ML13267A034

10 CFR 50.46 - 30-Day Report for Watts Bar, Unit 1

ML13267A034
Person / Time
Site:	Watts Bar
Issue date:	08/28/2013
From:	James Shea Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML13267A034 (22)

Text

Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 August 28, 2013 10 CFR 50.46 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390

Subject:

10 CFR 50.46 Day Report for Watts Bar, Unit 1

Reference:

TVA Letter to NRC, "10 CFR 50.46 Day and Annual Report for 2012,"

dated April 25, 2013 [ML13120A005]

The purpose of this letter is to provide a 30-day report of changes and errors to the calculated peak cladding temperature (PCT) for the Watts Bar Nuclear Plant (WBN), Unit 1, Emergency Core Cooling System (ECCS) evaluation model. This report is required in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.46, "Acceptance Criteria for Emergency Core Cooling Systems for Light-Water Nuclear Power Reactors,"

paragraph (a)(3)(ii).

The PCT changes and errors identified for WBN, Unit 1, in the referenced report submitted on April 25, 2013, when expressed as the cumulative sums of the absolute magnitudes exceed 50 degrees Fahrenheit (°F). In accordance with 10 CFR 50.46(a)(3)(ii), a holder of an operating license or construction permit is required to report changes and errors affecting an ECCS evaluation model to the NRC within 30 days when the cumulative sum of the absolute magnitudes of the resulting PCT changes exceeds 50°F. The licensee is also required to include with the report, a proposed schedule for providing a reanalysis or taking other action, as may be needed, to show compliance with the 10 CFR 50.46 requirements.

Westinghouse Electric Company (WEC) recently notified Tennessee Valley Authority (TVA) of changes and errors affecting the WCOBRA/ITRAC computer code used in the WEC Best Estimate Large Break LOCA (BE LBLOCA) evaluation model. The reported changes and errors are reportable to the NRC in a 30-day report for WBN, Unit 1, in accordance with 10 CFR 50.46(a)(3)(ii).

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U.S. Nuclear Regulatory Commission Page 2 August 28, 2013 As indicated in the enclosed report, the current updated (net) licensing basis PCT for the WBN, Unit 1, LBLOCA analysis of record (AOR) is now estimated to be 1812 0 F, a change of

-68 0 F from the previous (referenced) report. The updated (net) licensing basis PCT for the Small Break LOCA (SBLOCA) evaluation model is unchanged from the SBLOCA AOR baseline PCT, and remains at 1132 0 F.

The enclosed report demonstrates that the calculated PCTs for the ECCS LBLOCA and SBLOCA AORs for WBN, Units 1 and 2, are well below the limit of 22000 F. This provides the requisite demonstration of compliance with the 10 CFR 50.46 requirements. Therefore, TVA has concluded that no schedule for reanalysis or other action to show compliance is required.

There are no regulatory commitments in this letter. Please direct questions concerning this report to Clyde Mackaman at (423) 751-2834.

Respe ptly, ice Fesident, Nuclear Licensing

Enclosure:

Watts Bar Nuclear Plant, Unit 1, 10 CFR 50.46 30-Day Report cc (Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant

ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT 1 10 CFR 50.46 30-DAY REPORT In accordance with the reporting requirements of Title 10 of the Code of Federal Regulations (10 CFR) 50.46(a)(3)(ii), the following is a summary of the limiting design basis loss of coolant accident (LOCA) analysis results established using the current Watts Bar Nuclear Plant (WBN)

Emergency Core Cooling System (ECCS) evaluation models for Unit 1. This report describes the changes and errors affecting the calculated peak cladding temperatures (PCTs) since the last annual report.

The last 10 CFR 50.46 annual report for WBN, Unit 1, was submitted to the United States Nuclear Regulatory Commission (NRC) on April 25, 2013 (Reference 1). As indicated in the previous report, Westinghouse Electric Company (WEC) WCAP-14839, Revision 1, "Best Estimate Analysis of the Large Break Loss of Coolant Accident for the Watts Bar Nuclear Plant" (Reference 2), is the current Best Estimate Large Break LOCA (BE LBLOCA) analysis of record (AOR) for Unit 1, with a baseline PCT value of 1892 *F. The baseline PCT for the previous report corresponds to the Reflood 2 (late reflood) case. For this 30-day report, both Reflood 1 (early reflood) and Reflood 2 results are reported. The Reflood 1 case has a baseline PCT value of 1656 *F. The current Small Break LOCA (SBLOCA) AOR for Unit 1 is WTV-RSG-06-015, "LOCA & Non-LOCA Analysis Summary for Replacement Steam Generator for WBN Unit 1" (Reference 3), with a baseline PCT of 1132°F.

