ULNRC-06098, 10 CFR 50.46 Annual and Thirty Day Report, ECCS Evaluation Model Revisions

10 CFR 50.46 Annual and Thirty Day Report, ECCS Evaluation Model Revisions

ML14084A547
Person / Time
Site:	Callaway
Issue date:	03/25/2014
From:	Maglio S Ameren Missouri
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ULNRC-06098
Download: ML14084A547 (16)

Text

{{#Wiki_filter:~~ WAmeren MISSOURI Callaway Plant March 25, 2014 ULNRC-06098 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 10 CFR 50.46 Ladies and Gentlemen: DOCKET NUMBER 50-483 CALLAWAY PLANT UNIT 1 UNION ELECTRIC CO. FACILITY OPERATING LICENSE NPF-30 10 CFR 50.46 ANNUAL AND THIRTY DAY REPORT ECCS EVALUATION MODEL REVISIONS

References:

1) ULNRC-05260 dated 3-9-06

2) ULNRC-05378 dated 3-7-07

3) ULNRC-05475 dated 3-4-08

4) ULNRC-05600 dated 3-4-09

5) ULNRC-05683 dated 3-1-10

6) ULNRC-05769 dated 3-1-11

7) ULNRC-05840 dated 3-1-12

8) ULNRC-05968 dated 3-6-13 Ameren Missouri hereby submits the annual report required per 10 CFR 50.46(a)(3) for Callaway Plant. On March 14, 2014, Ameren Missouri was informed by Westinghouse that the absolute magnitude ofthe Large Break Loss of Coolant Accident (LBLOCA) penalty assessments that have accumulated since the current analysis of record (replacement steam generator analysis approved in Callaway License Amendment 168) exceeds 50°F. Therefore, this report is submitted within the requirements of 10 CFR 50.46(a)(3)(ii) and constitutes both the annual report and a 30-day report.

Attachment 1 to this letter describes changes to the Westinghouse ECCS Large Break and Small Break Loss of Coolant Accident (LOCA) Evaluation Models which have been implemented for Callaway during the time period from March 2013 to March 2014. Attachment 2 provides an ECCS Evaluation Model Margin Assessment which accounts for all peak cladding temperature (PCT) changes resulting from the resolution of prior issues as they apply to Callaway. References 1 through 8 provided annual 10 CFR 50.46 reports that were issued after the LOCA analyses were revised to reflect the installation of the replacement steam generators in 2005. ........................................................................................................................... PO Box 620 Fulton, MD 65251 AmerenMissouri.com STARS* Alliance

ULNRC-06098 March 25, 2014 Page2 Based on the criteria and reporting requirements of 10 CFR 50.46(a)(3)(ii), as clarified in Section 5.1 ofWCAP-13451, "Westinghouse Methodology for Implementation of 10 CFR 50.46 Reporting," the cumulative absolute value of the PCT penalty assessments since the Large Break LOCA analysis of record is significant and requires a 30-day report. The regulation also requires a "proposed schedule for providing a reanalysis or taking other action as may be needed to show compliance with Section 50.46 requirements." Although the PCT values determined in the Large Break and Small Break LOCA analyses of record, when combined with all PCT margin allocations, remain below the 2200°F regulatory limit, Ameren Missouri will reanalyze the Large Break and Small Break Loss of Coolant Accidents using the Full Spectrum LOCA methodology pursuant to the NRC-approved version of WCAP-16996-P, "Realistic LOCA Evaluation methodology Applied to the Full Spectrum of Break Sizes (FULL SPECTRUM LOCA Methodology)," which is still under NRC review. This reanalysis will be completed on a schedule to be determined as part of the 10 CFR 50.46c rulemaking process. summarizes this new commitment. If you have any questions on this report, please contact Mr. Tom Elwood at (314) 225-1905. Sincerely,

                                                              ~t>ot-{ A.. ~

Scott A. Maglio Manager, Regulatory Affairs GGY/nls Attachments

ULNRC-06098 March 25, 2014 Page 3 cc: Mr. Marc L. Dapas Regional Administrator U.S. Nuclear Regulatory Commission Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. Fred Lyon Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Stop 0-8B 1 Washington, DC 20555-2738

