TMI-12-157, Submittal of Relief Request RR-12-02 Concerning the Installation of a Full Structural Weld Overlay on the Lower Cold Leg Letdown Nozzle Dissimilar Metal Welds and Alloy 600 Safe-End

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Submittal of Relief Request RR-12-02 Concerning the Installation of a Full Structural Weld Overlay on the Lower Cold Leg Letdown Nozzle Dissimilar Metal Welds and Alloy 600 Safe-End
ML12292A584
Person / Time
Site: Three Mile Island Constellation icon.png
Issue date: 10/18/2012
From: Jesse M
Exelon Generation Co
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
TMI-12-157
Download: ML12292A584 (13)
v • d • e


Text

10 CFR 50.55a TMI-12-157 October 18, 2012 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Three Mile Island Nuclear Station, Unit 1 Renewed Facility Operating License No. DPR-50 NRC Docket No. 50-289

Subject:

Submittal of Relief Request RR-12-02 Concerning the Installation of a Full Structural Weld Overlay on the Lower Cold Leg Letdown Nozzle Dissimilar Metal Welds and Alloy 600 Safe-End Attached for your review is a relief request associated with the fourth Inservice Inspection (lSI) interval for Three Mile Island Nuclear Station (TMI), Unit 1. TMI, Unit 1 is proposing to perform a weld overlay of the lower cold leg letdown nozzle dissimilar metal welds (DMWs) and Alloy 600 safe-end. The fourth interval of the TMI, Unit 1 lSI program complies with the 2004 Edition, no Addenda, of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code. We request your approval by October 18, 2013.

A summary of the regulatory commitments contained in this submittal is provided in . Attachment 2 contains Relief Request RR-12-02.

If you have any questions concerning this letter, please contact Tom Loomis at (610) 765-5510.

Respectfu Ily, Michael D. Jesse Director - licenSing egulatory Affairs Exelon Generation Company, LLC Attachments: 1) Summary of Commitments

2) Relief Request RR-12-02 cc: Regional Administrator, Region I, USNRC USNRC Senior Resident Inspector, TMI USNRC Project Manager, [TMI] USNRC

ATTACHMENT 1 Summary of Commitments

Attachment 1 Summary of Commitments The following table identifies commitments made in this document. (Any other actions discussed in the submittal represent intended or planned actions. They are described to the NRC for the NRC's information and are not regulatory commitments.)

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

(Yes/No)

Exelon Generation Company, Within 30 days Yes No LLC commits to providing the after the completion results of the ultrasonic of the last examination of the Full ultrasonic Structural Weld Overlay on the exam ination of the TMI, Unit 1 lower cold leg weld overlays letdown nozzle dissimilar metal during the fall 2013 welds and Alloy 600 safe-end. TMI, Unit 1 T1 R20 refueling outage.

The results will include:

  • A list of the indications detected,
  • The disposition of all the indications using the standards of ASME Code Cases N-740-2 and N-770-1,
  • The type and, if possible, nature of the indications.

Also included in the results will be a discussion of any repairs to the overlay material.

ATTACHMENT 2 Relief Request RR-12-02

10 CFR 50.55a RELIEF REQUEST RR-12-02 Revision 0 (Page 1 of 9)

Alternative Requirements for Installation of a Full Structural Weld Overlay on the Lower Cold Leg Letdown Nozzle Dissimilar Metal Welds and Alloy 600 Safe-End in Accordance with 10 CFR 50.55a(a)(3)(i) 1.0 ASME CODE COMPONENT(S) AFFECTED Code Class: 1

Reference:

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

Description:

Full SWOL of the 'C' Cold Leg Letdown Nozzle and Safe-End DMWs Component Number(s): See Table 1A for listing Drawing Number: 1D-ISI-MU-004 / R1 2.0 APPLICABLE CODE EDITION AND ADDENDA The Three Mile Island Nuclear Station, Unit 1, complies with the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, 2004 Edition, no Addenda.

