ML12058A415

Relief Request N1-I4-CMP-001, Justification of Length of Proposed Weld Overlay for Steam Generator Hot Leg Nozzles

ML12058A415
Person / Time
Site:	North Anna
Issue date:	02/23/2012
From:	Hartz L Dominion, Virginia Electric & Power Co (VEPCO)
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
12-093
Download: ML12058A415 (6)

Text

VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 February 23, 2012 U.S. Nuclear Regulatory Commission Serial No.12-093 Attention: Document Control Desk NLOS/ETS One White Flint North Docket No. 50-338 11555 Rockville Pike License No. NPF-4 Rockville, MD 20852-2738 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)

NORTH ANNA POWER STATION UNIT 1 RELIEF REQUEST N1-14-CMP-001 JUSTIFICATION OF LENGTH OF PROPOSED WELD OVERLAY FOR STEAM GENERATOR HOT LEG NOZZLES In a March 30, 2011 letter (Serial No.11-120), as supplemented on June 29, 2011 (Serial No.11-366) and November 10, 2011 (Serial No.11-625), Dominion requested NRC approval for proposed alternatives to certain (ASME Code) Section XI-2004 Edition requirements associated with Steam Generator (SG) hot leg nozzle repairs. The proposed alternative will permit the application of a full structural weld overlay (FSWOL) on the Steam Generator hot leg nozzles for North Anna Unit 1. The weld overlays are required to mitigate the potential for primary water stress corrosion cracking (PWSCC) susceptibility of the dissimilar metal welds (DMW). In a January 27, 2012 letter, the NRC approved Relief Request N1-/4-CMP-001. However, the accompanying safety evaluation identifies, as ~

staff understanding, that the weld overlay length would be 0.75 -vRt applied axially on bot~

sides of the susceptible weld.  !

I i

In a phone call on February 15, 2012 with the NRC staff to discuss the sizing requirements I for the FSWOLs delineated in the staff's SER, Dominion informed the NRC that it was physically impossible to meet one of the requirements delineated in the staff's safety evaluation report (SER. Specifically, the 0.75v'Rt length for the weld overlay cannot be used on the pipe end due to structural interferences from the SG lower support assembly]

Extension of the overlay further towards the SG is not feasible due to the excessiv~

amount of nozzle machining that would be necessary. I I

The proposed FSWOL has been designed to meet the relevant Code requirements (speoifically NB-3200) for transfer of the load for a postulated flaw back into the bas~

material. The associated analysis considered design basis loads with the required safety factors applied. Therefore, the proposed FSWOL

• meets quality and safety standards)I However, the SER discussed imposing a 0.75y'Ht length. This is mentioned in Cod~

Case N-740-2 as a length that usually satisfies load redistribution. However, if a location'~

actual loading is small, load redistribution can be achieved with much shorter lengths. Ir this case, this is achieved at a distance less than 0.75\/Rt. To ensure future lSI of th¢ DIVIWs will meet Code Case N-770-1 requirements, the weld overlay length on each sid~

of the DMW will need to be somewhat greater than the length required to satisfy NB-320p requirements. Specifically, the overlay will extend on each side of the susceptible materi,/

I

Serial No. 12-0~3 Docket No. 50-3~8 Justification for L~~~~ ~v~;~

Page 2 013 by a minimum of 3.89" on the nozzle side and 4.98" minimum on the stainless steel sile before it ties back into the adjoining base metal.

In summary, the proposed weld overlay le.ngth~ selected are less t~an the I~~gl h calculated by 0.75*lRt due to the constraints Imposed by the physical condltlo~s associated with the DMW. However, the weld overlay length is bounded by analysis al d technically acceptable. The attachment provides sketches and a photo that shows t e WOL dimensions and the physical obstructions, respectively.

Dominion requests the NRC's approval of the proposed sizing of the FSWOL on the Stea Generator hot leg nozzles.

As noted in the original relief request the applicable stress reports will be provided to tIe NRC prior to entry into Mode 4 following the completion of the weld overlays.

If you have any questions regarding this submittal, please contact Mr. Thomas Shaub t (804) 273-2763.

Very truly yours,

~-L.

Leslie N. Hartz u.... ,-',

~~

Vice President - Nuclear Support Senn6es Attachment Sketches and Photo of WOL Dimensions and Obstructions Commitments made in this letter: None

Serial No.12-093 Docket No. 50-338 Justification for Length of WOL Weld Overlay Page 3 of 3 cc: U.S. Nuclear Regulatory Commission Region II Marquis One Tower 245 Peachtree Center Ave" NE Suite 1200 Atlanta, Georgia 30303-1257 Mr. J. E. Reasor, Jr.

Old Dominion Electric Cooperative Innsbrook Corporate Center 4201 Dominion Blvd.

Suite 300 Glen Allen, Virginia 23060 NRC Senior Resident Inspector North Anna Power Station Dr. V. Sreenivas NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 08 G-9A Rockville, Maryland 20852 Ms. K. R. Cotton NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 08 G-9A Rockville, Maryland 20852 Mr. M. M. Grace Authorized Nuclear Insurance Inspector North Anna Power Station

Serial No.12-093 Docket No. 50-338 Attachment Sketches and Photo of WOL Dimensions and Obstructions Virginia Electric and Power Company (Dominion)

North Anna Power Station Unit 1

Serial No.12-093 Docket No. 50-338 Justification for Length of WOL Attachment Page 1 of 2 Estimate of O.7S"RT weld length location on SG Nozzle Minimum and Maximum Weld Dimensions

Serial No.12-093 Docket No. 50-338 Justification for Length of WOL Attachment Page 2 of 2 These structural members would interfere with tooling for machining, welding, & sanding operations if overlay was extended past the safe end for the - 8" axial length for O.75\/Rt.