Tables 1 and 2 detail the accumulated PCT effects resulting from the changes and errors in the LBLOCA and SBLOCA analyses since each of the respective AORs (References 2 and 3) was established for WBN, Unit 1. Changes and errors that were not previously identified in either the most recent 10 CFR 50.46 annual report or 30-day report are detailed in the Notes section following the tables.

As indicated in Table 1 for WBN, Unit 1, the current updated (net) licensing basis PCT for the LBLOCA analysis is 1812'F. This is a 680 F decrease in PCT from the last annual report (Reference 1). Note that in the last annual report, the late reflood (Reflood 2) case was the most limiting for PCT; however, with the most recently reported errors from WEC, the early reflood (Reflood 1) analysis case now results in a more limiting PCT. Both the early and late reflood cases are reported in Table 1. The WBN, Unit 1, updated (net) licensing basis PCT value of 11 32 0 F for the SBLOCA is unchanged from the SBLOCA AOR baseline PCT, as reflected in the previous reports.

In accordance with 10 CFR 50.46(a)(3)(ii), future changes affecting WBN, Unit 1, will be considered significant for reporting purposes because the absolute magnitude of the accumulated changes and errors affecting the calculated PCT since the last LBLOCA reanalysis was performed (Reference 2) exceeds 50 0 F.

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ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT I 10 CFR 50.46 30-DAY REPORT TABLE 1 (Sheet I of 3)

Summary of Changes to WBN, Unit 1, PCT for LBLOCA Reflood I Reflood 2 APCT IAPCTI APCT IAPCTI Year Description (OF) (OF) (OF) (=F) Notes References 1998 BE LBLOCA AOR Baseline PCT 1656 - - - 1892 --- --- 2 1999 Vessel Channel DX Error 56 56 -4 4 --- 7 2000 Increased Accumulator Room 4 4 4 4 --- 7 Temperature Evaluation 2000 1.4% Uprate Evaluation 12 12 12 12 --- 7 2000 Accumulator Line/Pressurizer 37 -131 131 --- 7 Surge Line Data Evaluation 2000 MONTECF Decay Heat 4 4 4 4 --- 8 Uncertainty Error 2001 WBN Specific LBLOCA Vessel 0 0 0 0 9 Geometry Input Errors 2003 Input Error Resulting in 60 60 0 0 10 Incomplete Solution Matrix 2003 Tavg Bias Error 8 8 8 8 10 2004 Increased Stroke Time for ECCS 0 0 0 0 --- 11 Valves 0_0_0_0_11 2004 Revised Blowdown Heatup 5 5 II Uncertainty Distribution 2006 Replacement Steam Generators -50 50 -10 10 --- 12 (D3 to 68AXP) 2006 HOTSPOTTM Fuel Relocation 0 0 65 65 --- 12 Error I I I II_ I E-2 of 11

ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT 1 10 CFR 50.46 30-DAY REPORT TABLE I (Sheet 2 of 3)

Summary of Changes to WBN, Unit 1, PCT for LBLOCA Reflood I Reflood 2 APCT IAPCTI APCT IAPCTI Year Description (OF) (OF) (OF) (OF) Notes References 2012 PMID/PBOT Violation Evaluation 20 20 20 20 5, 6 2012 TCD and Peaking Factor 114 114 15 15 --- 5,6 Burndown 114_114 15_15_5,_6 2013 WCOBRA/TRACTM History File 0 0 0 0 4 Dimension Error 2013 General Code Maintenance 0 0 0 0 --- 1 TM 2013 HOTSPOT Burst Temperature 0 0 0 0 1 Calculation for ZIRLOTM Cladding 2013 HOTSPOTTM Iteration Algorithm for Calculation Initial Fuel Pellet 0 0 0 0 --- I Average Temperature 2013 WCOBRA/TRACTM Automated 0 0 0 0 1 Restart Process Logic Error 2013 Rod Internal Pressure Calculation 0 0 0 0 1 Error 2013 Elevations for Heat Slab 0 0 Temperature Initialization 2013 Heat Transfer Model Error 0 0 0 0 2 Corrections 2013 Correction to Heat Transfer Node 0 0 0 0 3 Initialization .0_0_0_0 _ 3 2013 Mass Conservation Error Fix 0 0 0 0 4 2013 Correction to Split Channel 0 0 0 0 5 Momentum Equation 2013 Heat Transfer Logic Correction for 0 0 0 0 6 Rod Burst Calculation 2013 Changes to Vessel Superheated 0 0 0 0 7 ---

