DCL-17-083, Request for Approval of Alternative for Application of Full Structural Weld Overlay, REP-RHR-SWOL

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Request for Approval of Alternative for Application of Full Structural Weld Overlay, REP-RHR-SWOL
ML17269A220
Person / Time
Site: Diablo Canyon  Pacific Gas & Electric icon.png
Issue date: 09/26/2017
From: Welsch J
Pacific Gas & Electric Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
DCL-17-083
Download: ML17269A220 (29)
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Text

Pacific Gas and Electric Company James M. Welsch Vice President, Nuclear Generation Diablo Canyon Power Plant Mail Code 104/6 P. 0. Box 56 Avila Beach, CA 93424 805.545.3242 Internal: 691.3242 September 26, 2017 Fax: 805.545.4884 PG&E Letter DCL-17-083 U.S. Nuclear Regulatory Commission A TIN: Document Control Desk Washington, DC 20555-0001 10 CFR 50.55a Diablo Canyon Units 1 and 2 Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Request for Approval of Alternative for Application of Full Structural Weld Overlay, REP-RHR-SWOL. Units 1 and 2

References:

1.
2.
3.
4.
5.

PG&E Letter DCL-17-049, "Flaw Evaluation of Unit 2 Residual Heat Removal Suction Weld Joint," dated May 18, 2017 PG&E Letter DCL-17-070, "Flaw Evaluation of Unit 1 Residual Heat Removal Suction Weld Joint," dated August 17, 2017 American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI, 2007 Edition with 2008 Addenda, Article IWA-4000 American Society of Mechanical Engineers Boiler and Pressure Vessel, Code,Section XI, 2007 Edition with 2008 Addenda, Appendix VIII, Supplement 11 EPRI Report 1026510, "Nondestructive Evaluation: Performance Demonstration Initiative (POl) Comparison to ASME Section XI, Appendix Vlll2007 Edition with 2008 Addendum, and 10CFR50.55a, Year 2011," EPRI, Palo Alto, California (2012)

Dear Commissioners and Staff:

In accordance with 10 CFR 50.55a, "Codes and standards," paragraph (z)(1 ),

Pacific Gas and Electric Company (PG&E) hereby requests NRC approval of an alternative for the fourth 1 0-year interval of the in-service inspection program.

PG&E identified a circumferentially oriented flaw in the Unit 2 residual heat removal (RHR) suction pipe at weld joint WIB-245, during the Unit 2 nineteenth refueling outage (Reference 1 ). PG&E also identified a circumferentially oriented flaw in the Unit 1 RHR suction pipe at weld joint WIB-228, during the Unit 1 twentieth refueling outage (Reference 2). Temperature monitoring of the RHR lines for both Units 1 and 2 indicated that thermal stratification and temperature cycling are present at both of these weld locations. These flaws were evaluated, including a flaw growth analysis, in accordance with ASME Code,Section XI criteria, and continued operation of both units for an additional operating cycle was shown to be acceptable (References 1 and 2). Both of these evaluations show that thermal fatigue is a A member of the STARS Allian<;e Callaway

  • Diablo Canyon
  • Palo Verde
  • Wolf Creek

Document Control Desk September 26, 2017 Page 2 PG&E Letter DCL-17-083 major contributor to the overall flaw growth. PG&E has determined that the primary degradation mechanism is thermal fatigue based on the data obtained from temperature monitoring in both units, and also based on the evaluations presented in References 1 and 2.

PG&E is proposing to repair the detected flaws in the RHR Pipe-to-Elbow Welds WIB-228 and WIB-245, by installing a full structural weld overlay (SWOL) as an alternative to the requirements in Reference 3. The proposed SWOL will be designed and evaluated for mitigation of both thermal fatigue and stress corrosion cracking under the conservative assumption that both degradation mechanisms are active. The details of the alternative are provided in the Enclosure. The alternative is based on American Society of Mechanical Engineers Code Case N-740-2, as modified and supplemented in the Enclosure. In addition, PG&E is proposing to perform the associated ultrasonic examinations of these two weld overlays in accordance with Reference 4, except as modified by the Performance Demonstration Initiative for full SWOLs [Reference 5] as an alternative to the requirements in Reference 4 alone.

This request is submitted for NRC approval under the provision of 10 CFR 50.55a(z)(1) as an alternative that provides an acceptable level of quality and safety. PG&E requests approval of this request by January 12, 2018. This would allow PG&E to install the weld overlay for RHR Pipe-to-Elbow Weld, WIB-245, during the Unit 2 twentieth refueling outage, which is scheduled to begin on February 11, 2018.

PG&E makes no new or revised regulatory commitments (as defined by NEI 99-04) in this letter. If you have any questions or require additional information, please contact Mr. Hossein Hamzehee at (805) 545-4720.

Vice President, Nuclear Generation rntt/4231/50915941-19 Enclosure cc:

Diablo Distribution cc/enc:

Scott A. Morris, NRC Region IV Administrator (Acting)

Christopher W. Newport, NRC Senior Resident Inspector Gonzalo L. Perez, Branch Chief, California Department of Public Health Balwant K. Singal, NRC Senior Project Manager State of California, Pressure Vessel Unit A member of the STARS Alliance Callaway

  • Diablo Canyon
  • Palo Verde
  • Wolf Creek

Enclosure PG&E Letter DCL-17 -083 10 CFR 50.55a Request Number REP-RHR-SWOL Proposed Alternative In Accordance with 10 CFR 50.55a(z)(1)

-- Alternative Provides Acceptable Level of Quality and Safety --

Enclosure PG&E Letter DCL-17 -083

1. AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) CODE COMPONENT AFFECTED Class 1 similar metal welds with inside surface indications in existing weld metal and the heat affected zone of austenitic stainless steel base metal are listed in Table 1, below:

