ML050670165
| ML050670165 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 03/04/2005 |
| From: | Howe A NRC/NRR/DLPM/LPD4 |
| To: | Edington R Nebraska Public Power District (NPPD) |
| Honcharik M, NRR/DLPM, 301-415-1774 | |
| References | |
| TAC MC4954 | |
| Download: ML050670165 (11) | |
Text
March 4, 2005 Mr. Randall K. Edington Vice President-Nuclear and CNO Nebraska Public Power District P.O. Box 98 Brownville, NE 68321
SUBJECT:
COOPER NUCLEAR STATION - RE: REQUEST RI-35 FOR RELIEF FROM THE REQUIREMENTS OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) BOILER AND PRESSURE VESSEL CODE (CODE)
Dear Mr. Edington:
By letter dated October 25, 2004, as supplemented by letter dated January 5, 2005, Nebraska Public Power District submitted requests for the use of alternatives to certain ASME Code Section XI requirements at Cooper Nuclear Station.
The proposed alternative for relief request RI-35 provides an acceptable level of quality and safety. Therefore, pursuant to Section 50.55a(a)(3)(i) of Title 10 of the Code of Federal Regulations, the NRC staff authorizes the use of relief request RI-35 for all future outages and the remaining service life of this weld. The NRC staff's safety evaluation for RI-35 is enclosed.
Sincerely,
/RA/
Allen G. Howe, Chief, Section 1 Project Directorate IV Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-298
Enclosure:
Safety Evaluation cc w/encl: See next page
March 4, 2005 Mr. Randall K. Edington Vice President-Nuclear and CNO Nebraska Public Power District P.O. Box 98 Brownville, NE 68321
SUBJECT:
COOPER NUCLEAR STATION - RE: REQUEST RI-35 FOR RELIEF FROM THE REQUIREMENTS OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) BOILER AND PRESSURE VESSEL CODE (CODE)
Dear Mr. Edington:
By letter dated October 25, 2004, as supplemented by letter dated January 5, 2005, Nebraska Public Power District submitted requests for the use of alternatives to certain ASME Code Section XI requirements at Cooper Nuclear Station.
The proposed alternative for relief request RI-35 provides an acceptable level of quality and safety. Therefore, pursuant to Section 50.55a(a)(3)(i) of Title 10 of the Code of Federal Regulations, the NRC staff authorizes the use of relief request RI-35 for all future outages and the remaining service life of this weld. The NRC staff's safety evaluation for RI-35 is enclosed.
Sincerely,
/RA/
Allen G. Howe, Chief, Section 1 Project Directorate IV Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-298
Enclosure:
Safety Evaluation cc w/encl: See next page DISTRIBUTION:
PUBLIC RidsOgcRp PDIV-1 Reading RidsAcrsAcnwMailCenter RidsNrrDlpmLpdiv (HBerkow)
MHartzman RidsNrrDlpmLpdiv1 (AHowe)
GGeorgiev RidsNrrPMMHoncharik JDixon-Herrity RidsNrrLADJohnson RidsRgn4MailCenter (AHowell)
Accession No. ML050670165 OFFICE PDIV-1/PM PDIV-1/LA EMCB-SC EMEB-B/SC OGC (NLO)
PDIV-1/SC NAME MHoncharik DJohnson TChan*
KManoly*
RHoefling AHowe DATE 2/18/05 2/18/05 2/1/05 2/1/05 2/25/05 3/4/05 OFFICIAL RECORD COPY
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST NO. RI-35 NEBRASKA PUBLIC POWER DISTRICT COOPER NUCLEAR STATION DOCKET NO. 50-298
1.0 INTRODUCTION
By letter dated October 25, 2004, (Reference 1) and supplement dated January 5, 2005, (Reference 2), Nebraska Public Power District (the licensee) requested relief from the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code),Section XI (Reference 3) for Class 1 welds at Cooper Nuclear Station (CNS). Relief request RI-35 proposed the use of an alternative weld repair method to repair the reactor pressure vessel (RPV) control rod drive (CRD) nozzle-to-cap austenitic to ferritic steel welds. Specifically, the licensee proposed to perform a weld overlay over the existing weld using corrosion resistant Alloy 52 weld material.