Steam Properties 2013 Update to Metal Density 0 0 0 0 8 ---

Reference Temperatures 2013 Decay Heat Model Error 0 0 0 0 9 ---

Corrections E-3 of 11

ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT I 10 CFR 50.46 30-DAY REPORT TABLE 1 (Sheet 3 of 3)

Summary of Changes to WBN, Unit 1, PCT for LBLOCA Reflood I Reflood 2 APCT IAPCTI APCT jAPCTI Year Description (OF) (OF) ( 1F) (OF) Notes References 2013 Correction to the Pipe Exit 0 0 0 0 10 ---

Pressure Drop Error 2013 WCOBRAITRAC File Dimension 0 0 0 0 11 Error Correction 2013 Revised Heat Transfer Multiplier -40 40 -85 85 12 ---

Distributions Updated (net) licensing basis PCT

--- 1795 ----

AORPCT+APCT1812 Cumulative sum of PCT changes --- 410 --- 363 ---

I

_ 1APCTI I I I I I E-4 of 11

ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT I 10 CFR 50.46 30-DAY REPORT NOTES:

1) Elevations for Heat Slab Temperature Initialization An error was discovered in the WCOBRA/TRAC computer code whereby an incorrect value would be used in the initial fuel rod temperature calculation for a fuel rod heat transfer node if that node elevation was specified outside of the bounds of the temperature initialization table. This problem has been evaluated for impact on existing analyses and its resolution represents a Discretionary Change in accordance with Section 4.1.1 of WCAP-1 3451 (Reference 13).

Based on inspection of plant analysis input, it was concluded that the input decks for existing analyses are not affected by this error, leading to an estimated PCT effect of 0°F.

2) Heat Transfer Model Error Corrections Several related changes were made to WCOBRA/TRAC to correct errors discovered which affected the heat transfer models. These errors included calculation of the entrained liquid fraction used in calculation of the drop wall heat flux, application of the grid enhancement factor for grid temperature calculation, calculation of the Reynold's number used in the Wong-Hochrieter correlation for the heat transfer coefficient from fuel rods to vapor, fuel rod initialization and calculation of cladding inner radius with creep, application of grid and two phase enhancement factors and radiation component in single phase vapor heat transfer, and reset of the critical heat flux temperature when J=2. These errors have been evaluated to estimate the effect on existing LBLOCA analysis results. Correction of these errors represents a closely-related group of Non-Discretionary Changes in accordance with Section 4.1.2 of WCAP-1 3451.

Based on the results of representative plant calculations, separate effects and integral effects test simulations, it is concluded that the error corrections have a negligible local effect on heat transfer, leading to an estimated PCT effect of 0°F.

3) Correction to Heat Transfer Node Initialization An error was discovered in the heat transfer node initialization logic in WCOBRA/TRAC whereby the heat transfer node center locations could be inconsistent with the geometric node center elevations. The primary effects of this issue are on the interpolated fluid properties and grid turbulent mixing enhancement at the heat transfer node. This problem has been evaluated for impact on existing analyses and its resolution represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451.

Based on engineering judgment and the results from a matrix of representative plant calculations, it is concluded that the effect of this error is within the code resolution, leading to an estimated PCT effect of 0°F.

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ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT I 10 CFR 50.46 30-DAY REPORT

4) Mass Conservation Error Fix It was identified that mass was not conserved in WCOBRA/TRAC one-dimensional component cells when void fraction values were calculated to be slightly out of the physical range (greater than 1.0 or smaller than 0.0). This was observed to result in artificial mass generation on the secondary side of steam generator components. Correction of this problem represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451.

This error was observed to primarily affect the mass on the secondary side of the steam generator. This issue was judged to have a negligible effect on existing LBLOCA analysis results, leading to an estimated PCT effect of 0°F.

5) Correction to Split Channel Momentum Equation An error was discovered in the momentum equation calculations for split channels in WCOBRA/TRAC. This error affects the (1) continuity area of the phantom/boundary bottom cell; (2) bottom and top continuity area correction factors for the channel inlet at the bottom of a section and for the channel outlet at the top of a section; and (3) drop entrainment mass rate per unit volume and drop de-entrainment mass rate per unit volume contributions to the momentum calculations for split channels. This problem has been evaluated for effect on existing analyses and its resolution represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-1 3451.

Based on the results from a matrix of representative plant calculations, it is concluded that the effect of this error on the quantities directly affected by the momentum equation calculations for split channels (velocities, flows, etc.) is negligible, leading to an estimated PCT effect of 0°F.

