E >

1.0 MeV) and as such the material in the area of this repair is not expected to have decreased fracture toughness and ductility associated with damage of low alloy steels in the beltline region. In the lower head region of the reactor vessel, the thermal neutron fluence (E < 0.5 eV) is predicted to be below the threshold of concern for weldability based upon the findings in BWRVIP-97-A, which shows that vessel internals components below the core plate are all considered within the generic weldability boundary. This weld overlay will be installed external to the

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative reactor vessel below the core plate elevation, therefore there is not a weldability concern for the repair.

(g) A new weld overlay shall not be installed over the top No The proposed alternative is the first N/A of an existing weld overlay that has been in service. application of a weld overlay repair in this location.

2 CRACK GROWTH AND DESIGN The weld overlay is designed using the guidance of ASME Section XI Code Case N-740-2 and Non-Mandatory Appendix Q as described in the proposed alternative.

3 EXAMINATION

In lieu of all other examination requirements, the Yes The requirements for qualification of Ultrasonic examination examination requirements of this Case shall be met for ultrasonic examination personnel in IWA-personnel shall be the life of the overlay. Nondestructive examination 2300 of the 2013 Edition of ASME Section XI qualified in accordance methods shall be in accordance with IWA-2200, have been approved by the NRC in 10 CFR with IWA-2300.

except as specified herein. Nondestructive 50.55a.

examination personnel shall be qualified in accordance Ultrasonic examination with IWA-2300. Ultrasonic examination procedures ASME Section XI Code Case N-653-2 is procedures will be and personnel shall be qualified in accordance included in Table 1 of Regulatory Guide qualified in accordance with Appendix VIII, Supplement 11. The 1.147, Revision 20 and is listed as available with the requirements of examination shall be performed to the maximum extent for use in the NMP1 ISI Program. ASME Section XI Code practicable, for axial and circumferential flaws. If 100% Case N-653-2, coverage of the required volume for axial flaws cannot Qualification Requirements for Full be achieved, but essentially 100% coverage for Structural Overlaid circumferential flaws (100% of the susceptible Wrought Austenitic Piping volume) can be achieved, the examination for axial Welds.

flaws shall be per-formed to achieve the maximum coverage practicable, with limitations noted in the

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative examination report. The ex-amination coverage requirements shall be considered to be met. For cast stainless steel components for which no supplement is available in Appendix VIII, the weld volume shall be examined using Appendix VIII procedures to the maximum extent practicable.

(a) Acceptance Examination Yes The surface finish requirements of N-740-2 Ultrasonic examination (1) The weld overlay shall have a surface finish of are the same as ASME Section XI, Non-procedures will be 250 in. (6.3 m) RMS or better and contour that Mandatory Appendix Q, Article Q-4100 which qualified in accordance permits ultrasonic examination in accordance with has been accepted for use by the NRC. with the requirements of procedures qualified in accordance with Appendix ASME Section XI Code VIII. The weld overlay shall be inspected to verify ASME Section XI Code Case N-653-2 is Case N-653-2, acceptable configuration. included in Table 1 of Regulatory Guide Qualification 1.147, Revision 20 and is listed as available Requirements for Full for use in the NMP1 ISI Program. Structural Overlaid Wrought Austenitic Piping Welds.

(2) The weld overlay and the adjacent base material Yes The surface examinations requirements and The proposed alternative for at least 1/2 in. (13 mm) from each side of the overlay acceptance criteria for the weld overlay and eliminates the 48-hour shall be examined using the liquid penetrant method. adjacent base material are equivalent to hold time prior to The weld overlay shall satisfy the surface examination ASME Section XI, Non-Mandatory Appendix performance of NDE as acceptance criteria for welds of the Construction Code Q, Article Q-4100 which has been accepted discussed below.

or NB-5300. The adjacent base material shall satisfy for use by the NRC.

the surface examination acceptance criteria for base material of the Construction Code or NB-2500. If Elimination of the 48-hour hold prior to ambient temperature temper bead welding is performance of NDE is discussed below.

performed, the liquid penetrant examination of the completed weld overlay shall be conducted no sooner than 48 hr following completion of the three tempering layers over the ferritic steel.