2.0 REGULATORY EVALUATION
The regulation at Section 50.55a(g)(4) of Title 10 of the Code of Federal Regulations (10 CFR) specifies that inservice inspections (ISI) of nuclear power plant components shall be performed in accordance with the requirements of Reference 3, except where specific relief has been granted by the NRC pursuant to 10 CFR 50.55a(g)(6)(i). The regulation at 10 CFR 50.55a(a)(3)(i) states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if the proposed alternatives would provide an acceptable level of quality and safety.
The regulation at 10 CFR 50.55a(g)(5)(iii) states, in part, that if the licensee has determined that conformance with certain code requirements is impractical for its facility, the licensee shall notify the Commission and submit information to support the determinations.
3.0 EVALUATION OF RELIEF REQUEST RI-35 Weld overlay repair on CRD nozzle-to-cap austenitic to ferritic welds.
The Items for which Relief is Requested:
Code Class:
1
Reference:
IWA-4000, IWB-4000 Examination Category:
B-F Item Numbers:
B5.10 Item
Description:
Weld Overlay Repair Component Numbers:
RCA-BF-1 Code Requirement:
IWA-4000 and IWB-4000 of ASME Section XI require repairs to be performed in accordance with the Owners Design Specification and the original construction Code of the component or system.
Licensees Proposed Alternative and Basis for Use (as stated in Reference 1):
A full structural weld overlay repair will be designed consistent with the requirements of NUREG-0313, Revision 2, Section 4 (which was implemented by Generic Letter (GL) 88-01), ASME Code Cases N-504-2, N-638, and ASME,Section XI, Paragraph IWB-3640. The design will assume a through wall crack for 360E. It will be applied, if needed, for the weldment associated with the austenitic (nickel-based) to ferritic RPV CRD return line nozzle-to-cap weld. This weldment falls within the scope of GL 88-01 and is potentially susceptible to intergranular stress corrosion cracking (IGSCC).
No RPV drain down is planned for the overlay, nor for the seal weld repair, if one is necessary. The weld overlay will be completed with water on the inside surface of the nozzle and end cap. The alternative provides an acceptable level of quality and safety without the need for draining the RPV or applying preheat and post weld heat treatments.
EXAMINATION AND REPAIR REQUIREMENTS Welder Qualification and Welding Procedures-Welders and welding procedures will be qualified in accordance with ASME Section IX and any special requirements from Section XI or applicable code cases. A manual shielded metal arc weld (SMAW) procedure will be qualified to facilitate localized repairs and to provide a seal weld, prior to depositing the overlay. This procedure will make use of UNS W86152 SMAW electrodes consistent with the requirements of ASME Section IX.
Welding Wire Material - The conditions which could initiate the cracking of the N10 nozzle are IGSCC and/or interdendritic stress corrosion cracking (IDSCC) at the inside diameter of the N10 nozzle due to geometric discontinuities and residual repair weld stresses in an oxidizing environment. A consumable welding wire highly resistant to IGSCC and IDSCC will be used for the overlay material. (Note: IGSCC and IDSCC refer to essentially the same phenomenon in the base metal and weld material respectively.
For the purpose of this request they are synonymous.) This weld overlay material, designated UNS N06052, is a nickel-based weld filler material, commonly referred to as Alloy 52, and will be applied using the gas tungsten arc welding (GTAW) process.
Alloy 52 is identified as F-No. 43 Grouping for Ni-Cr-Fe, classification UNS N06052 Filler Metal. Alloy 52 contains about 30% chromium that imparts excellent corrosion resistance to this material. Alloy 152 welding wire may be used for seal welding activities.
