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:	Shea J W 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 37402August 28, 201310 CFR 50.46ATTN: Document Control DeskU.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 1Facility Operating License No. NPF-90NRC 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 thecalculated peak cladding temperature (PCT) for the Watts Bar Nuclear Plant (WBN), Unit 1,Emergency Core Cooling System (ECCS) evaluation model. This report is required inaccordance 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 ofan 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 theabsolute magnitudes of the resulting PCT changes exceeds 50°F. The licensee is alsorequired to include with the report, a proposed schedule for providing a reanalysis or takingother 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 BestEstimate Large Break LOCA (BE LBLOCA) evaluation model. The reported changes anderrors are reportable to the NRC in a 30-day report for WBN, Unit 1, in accordance with10 CFR 50.46(a)(3)(ii).

Printed onr~ ecycled paper "AtU2 ,

U.S. Nuclear Regulatory Commission Page 2August 28, 2013As indicated in the enclosed report, the current updated (net) licensing basis PCT for theWBN, Unit 1, LBLOCA analysis of record (AOR) is now estimated to be 18120F, a change of-680F from the previous (referenced) report. The updated (net) licensing basis PCT for theSmall Break LOCA (SBLOCA) evaluation model is unchanged from the SBLOCA AORbaseline PCT, and remains at 11320F.The enclosed report demonstrates that the calculated PCTs for the ECCS LBLOCA andSBLOCA AORs for WBN, Units 1 and 2, are well below the limit of 22000F. This providesthe 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 isrequired.

There are no regulatory commitments in this letter. Please direct questions concerning thisreport 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 Reportcc (Enclosure):

NRC Regional Administrator

-Region IINRC Senior Resident Inspector

-Watts Bar Nuclear Plant ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT 110 CFR 50.46 30-DAY REPORTIn 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 coolantaccident (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 thelast annual report.The last 10 CFR 50.46 annual report for WBN, Unit 1, was submitted to the United StatesNuclear Regulatory Commission (NRC) on April 25, 2013 (Reference 1). As indicated in theprevious report, Westinghouse Electric Company (WEC) WCAP-14839, Revision 1, "BestEstimate Analysis of the Large Break Loss of Coolant Accident for the Watts Bar NuclearPlant" (Reference 2), is the current Best Estimate Large Break LOCA (BE LBLOCA) analysis ofrecord (AOR) for Unit 1, with a baseline PCT value of 1892 *F. The baseline PCT for theprevious report corresponds to the Reflood 2 (late reflood) case. For this 30-day report, bothReflood 1 (early reflood) and Reflood 2 results are reported.

The Reflood 1 case has a baselinePCT value of 1656 *F. The current Small Break LOCA (SBLOCA)

AOR for Unit 1 isWTV-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 theLBLOCA and SBLOCA analyses since each of the respective AORs (References 2 and 3) wasestablished for WBN, Unit 1. Changes and errors that were not previously identified in eitherthe most recent 10 CFR 50.46 annual report or 30-day report are detailed in the Notes sectionfollowing the tables.As indicated in Table 1 for WBN, Unit 1, the current updated (net) licensing basis PCT for theLBLOCA analysis is 1812'F. This is a 680F decrease in PCT from the last annual report(Reference 1). Note that in the last annual report, the late reflood (Reflood

2) case was themost limiting for PCT; however, with the most recently reported errors from WEC, the earlyreflood (Reflood

1) analysis case now results in a more limiting PCT. Both the early and latereflood cases are reported in Table 1. The WBN, Unit 1, updated (net) licensing basis PCTvalue of 11 320F for the SBLOCA is unchanged from the SBLOCA AOR baseline PCT, asreflected in the previous reports.In accordance with 10 CFR 50.46(a)(3)(ii),

future changes affecting WBN, Unit 1, will beconsidered significant for reporting purposes because the absolute magnitude of theaccumulated changes and errors affecting the calculated PCT since the last LBLOCA reanalysis was performed (Reference