Table 1 -Affected Code Components Unit Weld Description Nominal Materials of Construction*

Designator Size (per ASME Code,Section II) 1 WIB-228 RHR Pipe-to-Elbow Weld 14inch Pipe: SA-376 TP316 Elbow: SA-403 TP316 Weld: SFA-5.9 ER308 SFA-5.4 E308 2

WIB-245 RHR Pipe-to-Elbow Weld 14inch Pipe: SA-376 TP316 Elbow: SA-403 TP316 Weld: SFA-5.9 ER308 Notes: RHR = Residual Heat Removal

  • Definition of nominal weld and base metals are listed as defined in ASME Code,Section II, as referenced by ASME Code, Section Ill.
2. APPLICABLE CODE EDITION and ADDENDA Diablo Canyon Power Plant (DCPP) is currently in the fourth 1 0-year in-service inspection (lSI) interval. ASME Boiler and Pressure Vessel Code (Code) of record for the current 1 0-year lSI interval isSection XI, 2007 Edition, with the 2008 Addenda (Reference 1 ). This Edition is also used for the Repair/Replacement Program.
3. APPLICABLE CODE REQUIREMENT The following codes are applicable:

American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI, 2007 Edition, with the 2008 Addenda, Article IWA-4000 (Reference 1 ).

American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI, 2007 Edition, with the 2008 Addenda, Appendix VIII, Supplement 11, "Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds," (Reference 2).

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4. REASON FOR PROPOSED ALTERNATIVE Enclosure PG&E Letter DCL-17 -083 Pacific Gas and Electric Company (PG&E) identified a circumferentially oriented flaw in the Unit 1 RHR suction pipe at weld joint WIB-228, during the Unit 1 twentieth refueling outage (Reference 8). The pipe wall thickness at this location is 1.4 inches. The measured circumferential length of the ultrasonic flaw indication is 6 inches outside diameter (OD) length, with a calculated circumferential inside diameter (I D) length of 4.8 inches. The flaw is connected to the ID surface, with a through-wall (radial) depth of 0.2 inches and a remaining ligament between the deepest point of the flaw and the OD of 1.20 inches. In Reference 8, this flaw was evaluated, including a flaw growth analysis, in accordance with ASME Code,Section XI criteria, and continued operation of Unit 1 for a period in excess of one additional operating cycle was shown to be acceptable. The configuration of the flaw is shown in Figure 1, with the flaw located in the lower quadrant of the elbow-to-pipe weld on the side closest to the horizontal pipe run downstream from the elbow.

PG&E identified a circumferentially oriented flaw in the Unit 2 RHR suction pipe at weld joint WIB-245, during the Unit 2 nineteenth refueling outage (Reference 7). The pipe wall thickness at this location is 1.42 inches. The measured circumferential length of the ultrasonic flaw indication is 8 inches OD length, with a calculated circumferentiaiiD length of 6.4 inches. The flaw is connected to the ID surface, with a through-wall (radial) depth of 0.34 inches and,

a remaining ligament between the deepest point of the flaw and the OD of 1.08 inches. In Reference 7, this flaw was evaluated, including a flaw growth analysis, in accordance with ASME Code,Section XI criteria, and continued operation of Unit 2 for a period in excess of one additional operating cycle was shown to be acceptable. The configuration of the flaw is shown in Figure 2, with the flaw also located in the lower quadrant of the elbow-to-pipe weld on the side also closest to the horizontal pipe run downstream from the elbow.

Based on the above Non-Destructive Examination (NDE) evaluation, the detected flaws in Unit 1 and Unit 2 are physically located in the same quadrant relative to the direction of the downstream 90-degree elbow, and are generally at the same angular position on the cross-section. This indicates the cause of the flaw and its growth in both units is due to the same degradation mechanism.

At the time of the discoveries, the examination scope was expanded per the ASME Code,Section XI, paragraph IWB-2430, "Additional Examinations," to include additional welds where required. No additional indications were identified during the expanded scope examinations of the additional welds.

PG&E reviewed the Unit 1 fabrication records for WIB-228 and found no evidence of ID weld repair during construction. Similar review of the Unit 2 fabrication records for WIB-245 determined that the weld ID was subjected to surface grinding during construction, but there was no evidence of ID weld repair Page 2 of 18

Enclosure PG&E Letter DCL-17 -083 after the grinding. Accordingly, no ID weld repairs have been performed on either WIB-228 or WIB-245.

During the refueling outages in which the flaws were detected, PG&E investigated the possible cause for the flaws. PG&E ruled out vibration as a possible cause based on the inspections results, which concluded that physical evidence indicative of excessive vibration was not present. PG&E conducted temperature monitoring for both Unit 1 and Unit 2 from plant startup through several days of full power operation using temporary thermocouples installed on the RHR piping. The recorded temperature data indicated that thermal stratification and temperature cycling are present at the 45-degree elbow in both units. A summary of the Unit 2 pertinent temperature data that was used to define the cyclic frequencies and stress amplitudes as input to the ASME Section XI flaw growth evaluations is presented in References 7 and 8. These flaw growth evaluations show that thermal fatigue is a major contributor to the overall flaw growth. PG&E has determined that the primary degradation mechanism is thermal fatigue, based on the data from temperature monitoring in both units and also based on the evaluations presented in References 7 and 8.

PG&E considered the following options for repair of the flaws:

Local repair of the weld flaw. This option is deemed undesirable due to a significant amount of time in the radiation area.

Complete removal of the flawed weld and base metal and replacement by welding in accordance with IWA-4000. This option is also deemed undesirable due to a significant amount of time in the radiation area. It also requires handling and disposal of radioactive waste material.