Weld Overlay Design - The weld overlay will extend around the full circumference of the nozzle weldment location in accordance with NUREG-0313, Revision 2, Code Case N-504-2 and GL 88-01, and BWRVIP-75. The specific thickness and length will be computed according to guidance provided in ASME Section XI, Code Case N-504-2 and ASME Section XI, Paragraph IWB-3640, 1989 Edition. The overlay will completely cover the indication location and the Alloy 182 weld deposit butter with the highly corrosion resistant Alloy 52 material. In order to accomplish this objective, it will be necessary to weld on the low alloy steel nozzle material. A temper bead welding approach will be used for this purpose according to provisions of ASME Code Case N-638. This code case provides for machine GTAW temper bead weld repairs to P No. 3 nozzle materials (SA 508 Class 2) at ambient temperature. The temper bead approach was selected because temper bead welding supplants the requirement for post weld heat treatment (PWHT) of heat-affected zones in welded low alloy steel material.
Examination Requirements - The repair, pre-service inspection and inservice inspection (ISI) examination of the weld overlay repair will be performed in accordance with the ISI Program, NUREG-0313, Revision 2, GL 88-01, and approved plant procedures as specified by the ISI Repair/Replacement Program. The weld overlay will be examined in accordance with the industry-developed Performance Demonstration Initiative (PDI) procedure. As required by Code Case N-416-2, Non-Destructive Examination will be performed to ASME Section III, 1992 Edition, Subsection NB requirements to the extent practical. Since a weld overlay repair is not described in ASME Section III, a description of the required examinations is provided in the following table. The acceptance criteria for the volumetric examinations will be ASME Section XI, Paragraph IWB-3514, "Standards for Examination Category B-F, Pressure Retaining Dissimilar Metal Welds, and Category B-J, Pressure Retaining Welds In Piping."
Examination Description Method Technique Reference Weld and End Cap Overlay Surface Area Preparation PT
[Penetrant Testing]
Visible Dye N-504-2 First Two Weld Overlay Layers Surface Examination PT Visible Dye N-504-2 First Two Weld Overlay Layers Thickness Measurements UT
[Ultrasonic Testing] or Mechanical 0E Long. UT or Mechanical Height Measurement N-504-2 Completed Overlay Thickness Measurements UT or Mechanical 0E Long. UT or Mechanical Height Measurement N-504-2 Surface Exam of Final Overlay Surface and Adjacent Band within 1.5t of weld overlay.
This is also the Preservice Surface Examination.
PT Visible Dye NB-5350 IWB-3514 N-638 N-504-2 Volumetric Exam of Final Overlay and Adjacent Band within 1.5t of weld overlay.
This is also the Preservice Volumetric Examination.
UT PDI Procedure ASME XI Appendix VIII Preservice Baseline Exam of Final Overlay Outer 25% of Underlying Pipe Wall to Identify Original Flaws UT 60E Ref. Long.
OD [outer diameter]
Creeping Wave N-504-2 ALTERNATIVE TO REPAIR REQUIREMENTS The repair will utilize ASME Code Case N-504-2, "Alternative Rules for Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping," and Code Case N-638, "Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique," with the following exceptions and clarifications.
Clarification of Code Case N-504-2 for Applicability to Nickel-Based Austenitic Steel -
Code Case N-504-2 was prepared specifically for austenitic stainless steel material. An alternate application to nickel-based austenitic materials (i.e., Alloy 52) is requested due to the specific configuration of the nickel-based austenitic weldment.
Exception from Code Case N-504-2 Paragraph (b) - Code Case N-504-2 paragraph (b) requires that the reinforcement weld metal shall be low carbon (0.035 % maximum) austenitic stainless steel. In this application, a nickel-based filler is required and Alloy 52 has been selected in place of low carbon austenitic stainless steel.
Exception from Code Case N-504-2 Paragraph (e) - Code Case N-504-2 paragraph (e) requires as-deposited delta ferrite measurements of at least 7.5 FN for the weld reinforcement. These measurements have no meaning for nickel-based materials and will not be performed for this overlay.
Exception from Code Case N-504-2 Paragraph (h) - Code Case N-504-2 paragraph (h) requires a system hydrostatic test of completed repairs if the repaired flaw penetrated the original pressure boundary or if there is any observed indication of the flaw penetrating the pressure boundary during repairs. A system leak test of completed repairs will be used in lieu of a hydrostatic test.
