ML042890192
| ML042890192 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 10/07/2004 |
| From: | Ross-Lee M NRC/NRR/DLPM/LPD2 |
| To: | Baron H Duke Energy Corp |
| SHea J, 415-1388, NRR/DLPM | |
| References | |
| RR-04-GO-001, TAC MC3971, TAC MC3973 | |
| Download: ML042890192 (10) | |
Text
October 7, 2004 Mr. Henry B. Baron Group Vice President and Chief Nuclear Officer Duke Energy Corporation 526 South Church Street P. O. Box 1006 Charlotte, NC 28201-1006
SUBJECT:
CATAWBA NUCLEAR STATION, UNIT 2 AND OCONEE NUCLEAR STATION, UNIT 3 - REQUEST FOR RELIEF FOR USE OF AN ALTERNATE CODE CASE TO PERFORM VOLUMETRIC EXAMINATION OF THE REACTOR PRESSURE VESSEL NOZZLE WELDS RR-04-GO-001 (TAC NOS. MC3971, AND MC3973)
Dear Mr. Baron:
By letter to the U.S. Nuclear Regulatory Commission (NRC) dated August 6, 2004, as supplemented by letter dated September 15, 2004, Duke Energy Corporation, the licensee for Catawba Nuclear Station (Catawba), Unit 2, and Oconee Nuclear Station (Oconee), Unit 3, requested the use of an alternative to the American Society of Mechanical Engineers (ASME)
Boiler and Pressure Vessel Code (Code),Section XI, 1998 Edition with no Addenda, Figures IWB-2500-7 (a) and (b). Specifically, the licensee requested to use Code Case N-613-1 to incorporate reduced ultrasonic examination volume requirements for reactor pressure vessel nozzle-to-vessel welds.
The NRC staff has completed its review of the subject request for relief. As documented in the enclosed Safety Evaluation, the NRC staff concludes that the proposed alternative provides an acceptable level of quality and safety. Therefore, the NRC staff authorizes the proposed alternative pursuant to Title 10 of the Code of Federal Regulations, Section 50.55a(a)(3)(i), for the second 10-year inservice inspection (ISI) interval at Catawba, Unit 2, and for the third ISI interval at Oconee, Unit 3.
All other requirements of the ASME Code, Sections III and XI, for which relief has not been specifically requested remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.
Sincerely,
/RA/
Mary Jane Ross-Lee, Acting Chief, Section 1 Project Directorate II Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-414, and 50-287
Enclosure:
As stated cc w/encl: See next page
ML042890192 NRR-028 OFFICE PDII-1:PM PDII-1:LA (A)
DE/SC OGC PDII-1:SC (A)
NAME JShea DClarke SCoffin MWoods MRoss-Lee DATE 9/21/04 9/22/04 9/28/04 10/6/04 10/7/04
Catawba Nuclear Station Oconee Nuclear Station cc:
Ms. Lisa F. Vaughn Duke Energy Corporation 422 South Church Street Mail Code - PB05E P.O. Box 1244 Charlotte, North Carolina 28201-1244 Anne Cottingham, Esquire Winston and Strawn 1400 L Street, NW.
Washington, DC 20005 Mr. Peter R. Harden, IV, Vice President Customer Relations and Sales Westinghouse Electric Company 6000 Fairview Road, 12th Floor Charlotte, North Carolina 28210 County Manager of York County York County Courthouse York, South Carolina 29745 Mr. Richard M. Fry, Director Division of Radiation Protection NC Dept. of Env., Health, & Nat. Resources 3825 Barrett Drive Raleigh, North Carolina 27609-7721 Ms. Karen E. Long, Asst. Attorney General NC Department of Justice P.O. Box 629 Raleigh, North Carolina 27602 Mr. R. L. Gill, Jr., Manager Nuclear Regulatory Issues and Industry Affairs Duke Energy Corporation 526 South Church Street - Mail Stop EC05P Charlotte, North Carolina 28202 NCEM REP Program Manager 4713 Mail Service Center Raleigh, North Carolina 27699-4713 Mr. T. Richard Puryear Owners Group (NCEMC)