Overlay on the existing weld using austenitic stainless steel overlay material in accordance with Code Case N-504-4 and Section XI Appendix Q. This option provides a thick weld overlay, which may not generate sufficient compressive stress to mitigate flaw growth: Also the size of the weld overlay may require additional redesign and modification of adjacent pipe rupture restraints, which would result in additional radiation exposure.

Overlay using Alloy 52M material in accordance with Code Case N-7 40-2 with additional provisions. This option generates increased compressive stress to mitigate thermal fatigue flaw growth and is composed of corrosion resistant material, which will mitigate conservatively assumed stress corrosion cracking. This option also provides a thinner overlay, which does not require significant modification of adjacent structures, and requires the shortest amount of time in a radiation area for installation compared to the other viable options.

PG&E proposes to repair the detected flaws in the RHR Pipe-to-Elbow Welds WIB-228 and WIB-245 by installing a full structural weld overlay (SWOL) using the methodology in Code Case N-7 40-2. This approach provides an alternative Page 3 of 18

Enclosure PG&E Letter DCL-17 -083 to replacement of the component as a means of restoring full component integrity. In References 7 and 8, the flaw growth evaluations conservatively assumed the combined contribution of thermal fatigue and stress corrosion cracking to justify continued operation until repairs can be implemented.

Consistent with this assessment, the proposed SWOL repair will be evaluated for mitigation of both.thermal fatigue and stress corrosion cracking under the conservative assumption that both degradation mechanisms are active. This approach is also consistent with the requirements of Code Case N-7 40-2.

Specifics of the SWOL analysis and evaluation are contained in Section 5.0 of this Enclosure.

5. PROPOSED ALTERNATIVE AND BASIS FOR USE Pursuant to 10 CFR 50.55a(z)(1 ), PG&E proposes an alternative to the ASME Code requirements that are identified in Section 3 of this Enclosure. The alternative consists of installation of a SWOL that replaces the structural function of the existing weld containing the flaw. This alternative is based on the methodology contained in ASME Code Case N-740-2 (Reference 3).

The SWOL will be designed, installed and examined in accordance with Code Case N-7 40-2. Schematic representation of the SWOL for the pipe-to-elbow weld configuration is presented in Figure 3. The SWOL design is applicable for both Unit 1 and Unit 2.

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

The SWOL location (Unit 1 and Unit 2) is external to the reactor pressure vessel and not exposed to high fluence. The SWOL location is predicted to have thermal neutron (E < 0.5 eV) fluence less than 1 x 1017 neutrons per cm2 prior to welding, therefore no special welding requirements are necessary.

The SWOL is not being installed on top of an existing weld overlay that has been in service.

The interpass temperature will be measured by direct measuring devices (e.g.

thermocouples, pyrometers, temperature indicating crayons). The interpass temperature will be determined by heat flow calculations when it is impractical to use the direct measurement methods only if there are extenuating radiological conditions.

ASME Code Case N-7 40-2 provides requirements for application of the SWOL on welds joining P-No. 8 and P-No. 43, and permits extension of the SWOL over an adjacent weld joining P-No. 8 to P-No. 8 materials, if necessary for ultrasonic examination. This request for alternative is for installation of the SWOL on a weld joining P-No. 8 toP-No. 8 materials. In this situation, the use of the Code Page 4 of 18

Enclosure PG&E Letter DCL-17 -083 Case specified filler metal applied to the P-No. 8 to P-No.8 buttweld is permissible per the Code Case, and will not require a change to the filler metal used to apply the SWOL.

ASME Code Case N-7 40-2 was selected as the appropriate Code Case for this application, based on the utilization of SFA-5.14 ERNiCrFe-7A (Alloy 52M) filler metal for the repair. The increased yield strength of the ERNiCrFe-7A filler metal, over austenitic stainless steel, results in improved compressive weld residual stresses in the weldment and base metal, and thus mitigation of potential flaw growth from thermal fatigue. The higher ultimate strength of the ERNiCrFe-7A filler metal over that of austenitic stainless steel, allows for reduced SWOL weld volumes, resulting in reduced welding times, and reduced radiological exposure. In addition, this weld filler material provides a superior resistance to stress corrosion cracking (SCC). This material property will mitigate flaw growth from potential SCC, if any. This request for alternative takes no technical exceptions from the Code Case, other than use of a Performance Demonstration Initiative (POl) qualified NDE procedure.

The provisions of ASME Code Case N-740-2, Appendix I (Temper Bead) are not required. Appendix I is only applicable when the SWOL will be deposited on ferritic materials with impact properties sensitive to quenching and tempering.

The P-No. 8 materials in this application have an austenitic microstructure which excludes the need for temper bead welding in the application described in this request for alternative.

During post-overlay examinations, the ASME Code,Section XI acceptance standards will be applied for identification and evaluation of potential flaw indications, within the SWOL. These acceptance criteria for SWOL installation are consistent with previous criteria approved by the NRC for weld overlay installations that are listed in Section 8 of this Enclosure. Weld overlays have been used for repair and mitigation of cracking of similar and dissimilar metal welds (DMWs) in pressurized water reactors (PWRs) for many years.