3.0 APPLICABLE CODE REQUIREMENT

1. USAS B31 .1, Power Piping, 1967 Edition.
2. USAS B31.7, Nuclear Power Piping, February 1968 Draft Including June 1968 Errata.
3. ASME Code,Section XI, 2001 Edition, no Addenda, Appendix VIII, Supplement 11 .
4. ASME Code,Section XI, 2004 Edition, no Addenda, IWA-4000, "Repair/

Replacement Activities."

5. ASME Code Section XI, Appendix VIII, Supplement 11, as modified by 10 CFR 50.55a, provides qualification requirements for ultrasonic (UT) examination of FSWOLs.
6. 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."

10 CFR 50.55a RELIEF REQUEST RR-12-02 Revision 0 (Page 2 of 9)

7. ASME Code Case N-722-1, "Additional Examinations for PWR Pressure Retaining Welds in Class 1 Components Fabricated With Alloy 600/82/182 Materials,Section XI, Division 1," as modified by 10 CFR SO.SSa(g}(6)(ii)(E).
8. ASME Code Case N-770-1, "Alternative Examination Requirements and Acceptance Standards for Class 1 PWR Piping and Vessel Nozzle Butt Welds Fabricated With UNS N06082 or UNS W86182 Weld Filler Material With or Without Application of Listed Mitigation Activities,Section XI, Division 1," as modified by 10 CFR SO.SSa(g)(6)(ii)(F).

4.0 REASON FOR REQUEST Dissimilar metal welds (DMWs) on U.S. Pressurized Water Reactor (PWR) Reactor Coolant System (RCS) components often consist of Alloy 821182 weld material to connect stainless steel pipe or safe-ends to vessel nozzles and piping nozzles (branch connections), which are generally constructed using carbon or low alloy ferritic steel. These welds have shown a propensity for Primary Water Stress Corrosion Cracking (PWSCC) degradation.

Exelon Generation Company, LLC (Exelon) is taking a proactive approach in addressing Alloy 600 PWSCC degradation by applying a preemptive Full Structural Weld Overlay (FSWOL) to the 'C' lower cold leg letdown nozzle safe-end to nozzle DMW, Alloy 600 safe-end, and elbow to safe-end DMW. See Table 1B for component materials. TMI, Unit 1 plans to install the FSWOL during the T1 R20 refueling outage in fall 2013. The weld overlay is also being installed to obtain a condition that allows UT examination of the DMWs. The current nozzle, safe-end, and elbow condition prevent examination of the DMWs in accordance with Code Case N-770-1. The current configuration allows no coverage for circumferential flaws and 37.6% coverage for axial flaws on the safe-end to elbow DMW.

FSWOLs have been used for several years on piping of both Boiling Water Reactor (BWR) and PWR components to arrest the growth of existing flaws while establishing a new structural pressure boundary. Currently, there are no generically accepted criteria for a licensee to apply a FSWOL onto Alloy 82/182 DMWs. ASME Code Section XI, 2004 Edition, no Addenda is applicable for the TMI, Unit 1 Section XI Repair/Replacement Program, but does not contain the needed requirements for FSWOLs. FSWOLs have been applied to DMWs in other components in the PWR industry. This request proposes to use the guidance of ASME Section XI Code Case N-740-2, for application of a FSWOL to the lower cold leg letdown nozzle safe-end to nozzle DMW, Alloy 600 safe-end, and elbow to safe-end DMW at TMI, Unit 1 (see Figure 1). This request describes the requirements Exelon proposes to use to design and install a FSWOL on the letdown nozzle DMWs and safe-end.

10 CFR 50.55a RELIEF REQUEST RR-12-02 Revision 0 (Page 3 of 9)

The welding will be performed utilizing a mechanized 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.

When temper bead welding is not required, manual GTAW with Alloy 52M is an acceptable alternative to the mechanized GTAW for local repairs of weld defects or if additional weld metal is required locally to form the final FSWOL contour. Shielded metal arc welding (SMAW) using Alloy 152 (ENiCrFe-7), or GTAW using Alloy 82 (ERNiCr-3), would only be used to repair indications in the existing DMWs prior to FSWOL initiation. Alloy 82 (ERNiCr-3) will be used for a small segment of the sulfur mitigation layer to bridge between the stainless steel elbow and existing Alloy 82 DMW.

