RC-07-0021, Inspection and Mitigation Plan/Schedule of Alloy 82/182 Pressurizer Butt Welds (C-04-1719)

Inspection and Mitigation Plan/Schedule of Alloy 82/182 Pressurizer Butt Welds (C-04-1719)

ML070330144
Person / Time
Site:	Summer
Issue date:	01/31/2007
From:	Archie J South Carolina Electric & Gas Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
C-04-1719, RC-07-0021
Download: ML070330144 (8)

Text

Jeffrey B. Archie Vice President,Nuclear Operations 803.345.4214 January 31, 2007 RC-07-0021 A SCANA COMPANY U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

Subject:

VIRGIL C. SUMMER NUCLEAR STATION (VCSNS)

DOCKET NO. 50/395 OPERATING LICENSE NO. NPF-12 INSPECTION AND MITIGATION OF ALLOY 82/182 PRESSURIZER BUTT WELDS (C-04-1719)

Reference:

Marvin S. Fertel (NEI) Letter to Luis A. Reyes (NRC), Industry Actions Associated with Potential Generic Implications of Wolf Creek Inspection Findings, January 26, 2007 In October of 2006, while performing inspections of its pressurizer Alloy 82/182 butt welds in accordance with MRP-1 39, a PWR licensee discovered several circumferential indications in its pressunzer surge, safety and relief nozzles. Because of the potential importance of this issue, SCE&G is submitting this letter as notification of VCSNS actions taken or planned for inspecting or mitigating Alloy 82/182 butt welds on pressurizer spray, surge and relief lines.

Inspection of pressurizer Alloy 82/182 butt welds at VCSNS has not yet been completed, but SCE&G will complete the inspection and mitigation activities on these locations during the next refueling outage (RF17) currently scheduled for April 2008. Justification for delaying these activities beyond December 31, 2007 is provided in Attachment I. Details concerning the VCSNS inspection and mitigation activities are provided by Attachment II. Future inspections of pressurizer dissimilar metal (DM) butt welds at VCSNS will be performed in accordance with industry guidance (MRP-139).

In addition to the inspection and mitigation activities described above, low threshold procedures for monitoring primary system leakage are in place for VCSNS. If VCSNS should shut down due to excessive pdmary system unidentified leakage and, if the leakage can not be confirmed to originate from a source other than the pressurizer, a bare metal visual (BMV) examination of Alloy 82/182 butt weld locations on the pressurizer will be performed to determine whether the leakage originated at those locations.

Consistent with the actions discussed in the referenced letter, SCE&G is evaluating enhancements to leakage monitoring procedures for VCSNS and will provide the details of these actions to the NRC by March 31, 2007.

In addition, SCE&G is assessing the feasibility of on-line monitoring equipment for the VCSNS pressurizer to provide diverse leakage detection capabilities. The details of these actions will be provided to the NRC by May 31, 2007.

SCE&G I Virgil C.Summer Nuclear Station - P.0. Box 88 - Jenkinsville, South Carolina 29065

• T(803) 345.5209

• www.scna.com

Document Control Desk Letter C-04-1719 RC-07-0021 Page 2 of 2 SCE&G is also participating in, and sharing the cost of, a newly developed EPRI project to perform additional refined crack growth calculations of the limiting pressurizer nozzle Alloy 82/182 weld configuration using 3-dimensional finite element analysis.

Commitments made through this letter are identified in Attachment IV.

The NRC will be informed if SCE&G deviates from any of the actions described in this letter.

SCE&G staff is available to meet with the NRC to discuss any of the information contained in this letter.

Should you have questions, please call Mr. Bruce Thompson at (803) 931-5042.

Very tru y rs,

/

Jeffrey B. Archie JWT/JBA/dr Attachment I Inspection and Mitigation Plan/Schedule for Alloy 82/182 Pressurizer Butt Welds at V.C. Summer Nuclear Station (VCSNS)

Attachment II Inspection and Mitigation Summary for Alloy 82/182 Pressurizer Butt Welds Attachment III Previous ISI Program Examinations for Alloy 82/182 Pressurizer Butt Welds Attachment IV List of Commitments c: K. B. Marsh S. A. Byrne N. S. Cams J. H. Hamilton R. J. White W. D. Travers R. E. Martin NRC Resident Inspector K. M. Sutton J. Riley (NEI)

NSRC RTS (C-04-1719)

File (815.02)

DMS (RC-07-0021)

Document Control Desk Letter Attachment I C-04-1719 RC-07-0021 Page 1 of 3 INSPECTION AND MITIGATION PLAN / SCHEDULE OF ALLOY 82/182 PRESSURIZER BUTT WELDS AT V. C. SUMMER NUCLEAR STATION (VCSNS)

Inspection and mitigation activities at VCSNS will be completed during the next refueling outage (RF1 7) currently scheduled for April 2008. The activities necessary to effectively address this issue warrant additional time beyond the MRP-1 39 prescribed end date of December 31, 2007.