Catawba Nuclear Station Duke Energy Corporation 4800 Concord Road York, South Carolina 29745 Mr. Lee Keller, Manager Regulatory Compliance Catawba Nuclear Station Duke Energy Corporation 4800 Concord Road York, South Carolina 29745 North Carolina Municipal Power Agency Number 1 1427 Meadowwood Boulevard P.O. Box 29513 Raleigh, North Carolina 27626-0513 Piedmont Municipal Power Agency 121 Village Drive Greer, South Carolina 29651 Saluda River Electric P.O. Box 929 Laurens, South Carolina 29360 Henry Porter, Assistant Director - DWM Bureau of Solid and Hazardous Waste Dept. of Health & Env. Control 2600 Bull Street Columbia, South Carolina 29201-1708 NC Electric Membership Corporation P.O. Box 27306 Raleigh, North Carolina 27611 Senior Resident Inspector U.S. Nuclear Regulatory Commission 4830 Concord Road York, South Carolina 29745
Catawba Nuclear Station Oconee Nuclear Station cc:
Manager, LIS NUS Corporation 2650 McCormick Drive, 3rd Floor Clearwater, Florida 34619-1035 Senior Resident Inspector U.S. Nuclear Regulatory Commission 7812B Rochester Highway Seneca, South Carolina 29672 Mr. Michael A. Schoppman Framatome ANP 1911 North Ft. Myer Drive Suite 705 Rosslyn, Virginia 22209 Mr. B. G. Davenport, Manager Regulatory Compliance Oconee Nuclear Site Duke Energy Corporation 7800 Rochester Highway - MS ONO3RC Seneca, South Carolina 29672 Mr. Dhiaa Jamil Vice President Catawba Nuclear Station Duke Energy Corporation 4800 Concord Road York, South Carolina 29745 Mr. Ronald A. Jones, Vice President Oconee Nuclear Station Duke Energy Corporation 7800 Rochester Highway Seneca, South Carolina 29672 Ms. Mary Olson Director of the Southeast Office Nuclear Information and Resource Service 729 Haywood Road, 1-A P.O. Box 7586 Asheville, North Carolina 28802
ENCLOSURE SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST CODE CASE N-613-1 FOR NOZZLE-TO-VESSEL WELD INSPECTIONS CATAWBA NUCLEAR STATION, UNIT 2, AND OCONEE NUCLEAR STATION, UNIT 3 DOCKET NOS. 50-414 AND 50-287
1.0 INTRODUCTION
By letter to the U.S. Nuclear Regulatory Commission (NRC) dated August 6, 2004, as supplemented by letter dated September 15, 2004, Duke Energy Corporation, the licensee for Catawba Nuclear Station (Catawba), Unit 2, and Oconee Nuclear Station (Oconee), Unit 3, submitted a request for relief, Relief Request 04-GO-001, from the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code),
Section XI, 1998 Edition with no Addenda, Figures IWB-2500-7 (a) and (b). Specifically, the licensee requested to use Code Case N-613-1 to incorporate reduced ultrasonic examination (UT) volume requirements for reactor pressure vessel (RPV) nozzle-to-vessel welds for the second 10-year inservice inspection (ISI) interval at Catawba, Unit 2, and for the third 10-year ISI interval at Oconee, Unit 3.
2.0 REGULATORY EVALUATION
2.1 Applicable Requirements The ISI of ASME Code, Class 1, 2, and 3, components shall be performed in accordance with Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, of the ASME Code and applicable addenda as required by Title 10 of the Code of Federal Regulations (10 CFR), Section 50.55a(g), except where specific relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). Section 50.55a(a)(3)(i) states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if the licensee demonstrates that (i) the proposed alternatives would 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.
Pursuant to 10 CFR 50.55a(g)(4), ASME Code, Class 1, 2, and 3, components (including supports) shall meet the requirements, except the design and access provisions and the pre-service examination requirements, set forth in the ASME Code,Section XI, to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulation requires 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.
ASME Code,Section XI, 1989 Edition with no Addenda is the applicable code of record for the units requesting relief. Catawba, Unit 2, is in the second 10-year ISI interval, which started August 19, 1996, and ends August 19, 2006. Oconee, Unit 3, is in the third 10-year ISI interval, which started December 16, 1994 and ends December 16, 2004.
3.0 TECHNICAL EVALUATION
3.1 Systems/Components For Which Relief Is Requested Relief is being requested for ASME Code,Section XI, Class 1, RPV nozzle-to-vessel welds.