Use of Code Case N-638 Applicability - Code Case N-638 will be applied for that portion of the weld overlay repair over the nozzle material.
BASIS FOR THE ALTERNATIVE Clarification of Code Case N-504-2 for Applicability to Nickel-Based Austenitic Steel -
The weldment being addressed is austenitic material having a mechanical behavior similar to austenitic stainless steel. The weldment is designed to be highly resistant to IGSCC and is compatible with the existing weldment and base metal materials.
Accordingly, this alternative provides an acceptable level of quality and safety.
Therefore, Code Case N-504-2 should be interpreted to apply equally to both materials.
Exception from Code Case N-504-2 Paragraph (b) - A consumable welding wire highly resistant to IGSCC was selected for the overlay material. This material, designated UNS N06052 is a nickel-based alloy weld filler material, commonly referred to as Alloy 52, and will be applied using the GTAW process. Alloy 52 contains about 30%
chromium that imparts excellent stress corrosion cracking resistance to this material. By comparison, Alloy 82, is identified as an IGSCC resistant material in NUREG-0313 Revision 2 and contains about 18 to 22% chromium while Alloy 182 has a nominal chromium composition of 13 to 17%. Alloy 52 with its high chromium content provides a high level of resistance to IGSCC consistent with the requirements of the Code Case.
Therefore, this alternative provides an acceptable level of quality and safety.
Exception from Code Case N-504-2 Paragraph (e) - The composition of nickel-based Alloy 52 is such that delta ferrite is not formed during welding. Ferrite measurement requirements were developed for weld of 300 series stainless steel that require delta ferrite to develop corrosion resistance. Weld of Alloy 52 and Alloy 152 are 100%
austenitic and contain no delta ferrite due to the high nickel composition (approximately 60% Ni and low iron content). Alloy 52 with its high chromium content provides a high level of resistance to IGSCC consistent with the purpose for the delta ferrite requirements for stainless steels of the Code Case. Therefore, this alternative provides an acceptable level of quality and safety.
Exception from Code Case N-504-2 Paragraph (h) - In lieu of the hydrostatic pressure test requirements defined in Code Case N-504-2, a system pressure test shall be performed in accordance with the Third Interval ISI Program and Code Case N-416-2 with the exception that the volumetric examination performed shall be an ultrasonic examination of the weld overlay. As required by Regulatory Guide 1.147, Revision 13, for Code Case N-416-2, the hold times for the inservice test will be consistent with the requirements of IWA-5213 of the 1989 Edition of ASME Section XI. These alternative requirements are sufficient to demonstrate that the overlay is of adequate quality to ensure the pressure boundary integrity. Accordingly, this alternative provides an acceptable level of quality and safety.
Use of Code Case N-638 Applicability - Code Case N-638 was developed for temper bead applications to similar and dissimilar metals. It permits the use of machine GTAW at ambient temperature without the use of preheat or PWHT on Class 1, 2, and 3 components. Temper bead welding methodology is not new. Numerous applications over the past decade have demonstrated the acceptability of temper bead technology in nuclear environments. Temper bead welding achieves HAZ tempering and grain refinement without subsequent PWHT. Excellent HAZ toughness and ductility are produced. Use of Code Case N-638 has been accepted in Regulatory Guide 1.147 Revision 13 as providing an acceptable level of quality and safety.
Licensees Reason for Request (as stated Reference 1):
RCA-BF-1 is the Reactor Pressure Vessel (RPV) Control Rod Drive (CRD) nozzle-to-cap austenitic to ferritic weld. A weld inspection is planned during Refueling Outage 22. If a flaw is detected, then a repair method with a more corrosion resistant material will require draining the RPV. In addition, preheat and post weld heat treatment are required for welding on nozzle material by ASME Section III, Subparagraph NB4622.7. These requirements are highly impractical without draining the RPV, and may distort the P3 components involved. If the RPV is drained, the radiation dose rates in the nozzle area would increase significantly, resulting in increased personnel exposure. In summary, this request is being made to avoid unnecessary personnel exposure, and the potentially significant impacts on the outage schedule.