NRC Generic Letter 88-01, "NRC Position on IGSCC in BWR Austenitic Stainless Steel Piping," approved the use of ASME Code,Section XI inspection procedures for determining the acceptability of installed weld overlays in boiling water reactor (BWR) reactor coolant pressure boundary piping. In addition, the NRC has conditionally accepted ASME Code Case N-504-4 (Reference 5) in Regulatory Guide (RG) 1.147, Revision 17. ASME Code Case N-504-4 was developed to codify the BWR weld overlay experience for similar metal welds using similar metal filler material. Code Case N-7 40-2 has since been developed and approved by ASME for use on DMWs using an SCC resistant nickel-based filler metal. ASME Code Case N-740-2 has not yet been approved for use by the NRC (RG 1.193, Revision 4). The following three issues are cited in RG 1.193, Revision 4:

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Enclosure PG&E Letter DCL-17 -083 a) The definition of nominal weld and base material appear to be inconsistent with the provisions of ASME Section Ill.

b) Lack of detail for how to perform the flaw growth or design analysis.

c) Lack of additional details on the design of the overlays.

These issues are addressed in this request and the details are presented below:

a) The NRC's position was that the definition of the SWOL material was not clearly specified in ASME Code Case N-740-2. In this request for alternative, the definition of nominal weld and base metals, the buffer layer material and the SWOL filler material are clearly specified in the following paragraphs in order to address the issue. The materials are defined in ASME Code,Section II and Section IX as referenced in ASME Code, Section Ill, Article NB-2000.

Definition of nominal weld and base metals: The affected components and the materials of construction of pipe, elbow and weld associated with the SWOL application are presented in Section 1, Table 1 of this Enclosure. The base metals are defined in ASME Code,Section IX, as P-No. 8. The filler metal for the existing joining weld is defined in ASME Code,Section IX, as A-8 filler metal.

Definition of buffer layer material: All filler metals used for the buffer layers will be specified and purchased in accordance with ASME Code Section II, Part C, and certified to ASME Code Section Ill. One or more stainless steel buffer layer(s), utilizing either SFA-5.9 ER308L, ER309L, or ER316L will be deposited over the stainless steel components to reduce the potential for hot cracking of the Alloy 52M overlay deposit. The filler material used will meet the minimum material specification requirements for delta ferrite. The implementation of buffer layers is presented schematically in Figure 4. The thickness of the buffer layer(s) will not be credited as structural thickness in the design calculations.

Definition of SWOL filler material: All filler metals used for the SWOL will be specified and purchased in accordance with ASME Code Section II, Part C, and certified to ASME Code Section Ill. The body of the SWOL will use SFA-5.14 ERNiCrFe-7;A. This material contains a specified minimum chromium (Cr) content of at least 28 percent. The Cr content of the first layer of deposited weld metal will be determined by chemical analysis of a representative coupon taken from a mockup that will be prepared in accordance with the welding procedure specification for the production weld, and shall demonstrate a minimum Cr content of at least 24 percent. The thickness of the first layer and subsequent layers will be credited toward the required SWOL thickness.

b) Crack growth calculations as required by Code Case N-7 40-2 will be performed as part of a design package. Flaw characterization and evaluation requirements are based on the as-found flaw, or postulated 75 percent through original wall-thickness axial and circumferential flaw, whichever is greater. For the postulated Page 6 of 18

Enclosure PG&E Letter OCL-17 -083 flaws, the axial flaw length shall be 1.5 inches (38 mm). The circumferential flaw length shall be assumed to be 360 degrees. The size of all flaws will be projected to the end of the design life of the overlay, which will be a minimum of 10 years, which exceeds the remaining operating license duration for each Unit.

PG&E will evaluate the SWOL, with the postulated flaw, for all the design transients and the observed thermal cycling phenomena. Crack growth, considering the effects of two different flaw growth mechanisms: fatigue crack growth and SCC, will be evaluated in accordance with ASME Code,Section XI, IWB-3640. If the flaw is at or near the boundary of two different materials, evaluation of flaw growth in both materials will be evaluated.

c) Analyses and Verifications The design, analysis, and inspection requirements of the weld overlay are listed below:

The analyses and verifications that are listed below shall meet or exceed the criteria specified in Code Case N-7 40-2 or in the applicable alternatives that are proposed in this request.

1. Component specific stress analyses shall be performed to establish a residual stress profile in the weld. The analyses shall conservatively consider an 10 weld repair from original construction. *10 weld repairs shall be assumed in these analyses to conservatively bound any actual weld repairs that may have occurred during original construction. As noted previously, PG&E has reviewed the fabrication records for WIB-228 and WIB-245 and found no evidence of 10 repair by welding during the production of these welds. The analysis shall then simulate application of the weld overlays to determine the final residual stress profile. Post weld overlay residual stresses at normal operating conditions, and under cyclic thermal conditions, will be shown to result in an improved stress state in the component that reduces the probability for further crack propagation.

Fracture mechanics analyses will be performed to predict crack growth.

Crack growth due to thermal fatigue and possible SCC in the original (existing) similar metal weld will be evaluated. The crack growth analyses will consider all design loads and transients, the thermal stratification and cycling loads, plus the post weld overlay through-wall residual stress distributions. A summary of the Unit 1 and Unit 2 combined pertinent temperature data will be included in the crack growth evaluation documentation. The crack growth analyses will determine the time period for the postulated cracks to reach the allowable flaw size after installation of the weld overlay. The allowable flaw size will be determined in accordance with ASME Section XI, Appendix C for the SWOL geometry. This time period will meet or exceed the design requirement of the weld overlay (i.e., continued operation of both the units until the expiration of the current operating license).

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Enclosure PG&E Letter DCL-17 -083

2. The analyses will demonstrate that the application of the weld overlays does not impact the conclusions of the existing piping analysis reports. The analyses will also demonstrate that ASME Code Section Ill stress and fatigue criteria, for both design loadings and the observed thermal cycling phenomena, are continued to be met for those piping components that are affected by the overlay (if any).
3. The total added weight on the piping systems due to the overlay will be evaluated for potential impact on piping system stresses and dynamic characteristics.