There are eight main coolant loop nozzle-to-vessel welds at Catawba, Unit 2 and Oconee, Unit 3, has six main coolant loop nozzle-to-vessel welds plus two core flood nozzle-to-vessel welds. These are listed as follows:
Catawba, Unit 2 Welds; Component ID Description Azimuth Code Case N-613-1 Figure 2RPV-107-121B Outlet Nozzle 22° 1
2RPV-105-121B Inlet Nozzle 67° 1
2RPV-105-121A Inlet Nozzle 113° 1
2RPV-107-121A Outlet Nozzle 158° 1
2RPV-107-121D Outlet Nozzle 202° 1
2RPV-105-121D Inlet Nozzle 247° 1
2RPV-105-121C Inlet Nozzle 293° 1
2RPV-107-121C Outlet Nozzle 338° 1
Oconee, Unit 3 Welds; Component ID Description Azimuth Code Case N-613-1 Figure 3-RPV-WR13 Outlet Nozzle X axis 1
3-RPV-WR13A Outlet Nozzle Z axis 1
3-RPV-WR12 Inlet Nozzle W-X axis 1
3-RPV-WR12A Inlet Nozzle X-Y axis 1
3-RPV-WR12B Inlet Nozzle Y-Z axis 1
3-RPV-W12C Inlet Nozzle Z-W axis 1
3-RPV-WR54 Core Flood Nozzle W axis 2
3-RPV-WR54A Core Flood Nozzle Y axis 2
3.2 Code Requirements From Which Relief Is Requested Pursuant to 10 CFR 50.55a(a)(3)(i), the licensee is requesting relief from ASME Code,Section XI, 1989 Edition, Table IWB-2500-1, Examination Category B-D, Full Penetration Welds of Nozzles in Vessels, Code Item B3.9; Figures IWB-2500-7 (a) and (b), for defining the examination volume requirements for UT of nozzle-to-vessel welds. Specifically, the licensee is
requesting relief from the ts/2 (ts is equal to the vessel wall thickness) examination volume requirements of Figures IWB-2500-7 (a) and (b).
3.3 Licensees Proposed Alternative The licensee proposes to use a reduced UT volume, which extends to 1/2-inch from the widest part of the weld, in lieu of the examination volume requirements of ASME Code,Section XI, Figures IWB-2500-7 (a) and (b), which specify a UT volume extending to a distance of ts/2 from the widest part of the weld.
3.4 Licensees Basis for Use of Proposed Alternative The required examination volume for the RPV nozzle-to-vessel welds extends far beyond the weld into the base material and is unnecessarily large. The ASME Code,Section XI examination volume for the pressure retaining nozzle-to-vessel welds extends from the edge of the weld on the nozzle side and includes a substantial portion of the nozzle forging (inward) and the RPV upper shell course (outward). This large volume causes a major increase in examination time with no resultant increase in quality or safety. The proposed alternative would define the examination volume as the weld and 1/2-inch of base material on each side of the widest portion of the weld. This base material examination volume was ultrasonically examined during preservice and subsequent ISIs. The examination results showed that there were no recordable indications outside of the volume defined in Code Case N-613-1.
As an alternative to the requirements of ASME Code,Section XI, Figures IWB-2500-7 (a) and (b), the licensee proposes to reduce the examination volume as described by Code Case N-613-1 and as represented in illustrative vendor scan plans that were included as part of the licensees submittal. The scan plans are derived from the vessel manufacturer design drawings which are the most dependable source for weld location, size, and thickness. Code Case N-613-1, Figure 1, will be used for the RPV main coolant loop nozzle-to-vessel welds at Catawba, Unit 2, and Oconee, Unit 3. Code Case N-613-1, Figure 2, will be used for Oconee, Unit 3, core flood nozzle-to-vessel welds. As added conservatism, the vendor scan plans have included an additional 1/2-inch of scan path to ensure that the boundaries of the weld are covered by the ultrasonic beams.
Stresses caused by welding are concentrated at the weld and heat affected zone. Post weld heat treatment reduces these stresses and any residual stresses decrease as a function of the distance from the weld.
Operational stresses originate from internal pressure in the vessel and temperature changes occurring during transients. These stresses are limited by design to ensure that ASME Code stress limits are not exceeded. Additionally, a fatigue analysis is required by ASME Code,Section III, to ensure that flaws are unlikely to initiate during operation. Compared to the code limit of 1.0, the fatigue usage in the nozzle-to-shell weld regions are as follows:
Catawba, Unit 2 0.4472 Oconee, Unit 3 0.634 Because stresses are reduced by post weld heat treatment and design requirements, the occurrence of flaws during service is unlikely.
During preceding UTs conducted in the first 10-year interval at Catawba, Unit 2, and the first and second 10-year intervals at Oconee, Unit 3, no indications were found in the RPV nozzle-to-vessel weld examination volume excluded by Code Case N-613-1. These examinations were conducted from the inside surface of the RPV and the inside diameter (ID) of the nozzle in accordance with ASME Code,Section V, Article 4, and Regulatory Guide (RG) 1.150, Rev. 1. The previous UTs used an automated system to acquire, analyze and store data. The UTs scheduled for the current interval will use personnel, automated equipment, and procedures qualified in accordance with ASME Code,Section XI, Appendix VIII, Supplements 4, 6, and 7, 1995 Edition through the 1996 Addenda. The licensee is confident that satisfactory comparisons can be made between past and present examinations if necessary. Use of the proposed alternative will provide an acceptable level of quality and safety.