ULNRC-06098 March 25, 2014 Page4 Index and send hardcopy to QA File A160.0761 Hardcopy: Certrec Corporation 4150 International Plaza Suite 820 Fort Worth, TX 76109 (Certrec receives ALL attachments as long as they are non-safeguards and may be publicly disclosed.) Electronic distribution for the following can be made via Responses and Reports ULNRC Distribution: F. M. Diya C. 0. Reasoner III D. W. Neterer L. H. Graessle B. L. Cox S. A. Maglio T. B. Elwood Corporate Communications NSRB Secretary G. G. Yates Mr. Tim Diemler, Director (SEMA) Mr. Darrell Chute, Senior REP Planner (SEMA) STARS Regulatory Affairs Mr. John O'Neill (Pillsbury Winthrop Shaw Pittman LLP) Ms. Leanne Tippett-Mosby (DNR)

ULNRC-06098 ATTACHMENT ONE CHANGES TO THE WESTINGHOUSE ECCS EVALUATION MODEL AND PCT PENALTY ASSESSMENTS

ULNRC-06098 TABLE OF CONTENTS

1. EVALUATION OF CHANGES TO GRID BLOCKAGE RATIO AND POROSITY

2. BASH-EM EVALUATION OF FUEL PELLET THERMAL CONDUCTIVITY DEGRADATION

3. LOCBART ROD-TO-ROD RADIATION HEAT TRANSFER COEFFICIENT

4. SATAN6 FUEL ROD GAP HEAT TRANSFER COEFFICIENT CALCULATION

5. BASH QUENCH FRONT MODEL INDEXING ERROR

6. SBLOCTA CLADDING STRAIN REQUIREMENT FOR FUEL ROD BURST

7. GENERAL CODE MAINTENANCE 1

ULNRC-06098

1. EVALUATION OF CHANGES TO GRID BLOCKAGE RATIO AND POROSITY A change in the methodology used to calculate grid blockage ratio and porosity for 17x 17 OFA fuel resulted in a change to the grid inputs used in the 1981 Appendix K Large Break LOCA Evaluation Model with BASH (BASH-EM) which affects the grid heat transfer in the LOCBART fuel rod heatup calculation. This change represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451.

Plant-specific fuel rod heatup calculations were completed using the recalculated grid blockage ratio and porosity values as inputs, resulting in an estimated peak cladding temperature (PCT) impact of+ 17°F for Large Break LOCA(LBLOCA) analysis results.

2. BASH-EM EVALUATION OF FUEL PELLET THERMAL CONDUCTIVITY DEGRADATION An evaluation has been completed to estimate the effect of fuel pellet thermal conductivity degradation (TCD) on peak cladding temperature (PCT) for the Callaway analysis using the 1981 Westinghouse Large Break LOCA Evaluation Model with BASH (BASH-EM) and the LOCBART Transient Extension Method (LTEM). The use ofLTEM (WCAP-10266-P-A, Revision 2, Addendum 3-A, Revision 1, "Incorporation ofthe LOCBART Transient Extension Method into the 1981 Westinghouse Large Break LOCA Evaluation Model with BASH (BASH-EM)," October 2007) was accepted for 10 CFR 50.46 reporting in the NRC Safety Evaluation on LTEM dated September 17, 2007 (Section 4.0, Limitation and Condition # 1).