2) exceeds 500F.E-1 of 11 ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT I10 CFR 50.46 30-DAY REPORTTABLE 1(Sheet I of 3)Summary of Changes to WBN, Unit 1, PCT for LBLOCAReflood I Reflood 2APCT IAPCTI APCT IAPCTIYear Description (OF) (OF) (OF) (=F) Notes References 1998 BE LBLOCA AOR Baseline PCT 1656 ---1892 --- --- 21999 Vessel Channel DX Error 56 56 -4 4 --- 72000 Increased Accumulator Room 4 4 4 4 --- 7Temperature Evaluation 2000 1.4% Uprate Evaluation 12 12 12 12 --- 72000 Accumulator Line/Pressurizer 37 -131 131 --- 7Surge Line Data Evaluation 2000 MONTECF Decay Heat 4 4 4 4 --- 8Uncertainty Error2001 WBN Specific LBLOCA Vessel 0 0 0 0 9Geometry Input Errors2003 Input Error Resulting in 60 60 0 0 10Incomplete Solution Matrix2003 Tavg Bias Error 8 8 8 8 102004 Increased Stroke Time for ECCS 0 0 0 0 --- 11Valves 0_0_0_0_11 2004 Revised Blowdown Heatup 5 5 IIUncertainty Distribution 2006 Replacement Steam Generators

-50 50 -10 10 --- 12(D3 to 68AXP)2006 HOTSPOTTM Fuel Relocation 0 0 65 65 --- 12Error I I I II_ IE-2 of 11 ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT 110 CFR 50.46 30-DAY REPORTTABLE I(Sheet 2 of 3)Summary of Changes to WBN, Unit 1,PCT for LBLOCAReflood I Reflood 2APCT IAPCTI APCT IAPCTIYear Description (OF) (OF) (OF) (OF) Notes References 2012 PMID/PBOT Violation Evaluation 20 20 20 20 5, 62012 TCD and Peaking Factor 114 114 15 15 --- 5,6Burndown 114_114 15_15_5,_6 2013 WCOBRA/TRACTM History File 0 0 0 0 4Dimension Error2013 General Code Maintenance 0 0 0 0 --- 12013 HOTSPOTTM Burst Temperature Calculation for ZIRLOTM Cladding 0 0 0 0 12013 HOTSPOTTM Iteration Algorithm for Calculation Initial Fuel Pellet 0 0 0 0 --- IAverage Temperature 2013 WCOBRA/TRACTM Automated 0 0 0 0 1Restart Process Logic Error2013 Rod Internal Pressure Calculation 0 0 0 0 1Error2013 Elevations for Heat Slab 0 0Temperature Initialization 2013 Heat Transfer Model Error 0 0 0 0 2Corrections 2013 Correction to Heat Transfer Node 0 0 0 0 3Initialization

.0_0_0_0

_ 32013 Mass Conservation Error Fix 0 0 0 0 42013 Correction to Split Channel 0 0 0 0 5Momentum Equation2013 Heat Transfer Logic Correction for 0 0 0 0 6Rod 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 I10 CFR 50.46 30-DAY REPORTTABLE 1(Sheet 3 of 3)Summary of Changes to WBN, Unit 1, PCT for LBLOCAReflood I Reflood 2APCT IAPCTI APCT jAPCTIYear Description (OF) (OF) ( 1F) (OF) Notes References 2013 Correction to the Pipe Exit 0 0 0 0 10 ---Pressure Drop Error2013 WCOBRAITRAC File Dimension 0 0 0 0 11Error Correction 2013 Revised Heat Transfer Multiplier

-40 40 -85 85 12 ---Distributions Updated (net) licensing basisPCTAORPCT+APCT1812

--- 1795 --- -Cumulative sum of PCTchanges --- 410 --- 363 ---_ I 1APCTI I I I I IE-4 of 11 ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT I10 CFR 50.46 30-DAY REPORTNOTES:1) Elevations for Heat Slab Temperature Initialization An error was discovered in the WCOBRA/TRAC computer code whereby an incorrect valuewould be used in the initial fuel rod temperature calculation for a fuel rod heat transfer nodeif 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 forexisting 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 whichaffected the heat transfer models. These errors included calculation of the entrained liquidfraction 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 theWong-Hochrieter correlation for the heat transfer coefficient from fuel rods to vapor, fuel rodinitialization and calculation of cladding inner radius with creep, application of grid and twophase 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 errorsrepresents a closely-related group of Non-Discretionary Changes in accordance withSection 4.1.2 of WCAP-1 3451.Based on the results of representative plant calculations, separate effects and integraleffects test simulations, it is concluded that the error corrections have a negligible localeffect 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 fluidproperties and grid turbulent mixing enhancement at the heat transfer node. This problemhas been evaluated for impact on existing analyses and its resolution represents aNon-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451.

