ML14175A959

Prairie Island, Units 1 and 2, 2013 Annual Report of Changes and Errors to the Emergency Core Cooling System (ECCS) Evaluation Models

ML14175A959
Person / Time
Site:	Prairie Island
Issue date:	06/23/2014
From:	Davison K Northern States Power Co, Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-PI-14-060
Download: ML14175A959 (57)

Text

Xcel Energy JUN 2 3 2014 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington DC 20555-0001 Prairie Island Nuclear Generating Plant, Units 1 and 2 Dockets 50-282 and 50-306 Renewed License Nos. DPR-42 and DPR-60 L-PI-14-060 10 CFR 50.46 2013 Annual Report of Changes and Errors to the Prairie Island Nuclear Generating Plant (PINGP) Emergency Core Cooling System (ECCS) Evaluation Models Pursuant to 10 CFR 50.46, Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM") submits the 2013 annual report of changes and errors to the PINGP Units 1 and 2 ECCS evaluation models. In January 2014, Prairie Island Unit 2 transitioned from the Large Break Loss of Coolant Accident (LBLOCA) analysis described in WCAP 16891-P to the Large Break LOCA analysis described in WCAP 17783-P. Since the current PINGP Unit 2 analysis of record (AOR) is WCAP 17783-P, the annual report will reference this analysis.

Therefore, the peak cladding temperature (PCT) rack-up sheets for Unit 2 will reference WCAP 17783-P rather than WCAP 16891-P. This transition was due to the Unit 2 Steam Generator replacement.

The change in WCAP numbers unifies the two units, thus there is no new analysis (refer to L-PI-14-053).

Following the Unit 2 Steam Generator replacement, the Unit 2 Small Break LOCA Analysis of Record (AOR) was changed to the current Unit 1 Analysis of Record. Two changes to the PCT for PINGP Unit 1 and Unit 2 occurred since the last annual report for the large break LOCA analysis.

The changes to the PCT were a -2 degree Fahrenheit (F) penalty to account for revised heat transfer multiplier distributions, and a +25 degree F penalty to account for errors in the burst strain application.

Enclosure 1 contains the "Non-Plant Specific (LOCA) Errors and Changes" and summarizes the changes made to both the large break LOCA (LBLOCA) and small break LOCA (SBLOCA) analysis.

The SBLOCA and LBLOCA peak clad temperature (PCT) assessment sheets for Unit 1 and Unit 2 are included in Enclosure

2. The limiting LOCA analysis PCT for PINGP Unit 1 and Unit 2, with consideration of all 10 CFR 50.46 assessments, remains the LBLOCA analysis as summarized in Enclosure

2. 1717 Wakonade Drive East

• Welch, Minnesota 55089-9642 Telephone:

651.388.1121 Document Control Desk Page 2 A historical summary of the LOCA PCT for both Prairie Island Unit 1 and Unit 2 changes and errors to the LBLOCA and SBLOCA Evaluation Models are included in Enclosure

2. Enclosure 3 is the Westinghouse Letter L TR-LIS-14-98.

Summary of Commitments This letter contains no new commitments and no revisions to existing commitments.

Kevin Davison Site Vice-President, Prairie Island Nuclear Generating Plant Northern States Power Company -Minnesota Enclosures (3) cc: Regional Administrator, Region Ill, USNRC Project Manager, Prairie Island Nuclear Generating Plant, USNRC Resident Inspector, Prairie Island Nuclear Generating Plant, USNRC ENCLOSURE 1 Non-Plant Specific LOCA Errors and Changes 20 Pages Follow Attachment to LTR-LIS-14-98 GENERAL CODE MAINTENANCE Background March 17, 2014 Page 1 of27 Various changes have been made to enhance the usability of codes and to streamline future analyses.

Examples of these changes include modifying input variable definitions, units and defaults; improving the input diagnostic checks; enhancing the code output; optimizing active coding; and eliminating inactive coding. These changes represent Discretionary Changes that will be implemented on a forward-fit basis in accordance with Section 4.1.1 ofWCAP-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Bre'ak LOCA Evaluation Model Using ASTRUM Estimated Effect The nature of these changes leads to an estimated Peale Cladding Temperature (PCT) impact of 0°F.

