ML080790563

Relief Request 1-RR-4-6 for Piping Weld Examination Coverage for the Fourth Inservice Inspection Interval

ML080790563
Person / Time
Site:	Prairie Island
Issue date:	05/09/2008
From:	Lois James NRC/NRR/ADRO/DORL/LPLIII-1
To:	Wadley M Nuclear Management Co
Chawla, ML, NRR/DLPM/LPD III-2, 415-8371
References
TAC MD5593
Download: ML080790563 (8)

Text

May 9, 2008 Mr. Michael D. Wadley Site Vice President Prairie Island Nuclear Generating Plant Nuclear Management Company, LLC 1717 Wakonade Drive East Welch, MN 55089

SUBJECT:

PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNIT 1 - RELIEF REQUEST 1-RR-4-6 FOR PIPING WELD EXAMINATION COVERAGE FOR THE FOURTH INSERVICE INSPECTION INTERVAL (TAC NO. MD5593)

Dear Mr. Wadley:

By letter dated May 11, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML071370392), Nuclear Management Company, LLC (NMC),

submitted Relief Request Number 1-RR-4-6, Revision 0 for the fourth 10-year inservice inspection (ISI) interval at the Prairie Island Nuclear Generating Plant (PINGP), Unit 1. NMC requested relief from American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, Table IWB-2500-1 requirements for piping weld selection and examination volumes of the reducer to valve weld (W-17) in the safety injection system.

The U.S. Nuclear Regulatory Commission (NRC) staff has reviewed your proposal and concludes that subject relief request is acceptable as discussed in the enclosed safety evaluation. Based on the information submitted, the NRC staff concludes that the proposed alternative would provide an acceptable level of quality and safety because the examination coverage achieved will most likely detect any significant degradation, if present, and that the examination coverage achieved would provide reasonable assurance of the structural integrity of weld W-17.

Therefore, pursuant to Title 10 of the Code of Federal Regulations (CFR) Section 50.55a(a)(3)(i), use of Relief Request 1-RR-4-6, Revision 0, is authorized for the reduced volumetric examination coverage of the reducer to valve weld (W-17) in the system injection system at PINGP, Unit 1 for the fourth 10-year ISI interval (December 21, 2004, to December 20, 2014).

M. Wadley If you have any questions, please contact me at (301) 415-8371.

Sincerely,

/RA/

Lois M. James, Chief Plant Licensing Branch III-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-282

Enclosure:

Safety Evaluation cc w/encl: See next page

ML080790563 *Memo Dated 3/3/2008 **See previous concurrence OFFICE NRR/LPL3-1/PM NRR/LPL3-1/LA NRR/DCI/BC OGC NRR/LPL3-1/BC NAME MChawla JC for BTully ** TChan

• MSpencer LJames NLO DATE 05/07/08 3/24/08 03/ 03 / 08 05/07/08 05/ 09 /08 Prairie Island Nuclear Generating Plant, Units 1 and 2 cc:

Peter M. Glass Tribal Council Assistant General Counsel Prairie Island Indian Community Xcel Energy Services, Inc. ATTN: Environmental Department 414 Nicollet Mall 5636 Sturgeon Lake Road Minneapolis, MN 55401 Welch, MN 55089 Manager, Regulatory Affairs Nuclear Asset Manager Prairie Island Nuclear Generating Plant Xcel Energy, Inc.

Nuclear Management Company, LLC 414 Nicollet Mall, R.S. 8 1717 Wakonade Drive East Minneapolis, MN 55401 Welch, MN 55089 Dennis L. Koehl Manager - Environmental Protection Chief Nuclear Officer Division Nuclear Management Company, LLC Minnesota Attorney General=s Office 700 First Street 445 Minnesota St., Suite 900 Hudson, WI 54016 St. Paul, MN 55101-2127 Joel P. Sorenson U.S. Nuclear Regulatory Commission Director, Site Operations Resident Inspector's Office Prairie Island Nuclear Generating Plant 1719 Wakonade Drive East Nuclear Management Company, LLC Welch, MN 55089-9642 1717 Wakonade Drive East Welch, MN 55089 Administrator Goodhue County Courthouse Box 408 Red Wing, MN 55066-0408 Commissioner Minnesota Department of Commerce 85 7th Place East, Suite 500 St. Paul, MN 55101-2198 July 2006

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST NUMBER 1-RR-4-6, REVISION 0 LIMITED VOLUMETRIC EXAMINATION COVERAGE SAFETY INJECTION SYSTEM PIPING NUCLEAR MANAGEMENT COMPANY, LLC.

