SBK-L-12264, Nuclear Fuel Pellet Thermal Conductivity Degradation Impact on Current Seabrook Be LBLOCA Analysis Using the 1996 Cqd Methodology 10 CFR 50.46 30-Day Report

Nuclear Fuel Pellet Thermal Conductivity Degradation Impact on Current Seabrook Be LBLOCA Analysis Using the 1996 Cqd Methodology 10 CFR 50.46 30-Day Report

ML12362A371
Person / Time
Site:	Seabrook
Issue date:	12/21/2012
From:	O'Keefe M NextEra Energy Seabrook
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
SBK-L-12264
Download: ML12362A371 (9)

Text

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,#ýEA ROK December 21, 2012 Docket No. 50-443 SBK-L-12264 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001 Seabrook Station Nuclear Fuel Pellet Thermal Conductivity Degradation Impact On Current Seabrook BE LBLOCA Analysis Using the 1996 CQD Methodology 10 CFR 50.46 30-Day Report

Reference:

Letter from M. O'Keefe (NextEra) to U.S. Nuclear Regulatory Commission (SBK-L-12126, Docket No. 50-443), "Seabrook Station, Annual Reporting of Changes to, or Errors in, Emergency Core Cooling System Models or Applications,"

July 16, 2012.

In accordance with the requirements of 10 CFR 50.46(a)(3)(ii), NextEra Energy Seabrook, LLC (NextEra) submits a tabulation of the current Large Break and Small Break LOCA PCT margin utilization tables applicable to Seabrook Station. NextEra Energy Seabrook letter SBK-L-12126, documented the 2011 Annual Report of Peak Clad Temperature (PCT) for the Small Break Loss of Coolant Accident (SBLOCA) and the Large Break Loss of Coolant Accident (LBLOCA) for the Seabrook Station. The reported LBLOCA PCT and cumulative change were 1789 °F and 5 °F, respectively.

10 CFR 50.46(a)(3)(ii) requires that changes to the LBLOCA Evaluation Model (EM) and SBLOCA EM PCT exceeding 50 OF be reported to the NRC within 30 days. This 30-day report documents the results of the evaluation performed by Westinghouse Electric Company, LLC to address the effect of nuclear fuel pellet thermal conductivity degradation (TCD) on the Seabrook Station LBLOCA Code Qualified Document (CQD) EM.

Enclosure 1 summarizes the assessment made to the Seabrook Station LBLOCA CQD EM to account for TCD effects. Taýle 2 in Enclosure 1 provides the new LBLOCA PCT rackup for Seabrook Station that accounts for the TCD effects and power peaking burndown. Enclosure 2 provides supplemental information on TCD effects. The new LBLOCA predicted values for the PCT and the cumulative change are 1914 OF and 130 °F, respectively.

NextEra Energy Seabrook, LLC, P.O. Box 300, Lafayette Road, Seabrook, NH 03874 A002.,.

U. S. Nuclear Regulatory Commission SBK-L-12264/ Page 2 10 CFR 50.46(a)(3)(ii) also requires that a schedule for reanalysis be provided or compliance with the requirements of the regulation be shown. Continued compliance with 10 CFR 50.46 requirements is demonstrated by the total estimated new PCT value of 1914 OF remaining well below the limit of 2200 OF. NextEra is continuing to monitor industry initiatives to incorporate the affects of TCD on approved EMs and will provide further updates in accordance with 10CFR50.46 as necessary.

Should you have any questions regarding this report, please contact me at (603) 773-7745.

Sincerely, NextEra Energy Seabrook, LLC Micha-i O'Keefe r Licensing Manager cc: NRC Region I Administrator J. Lamb, NRC Project Manager, Project Directorate 1-2 NRC Senior Resident Inspector

ENCLOSURE 1 TO SBK-L-12264

Background

Fuel pellet thermal conductivity degradation (TCD) and peaking factor burndown were not explicitly considered in the Seabrook Large Break Loss-of-Coolant Accident (LBLOCA) Analysis of Record (AOR). Nuclear Regulatory Commission (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 clad temperature (PCT) results in realistic emergency core cooling system (ECCS) evaluation models. This evaluation provides an estimated effect of TCD and peaking factor burndown on the PCT calculation for the ECCS at Seabrook. This change represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451 (Reference 2).

