ML14143A253

Watts Bar, Unit 2, Response to Audit for the Fuel Rod Design Effects of Thermal Conductivity Degradation

ML14143A253
Person / Time
Site:	Watts Bar
Issue date:	05/22/2014
From:	Kersting P J Westinghouse
To:	Office of Nuclear Reactor Regulation
References
CN-WATTS-122, Rev. 0
Download: ML14143A253 (26)

Text

ENCLOSURE 3Tennessee Valley AuthorityWatts Bar Nuclear Plant, Unit 2Docket No. 50-391NON-PROPRIETARY ATTACHMENT TO WESTINGHOUSE LETTER TO TVA WBT-D-4833,DATED MAY 16, 2014, "TDC NRC AUDIT"E3-1 Westinghouse Non-Proprietary Class 3CE- 14-3 71, Attachment 2CE-14-371, Attachment 2Response to Watts Bar Unit 2 NRC Audit for the Fuel Rod Design Effects of ThermalConductivity Degradation, Non-Proprietary02014 Westinghouse Electric Company LLC. All rights reserved.Core Engineering Memo Template Version 1-0 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-1 22 1 0 A-iWestinghouse Response to NRC Request for Additional Information forAudit of Westinghouse Evaluation of Fuel Thermal Conductivity Degradation forWatts Bar Unit 2 FuelAuthored:Paul J. KerstingPWR Core Methods, Methods & TechnologyVerified:Tim M. CredeFuel Rod and Thermal Hydraulic Design, Core EngineeringApproved:Keith J. DrudyPWR Core Methods, Methods & Technology