PRAIRIE ISLAND NUCLEAR GENERATING PLANT UNIT 1 DOCKET NUMBER 50-282

1.0 INTRODUCTION

By letter dated May 11, 2007, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML071370392) Nuclear Management Company, LLC (NMC), submitted Relief Request Number 1-RR-4-6, Revision 0, for the fourth 10-year inservice inspection (ISI) interval at the Prairie Island Nuclear Generating Plant (PINGP), Unit 1. NMC requested relief from American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, Table IWB-2500-1 requirements for piping weld selection and examination volumes.

The proposed relief would allow 50 percent ultrasonic examination coverage in lieu of the Code-required 100 percent volumetric coverage for the reducer-to-valve weld (W-17) in the safety injection system piping at PINGP Unit 1.

2.0 REGULATORY EVALUATION

The ISI of ASME Code Class 1, Class 2, and Class 3 components shall be performed in accordance with the ASME Code,Section XI, Rules for Inservice Inspection (ISI) of Nuclear Power Plant Components, and applicable edition and addenda as required by Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g), except where specific relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). Paragraph 10 CFR 50.55a(g)(6)(i) states that . . . the Commission will evaluate determinations . . . that [ASME] code requirements are impractical. The Commission may grant such relief and may impose such alternative requirements as it determines is authorized by law and will not endanger life or property or the common defense and security, and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.

Pursuant to 10 CFR 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, ARules for

M. Wadley 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. Pursuant to 10 CFR 50.55a(a)(3), alternatives to the ASME Code requirements may be authorized by the NRC, if the licensee demonstrates that; (i) the proposed alternative provides an acceptable level of quality and safety, or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without compensating increase in the level of quality and safety. 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 code of record is the 1998 edition with 2000 addenda for the fourth 10-year ISI interval at PINGP, Unit 1, which is effective from December 21, 2004 through December 20, 2014.

3.0 PROPOSED RELIEF REQUEST 1-RR-4-6 3.1 System/Components Affected Component Numbers: Summary Number 300655-Rl, Weld W-17, Reducer-to-Valve Weld, of the safety injection system.

Examination Category: R-A Item Number: R1.16-5

==

Description:==

Elements Subject to lntergranular Stress Corrosion Cracking, Risk Category 5 3.2 Applicable Code Requirement, Edition and Addenda The applicable Code Edition and Addenda for PINGP Unit 1 fourth 10-year ISI is the 1998 Edition with 2000 Addenda (1998A00 Edition), which requires 100 percent examination coverage of ISI components per Table IWB-2500-1.

By letters dated December 29, 2004 (Adams Accession No. ML043650201) and August 30, 2005 (Adams Accession No. ML052430399), NMC submitted Relief Request 1-RR-4-5 to implement the risk-informed (RI) ISI program for the subject piping and weld. By letter dated January 5, 2006 (Adams Accession No. ML053270079), the U.S. Nuclear Regulatory Commission (NRC) approved the use of Relief Request 1-RR-4-5. Relief Request 1-RR-4-5 was based on ASME Code Case N-578 and Electric Power Research institute (EPRI)

TR-112657B-A as an alternative to existing ASME Code,Section XI requirements for piping weld selection and examination volumes.

ASME Code Case N-578, ltem Number R1.16, entails a volumetric examination method of essentially 100 percent of the examination volume identified in Figure IWB-2500-8(c). Per the RI-ISI program, the volumetric examination volume must be extended to 1/2-inch beyond each side of the base material thickness transition or the counter bore. In addition, ultrasonic test (UT) examinations for welds in piping must be performed using procedures, personnel, and equipment qualified to the requirements of Appendix VIII of the ASME Code,Section XI, 1995 Edition with the 1996 Addenda, Performance Demonstration for Ultrasonic Examinations Systems.

M. Wadley 3.3 Proposed Alternatives and Basis Pursuant to 10 CFR 50.55a(g)(5)(iii), NMC requested relief to use a limited UT scan of 50 percent instead of the essentially 100 percent volumetric coverage of the reducer-to-valve weld (W-17), that was authorized by the NRC in 2006. The alternative volumetric examination was performed during the 2006 PINGP, Unit 1 refueling outage. In addition, the weld is included in the boundary examined by visual examination VT-2 during pressure testing. Pressure testing was completed on June 2, 2006, with no evidence of leakage identified in the vicinity of the weld.