(3) The examination volume A-B-C-D in Figure Yes The ultrasonic examination requirements, The proposed alternative 1(a) shall be ultrasonically examined to assure including unacceptable conditions and eliminates the 48-hour adequate fusion (i.e., adequate bond) with the base acceptance standards for planar flaws in the hold time prior to

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative material and to detect welding flaws, such as interbead weld overlay of Code Case N-740-2 are performance of NDE as lack of fusion, inclusions, or cracks. The interface C-D equivalent to the rules of ASME Section XI, discussed below.

shown between the overlay and weld includes the Non-Mandatory Appendix Q, Article Q-4100 bond and heat-affected zone from the overlay. If and Figure Q-4100-1 which have been The examination volume ambient temperature temper bead welding is accepted for use by the NRC. identified in Code Case performed, the ultrasonic examination shall be N-740-2, Figure 1 will not conducted no sooner than 48 hr following ASME Section XI, Non-Mandatory Appendix be examined. In lieu of completion of the three tempering layers over the Q, has been accepted by the NRC for this requirement, the ferritic steel. Planar flaws detected in the weld defining the acceptance examination volume examination volume A-B-overlay acceptance examination shall meet the for weld overlay repairs. C-D in Non-Mandatory preservice examination standards of IWB-3514. In Appendix Q, Figure Q-applying the acceptance standards to planar Because the proposed alternative does not 4100-1 will be used.

indications, the thickness, t1, or t2 defined in take structural credit for the weld overlay, Figure 1(b), shall be used as the nominal wall Figure 1(b) of N-740-2 is not required for thickness in IWB-3514, provided the base material defining the acceptance standards for the be-neath the flaw (i.e., safe end, nozzle, or piping weld overlay.

material) is not susceptible to SCC. For susceptible material, t shall be used. If a flaw in 1

the overlay crosses the boundary be-tween the two regions, the more conservative of the two dimensions (t1 or t2 ) shall be used. Laminar flaws in the weld overlay shall meet the following requirements:

(-a) The acceptance standards of IWB-3514 shall be met, Yes The acceptance standards for laminar flaws N/A with the additional limitation that the total laminar flaw area in the weld overlay of Code Case N-740-2 shall not exceed 10% of the weld surface area and that no are equivalent to the rules of ASME Section linear dimension of the laminar flaw area shall exceed the XI, Non-Mandatory Appendix Q, Article Q-greater of 3 in. (76 mm) or 10% of the pipe circumference. 4100 which has been accepted for use by the NRC.

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative

(-b) For examination volume A-B-C-D in Figure 1 (a), the Yes The acceptance standards for laminar flaws The examination volume reduction in coverage due to laminar flaws shall be less than in the weld overlay of Code Case N-740-2 identified in Code Case 10%. The uninspectable volume is the volume in the weld are equivalent to the rules of ASME Section N-740-2, Figure 1 will not overlay underneath the laminar flaws for which coverage XI, Non-Mandatory Appendix Q, Article Q-be examined. In lieu of cannot be achieved with the angle beam examination 4100 which has been accepted for use by this requirement, the method. the NRC. examination volume A-B-C-D in Non-Mandatory ASME Section XI, Non-Mandatory Appendix Appendix Q, Figure Q-Q, Figure Q-4100-1 has been accepted by 4100-1 will be used.

the NRC for defining the acceptance examination volume for weld overlay repairs.

Figure Q-4100-1 is equivalent to Code Case N-740-2, Figure 1(a).

(-c) Any uninspectable volume in the weld overlay shall be Yes The acceptance standards for laminar flaws N/A assumed to contain the largest radial planar flaw that could in the weld overlay of Code Case N-740-2 exist within that volume. This assumed flaw shall meet the are equivalent to the rules of ASME Section preservice examination acceptance standards of IWB-3514, XI, Non-Mandatory Appendix Q, Article Q-with nominal wall thickness as defined above the planar 4100 which has been accepted for use by flaws. Alternatively, the assumed flaw shall be evaluated and the NRC.

meet the requirements of IWB-3640, IWC-3640, and IWD-3640, as applicable. Both axial and circumferential planar flaws shall be assumed.

(4) After completion of all welding activities, VT-3 visual Yes A VT-3 visual examination of all affected examination shall be performed on all affected restraints, restraints, supports, or snubbers (if supports, and snubbers, to verify that design tolerances are applicable) will be performed to ensure that met. they have been returned to the design configuration following application of the weld overlay.

N-740-2 Figure 1, Acceptance Examination Volume and No ASME Section XI, Non-Mandatory Appendix The examination volume Thickness Definitions Q, Figure Q-4100-1 has been accepted by identified in Code Case the NRC for defining the acceptance N-740-2, Figure 1 will not examination volume for weld overlay repairs. be examined. In lieu of this requirement, the

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative Figure Q-4100-1 is equivalent to Code Case examination volume A-B-N-740-2, Figure 1(a). C-D in Non-Mandatory Appendix Q, Figure Q-Because the proposed alternative does not 4100-1 will be used.

take structural credit for the weld overlay, Figure 1(b) of N-740-2 is not required for defining the acceptance standards for the weld overlay.