VCSNS utilized the last scheduled outage (RF-16 in October 2006) after MRP-139 was issued (September 2005) to plan the mitigation weld overlays. It was determined that the pressurizer welds could not be inspected in accordance with MRP-139 inspection requirements at all six pressurizer locations. In order to adequately plan implementation, address interference with the "as built" configuration, and minimize radiation dose during implementation, a pre-implementation walk-down was necessary. VCSNS has completed the necessary walk-downs, performed laser profiling to support design and implementation activities, and awarded a contract to perform full structural weld overlay application. The application of the structural weld overlay will allow the welds to be inspected in accordance with MRP-1 39. The weld overlay design process requires approximately seven months of engineering evaluation and design analysis to develop the appropriate weld overlay configuration. Upon issuance of the design package, three months is required for tooling design, welder qualification and the weld and NDE process mock-up and demonstration. Pre-outage planning and preparations require approximately three months following the completion of the mock-up demonstration. This allows for an appropriate amount of time to ensure ALARA planning as well as any specific plant support such as shielding, scaffolding and other logistical needs. Finally, a one month period is expected for contractor mobilization. The schedule outlined above provides assurance that the activity can be effectively completed, while assuring the radiological and industrial safety of the plant staff and our contractors.

This schedule is acceptable based on the following:

PREVIOUS INSPECTION RESULTS Bare Metal Visual (BMV) inspections of the dissimilar metal (DM) Pressurizer welds were made in the Spring 2005 outage (RF-15) and also in the Fall of 2006 outage (RF16) as required by NRC Bulletin 2004-01, INSPECTION OF ALLOY 82/182/600 MATERIALS USED IN THE FABRICATION OF PRESSURIZER PENETRATIONS AND STEAM SPACE PIPING CONNECTIONS AT PRESSURIZED-WATER REACTORS. Neither of these inspections identified any leakage. Volumetric and surface inspections (ultrasonic and dye penetrant) were performed on the subject welds in the period from September 1994 through April 1999 using non-PDI (Performance Demonstration Initiative) techniques with coverage and results shown in Attachment II1. There were no recordable or reportable flaws from these pressurizer weld examinations.

WELD FABRICATION REVIEWS An assessment of original fabrication weld documentation to identify welds that may have been reworked is currently in process. VCSNS has contracted with Westinghouse to perform a comprehensive review of the factory fabrication DM weld history.

The assessment is scheduled to be completed in mid-February 2007. SCE&G will make every effort to provide the NRC an update on the assessment results by February 28, 2007 but accounting for possible delays due to vendor delivery and/or SCE&G review and acceptance, no later than March 31, 2007.

Document Control Desk Letter Attachment I C-04-1719 RC-07-0021 Page 2 of 3 ENHANCED LEAKAGE MONITORING FOR UNIDENTIFIED PRIMARY SYSTEM LEAKAGE The VCS Reactor Coolant System (RCS) Leakage Management Program monitors RCS leakage at a very low threshold. While the VCSNS Technical Specifications 3.4.6.2 specifies that NO pressure boundary leakage is acceptable and that up to 1 gpm is allowed as unidentified leakage, the VCSNS monitoring thresholds are established to ensure that the Technical Specification requirements are not challenged. VCSNS monitors more frequently than required by Technical Specifications.

The current program identifies action levels which begin with a validated change in leakage rate of 0.05 gpm above the existing normal leak rate for a period of 3 days. Additional action levels have been established at a total unidentified leakage rate of 0.2 gpm and 0.6 gpm with prescribed actions to determine the source, evaluate and eliminate the source of the leakage.

Various other procedures are utilized to perform measurements and determine the source of leakage.