The performance of the single-sided UT examination, in addition to the performance of the visual VT-2 examination, provides the best examination coverage possible within the limitations of the current design configuration.

Additionally, the previous ASME Code Section XI program did not select any of these risk category 5 reactor coolant system (RCS) welds for inspection. The RI-ISI program selected one of these category 5 welds for inspection [in 2006]. Therefore, there was a small decrease in risk by implementing the RI-ISI inspection. If PINGP, Unit 1 was not to take credit for this examination, there would be no change in risk between the previous ASME Code,Section XI program and the current RI-ISI programs for this risk category in the RCS.

3.4 Duration NMC requests approval of Relief Request 1-RR-4-6, Revision 0, for the duration of the fourth 10-year ISI interval, which runs from December 21, 2004 through December 20, 2014.

4.0 STAFF EVALUATION Pursuant to 10 CFR 50.55a(g)(5)(iii), NMC proposed Relief Request 1-RR-4-6, Revision 0, on the basis that compliance with the ASME Code requirement to examine weld W-17 is impractical due to limited accessibility for the examination which was caused by piping design. Although the licensee requested relief under 10 CFR 50.55a(g)(5)(iii) on the basis of impracticality, the NRC staff evaluated the request under 10 CFR 50.55a(a)(3)(i) under which alternatives may be authorized if they provide an acceptable level of quality and safety. The piping system was designed and constructed with limited accessibility due to component configurations and/or physical barriers for which 100 percent examination coverage was not achievable on the reducer-to-valve weld, W-17, during the 2006 refueling outage inspection. The reducer-to-valve weld, W-17, is located in the safety injection system piping. The reducer and valve material are austenitic stainless steel.

The W-17 weld was subject to volumetric UT examination using personnel and procedures qualified in accordance with ASME Code,Section XI, Appendix VIII, Supplement 2, during the 2006 PINGP Unit 1 refueling outage. The UT examination was conducted using 45 degree shear and 60 degree longitudinal transducers. The examination could only be performed on 50 percent of the volume in both the axial and circumferential directions from the reducer side of the weld due to the weld joint configuration connection to the valve. NMC could not examine the subject weld from the valve side. The credited volumetric examination of the Weld Required Volume (WRV) was limited to 50 percent and only a single-sided examination could be achieved.

It should be noted that the volumetric examination was performed through 92.8 percent of the ASME Code WRV. However, the procedure used is not qualified for the detection of flaws on

M. Wadley the far side (the valve side) of single sided access examinations on austenitic stainless steel piping welds. The technique used for the far side is a best effort examination. The licensees UT procedure is based on the Performance Demonstration Initiative (PDI) program which is an UT examination program to satisfy the requirements of the ASME Code,Section XI, Appendix VIII. The NRC has approved the PDI program per 10 CFR 50.55a.

NMC reviewed the remaining welds within the subject pipe segment and risk group and determined no other welds would produce greater ASME Code required coverage than that obtained on the weld examination performed on weld W-17. NMC stated that due to the limited number of welds within this pipe segment and risk group, no other weld selection was possible for the 100 percent examination coverage, in terms of risk reduction.

The W-17 weld is part of the RI-ISI program. From the RI-ISI perspective, if weld W-17 is not examined, the risk will not be changed between the previousSection XI ISI program and the current RI-ISI program for this risk category in the RCS. Therefore, in terms of risk, it is immaterial if the volumetric examination of the W-17 weld achieved 50 or 100 percent examination coverage.

The NRC staff finds that NMC provided a best effort examination and achieved a 92.8 percent of the code weld required volume, although only 50 percent of the coverage can be credited to satisfy the code requirement. The staff concludes that the examination coverage achieved will most likely detect any significant degradation, if present, and that the examination coverage achieved provides reasonable assurance of the structural integrity of weld W-17.

5.0 CONCLUSION

Based on the information submitted, the staff concludes that the proposed alternative would provide an acceptable level of quality and safety because the examination coverage achieved will most likely detect any significant degradation, if present, and that the examination coverage achieved provides reasonable assurance of the structural integrity of weld W-17. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), relief is granted for Relief Request 1-RR-4-6, Revision 0, for piping weld selection and the reduced volumetric examination coverage of the reducer to valve weld, W-17, in the system injection system at PINGP, Unit 1 for the fourth 10-year ISI interval (December 21, 2004, to December 20, 2014).

All other requirements of the ASME Code, for which relief has not been specifically requested and approved, remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.

Principal Contributor: J. Tsao, NRR Date: May 9, 2008