ML073230183

Request for Alternative RR-A31 for Pressurizer J-Groove Nozzle Weld Repairs (Tac No. MD5956)

ML073230183
Person / Time
Site:	Davis Besse
Issue date:	12/14/2007
From:	Russell Gibbs NRC/NRR/ADRO/DORL/LPLIII-2
To:	Bezilla M FirstEnergy Nuclear Operating Co
Wengert, Thomas J, NRR/DORL, 415-4037
References
TAC MD5956
Download: ML073230183 (4)

Text

December 14, 2007 Mr. Mark B. Bezilla Site Vice President FirstEnergy Nuclear Operating Company Davis-Besse Nuclear Power Station Mail Stop A-DB-3080 5501 North State Route 2 Oak Harbor, OH 43449-9760

SUBJECT:

DAVIS-BESSE NUCLEAR POWER STATION, UNIT NO. 1- RELIEF REQUEST NO. A31 FOR ALTERNATIVE FOR PRESSURIZER J-GROOVE NOZZLE WELD REPAIRS (TAC NO. MD5956)

Dear Mr. Bezilla:

By letter dated July 3, 2007, FirstEnergy Nuclear Operating Company (the licensee) requested U.S. Nuclear Regulatory Commission (NRC) approval of Relief Request (RR)-A31, which requests relief from the requirement that, when ambient temperature temper bead welding is used, the nondestructive examinations (NDE) are required to be conducted at least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the overlay reaches ambient temperature. In addition, the NDE are required to be conducted over the area to be welded and within a band around the area of at least 1.5 times the component thickness, or 5 inches, whichever is less. Through RR-A31, the licensee proposed to allow performance of the NDE over the area to be welded and a 0.5-inch band, 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the third temper bead weld layer is completed for the Davis-Besse Nuclear Power Station, Unit No. 1 (DBNPS).

The NRC staff has reviewed the licensees submittal and has determined that the proposed modification of the inspection area and 48-hour hold time requirement provides an acceptable level of quality and safety. Therefore, pursuant to Title 10 of the Code of Federal Regulations 50.55a(a)(3)(i), the NRC staff authorizes RR-A31. This authorization is applicable through the third 10-year inservice inspection interval at DBNPS, which is scheduled to be completed in September 2012, and only when welding is performed in accordance with RR-A31 for the repair of pressurizer J-groove welded nozzles at DBNPS.

M. Bezilla The NRC staff's safety evaluation is enclosed. This completes the NRC staffs review under TAC No. MD5956. If you have any questions concerning this matter, please call Thomas Wengert of my staff at 301-415-4037.

Sincerely,

/RA/

Russell Gibbs, Chief Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-346

Enclosure:

Safety Evaluation cc w/encl: See next page

The NRC staff's safety evaluation is enclosed. This completes the NRC staffs review under TAC No. MD5956. If you have any questions concerning this matter, please call Thomas Wengert of my staff at 301-415-4037.

Sincerely,

/RA/

Russell Gibbs, Chief Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-346

Enclosure:

Safety Evaluation cc w/encl: See next page DISTRIBUTION:

PUBLIC RidsOgcRp LPL3-2 R/F RidsRgn3MailCenter RidsAcrsAcnwMailCenter TBloomer, EDO Region III RidsNrrDorlLpl3-2 JCollins, NRR RidsNrrLAEWhitt RidsNrrDciCpnb RidsNrrPMTWengert ADAMS Accession No.: ML073230183 OFFICE LPL3-2/PM LPL3-2/LA DCI/CPNB/BC OGC LPL3-2/BC NAME TWengert EWhitt TChan MSmith RGibbs DATE 12/12/07 12/12/07 12/14/07 12/13/07 12/14/07 OFFICIAL AGENCY RECORD

Davis-Besse Nuclear Power Station, Unit No. 1 cc:

Manager, Site Regulatory Compliance President, Board of County FirstEnergy Nuclear Operating Company Commissioners of Ottawa County Davis-Besse Nuclear Power Station Port Clinton, OH 43252 Mail Stop A-DB-3065 5501 North State Route 2 President, Board of County Oak Harbor, OH 43449-9760 Commissioners of Lucas County One Government Center, Suite 800 Director, Ohio Department of Commerce Toledo, OH 43604-6506 Division of Industrial Compliance Bureau of Operations & Maintenance The Honorable Dennis J. Kucinich 6606 Tussing Road United States House of Representatives P.O. Box 4009 Washington, D.C. 20515 Reynoldsburg, OH 43068-9009 Resident Inspector The Honorable Dennis J. Kucinich U.S. Nuclear Regulatory Commission United States House of Representatives 5503 North State Route 2 14400 Detroit Avenue Oak Harbor, OH 43449-9760 Lakewood, OH 44107 Stephen Helmer Joseph J. Hagan Supervisor, Technical Support Section President and Chief Nuclear Officer Bureau of Radiation Protection FirstEnergy Nuclear Operating Company Ohio Department of Health Mail Stop A-GO-14 th 35 East Chestnut Street, 7 Floor 76 South Main Street Columbus, OH 43215 Akron, OH 44308 Carol OClaire, Chief, Radiological Branch David W. Jenkins, Attorney Ohio Emergency Management Agency FirstEnergy Corporation 2855 West Dublin Granville Road Mail Stop A-GO-15 Columbus, OH 43235-2206 76 South Main Street Akron, OH 44308 Zack A. Clayton DERR Danny L. Pace Ohio Environmental Protection Agency Senior Vice President, Fleet Engineering P.O. Box 1049 FirstEnergy Nuclear Operating Company Columbus, OH 43266-0149 Mail Stop A-GO-14 76 South Main Street State of Ohio Akron, OH 44308 Public Utilities Commission 180 East Broad Street Manager, Fleet Licensing Columbus, OH 43266-0573 FirstEnergy Nuclear Operating Company Mail Stop A-GO-2 Attorney General 76 South Main Street Office of Attorney General Akron, OH 44308 30 East Broad Street Columbus, OH 43216

Davis-Besse Nuclear Power Station, Unit No. 1 cc:

Richard Anderson Director, Fleet Regulatory Affairs Vice President, Nuclear Support FirstEnergy Nuclear Operating Company FirstEnergy Nuclear Operating Company Mail Stop A-GO-2 Mail Stop A-GO-14 76 South Main Street 76 South Main Street Akron, OH 44308 Akron, OH 44308 Jeannie M. Rinckel James H. Lash Vice President, Fleet Oversight Senior Vice President of Operations FirstEnergy Nuclear Operating Company and Chief Operating Officer Mail Stop A-GO-14 FirstEnergy Nuclear Operating Company 76 South Main Street Mail Stop A-GO-14 Akron, OH 44308 76 South Main Street Akron, OH 44308

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO RELIEF REQUEST NO. A31 FOR ALTERNATIVE FOR 48-HOUR HOLD PERIOD FOLLOWING THE THIRD TEMPER BEAD LAYER FIRSTENERGY NUCLEAR OPERATING COMPANY DAVIS-BESSE NUCLEAR POWER STATION, UNIT NO. 1 DOCKET NUMBER 50-346

1.0 INTRODUCTION

By letter dated July 3, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML071870412), FirstEnergy Nuclear Operating Company (the licensee), requested U.S. Nuclear Regulatory Commission (NRC) approval to modify the requirements for post inspection and 48-hour hold time requirement for application of temper bead welding as defined in Relief Request (RR)-A31. American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) Case N-638-1, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW [gas tungsten arc welding] Temper Bead Technique, is an NRC conditionally acceptable ASME Code Case. It requires when temper bead welding is used in weld overlay of dissimilar metal butt welds, the nondestructive examinations (NDE) are required to be conducted at least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the overlay reaches ambient temperature. In addition, it requires that NDE be performed over the area to be welded and within a band around the area of at least 1.5 times the component thickness, or 5 inches, whichever is less. The licensee, through RR-A31, proposes to change this requirement to allow performance of the NDE, over the area to be welded and within a band of 0.5 inches at 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the third temper bead weld layer is completed.