(a) Preservice Inspection Yes The examination volume specified in Figure The rules for weld (1) The examination volume in Figure 2 shall be 5.1-2 is identical to that in Nonmandatory overlays on cast ultrasonically examined. The angle beam shall be directed Appendix Q, Figure Q-4300-1 and N-740-2, austenitic stainless steel perpendicular and parallel to the piping axis, with scanning Figure 2. base materials is not performed in four directions, to locate and size any planar applicable based on the flaw that have propagated into the outer 25% of the base configuration.

metal thickness or into the weld overlay. For weld overlays on cast austenitic stainless steel base materials, if a

100% through-wall flaw is used for crack growth, only planar flaws that have propagated into the weld overlay, or are in the overlay, are required to be located and sized.

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative (2) The preservice examination acceptance standards of Yes The preservice examination acceptance In lieu of the IWB-3514 shall be met for the weld overlay. In applying the standards of Code Case N-740-2 are requirements of 2(b) of acceptance standards to planar indications, the equivalent to the rules of ASME Section XI, Code Case N-740-2, the thickness, t 1 or t 2, defined in Figure 1(b), shall be used Non-Mandatory Appendix Q, Article Q-4200. design of the weld as the nominal wall thickness in IWB-3514, provided the overlay will utilize the base material beneath the flaw (i.e., safe end, nozzle, or Since the proposed alternative does not take requirements described in piping material) is not susceptible to SCC. For structural credit for the weld overlay, Figure 5.1.3(b) of the proposed susceptible material, t shall be used. Planar flaws in the 1(b) of N-740-2 is not required for defining alternative as described 1 the examination volume for preservice above.

outer 25% of the base metal thickness shall meet the examinations of the weld overlay.

design analysis requirements of 2(b).

(3) The flaw evaluation requirements of IWB-3640, IWC-Yes Indications identified during preservice N/A 3640, or IWD-3640 shall not be applied to planar flaws, inspection of the weld overlay shall not be identified during preservice examination, that exceed the accepted by evaluation. Any flaws identified preservice examination acceptance standards of IWB-during preservice inspection are required to 3514. be repaired or reduced to an acceptable size.

This will be applied only to the weld overlay volume.

(a) Inservice Inspection No Since the proposed alternative is only N/A (1) The weld overlay examination shall be added to the applicable for a single cycle, the inservice inspection plan. The weld overlay inspection interval shall inspection requirements of N-740-2 are not not be greater than the life of the overlay as determined in applicable. Inservice inspection 2(a) above. All weld overlays shall be examined prior to the requirements will be addressed in the end of their design life. subsequent proposed alternative for a permanent repair.

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative (2) The weld overlay examination volume in Figure 2 No Since the proposed alternative is only N/A shall be ultrasonically examined during the first or second applicable for a single cycle, the inservice refueling outage following application. Alternatively, for inspection requirements of N-740-2 are not mitigative weld overlays, in which pre-overlay examinations applicable. Inservice inspection are performed in accordance with 2(a)(3), post-overlay requirements will be addressed in the examinations are performed in accordance with (a) and (b), subsequent proposed alternative for a and no inside-surface-connected planar flaws are permanent repair.

discovered, the overlay may be placed immediately into the population to be examined in accordance with (5).

(3) The weld overlay examination volume in Figure 2 No Since the proposed alternative is only N/A shall be ultrasonically examined to determine if any new or applicable for a single cycle, the inservice existing planar flaws have propagated into the outer 25% of inspection requirements of N-740-2 are not the base material thickness or into the overlay. The angle applicable. Inservice inspection beam shall be directed perpendicular and parallel to the requirements will be addressed in the piping axis, with scanning performed in four directions. subsequent proposed alternative for a permanent repair.

(4) The weld overlay shall meet the inservice No Since the proposed alternative is only N/A examination acceptance standards of IWB-3514. In applicable for a single cycle, the inservice applying the acceptance standards to planar indications, the inspection requirements of N-740-2 are not thickness, t1 or t2, defined in Figure 1, sketch (b), shall be applicable. Inservice inspection used as the nominal wall thickness in IWB-3514, provided requirements will be addressed in the the base material beneath the flaw (i.e., safe end, nozzle, subsequent proposed alternative for a or piping material) is not susceptible to SCC. For permanent repair.

susceptible material, t 1 shall be used. If the acceptance standards of IWB-3514 cannot be met, the weld overlay shall meet the acceptance standards of IWB-3600, IWC-3600, or IWD-3600, as applicable. If a planar flaw is detected in the outer 25% of the base material thickness shall meet the design analysis requirements of 2. Any indication characterized as stress corrosion cracking in the weld overlay material is unacceptable.