6) Heat Transfer Logic Correction for Rod Burst Calculation A change was made to the WCOBRATRAC coding to correct an error which had disabled rod burst in separate effect test simulations. This change represents a Discretionary Change in accordance with Section 4.1.1 of WCAP-1 3451.

Based on the nature of the change and the evaluation model requirements for plant modeling in WEC BE LBLOCA analyses with WCOBRAITRAC, it is judged that existing analyses are not affected by this change, leading to an estimated PCT effect of 0°F.

7) Changes to Vessel Superheated Steam Properties Several related changes were made to the WCOBRA/TRAC coding for the vessel super-heated water properties, including updating the HGAS subroutine coding to be consistent with Equation 10-6 of Reference 14, updating the approximation of the enthalpy in the TGAS subroutine to be consistent with the HGAS subroutine coding, and updating the temperature iteration method and convergence criteria in the TGAS subroutine. These E-6 of 11

ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT 1 10 CFR 50.46 30-DAY REPORT changes represent a closely-related group of Non-Discretionary Changes in accordance with Section 4.1.2 of WCAP-1 3451.

The updates to the calculations of the superheated steam properties had generally less than a 1OF impact on the resulting steam temperature values, leading to an estimated PCT effect of 0°F.

8) Update to Metal Density Reference Temperatures It was identified that for one-dimensional components in which heat transfer to stainless steel 304 or 316 is modeled, the reference temperature for the metal density calculation was allowed to vary; as a result, the total metal mass was not preserved. Correction of this problem represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451.

This change primarily affects the reactor coolant system loop piping modeled in the LBLOCA WCOBRA/TRAC models. It was judged that the effect of this change on the PCT results was negligible, leading to an estimated PCT effect of 00 F.

9) Decay Heat Model Error Corrections The decay heat model in WCOBRA/TRAC was updated to correct the erroneously coded value of the yield fraction directly from fission for Group 19 of Plutonium-239, and to include the term for uncertainty in the prompt energy per fission in the calculation of the decay heat power uncertainty. Correction of these errors represents a closely-related group of Non-Discretionary Changes in accordance with Section 4.1.2 of WCAP-1 3451.

These changes have a negligible effect on the calculated decay heat power, leading to an estimated PCT effect of 0°F.

10) Correction to the Pipe Exit Pressure Drop Error An error was discovered in WCOBRA/TRAC whereby the frictional pressure drop at the split break tee connection to the break component was incorrectly calculated using the tee hydraulic diameter instead of the break component length input. This error has been evaluated for impact on existing analyses and its resolution represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-1 3451.

Based on the results from a matrix of representative plant calculations, it is concluded that the effect of this error on the pressure at the break and the break flow is negligible, leading to an estimated PCT effect of 0°F.

11) WCOBRA/TRAC U19 File Dimension Error Correction A problem was identified in the dimension of an array used to generate the u19 (FORTRAN Input/Output Unit 19) file in WCOBRA/TRAC. The u19 file is read during HSDRIVER execution and provides information needed to generate the HOTSPOT thermal-hydraulic E-7 of 11

ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT 1 10 CFR 50.46 30-DAY REPORT history and user input files. The array used to write the desired information to the u19 file is dimensioned to 2000 in WCOBRA/TRAC. However, it is possible for more than 2000 curves to be written to the u19 file. If that is the case, it is possible that the curves would not be stored correctly on the u19 file. A survey of current BE LBLOCA analyses indicated that the majority of plants had less than 2000 curves in their u19 files; therefore, these plants are not affected by the change. For those plants with more than 2000 curves, plant-specific sensitivity calculations indicated that resolution of this issue does not affect the PCT calculation for prior analyses. This represents a Discretionary Change in accordance with Section 4.1.1 of WCAP-1 3451.

Resolution of this issue does not affect the PCT calculation for prior LBLOCA analyses, leading to an estimated PCT effect of 0°F.

12) Revised Heat Transfer Multiplier Distributions Several changes and error corrections were made to WCOBRA/TRAC, and the effects of these changes on the heat transfer multiplier uncertainty distributions were investigated.

During this investigation, errors were discovered in the development of the original multiplier distributions, including errors in the grid locations specified in the WCOBRA/TRAC models for the Refill and Reflood tests modeling the G2 test facility, and errors in processing test data used to develop the reflood heat transfer multiplier distribution. Therefore, the blowdown heatup, blowdown cooling, refill, and reflood heat transfer multiplier distributions were redeveloped. For the reflood heat transfer multiplier development, the evaluation time windows for each set of test experimental data and each test simulation were separately defined based on the time at which the test or simulation exhibited dispersed flow film boiling heat transfer conditions characteristic of the reflood time period. The revised heat transfer multiplier distributions have been evaluated for effect on existing analyses.