4. Axial shrinkage will be measured before and after the weld overlay application. Shrinkage stresses arising from the weld overlays at other locations in the piping systems will be demonstrated to not have an adverse effect on the systems. Clearances of affected supports and restraints will be checked after the overlay repair, and will be reset within the design ranges as required.

5. The as-built dimension of the weld overlays will be measured and evaluated to demonstrate that the as-built dimensions equal or exceed the minimum design dimensions of the overlays.

IWB-3134 states, "Analytical evaluation of examination results as required by IWB-3132.3 shall be submitted to the regulatory authority having jurisdiction at the plant site." In accordance with the requirements of IWB-3134, summaries of the analytical evaluation results associated with Items 1 through 3 listed above will be completed prior to the applicable outages and submitted to the NRC following installation of the weld overlays.

Items 4 and 5 will be performed following installation of the weld overlays and results will be included in the design modification package closure documents. This information will be made available to NRC Resident or Field Inspectors for review.

The application of SWOL's to both BWR and PWR systems has been documented in Reference 6 and has been endorsed by the NRC (ADAMS Accession No:

ML101660468).

Nondestructive Examination Procedures and Inspections NDE inspections will be performed in accordance with Code Case N-740-2 and Code Case N-653-1, except as noted herein.

As a part of the design of the SWOL, the SWOL length, surface finish, and flatness are specified to allow for post-installation, qualified ASME Code Section XI, Appendix VIII ultrasonic test (UT) examinations, as implemented through the Electric Page 8 of 18

Enclosure PG&E Letter DCL-17 -083 Power Research Institute (EPRI) POl Program (Reference 4 ). The ASME Code implementation requirements of the POl Program are contained in ASME Code Case N-653-1, which is approved in the Draft Revision 18 of NUREG 1.147 (Reference 1 0). SWOL inspections as implemented through the POl program, now incorporated in Code Case N-653-1, have been referenced previously in other SWOL alternative requests, as provided in Section 8 below. Comparison of ASME Code,Section XI, Appendix VIII, Supplement 11 and the POl Program is provided in.

The proposed alternative examinations include the SWOL and the required volume of the base material and original weld underneath the SWOL. The examinations specified in this proposed alternative provide adequate assurance of structural integrity for the following reasons:

The UT examinations that will be performed with the proposed alternative are in accordance with ASME Code Section XI, Appendix VIII, Supplement 11 (Reference 2), as implemented through the POl Program.

The proposed alternative examinations are considered more sensitive for detection of defects, either from fabrication or service-induced, than ASME Code, Section Ill radiography or UT methods. Further, construction flaws are included in the POl qualification sample sets for evaluating procedures and personnel.

The results from the proposed alternative examinations will be verified using acceptance criteria and evaluation methodology specified in ASME Code,Section XI. These criteria consider 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 size(s) for planar flaws (i.e.,

Table IWB-3514-2) and for laminar flaws (i.e., Table IWB-3514-3).

Any planar flaws found in the SWOL during either the weld overlay acceptance or preservice examinations are required to meet the preservice standards of ASME Code,Section XI, Table IWB-3514-2, as supplemented in Code Case N-7 40-2 Any laminar flaws found in the SWOL during either the weld overlay acceptance or preservice examinations are required to meet the preservice standards of ASME Code,Section XI, Table IWB-3514-3, as supplemented in Code Case N-740-2.

Ultrasonic examination will be performed to the maximum extent achievable and the total volume will be greater than 90 percent of the required examination volume in accordance with Code Case N-740-2. Schematic representation of the required ultrasonic examination volume is shown in Figure 5.

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Pre-Overlay Examinations Enclosure PG&E Letter DCL-17 -083 Qualified ultrasonic examinations will be conducted prior to the installation of the weld overlay and the flaw size will be determined.

Post-Overlay Examinations Two examinations will be conducted, after installation of the weld overlay: the acceptance examination of the overlay and the preservice inspection. The purpose of the acceptance examination is to assure a quality overlay was installed. The purpose of the preservice inspection is to locate and size any i'ndications and to provide a baseline for future examinations. These two examinations will be performed during the same time period, although listed separately.

PG&E will provide the following information to the NRC Resident or Field Inspectors for review, within 14 days after the completion of ultrasonic examination of the SWOL installation:

1. The acceptance examination results of the weld overlay(s),
2. The preservice inspection results of the weld overlay(s), and
3. A description of any repairs to the overlay material and/or base metal and the reason for repair.

Subsequent in-service inspections will be per Code Case N-7 40-2 for the current interval. The weld overlay examination will be added to the current fourth interval lSI plan. The weld overlay will be ultrasonically examined during the subsequent refueling outages, as required by Code Case N-740-2.

6. CONCLUSION PG&E proposes to repair the detected flaws in the RHR Pipe-to-Elbow Welds WIB-228 and WIB-245, in Unit 1 and Unit 2 respectively, by installing a full SWOL. The proposed SWOL will be designed and evaluated for mitigation of both thermal fatigue and stress corrosion cracking under the conservative assumption that both degradation mechanisms are active. Implementation of the SWOL alternative to IWA-4000 of ASME Code,Section XI described in this request produces an effective repair and mitigation of the identified welds and maintains the component geometry. It will also permit ASME Code, Appendix VIII UT examinations as implemented through the POl Program. Several SWOLs have been installed successfully for many years, for both similar metal welds and DMWs, in both PWR and BWR applications. The proposed alternative provides improved structural integrity and reduces the likelihood of leakage for the reactor coolant system at the RHR Pipe-to-Elbow Weld. Accordingly, the use of the proposed alternative provides an acceptable level of quality and safety in accordance with 10 CFR 50.55a(z)(1 ).