RCS leakage is given a high priority by management which is reflected by taking actions above and beyond the procedure requirements on a routine basis:

" RCS unidentified leakage trend is part of the daily Plant Information Meetings and included in the Management Duty Supervisors daily report.

" The RCS Leakage Program Manager provides weekly updates to Operations.

" RCS leakage is a point of discussion at senior plant management meetings.

If VCSNS should shut down due to excessive primary system unidentified leakage and if the leakage cannot be confirmed to originate from a source other than the pressurizer, a bare metal visual examination of the DM butt weld locations on the pressurizer will be performed to determine whether the leakage originated from those locations.

PWR OWNERS GROUP ENHANCED LEAK DETECTION In addition to the current RCS leakage monitoring program, VCSNS is currently evaluating the documents issued by the PWR Owners Group with respect to enhanced processes and methods of calculating RCS leakage.

SCE&G will update our response concerning this subject by March 31, 2007 in a follow-up letter.

INDUSTRY SAFETY ASSESSMENT The conclusions from the butt weld safety assessment, MRP-1 09, indicate that there is no immediate safety concern associated with PWSCC of Alloy 82/182 butt welds based on the following:

" The case of the longitudinal flaw is a safe situation, because the length of the flaw is limited to the width of the weld material (-2.5"), which is less than the critical flaw size for burst.

(MRP-109, Sect. 7)

" The circumferential crack growth analysis results for the Westinghouse designed spray nozzle showed it would take at least 2.5 years to propagate a flaw to a critical crack length from a 1 GPM leak. (MRP-109, Table 5-3 and Section 7)

• A very small number of leaks/cracks have been identified given the large number of locations worldwide. (MRP-139, Sect. 4.3)

Document Control Desk Letter Attachment I C-04-1719 RC-07-0021 Page 3 of 3

" Axial cracking is much more likely than circumferential. (MRP-109 and MRP-1 39, Sect.1)

• Probabilistic analysis shows the impact of butt weld PWSCC on CDF is insignificant, but probability of leaks is not. (MRP-139, Sect. 1.3)

" The potential for boric acid corrosion (BAC) is considered low for all Alloy 82/182 pressurizer joint upper head locations since any leak at operating conditions would be essentially pure water/steam with little boric acid carryover to cause corrosion.

" The potential for BAC of the surge line as well as the top head pressurizer joint locations is addressed by the bare metal visual inspections.

" The Susceptibility Analysis performed by Westinghouse and documented in WCAP-1 6388, "PWSCC Susceptibility Assessment of the Alloy 600 and Alloy 82/182 Components in V. C.

Summer Nuclear Station", indicates a very low probability of PWSCC failure of these components prior to the Spring 2008 outage timeframe.

As a result of the circumferential indications found in October 2006, the industry, through EPRI MRP, reviewed the Alloy 82/182 Pipe Butt Weld Safety Assessment (MRP-1 13) and the Primary System Piping Butt Weld Inspection and Evaluation Guideline (MRP-139). This review can be found in the white paper titled "Implications of Wolf Creek Pressurizer Butt Weld Indications to Safety Assessment and Inspection Requirements." The conclusions from the industry review included:

• MRP-113 and MRP-139 remain valid.

• Critical flaw sizes are several times larger than the indications observed in October 2006.

• Bare metal visual inspections during the last refueling outage (October 2006 for VCSNS) ensure a low risk of leaks and an extremely low risk of rupture through the spring of 2008.

Document Control Desk Letter Attachment II C-04-1719 RC-07-0021 Page 1 of 1 Inspection and Mitigation Summary for Alloy 82/182 Pressurizer Butt Welds Nozzle MRP-139 Volumetric Mitigation Inspection Requirement Met Completed or to or to be Met be Completed Comments Function Susceptible Material Outage Start Date Outage Designation Description Designation (MMIYYYY) Designation Spray! Nozzle-to safe end weld RF17 04/2008 RF17 Structural Weld Overlay followed by PDI Qualified CGE-1-4503-46DM Inspection Surge / Nozzle-to safe end weld RF17 04/2008 RF17 Structural Weld Overlay followed by PDI Qualified CGE-1-4500A-1 DM Inspection Safety 801 OA / Nozzle-to safe end weld RF17 04/2008 RF17 Structural Weld Overlay followed by PDI Qualified CGE-1-4501-12DM Inspection Safety 8010B / Nozzle-to safe end weld RF17 04/2008 RF17 Structural Weld Overlay followed by PDI Qualified CGE-1-4501-1 DM Inspection Safety 8010C / Nozzle-to safe end weld RF17 04/2008 RF17 Structural Weld Overlay followed by PDI Qualified CGE-1-4501-23DM Inspection Relief -PORV's/ Nozzle-to safe end weld RF17 04/2008 RF1 7 Structural Weld Overlay followed by PDI Qualified CGE-1-4502-1D M Inspection