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative (5) Weld overlay examination volumes in Figure 2 that No Since the proposed alternative is only N/A show no indication of planar flaw growth or new planar applicable for a single cycle, the inservice flaws shall be placed into a population to be examined on a inspection requirements of N-740-2 are not sample basis, except as required by (1). Twenty-five applicable. Inservice inspection percent of this population shall be examined once during requirements will be addressed in the each inspection interval. subsequent proposed alternative for a permanent repair.

(6) If inservice examinations reveal planar flaw No Since the proposed alternative is only N/A growth, or new planar flaws, meeting the acceptance applicable for a single cycle, the inservice standards of IWB-3514, IWB-3600, IWC-3600, or IWB-inspection requirements of N-740-2 are not 3600, the weld overlay examination volume shall be applicable. Inservice inspection reexamined during the first or second refueling outage requirements will be addressed in the following discovery of the growth or new flaws. subsequent proposed alternative for a permanent repair.

(7) For weld overlay examination volumes with un-No Since the proposed alternative is only N/A acceptable indications in accordance with (4), the weld applicable for a single cycle, the inservice overlay, and original defective weld shall be removed. A inspection requirements of N-740-2 are not repair/replacement activity shall be performed in accor-applicable. Inservice inspection dance with IWA-4000. requirements will be addressed in the subsequent proposed alternative for a permanent repair.

(8) If preservice and inservice examinations in accordance No Since the proposed alternative is only N/A with ASME Section XI, Appendix VIII, Supplement 11 cannot applicable for a single cycle, the inservice be performed for the entire weld overlay examination volume inspection requirements of N-740-2 are not in Figure 2 because of cast austenitic stainless steel items, applicable. Inservice inspection and a 100% initial flaw assumption is not used in the crack requirements will be addressed in the growth evaluation of 2(a), a 75% through-wall depth may be subsequent proposed alternative for a assumed in the crack growth calculation, provided that the permanent repair.

required examination volume is examined at a higher frequency than the requirements in (c). The subject weld shall be ultrasonically examined during the first or second refueling outage following the weld overlay installation. If ultrasonic examination is performed prior to weld overlay installation and after installation without detecting any planar flaws in the original weld or the weld overlay, then the

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative ultrasonic examination during the first or second refueling outage is not required. After the first inservice examination, the required examination volume shall be ultrasonically examined every 10 years from the date of the installation until such time when ultrasonic examination is qualified to examine the cast austenitic stainless-steel portion of the required inspection volume in accordance with the performance demonstration requirements of ASME Code,Section XI, Appendix VIII. The inspection of the overlaid weld shall not be credited to satisfy the requirement of the 25%

inspection sample every ten years of overlaid welds without cast stainless steel materials. After the required examination volume is examined by qualified ultrasonic examination for the cast austenitic stainless-steel material and no planar flaws are detected, the weld may be placed in the 25%

inspection sample population in accordance with (5).

N-740-2 Figure 2, Preservice and Inservice Examination Yes ASME Section XI, Non-Mandatory Appendix Volume Q, Figure Q-4300-1 has been accepted for use by the NRC for defining the preservice and inservice examination volume for weld overlay repairs. Figure Q-4300-1 is equivalent to figure N-740-2, Figure 2.

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Included in Exceptions to N-740-2 Code Case N-740-2 Requirement Proposed Justification (highlighted in bold)

Alternative 4 PRESSURE TESTING Yes A system leakage test and VT-2 visual N/A A system leakage test shall be performed in accordance examination shall be performed on the weld with IWA-5000. overlay in accordance with IWA-5000 following completion of the weld overlay and acceptance examinations.

5 DOCUMENTATION Yes Documentation of the use of this Code Case NMP1 utilizes the Use of this Case shall be documented on Form NIS-2. in the post outage summary report is an alternate reporting administrative requirement. requirements of Code Case N-532-5, which is approved for use in Regulatory Guide 1.147, Revision 20.

MANDATORY APPENDIX I, AMBIENT-TEMPERATURE No Code Case N-638-10, Similar and Dissimilar The proposed alternative TEMPER BEAD WELDING Metal Welding Using Ambient Temperature will utilize the rules of Machine GTAW Temper Bead Technique is Code Case N-638-10 to listed in Table 1 of Regulatory Guide 1.147 apply the weld overlay Revision 20. with the exception of the 48-hour hold prior to Removal of the 48-hour hold is consistent completion of NDE. In with the requirements of ASME Code Case lieu of the 48-hour hold N-888-1 and is supported by the white paper NDE may be performed that was developed for the proposed change. after completion of the Although this ASME Code Case is not weld overlay.

approved in Regulatory Guide 1.147, it has been approved by the ASME Section XI Standards Committee. The white paper has also been accepted for publication in the 2023 PVP Conference Proceedings in July 2023, PVP2023-107489. A copy of the white paper supporting elimination of the 48-hour hold is included in Attachment 4.

