ML083150640

Corrected Page to Use Structural Weld Overlay and Alternative Examination Techniques on Safe End Dissimilar Metal Welds

ML083150640
Person / Time
Site:	Saint Lucie
Issue date:	11/19/2008
From:	Mozafari B Plant Licensing Branch II
To:	Stall J Florida Power & Light Co
Orf, Tracy J.; NRR/DORL 415-2788
References
TAC MD9256
Download: ML083150640 (3)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 November 19, 2008 Mr. J. A. Stall Senior Vice President, Nuclear and Chief Nuclear Officer Florida Power and Light Company P.O. Box 14000 Juno Beach, Florida 33408-0420 SLlB..IECT: ST. LUCIE, UNIT 1 - CORRECTED PAGE TO SAFETY EVALUATION OF RELIEF REQUEST TO USE STRUCTURAL WELD OVERLAY AND ALTERNATIVE EXAMINATION TECHNIQUES ON SAFE END DISSIMILAR METAL WELDS (TAC NO. MD9256)

Dear Mr. Stall:

On November 3, 2008, the U.S. Nuclear Regulatory commission (NRC) authorized an alternative to the repair requirements of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, for St. Lucie, Unit 1. The alternative uses a full structural weld overlay with temper bead welding for repair and the Performance Demonstration Initiative program for inspection as alternatives to the requirements of ASME Code,Section XI.

Subsequently, the St. Lucie licensing staff informed the NRC staff of statements in need of clarification in the safety evaluation (SE) supporting the relief request. Specifically, the discussion of delta ferrite measurements also mentions the alloys ER308L and ER309L, although they are not used as filler material in the subject overlays.

The NRC staff reviewed these comments and agreed that the SE should be corrected. The NRC staff also concluded that the changes correct inaccuracies or misstatements in the SE, but do not change the technical evaluation or conclusions of the SE. The enclosed SE page 9 corrects the error and is annotated to show the correction. The page previously issued with the amendment should be replaced with the enclosed page.

We appreciate the constructive input from the St. Lucie licensing staff and apologize for any inconvenience resulting from the changes.

Sincerely,

~ ()r I 'fJ ,\,ld

...,:::>~ el(t.v t ,W t'lv~&' r.\L Brenda L. Mozafari, Senior oject Manager Plant Licensing Branch 11-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No.: 50-335

Enclosure:

Revised SE page cc w/enclosure: Distribution via ListServ

-9 years on piping of both boiling and pressurized-water reactors to inhibit the growth of flaws while establishing a new structural pressure boundary. The SWOLs will control growth in PWSCC flaws and maintain weld integrity by producing compressive stress in the DMW. The full SWOLs will be sized to meet all structural requirements independent of the existing weld and will produce a favorable surface for UT examination. Due to their close proximity adjacent SS safe end-to-piping SMW will be incorporated into the area of the weld overlay.

4.1 General Requirements ASIVIE Code Case N-504-3 and Nonmandatory Appendix Q (a contingent requirement of Code Case N-504-3 in accordance with RG 1.147, Revision 15) of ASME Code Section XI, require certain specification and surface conditions of the applicable base metal (LAS, CS, SS, and Alloy 82/182), the weld overlay filler metal (Alloy 52M) and the Cr content of weld overlay deposits. Section 1 of Attachment 2 to RR-2, Rev. 1, provides corresponding requirements, with modifications. FPL will deposit a barrier layer of ER308L or ER309L SS filler metal on the base metal prior to weld overlay as a contingency for preventing possible hot cracking, which may result from high sulfur content in austenitic SS base material. The tendency of certain metals to exhibit hot cracking is caused by the segregation at grain boundaries of low-melting constituents (e.g., sulfur) in the weld metal. This may result in grain-boundary tearing under thermal contraction stresses. Hot cracking may be minimized by employing low impurity welding metals.

FPL stated that a SS barrier layer of alloy ER308L or ER309L, will be utilized over the appropriate base materials due to the uncertainty in establishing impurity thresholds for successful Alloy 52M SWOLs. FPL also stated that the proposed SWOL design does not take structural credit for the buffer/barrier weld layer. FPL will install the barrier layer on the austenitic SS pipe and safe end only and stop short of the Alloy 82/182 weld material. The final tie-in to the existing nickel Alloy 82/182 weld may be performed with nickel Alloy 82 weld metal. Welding over the nickel base ENiCrFe-3 (Alloy 182) joint with an iron based ER308L or ER309L electrode may cause cracking in the SS barrier layer.

FPL stated further that the SS barrier layer will be deposited with a welding procedure that has been qualified in accordance with the ASME Code,Section IX. Liquid penetrant (PT) examinations will be performed on the barrier layer surface and its volume will be included in the final UT of the overlay.

Delta ferrite (FN) measurements are not required per Attachment 2 of RR-2, Rev. 1, for weld overlay repairs made of Alloy 52/52M weld metal. Welds of Alloy 52/52M are 100 percent austenitic and contain no delta ferrite due to their high nickel composition (approximately 60 percent nickel). FPL's vendor performed a mockup and the chromium (Cr) content of the first overlaid layer was verified at the 24 percent minimum Cr value specified in accordance with Section 1(e) of Attachment 2 to RR-2, Rev. 1. Furthermore, FPL states that the same heat number of weld wire and welding parameters used in qualification welding for the mockup first overlaid layer will be used for the first overlaid layer of the production SWOLs.

'.. ML083150640 NRR-106 OFFICE LPL2-2/PM LPLlI-2/PM LPLlI-2/LA CPNB/BC LPLlI-2/BC NAME TOrf BMoroney for BClayton TChan TBoyce BMozafari DATE 11/12/08 11/13/08 11/12/08 11/18/08 11/19/08