ML12296A226

Watts, Unit 2, 10 CFR 50.46 Estimated Increase in Peak Clad Temperature (PCT) Due to the Effect of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown Not Being Considered - 30 Day Report

ML12296A226
Person / Time
Site:	Watts Bar
Issue date:	10/16/2012
From:	Hruby R Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML12296A226 (5)

Text

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• Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381-2000 October 16, 2012 10 CFR 50.46 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 2 NRC Docket No. 50-391

Subject:

WATTS BAR NUCLEAR PLANT (WBN) UNIT 2 - 10 CFR 50.46 - ESTIMATED INCREASE IN PEAK CLAD TEMPERATURE (PCT) DUE TO THE EFFECT OF FUEL PELLET THERMAL CONDUCTIVITY DEGRADATION AND PEAKING FACTOR BURNDOWN NOT BEING CONSIDERED - 30 DAY REPORT Reference 1: Supplemental Safety Evaluation Report (SSER) 24, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2, Docket No. 50-391, Tennessee Valley Authority," published September 2011 The purpose of this letter is to report, in accordance with 10 CFR 50.46, a significant change in PCT of greater than 50 degrees (i.e., 175°F increase). TVA was recently notified by Westinghouse letter, LTR-LIS-12-413, dated September 20, 2012, that fuel pellet thermal conductivity degradation (TCD) and peaking factor burndown were not explicitly considered in the Watts Bar Unit 2 Best Estimate Large Break Loss-of-Coolant Accident (BE LBLOCA)

Analysis of Record (AOR). Taking TCD and peaking factor burndown into account resulted in the 175 0 F increase in PCT. This results in a new PCT of 1,727°F, replacing the 1,552 0 F value previously accepted by NRC in Reference 1.

Enclosure 1 provides an evaluation of this estimated effect. Since the estimated increase of 175 0 F PCT is based on the generic Westinghouse Owner's Group analysis, a specific WBN Unit 2 analysis will be performed to provide a unit-specific AOR PCT value prior to Unit 2 licensing. This action is captured as SSER open item no. 61; therefore, this action does not represent a new commitment. Enclosure 2 provides the Unit 2 Westinghouse Rackup Sheet.

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U.S. Nuclear Regulatory Commission Page 2 October 16, 2012 There are no new commitments made in this letter.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 1 6 th day of October, 2012.

If you have any questions, please contact me at (423) 365-2004.

Respectfully, Raymond A. Hruby, Jr.

General Manager, Technical Services Watts Bar Unit 2

Enclosures:

1. Evaluation of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown

2. Westinghouse Rackup Sheet cc (Enclosures):

U. S. Nuclear Regulatory Commission Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, Georgia 30303-1257 NRC Resident Inspector Unit 2 Watts Bar Nuclear Plant 1260 Nuclear Plant Road Spring City, Tennessee 37381

Enclosure I Evaluation of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown

Background

Fuel pellet thermal conductivity degradation (TCD) and peaking factor burndown were not explicitly considered in the Watts Bar Unit 2 Best Estimate Large Break Loss-of-Coolant Accident (BE LBLOCA) Analysis of Record (AOR). NRC Information Notice 2011-21 (Reference 1) notified addressees of recent information obtained concerning the impact of irradiation on fuel thermal conductivity and its potential to cause significantly higher predicted peak cladding temperature (PCT) results in realistic emergency core cooling system (ECCS) evaluation models. This evaluation provides an estimated effect of fuel pellet TCD and peaking factor burndown on the PCT calculation for the WBN Unit 2 BE LBLOCA AOR. This change represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451 (Reference 2).

Affected Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect A quantitative evaluation, as discussed in Reference 3, was performed to assess the PCT effect of fuel pellet TCD and peaking factor burndown on the WBN Unit 2 BE LBLOCA analysis and concluded that the estimated PCT impact is 175 0 F for 10 CFR 50.46 reporting purposes. The peaking factor burndown included in the evaluation is provided in Table 1 and is conservative for the first cycle. Tennessee Valley Authority and its vendor, Westinghouse Electric Company LLC, utilize processes which ensure the LOCA analysis input values conservatively bound the as-operated plant values for those parameters and will be validated as part of the reload design process.

Table 1: Peaking Factors Assumed in the Evaluation of TCD Rod Burnup (MWd/MTU) FdH (1), (2) FQ Transient (1) FQ Steady-State 0 1.650 2.500 2.000 30,000 1.650 2.500 2.000 60,000 1.400 1.875 1.500 62,000 1.400 1.875 1.500 (1) Includes uncertainties.

(2) Hot assembly average power follows the same burndown, since it is a function of FdH.

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Enclosure I References

1. NRC Information Notice 2011-21, McGinty, T. J., and Dudes, L. A., "Realistic Emergency Core Cooling System Evaluation Model Effects Resulting From Nuclear Fuel Thermal Conductivity Degradation," December 13, 2011. (NRC ADAMS #

ML113430785)

2. WCAP-13451, "Westinghouse Methodology for Implementation of 10 CFR 50.46 Reporting," October 1992.

3. OG-12-386, "For Information Only - Input Supporting the PWROG LBLOCA Program Regarding Nuclear Fuel Thermal Conductivity Degradation (PA-ASC-1073, Revision 0) (Proprietary/Non-Proprietary)," September 18, 2012.

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Enclosure 2 Westinghouse Rackup Sheet Westinghouse LOCA Peak Clad Temperature Summary for ASTRUM Best Estimate Large Break Plant Name: Watts Bar Unit 2 Future Utiliq"Name: Tennessee Valley Authority Reision Date: 9/20/2012 Analvsit Information EM: ASTRUTIM (2004) Analysis Date: 10114/2009 Limiting Break Size: Split FQ: 2.5 FdH: 1.65 Fuel: RFA-2 SGTP (%): 10 Notes:

Clad Temp (IF) Ref. Notes LICENSING BASIS Analysis-Of-Record PCT 15152 1 PCT ASSESSMENTS (Delta PCT)

A. PRIOR ECCS MODEL ASSESSMENTS I . None 0 B. PLANN,-ED PLANT MODIFICATION EVALUATIONS I . None 0 C. 2012 ECCS MODEL ASSESSMENTS I . Evaluation of Fuel Pellet Thermal Conductivity Degradation and 175 2 Peaking Factor Burndown D. OTHER*

1 - None 0 LICENSING BASIS PCT + PCT ASSESSMENTS PCT = 1727

- It is recommended that the licensee determine if these PCT allocations should be considered with respect To 10 CFR 50.46 reporting requirements.

References:

1 . WCAP- I7093-P. Revision 0. "Best-Estimate Anals-sis of the Large-Break Loss-of-Coolant Accident for Watts Bar Unit 2 Nuclear Power Plant Using the ASTRU`-M Methodology." December 2009.

2 . LTR-LIS-12-413. -Watts Bar Units I and 2. 10 CFR 30.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Bundosn.s" September 20. 2012.

Notes:

(a) This evaluation credits peaking factor bumdown, see Reference 2.

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