ML082530112
| ML082530112 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 09/16/2008 |
| From: | Goodwin C Plant Licensing Branch III |
| To: | Allen B FirstEnergy Nuclear Operating Co |
| Goodwin, Cameron/DORL, 415-3719 | |
| References | |
| TAC MD8105 | |
| Download: ML082530112 (7) | |
Text
September 16, 2008 Mr. Barry S. Allen 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 -
SUMMARY
OF DESIGN AND STRESS ANALYSES OF WELD OVERLAYS OF DISSIMILAR METAL WELDS OF PRESSURIZER AND HOT-LEG NOZZLES (TAC NO. MD8105)
Dear Mr. Allen:
By letter to the U.S. Nuclear Regulatory Commission (NRC) dated February 15, 2007, as supplemented by letters dated June 28, September 28, and November 19, 2007, FirstEnergy Nuclear Operating Company (FENOC) submitted Relief Request (RR)-A30, Revision 2, as an alternative to American Society of Mechanical Engineers Code,Section XI, requirements in support of weld overlay repairs, for the Davis-Besse Nuclear Power Station, Unit No. 1. RR-A30, Revision 2, provides weld overlays of dissimilar metal welds of pressurizer nozzles, hot-leg decay heat line nozzle, and hot-leg surge line nozzle. By letter dated December 20, 2007, the NRC authorized RR-A30, Revision 2, for the weld overlay repairs.
In RR-A30, Revision 2, the licensee committed to submit the final ultrasonic examination results of the weld overlays within 14 days of the completion of the examination. The final ultrasonic examination was performed on January 22, 2008. By letter dated February 8, 2008, the licensee submitted the results of its weld overlay ultrasonic examination. By letter dated June 20, 2008, the NRC staff requested additional information to complete its review. FENOC responded to this request by letter dated July 21, 2008. The enclosure is the NRC staffs summary of the subject examination.
Sincerely,
/RA/
Cameron S. Goodwin, Project Manager Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-346
Enclosure:
Summary of Ultrasonic Weld Overlay Examination cc w/encl: See next page
September 16, 2008 Mr. Barry S. Allen 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 -
SUMMARY
OF DESIGN AND STRESS ANALYSES OF WELD OVERLAYS OF DISSIMILAR METAL WELDS OF PRESSURIZER AND HOT-LEG NOZZLES (TAC NO. MD8105)
Dear Mr. Allen:
By letter to the U.S. Nuclear Regulatory Commission (NRC) dated February 15, 2007, as supplemented by letters dated June 28, September 28, and November 19, 2007, FirstEnergy Nuclear Operating Company (FENOC) submitted Relief Request (RR)-A30, Revision 2, as an alternative to American Society of Mechanical Engineers Code,Section XI, requirements in support of weld overlay repairs, for the Davis-Besse Nuclear Power Station, Unit No. 1. RR-A30, Revision 2, provides weld overlays of dissimilar metal welds of pressurizer nozzles, hot-leg decay heat line nozzle, and hot-leg surge line nozzle. By letter dated December 20, 2007, the NRC authorized RR-A30, Revision 2, for the weld overlay repairs.
In RR-A30, Revision 2, the licensee committed to submit the final ultrasonic examination results of the weld overlays within 14 days of the completion of the examination. The final ultrasonic examination was performed on January 22, 2008. By letter dated February 8, 2008, the licensee submitted the results of its weld overlay ultrasonic examination. By letter dated June 20, 2008, the NRC staff requested additional information to complete its review. FENOC responded to this request by letter dated July 21, 2008. The enclosure is the NRC staffs summary of the subject examination.