Evaluation:
The licensee stated that a weld inspection is planned during Refueling Outage 22. During the inspection, the licensee is scheduled to inspect CRD nozzle-to-cap austenitic to ferritic weld identified as RCA-BF-1. If a flaw is detected, current ASME Code weld repair rules specify a weld repair method that will require draining of the RPV. Further, preheat and post weld heat treatment are required for welding on nozzle material by ASME Code,Section III, Subparagraph NB-4622.7. These requirements are highly impractical because it would require draining of the RPV, and also post weld heat treatment of nozzle material. Post weld heat treatment may distort the nozzle material, which is classified as P3 material by ASME Code,Section IX. If the RPV is drained, the radiation dose rates in the nozzle area would increase significantly, resulting in increased personnel exposure.
Instead of following the requirements of the ASME Code, the licensee proposed to perform a full structural weld overlay repair. If needed, the weld overlay will be applied over the existing weld, which is a dissimilar austenitic stainless to ferritic RPV CRD return line nozzle-to-cap weld. The licensee does not plan to drain down the RPV for the overlay, nor for the seal weld repair. The weld overlay will be completed with water on the inside surface of the nozzle and end cap.
The weld overlay thickness and length were designed consistent with the requirements of NUREG-0313, Revision 2, ASME Code Case N-504-2, and ASME Code,Section XI, Paragraph IWB-3640. In accordance with Code Case N-504-2, the design assumed a through wall crack for the entire circumference of the nozzle-to-cap weld. The loading consisted of the internal design pressure only, as no external thermal or mechanical bending moments act on the cap.
In accordance with the provisions of IWB-3640, the required weld overlay thickness was determined as 0.25 inches. The required length and end slopes of the weld were also determined in accordance with the provisions of Code Case N-504-2. As stated in the Code Case, the appropriate Class 1 stress limits for primary local and bending stresses and secondary peak stresses prescribed in ASME Code,Section III, 1974 through winter 1975, are considered satisfied when the length and end slopes are determined in accordance with the provisions of the Code Case. The licensee stated that the ASME Code,Section III, Class 1 fatigue cumulative usage factor (CUF) for the original design of the CRD nozzle was 0.022.
The licensee also stated that the capping of the nozzle eliminated the weight of the CRD return piping and most thermal stresses, and therefore this is considered a bounding limit for the cap.
The staff has found that any increase in the nozzle fatigue CUF due to the weld overlay will most likely be minimal. Based on these considerations, the staff finds the design of the weld overlay reasonable and acceptable.
The licensee also stated that welders and welding procedures will be qualified in accordance with ASME Code,Section IX and any special requirements from Section XI or applicable code cases. This would ensure that the deposition of weld overlay are accomplished using ASME Code qualified welders and welding procedures.
The proposed weld overlay material to be deposited over existing weld RCA-BF-1 is Alloy 52.
Alloy 52 is identified as F-No. 43 Grouping for Ni-Cr-Fe, classification UNS N06052 Filler Metal and has been previously approved by the NRC staff. Alloy 52 is a nickel-based alloy that contains about 30% chromium, which provides for excellent corrosion resistance in reactor coolant environment.
The licensee stated that in lieu of the hydrostatic pressure test requirements defined in Code Case N-504-2, a system pressure test will be performed in accordance with Code Case N-416-2 with the exception that the volumetric examination performed shall be an ultrasonic examination of the weld overlay. The hold times for the inservice test will be consistent with the requirements of IWA-5213 of the 1989 Edition of ASME Code,Section XI. The staff finds these alternative requirements acceptable, because the ultrasonic examination of the overlay will ensure that the overlay is free from fabrication-induced defects and the structural integrity of the overlay will be tested by the system pressure test. Therefore, the staff finds the proposed alternative provides an acceptable level of quality and safety.