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ATTACHMENT 4

Ambient Temperature Temper Bead-Elimination of 48-Hour Hold Time from N-888 When using Austenitic Filler Material

White Paper

1.0 Introduction and Background

In welding, the presence of hydrogen in the weld metal or heat affected zone (HAZ) can cause hydrogen-induced cracking (HIC) occurring phenomena that occurs after the weldment has cooled to at or near room temperature. HIC is largely dependent upon three main factors, diffusible hydrogen, residual stress and susceptible microstructure. There are many theories on the mechanism for HIC, however, it is well understood that HIC requires simultaneous presence of a threshold level of hydrogen, a susceptible brittle microstructure and tensile stress. Additionally, the temperature must be in the range of 32 to 212°F (0 to 100°C). Elimination of just one of these four contributing factors will prevent HIC. [1]

Two early overlay (WOL) repairs involving temper bead welding were applied to two core spray nozzle-to-safe end joints at the Vermont Yankee boiling water reactor (BWR) in 1986 to mitigate intergranular stress corrosion cracking [2]. To avoid post weld heat treatment, temper bead was deployed when installing the repair overlay on the low alloy steel SA-508 Class 2 (P-No. 3 Group 3) reactor pressure vessel nozzle. This early application of temper bead welding required elevated preheat and a post weld hydrogen bake.

As the industry experienced an increased need for temper bead welding the requirement for preheating and post weld bake made temper bead welding complicated. EPRI responded to the industry concern and conducted studies that demonstrated that repair to low alloy steel pressure vessel components could be made without the need for preheat or post weld bake

[3,4]. As a result of these studies the preheat and post weld bake requirements were not included in Case N-638 for ambient temperature temper bead welding with machine GTAW.

Deployment of the ambient temperature temper bead technique has been highly successful for many years with no evidence of HIC detected by nondestructive examination (NDE).

During the past twenty years, many temper bead weld overlay repairs were successfully performed on BWRs and PWRs using ambient temperature temper bead technique, as illustrated in Table 1. The operating experience shows that with hundreds of ambient temperature temper bead applications, there has not been a single reported occurrence of hydrogen induced cracking.

Case N-888 is the culmination of temper bead code cases that have been produced over the years, combining requirements from N-638, N-839, and Appendix I in cases such as N-740 and N-754, etc. Case N-888 applies to temper bead of P-No. 1 or P-No. 3 materials and their associated welds or welds joining P-No. 8 or P-No. 43 materials to P-No. 1 or P-No 3 materials. Additionally, Case N-888 provides provisions to allow for ambient temperature preheat with no post weld bake. However, the post weld 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold at ambient temperature

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has remained as a requirement in N-888. This 48-hour delay between welding completion and cooling to ambient temperature and the final nondestructive examination (NDE) of the fully welded component is intended to assure detection of delayed hydrogen cracking that is known to occur up to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the weldment is at ambient temperature.

The post weld 48-hour delay following cooling to ambient temperature has resulted in a considerable cost burden to utilities. As there are significant economic advantages associated with eliminating the 48-hour hold time and immediately performing NDE following the completed weld, it is important to determine the technical advantages and disadvantages of making such a change.

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Table 1: Successfully Implemented Repairs Completed Using Temper Bead Technique from 2002-2021

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2.0 Objective The objective of this white paper is to provide technical justification to eliminate the 48-hour delay when using austenitic filler materials in the temper bead welding process for P-No. 1 and P-No. 3 ferritic materials. The industry and regulatory technical concerns related to this change are examined and the technical bases for changing the requirements for the 48-hour delay are presented. Discussion from white paper for Ambient Temperature Temper bead

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Weld Overlay Gas Tungsten Arc Welding by Hermann and Associates [9] are included in this white paper.

If adopted, it is expected that the change in the 48-hour delay requirement will become part of a revision to the current ASME Section XI Case N-888 that currently allows for ambient temperature temper bead repairs but requires 48-hour delay after the initial three temper bead layers prior to final NDE.

3.0 Technical Issues Related to the 48 Hour Delay The reasons for performing the final NDE after the 48-hour delay is the recognition that alloy steels can become susceptible to HIC. There are two primary weld cracking mechanisms of concern for low alloy steels during cooling or after reaching ambient temperature. These are cold cracking of high restraint geometries (weld shrinkage-induced) and hydrogen induced cracking (HIC), often referred to as hydrogen delayed cracking. Cold cracking occurs immediately as the weldment cools to ambient temperature. In contrast, HIC can occur immediately during cooling to ambient temperature or up to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after reaching ambient temperature. Cold cracking that occurs with high restraint weldments would therefore be detected by NDE performed immediately after the weldment is complete.

