ML083380201
| ML083380201 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 11/25/2008 |
| From: | Brandon M Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML083380201 (8) | |
Text
Tennessee Valley Authority, Post Office Box 2000, Decatur, Alabama 35609-2000 November 25, 2008 10 CFR 50.55a U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Stop: OWFN P1-35 Washington, D.C. 20555-0001 In the Matter of
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Docket No. 50-259 Tennessee Valley Authority
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BROWNS FERRY NUCLEAR PLANT (BFN) - UNIT 1 - AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) SECTION XI, INSERVICE INSPECTION PROGRAM FOR THE SECOND TEN-YEAR INSPECTION INTERVAL - REQUEST FOR RELIEF 1-ISI-22 Browns Ferry Nuclear Plant, Unit 1, is proposing an alternative to the requirements of ASME Boiler and Pressure Vessel Code, Code Case N-504-3, Alternative Rules for Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping, Section Xl, Division 1, Paragraph (h). The alternative is proposed pursuant to the provisions of paragraph 50.55a(a)(3)(i) of Title 10 of the Code of Federal Regulations (10 CFR) as an alternative that would provide an acceptable level of quality and safety.
TVA proposes to utilize a system leakage test in accordance with IWA-5000 at nominal operating pressure and temperature in lieu of the system hydrostatic test required by Paragraph (h) of Code Case N-504-3, following the weld overlay repair for a through wall leak of the Safe-end on the Ni 1 B RPV Nozzle. TVA considers this alternative would provide an acceptable level of quality and safety. TVA's request for relief 1-ISI-22 is provided in Enclosure 1 of this submittal.
U.S. Nuclear Regulatory Commission Page 2 November 25, 2008 A summary of the commitment made in this submittal is contained in Enclosure 2 TVA requests approval of this request for relief by 0900 CST on November 27, 2008, in order to support transition to Mode 2 (i.e. startup) for Cycle 8 operation.
If you have any questions, please contact me at (256) 729-2636.
Sincerely, Michael K. Brandon Interim Manager of Licensing and Industry Affairs Enclosures cc: See Page 3
U.S. Nuclear Regulatory Commission Page 3 November 25, 2008 cc (Enclosures):
Mr. Eugene F. Guthrie, Branch Chief U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-8931 NRC Resident Inspector Browns Ferry Nuclear Plant 10833 Shaw Road Athens, Alabama 35611-6970 Ms. Eva A. Brown, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North (MS 08G9) 11555 Rockville Pike Rockville, Maryland 20852-2739
ENCLOSURE1 TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)
UNIT 1 AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) SECTION XI, INSERVICE INSPECTION (ISI) PROGRAM SECOND TEN-YEAR INSPECTION INTERVAL.
REQUEST FOR RELIEF 1-ISI-22 EXECUTIVE
SUMMARY
- Leakage was observed from the 2-inch N-11 B-1 process pipe to safe-end location associated with Feedwater level instrumentation during the scheduled BFN Unit 1 Cycle 7 refueling outage pressure test. This leakage was characterized as approximately 15 drops per minute. Further characterization of the flaw utilizing a PDI/IGSCC qualified ultrasonic procedure determined the flaw to be oriented circumferentially and approximately 1.1 inches in length (ID). The flaw is located approximately 0.5 inches from the weld centerline in the safe-end side of the weld joint adjacent to the heat affected zone. Weld overlay in accordance with Code Case N-504-3 as conditioned in Regulatory Guide 1.147, Rev. 15, with Appendix Q of ASME Section XI was determined to be the best repair method.
This relief request proposes an alternative to paragraph (h) of Code Case N-504-3 which requires a system hydrostatic test, in accordance with IWA-5000, if the flaw penetrated the original pressure boundary prior to welding.
The alternative is proposed pursuant to the provisions of 10CFR 50.55a(a)(3)(i) as an alternative that provides an acceptable level of quality and safety.
Unit: One (1)
ISI Interval: ASME Section XI, Second Ten-Year ISI Inspection Interval (June 2, 2008 to June 1,2017)
Systems: Reactor Feedwater System Components: Class 1 pressure retaining components ASME Code Class: ASME Code Class 1 equivalent ASME Section XI Code Edition: 2001 Edition, 2003 Addenda Code Table: IWB-2500-1 Examination Cateaorv: B-P Examination Item Number: B15.10 E1-1
Code Requirement: ASME Boiler and Pressure Vessel Code, Code Case N-504-3, Alternative Rules for Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping,Section XI, Division 1, Paragraph (h) states that if the flaw penetrated the original pressure boundary prior to welding, a system hydrostatic test shall be performed in accordance with IWA-5000.
Code Requirement From Which Relief Is Requested: Relief is requested from Paragraph (h) of Code Case N-504-3 which requires a system hydrostatic test, in accordance with IWA-5000, if the flaw penetrated the original pressure boundary prior to welding.
LIST OF ITEMS ASSOCIATED WITH THE RELIEF REQUEST: Safe-end on the N-i 1 B RPV nozzle; specifically, adjacent to the outboard weld, N-11 B-1, connecting the safe-end to the process piping.
BASIS FOR RELIEF REQUEST: The performance of a system leakage test at nominal operating pressure versus a hydrostatic pressure test at an elevated pressure, above nominal operating pressure, has been reviewed by the ASME Code Committee and by the NRC. This review resulted in the development of both the Code Case N-416 series and the N-498 series and their subsequent incorporation into ASME Section XI Code beginning with the 1998 Edition, 1999 Addenda. The precedence developed acknowledges that the hydrostatic pressure test provides minimal additional benefit, above that provided by a pressure test at nominal operating pressure, to the proof or verification of the quality and acceptability of the repairs. Repairs performed using approved welding programs and NDE based on the methods and acceptance criteria required by Section III, in addition to a system leakage test performed at nominal operating pressure, show that minimal benefit is gained from the added challenge to the piping system provided by an elevated pressure associated with a hydrostatic test. Stress induced in this piping geometry does not exceed 50% of the material stress allowables during either the system leakage test, performed at nominal operating pressure or the system hydrostatic pressure test, performed above operating pressure.