Document Control Desk Letter Attachment III C-04-1719 RC-07-0021 Page 1 of 1 Previous ISI Program Examinations for Alloy 82/182 Pressurizer Butt Welds Nozzle Previous ISI/ UT examinations Bare Metal Visual Examinations Function / Susceptible RF-15 RF-16 Designation Material Outage Date NDE Designation PT/UT Spring 2005 Fall-2006 Designation_ Description 4/8/99 PT-No Recordable Surface Indications BMV-No Evidence of BMV-No Evidence of Boric Acid Spray Nozzle-to safe end CGE-1-4503-46DM weld 4/19/99 UT-No Recordable Indications Boric Acid Leakage Leakage

-90.38% Estimated Coverage Surface PT- No Recordable Surge Nozzle-to safe end 4 Indications BMV-No Evidence of BMV-No Evidence of Boric Acid CGE-1-4500A-1DM weld UT-No Recordable Indications Boric Acid Leakage Leakage 100% Coverage Safety 9/23/94 Surface PT- No Recordable Nozzle-to safe end Indications BMV-No Evidence of BMV-No Evidence of Boric Acid 8010A Leakage CGE-1-4501-12DM weld 9/28/94 & UT-No Recordable Indications Boric Acid Leakage 10/1/94 100% Coverage 9/23/94 Surface PT- No Recordable Safety Nozzle-to safe end Indications BMV-No Evidence of BMV-No Evidence of Boric Acid 801GB 8010B weld 9/28/94 & UT-No 100%

Recordable Indications Coverage Boric Acid Leakage Leakage CGE-1-4501-IDM 10/1/94 Surface PT- No Recordable Safety Nozzle-to safe end Indications BMV-No Evidence of BMV-No Evidence of Boric Acid 80100 801 weld 9/28/94 & UT-No Recordable Indications Boric Acid Leakage Leakage CGE-1-4501-23DM 10/1/94 100% Coverage Relief Nozzle-to safe end 9/23/94 Surface PT- No Recordable Indications BMV-No Evidence of BMV-No Evidence of Boric Acid CGE-1-4502-1DV 9/28/94 & UT-No Recordable Indications Boric Acid Leakage Leakage 10/1/94 100% Coverage

Document Control Desk Letter Attachment IV C-04-1719 RC-07-0021 Page 1 of 1 List of Commitments Alloy 82/182 Program Enhancements COMMITTED COMMITMENT TYPE No. COMMITMENT DATE OR ONE-TIME ACTION PROGRAMMATIC ATO "OUTAGE" (YeslNo) ACTION

_____ ____________________________ _______________ __ ___ ___ ___ (Yes/No)

Inspection and Mitigation activities at April 30, 2008 Yes No VCSNS will be completed during the next refueling outage (RF17) currently scheduled for April 2008.

Future inspections of pressurizer As required by No Yes dissimilar metal (DM) butt welds at MRP-139 VCSNS will be performed in accordance with industry guidance (MRP-1 39).

Perform an assessment of original March 31,2007 Yes No fabrication welds documentation to identify welds that may have been reworked and provide results to NRC.

If VCSNS should shutdown due to Upon Occurrence Yes No excessive primary system unidentified leakage and if the leakage cannot be confirmed to originate from a source other than the pressurizer, a bare metal visual examination of the dissimilar metal butt weld locations on the pressurizer will be performed to determine if the leakage originated from those locations.

SCE&G is evaluating PWR Owners March 31, 2007 Yes No Group documents with respect to enhanced leak detection processes and methods of calculating RCS leakage. Results will be provided to the NRC.

SCE&G is assessing the feasibility of May 31, 2007 Yes No on-line monitoring equipment for the VCSNS pressurizer to provide diverse leakage detection capabilities. The details of these actions will be provided to the NRC.