The Callaway LBLOCA analysis is licensed with the BASH EM (Reference 1 below) including the Revision 0 version of Reference 2 (WCAP-10266-P, Revision 2, Addendum 3, Revision 0, December 2002, cited as Reference 4.5 in the NRC Safety Evaluation for Callaway License Amendment 168). Initial fuel pellet average temperatures and rod internal pressures which account for TCD were calculated using the PAD fuel performance code with an unlicensed version of the fuel pellet thermal conductivity model (referred to as PAD 4.0+ TCD herein). For the Callaway Appendix K LBLOCA calculations, the fuel temperature and rod internal pressure (RIP) input is taken from representative fuel performance data that is calculated using the method discussed in Reference 3. The LOCA calculations also made use of unlicensed fuel thermal conductivity models to account for TCD. The thermal conductivity models used in the BASH EM evaluation are based on the FRAPCON Version 3.3 model. It is recognized that the fuel pellet thermal conductivity models used in the large break calculations are different than that used in PAD 4.0+TCD to generate the initial pellet average temperatures. However, the model used in the BASH EM evaluation accounts for thermal conductivity degradation and achieves more accurate fuel rod temperature initializations compared to a model not accounting for TCD; this is judged to be adequate for the purposes of this assessment. For the evaluation described herein, the only margin credited is the decrease in assembly power and peaking factors (denoted as "bumdown") that results from the depletion of fissionable isotopes beginning around middle-of-life (MOL) and extending to end-of-life (EOL). The rod average bumup is defined here as zero at beginning-of-life (BOL) and limited by the NRC to a maximum of 2

ULNRC-06098 62 MWd/MTU at EOL. The peaking factor bumdown used in the evaluation is provided in Table 1 below. That table is conservative for the current operating cycle and will be validated for future cycles as part of the reload design process. Callaway reload design processes assure that the corresponding LOCA analysis input parameters conservatively bound the as-operated plant values. Table 1: Peaking Factors Assumed in the Evaluation of TCD Rod Burnup (GWD/MTU) F (t, 2) Fo<*>

                                                      ~H 0                                  1.65                                     2.50 30                                  1.65                                     2.50 60                                  1.40                                     2.00 62                                  1.40                                     2.00

1. Includes uncertainties

2. Hot assembly average power (PHA) follows the same burndown since it is a function ofF flH*

The BASH EM calculations consisted of re-executing the limiting PCT case from the Callaway Analysis of Record (AOR). In order to estimate the impact of TCD, the limiting PCT case was first executed using the latest code versions and methodology to form a baseline for comparison. Both the baseline and TCD calculations include use of the approved version of the LOCBART transient extension method (LTEM) (Reference 2), which is used to extend BASH EM transients beyond the point at which downcomer boiling is predicted to occur in BASH. This method correlates the boiling-induced reduction in downcomer driving head to a corresponding reduction in the core inlet flooding rate for use in the LOCBART calculation. The TCD calculations were completed using the same methods used in the baseline calculations, but also included:

1. Fuel Bumup The BASH EM TCD calculations considered a range ofbumups from BOL to EOL. The bumup value for a given BASH EM calculation is based on the hot rod modeled in LOCBART and is also applied to the core average rods modeled in SATAN-VI and BASH; the hot assembly average rods modeled in SATAN-VI and LOCBART; and the adjacent rod modeled in LOCBART. Use of the hot rod bumup for the other rods is considered to be representative-to-conservative when the effects ofTCD are included in the analysis.

2. Thermal Conductivity Degradation As discussed herein, the BASH EM calculations used the FRAPCON Version 3.3 U02 pellet thermal conductivity model which accounts for TCD. This model was activated in the SATAN-VI, BASH, and LOCBART codes to ensure proper fuel rod initialization and transient pellet thermal conductivity calculations.

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3. Changes in Fuel Rod Performance Input Representative steady state pellet average temperatures and rod internal pressures were obtained from a version ofthe PAD code that accounts for TCD (PAD 4.0+TCD). As stated herein, even though the pellet thermal conductivity models used in PAD 4.0+TCD and the BASH EM calculations are different, the two models are similar, which is judged to be adequate for the purposes of estimating the PCT impact ofTCD.

4. Bumdown All calculations considered the effects of assembly power and peaking factor bumdown. Plant-specific bumdown credits were taken and are shown in Table 1.

