1CAN040902, 10 CFR 50.46 Report - Significant Change in Peak Cladding Temperature

10 CFR 50.46 Report - Significant Change in Peak Cladding Temperature

ML090920271
Person / Time
Site:	Arkansas Nuclear
Issue date:	04/01/2009
From:	David Bice Entergy Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
1CAN040902
Download: ML090920271 (5)

Text

Entergy Operations, Inc.

1448 S.R. 333 Russellville, AR 72802 Tel 479-858-4710 David B. Bice Acting Manager, Licensing Arkansas Nuclear One 1CAN040902 April 1, 2009 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001

Subject:

10 CFR 50.46 Report - Significant Change in Peak Cladding Temperature Arkansas Nuclear One - Unit 1 Docket No. 50-313 License No. DPR-51

Dear Sir or Madam:

Pursuant to 10 CFR 50.46(a)(3)(ii), the following information is provided concerning a change to the Arkansas Nuclear One, Unit 1 (ANO-1) Emergency Core Cooling System (ECCS) analyses. On March 6, 2009, AREVA notified ANO of a change in the ECCS analyses that resulted in an increase in the estimated peak cladding temperature (PCT) of greater than 50 F from the previous temperature calculated for the small break loss of coolant accident (SBLOCA) limiting plant transient. The change is discussed below.

An error was discovered in the enhanced once-through steam generator (EOTSG) emergency feedwater (EFW) tube wetting model and the consideration of the potential increase in the gap between the EOTSG 15th tube support plate and steam generator tube shroud, as compared to the gap that existed in the original once-through steam generator (OTSG). This change was made to aid in fabrication of the EOTSG, but the effects were not adequately considered on the EFW wetting model utilized in the ANO-1 SBLOCA analyses. The 15th tube support plate is located below the EFW nozzle, nominally allowing the injected EFW to pool and penetrate the tube nest. This penetration is important to raising the thermal center during natural circulation and inducing boiler-condenser cooling (BCC) at the upper elevations of the tubes during the reactor coolant system (RCS) drain down phase of a SBLOCA. High-elevation BCC condenses tube-side steam, and the condensate promotes natural circulation in the RCS and augments liquid inventory in a faulted RCS. However, a large gap area will result in bypass of a portion of the EFW flow and hinder EFW penetration into the bundle, thereby reducing the effectiveness of high elevation BCC. Since the EFW wetting model is not utilized in large break loss of coolant accident (LBLOCA) analyses, this error only affects SBLOCA analyses with the EOTSG. New SBLOCA analyses were performed

1CAN040902 Page 2 that considered the effects of the larger gap on the EFW wetting model and as a result, the PCT for the SBLOCA limiting plant transient increased to 1282 F. This PCT is a 102 F increase over the previous analyses of record PCT for the SBLOCA limiting plant transient.

As stated above, the EFW wetting model is not utilized in LBLOCA analyses. Therefore, the PCT for LBLOCA and the linear heat rate limits are unaffected by the error. In addition, the PCT for the LBLOCA limiting plant transient remains the overall ECCS analysis limiting plant transient for ANO-1.

The enclosure tabulates the effect of the error correction on the limiting PCT for the ANO-1 LOCA licensing basis with the EOTSG. Note that ANO-1 completed transition to a full core of Mark B-HTP fuel during its fall 2008 refueling outage.

Should you have any questions regarding this submittal, please contact me.

Sincerely, DBB/rs Attachment - Peak Cladding Temperature Change for SBLOCA Analyses

1CAN040902 Page 3 cc: Mr. Elmo E. Collins Regional Administrator U. S. Nuclear Regulatory Commission Region IV 612 Lamar Blvd., Suite 400 Arlington, TX 76011-4125 NRC Senior Resident Inspector Arkansas Nuclear One P.O. Box 310 London, AR 72847 U.S. Nuclear Regulatory Commission Attn: Mr. Alan B. Wang MS O-7 D1 Washington, DC 20555-0001 Mr. Bernard R. Bevill Arkansas Department of Health Radiation Control Section 4815 West Markham Street Slot #30 Little Rock, AR 72205

Attachment 1CAN040902 Peak Cladding Temperature Change for SBLOCA Analyses

Attachment to 1CAN040902 LOCA Licensing Activity for ANO Unit 1 Plant Name: Arkansas Nuclear One - Unit 1 LOCA Spectrum Utility Name: Entergy Nuclear South Mark-B-HTP SBLOCA LBLOCA Reporting Category Description PCT Previous Licensing Basis 2008.1 F 1179.7 F Analyzed Analyzed EM R0.9 EM R0.9 Application Error EOTSG EFW Tube Wetting Model N/A 1282 F Analyzed EM R0.9 Revised Licensing Basis 2008.1 F 1282 F Analyzed Analyzed EM R0.9 EM R0.9 Page 1 of 1