2.0 REGULATORY EVALUATION

Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) must meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, Rules for Inservice Inspection (ISI) of Nuclear Power Plant Components, to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examination of components and system pressure tests conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code, incorporated by reference in 10 CFR 50.55a(b), 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein.

The ISI Code of Record for Davis-Besse Nuclear Power Station, Unit No. 1 (DBNPS) third 10-year ISI interval, which started in September 2000 and scheduled to be complete in September 2012, is the 1995 Edition, 1996 Addenda of Section XI of the ASME Code.

Pursuant to 10 CFR 50.55a(a)(3), alternatives to requirements may be authorized by the NRC if the licensee demonstrates that: (i) the proposed alternatives provide an acceptable level of quality and safety, or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

The licensee sets forth RR-A31 as a proposed alternative that provides an acceptable level of quality and safety. The requirement of 10 CFR 50.55a(a)(3)(i) provides the regulatory basis to evaluate the proposed modification.

3.0 TECHNICAL EVALUATION

3.1 Requirements for Which Relief is Requested Section 50.55a(b) of 10 CFR approves the use of NRC Regulatory Guide 1.147, Inservice Inspection Code Case Acceptability, ASME Code,Section XI, Division 1, Revision 14. NRC Regulatory Guide 1.147, Revision 14, lists ASME Code Case N-638-1 as a conditionally acceptable Section XI Code Case. ASME Code Case N-638-1 states, in part, that the final weld surface, including a band around the area of the lesser of 1.5 times the component thickness or 5 inches, shall be examined using NDE methods when the completed weld has been at ambient temperature for at least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />.

3.2 Licensees Proposed Alternative The licensee, through RR-A31, proposes to commence the 48-hour hold period after application of the third layer of the weld pad overlay. In addition, the licensee proposes to use a 0.5-inch band adjacent to the weld for examination.

3.3 Components for Which Relief is Requested The licensee will perform proactive repairs for nine ASME Code Class 1 pressurizer J-groove weld nozzles at DBNPS. The nozzles are all 1.5 inches or less in diameter and consist of the vent, level sensing, sample and thermowell nozzles protruding from the pressurizer. These nozzles were installed with J-groove welds applied on the interior surface of the pressurizer.

3.4 NRC Staff Evaluation ASME Code Case N-638-1 requires that when temper bead welding is used, surface and ultrasonic examinations shall be performed over the area welded and within a band around the area of at least 1.5 times the component thickness. The liquid penetrant (surface) and ultrasonic NDE examinations required are capable of detecting hydrogen cracking.

As a proposed alternative, the licensee intends to examine the area welded and only a 0.5-inch band immediately adjacent to the weld. ASME Code Case N-638 was originally written to be applied to the repair of partial and full penetration groove welds. However, nothing in the ASME Code Case precludes its use in other applications, such as the licensees proposed application of a weld pad deposited over the pressurizer alloy steel base metal. The welding principles involved and application of the weld filler metal are the same as for a groove weld design. The

weld pad filler metal specified for the subject repair is nickel based Alloy 52M and will be applied as a weld buildup using a GTAW temper bead process. The Alloy 52M filler metal is more ductile than the pressurizer low alloy steel base metal. The thickness of weld pad is much less than the pressurizer lower head nominal thickness. The weld pad itself is also a relatively small square design. Therefore, the residual stress built up in the base metal as a result of weldment contraction will be much less than that from a full penetration groove weld. Because this is a surface application utilizing the temper bead process, there will be minimal impact to the volume of metal in the area surrounding the weld. Since this weld is applied to the exterior surface of the pressurizer vessel, there is no additional useful information that can be gained by extending an examination beyond the adjacent area surrounding the weld. The NRC staff has previously found that a 0.5-inch inspection band adjacent to the area provides reasonable assurance of structural integrity for both weld pads and dissimilar metal weld applications.