Results This change represents a Non-Discretionary Change in accordance with Section 4.1.2 ofWCAP-13451. The effect was determined on a plant-specific basis resulting in an estimated PCT impact of +24°F for Large Break LOCA analysis results as listed in Table 2. The results of the Callaway BASH EM TCD evaluation include the rebaseline and TCD 8PCT values. The main reason for the change in PCT from the AOR to the rebaseline can be attributed to the use ofthe LTEM. As stated above the LTEM is used to extend BASH beyond the point where boiling in the downcomer occurs. The PCT impact due to TCD is 0°F. A review of the results shows that the calculation was limited at BOL due to high IFBA burst blockage penalties. Table 2: Callaway Results

                                                                       ~PCT   (°F)

Rebaseline of AOR 24 Effect of TCD and Bumdown on PCT 0

References:

1. WCAP-10266-P-A, Revision 2, "The 1981 Version of the Westinghouse ECCS Evaluation Model Using the BASH Code," March 1987.

2. WCAP-10266-P-A, Revision 2, Addendum 3-A, Revision 1, "Incorporation ofthe LOCBART Transient Extension Method into the 1981 Westinghouse Large Break LOCA Evaluation Model with BASH (BASH-EM)," October 2007.

3. LTR-NRC-12-27, "Westinghouse Input Supporting Licensee Response to NRC 10 CFR 50.54(f)

Letter Regarding Nuclear Fuel Thermal Conductivity Degradation (Proprietary/Non-Proprietary)," March 2012. 4

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4. WCAP-8302, "SATAN VI Program: Comprehensive Space-Time Dependent Analysis of Loss-of-Coolant," June 1974 (approved in Reference 5 below).

5. WCAP-8471-P-A, "The Westinghouse ECCS Evaluation Model: Supplementary Information," April 1975.

6. WCAP-8327, "Containment Pressure Analysis Code (COCO)," July 1974 (approved in Reference 5 above).

7. WCAP-8301, "LOCTA-IV Program: Loss-of-Coolant Transient Analysis," June 1974 (approved in Reference 5 above).

8. WCAP-9561-P-A, "BART-AI: A Computer Code for the Best Estimate Analysis of Reflood Transients," March 1984.

9. WCAP-9220-P-A, Revision 1, "Westinghouse ECCS Evaluation Model, 1981 Version," February 1982.

10. WCAP-10484-P-A, "Spacer Grid Heat Transfer Effects During Reflood," March 1991 (cited as Reference 2-8 in Reference 2 above).

11. WCAP-1 0484-P-A, Addendum 1, "Spacer Grid Heat Transfer Effects During Reflood," September 1993 (cited as References 2-9 and 6-7 in Reference 2 above).

3. LOCBART ROD-TO-ROD RADIATION HEAT TRANSFER COEFFICIENT An error was discovered in the LOCBART code that impacts the calculation of the rod-to-rod radiation heat transfer coefficient. The error was corrected and test cases were performed to determine the potential impact on the results. The test case results demonstrated that correcting the code error had a negligible impact on calculated results. This change represents a Non-Discretionary change to the evaluation model as described in Section 4.1.2 of WCAP-13451.

Validation testing showed a negligible impact on calculated results leading to an estimated PCT impact of 0°F for Large Break LOCA analysis results.

4. SATAN6 FUEL ROD GAP HEAT TRANSFER COEFFICIENT CALCULATION Two errors were identified in the SATAN6 calculation ofthe radiation term ofthe fuel rod gap heat transfer coefficient. First, an incorrect temperature is used in the cladding emissivity calculation; second, a geometrical term is missing from the radiation heat transfer coefficient calculation. These errors correspond to a closely related group of Non-Discretionary Changes as described in Section 4.1.2 of WCAP-13451.

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ULNRC-06098 A set of hand calculations was completed showing a negligible impact on the fuel rod gap heat transfer coefficient in SATAN6leading to an estimated PCT impact of0°F for Large Break LOCA analysis results.

5. BASH QUENCH FRONT MODEL INDEXING ERROR A condition was observed in calculations completed with the BASH computer code relating to an isotherm indexing variable in the quench front model that results in oscillatory quench front behavior above the peak power elevation for select cases. An updated version of the BASH computer code was used to estimate the effect of the quench front oscillations on the resulting core inlet flooding rate used by LOCBART for calculating the peak cladding temperature (PCT). This represents a Non-Discretionary Change as described in Section 4.1.2 of WCAP-13451.