Resolution of these issues represents a closely related group of Non-Discretionary Changes in accordance with Section 4.1.2 of WCAP-13451. The attachment to this enclosure provides additional information on the evaluation of the heat transfer multiplier distributions.

The information, as provided by WEC, has been redacted to only include the information in Attachment 1 of the document for Code Qualification Document (CQD) licensed plants, which is applicable to WBN, Unit 1.

A plant transient calculation representative of WBN, Unit 1, transient behavior was performed with the latest version of WCOBRA/TRAC. Using this transient, HOTSPOT calculations were performed with both the original and revised heat transfer multiplier distributions. Based on the change in the 95t, percentile results, estimated PCT effects of

-40°F for Reflood 1 and -85°F for Reflood 2 have been established for 10 CFR 50.46 reporting purposes for WBN, Unit 1.

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ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT 1 10 CFR 50.46 30-DAY REPORT TABLE 2 Summary of Changes to WBN, Unit 1, PCT for SBLOCA Year Description SBLOCA SBLOCA Notes References APCT IAPCTI (OF) _

2006 SBLOCA AOR Baseline PCT 1132 --- --- 3 2013 NOTRUMP-EMTM Fuel Pellet TCD Evaluation of [ 1 Updated (net) licensing basis PCT AOR PCT + I APCT 1132 --- ---

Cumulative sum of PCT changes --- 0 ---

ZIIAPCTI E-9 of 11

ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT I 10 CFR 50.46 30-DAY REPORT REFERENCES

1. Letter from TVA to NRC, "10 CFR 50.46 Day and Annual Report for 2012," dated April 25, 2013 [ML13120A005]

2. WCAP-14839, Revision 1, "Best Estimate Analysis of the Large Break Loss of Coolant Accident for the Watts Bar Nuclear Plant," September 1998

3. WTV-RSG-06-015, "LOCA & Non-LOCA Analysis Summary for Replacement Steam Generator," February 2006

4. Letter from TVA to NRC, "10 CFR 50.46 Day Report for Watts Bar Unit 1," dated March 19, 2013 [ML13080A405]

5. Letter from TVA to NRC, "Supplement to 10 CFR 50.46 Day Special Report," dated February 13, 2013 [ML13046A002]

6. Letter from TVA to NRC, "10 CFR 50.46 Day Special Report," dated October 18, 2012 [ML12296A254]

7. Letter from TVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 - Emergency Core Cooling System (ECCS) Evaluation Model Changes Day Report and Annual Notification and Reporting for 2000," dated October 26, 2000 [ML003764646]

8. Letter from TVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 - Emergency Core Cooling System (ECCS) Evaluation Model Changes Day Report and Revised Annual Notification Report for 2000," dated September 7, 2001 [ML012570290]

9. Letter from WVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 - Emergency Core Cooling System (ECCS) Evaluation Model Changes - Annual Notification and Reporting for 2001," dated April 3, 2002 [ML021070404]

10. Letter from WVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 - Emergency Core Cooling System (ECCS) Evaluation Model Changes Day Report and Revised Annual Notification and Reporting for 2003," dated April 19, 2004 [ML041130196]

11. Letter from WVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 - Emergency Core Cooling System (ECCS) Evaluation Model Changes - Annual Notification and Reporting for 2004," dated April 19, 2005 [ML051120164]

12. Letter from TVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 - Emergency Core Cooling System (ECCS) Evaluation Model Changes Day Report and Annual Notification and Reporting for 2006," dated July 3, 2007 [ML071860388]

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ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT 1 10 CFR 50.46 30-DAY REPORT REFERENCES (continued)

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

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

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ATTACHMENT WATTS BAR NUCLEAR PLANT, UNIT I 10 CFR 50.46 30-DAY REPORT ADDITIONAL INFORMATION ON THE EVALUATION OF REVISED HEAT TRANSFER MULTIPLIER DISTRIBUTIONS

Westinghouse Non-Proprietary Class 3

• Westinghouse From: LOCA Integrated Services I Date: August 14, 2013 Phone: (412) 374-5241 Our Ref: LTR-LIS- 13-406

Subject:

Additional Information on the Evaluation of Revised Heat Transfer Multiplier Distributions Attachments: 1. Additional Information on the Evaluation of Revised Heat Transfer Multiplier Distributions for Plants Licensed with the CQD EM (7 pages, including cover page)

2. Additional Information on the Evaluation of Revised Heat Transfer Multiplier Distributions for Plants Licensed with the ASTRUM EM (7 pages, including cover page)

References:

1. LTR-LIS-13-346, "10 CFR 50.46 Notification and Reporting for WCOBRAiTRAC Changes and Error Corrections," July 2013.

Plants which are licensed with Best Estimate Large Break LOCA methodologies (both CQD and ASTRUM evaluation models (EMs)) recently received 10 CFR 50.46 reporting text for a group of error corrections to WCOBRA/TRAC in Reference [1]. In addition, each plant received a plant-specific letter which included 10 CFR 50.46 reporting text for revised heat transfer multiplier distributions. Subsequent to the release of this information, some utilities requested additional information to better understand the evaluation of the heat transfer multiplier distributions. Additional information for plants licensed with the CQD EM is included in Attachment 1, and additional information for plants licensed with the ASTRUM EM is included in Attachment 2.

Since the WCOBRAiTRAC calculations for the heat transfer multiplier distribution evaluations used the latest released code versions which incorporated correction of the errors identified in Reference [1], it is recommended that the reporting pages included in Reference [1] be submitted at the time the 10 CFR 50.46 report for the revised heat transfer multiplier distributions is submitted.

Please contact the undersigned if there are any questions concerning this information.

Author: (electronicallyapproved)* Author: (electronicallyapproved)*

-Jarrett D. Valeri Meghan E. McCloskey LOCA Integrated Services I LOCA Integrated Services I Verifier: (electronicallyapproved)* Approved: (electronicallyapproved)*

Mitchell E. Nissley Amy J. Colussy Safety Analysis and Licensing LOCA Integrated Services I

• Electronicallyapprovedrecordsare authenticatedin the electronic document management system.

©2013 Westinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 of LTR-LIS-13-406 August 14, 2013 Page 1 of 7 Attachment 1:

Additional Information on the Evaluation of Revised Heat Transfer Multiplier Distributions for Plants Licensed with the CQD EM (7 pages, including cover page)

©2013 Westinghouse Electric Company LLC All Rights Reserved

Attachment I of LTR-LIS- 13-406 August 14, 2013 Page 2 of 7 1.0 Background on Error Identification and Reporting As a result of code development and maintenance, several errors in the WCOBRA/TRAC code used for best estimate large break loss of coolant (BELOCA) analysis in the Code Qualification Document (CQD, Reference [1 ]) and ASTRUM (Reference [2]) evaluation models (EMs) were identified. Some of the errors affected the WCOBRA/TRAC heat transfer models, the heat transfer node initialization or the heat transfer renoding logic, as well as other models. These changes to WCOBRA/TRAC were described in Reference [3].

As a result of these changes, the following uncertainty distributions used in the CQD and ASTRUM EMs were investigated for potential impact:

• Critical flow

• Downcomer condensation

" Upper plenum drain distribution (condensation and interfacial drag for upper plenum injection)

• Blowdown heatup heat transfer

• Blowdown cooling heat transfer

" Refill heat transfer

• Reflood heat transfer The results for the Separate Effects Tests (SETs) and Integral Effects Tests (lETs) used to determine 'each of the potentially impacted uncertainty distributions were examined, comparing results between the latest version of WCOBRA/TRAC (Version MOD7A Revision 8, with all of the errors listed in Reference [3]

corrected) and WCOBRA/TRAC Version MOD7A Revision 6 (which was used in the licensing of the ASTRUM EM in Reference [2]). It was determined that the results for the SETs and lETs used to develop the critical flow, downcomer condensation, and upper plenum drain uncertainty distributions were sufficiently similar; therefore, those distributions did not require changes. It was also confirmed that emergency core cooling (ECC) bypass predictions remain conservative. However, it was determined that the heat transfer multiplier distributions required additional investigation.

During the investigation into the potential impact on the heat transfer multiplier distributions, errors were identified in the development of the original multiplier distributions, including errors in the grid locations specified in the WCOBRA/TRAC models for the G2 Refill and G2 Reflood SETs, and errors in processing test data used to develop the reflood heat transfer multiplier distribution. These errors were also corrected and, using latest released version of WCOBRA/TRAC, the revised blowdown heatup, blowdown cooling, refill and reflood heat transfer multiplier distributions were determined.

2.0 Revised Distributions and Expected Effects 2.1 Background on Heat Transfer Multiplier Sampling In order to sample heat transfer multipliers, a percentile for each time period heat transfer multiplier is sampled. That point is then converted to the heat transfer multiplier value based on the cumulative distribution function (CDF) of the time period heat transfer multiplier. Figure 1 illustrates this concept for a change from an old distribution to a new one (note that this CDF does not represent any actual CDF for the heat transfer multipliers, but is used simply for demonstration). For example, if the 25t"percentile is sampled, Figure 1 shows that a multiplier of about 0.65 would be obtained for the old distribution. For the new distribution, the sampled 25h percentile would result in a multiplier of about 1.15.