Attachment to LTR-LIS-14-98 BURST ELEVATION SELECTION Background March 17,2014 Page 2 of27 It is stated on page 11-20 of WCAP-16009-P-A that the burst option is applied at the elevation corresponding to the (Y{COBRA/TRAC) hurst elevation for the hot assembly rod. This approach was modified to apply the burst option at the HOTSPOT predicted burst elevation as described on page 19 of Attachment 1 to LTR-NRC-06-8.

The HOTSPOT code has been updated to incorporate the following changes to the burst elevation selection logic if multiple nodes burst at the same time: (1) the node that has the highest cladding temperature at the time of burst is selected; (2) if multiple nodes have the same burst time and cladding temperature at the time of burst, the lowest ordered elevation of those nodes is selected.

These changes represent a closely-related group of Discretionary Changes in accordance with Section4.1.1 ofWCAP-13451.

Affected Evaluation Model(s) 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect This improvement in burst elevation selection is a forward-fit change, leading to an estimated Peak Cladding Temperature (PCT) impact of0°F.

Attachment to LTR-LIS-14-98 ELEVATIONS FOR HEAT SLAB TEMPERATURE INITIALIZATION March 17, 2014 Page 3 of27 An error was discovered in WCOBRA/TRAC 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 ofWCAF-13451. Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect Based on inspection of plant analysis input, it was concluded that the input decks for existing analyses are not impacted by this error, leading to an estimated peak cladding temperature impact of0°F.

Attachment to HEAT TRANSFER LOGIC CORRECTION FOR ROD BURST CALCULATION Background March 17,2014 Page4 of27 A change was made to the WCOBRA/TRAC 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 Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect Based on the nature of the change and the evaluation model requirements for plant modeling in Westinghouse best estimate large break LOCA analyses with WCOBRA!TRAC, it is judged that existing analyses are not impacted by this change, leading to an estimated peak cladding temperature impact of 0°F.

Attachment to LTR-LIS-14-98 WCOBRAITRAC U19 FILE DIMENSION ERROR CORRECTION Background March 17,2014 Page 5 of27 A problem was identified in the dimension of an array used to generate the ul9 file in WCOBRA/TRAC.

The u19 file is read during HSDRIVER execution and provides information needed to generate the HOTSPOT thermal-hydraulic history and user input files. The array used to write the desired information to the u19 file is dimensioned to 2000 in WCOBRA/TRAC.

It is possible, however, for more than 2000 curves to be written to the ul9 file. If that is the case, it is possible that the curves would not be stored correctly on the ul9 file. A survey of current Best Estimate Large Break LOCA 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 impact the peak cladding temperature (PCT) calculation for prior analyses.

This represents a Discretionary Change in accordance with Section 4.1.1 of WCAP-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect As discussed in the Background section, resolution of this issue does not impact the peak cladding temperature calculation for prior LBLOCA analyses, leading to an estimated peak cladding temperature impact of 0°F.

Attachment to LTR"LIS" 14"98 HEAT TRANSFER MODEL ERROR CORRECTIONS Background March 17, 2014 Page 6 of27 Several related changes were made to WCOBRA/TRAC .to correct errors discovered which affected the heat transfer models. These errors included of the entrained liquid fraction used in calculation

• of the drop wall beat 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 impact on existing LBLOCA analysis results. Co)Iection of these errors represents a closely-related group of Non" Discretionary Changes in accordance

• • with Section 4.1.2 of WCM-13451.

Affected Evaluation Model{s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect 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 peak cladding temperature impact of 0°F.

Attachment to LTR-LIS-14-98 CORRECTION TO HEAT TRANSFER :NODE INITIALIZATION Background March 17, 2014 Page 7 of27 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 iri accordance with Section 4.1.2 of WCAP-13451. Mfected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect 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 peak cladding temperature impact of 0°F.