Also, in a previous action, relief has been granted from the hydrostatic pressure test requirement associated with Code Case N-504-3 to the Cooper Nuclear Station (ML0821304i183). The basis of the referenced relief was that precedence for use of a leak test at normal operating temperature and pressure in lieu of a hydrostatic test has been set with Code Case N-416-1 that has been incorporated in ASME Code,Section XI. The NRC staff concluded that the alternative provided an acceptable level of quality and safety. The referenced conditions at the Cooper facility are considered directly applicable to the conditions in question at BFN Unit 1. The Cooper relief request was submitted as a contingency for disposition of examination results of multiple dissimilar and similar metal welds and the portion related to exception from the requirements of paragraph (h) of Code Case N-504-3 is similar to this relief request.
ALTERNATIVE EXAMINATION: In lieu of the system hydrostatic test required by Paragraph (h) of Code Case N-504-3, TVA proposes to utilize a system leakage test, in accordance with IWA-5000, at nominal operating pressure and temperature. This pressure test will be performed following completion of NDE required by Code Case N-504-3,Section XI Nonmandatory Appendix Q, and the construction code (Section III). The ultrasonic (UT) examinations performed are Performance Demonstration Initiative (PDI) qualified methods and are capable of identifying flaws indicative of intergranular stress corrosion cracking (IGSCC).
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JUSTIFICATION FOR THE GRANTING OF RELIEF: Indications of leakage identified through visual VT-2 examinations during either a system leakage test or a system hydrostatic test will not be significantly different between the two tests. The magnitudes of pressure required by those exams will not induce significant differences in leakage rates, should a through-wall leak already exist, and will not create a significant difference in the magnitude of the structural challenge to the material based on the stress allowables associated with the applicable materials.
The safe-end material in question is ASME SA336 GR F8 with a 2.44 inch nominal outside diameter and a 0.242 inch wall thickness (0.206 inch minimum). As an example of the stresses generated in this material during the two pressure tests in question, the following comparisons are presented. The stress generated in the material during the pressure test at nominal operating pressure was less than 30% of the allowable stress and the stress generated by the hydrostatic pressure test was in the low 30% region of the allowable stress for that material. Material stress conditions in these ranges would not tend to drive flaw growth to such an extent that leakage would be generated or significantly increased.
Therefore, no significant observable differences would be provided by the performance of the hydrostatic pressure test and the system leakage test would provide an acceptable alternative. This is the general logic behind the acceptance of both the Code Case N-416 series and the N-498 series and the eventual removal of the hydrostatic test requirements from the Section XI Code as a periodic pressure test requirement.
IMPLEMENTATION SCHEDULE: This request for relief is applicable to the Second Ten-Year Inspection Interval for BFN Unit 1 (June 2, 2008 to Junel, 2017).
REFERENCES:
TVA drawing 1-47E803-5, Revision 2 ADDITIONAL INFORMATION: The stainless steel Safe-End is fabricated from ASME SA-336 Gr. F8 and is welded to 2 inch Schedule 80, ASTM A312 or A376, Gr TP304 or TP316 piping, according to the Bill of Materials (47BM600-1, sheet 13 of 15) for this piping.
The proposed overlay will be comprised of ASME SFA 5.9 Type ER308/308L dual certified welding filler material. The Certificate of Analysis for this material certifies that the as-welded Ferrite Number (FN) has been tested to be 10 FN (by Magna Gage) and 12 FN (by WRC calculation through chemical analysis).
The use of Automated GTAW process to apply this overlay ensures the least change in chemical composition from the wire to the deposit and further ensures limited dilution carryover as subsequent weld passes are applied, therefore ensuring the minimum FN in the weld deposit is achieved in the first clean weld layer above the seal pass, and subsequent layers, of the designed overlay thickness.
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The extent of condition for Unit 1 was determined to be other nozzle safe-end to process pipe welds fabricated using similar materials and processes. These nozzle safe-ends are also 2-inch diameter and similar thicknesses. The nozzle numbers associated with these safe-end to process pipe welds are N-11 A, N-1 2A, N-1 2B, N-1 6A, N-1i6B and N-1 0. The PDI qualified ultrasonic examination of these nozzles has been completed as part of the corrective actions associated with BFN Problem Evaluation Report (PIER) 157918 and no recordable indications were identified. This examination included the base metal of the safe-end up to the safe-end transition taper.
The N-11 B-1 safe-end overlay will be entered into the Unit 1 BFN Inservice Inspection Program (1-SI-3.3.1.A) and future examinations of this overlay will be in accordance with ASME Section Xl Nonmandatory Appendix Q.
TVA will perform additional PDI qualified ultrasonic examinations on the six similar Unit 1 nozzle safe-end to process pipe welds during the next refueling outage (UlC8). These welds are associated with nozzles N-11A, N-12A, N-12B, N-16A, N-16B and N-10.
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ENCLOSURE2 TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)
UNIT 1 AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) SECTION XI, INSERVICE INSPECTION (ISI) PROGRAM SECOND TEN-YEAR INSPECTION INTERVAL.
SUMMARY
OF COMMITTMENT Six Unit 1 nozzle safe-end to process pipe welds associated with RPV nozzles N-1 1-A, N-12-A, N-12-B, N-16-A, N-16-B and N-10 will be rexamined by PDI qualified UT methods during the U1C8 refueling outage.
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