Affected Evaluation Model 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model Estimated Effect A quantitative evaluation using a method similar to that described in Reference 3 was performed to assess the PCT effect of TCD and peaking factor burndown with other considerations of burnup on the Seabrook LBLOCA analysis and concluded that the estimated PCT impact is a penalty of 125*F for Reflood 1 and a penalty of 180°F for Reflood 2 for 10 CFR 50.46 reporting purposes. With these new penalties, Reflood 1 PCT remains limiting. The peaking factor burndown included in the evaluation is provided in Table 1. NextEra and its vendor, Westinghouse Electric Company LLC, utilize processes which ensure that the LOCA analysis input values conservatively bound the as-operated plant values for those parameters.

Table 1: Peaking Factors Assumed in the Evaluation of TCD Rod Burnup FdH (1),(2) FQ Transient (1) FQ Steady-State (MWdIMTU) 0 1.65 2.50 2.00 30,000 1.65 2.50 2.00 60,000 1.40 2.00 1.60 62,000 1.40 2.00 1.60 (1) Includes uncertainties.

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

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. LTR-NRC-12-27, Letter from J. A. Gresham (Westinghouse) to NRC, 'Westinghouse Input Supporting Licensee Response to NRC 10 CFR 50.54(f) Letter Regarding Nuclear Fuel Thermal Conductivity Degradation (Proprietary/Non-Proprietary)," March 7, 2012.

Table 2 Seabrook LBLOCA PCT Rackup Peak Clad Cumulative Temperature Change LBLOCA 2011 10 CFR 50.46 Annual Report (Reference 1) 1789 OF 5 OF TCD Impact 125 0F 125 OF Reference

1. Letter from M. O'Keefe to the USNRC, "Seabrook Station, Annual Reporting of Changes to, or Errors in Emergency Core Cooling System Models or Applications," SBK-L-12126, Docket No.

50-443, July 16, 2012.

ENCLOSURE 2 TO SBK-L-12264 ENCLOSURE 2 EVALUATION OF FUEL PELLET THERMAL CONDUCTIVITY DEGRADATION AND POWER PEAKING BURNDOWN SUPPLEMENTAL INFORMATION 1.0 Background The Nuclear Regulatory Commission (NRC) approved 1996 Westinghouse Best Estimate Large Break Loss-of-Coolant Accident (LOCA) Evaluation Model (Reference 1) is based on the PAD 3.4 fuel performance code (Reference 2). Upon NRC approval of PAD 4.0 (Reference 3), its usage was extended to the 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model, as reported to the NRC in Reference 4. The Seabrook Large-Break LOCA (LBLOCA) analysis utilized fuel rod design input from PAD 4.0. PAD 3.4 and 4.0 were licensed without explicitly considering fuel pellet thermal conductivity degradation (TCD) with burnup. Explicit modeling of fuel pellet TCD in the fuel performance code leads to changes in the fuel rod design parameters beyond' beginning-of-life which are input to the LBLOCA analysis. The effects of explicitly modeling fuel pellet TCD on the Seabrook LBLOCA.analysis (Reference 5) have been considered. The modeling of fuel pellet TCD is a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-1 3451 (Reference 6).

Fuel performance data that accounts for fuel pellet TCD (using an unlicensed model) was used as input to the Seabrook evaluation. The new PAD fuel performance data was generated with a representative model that includes explicit modeling of fuel pellet TCD. Therefore, the evaluations performed consider the fuel pellet TCD effects cited in NRC Information Notice 2011-21 (Reference 7).