Based on engineering judgment and the results from a matrix of representative plantcalculations, it is concluded that the effect of this error is within the code resolution, leadingto an estimated PCT effect of 0°F.E-5 of 11 ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT I10 CFR 50.46 30-DAY REPORT4) Mass Conservation Error FixIt 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 physicalrange (greater than 1.0 or smaller than 0.0). This was observed to result in artificial massgeneration on the secondary side of steam generator components.

Correction of thisproblem represents a Non-Discretionary Change in accordance with Section 4.1.2 ofWCAP-13451.

This error was observed to primarily affect the mass on the secondary side of the steamgenerator.

This issue was judged to have a negligible effect on existing LBLOCA analysisresults, leading to an estimated PCT effect of 0°F.5) Correction to Split Channel Momentum EquationAn error was discovered in the momentum equation calculations for split channels inWCOBRA/TRAC.

This error affects the (1) continuity area of the phantom/boundary bottomcell; (2) bottom and top continuity area correction factors for the channel inlet at the bottomof a section and for the channel outlet at the top of a section; and (3) drop entrainment massrate per unit volume and drop de-entrainment mass rate per unit volume contributions to themomentum calculations for split channels.

This problem has been evaluated for effect onexisting 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 thatthe effect of this error on the quantities directly affected by the momentum equationcalculations 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 disabledrod 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 plantmodeling in WEC BE LBLOCA analyses with WCOBRAITRAC, it is judged that existinganalyses 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 vesselsuper-heated water properties, including updating the HGAS subroutine coding to beconsistent with Equation 10-6 of Reference 14, updating the approximation of the enthalpyin the TGAS subroutine to be consistent with the HGAS subroutine coding, and updating thetemperature iteration method and convergence criteria in the TGAS subroutine.

TheseE-6 of 11 ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT 110 CFR 50.46 30-DAY REPORTchanges 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 thana 1 OF impact on the resulting steam temperature values, leading to an estimated PCT effectof 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 wasallowed to vary; as a result, the total metal mass was not preserved.

Correction of thisproblem represents a Non-Discretionary Change in accordance with Section 4.1.2 ofWCAP-13451.

This change primarily affects the reactor coolant system loop piping modeled in theLBLOCA WCOBRA/TRAC models. It was judged that the effect of this change on the PCTresults was negligible, leading to an estimated PCT effect of 00F.9) Decay Heat Model Error Corrections The decay heat model in WCOBRA/TRAC was updated to correct the erroneously codedvalue of the yield fraction directly from fission for Group 19 of Plutonium-239, and to includethe term for uncertainty in the prompt energy per fission in the calculation of the decay heatpower uncertainty.

Correction of these errors represents a closely-related group ofNon-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 anestimated PCT effect of 0°F.10) Correction to the Pipe Exit Pressure Drop ErrorAn error was discovered in WCOBRA/TRAC whereby the frictional pressure drop at the splitbreak tee connection to the break component was incorrectly calculated using the teehydraulic diameter instead of the break component length input. This error has beenevaluated 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 thatthe effect of this error on the pressure at the break and the break flow is negligible, leadingto 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 (FORTRANInput/Output Unit 19) file in WCOBRA/TRAC.

The u19 file is read during HSDRIVERexecution and provides information needed to generate the HOTSPOT thermal-hydraulic E-7 of 11 ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT 110 CFR 50.46 30-DAY REPORThistory and user input files. The array used to write the desired information to the u19 file isdimensioned to 2000 in WCOBRA/TRAC.

However, it is possible for more than 2000 curvesto be written to the u19 file. If that is the case, it is possible that the curves would not bestored correctly on the u19 file. A survey of current BE LBLOCA analyses indicated that themajority of plants had less than 2000 curves in their u19 files; therefore, these plants are notaffected 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 PCTcalculation for prior analyses.

This represents a Discretionary Change in accordance withSection 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 ofthese 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 modelsfor the Refill and Reflood tests modeling the G2 test facility, and errors in processing testdata used to develop the reflood heat transfer multiplier distribution.