EPRI studies [4] have indicated that cold cracking occurs under conditions of high geometrical restraint especially where low toughness HAZs are potentially present.

Restraint mechanisms can occur either hot (resulting in intergranular or interdendritic cracking), or cold (resulting in transgranular cracking of material having marginal toughness).

Cold cracking occurs immediately as the weld deposit cools to ambient temperature. Proper joint design, appropriate welding procedures and bead sequences, are practical solutions that avoid critical cold cracking conditions. This form of cracking is addressed effectively by the ASME code guidance including welding procedure qualification testing and by in-process and or post-weld inspections.

The other form of cracking at ambient temperature, which is the focus of this white paper, is HIC. This cracking mechanism manifests itself as intergranular cracking of prior austenite grain boundaries and in contrast to cold cracking generally occurs during welding, but also up to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after cooling to ambient temperature. It is produced by the action of internal tensile stresses acting on low toughness HAZs (generally characterized by inadequate tempering of weld related transformation products). The most widely accepted theory suggests that the internal stresses will be produced from localized buildup of monatomic hydrogen. Monatomic hydrogen can be entrapped during weld solidification, and will tend to migrate, over time, to prior austenite grain boundaries or other microstructure defect locations. As concentrations build, the monatomic hydrogen will recombine to form molecular hydrogen, thus generating highly localized internal stresses at these internal defect locations. Monatomic hydrogen is produced when moisture or hydrocarbons interact with the welding arc and molten weld pool.

The concerns with and driving factors that cause hydrogen induced cracking have been identified. These issues are fundamental welding and heat treatment issues related to temper bead welding, requiring a technical resolution prior to modification of the current

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ASME Code Cases N-888 by the ASME Code and the technical community. Specific concerns relate to the following issues:

-Microstructure

-Sources for Hydrogen Introduction

-Diffusivity and Solubility of Hydrogen In the following discussion of this white paper each of these factors is briefly described to provide insight into the impact and proper management of these factors that cause HIC.

4.0 Discussion of Technical Issues Related to the 48 Hour Delay Microstructure:

C-Mn and low alloy steels can have a range of weld microstructures which is dependent upon both specific composition of the steel and the welding process/parameters used.

Generally, untempered martensitic and untempered bainitic microstructures are the most susceptible to hydrogen cracking. These microstructures are produced when rapid cooling occurs from the dynamic upper critical (Ac3) transformation temperature [1]. Generally, a critical hardness level necessary to promote hydrogen cracking is on the order of Rc 35 for materials with high hydrogen and Rc 45 for low level of hydrogen. Maintaining hardness levels below these thresholds generally avoids hydrogen cracking [1].

EPRI has examined in detail the effects of welding on the hardening of low alloy steels. The microstructure evaluations and hardness measurements discussed in EPRI reports [4, 5, 6]

have described the effects of temper bead welding on the toughness and hardness of P-No.

3 materials. The research results have illustrated that the microstructure in the low alloy steel (P-No. 3) beneath the temper bead WOL in the weld HAZ consists of a structure that is tempered martensite or tempered bainite and has maximum hardness at a distance of 2 to 3 mm (80 to 120 mils) beneath the surface of the order of 280 to 300 KHN (28 to 30Rc) or lower. The research outlines that the microstructure resulting from temper bead welding is highly resistant to HIC. Additionally, hardness would not be a concern provided there are adequate hydrogen controls are in place.

Furthermore, materials having face-centered-cubic (FCC) crystal structures such as austenitic stainless steels (300 series) and nickel base alloys such as Inconel are not susceptible to hydrogen induced cracking. The reason is that FCC atomic structures have ample unit cell volume space to accommodate atomic (diffusible) hydrogen. It is noted that the diffusion of hydrogen at a given temperature is slightly higher in body-centered-cubic (BCC) materials, ferritic steels, than it is in FCC austenitic materials. The FCC crystal structure has increased capacity to strain significantly without cracking (ductility) providing acceptable levels of toughness capable of resisting HIC. The inherent ability to deform and accommodate diffusible hydrogen are the reasons austenitic stainless steel and nickel base coated electrodes do not have low hydrogen designators that are found for ferritic weld materials [6]. Since the ferritic HAZ is in a tempered condition and an FCC filler material is used, a susceptible microstructure susceptible to HIC is highly unlikely.

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Presence/sources of Hydrogen:

Hydrogen can be introduced into the weld from several sources. These include 1) hydrogen in the original base material, 2) moisture in electrode coatings and fluxes, 3) organic contaminants (grease or oils), 4) hydrogen in the shielding gas and 5) humidity in the atmosphere.