Sincerely,
/RA/
Cameron S. Goodwin, Project Manager Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-346
Enclosure:
Summary of Ultrasonic Weld Overlay Examination cc w/encl: See next page DISTRIBUTION:
PUBLIC LPL3-2 R/F RidsNrrDorlLpl3-2 RidsNrrPMDavisBesse RidsNrrLATHarris RidsAcrsAcnw&mMailCenter RidsOgcRp RidsRgn3MailCenter RidsNrrDorlDpr ADAMS Accession Number: ML082530112 OFFICE LPL3-2/PM LPL3-2/LA LPL3-2/BC NAME CGoodwin THarris RGibbs DATE 9 / 10 /08 9 / 10 /08 9 / 16 /08 OFFICIAL RECORD COPY
Davis-Besse Nuclear Power Station, Unit No. 1 cc:
Manager, Site Regulatory Compliance FirstEnergy Nuclear Operating Company Davis-Besse Nuclear Power Station Mail Stop A-DB-3065 5501 North State Route 2 Oak Harbor, OH 43449-9760 Director, Ohio Department of Commerce Division of Industrial Compliance Bureau of Operations & Maintenance 6606 Tussing Road P.O. Box 4009 Reynoldsburg, OH 43068-9009 Resident Inspector U.S. Nuclear Regulatory Commission 5503 North State Route 2 Oak Harbor, OH 43449-9760 Stephen Helmer Supervisor, Technical Support Section Bureau of Radiation Protection Ohio Department of Health 35 East Chestnut Street, 7th Floor Columbus, OH 43215 Carol O=Claire, Chief, Radiological Branch Ohio Emergency Management Agency 2855 West Dublin Granville Road Columbus, OH 43235-2206 Zack A. Clayton DERR Ohio Environmental Protection Agency P.O. Box 1049 Columbus, OH 43266-0149 State of Ohio - Transportation Department Public Utilities Commission 180 East Broad Street Columbus, OH 43266-0573 Principal Assistant Attorney General Environmental Enforcement Section State Office Tower 30 East Broad Street, 25th Floor Columbus, OH 43215 President, Board of County Commissioners of Ottawa County Port Clinton, OH 43252 President, Board of County Commissioners of Lucas County One Government Center, Suite 800 Toledo, OH 43604-6506 The Honorable Dennis J. Kucinich United States House of Representatives Washington, D.C. 20515 The Honorable Dennis J. Kucinich United States House of Representatives 14400 Detroit Avenue Lakewood, OH 44107 Joseph J. Hagan President and Chief Nuclear Officer FirstEnergy Nuclear Operating Company Mail Stop A-GO-19 76 South Main Street Akron, OH 44308 David W. Jenkins, Attorney FirstEnergy Corporation Mail Stop A-GO-15 76 South Main Street Akron, OH 44308 Danny L. Pace Senior Vice President, Fleet Engineering FirstEnergy Nuclear Operating Company Mail Stop A-GO-14 76 South Main Street Akron, OH 44308 Manager, Fleet Licensing FirstEnergy Nuclear Operating Company Mail Stop A-GO-2 76 South Main Street Akron, OH 44308
Davis-Besse Nuclear Power Station, Unit No. 1 Director, Fleet Regulatory Affairs FirstEnergy Nuclear Operating Company Mail Stop A-GO-2 76 South Main Street Akron, OH 44308 Jeannie M. Rinckel Vice President, Fleet Oversight FirstEnergy Nuclear Operating Company Mail Stop A-GO-14 76 South Main Street Akron, OH 44308 Paul A. Harden Vice President, Nuclear Support FirstEnergy Nuclear Operating Company Mail Stop A-GO-14 76 South Main Street Akron, OH 44308 James H. Lash Senior Vice President of Operations and Chief Operating Officer FirstEnergy Nuclear Operating Company Mail Stop A-GO-14 76 South Main Street Akron, OH 44308
Enclosure
SUMMARY
OF DESIGN AND STRESS ANALYSES OF WELD OVERLAYS OF DISSIMILAR METAL WELDS OF PRESSURIZER AND HOT-LEG NOZZLES DAVIS-BESSE NUCLEAR POWER STATION, UNIT NO. 1 DOCKET NO. 50-346
1.0 INTRODUCTION
By letter to the U.S. Nuclear Regulatory Commission (NRC) dated February 15, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML071020195), as supplemented by letters dated June 28, September 28, and November 19, 2007 (ADAMS Accession Nos. ML071840039, ML072750034, and ML073040095, respectively),
FirstEnergy Nuclear Operating Company (FENOC) submitted Relief Request (RR)-A30, Revision 2, as an alternative to American Society of Mechanical Engineers (ASME Code,)
Section XI requirements in support of weld overlay repairs, for the Davis-Besse Nuclear Power Station, Unit No. 1 (DBNPS). RR-A30, Revision 2, provides weld overlays of dissimilar metal welds of pressurizer nozzles, hot-leg decay heat line nozzle, and hot-leg surge line nozzle. By letter dated December 20, 2007 (ADAMS Accession No. ML073190511), the NRC authorized RR-A30, Revision 2, for the weld overlay repairs.
In RR-A30, Revision 2, the licensee committed to submit the final ultrasonic examination results of the weld overlays within 14 days of the completion of the examination. The final ultrasonic examination was performed on January 22, 2008. By letter dated February 8, 2008 (ADAMS Accession No. ML080430445), the licensee submitted the results of its weld overlay ultrasonic examination. By letter dated June 20, 2008 (ADAMS Accession No. ML081650141), the NRC staff requested additional information to complete its review. FENOC responded to this request by letter dated July 21, 2008 (ADAMS Accession No. ML082050231).
2.0 DISCUSSION In accordance with NRC-approved RR-A30, Revision 2, the licensee performed design and stress analyses for the weld overlay of the following dissimilar metal welds: pressurizer safety nozzle welds (RC-PZR-WP-91-W/X and RC-PZR-WP-91-Y/Z), pressurizer relief nozzle weld (RC-PZR-WP-91-Z/W), pressurizer spray nozzle weld (RC-PZR-WP-102), pressurizer surge nozzle weld (RC-PZR-WP-23), hot-leg Surge nozzle weld (RC-MK-A-82-FW54), and hot-leg decay heat nozzle weld (DH-33A-CCA-4-1-FW1).