Therefore, theblowdown heatup, blowdown

cooling, refill, and reflood heat transfer multiplier distributions were redeveloped.

For the reflood heat transfer multiplier development, the evaluation timewindows 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 filmboiling heat transfer conditions characteristic of the reflood time period. The revised heattransfer multiplier distributions have been evaluated for effect on existing analyses.

Resolution of these issues represents a closely related group of Non-Discretionary Changesin 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 inAttachment 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 wasperformed with the latest version of WCOBRA/TRAC.

Using this transient, HOTSPOTcalculations 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 50.46reporting purposes for WBN, Unit 1.E-8 of 11 ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT 110 CFR 50.46 30-DAY REPORTTABLE 2Summary of Changes to WBN, Unit 1, PCT for SBLOCAYear Description SBLOCA SBLOCA Notes References APCT IAPCTI(OF) _2006 SBLOCA AOR Baseline PCT 1132 --- ---32013 NOTRUMP-EMTM Evaluation of [ 1Fuel Pellet TCDUpdated (net) licensing basisPCTAOR PCT + I APCT 1132 --- ---Cumulative sum of PCTchanges --- 0 ---ZI IAPCTIE-9 of 11 ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT I10 CFR 50.46 30-DAY REPORTREFERENCES

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

2. WCAP-14839, Revision 1, "Best Estimate Analysis of the Large Break Loss of CoolantAccident for the Watts Bar Nuclear Plant," September 19983. WTV-RSG-06-015, "LOCA & Non-LOCA Analysis Summary for Replacement SteamGenerator,"

February 20064. Letter from TVA to NRC, "10 CFR 50.46 Day Report for Watts Bar Unit 1," datedMarch 19, 2013 [ML13080A405]

5. Letter from TVA to NRC, "Supplement to 10 CFR 50.46 Day Special Report,"

datedFebruary 13, 2013 [ML13046A002]

6. Letter from TVA to NRC, "10 CFR 50.46 Day Special Report,"

datedOctober 18, 2012 [ML12296A254]

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

8. Letter from TVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 -Emergency CoreCooling System (ECCS) Evaluation Model Changes Day Report and RevisedAnnual Notification Report for 2000," dated September 7, 2001 [ML01 2570290]9. Letter from WVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 -Emergency CoreCooling 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 CoreCooling System (ECCS) Evaluation Model Changes Day Report and RevisedAnnual Notification and Reporting for 2003," dated April 19, 2004 [ML041130196]

11. Letter from WVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 -Emergency CoreCooling 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 CoreCooling System (ECCS) Evaluation Model Changes Day Report and AnnualNotification and Reporting for 2006," dated July 3, 2007 [ML071860388]

E-10 of 11 ENCLOSURE WATTS BAR NUCLEAR PLANT, UNIT 110 CFR 50.46 30-DAY REPORTREFERENCES (continued)

13. WCAP-13451,

'Westinghouse Methodology for Implementation of 10 CFR 50.46Reporting,"

October 1992.14. WCAP-12945-P-A, Volume 1, Revision 2, and Volumes 2 through 5, Revision 1, "CodeQualification Document for Best Estimate LOCA Analysis,"

1998.E-11 of 11 ATTACHMENT WATTS BAR NUCLEAR PLANT, UNIT I10 CFR 50.46 30-DAY REPORTADDITIONAL INFORMATION ON THE EVALUATION OF REVISEDHEAT TRANSFER MULTIPLIER DISTRIBUTIONS Westinghouse Non-Proprietary Class 3* Westinghouse From:Phone:Our Ref:

Subject:

Attachments:

References:

LOCA Integrated Services I Date: August 14, 2013(412) 374-5241LTR-LIS-13-406Additional Information on the Evaluation of Revised Heat Transfer Multiplier Distributions

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)1. LTR-LIS-13-346, "10 CFR 50.46 Notification and Reporting for WCOBRAiTRAC Changesand Error Corrections,"

July 2013.Plants which are licensed with Best Estimate Large Break LOCA methodologies (both CQD andASTRUM evaluation models (EMs)) recently received 10 CFR 50.46 reporting text for a group of errorcorrections to WCOBRA/TRAC in Reference

[ 1 ]. In addition, each plant received a plant-specific letterwhich 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 theevaluation of the heat transfer multiplier distributions.