The reduction of diffusible hydrogen in temper bead and non-temper bead weldments begins with implementing low hydrogen weld practices. These practices originate with Federal requirements that nuclear utilities control special processes such as welding and design and fabricate components to various codes and standards. These requirements, when followed, will effectively eliminate the contamination, and minimize the environment pathways.

Cleanliness of surfaces to be welded are mandated by Code and subsequently implemented via adherence to sound welding programs. The controls and requirements for cleanliness of the welded surface at nuclear utilities significantly reduce the likelihood of hydrogen entering the weld from surface contamination. Furthermore, repair and replacement applications typically deal with components that have been at operating temperatures above 390ºF (200ºC) for many years and any hydrogen present in the base material would have diffused from the steel and escaped to the atmosphere. Thus, surface contaminants and the base materials are not expected to be a significant source of diffusible hydrogen.

For SMAW, main pathway for diffusible hydrogen to enter the weldment will be the electrode coating. Welding programs primarily maintain low moisture in electrode coatings through procurement via an approved supplier, controlled storage conditions, and conservative exposure durations. The conservative exposure duration and coatings that resist moisture uptake minimize the amount of additional moisture in the coated electrode taking into consideration that moisture uptake is a function of time, temperature, and relative humidity.

Extensive testing by the EPRI Welding and Repair Technology Center shows there is an extremely low probability of HIC with H4 and H4R electrodes. EPRI performed diffusible hydrogen analysis per AWS A4.3 via gas chromatography on thirteen commercially available electrodes. Electrodes with AWS E7018, E8018 and E9018 from multiple vendors exposed at 27°C at 80% relative humidity (HR) for exposure times from 0 to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Many of the electrodes did not have R moisture resistant coating.

Figure 1 shows EPRI diffusible hydrogen test results for the thirteen lots of low hydrogen electrodes. All H4R electrodes exhibited < 16ml/100g of diffusible hydrogen at 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of exposure. Figure 3 shows that new electrodes without exposure have < 2ml/100g diffusible hydrogen. Only one of the electrodes tested at the extremely aggressive 27°C and 80%

Relative Humidity (HR) 72-hour exposure had diffusible hydrogen > 4 ml/100g. This demonstrates that exposure limits in the field of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or less is adequate to assure electrodes maintain the H4R limit. Ferritic electrodes were verified to have less than 4ml/100g diffusible hydrogen [6]. Testing verifies that ambient temperature is acceptable, post weld hydrogen bakeout is not needed, and a 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold at ambient temperature prior to performing final NDE is unnecessary and diffusible hydrogen levels will be below any susceptibility threshold that supports HIC.

For GTAW, EPRI performed studies investigating the diffusion of hydrogen into low alloy pressure vessel steels [4]. Due to the little information published at the time, EPRI decided to generate experimental data that would provide information on the levels of diffusible

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hydrogen associated with GTAW welding. The experimentation included individual sets of diffusible hydrogen tests as follows:

1. determination of diffusible hydrogen levels for the GTAW process under severe welding and environmental conditions simulating (or exceeding) repair welding conditions which may be expected in a nuclear plant.

2. measurement of diffusible hydrogen levels for various shieling gas dew point temperatures

3. examination of diffusible hydrogen levels for modern off-the-shelf filler wires Discussion of these items can be found in the EPRI documents and will not be reiterated in this report. The results demonstrate that introducing hydrogen is unlikely with the GTAW process. The typical hydrogen content for the GTAW process is less than 1.0mL/100g.

Therefore, hydrogen cracking is extremely unlikely.

Figure 1. Results of EPRI diffusible hydrogen testing at 27°C 80% Relative Humidity (HR) for zero to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of exposure [6]

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Figure 2. Graph showing slight increase of diffusible hydrogen after exposure of 24 and 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> [6]

Diffusivity and Solubility of Hydrogen Diffusivity and solubility of hydrogen in ferritic, martensitic, and austenitic steels is an important factor to consider. Materials having face-centered-cubic (FCC) crystal structures such as austenitic stainless steels (300 series) and nickel base Inconels generally are not considered to be susceptible to hydrogen delayed cracking as discussed in the microstructure section, above. Additionally, due to the temperatures expected during the welding of the temper bead layers, and during the welding of any non-temper bead layers, the temperature should be sufficient for the hydrogen to diffuse out of the HAZ, either escaping the structure or diffusing into the austenite, where it can be held in much greater quantities. The diffusion rate is clearly from the ferrite to the austenite and whatever hydrogen remains will reside in the austenite, which has little to no propensity to hydrogen related cracking.

Use of fully austenitic weld metal on ferritic base material is a technique that has been used for decades to install welds on ferritic base materials with high potential of HIC.