2.0 Large Break LOCA Input Parameters and Assumptions The evaluation of fuel TCD and peaking factor burndown considered the following input parameter changes to the LBLOCA analysis:

• Fuel rod design data with PAD 4.0 + TCD

" Peaking factor burndown shown in Table 1 Table 1: Peaking Factors Assumed in the Evaluation of TCD Rod Burnup FdH (1),(2) FQ Transient (1) FQ Steady State (MWd/MTU) 0 1.65 2.50 2.00 30,000 1.65 2.50 2.00 60,000 1.40 2.00 1.60 62,000 1.40 2.00 1.60 (1) Includes uncertainties.

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

d ENCLOSURE2 EVALUATION OF FUEL PELLET THERMAL CONDUCTIVITY DEGRADATION AND POWER PEAKING BURNDOWN SUPPLEMENTAL INFORMATION 3.0 Large Break LOCA Description of Evaluation A quantitative evaluation using a method similar to that described in Reference 8 was performed to assess the peak clad temperature (PCT) effect of TCD and peaking factor burndown with other considerations of burnup on the Seabrook LBLOCA analysis. However, the Seabrook TCD evaluation utilizes a different burnup selection, makes no changes to design inputs beyond peaking factor burndown, and considers both the Reference Transient as well as the Limiting Split case from the Analysis-of-Record (AOR).

In addition, a quantitative evaluation was performed for oxidation.

4.0 Large Break LOCA Results The results of the evaluation are presented in Table 2.

Table 2: Fuel Pellet TCD Evaluation Results Evaluation Reflood 1 PCT (OF) Reflood 2 PCT (*F)

Starting Rackup PCT 1789 1729 TCD (including burndown) 125 180 Final New Rackup PCT 1914 1909 With these new evaluations, acceptance criterion 10 CFR 50.46(b)(1) is met as follows:

= Calculated Peak Clad Temperature (PCT) = 1914 OF < 2200 OF A quantitative evaluation was performed for oxidation, and new MLO and CWO results are presented below. As such, acceptance criteria 10 CFR 50.46(b)(2) and (b)(3) are met as follows:

• Calculated Maximum Local Oxidation (MLO) = 7.8% < 17%

• Calculated Core Wide Oxidation (CWO) = 0.34% < 1%

Based on the PCT and oxidation results herein, and the existing grid crush calculations, it was determined that acceptance criterion 10 CFR 50.46(b)(4) "Coolable Geometry" continues to be met.

Based on the demonstration of coolable geometry and an evaluation of TCD on long term core cooling, it was concluded that acceptance criterion 10 CFR 50.46(b)(5) "Long Term Core Cooling" continues to be met with respect to this evaluation.

As a result, all of the 10 CFR 50.46 acceptance criteria are met for the Seabrook LBLOCA analysis when considering the changes for TCD evaluated herein.

ENCLOSURE2 EVALUATION OF FUEL PELLET THERMAL CONDUCTIVITY DEGRADATION AND POWER PEAKING BURNDOWN SUPPLEMENTAL INFORMATION 5.0 References

1. WCAP-12945-P-A, Volume 1, Revision 2, and Volumes 2 through 5, Revision 1, "Code Qualification Document for Best Estimate LOCA Analysis," March 1998.

2. WCAP-10851-P-A, "Improved Fuel Performance Models for Westinghouse Fuel Rod Design and Safety Evaluations," August 1988.

3. WCAP-15063-P-A with Errata, Revision 1, "Westinghouse Improved Performance Analysis and Design Model (PAD 4.0)," July 2000.

4. LTR-NRC-01-6, "10 CFR 50.46 Annual Notification and Reporting for 2000," March 13, 2001.

5. WCAP-16254-P, "Best-Estimate Analysis of the Large Break Loss of Coolant Accident for the Seabrook Station," May 2004.

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

7. 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)

8. LTR-NRC-12-27, "Westinghouse Input Supporting Licensee Response to NRC 10CFR50.54(f) Letter Regarding Nuclear Fuel Thermal Conductivity Degradation (Proprietary/Non-Proprietary)," March 7, 2012.