ML093360185
| ML093360185 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 11/30/2009 |
| From: | Krich R Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML093360185 (5) | |
Text
Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402-2801 November 30, 2009 10 CFR 50.4 10 CFR 50.46 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Sequoyah Nuclear Plant, Units 1 and 2 Facility Operating License Nos. DPR-77 and DPR-79 NRC Docket Nos. 50-327 and 50-328
Subject:
10 CFR 50.46 Annual Report of Non-Significant Changes
Reference:
TVA letter to NRC dated November 24, 2008, "Sequoyah Nuclear Plant -
10 CFR 50.46 Annual Report of Non-Significant Changes" The purpose of this letter is to provide the current status of the calculated peak cladding temperature (PCT) for the Sequoyah Nuclear Plant emergency core cooling system (ECCS) evaluation model. This submittal satisfies the annual reporting requirements in accordance with 10 CFR 50.46(a)(3)(ii). The enclosure contains a summary of the changesto the calculated PCT made since the submittal to NRC in the reference letter.
There are no regulatory commitments in this letter. Please direct questions concerning this issue to Beth A. Wetzel at (423) 843-7170.
Sincerely, M. Krich Vice President Nuclear Licensing Enclosure oo~
Printed on recycled paper
U.S. Nuclear Regulatory Commission Page 2 November 30, 2009 cc (Enclosure):
NRC Regional Administrator-Region II NRC Senior Resident Inspector - Sequoyah Nuclear Plant Division of Radiological Health - State of Tennessee
ENCLOSURE TENNESSEE VALLEY AUTHORITY (TVA)
SEQUOYAH NUCLEAR PLANT (SQN)
UNITS 1 AND 2 10 CFR 50.46 ANNUAL REPORT OF NON-SIGNIFICANT CHANGES In accordance with the annual reporting requirements of 10CFR50.46 (a)(3)(ii), the following is a summary of the limiting design basis accident (loss-of-coolant accident) analysis results established using the current SQN emergency core cooling system (ECCS) evaluation model.
The licensing basis peak cladding temperature (PCT) was 2002 degrees Fahrenheit (F) as of November 24, 2008.
Large Break Loss of Coolant Accident (LB LOCA)
PCT Previous Licensing Basis PCT (November 24, 2008)
- 1.
Radiat ionr Heat Transfer Model Error (AREVA Letter FAB09-24)
- 2.
Fuel Pellet Thermal Conductivity Non-Conservatism (AREVA Letter FAB09-362)
- 3.
S-RELAP5 Point Kinetics Model Coding Errors (AREVA Letter FAB09-334) 2002 degrees F
+ 5 degrees F
+ 8 degrees F
- 30 degrees F 1985 degrees F
- 17 degrees F See Item I See Item 2 See Item 3 Updated Licensing Basis PCT Net Change Small Break Loss of Coolant Accident (SB LOCA)
Previous Licensing Basis PCT (November 24, 2008)
Updated Licensing Basis PCT Net Change PCT 1403 degrees F 1403 degrees F None E-1
- 1) RADIATION TO FLUID HEAT TRANSFER MODELING ERROR
Background
During the development of a new radiation heat transfer model supporting a planned revision to the AREVA realistic large break loss-of-coolant accident (RLBLOCA) analysis methodology, a discrepancy between the radiation heat transfer model used by the current RLBLOCA methodology (S-RELAP5 computer code) and other published models was discovered. The discrepancy involved a figure which was used as the basis for determining water vapor emissivity correlation coefficients in the radiation to fluid heat transfer model.
Review of the figure indicates that it originated from a published industry model and was added to the S-RELAP5 code in the late 1970s or early 1980s. Comparison of the figure to other industry models indicates that the data in the figure is incorrect such that the radiation to fluid correlation under predicts the radiative heat transfer. The S-RELAP5 computer code was used in the current SQN RLBLOCA analysis.
Results AREVA has replaced the incorrect input file with data from current industry radiation heat transfer models. Based on sensitivity studies, AREVA has bounded the effect of the radiative heat transfer under prediction on the SQN ECCS evaluation model. A penalty of 5 degrees F has been applied to the limiting calculated fuel cladding temperature to conservatively bound the effect of the error on the SQN analysis.
2)' FUEL PELLET THERMAL CONDUCTIVITY NON-CONSERVATISM
Background
An internal AREVA review of the RODEX series of computer codes indentified an issue with the ability of the codes to account for core burn-up dependent thermal conductivity. Upon investigation, it was found that the codes under predicted fuel pellet temperatures at core burn-ups near and beyond 20 GWd/MTU. The RODEX3A computer code is used in the SQN RLBLOCA analysis to initialize fuel pellet temperatures. Review of the limiting SQN RLBLOCA analysis indicates that the modeled fuel burn-up was 21 GWd/MTU. As such, the initial fuel pellet temperatures from the RODEX3A computer code used in the SQN analysis are affected by the burn-up dependent thermal conductivity issue.
Results AREVA has compared the RODEX3A temperature predications to an expanded fuel pellet temperature data base and established a proportional adjustment to the fuel temperature calculation, which conservatively bounds the thermal conductivity issue. Based on this adjustment, a penalty of 8 degrees F has been applied to the SQN limiting calculated fuel cladding temperature to address the effect of the initial temperature under prediction on the analysis.
- 3) S-RELAP5 POINT KINETICS MODEL CODING ERRORS
Background
AREVA has identified two computer coding errors in the S-RELAP5 computer code used in the SQN RLBLOCA analysis. One error involves the coding of the point kinetics model.
Changes made with respect to a previous kinetics error were identified as being incorrect.
E-2
The second error involves incorrect programming associated with the heat conduction solution. The error involves the use of an incorrect heat capacity when evaluating the right boundary mesh point. Instead of using the last (adjacent) mesh interval heat capacity, the code incorrectly uses the next to last mesh interval heat capacity.
Results Corrections to the computer coding errors were incorporated into a revised version of the S-RELAP5 computer code. Sensitivity studies were performed using the updated code for the SQN ECCS evaluation model. The studies established a 30 degrees F peak fuel cladding temperature reduction for the limiting SQN RLBLOCA analysis.
E-3