Attachment to MASS CONSERVATION ERROR FIX Background March 17, 2014 Page 8 of27 It was identified that mass was not conserved in WCOBRAffRAC 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

Change in accon;lance with Section 4.1.2 of 13451. Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect 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 impact on existing LBLOCA analysis results, leading to an estimated peak cladding temperature impact of0°F.

Attachment to LTR-LIS-14-98 CORRECTION TO SPLIT CHANNEL MOMENTUM EQUATION Background March 17,2014 Page 9 of27 An error was discovered in the momentum equation calculations for split channels in WCOBRA/TRAC.

This error impacts 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 impact on existing analyses and its resolution represents a Non-Discretionary Change in accordance with Section 4.1.2 ofWCAP-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect Based on the results from a matrix of representative plant calculations, it is concluded that the effect of this error on the quantities directly impacted by the momentum equation calculations for split channels (velocities, flows, etc.) is negligible, leading to an estimated peak cladding temperature impact of0°F.

Attachment to LTR-LIS-14-98 CHANGES TO VESSEL SUPERHEATED STEAM PROPERTIES Background March 17,2014 Page 10 of27 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 WCAP-12945-P'-A Equation 10-6, 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 changes represent a closely-related group ofNon-Discretionary Changes in accordance with Section 4.1.2 ofWCAP-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect The updates to the calculations of the superheated steam properties had generally less than 1 op impact on the resulting steam temperature values, leading to an estimated peak cladding temperature impact of0°F.

Attachment to LTR-LIS-14-98 UPDATE TO METAL DENSITY REFERENCE TEMPERATURES Background March 17, 2014 Page 11 of27 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 vazy; 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-134?

1. Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model 'Using ASTRUM Estimated Effect This change primarily impacts the reactor coolant system loop piping modeled in the large break coolant accident (LBLOCA) WCOBRA/TRAC models. It*was judged that the effect of this change on the peak cladding temperature results was negligible, leading to an estimated peak cladding temperature impact of 0°F.

Attachment to LTR-LIS-14-98 DECAY HEAT MODEL CORRECTIONS Background March 17, 2014 Page 12 of27 The decay heat model in the WCOBRAJTRAC code was updated to correct the erroneously coded value of the yield fraction directly from fission for Group 1.9 ofPu-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 ofNon-Discretionary Changes in accordance with Section 4.1.2 ofWCAP-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect These changes have a negligible impact on the calculated decay heat power, leading to an estimated peak cladding temperature impact of 0°F.

Attachment to LTR-LIS-14-98 CORRECTION TO THE PIPE EXIT PRESSURE DROP ERROR Background March 17,2014 Page 13 of27 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.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect 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 peak cladding temperature impact of 0°F.

Attachment to LTR-LIS-14-98 GRID HEAT TRANSFER ENHANCEMENT CALCULATION March 17, 2014 Page 14 of27 Background . An issue was identified which could affect the calculation of the heat transfer at gridded elevations for Best-Estimate (BE) Large-Break Loss-of-Coolant Accident (LBLOCA) Evaluation Models (EMs). For a specific input condition, the grid heat transfer enhancement factor is calculated based on an erroneous core geometry, which can cause an over-prediction of the heat transfer coefficient at gridded elevations.

This issue has been evaluated to estimate the impact on existing LBLOCA analysis results. The resolution of this issue represents a Non-Discretionary Change in accordance With Section 4.1.2 ofWCAP-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect The effect described above was judged to have a negligible effect on existing LBLOCA analysis results, leading to an estimated Peak Cladding Temperature (PCT) impact of 0°F.

Attachment to LTR-LIS-14-98 REVISED HEAT TRANSFER MULTIPLIER DISTRIBUTIONS Background March 17,2014 Page 15 of27 Several changes and error corrections were made to WCOBRA/TRAC and the impacts 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 G2 Refill and G2 Reflood tests, and errors in processing test data used to develop the reflood heat transfer multiplier distribution.

Therefore, the blowdo'Wn beatup, 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 beat transfer conditions characteristic of the reflood time period. The revised beat transfer multiplier distributions have been evaluated for impact on existing analyses.