Additional information for plants licensed with theCQD EM is included in Attachment 1, and additional information for plants licensed with the ASTRUMEM is included in Attachment 2.Since the WCOBRAiTRAC calculations for the heat transfer multiplier distribution evaluations used thelatest released code versions which incorporated correction of the errors identified in Reference

[1], it isrecommended that the reporting pages included in Reference

[1] be submitted at the time the 10 CFR50.46 report for the revised heat transfer multiplier distributions is submitted.

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

Author: (electronically approved)

• -Jarrett D. ValeriLOCA Integrated Services IVerifier:

(electronically approved)

• Mitchell E. NissleySafety Analysis and Licensing Author: (electronically approved)

• Meghan E. McCloskey LOCA Integrated Services IApproved:

(electronically approved)*

Amy J. ColussyLOCA Integrated Services I*Electronically approved records are authenticated in the electronic document management system.©2013 Westinghouse Electric Company LLCAll Rights Reserved Westinghouse Non-Proprietary Class 3August 14, 2013Attachment 1 of LTR-LIS-13-406 Page 1 of 7Attachment 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 LLCAll Rights Reserved Attachment I of LTR-LIS-13-406August 14, 2013Page 2 of 71.0 Background on Error Identification and Reporting As a result of code development and maintenance, several errors in the WCOBRA/TRAC code used forbest 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 theerrors affected the WCOBRA/TRAC heat transfer models, the heat transfer node initialization or the heattransfer renoding logic, as well as other models. These changes to WCOBRA/TRAC were described inReference

[3].As a result of these changes, the following uncertainty distributions used in the CQD and ASTRUM EMswere 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 transferThe results for the Separate Effects Tests (SETs) and Integral Effects Tests (lETs) used to determine

'eachof the potentially impacted uncertainty distributions were examined, comparing results between the latestversion 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 theASTRUM EM in Reference

[2]). It was determined that the results for the SETs and lETs used todevelop 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 thatemergency core cooling (ECC) bypass predictions remain conservative.

However, it was determined thatthe heat transfer multiplier distributions required additional investigation.

During the investigation into the potential impact on the heat transfer multiplier distributions, errors wereidentified 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 inprocessing test data used to develop the reflood heat transfer multiplier distribution.

These errors werealso 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 Effects2.1 Background on Heat Transfer Multiplier SamplingIn order to sample heat transfer multipliers, a percentile for each time period heat transfer multiplier issampled.

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 conceptfor a change from an old distribution to a new one (note that this CDF does not represent any actual CDFfor 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.

Forthe new distribution, the sampled 25h percentile would result in a multiplier of about 1.15.

Attachment I of LTR-LIS-13-406 August 14, 2013Page 3 of 72.2 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 themiddle 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 throughthe 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 thechange 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 timeperiod.* Reflood heat transfer multipliers increased at the bottom end of the range and the middle, andthen 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 thefirst 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 arediscussed in the following subsections.

2.3 Blowdown LimitedBlowdown limited plants are only affected by the changes to the blowdown heatup heat transfermultiplier CDF. The increased heat transfer multipliers have a small benefit on PCT since the blowdownheatup time period is short.2.4 Early Reflood LimitedEarly reflood limited plants are affected by the changes to all of the heat transfer multiplier CDFs. Theeffects of the changes to the blowdown heatup and blowdown cooling heat transfer multiplier CDFs arelimited since much of their effect diminishes through refill and the beginning of reflood.

The effects ofthe changes to the refill heat transfer multiplier CDF are more pronounced since the early reflood PCToccurs 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 LimitedMid reflood limited plants are affected by the changes to all of the heat transfer multiplier CDFs. Theeffects of the changes to the blowdown heatup and blowdown cooling heat transfer multiplier CDFs are Attachment I of LTR-LIS-13-406August 14, 2013Page 4 of 7very limited since most of their effect diminishes through refill and early reflood.

The effects of thechanges to the refill heat transfer multiplier CDF are limited since most of their effect diminishes throughearly 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 LimitedLate 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 transfermultiplier CDFs are negligible since their effect diminishes entirely throughout the lengthy refloodperiod. The effect of the change to the reflood heat transfer multiplier CDF can be significant due to thelonger time over which the multiplier is applied prior to the PCT time.3.0 Methodology for the Estimate of Effect3.1 Selection and Description of Representative Transients Representative PCT transients were used in determining the estimated PCT effect due to the revised heattransfer multiplier distributions.