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7. DURATION OF PROPOSED ALTERNATIVE Enclosure PG&E Letter DCL-17-083 The provisions of this alternative are applicable to the fourth 1 0-year lSI intervals for DCPP Unit 1 which commenced on May 7, 2015, and will end on November 2, 2024 (end of operating license); and for DCPP Unit 2 which commenced on March 13, 2016, and will end August 26, 2025 (end of operating license). The SWOL installed in accordance with the provisions of this alternative will remain in place until the expiration of the current operating license of both units.
8. PRECEDENTS The proposed alternative is similar to the alternatives that have been previously approved by the NRC, for several plants, that are listed below:
1. Brunswick Nuclear Power Plant Serial: BSEP 17-0033, "Proposed In-service Inspection Alternative for Application of Dissimilar Metal Weld Full Structural Overlay," dated April6, 2017 (ADAMS Accession No: ML17096A619). Verbal Authorization: NRC Memorandum, "Brunswick Steam Electric Plant, Unit 2-Verbal Authorization of Relief Request for Reactor Vessel Closure Head Penetration Nozzle N9 Repair (CAC. No. MF9561) dated May 9, 2017 (ADAMS Accession No: ML17096A333).
2. Edwin I Hatch Nuclear Plant Letter NL-15-1146, "Proposed Alternative in Accordance with 10 CFR 50.55a(z)(1) Application of Dissimilar Weld Full-Structural Weld Overlays," dated July 2, 2015 (ADAMS Accession No:

ML15183A354). NRC Letter, "Edwin I. Hatch Nuclear Plant, Unit No. 1 -

Relief from the Requirements of the ASME Code (CAC No. MF6453)," dated December 18, 2015 (ADAMS Accession No: ML15349A973). Edwin I Hatch Nuclear Plant Letter NL-15-1621, "Response to Request for Additional Information on Proposed In-Service Inspection Alternative to Install Four Full Structural Weld Overlays," dated September 15, 2015 (ADAMS Accession No: ML15258A551).

NOTE: RAI Response from Edwin Hatch Nuclear Plant indicates that one of the welds (i.e., weld-13) is a stainless steel weld joining two sections of stainless piping material (Reference ML15258A551 ).

3. Calvert Cliffs Nuclear Power Plant Letter, "Request for Approval of Alternative (Relief Request) for Dissimilar Metal Weld Repairs (ISI-04-05)," dated May 18, 2010 (ADAMS Accession No: ML101410060). NRC Letter, "Calvert Cliffs Nuclear Power Plant, Unit Nos. 1 and 2 - Relief from the Requirements of the ASME Code (TAC Nos. ME3963 and ME3964)," dated February 24, 2011 (ADAMS Accession No: ML110410062).

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Enclosure PG&E Letter DCL-17 -083 The NRC found the use of the ASME Code,Section XI, Appendix VIII, Supplement 11 UT examinations by PDI qualified procedures acceptable, for identifying both construction and service induced flaws, in the following Safety Evaluation Reports (SER):

1. NRC Letter, "Summary of January 30, 2017, Teleconference with Entergy Nuclear Operations, Inc. Regarding Verbal Authorization for Relief Reguest RR-21 for the James A FitzPatrick Nuclear Power Plant (CAC No. MF9128),"

dated February 8, 2017 (ADAMS Accession No: ML17031A280).

2. NRC Letter, "Millstone Power Station, Unit No. 2-Alternative Use of Weld Overlay as Repair and Mitigation Technique (TAC No. MF3918)," dated April 24, 2015 (ADAMS Accession No: ML15082A409).
3. NRC Letter, "Edwin I Hatch Nuclear Plant, Unit No. 1-Relief from the Requirements of the ASME Code (CAC No. MF6453," dated December 18, 2015 (ADAMS Accession No: ML15349A973)

The NRC also accepted the use of ASME Code,Section XI acceptance standards (with certain restrictions similar to those proposed herein) for disposition of flaws identified in a weld overlay by PDI qualified UT examinations, in the following SER:

1. NRC Letter, "Three Mile Island Nuclear Station, Unit 1 (TMI-1) Request for Relief from Flaw Removal, Heat Treatment, and Nondestructive Examination Requirements for the Third 1 0-Year lnservice Inspection (lSI) Interval (TAC No. MC1201)," dated July 21, 2004 (ADAMS Accession No: ML041670510).
9. REFERENCES
1.

ASME Boiler and Pressure Vessel Code,Section XI, 2007 Edition, 2008 Addenda.

2.

ASME Boiler and Pressure Vessel Code,Section XI, 2007 Edition, 2008 Addenda Appendix VIII, Supplement 11, "Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds."

3.

ASME Code Case N-740-2, "Dissimilar Metal Weld Overlay for Repair or Mitigation of Class 1, 2, and 3 Items.

4.

EPRI Report 1026510, "Nondestructive Evaluation: Performance Demonstration Initiative (PDI) Comparison to ASME Section XI, Appendix Vlll2007 Edition with 2008 Addendum, and 10CFR50.55a, Year 2011".

EPRI, Palo Alto, CA: 2012.

5.

ASME Code Case N-504-4, "Alternative Rules for Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping."

Page 12 of 18

Enclosure PG&E Letter DCL-17 -083

6.

Materials Reliability Program: Technical Basis for Preemptive Weld Overlays for Alloy 82/182 Butt Welds in PWRs (MRP-169) Revision 1.

EPRI, Palo Alto, CA: 2008. 1016602.

7.

PG&E Letter DCL-17-049, "Flaw Evaluation of Unit 2 Residual Heat Removal Suction Weld Joint," dated May 18, 2017.

B.