Resolution of these issues represents a closely related group of Non-Discretionary Changes in accordance with Section 4.1.2 ofWCAP-13451.

Mfected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect A plant transient calculation representative of Prairie Island Unit 1 and Unit 2 transient behavior was performed with the latest version of WCOBRA/TRAC.

Using this transient, a matrix of HOTSPOT calculations was performed to estimate the effect of the heat transfer multiplier distribution changes. Using these results and considering the heat transfer multiplier uncertainty attributes from limiting cases for Prairie Island Unit 1 and Unit 2, an estimated PCT effect of -2°F bas been established for 10 CFR 50.46 reporting purposes for Prairie Island Unit 1 and Unit 2 (future RSG AOR) and an estimated PCT effect of -16°F has been established for 10 CFR 50.46 reporting purposes for Prairie Island Unit 2 (current AOR).

Attachment to LTR-LIS-14-98 ERROR IN BURST STRAIN APPLICATION Background March 17,2014 Page 16 of27 An error in the application of the burst strain was discovered in HOTSPOT. The equation for the application of the burst strain is given as Equation 7-69 in WCAP-16009-P-A and in WCAP-12945-P-A.

The outer radius of the cladding after burst occurs should be calculated based on the burst strain, and the inner radius of the cladding should be calculated based on the outer radius. In HOTSPOT, the burst strain is applied to the calculation of the cladding inner radius. The cladding outer radius is then calculated based on the inner radius. As such, the burst strain is incorrectly applied to the inner radius rather than the outer radius, which impacts the resulting cladding geometry at the burst elevation after burst occurs. Correction of the erroneous calculation results in thinner cladding at the burst node and more fuel relocating into the burst node, leading to an increase in the Peak Cladding Temperature (PCT) at the burst node. This issue has been evaluated to estimate the impact on existing Best-Estimate (BE) Large-Break Loss-of-Coolant Accident (LBLOCA) analysis results. The resolution of this issue represents a Discretionary Change in accordance with Section 4.1.2 ofWCAP-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect The issue described above was evaluated based on the results of executing the most limiting plant-specific HOTSPOT runs for similar plants with a HOTSPOT version that includes the correction of this error. This resulted in an estimated PCT impact of 25°F for Prairie Island Units 1 and 2.

Attachment to LTR-LIS-14-98 CHANGES TO GRID BLOCKAGE RATIO AND POROSITY Background March 17,2014 Page 17 of27 A change in the methodology used to calculate grid blockage ratio and porosity for Westinghouse fuel resulted in a change to the grid inputs for large break loss-of-coolant accident (LBLOCA) analyses.

Grid inputs affect heat transfer in the core during a LBLOCA. This change represents a Non-Discretionary Change in accordance with Se<?tion 4.1.2 ofWCAP-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estim!!-te Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRl.JM Estimated Effect The updates to the methodology to calculate grid blockage ratio and

• porosity used as input in Westinghouse LBLOCA models resuited in a negligible change to heat transfer in the core for the fuel type used in Prairie Island Unit 1 and Unit 2. The estimated penalty associated with the changes is 0°F for 10 CFR 50.46 reporting purposes.

Attachment to LTR-LIS-14-98 March 17,2014 Page 18 of27 INITIAL FUEL PELLET AVERAGE TEMPERATURE UNCERTAINTY CALCULATION Background In the Automated Statistical Treatment of Uncertainty Method (ASTRUM) Best-Estimate (BE) Break Loss-of-Coolant Accident (LBLOCA) Evaluation Model (EM), uncertainties are applied to the gap heat transfer coefficient and pellet thermal conductivity to capture the uncertainty in the initial fuel pellet average temperature.

This approach was compared to the initial fuel pellet average temperature uncertainties predicted by the PAD code at beginning-of-life conditions and found to be conservative in Section 25-4-2-4 of WCAP-12945-P-A.

However, the initial fuel pellet average temperature uncertainty range analyzed at higher burn ups in the ASTRUM EM is much wider than the uncertainty range predicted by the PAD code, which may result in excessively low or high analyzed initial fuel pellet average temperatures.