The licensee performed stress analyses in accordance with Subarticles NB-3200 and NB-3600 of ASME Code,Section III, that supplement existing piping, safe end, and nozzle stress reports, to demonstrate that the overlaid components continue to meet ASME Code,Section III, requirements. The original construction Code for the pressurizer was ASME,Section III, 1968 Edition, Summer 1968 Addenda, and for the hot-leg was USA Standards (USAS), B31.7, 1968 Draft. However, as allowed by ASME Section XI, ASME Code editions and addenda later than the original construction ASME Code may be used. The ASME Code,Section III, 1998 Edition through the 2000 Addenda, and the 2001 Edition through the 2003 Addenda were used for these analyses. The analyses show that the stresses and fatigue usage in the weld overlaid nozzles are within the applicable ASME Code limits.
The licensee calculated weld residual stresses for the subject weld overlays by detailed elastic-plastic finite element analyses. The residual stresses in the inside diameter region of the pipe wall are shown to be in compression which satisfies the design requirements of the RR to minimize crack initiation and growth.
As required by the subject RR, the licensee also performed crack growth calculations assuming a flaw originates from the inside surface of the weld with a depth of 75 percent through the thickness of the weld. This is the worst case assumed flaw specified in the RR. The amount of time it takes for the assumed flaw in the original weld to reach the overlay is then calculated.
The NRC staff noted that the stress analysis results show that the times for the postulated circumferential flaw (75 percent through-wall) to reach the design basis flaw size (100 percent through-wall) for the hot-leg surge nozzle weld and hot-leg decay heat nozzle weld are 2.58 years (31 months) and 6 years, respectively. The NRC staff notes that the postulated flaw may exist in the weld because ultrasonic testing (UT) has not been demonstrated to reliably examine the weld region that is 75 percent through-wall thickness from the inside surface of the weld once a weld overlay is installed. In addition, the licensee did not perform a UT examination prior to weld overlay installation.
The RR requires that the overlaid dissimilar metal welds be inspected during the first or second refueling outage after the overlay installation. If no indication is detected, the weld will be included in a sample population. Twenty-five percent of the sample population will be inspected every 10 years. The inspection requirements of the RR imply that the inspection interval for the hot-leg surge and decay heat nozzle welds may be 10 years or longer. In light of the potential aggressive crack growth, the NRC staff questioned the adequacy of an inspection interval of 10 years.
In the July 21, 2008 letter, the licensee clarified that a 10-year inspection interval is not used to monitor the structural integrity of the hot-leg surge nozzle weld overlay. Based on the crack growth results, the licensee decided not to place the hot-leg surge nozzle weld overlay into the standard inspection interval of 25 percent of the sample population every 10 years. This weld is scheduled for examination at a time that is less than the time for the postulated 75 percent through-wall flaw to reach the weld overlay. Presently, the hot-leg surge nozzle weld overlay is scheduled for examination every refueling outage, which is every 2 years. The NRC staff finds that an inspection interval of every refueling outage (about 2 years) for the hot-leg surge nozzle weld is acceptable because the 2-year inspection interval will ensure the structural integrity of the hot-leg surge nozzle weld.
As for the hot-eg decay heat nozzle weld, the licensee reanalyzed the crack growth because the original analysis was overly conservative in using a higher design temperature for the crack growth rate evaluation. The revised analysis uses a more realistic lower temperature that more accurately reflects the temperature at the hot-leg decay heat nozzle location. This lower temperature results in reduced crack growth rates, which increased the time needed for the crack to grow from 75 percent to 100 percent through-wall depth for the hot-leg decay heat nozzle. The NRC staff notes that during weld overlay installation of the hot-leg decay heat nozzle weld, a subsurface axial flaw became 100 percent through-wall and caused leakage. The licensee stated that the axial flaw was included in the crack growth calculation.
The revised crack growth analysis showed that postulated flaws in the hot-leg decay heat nozzle will reach the design flaw size beyond 10 years. Presently, the hot-leg decay heat nozzle weld overlay is scheduled for examination every 10 years. The NRC staff finds that the 10-year inspection frequency is shorter than the crack growth period from the assumed initial flaw size to the design flaw size. Therefore, the 10-year inspection frequency is acceptable to monitor and thus to ensure the structural integrity of the hot-leg decay heat nozzle weld.
3.0 CONCLUSION
On the basis of the above review, the NRC staff finds that the design and analyses of weld overlays for pressurizer and hot-leg dissimilar metal welds at the DBNPS satisfy the commitments specified in RR-A30, Revision 2.