PG&E Letter DCL-17-070, "Flaw Evaluation of Unit 1 Residual Heat Removal Suction Weld Joint," dated August 17, 2017.

9.

ASME Code Case N-653-1, "Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds,"Section XI, Division 1.

1 o.

Draft Regulatory Guide DG-1296, "lnservice Inspection Code Case Acceptability, ASME Section XI, Division 1." dated March 2016 (Proposed Revision 18 of Regulatory Guide 1.147, dated March 2016).

Page 13 of 18

Enclosure PG&E Letter DCL-17 -083 Figure 1 - Unit 1 - Configuration of Circumferential Flaw in RHR Pipe-to-Elbow Weld, WIB-228 Line 109 Weld WIB-228 DOWNSTREAM ELBOW

<1 FLOW TD 0" REF IONA*A lOOKING W ITH HOW NOT TO SCALE NOTE: This sketch is provided to show the relative positions of the flaw and the downstream elbow (for illustration purposes only).

Page 14 of 18

Enclosure PG&E Letter DC L 083 Figure 2-Unit 2-Configuration of Circumferential Flaw in RHR Pipe-to-Elbow Weld, WIB-245 NOT TO SCALE TOC ECT IONA*A lOOKING WIHi LOW Line 109 Weld WIB-245 20" DOWNSTREAM ELBOW FLOW 12'"

'"'A NOTE: This sketch is provided to show the relative positions of the flaw and the downstream elbow (for illustration purposes only).

Page 15 of 18

Enclosure PG&E Letter DCL-17 -083 Figure 3 - Schematic Representation of the SWOL ELBOW Page 16 of 18

Enclosure PG&E Letter DCL-17-083 Figure 4 : Schematic Representation of the Buffer Layer Stainless Steel Stainless Steel D ER308L/ER309L/ER316L Buffer Layers D ERNiCrFe-7 A Weld Overlay Page 17 of 18

Enclosure PG&E Letter DCL-17-083 Figure 5: Schematic Representation of the Ultrasonic Examination Volume EXAMINATION VOLUME SWOL Acceptance Examination Volume INSPECTION ZONE SWOL Preservice and lnservice Examination Volume Page 18 of 18

Enclosure PG&E Letter DCL-17 -083 Proposed Changes to ASME Code,Section XI, Appendix VIII for Compatibility with the Performance Demonstration Initiative (PDI) Program

Enclosure PG&E Letter DCL-17 -083 Proposed Changes to ASME Code,Section XI, Appendix VIII for Compatibility with the Performance Demonstration Initiative (POl) Program Supplement 11 -Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds 1.0 SPECIMEN REQUIREMENTS Qualification test specimens shall meet the requirements listed herein, unless a set of specimens is designed to accommodate specific limitations stated in the scope of the examination procedure (e.g., pipe size, weld joint configuration, access limitations). The same specimens may be used to demonstrate both detection and sizing qualification.

1.1 General The specimen set shall conform to the following requirements.

(a) Specimens shall have sufficient volume to minimize spurious reflections that may interfere with the interpretation process.

(b) The specimen set shall consist of at least three specimens having different nominal pipe diameters and overlay thicknesses. They shall include the minimum and maximum nominal pipe diameters for which the examination procedure is applicable. Pipe diameters within a range of 0.9 to 1.5 times a nominal diameter shall be considered equivalent. If the procedure is applicable to pipe diameters of 24 inches (600 mm) or larger, the specimen set must include at least one specimen 24 inches (600 mm) or larger but need not include the maximum diameter. The specimen set shall include at least one specimen with overlay not thicker than 0.1 inches PDI Program:

The Proposed Alternative to Supplement 11 Requirements Title Alternative: "Qualification Requirements for Overlaid Wrought Austenitic Piping Welds:

Basis: The title was clarified to be applicable for all overlays on wrought austenitic piping welds. The specific qualification shall detail the range of qualification.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Page 1 of 7

Supplement 11 -Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds (2.5 mm) more than the minimum thickness, and at least one specimen with overlay not thinner than 0.25 inches (6 mm) less than the maximum for which the examination procedure is applicable.

(c) The surface condition of at least two specimens shall approximate the roughest surface condition for which the examination procedure is applicable.

(d) Flaw Conditions (1) Base metal flaws. All flaws must be cracks in or near the approximate butt weld heat-affected zone, open to the inside surface, and extending at least 75 percent through the base metal wall. Flaws may extend 100 percent through the base metal and into the overlay material; in this case, intentional overlay fabrication flaws shall not interfere with ultrasonic detection or characterization of the cracking. Specimens containing intergranular stress corrosion cracking shall be used when available.

(2) (2) Overlay fabrication flaws. At least 40 percent of the flaws shall be noncrack fabrication flaws (e.g.,

sidewall lack of fusion or laminar lack of bond) in the overlay or the pipe-to-overlay interface. At least 20 percent of the flaws shall be cracks. The balance of the flaws shall be of either type.

(e) Detection Specimens

( 1) At least 20 percent but less than 40 percent of the base metal flaws shall be oriented within +/-20 deg of the pipe axial direction. The remainder shall be oriented circumferentially. Flaws shall not be open to any surface to which the candidate has physical or visual access.

(2) Specimens shall be divided into base metal and overlay fabrication grading units. Each specimen shall contain one or both types of grading units. Flaws shall Enclosure PG&E Letter DCL-17-083 PDI Program:

The Proposed Alternative to Supplement 11 Requirements Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Page 2 of 7

Supplement 11 - Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds not interfere with ultrasonic detection or characterization of other flaws.

(a)(1) A base metal grading unit includes the overlay material and the outer 25 percent of the original overlaid weld.