The staff finds the licensee's weld overlay repair method acceptable because the design complies with the requirements of NUREG-0313, Revision 2, ASME Code Case N-504-2, and ASME Code,Section XI, Paragraph IWB-3640. In addition the weld overlay will be designed to contain a through wall crack 360 degrees in circumferential extent, which would ensure structural integrity of the weld. The proposed weld overlay material to be deposited over existing weld RCA-BF-1 is Alloy 52, which the NRC staff has approved for use in dissimilar weld repairs. Alloy 52 is a nickel-based alloy that has demonstrated excellent corrosion resistance in reactor coolant environment. Also, welders and welding procedures will be qualified in accordance with ASME Code,Section IX and any special requirements from Section XI or applicable code cases. This would ensure that the deposition of weld overlay is accomplished using ASME Code qualified welders and welding procedures. The completed weld overlay would be ultrasonically examined and system pressure tested in accordance with the requirements of Code Case N-416-2. Therefore, the proposed weld overlay repair method provides an acceptable level of quality and safety without the need for draining the RPV or applying preheat and post weld heat treatments.
4.0 CONCLUSION
Based on the information provided in References 1 and 2, the NRC staff concludes that the licensee has provided an acceptable alternative to the requirements of ASME Code,Section XI for the proposed weld overlay repair of weld RCA-BF-1 at CNS. The proposed weld overlay repair method provides an acceptable alternative to the weld repair requirements specified in ASME Code, Sections III and XI. Therefore, the proposed alternative is authorized pursuant to 10 CFR 50.55a(a)(3)(i) for CNS for all future outages and for the remaining service life of this weld. All other ASME Code,Section III or XI, requirements for which relief was not specifically requested and authorized herein by the NRC staff remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.
5.0 REFERENCES
1.
Letter from R. Edington (NPPD) to NRC, Inservice Inspection Relief Request RI-35, October 25, 2004. ADAMS accession no. ML043030310.
2.
Letter from R. Edington (NPPD) to NRC, Response to Requests for Additional Information Regarding Relief Request RI-35, January 5, 2005. ADAMS accession no. ML050110236.
3.
Section XI of the ASME Boiler & Pressure Vessel Code, Rules for Inservice Inspection of Nuclear Power Plant Components, 1989 Edition, No Addenda.
Principal Contributor: G. Georgiev M. Hartzman Date: March 4, 2005
January 2005 Cooper Nuclear Station cc:
Mr. William J. Fehrman President and Chief Executive Officer Nebraska Public Power District 1414 15th Street Columbus, NE 68601 Michael T. Boyce Nuclear Asset Manager Nebraska Public Power District 1414 15th Street Columbus, NE 68601 Mr. John R. McClure Vice President and General Counsel Nebraska Public Power District P. O. Box 499 Columbus, NE 68602-0499 Mr. Paul V. Fleming Licensing Manager Nebraska Public Power District P.O. Box 98 Brownville, NE 68321 Mr. Michael J. Linder, Director Nebraska Department of Environmental Quality P. O. Box 98922 Lincoln, NE 68509-8922 Chairman Nemaha County Board of Commissioners Nemaha County Courthouse 1824 N Street Auburn, NE 68305 Ms. Cheryl K. Rogers, Program Manager Nebraska Health & Human Services System Division of Public Health Assurance Consumer Services Section 301 Centennial Mall, South P. O. Box 95007 Lincoln, NE 68509-5007 Mr. Ronald A. Kucera, Director of Intergovernmental Cooperation Department of Natural Resources P.O. Box 176 Jefferson City, MO 65102 Senior Resident Inspector U.S. Nuclear Regulatory Commission P. O. Box 218 Brownville, NE 68321 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011 Jerry Uhlmann, Director State Emergency Management Agency P. O. Box 116 Jefferson City, MO 65101 Chief, Radiation and Asbestos Control Section Kansas Department of Health and Environment Bureau of Air and Radiation 1000 SW Jackson Suite 310 Topeka, KS 66612-1366 Mr. Daniel K. McGhee Bureau of Radiological Health Iowa Department of Public Health 401 SW 7th Street Suite D Des Moines, IA 50309 Mr. Scott Clardy, Director Section for Environmental Public Health P.O. Box 570 Jefferson City, MO 65102-0570 Jerry C. Roberts Director of Nuclear Safety Assurance Nebraska Public Power District P.O. Box 98 Brownville, NE 68321