LIC-10-0095, Response to Request for Additional Information (RAI) Regarding Relief from ASME Code Case N-722 Requirements for Visual Examination of Reactor Vessel Hot Leg Nozzle to Safe End Welds

Response to Request for Additional Information (RAI) Regarding Relief from ASME Code Case N-722 Requirements for Visual Examination of Reactor Vessel Hot Leg Nozzle to Safe End Welds

ML110840432
Person / Time
Site:	Fort Calhoun
Issue date:	11/04/2010
From:	Faulhaber H Omaha Public Power District
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LIC-10-0095, TAC ME4541
Download: ML110840432 (2)

Text

Omaha Public Power DlA7cd 444 South 16th Street Mall Omaha, NE 68102-2247 November 4, 2010 LIC-10-0095 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555

References:

1. Docket No. 50-285

2. Letter from OPPD (H. J. Faulhaber) to NRC (Document Control Desk), "10 CFR 50.55a Request Number RR-12, Omaha Public Power District (OPPD) Request for Relief from Code Case N-722 Visual Examination (VE) of the Reactor Vessel Hot Leg Nozzle to Safe End Dissimilar Metal Welds," dated August 16, 2010 (LIC 0065) (ML102300641)

3. Letter from NRC (Lynnea Wilkins) to OPPD (D. J. Bannister), "Fort Calhoun Station, Unit No. 1 - Request for Additional Information Re:

Request for Relief From Code Case N-722 Visual Examination of the Reactor Vessel Hot-Leg Nozzle-to-Safe End Dissimilar Metal Welds (TAC No. ME4541)," dated October 25, 2010

SUBJECT:

Response to Request for Additional Information (RAI) Regarding Request for Relief from ASME Code Case N-722 Requirements for Visual Examination of Reactor Vessel Hot Leg Nozzle to Safe End Welds In Reference 2, pursuant to 10 CFR 50.55a(a)(3)(i), the Omaha Public Power District (OPPD) requested NRC approval of an alternative to American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section Xl, Code Case N-722 visual examination (VE) requirements.

Specifically, for two reactor vessel (RV) hot leg nozzle to safe end dissimilar metal (DM) welds at Fort Calhoun Station, Unit No. 1, OPPD proposed to credit the following measures in lieu of the VE required by Code Case N-722:

1. Augmented examinations performed during previous refueling outages.

2. Deterministic analyses of hypothetical crack growth that result in a long period of time to reach ASME maximum allowable 75% through-wall cracking.

3. The addition of zinc to the reactor coolant system to mitigate primary water stress corrosion cracking.

Employment with Equal Opportunity

U. S. Nuclear Regulatory Commission LIC-10-0095 Page 2 In Reference 3, the NRC requested that OPPD provide additional information in order to complete its review. Accordingly, the requested information is attached.

To provide additional support for the requested relief, Westinghouse is normalizing eddy current test (ECT) data from the 2009 examination of these two RV hot leg nozzle-to-safe end DM welds and expects to finish in the late November to mid-December timeframe. OPPD will submit the results to the NRC shortly thereafter (AR 44658).

This data was collected from the inside diameter of the two RV hot leg nozzle-to-safe end DM welds and is therefore much more definitive than a qualitative outside diameter VE. The analysis will determine if the onset of stress corrosion cracking is imminent and provide additional support for the conclusion that cracks in the RV hot leg nozzle-to-safe end DM welds do not exist. No other commitments are contained in this submittal.

As an enhancement, prior to the start of the 2011 refueling outage, OPPD is revising Surveillance Test (ST) QC-ST-MX-3003, which currently requires a visual inspection under the RV and surrounding areas for signs of leakage or boric acid accumulation.

The enhancement will require that the RV nozzles be inspected for the presence of leakage and/or boric acid accumulation on the containment floor underneath them, the bio-shield wall near them, or on the bottom of the nozzle insulation.

If you have any questions regarding this submittal, please contact Mr. Bill Hansher at (402) 533-6894.

Sincerely, Harry J aber Division Manager-Nuclear Engineering HJF/BL/mle

Attachment:

OPPD Response to NRC Request for Additional Information c: E. E. Collins, NRC Regional Administrator, Region IV (w/o Enclosures)

L. E. Wilkins, NRC Project Manager J. C. Kirkland, NRC Senior Resident Inspector (w/o Enclosures)