This issue has been evaluated to estimate the impact on existing ASTRUM LBLOCA analysis results. The resolution of this issue represents a Non-Discretionary Change in accordance with Section 4.1.2 ofWCAP-13451.

Affected Evaluation Model(s) 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect The issue described above is judged to have either no effect or a negligible effect on existing LBLOCA analysis results, leading to an estimated Peak Cladding Temperature (PCT) impact of 0°F.

• Attachment to LTR-LIS-14-98 SBLOCTA CLADDING STRAIN REQUIREMENT FOR FUEL ROD BURST March 17,2014 Page 19 of27 Background An error was discovered in the minimum local strain required for burst for ZIRL01 cladding in the SBLOCTA code. The coding does not enforce reaching the minimum percent local strain threshold prior to calculating fuel rod burst. However, a review of licensing basis analyses revealed no instances of this error impacting calculated results. Resolution of this issue represents a Non-Discretionary Change to the Evaluation Model as described in Section 4.1.2 ofWCAP-13451.

Affected Evaluation Model(s) 1985 Westinghouse Small Break LOCA Evaluation Model with NOTRUMP Estimated Effect Based on a review of current licensing basis analyses, and the phenomena and physics of a small break LOCA transient, it is concluded that this error has a negligible effect on small break LOCA analysis results, leading to an estimated Peak Cladding Temperature (PCT) impact of 0°F. 1 ZIRLO is a registered trademark of Westinghouse Electric Company LLC, its affiliates and/or its subsidiaries in the United States of America and may be registered in other countries throughout the world. All rights reserved.

Unauthorized use is strictZv prohibited.

Other names may be trademarks of their respective owners Attachment to LTR-LIS-14-98 March 17,2014 Page20 of27 PRAIRIE ISLAND UNIT 2 EARLIER CONTAINMENT SPRAY ACTUATION TIME DUE TO DEGRADED FAN COOLER HEAT REMOVAL CAP A CITY Background

• During the installation of the replacement steam generators (RSGs) at Prairie Island Unit 2, fan coolers were damaged, resulting in a degraded heat removal capacity.

Due to the design' of the Prairie Island emergency core cooling system (ECCS), a complete interruption in high head safety injection (HHSI) flows can occur during the switchover to sump recirculation for the small break loss-of-coolant accident (SBLOCA) transient.

The Prairie Island analysis-of-record (AOR) uses containment pressurization calculations to determine the time when the containment sprays would actuate for the smaller break sizes (1.5-inch and 2-inch breaks). This ultimately dictates the time to switch to ECCS sump recirculation and therefore the flow interruption.

The containment pressurization calculations are impacted by the degraded fan coolers and result in an earlier containment spray actuation time. This change represents a Discretionary Change to the Evaluation Model as described at Section 4.1.2 of WCAP-13451.

Affected Evaluation Model(s) 1985 Westinghouse Small Break LOCA Evaluation Model with NOTRUMP Estimated Effect When considering the reduced heat transfer capability of the fan coolers for the 1.5-inch and 2-inch breaks, the containment spray pumps actuate earlier than modeled in the AOR but the interruption in ECCS flow during the switchover to sump recirculation still occurs after the core has recoveFed.

There is sufficient RCS inventory during the flow interruption such that additional, post-switchover core uncovery would not occur. Therefore, this issue is estimated as a 0°F PCT impact on the Prairie Island Unit 2 SBLOCA analysis with the RSGs installed.

ENCLOSURE 2 LOCA peak Clad Temperature Summary (Rack-Up Sheets) Prairie Island Nuclear Generating Plant (Includes plant specific changes and non-zero plant specific changes) 4 Pages Follow Attachment to LTR-LIS-14-98 March 17,2014 Page 21 of27 Westinghouse LOCA Peak Clad Temperature Summary for ASTRUM Best Estimate Large Break Plant Name: Utility Name: Revision Date: Prairie Island Unit 1 Xcel Energy, Inc 2/27/2014 Analysis Information Analysis FdH: 11/30/2007 1.77 Limiting Break Split FQ: 2.5 Fuel: 422 Vantage+ SGTP(%): 10 Notes: LICENSING BASIS Analysis-Of-Record PCT PCT ASSESSMENTS (Delta PCT) A. PRIOR ECCS MODEL ASSESSMENTS I . Evaluation of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Bum down B. PLANNED PLANT MODIFICATION EVALUATIONS I . None C. 2013 ECCS MODEL ASSESSMENTS I . Revised Heat Transfer Multiplier Distributions 2