The base metal grading unit shall extend circumferentially for at least 1 inch (25 mm) and shall start at the weld centerline and be wide enough in the axial direction to encompass one half of the original weld crown and at least.5 inches (13 mm) of the adjacent base material.

For axially-oriented discontinuities, the axial dimension of the base metal grading unit may encompass the original weld crown and at least.5 inches (13 mm) of the adjacent base materials.

(a)(2) When base metal flaws penetrate into the overlay material, the base metal grading unit shall not be used as part of any overlay grading unit.

(a)(3) Sufficient unflawed overlaid weld and base metal shall exist on all sides of the grading unit to preclude interfering reflections from adjacent flaws.

(b)(1) An overlay fabrication grading unit shall include the overlay material and the base metal-to-overlay interface for a length of at least 1 inch (25 mm).

(b )(2) Overlay fabrication grading units designed to be unflawed shall be separated by unflawed overlay material and unflawed base metal-to-overlay interface for at least 1 inch (25 mm) at both ends. Sufficient unflawed overlaid weld and base metal shall exist on both sides of the overlay fabrication grading unit to preclude interfering reflections from adjacent fla_ws. The specific area used in one overlay fabrication grading unit shall not be used in another overlay fabrication grading unit. Overlay fabrication grading units need not be spaced uniformly about the specimen.

Enclosure PG&E Letter DCL-17-083 PDI Program:

The Proposed Alternative to Supplement 11 Requirements Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Page 3 of 7

Supplement 11 -Qualification Requirements for Full Structural Overlaid WroughtAustenitic Piping Welds (b )(3) Detection sets shall be selected from Table VIIIS2-1. The minimum detection sample set is five flawed base metal grading units, ten unflawed base metal grading units, five flawed overlay fabrication grading units, and ten unflawed overlay fabrication grading units. For each type of grading unit, the set shall contain at least twice as many unflawed as flawed grading units. For initial procedure qualification, detection sets shall include the equivalent of three personnel qualification sets. To qualify new values of essential variables, at least one personnel qualification set is required.

(f) Sizing Specimen (1) The minimum number of flaws shall be ten. At least 30 percent of the flaws shall be overlay fabrication flaws. At least 40 percent of the flaws shall be open to the inside surface. To assess sizing capabilities, sizing sets shall contain a representative distribution of flaw dimensions. For initial procedure qualification, sizing sets shall include the equivalent of three personnel qualification sets. To qualify new values of essential variables, at least one personnel qualification set is required.

(2) At least 20 percent but less than 40 percent of the flaws shall be oriented axially. The remainder shall be oriented circumferentially. Flaws shall not be open to any surface to which the candidate has physical or visual access.

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

( 4) Depth sizing specimen sets shall include at least two distinct locations where a base metal flaw extends into the overlay material by at least 0.1 inches (2.5 mm) in the through-wall direction.

Enclosure PG&E Letter DCL-17 -083 PDI Program:

The Proposed Alternative to Supplement 11 Requirements Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case I

N-653-1.

I Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Page 4 of7

Supplement 11 -Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds 2.0 Conduct of Performance Demonstration The specimen inside surface and identification shall be concealed from the candidate. All examinations shall be completed prior to grading the results and presenting the results to the candidate.

Divulgence of particular specimen results or candidate viewing of unmasked specimens after the performance demonstration is prohibited. The overlay fabrication flaw test and the base metal flaw test may be performed separately.

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

2.2 Length Sizing Test (a) The length sizing test may be conducted separately or in conjunction with the detection test.

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

c) For a separate length sizing test, the regions of each specimen containing a flaw to be sized shall be identified to the candidate. The candidate shall determine the length of the flaw in each region.

(d) For flaws in base grading units, the candidate shall estimate the length of that part of the flaw that is in the outer 25 percent of the base wall thickness.

Enclosure PG&E Letter DCL-17-083 PDI Program:

The Proposed Alternative to Supplement 11 Requirements Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Page 5 of 7

Supplement 11 -Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds 2.3 Depth Sizing Test (a) Depth sizing consists of measuring the metal thickness above the flaw (i.e.,

remaining ligament), and may be conducted separately or in conjunction with the detection test.

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

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

3.0 ACCEPTANCE CRITERIA 3.1 Detection Acceptance Criteria (a) Examination procedures shall be qualified as follows:

(1) All flaws within the scope of the procedure shall be detected, and the results of the performance demonstration shall satisfy the acceptance criteria of Table VIIIS2-1 for false calls.

(2) At least one successful personnel demonstration shall be performed meeting the acceptance criteria defined in 3.1 (b).

(b) Examination equipment and personnel shall be considered qualified for detection if the results of the performance demonstration satisfy the acceptance criteria of Table VIII-S2-1 for both detection and false calls.

Enclosure PG&E Letter DCL-17-083 PDI Program:

The Proposed Alternative to Supplement 11 Requirements Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Page 6 of 7

Supplement 11 -Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds c) The criteria in 3.1 (a) and 3.1 (b) shall be satisfied separately by the demonstration results for base metal grading units and by those for overlay fabrication grading units.

3.2 Sizing Acceptance Criteria Examination procedures, equipment, and personnel are qualified for sizing when the results of the performance demonstration satisfy the following criteria.

(a) The root mean square (RMS) error of the flaw length measurements, as compared to the true flaw lengths, is less than or equal to 0.75 inches (19 mm).

The length of a base metal flaw is measured at the 75 percent through-base-metal position.

(b) The RMS error of the flaw depth measurements, as compared to the true flaw depths, is less than or equal to 0.125 inches (3.2 mm).

Enclosure PG&E Letter DCL-17-083 POl Program:

The Proposed Alternative to Supplement 11 Requirements Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Alternative: PD-QPI-303 meets Code Case N-653-1.

Page 7 of 7

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