Therefore the NRC staff finds this proposed alternative acceptable.

ASME Code Case N-638-1 requires that when temper bead welding is used, surface and ultrasonic examinations shall be performed when the completed weld has been at ambient temperature for least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. This delay was provided to allow sufficient time for hydrogen cracking to occur (if it is to occur) in the heat affected zone (HAZ) of ferritic materials prior to performing examinations, to ensure detection of hydrogen cracking by NDEs. However, based on research and industry experience, the Electric Power Research Institute (EPRI) has provided a technical basis for starting the 48-hour hold after completion of the third temper bead weld layer rather than waiting for the weld overlay to cool to ambient temperature.

EPRI found that weld layers beyond the third layer are not designed to provide tempering to the ferritic HAZ during ambient temperature temper bead welding. EPRI has documented their technical basis in Technical Update Report 1013558, Repair and Replacement Applications Center: Temperbead Welding Applications 48-Hour Hold Requirements for Ambient Temperature Temperbead Welding (ADAMS Accession No. ML070670060).

After evaluating all of the issues relevant to hydrogen cracking such as microstructure of susceptible materials, availability of hydrogen, applied stresses, temperature, and diffusivity and solubility of hydrogen in steels, EPRI concluded that: ...there appears to be no technical basis for waiting the 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 before beginning the NDE of the completed weld. There should be no hydrogen present, and even if it were present, the temper bead welded component should be very tolerant of the moisture .... EPRI also notes that over 20 weld overlays and 100 repairs have been performed using temper bead techniques on low alloy steel components over the last 20 years. During this time, there has never been an indication of hydrogen cracking by the NDEs performed after the 48-hour hold or by subsequent inservice inspections.

An ASME Technical Basis Paper (ADAMS Accession No. ML070790679) which supports the proposed revision to the 48-hour hold time requirement indicates that the introduction of hydrogen to the ferritic HAZ is limited to the first weld layer because this is the only weld layer that makes contact with the ferritic base material. The Technical Basis Paper states that while the potential for the introduction of hydrogen to the ferritic HAZ is negligible during subsequent weld layers, these layers provide a heat source that accelerates the dissipation of hydrogen from the ferritic HAZ in non-water backed applications. The Technical Basis Paper concludes

that there is sufficient delay time to facilitate the detection of potential hydrogen cracking when NDE is performed 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after completion of the third weld layer.

Furthermore, the solubility of hydrogen in austenitic weld materials such as Alloy 52M is much higher than that of ferritic materials while the diffusivity of hydrogen in austenitic materials is lower than that of ferritic materials. As a result, hydrogen in the ferritic HAZ tends to diffuse into the austenitic weld metal, which has a much higher solubility for hydrogen. This diffusion process is enhanced by heat supplied in subsequent weld layers.

Based on this information, the NRC staff finds that starting the 48-hour hold time after completion of the third temper bead weld layer is acceptable. The NRC staff finds that the licensee has provided sufficient technical justification to show that hydrogen cracking in the weld overlay would not likely occur under the proposed alternative. An NRC staff review of operational experience and research in this area has found no technical objection to the proposed alternative. Therefore, the NRC staff finds that it is not necessary to wait until 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the completed overlay has reached ambient temperature to perform NDE because any delayed hydrogen cracking, were it to occur, would be expected to occur within the 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> following completion of the third temper bead weld layer.

4.0 CONCLUSION

The NRC staff has reviewed the licensees submittal and determined that the proposed modification to perform NDE of the weld, including a 0.5-inch band around the area, 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after completion of the third temper bead weld layer will provide an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff authorizes the use of RR-A31. This authorization is applicable through the third 10-year inservice inspection interval at DBNPS, which is scheduled to be completed in September 2012, and only when welding is performed in accordance with RR-A31 for the repair of pressurizer J-groove welded nozzles at DBNPS.

All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in this RR remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

Principal Contributor: J. Collins, NRR Date: December 14, 2007