• Error in Burst Strain Application D. OTHER* I . None LICENSING BASIS PCT + PCT ASSESSMENTS Clad Temp (OF) 1765 227 0 -2 25 0 PCT= 2015 + It is recommended that the licensee determine if these PCT allocations should be considered with respect to 10 CFR 50.46 reporting requirements.

Reference Ref. 1 2 3 4 I . WCAP-16890-P, Revision l, "Best-Estimate Analysis ofthe Large-Break Loss-of-Coolant Accident for the Prairie Island Nuclear Plant Unit 1 Using ASTRUM Methodology," June 2008. Notes: 2 . L TR-LIS-12-414, "Prairie Island Units 1 and 2, I 0 CFR 50.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Bumdown," September 20, 2012. 3 . LTR-LIS-13-366, Revision 1, "Prairie Island Units I and 2 10 CFR 50.46 Report for Revised Heat Multiplier Distributions," August 2013. 4 . LTR-LIS-14-50, "Prairie Island Units I and 2 10 CFR 50.46 Report for the HOTSPOT Burst Strain Error Correction," January 2014. (a) This evaluation credits peaking factor bumdown, see Reference

2. Notes (a)

Attachment to LTR-LIS-14-98 Westinghouse LOCA Peak Clad Temperature Summary for Appendix K Small Break Plant Name: Utility Name: Revision Date: Prairie Island Unit 1 Xcel Energy, Inc 2/27/2014 March 17,2014 Page 22 of27 Analysis Information EM: NOTRUMP Analysis 1/21/2008 1.77 Limiting :Break 3 inch FQ: 2.5 FdH: Fuel: 422 Vantage+ SGTP (%): Notes: Zirlo (14X14), Framatome RSG LICENSING BASIS Analysis-Of-Record PCT PCT ASSESSMENTS (Delta PCT) 10 A. PRIOR ECCS MODEL ASSESSMENTS I . None B. PLANNED PLANT MODIFICATION EVALUATIONS I . None C. 2013 ECCS MODEL ASSESSMENTS I . None D. OTHER* I . None LICENSING BASIS PCT + PCT ASSESSMENTS Clad Temp (DF) Ref. Notes 959 0 0 0 0 PCT= 959

• It is recommended that the licensee detennine ifthese PCT allocations should be considered with respect to 10 CFR 50.46 reporting requirements.

Reference I . L TR-LIS-08-158, "Transmittal of Future Prairie Island Units I and 2 PCT Summaries," February 2008. Notes: None Attachment-to LTR-LIS-14-98 March 17,2014 Page 23 of27 Westinghouse LOCA Peak Clad Temperature.

Summary for ASTRUM Best Estimate Large Break Plant Name: Utility Name: Revision Date: Prairie Island Unit 2 Xcel Energy, Inc 2/27/2014 Analysis Information EM: ASTRUM (2004) Analysis Date: FQ: 2.5 FdH: Fuel: 422 Vantage+ SGTP(%): Notes: 11/30/2007 1.77 10 Limiting Break Size: Split Clad Temp (OF) Ref. LICENSING BASIS Analysis-Of-Record PCT PCT ASSESSMENTS (Delta PCT) A. PRIOR ECCS MODEL ASSESSMENTS I . Evaluation of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Bum down B. PLANNED PLANT MODIFICATION EVALUATIONS 1

• None C. 2013 ECCS MODEL ASSESSMENTS 1

• Revised Heat Transfer Multiplier Distributions 2 . Error in Burst Strain Application D. OTHER* I . None LICENSING BASIS PCT + PCT ASSESSMENTS PCT= 1765 227 0 -2 25 0 2015