Heat transfer multipliers are applied in HOTSPOT; the HOTSPOT codeperforms a one-dimensional conduction calculation modeling the effect of local uncertainties on the hotrod, using thermal hydraulic boundary conditions taken from WCOBRAiTRAC.

Plant characteristics determine the typical PCT transient behavior for the plant. Transients from different plants with similarPCT behavior tend to have fairly consistent thermal hydraulic characteristics around the hot rod. As aresult, the choice of representative plant was based on PCT transient behavior for the evaluation of therevised heat transfer multiplier distributions.

The representative transients discussed above were performed with the latest released version ofWCOBRA/TRAC, which incorporated correction of all of the errors listed in Reference

[3]. Therepresentative transients were similar to Reference Transient calculations.

Fuel performance data whichexplicitly reflects bumup-dependent effects of thermal conductivity degradation (TCD), calculated asdescribed in Reference 4, was used for the representative calculations.

3.2 Background of the CQD EMSection 2.1 gives a high level description of sampling methodology.

In the CQD EM, HOTSPOT runs1000 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 plantevaluations, two representative transients were executed to assess the early/mid reflood plants and latereflood plants; because the CQD EM individually tracks the Reflood 1 and Reflood 2 PCTs, onerepresentative plant was sufficient to represent both early and mid reflood plants.3.3 Estimates of EffectFor each representative transient, the WCOBRAITRAC calculation described in Section 3.1 wasexecuted.

The results from this WCOBRA/TRAC calculation provided boundary conditions for Attachment 1 of LTR-LIS-13-406August 14, 2013Page 5 of 7execution of the HOTSPOT code with the old and new heat transfer multiplier distributions.

Theestimated effect for the Blowdown, Reflood 1, and Reflood 2 time periods for each representative plantcalculation was determined from the 95th percentile HOTSPOT results using the old heat transfermultiplier distributions, and the 95th percentile HOTSPOT results using the revised heat transfermultiplier distributions.

For these evaluation calculations, the two latest released versions of HOTSPOTwere used; the only difference between these HOTSPOT versions that affects the calculated results is theheat transfer multiplier distributions.

3.4 Applicability of the TCD Evaluations It has been previously observed that explicitly considering TCD does not significantly impact the natureof 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 beexpected to have similar effect on the base and sensitivity calculations executed to evaluate the effects ofTCD and peaking factor burndown.

The revised heat transfer multiplier distributions do not invalidate theprior 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 Carlosimulations.

However, based on Section 28-3-2 of Reference

[1], as long as an EM change does notsubstantially change the nature of the transient, an estimate of effect based on a Reference Transient for arepresentative 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 aremeant to represent Reference Transient conditions (altered for the effects of TCD), the method usedherein is consistent with the approach described in Reference

[1].4.0 Summary of Effects and Observed TrendsAs described in Section 3.2, in the CQD EM, each HOTSPOT calculation is comprised of 1000calculations 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 forthe heat transfer multiplier evaluations.

As such, the results are indicative of generic trends due to theoverall 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 smallpenalty, which is consistent with the expectations from Section 2.4 due to the reduction in refill heattransfer 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 transfermultipliers over the low end of the range.

Attachment I of LTR-LIS-13-406 August 14, 2013Page 6 of 7For 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 thelate reflood limited representative transient, the Reflood I PCT experienced a moderate

benefit, which isconsistent with expectations from Section 2.5 due to the increase in reflood heat transfer multipliers overthe 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 transfermultipliers 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 andError 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.

Attachment 1 of LTR-LIS-13-406August 14, 2013Page 7 of 7r:a1.00 -0.95 -0.90 -0.85 -0.80 -0.75 -0.70 -0.65 -0.600.55 -0.50 -0.45 -OAO -0.35 -0.30 -0.25 -0.20 -0.15 -0.10 -0.05 -0.00 -0.00-Old--, New0.25 0.50 0.75 1.00 1.25 1.50Heat Transfer Multiplier H-]1.75 2.00 2.25 2.50Figure 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 simplyfor illustrative purposes)