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24 pages@2014 Westinghouse Electric Company LLCAll Rights ReservedO WestinghouseCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-1 22 1 o A-2Provided in this Attachment are the Westinghouse responses to the Nuclear Regulatory Commission(NRC) Requests for Additional Information (RAI) regarding the Watts Bar Unit 2 fuel rod design withfuel thermal conductivity degradation with burnup (TCD) effects in Reference 1. The NRC request isrepeated for each item, followed by the Westinghouse response.1. The NRC staff intends to run FRAPCON-3.4 benchmark calculations of the fuel roddesign. Provide the following inputs for FRAPCON 3.4.A. Rod Power History, KWlft as a function of GWdlMTU1. Bounding thermal-mechanical operating envelope for both fuel types (i.e., U02and IFBA)Response:It is understood that the NRC intends to perform audit analyses using the FRAPCON 3.4fuel performance code for the design parameters significantly impacted by TCD: rodinternal pressure, transient clad strain and power to fuel centerline melt. For the rodinternal pressure analysis and the power to melt analysis, Westinghouse uses aa1". Table 1 provides this [ ]acfor a limiting rod internal pressure analysis. In order to assess TCD impacts over the fullburnup capability of the fuel, an additional cycle of operation was added to the designpower history to obtain end of life rod burnup of [ ]ac This power history,illustrated in Figure 1,]a,C,For the transient clad strain analysis, Westinghouse]ac. The power history for the limiting transientclad strain analysis is given in Table 2 and Figure 2. The limiting strain results occurred [a,c,Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-1 22 1 0 A-3a,cTable IBounding Rod Power History for Limiting Rod Internal Pressure AnalysisCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-122 1 0 A-4Table 2Rod Power History for Limiting Transient Clad Strain Analysisa,cCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-122 1 0 A-5Figure 1Bounding Rod Power History for Limiting Rod Internal Pressure Analysisa,cCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-122 0 A-6Figure 2Rod Power History for Limiting Transient Clad Strain Analysisa,cCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-122 0 A-72. Discuss any application of rod power uncertaintiesResponse:The effects of uncertainties in the steady-state rod power history]a,c.In the calculation of the power to fuel melt limit, the fuel temperature is calculated as afunction of both power and burnup. Uncertainties on the actual transient power capabilityare applied on an event-specific basis outside of the fuel rod design analysis.For the transient clad strain analysis, uncertainties area,C3. Include power histories for different pellet designs for both fuel typesResponse:Reference limiting case power histories are provided in response to Item 1 .A.1 above.Ia,c.B. Axial Power Distribution (Fz at each axial node)1. Include AXPDs for different axial blanket configurations.Response:The power history provided for the rod internal pressure case in Table 1 has 34 burnupsteps. The axial power shapes corresponding to each burnup step for the rod internalpressure limiting rod case are given in Table 3. The rod internal pressure analysisI]ac but since FRAPCON 3.4 is limited to a maximum of 17 axial nodes, the axialpower shapes provided in Table 3 are defined for 17 equal axial nodes.The steady-state power history provided for the limiting transient clad strain case in Table2 has 28 time steps. The axial power shapes corresponding to each of these burnup stepsare given in Table 4. For the transient clad strain analysis,]a.c and since this is compatible with the FRAPCON 3.4 code capability, theshapes in Table 4 are defined for [ ac.Transient clad strain analyses are performedCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-1 22 1 0 A-8]". The magnitude of the localpower increase is determined by the nuclear design analysis []Sc. For the Watts Bar Unit 2 analysis for TCD, the maximum transientclad strain occurred [ ]a,c. The transient power increase is modeled []a,c]a'c uncertainties that can result in increased transient local power peaking areaccounted for in the clad strain analysis, as shown below.The transient axial power shapes for the best estimate transient, and for each of theseuncertainty cases, are provided in Table 5.Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-122 1 0 A-9Table 3Steady-State Axial Power Distributions by Burnup Step for Limiting Rod Internal PressureAnalysisa,cCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-122 1 0 A-10Table 3, ContinuedSteady-State Axial Power Distributions by Burnup Step for Limiting Rod Internal PressureAnalysisa,cCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-122 0 A-11ITable 3, ContinuedSteady-State Axial Power Distributions by Burnup Step for Limiting Rod Internal PressureAnalysisa,cCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-1 22 1 0 A-1 2Table 3, ContinuedSteady-State Axial Power Distributions by Burnup Step for Limiting Rod Internal PressureAnalysis a,cCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-1 22 0 A-13a,cTable 4Steady-State Axial Power Distributions for Limiting Transient Clad Strain AnalysisCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-1 22 1 0 A-14Table 5Clad Strain Analysis Transient Axial Power Distributions for Time Step 27a,cCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageLCN-WATTS-122 0 A-15C. Fuel Rod Design Specifications and Manufacturing Tolerances1. At a minimum, this should include those variables identified in the followingtable.Response:The requested table is provided as Table 6. In Watts Bar Unit 2, there are two fuel rodtypes: U02 and ZrB2 IFBA. The design parameters for both rod types are provided in Table6, and footnotes are used to identify characteristics that are unique to the IFBA fuel roddesign. This includes the percent of the rod with ZrB2 coated pellets] the IFBA coating thickness and B10 loading, the backfill pressure,a"c. All ofthe other parameters provided in the table are common to both rod types, with theexception of the fast flux factor. This value is dependent on both the fuel rod loading andthe power history modeled, and values are provided for the IFBA and U02 rods analyzedfor rod internal pressure and for transient clad strain.The Westinghouse fuel pellet design includes some features which are not directlymodeled in FRAPCON 3.4, based on the input description in Appendix A of Reference 2.This includes the pellet edge chamfer and the annular axial blanket pellets. Dimensions forthese features are provided in Table 6 to enable them to be accounted for in theFRAPCON 3.4 comparison analyses.Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-122 1 0 A-16Table 6FRAPCON 3.4 Input Parameters for Watts Bar Unit 2 Fuel Analysis]a,caxU1 12 ZrB2IFBA rods onlyCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-122 0 A-17Table 6FRAPCON 3.4 Input Parameters for Watts Bar Unit 2 Fuel Analysisa,c1 ZrB2 IFBA Rods Only2 ZIRLO is a trademark or registered trademark of Westinghouse Electric Company LLC, its affiliates and/or its subsidiariesin 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.Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-1 22 0 A-18Table 6FRAPCON 3.4 Input Parameters for Watts Bar Unit 2 Fuel Analysisa,cCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-122 0 A-192. For the following inputs from the above table, please provide tolerance values.Response:The requested tolerance values are provided in Table 7. Drawing tolerances are given asrequested, but it is noted that design analysesaxcTable 7Fuel Pellet and Cladding Tolerance Valuesa,cCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-122 1 0 A-203. For the AOO overpower (Fz vs. time) used in the clad strain calculation:i. Provide the input used (power vs. time)Response:The axial power distribution, in kW/ft, for the limiting Condition II transient clad straincalculation, is provided in response to Item 1.B.1 in Table 5. The transient is modeled]a,c. Table 5 provides the limiting Condition II transient power duty ona best estimate basis and also provides the impacts of several uncertainties on thetransient power, as discussed in response to Item 1 .B.1ii. Provide the predicted strain for both fuel typesResponse:The limiting transient clad strain results calculated for the U02 and for the ZrB2 IFBA fuelrods occurred [ ]a,c of the power history provided in Table 2 and are:U02 fuel rod [ ]a,cZrB2 IFBA fuel rod [ ],4. Provide the predicted power to melt limit (kwlft) vs. Burnup for both fuel typesResponse:Table 8 summarizes the predicted power to melt limit as a function of local burnup for bothZrB2IFBA and U02fuel. These results are also illustrated in Figure 3.Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-122 0 A-21Table 8ZrB2IFBA and U02Fuel Power to Melt as a Function of Local Burnupa,cCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-122 0 A-22Figure 3Power to Melt Limit for Watts Bar Unit 2 ZrB2IFBA and U02Fuel with TCDa,cCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-1 22 0 A-235. Provide the following for the Rod Internal Pressure case for both fuel types:i. BOL Void Wii. EOL Hot VViii. EOL RIPiv. EOL FGR (% release and moles of Gas)ResponseThe requested PAD 4.0 TCD results from the rod internal pressure analysis are provided inTable 9.Table 9Reference PAD 4.0 TCD Rod Internal Pressure Analysis Resultsa,cCore Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3WESTINGHOUSE ELECTRIC COMPANY LLCCalculation Note Number Revision PageCN-WATTS-122 0 A-24References1. WBT-TVA-2598, "PIN Request- Support of NRC Audit of the WEC work on ThermalConductivity Degradation.doc," March 7, 2014.2. NUREG/CR-7022, Volume 1, PNNL-19418, Volume 1, "FRAPCON 3.4: A Computer Code forthe Calculation of Steady-State Thermal-Mechanical Behavior of Oxide Fuel Rods for HighBurnup," March 2011.Core Engineering Word Version 15-1