• It is recommended that the licensee determine if these PCT allocations should be considered with respect to I 0 CFR 50.46 reporting requirements, References 2 3 4 Notes (a), (b) I . WCAP-17783-P, "Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for Prairie Island Units I and 2 with Replacement Steam Generators Using ASTRUM Methodology," June 2013. Notes: 2 , LTR-LIS-12-414, "Prairie Island Units I and 2, 10 CFR 50.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Bumdown," September 20, 2012. 3 , LTR-LIS-13-366, Revision I, "Prairie Island Units I and 2 10 CFR 50.46 Report for Revised Heat Transfer Multiplier Distributions," August 2013. 4 . LTR-LIS-14-50, "Prairie Island Units I and 2 10 CFR 50.46 Report for the HOTSPOT Burst Strain Error Correction," January 2014. (a) This evaluation credits peaking factor bumdown, see Reference

2. (b) The reporting text and line item originally identified for Unit I in Reference 2 is applicable to Unit 2 with RSGs.

Attachment to LTR-LIS-14-98 March 17, 2014 Page 25 of27 Westinghouse LOCA Clad Temperature Summary for Appendix K Small Break Plant Name: Utility Name: Revision Date: Prairie Island Unit 2 Xcel Energy, Inc 2/27/2014 Analysis Information EM: NOTRUMP Analysis Date: 1/21/2008 1.77 Limiting Break Size: 3 inch FQ: 2.5 FdH: Fuel: 422 Vantage+ SGTP (%): Notes: Zirlo (14X14), AREVA RSG LICENSING BASIS Analysis-Of-Record PCT PCT ASSESSMENTS (Delta PCT) 10 A. PRIOR ECCS MODEL ASSESSMENTS 1 . None B. PLANNED PLANT MODIFICATION EVALUATIONS I . None C. 2013 ECCS MODEL ASSESSMENTS I

• None D. OTHER* I . None LICENSING BASIS PCT + PCT ASSESSMENTS Clad Temp (OF) 959 0 0 0 0 PCT= 959

• It is recommended that the licensee detennine if these PCT allocations should be considered with respect to I 0 CFR 50.46 reporting requirements.

References I . LTR-LIS-08-158, "Transmittal ofFuture Prairie Island Units 1 and 2 PCT Summaries," February 2008. Ref. 1, 2 2 . LTR-LIS-13-274, "Prairie Island Units I and 2, 10 CFR 50.46 Summary Sheets for the Evaluation to Support the Unit 2 Installation of AREVA Model 56/19 Replacement Steam Generators (RSGs)," June 20 I 3. Notes: (a) The Unit I AOR is applicable to Unit 2 with the RSGs installed.

Notes a ENCLOSURE 3 Westinghouse Letter L TR-LIS-14-98 28 Pages Follow Westinghouse Non-Proprietary Class 3 Westinghouse Westinghouse Electric Company Engineering, Equipment and Major Projects 1000 Westinghouse Drive Cranberry Township, Pennsylvania 16066 USA Direct tel: (412) 374-2202 Direct fax: (724) 720-0857 e-mail: teoliscd@westinghouse.com Our ref: LTR-LIS-14-98 March 17,2014 Prairie Island Units 1 and 2 10 CFR 50.46 Annual Notification and Reporting for 2013

Dear Sir or Madam:

This is a notification of 10 CFR 50.46 reporting infonnation pertaining to the Westinghouse Electric Company Evaluation Models/analyses.

As committed to in WCAP-13451, Westinghouse Methodology for Implementation of 10 CFR 50.46 Reporting, Westinghouse is providing an Annual Report for Emergency Core Cooling System (ECCS) Evaluation Model changes and errors for the 2013 model year. Standardized reporting pages for all changes and errors for the Evaluation Models utilized for your plant(s) are enclosed, consistent with the commitment following the NUPIC audit in early 1999. Peak Clad Temperature (PCT) sheets are enclosed.

All necessary revisions for any zero, non-discretionary, PCT change to Section C have been included.