Repair/replacement activities associated with FSWOLs are required to address materials, welding parameters, personnel radiation exposure concerns, operational constraints, examination techniques, and procedural requirements.

5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE Pursuant to 10 CFR 50.55a(a}(3}(i), Exelon proposes applying a FSWOL designed in accordance with Code Case N-740-2 (Reference 5). Final UT examination of the finished FSWOL will be performed using Electric Power Research Institute (EPRI)

Performance Demonstration Initiative (PDI) demonstrated UT examination procedures and personnel in lieu of ASME Section XI, Appendix VIII, Supplement 11 (Reference 4) as proposed in an associated relief request (Reference 8) and found acceptable to the U.S. Nuclear Regulatory Commission (USNRC) (Reference 9).

Code Case N-740-2 has been used as a basis for applying FSWOLs at other PWR plants (References 6 and 7). The letdown nozzle FSWOL, described herein, will extend around the full circumference of the DMWs and safe-end as required by Code Case N-740-2. The specific thickness and length will be determined according to the guidance provided in Code Case N-740-2. The FSWOL will completely cover the DMWs and Alloy 600 safe-end and will also cover necessary adjacent ferritic steel nozzle and stainless steel elbow base material with Alloy 52M material to the extent that PWSCC susceptible material is mitigated and examination capability is maintained for adjacent welds. The purpose for this FSWOL approach is to produce a single FSWOL covering both DMWs thereby also providing the weld geometry required to perform the final UT examination and obtain the necessary examination volume coverage.

Prior to installation of the FSWOL, TMI, Unit 1 will complete a bare metal visual examination of the nozzle to safe-end and safe-end to elbow DMWs after the insulation is removed in the area around the nozzle and DMW areas to ensure that no through-wall (TW) cracks exist prior to applying the FSWOL. The visual examination will be completed in accordance with 10 CFR 50.55a(g)(6)(ii)(E}. No UT examinations in accordance with 10 CFR 50.55a(g)(6)(ii)(F) will be performed prior to performing the FSWOL. This approach will result in the welds affected by

10 CFR 50.55a RELIEF REQUEST RR-12-02 Revision 0 (Page 4 of 9) this FSWOL being classified as inspection Item F per Code Case N-770-1 after installation of the FSWOL Examinations of the completed FSWOL will be performed during the 2013 refueling outage as required by Code Cases N-740-2 and N-770-1 (as modified by 10 CFR SO.SSa(g)(6)(ii)(F)). Subsequent UT examinations will be performed as required by Code Case N-770-1 as modified by 10 CFR SO.SSa(g)(6)(ii)(F) or other requirements approved by the USNRC. Note that the USNRC staff has previously approved relief request 14R-OS of Reference 9 for the fourth lSI interval. This relief request addresses ASME Section XI, Appendix VIII, Supplement 11 qualification requirements for examination of FSWOLs. Relief Request 14R-OS is applicable to existing and future structural weld overlays and is applicable to all fourth lSI interval examinations on this weld overlay.

Preservice UT examination will be performed to the maximum extent practicable for searching for axial and circumferential flaws. Based upon the currently understood configuration and design, 100% UT examination coverage is anticipated in both circumferential directions searching for axially oriented flaws. Additionally, 100% UT examination coverage is anticipated in the downstream-oriented axial scan direction searching for circumferential flaws. The geometry of the stainless steel elbow (See Figure 1) limits UT examination coverage at the intrados of the elbow which results in a reduction of coverage. Therefore, UT examination scans in the upstream axial direction, searching for circumferential flaws are expected to achieve approximately 93% coverage. This coverage will not interrogate 100% of the susceptible material volume in one of the four directions in the intrados region shown in Figure 1. The combined coverage for all four examination directions is expected to be approximately 98% because of the inherent scan limitation of the elbow. However, depending on actual final conditions, UT examination coverage may be less than 98%, but it is still expected to at least be greater than 90%.