Attachment I of LTR-LIS-13-406 August 14, 2013 Page 3 of 7 2.2 Changes to the Heat Transfer Multiplier Distributions The CDFs of the heat transfer multipliers changed as follows:

• Blowdown heatup heat transfer multipliers increased for low multipliers and across most of the middle of the sampling range, and were mostly unchanged for the highest multipliers

• Blowdown cooling heat transfer multipliers decreased slightly from the top of the range through the middle, and were mostly unchanged for low multipliers

• Refill heat transfer multipliers decreased considerably at the top end of the range and gradually reduced to a slight decrease at the bottom end of the range. Although the magnitude of the change to the refill multiplier distribution was larger than that observed in the other distributions, the PCT impact is small because heat transfer rates are low during the nearly adiabatic refill time period.

• Reflood heat transfer multipliers increased at the bottom end of the range and the middle, and then decreased at the top end of the range.

The implications of these changes are dependent on the behavior of plant transients. For the assessment, plants were classified as follows:

" Blowdown limited: A limiting PCT typically within the first 20 seconds of the transient.

• Early reflood limited: A limiting PCT after the end of the refill time period, but within about the first 70 seconds of the transient.

• Mid reflood limited: A limiting PCT that is between the early and late reflood time periods.

• Late reflood limited: A limiting PCT generally after about 200 seconds.

The impacts from the changes to the heat transfer multiplier CDFs on each of these transient types are discussed in the following subsections.

2.3 Blowdown Limited Blowdown limited plants are only affected by the changes to the blowdown heatup heat transfer multiplier CDF. The increased heat transfer multipliers have a small benefit on PCT since the blowdown heatup time period is short.

2.4 Early Reflood Limited Early reflood limited plants are affected by the changes to all of the heat transfer multiplier CDFs. The effects of the changes to the blowdown heatup and blowdown cooling heat transfer multiplier CDFs are limited since much of their effect diminishes through refill and the beginning of reflood. The effects of the changes to the refill heat transfer multiplier CDF are more pronounced since the early reflood PCT occurs shortly after the end of refill. The effects of the changes to the reflood heat transfer multiplier CDF are limited since the run spends very little time in the reflood time period prior to the PCT time.

2.5 Mid Reflood Limited Mid reflood limited plants are affected by the changes to all of the heat transfer multiplier CDFs. The effects of the changes to the blowdown heatup and blowdown cooling heat transfer multiplier CDFs are

Attachment I of LTR-LIS- 13-406 August 14, 2013 Page 4 of 7 very limited since most of their effect diminishes through refill and early reflood. The effects of the changes to the refill heat transfer multiplier CDF are limited since most of their effect diminishes through early reflood. The effects of the changes to the reflood heat transfer multiplier CDF are more pronounced due to the time over which the multiplier is applied prior to the PCT time.

2.6 Late Reflood Limited Late reflood limited plants are predominately affected by the change to the reflood heat transfer multiplier CDF. The effects of the changes to the blowdown heatup, blowdown cooling, and refill heat transfer multiplier CDFs are negligible since their effect diminishes entirely throughout the lengthy reflood period. The effect of the change to the reflood heat transfer multiplier CDF can be significant due to the longer time over which the multiplier is applied prior to the PCT time.

3.0 Methodology for the Estimate of Effect 3.1 Selection and Description of Representative Transients Representative PCT transients were used in determining the estimated PCT effect due to the revised heat transfer multiplier distributions. Heat transfer multipliers are applied in HOTSPOT; the HOTSPOT code performs a one-dimensional conduction calculation modeling the effect of local uncertainties on the hot rod, using thermal hydraulic boundary conditions taken from WCOBRAiTRAC. Plant characteristics determine the typical PCT transient behavior for the plant. Transients from different plants with similar PCT behavior tend to have fairly consistent thermal hydraulic characteristics around the hot rod. As a result, the choice of representative plant was based on PCT transient behavior for the evaluation of the revised heat transfer multiplier distributions.

The representative transients discussed above were performed with the latest released version of WCOBRA/TRAC, which incorporated correction of all of the errors listed in Reference [3]. The representative transients were similar to Reference Transient calculations. Fuel performance data which explicitly reflects bumup-dependent effects of thermal conductivity degradation (TCD), calculated as described in Reference 4, was used for the representative calculations.