An updated version of the BASH computer code was developed to assess the impact of the oscillations for all impacted analyses. The validation results show a negligible impact on the resulting core inlet flooding rate leading to an estimated PCT impact of 0°F for Large Break LOCA analysis results.

6. SBLOCTA CLADDING STRAIN REQUIREMENT FOR FUEL ROD BURST An error was discovered in the minimum local strain required for burst for ZIRLOt cladding in the SBLOCTA code. The coding does not enforce reaching the minimum percent local strain threshold prior to calculating fuel rod burst. However, a review of licensing basis analyses revealed no instances of this error impacting calculated results. Resolution of this issue represents a Non-Discretionary Change to the Evaluation Model as described in Section 4.1.2 of WCAP-13451.

Based on a review of current licensing basis analyses, and the phenomena and physics of a small break LOCA transient, it is concluded that this error has a negligible effect leading to an estimated PCT impact of 0°F for Small Break LOCA analysis results. 1 ZIRLO is a registered trademark of Westinghouse Electric Company LLC, its affiliates and/or its subsidiaries in the United States of America and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly prohibited. Other names may be trademarks of their respective owners

7. GENERAL CODE MAINTENANCE Various changes have been made to enhance the usability of the codes and to help preclude errors in analyses. This includes items such as modifying input variable definitions, units, and defaults; improving the input diagnostic checks; enhancing the code output; optimizing active coding; and eliminating inactive coding. These changes have been evaluated for impact on existing Large Break LOCA analysis results and they represent Discretionary Changes that will be implemented on a forward-fit basis in accordance with Section 4.1.1 of WCAP-13451.

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ULNRC-06098 Westinghouse has judged this issue to have an estimated PCT impact of0°F on existing Large Break LOCA analysis results. 7

ULNRC-06098 ATTACHMENT TWO ECCS EVALUATION MODEL MARGIN ASSESSMENT FOR CALLAWAY

ULNRC-06098 LARGE BREAK LOCA A. ANALYSIS OF RECORD (AOR) PCT = 1939°F B. PRIOR ECCS MODEL ASSESSMENTS C. CURRENT LOCA MODEL ASSESSMENTS - March 2014 Changes to Grid Blockage Ratio and Porosity (Item 1 of Attachment 1) + 17°F TCD Evaluation - Rebaseline of Analysis of Record (Item 2 of Attachment 1) + 24 °F TCD Evaluation- Effect ofTCD and Assembly Power I Peaking Factor + 0°F Burndown (Item 2 of Attachment 1) LICENSING BASIS PCT +MARGIN ALLOCATIONS 1997°F ABSOLUTE MAGNITUDE OF MARGIN ALLOCATIONS 58°F SINCE LAST ANALYSIS OF RECORD OR LBLOCA 30-DA Y REPORT 1

ULNRC-06098 SMALL BREAK LOCA A. ANALYSIS OF RECORD (AOR) B. PRIOR ECCS MODEL ASSESSMENTS C. CURRENT ECCS MODEL ASSESSMENTS - March 2013 LICENSING BASIS PCT +MARGIN ALLOCATIONS ABSOLUTE MAGNITUDE OF MARGIN ALLOCATIONS SINCE LAST ANALYSIS OF RECORD OR SBLOCA 30-DA Y REPORT 2

ULNRC-06098 ATTACHMENT THREE REANALYSIS COMMITMENT The following table identifies those actions committed to by Ameren Missouri in this document. Any other statements in this document are provided for information purposes and are not considered commitments. Please direct questions regarding these commitments to Mr. Tom Elwood at (314) 225-1905. COMMITMENT Due Date/Event COMN Reanalyze LBLOCA and SBLOCA for In accordance 50392 Callaway Plant using the NRC-approved with the final version ofWCAP-16996-P, "Realistic LOCA rulemaking Evaluation methodology Applied to the Full package for 10 Spectrum of Break Sizes (FULL SPECTRUM CFR 50.46c as LOCA Methodology)" modified by approved exemptions}}