Per Code Case N-740-2, Paragraph 1.2(d), prior to FSWOL application, a liquid penetrant (PT) examination will be performed of the area where welding will occur, with the acceptance criteria that no indication with a major dimension greater than 1/16" is permitted. Rejectable indications will be removed or reduced to within the acceptance criteria, and the PT examination performed again. If any indication(s) do require repair, the repair will be completed and the area will again have a PT examination completed for final acceptance. TMI, Unit 1 intends to perform additional PT examination of the base metal/FSWOL as follows:

  • On the base metal and existing DMWs after surface conditioning but prior to installing the FSWOL
  • After excavation of any unacceptable flaws.
  • After grinding on unacceptable indications.
  • After completed repairs.

10 CFR 50.55a RELIEF REQUEST RR-12-02 Revision 0 (Page 5 of 9)

TMI, Unit 1 intends to perform UT examination of the completed FSWOL and after completing any repairs (if necessary) to the FSWOL. Exelon will provide the results of the UT examination of the FSWOL within 30 days after the completion of the last UT examination of the FSWOL during the fall 2013 TMI, Unit 1 T1 R20 refueling outage as described in Attachment 1.

The FSWOL will be designed per Code Case N-740-2. The design analyses will be available for USNRC staff review or submitted for review upon USNRC staff request.

The design analyses will include/evaluate the following aspects:

  • FSWOL structural sizing based on the maximum observed or assumed defect. Assumed flaw size is 100% TW circumferential flaw for the entire circumference and a 100% TW axial flaw that extends the combined length of the the Alloy 82 DMWs and Alloy 600 safe-end.
  • Design loads.
  • A finite element model of the nozzle and associated components.
  • Thermal and mechanical stress analyses.
  • Residual stress analysis that includes consideration of a severe inside diameter repair (assumed to be 50% TW, and 100% around the circumference, from the inside surface).
  • Crack growth evaluation that uses a conservative flaw growth rate and either assumes an existing detected flaw size or assumed flaw size (75% TW in both axial and circumferential directions), whichever is greater.
  • Effects of the FSWOL on the adjacent piping system.

Monitoring of preheat and interpass temperature is necessary to assure the field welding heat input remains within qualified parameters. Weld preheat temperature and heat input are monitored using calibrated contact pyrometers. The interpass temperature is measured multiple times within each layer.

Exelon intends to install one or more sulfur mitigation layer(s) to prevent hot cracking of the Alloy 52M material due to welding stainless steel materials. Exelon and the implementation vendor are aware of industry hot cracking that has been observed when welding Alloy 52M over a stainless steel material. In order to minimize the potential for cracking during installation of the letdown nozzle FSWOL at TMI, Unit 1, appropriate criteria and parameters have been established for control of the welding process. As an example, the welding heat input range has been determined to minimize weld metal contamination from the existing elbow materials. The FSWOL design includes no welding on cast stainless steel material, as the elbow construction is of wrought materials. Additionally, the elbow chemistries (from the Certified Material Test Report data) and weld geometry are reviewed to determine the level of risk for hot cracking when welding Alloy 52M over stainless steel base material. This review will result in specific mitigation efforts that will be employed during the installation of the FSWOL. Weld parameters and techniques specially

10 CFR 50.55a RELIEF REQUEST RR-12-02 Revision 0 (Page 6 of 9) developed for welding over stainless steel and Alloy 82 DMWs will be implemented to prevent cracking.

6.0 DURATION OF THE PROPOSED ALTERNATIVE The design and installation of the FSWOL are applicable to the remaining service life of the plant. Subsequent inservice examinations will be scheduled and performed in accordance with schedules and technical requirements acceptable to the USNRC as discussed in 10 CFR SO.SSa(g)(6)(ii)(F).