3.5 Staff Evaluation The licensee has requested relief from the UT volume requirements specified in Table IWB-2500-1, Examination Category B-D, Code Item B3.90, Figures IWB-2500-7 (a) through (d) pertaining to UT Examination of Full Penetration Nozzles in Vessels. The licensee proposes to use a reduced examination volume, extending to 1/2-inch from each side of the widest part of the nozzle-to-vessel weld in lieu of an examination volume extending to a distance equal to 1/2 the through-wall thickness from each side of the widest part of the nozzle-to-vessel weld, as required by Figures IWB-2500-7 (a) through (d).
The licensee provided a sketch showing the configuration of the nozzle-to-vessel weld and the revised examination volume. The specific weld configurations and revised examination volumes are depicted in ASME Code Case N-613-1 and the WesDyne sketches attached to the relief request submittal. The revised examination volume depicted in these sketches extends to 1/2-inch from each side of the widest part of the nozzle-to-vessel weld and is, therefore, consistent with licensees request for the reduced UT volume. All other aspects of the UT volumes for RPV nozzle-to-vessel welds remain unchanged in the licensees request. In response to additional information requested by the NRC staff the licensee provided a listing of all nozzle-to-vessel welds included within the scope of this relief request.
The acceptability of the reduced UT volume is based on prior full volumetric examinations of the welds and base metal, as well as the internal stress distribution near the weld. Prior full volumetric examinations of the nozzle-to-vessel welds included within the scope of this relief request cover the full volume of base metal, extending to a distance equal to 1/2 the through-wall thickness from each side of the widest part of the nozzle-to-vessel weld, as required by the ASME Code. This base metal region included in the original ASME Code volume was extensively examined during construction, preservice inspection, and prior ISIs. These examinations all show the ASME Code volume to be free of unacceptable flaws. The creation of flaws during plant service in the volume excluded from the proposed reduced examination volume is unlikely because of the low stress in the base metal away from the weld. The stresses caused by welding are concentrated at or near the weld. Cracks, should they initiate, occur in the highly-stressed area of the weld. The highly-stressed areas are within the volume included in the reduced examination volume proposed by the licensee. The prior full volume examinations of the base metal in addition to the examinations of the highly-stressed areas of the weld provide an acceptable level of quality and safety.
The weld volume and the adjacent base metal volume will be examined in accordance with Code Case N-613-1. The examinations shall consist of techniques and procedures qualified in accordance with the ASME Code,Section XI, Appendix VIII, Supplements 4, 6, and 7. The weld and base metal volumes will be interrogated from the nozzle bore using techniques and procedures specifically qualified to inspect the nozzle-to-vessel weld from the nozzle bore.
These procedures were qualified in January 2003 in accordance with ASME Code,Section XI, Appendix VIll, Supplement 7, as administered by the Performance Demonstration Initiative.
The nozzle-to-vessel examination volume is accessible from the vessel ID surface and will be examined in four orthogonal directions for the first 15 percent of weld thickness with respect to the vessel ID surface using ASME Code,Section XI, Appendix VIII, Supplement 4, qualified techniques. The remaining 85 percent of weld volume accessible from the vessel ID surface will be examined in two opposing circumferential scanning directions using ASME Code,Section XI, Appendix VIII, Supplement 6, qualified techniques to interrogate for transverse defects.
To ensure the extremities of the weld are included in the examination volume, a margin of 1/2-inch is conservatively added to the scanning path of all transducers in all directions as allowed by component geometry. This is standard practice for nozzle-to-shell, shell welds, and nozzle-to-pipe weld examinations. The sketches included in the licensees relief request reflect this additional conservatism. Based on this review of the documentation and associated drawings for all RPV nozzle-to-vessel welds, the licensee determined that no weld repairs are encapsulated within the existing nozzle-to-vessel welds. Therefore, since there are no repairs in the area to be examined which could extend past the original weld boundaries, the examination will encompass the entire weld and the examination will provide an acceptable level of quality and safety.
4.0 CONCLUSION
The NRC staff finds that the proposed alternative to reduce the UT volume to 1/2-inch from the widest part of the nozzle-to-vessel weld on each side of the weld crown, in lieu of 1/2 the through-wall thickness from the widest part of the nozzle-to-vessel weld on each side of the weld crown will provide an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the proposed alternative is authorized for ASME Code,Section XI, Class 1, RPV nozzle-to-vessel welds for the second 10-year ISI interval at Catawba, Unit 2, and for the third 10-year ISI interval at Oconee, Unit 3, unless during those intervals Code Case N-613-1 is published in a future version of RG 1.147, "Inservice Inspection Code Case Acceptability-ASME Section XI, Division 1." At that time, if the licensee intends to continue implementing this code case, it must follow all provisions of Code Case N-613-1 with limitations or conditions specified in RG 1.147, if any. All other requirements of the ASME Code, Sections III and XI, for which relief has not been specifically requested remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: J. Shea Date: October 7, 2004