ML12342A323

Reactor Pressure Vessel Head Weld Flaw Evaluation - Clarification Regarding Subsequent Examination of the Weld Flaw Indication

ML12342A323
Person / Time
Site:	Nine Mile Point
Issue date:	11/30/2012
From:	Swift P EDF Group, Nine Mile Point, Constellation Energy Nuclear Group
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC NE6721
Download: ML12342A323 (2)

Text

P.O. Box 63 CENGSM a joint venture of Lycoming, NY 13093 SConstellation Energy, NINE MILE POINT NUCLEAR STATION November 30, 2012 U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 ATTENTION: Document Control Desk

SUBJECT:

Nine Mile Point Nuclear Station Unit No. 1; Docket No. 50-220 Reactor Pressure Vessel Head Weld Flaw Evaluation - Clarification Regarding Subsequent Examination of the Weld Flaw Indication

REFERENCES:

(a) Letter from P. M. Swift (NMPNS) to Document Control Desk (NRC), dated June 28, 2011, Reactor Pressure Vessel Head Weld Flaw Evaluation (b) Letter from P. M. Swift (NMPNS) to Document Control Desk (NRC), dated May 7, 2012, Reactor Pressure Vessel Head Weld Flaw Evaluation - Response to NRC Request for Additional Information (c) Letter from B. Vaidya (NRC) to K. Langdon (NMPNS), dated July 2, 2012, Nine Mile Point Nuclear Station, Unit No. 1 Re: NRC Approval of Reactor Pressure Vessel Head Weld Flaw Evaluation (TAC No. ME6721)

By letter dated June 28, 2011 (Reference a), as supplemented by letter dated May 7, 2012 (Reference b),

Nine Mile Point Nuclear Station, LLC (NMPNS) submitted for NRC review and approval a structural flaw evaluation of a subsurface flaw indication found in a Nine Mile Point Unit 1 (NMP1) reactor pressure vessel (RPV) closure head weld during the 2011 refueling outage. In the safety evaluation transmitted by letter dated July 2, 2012 (Reference c), the NRC staff found that the flaw evaluation met the rules in the 2004 Edition of Section XI of the American Society of Mechanical Engineers (ASME)

Code, and concluded that the closure head weld joining the RPV closure flange forging to the head was acceptable for continued service provided that the subsequent examinations required by the ASME Code,Section XI, IWB-2420(b) are performed. Paragraph IWB-2420(b) requires that the area containing the analyzed flaw be reexamined during the "next three inspection periods listed in the schedule."

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Document Control Desk November 30, 2012 Page 2 In accordance with ASME Code Case N-526, "Alternative Requirements for Successive Inspections of Class 1 and 2 Vessels,Section XI, Division 1," NMPNS does not intend to perform re-examinations of the subject flaw indication. Code Case N-526 has been unconditionally accepted by the NRC in Regulatory Guide 1.147, Revision 16, and NMPNS has confirmed that all three of the conditions listed in the code case are met, namely:

(a) The flaw is characterized as subsurface in accordance with Fig. 1 [of the code case].

As described in Section 6.0 of the Attachment to Reference (a), the ultrasonic examinations performed during the 2011 refueling outage characterized the subject closure head weld indication as a subsurface planar flaw. The same conclusion is arrived at by plotting the flaw parameters (S = 1.9846 inches and a = 1.2319/2 = 0.61595 inches) on Figure 1 of Code Case N-526.

(b) The NDE [non-destructive examination] technique and evaluation that detected and characterized the flaw, with respect to both sizing and location, shall be documented in the flaw evaluation report.

The size and location of the flaw were determined using ultrasonic examination procedures, equipment, and personnel that are in accordance with ASME Section XI, Appendix VIII (as modified by the Performance Demonstration Initiative (PDI)), and have been qualified by the PDI at the Electric Power Research Institute (EPRI) NDE Center. The NDE techniques and the evaluation that characterized the flaw are incorporated by reference into the flaw evaluation report (Section 8.0, Item 1, of the Attachment to Reference a).

(c) The vessel containing the flaw is acceptable for continued service in accordance with IWB-3600, and the flaw is demonstrated acceptable for the intended service life of the vessel.

The evaluation performed in the Attachment to Reference (a), as supplemented by Reference (b),

demonstrates that the weld containing the flaw is acceptable for continued service in accordance with ASME Section XI, IWB-3600. Since an end-of-evaluation period of 60 years was used, the flaw is acceptable for the intended service life of the RPV.

This letter contains no new regulatory commitments. Should you have any questions regarding the information in this submittal, please contact John J. Dosa, Director Licensing, at (315) 349-5219.

Very truly yours, Paul M. Swift Manager Engineering Services PMS/DEV cc: Regional Administrator, Region I, NRC Project Manager, NRC Resident Inspector, NRC