7.0 PRECEDENTS Similar relief requests were approved for use in USNRC Safety Evaluation Reports (References 6 and 7).

8.0 REFERENCES

1. ASME Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," 2004 Edition, no Addenda.
2. USAS 831.7, Nuclear Power Piping, February 1968 Draft Including June 1968 Errata.
3. USAS 831.1, Power Piping, 1967 Edition.
4. ASME Code,Section XI, 2001 Edition, no Addenda, Appendix VIII, Supplement 11, "Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds."

S. 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.

6. N. L. Salgado (U.S. Nuclear Regulatory Commission) to D. A. Heacock (Virginia Electric and Power Company), "North Anna Power Station, Unit No.1 (North Anna Unit 1), Relief Request (RR) N1-14-CMP-001, Regarding the Use of Weld Overlays As An Alternative Repair Technique (TAC No. MES96S),"

dated January 27,2012 (ML11348A219).

7. N. L. Salgado (U.S. Nuclear Regulatory Commission) to G. H. Gellrich (Calvert Cliffs Nuclear Power Plant, LLC), "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 (ML110410062).

10 CFR 50.55a RELIEF REQUEST RR*12*02 Revision 0 (Page 7 of 9)

8. P. B. Cowan (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission, "Submittal of Relief Requests Associated with the Fourth Inservice Inspection (lSI) Interval," dated August 10, 2010 (ML102290162).
9. H. K Chemoff (U.S. Nuclear Regulatory Commission) to M. J. Pacilio (Exelon Generation Company, LLC), "Three Mile Island Nuclear Station, Unit 1 - Fourth Inservice Inspection Interval Relief Requests 14R-02, 14R-03, 14R-04, 14R-05, and 14R-06 TAC Nos. ME4519, ME4520, ME4521, ME4522 AND ME4523),"

dated July 20, 2011 (ML111730475).

10 CFR 50.55a RELIEF REQUEST RR-12-02 Revision 0 (Page 8 of 9)

TABLE 1A Component Identification TMI, Unit 1 'C' Cold Leg Safe-End to Nozzle and Elbow to Safe-End Weld Scheduled for FSWOL During Outage T1 R20*

NOZZLE Safe-End to Size Elbow to Safe-End N-722-1, Item No.

Nozzle Weld # Adjacent Weld # N-770-1, Inspection Item**

Letdown MU-394BM NPS 2Y2" MU-395BM B15.215, B

'The USNRC has not approved Leak Before Break (LBB) application to these welds; therefore, LBB does not apply to this overlay.

    • TMI relief request 14R-02 of Reference 9 identified that FSWOL locations will be removed from the Risk Informed Inservice Inspection (RISI) Program and examined under the Alloy 600 augmented lSI program that complies with the latest regulations. Code Cases N-722-1 and N-770-1 with additional requirements from 10 CFR 50.55a currently comprise the Alloy 600 augmented lSI program. The provided "Item No." and "Inspection Item" are based on N-722-1 and N-770-1 as modified by 10 CRF 50.55a. These code cases do not use "Examination Category" therefore none is applicable.

TABLE1B Component Material Weld Number Item Item Item MU-394BM Nozzle: P-No. 1 Weld: F-No. 43 Safe-End: P-No. 43 MU-395BM Safe-End: P-No. 43 Weld: F-No. 43 Elbow: P-No. 8

10 CFR 50.55a RELIEF REQUEST RR-12-02 Revision 0 (Page 9 of 9)

Figure 1- Examination Volume (Extradose and Intradose View)

I CARBON STEEL NOZZLE I

~TAINLESS

~TEEL CLAD I

1 I

I DMW I ALLOY 82 IMU-394BM

  • PSli,Si R-EQuiRED ~

EXAMINATION  !

VOLUME AREA OF REDUCED I

COVERAGE AT INTRADOS,

'--__-'I SAFE-END i ALLOY 600 (FOR UPSTREAM AXIAL SCAN ONLY)

I DMW I ALLOY 82

\MU-395BM I

\ \

\ \

\

\

EXTRADOS STAINLESS STEEL ELBOW

""- ...............

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