3.2 Background of the CQD EM Section 2.1 gives a high level description of sampling methodology. In the CQD EM, HOTSPOT runs 1000 calculations with randomly sampled local uncertainty attributes and produces 95th percentile results.

The CDFs of the local uncertainty attributes within HOTSPOT are not plant-specific. For the CQD plant evaluations, two representative transients were executed to assess the early/mid reflood plants and late reflood plants; because the CQD EM individually tracks the Reflood 1 and Reflood 2 PCTs, one representative plant was sufficient to represent both early and mid reflood plants.

3.3 Estimates of Effect For each representative transient, the WCOBRAITRAC calculation described in Section 3.1 was executed. The results from this WCOBRA/TRAC calculation provided boundary conditions for of LTR-LIS- 13-406 August 14, 2013 Page 5 of 7 execution of the HOTSPOT code with the old and new heat transfer multiplier distributions. The estimated effect for the Blowdown, Reflood 1, and Reflood 2 time periods for each representative plant calculation was determined from the 9 5th percentile HOTSPOT results using the old heat transfer multiplier distributions, and the 9 5th percentile HOTSPOT results using the revised heat transfer multiplier distributions. For these evaluation calculations, the two latest released versions of HOTSPOT were used; the only difference between these HOTSPOT versions that affects the calculated results is the heat transfer multiplier distributions.

3.4 Applicability of the TCD Evaluations It has been previously observed that explicitly considering TCD does not significantly impact the nature of the overall plant transient behavior and thermal-hydraulic response. In addition, the WCOBRA/TRAC calculations described in Section 3.1 were performed using fuel performance data which explicitly accounted for effects of TCD. Therefore, the revised heat transfer multiplier distributions would be expected to have similar effect on the base and sensitivity calculations executed to evaluate the effects of TCD and peaking factor burndown. The revised heat transfer multiplier distributions do not invalidate the prior estimated effects for TCD.

3.5 Applicability of the Uncertainty Calculations HOTSPOT runs are used in several steps of the uncertainty calculations in the CQD methodology; thus, the changes in heat transfer multiplier distributions could have impact on the final Monte Carlo simulations. However, based on Section 28-3-2 of Reference [1], as long as an EM change does not substantially change the nature of the transient, an estimate of effect based on a Reference Transient for a representative plant is sufficient. The heat transfer multiplier changes are only applied in HOTSPOT; therefore, the nature of the transient remains unchanged. Because the representative calculations are meant to represent Reference Transient conditions (altered for the effects of TCD), the method used herein is consistent with the approach described in Reference [1].

4.0 Summary of Effects and Observed Trends As described in Section 3.2, in the CQD EM, each HOTSPOT calculation is comprised of 1000 calculations where the local uncertainty attributes are sampled for each iteration from their respective distributions; the overall 95th percentile PCT results from the 1000 iterations are the result of interest for the heat transfer multiplier evaluations. As such, the results are indicative of generic trends due to the overall changes in the distributions.

For the early/mid reflood limited representative transient, the Reflood I PCT may be considered representative of early reflood PCT and Reflood 2 PCT may be considered representative of mid-reflood PCT. For the early/mid reflood limited representative transient, the Reflood I PCT experienced a small penalty, which is consistent with the expectations from Section 2.4 due to the reduction in refill heat transfer multipliers. The Reflood 2 PCT of this representative transient experienced a moderate benefit, which is consistent with expectations from Section 2.5 due to the increase in reflood heat transfer multipliers over the low end of the range.

Attachment I of LTR-LIS-13-406 August 14, 2013 Page 6 of 7 For the late reflood limited representative transient, the Reflood 1 PCT may be considered representative of mid-reflood PCT and Reflood 2 PCT may be considered representative of late-reflood PCT. For the late reflood limited representative transient, the Reflood I PCT experienced a moderate benefit, which is consistent with expectations from Section 2.5 due to the increase in reflood heat transfer multipliers over the low end of the range. The Reflood 2 PCT of this representative transient experienced a large benefit, which is consistent with expectations from Section 2.6 due to the increase in reflood heat transfer multipliers over the low end of the range and the longer time for which the multiplier is applied.

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- 16009-P-A, "Realistic Large-Break LOCA Evaluation Methodology Using the Automated Statistical Treatment Of Uncertainty Method (ASTRUM)," January 2005.

3. LTR-LIS-13-346, "10 CFR 50.46 Notification and Reporting for WCOBRA/TRAC Changes and Error Corrections," July 2013.

4. 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.

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Figure 1: Example Heat Transfer Multiplier Cumulative Distribution Function (Note that this CDF does not represent any actual CDF for the heat transfer multipliers, but is used simply for illustrative purposes)