ML060950474

Duke Energy Corporation, Oconee Nuclear Station Units 1, 2 and 3; Withdrawal of Unresolved Item 2005004-08 Response

ML060950474
Person / Time
Site:	Oconee
Issue date:	03/29/2006
From:	Brandi Hamilton Duke Power Co
To:	Document Control Desk, NRC/RGN-II
References
IR-05-004
Download: ML060950474 (5)

Text

jftDuke BRUCE H HAMILTON Vice President OPow^ere Oconee Nuclear Station Duke Power ONOIVP / 7800 Roct.erster Highway March 29, 2006 Seneca, SC 29672 864 885 3487 864 885 4208 fax U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 ATTENTION: Document Control Desk

SUBJECT:

Duke Energy Corporation Oconee Nuclear Station Units 1, 2 and 3 Docket Nos.: 50-269, 270 and 287 Withdrawal of Unresolved Item 2005004-08 Response

References:

(1) Integrated Inspection Report 05000269/2005004, 05000270/2005004, 05000287/2005004, (2) Duke letter to the NRC dated February 15, 2006, that provided supporting information in the disposition of Unresolved Items (URI) 2005004-10 and 2005004-08 as detailed in Ref. 1 above.

In Reference (2), Duke Energy Corporation (Duke) provided supporting information for the Staff's consideration in the disposition of Unresolved Items (URI) 2005004-10 and 2005004-03 as detailed in Reference (1). The purpose of this letter is to notify the Staff that the evaluation in Ref. 2 in connection with URI 2005004-08 contained two inaccuracies which were identified after the letter was sent. Accordingly, Duke is withdrawing that evaluation from further consideration.

Specifically, in Ref. 2, Attachment 2, Duke addressed two conditions from an evaluation of an Auxiliary Building (AB) HE:LB event:. The first condition was the potential flooding of Main Feedwater (MFDW) breaks located at the terminal end(s). Breaks at these locations are described in MDS Report OS-73.2, and form part of the HELB CLB. Duke affirms that the analysis of this condition described in Ref. 2, Attachment 2, is accurate. As initially identified by the NRC senior resident, the second condition involved the potential flooding from critical cracks in the MFDW System located in the AB. Associated with this condition, Duke reanalyzed the actual plant configuration and concluded that the description of AB interconnecting trenches was indeed, inaccurate. Specifically, it was stated in Ref. 2, Attachment 2, that "no direct pathways exist that would allow water to flow preferentially to one unit's HPI pump rooms via the pipe chase." This statement was based on an inadequate www.dukepower.com

Nuclear Regulatory Commission Withdrawal of URI 2005004-08 Response March 29, 2006 Page 2 visual inspection of the construction of interconnecting trenches. Additionally, based upon further review and discussions with industry peers, Duke has determined that the use in Ref. 2, Attachment 2, of a reduced discharge coefficient in connection with this event was not defensible based on current regulatory standards and industry best practices. For this reason, Duke's initial URI evaluation is being withdrawn.

In evaluating the AB HELB event addressed in URI 2005004-08, Duke was addressing a matter outside the CLB with regards to the choice of MFDW critical crack locations and the associated potential flooding issues. Specifically, upon a re-review of the design basis as described in MDS report OS-73.2, which was previously reviewed and approved by the Atomic Energy Commission (AEC), Duke has determined that critical cracks were properly addressed and eliminated from consideration based on stress. As stated in this report, certain MFDW break and crack locations had previously been analyzed with arbitrary break/crack loca:ions eliminated from consideration based on pipe stress resuLts. This rationale was based on reasonable engineering analysis and satisfied the overall intent of the HELB requirements established by the AEC at that time (Ref. "Safety Evaluation prepared by the Directorate of Licensing relating t:o the Oconee Nuclear Station, Units 2 and 3," dated July 6, 1973).

Consequently, the CLB does not identify any additional MFDW break/crack locations in the AB other than those provided in MDS Report OS-73.2.

Based on technical enhancements in HELB analysis criteria, Duke continues to evaluate prior assumptions used in the original 1973 report. As a part of the effort, Duke will seek to gain acceptance from the NRC to apply certain portions of BTP MEB --- 1 for determining critical crack locations. Following Staff approval of the MEB LAR, Duke will evaluate those critical crack locations and incorporate these into the licensing basis. In addition, modifications will be implemented by the end of 2007 that will eliminate the flooding potential to the AB due to HELBs occurring in the East Penetration Room.

Although Duke concludes that the conditions regarding the analysis of critical cracks in the MFDW system located in the AB described in URI 2005004-08 are outside the CLB, Duke believes that the assumptions in the CLB warrant submission of a Licensee Even: Report to the Staff. Duke continues in its efforts to completely reconstitute the HELB CLB in an effort to improve the overall HELB mitigation strategy.

Nuclear Regulatory Commission Withdrawal of URI 2005004-08 Response Marca 29, 2006 Page 3 If you have any questions or comments regarding these issues, please contact Stephen C. Newman of the Oconee Nuclear Site Regulatory Compliance Group at 864-885-4388.

Sincerely, Bruce H. Hamilton, Vice President Oconee Nuclear Site

Nuclear Regulatory Commission Withdrawal of URI 2005004-08 Response March 29, 2006 Page 4 CC: Mr. L. N. Olshan, Project Manager Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Stop 0-14 H25 Washington, D.C. 20555 Dr. W. D. Travers, Regional Administrator U.S. Nuclear Regulatory Commission - Region II Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303 Mr. M. E. Ernstes, Chief Branch 1 DRP U.S. Nuclear Regulatory Commission - Region II Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303 Mr. Robert E. Carroll U.S. Nuclear Regulatory Commission - Region II Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303 Mr. M. C. Shannon Senior Resident Inspector Oconee Nuclear Site

4 . I Nuclear Regulatory Commission Withdrawal of URI 2005004-08 Response March 29, 2006 Page 5 bcc: Lisa F. Vaughn David Repka Larry E. Nicholson T. Preston Gillespie George K. McAninch C. Jeff Thomas - MNS Randy D. Hart - CNS Robert L. Gill - NRI&IA B. Graham Davenport Stephen C. Newman Noel T. Clarkson Reene' V. Gambrell Timothy D. Brown Allen D. Park Judy E. Smith ONS Document Control ELL