Austenitic filler materials are used in applications where preheat or post weld bake out is not possible because hydrogen ( H+) has high solubility, Figure 3, and low diffusivity, Figure 4, in austenite relative to other phases and acts as a trap for hydrogen to prevent HIC. Figure 3 show the solubility of hydrogen in -Fe and -Fe. Note that -Fe is at the saturation limit at ~4ml/100g of hydrogen. At temperatures above ~1700° C the solubility of hydrogen in austenite (-Fe) is nearly five times that of ferrite (-Fe). The benefit regarding HIC is the hydrogen stays in the austenite and is not available to promote HIC.

Figure 4 shows the overall difference in hydrogen diffusion between ferritic and austenitic materials. The diffusion of hydrogen in ferritic material is orders of magnitude

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greater compared to austenite. Again, the obvious advantage regarding HIC prevention is the hydrogen is slow to diffuse out of the austenitic material. When comparing how hydrogen behaves in ferritic versus austenitic weldments the hydrogen stays within the austenitic material whereas in ferritic welds, it tends to diffuse into the base material. For a weld made with ferritic electrodes, the H+ is absorbed in the molten weld puddle and as the weld solidifies, it transforms from austenite to ferrite and the H+ is rejected and diffuses into the HAZ of the base material. When the HAZ transforms from austenite to martensite, the H+ becomes trapped in the brittle microstructure and causes cracking, Figure 5. However, with an austenitic electrode, H+ is absorbed in the molten weld puddle and there is no solid state transformation in the solidified weld metal so the H+

stays in the austenitic weld material. No diffusion of the H+ into the brittle martensite, thus avoiding the possibility of HIC, Figure 6. Schematics in Figure 5 and Figure 6 are adapted from Lippold and Granjon as shown in draft chapters 2 & 4 for Temper Bead Welding Process in Operating NPPs, International Atomic Energy Agency, [1, 8].

Figure 3 - Hydrogen solubility in ferritic and austenitic materials as a function of temperature

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Figure 4 - Diffusion Coefficient of hydrogen in ferritic and austenitic materials as a function of temperature

Figure 5 - Hydrogen movement with ferritic electrodes [8]

Figure 6 - Hydrogen movement with austenitic electrodes [8]

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5.0 Conclusion The temper bead technique has become an increasingly effective tool for performing repairs on carbon and low alloy steel (P-No. 1 and P-No. 3) materials. Case N-888 provisions allow for ambient temperature temper bead welding with no post weld bake.

However, the 48-hour hold at ambient temperature prior to performing the final weld acceptance NDE has remained a requirement. This white paper summarizes the technical basis to eliminate the 48-hour delay for temper bead welding when using austenitic filler materials. The data and testing by EPRI and other researchers show that when austenitic weld metal is used the level of diffusible hydrogen content in the ferritic base metal HAZ is too low to promote HIC. The 48 -hour hold requirement in Case N-888 can therefore be removed.

Lastly, field experience applying austenitic filler materials to hundreds of dissimilar metal weld overlays using the ambient temperature temper bead procedures has never experienced hydrogen delayed cracking nor would it be expected. The reason is simply that the final diffusible hydrogen content is low - well below any threshold level that would be required for hydrogen induced cracking. Table 1 outlines the last 20 years of temper bead weld repairs in the nuclear industry with no reported occurrence of HIC when using austenitic weld metal.

References

1. Welding metallurgy and Weldability, 2015, chapter 5, Hydrogen Induced Cracking -

John Lippold

2. Inconel Weld-Overlay Repair for Low-Alloy Steel Nozzle to Safe-End Joint, EPRI Palo Alto, CA: 1991. NP-7085-D.

3. ASME Case N-638, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Techniques,Section XI Division 1, September 24, 1999.

4. Ambient Temperature Preheat for Machine GTAW Temperbead Applications, EPRI Palo Alto, 1998. GC-111050.

5. Temperbead Welding Repair of Low Alloy Pressure Vessel Steels: Guidelines,

EPRI Palo Alto, CA: 1993. TR-103354. 1993.

6. Welding and Repair Technology Center: Shielded Metal Arc Temper Bead Welding, EPRI Palo Alto, CA: 2015. 3002005536.

7. 2021 ASME Boiler & Pressure Vessel Code,Section XI Rules for Inservice Inspection of Nuclear Power Plant Components, Division 1.

8. S.L. McCracken and N. Mohr, Draft Chapters 2 and 4 prepared for: Temper Bead Welding Process in Operating NPPs, International Atomic Energy Agency, Vienna, 2022.

9. Repair and Replacement Applications Center: Temperbead Welding Applications 48-Hour Hold Requirements for Ambient Temperature Temperbead Welding, EPRI, Palo Alto, CA:

2006.1013558.