Non-discretionary PCT impacts of oaF will generally not be presented on the PCT sheet. Any plant-specific errors in the application of the model for 2013 will also be provided in Section C with discussion enclosed or cited. The Evaluation Model changes and errors (except any plant-specific errors in the application of the model) will be provided to the NRC via Westinghouse letter. This infonnation is for your use in making a detennination relative to the reporting requirements of 10 CFR 50.46. The infonnation that is provided in this letter was prepared in accordance with Westinghouse's Quality Management System (QMS). Author: (Electronically Approved)*

Carmen D. Teolis Verified: (Electronically Approved)*

Danial W. Utley LOCA Integrated Services I Approved: (Electronically Approved)*

Kyler J. Gates Manager, LOCA Integrated Services II

Attachment:

10 CFR 50.46 Reporting Text and PCT Summary Sheets (27 Pages) LOCA Integrated Services II *Electronically appraved records are authenticated in the electronic document management system. © 2014 Westinghouse Electric Company LLC All Rights Reserved Attachment to LTR-LIS-14-98 GENERAL CODE MAINTENANCE Bacl{ground March 17,2014 Page 1 of27 Various changes have been made to enhance the usability of codes and to streamline future analyses.

Examples of these changes include modifying input variable definitions, units and defaults; improving the input diagnostic checks; enhancing the code output; optimizing active coding; and eliminating inactive coding. Thest1 changes represent Discretionary Changes that will be implemented on a forward-fit basis in accordance with Section4.1.1 ofWCAP-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect The nature of these changes leads to an estimated Peak Cladding Temperature (PCT) impact of 0°F.

Attachment to LTR-LIS-14-98 BURST ELEVATION SELECTION Background March 17,2014 Page 2 of27 It is stated on page 11-20 of WCAP-16009-P-A that the burst option is applied at the elevation corresponding to the QYCOBRAJTRAC) burst elevation for the hot assembly rod. This approach was modified to apply the burst option at the HOTSPOT predicted burst elevation as described on page 19 of Attachment 1 to LTR-NRC-06-8.

The HOTSPOT code has been updated to incorporate the following changes to the burst elevation selection logic if multiple nodes burst at the same time: (1) the node that has the highest cladding temperature at the time of burst is selected; (2) if multiple nodes have the same burst time and cladding temperature at the time of burst, the lowest ordered elevation of those nodes is selected.

These changes represent a closely-related group of Discretionary Changes in accordance with Section 4.1.1 of WCAP-13451.

Affected Evaluation Model(s) 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect This improvement in burst elevation selection is a forward-fit change, leading to an estimated Peak Cladding Temperature (PCT) impact of0°F.

Attachment to LTR-LIS-14-98 ELEVATIONS FOR HEAT SLAB TEl\'IPERATURE INITIALIZATION Background March 17, 2014 Page 3 of27 An error was discovered in WCOBRA/TRAC 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-13451. Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect Based on inspection of plant analysis input, it was concluded that the input decks for existing analyses are not impacted by this error, leading to an estimated peak cladding temperature impact of oop.

Attachment to LTR-LIS-14-98 HEAT TRANSFER LOGIC CORRECTION FOR ROD BURST CALCULATION Background March 17, 2014 Page4 of27 A change was made to the WCOBRA/TRAC 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-13451.

• Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model. 2004 Westinghouse Realistic Large Break LOCA Evaluation Model ASTRUM Estimated Effect Based on the nature of the change and the evaluation model requirements for plant morfeling in Westinghouse best estimate large break LOCA analyses with WCOBRA/TRAC, it is judged that existing analyses are not impacted by this change, leading to an estimated peak cladding temperature impact of 0°F.

Attachment to LTR-LIS-14-98 WCOBRA/TRAC U19 FILE DIMENSION ERROR CORRECTION Background March 17,2014 Page 5 of27 A problem was identified in the dimension of an array used to generate the u19 file in WCOBRA/TRAC.

The u19 file is read during HSDRIVER execution and provides information needed to generate the HOTSPOT thermal-hydraulic history and user input files. The array used to write the desired information to the u19 file is dimensioned to 2000 in WCOBRA/TRAC.

It is possible, however, 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 ul9 file. A survey of current Best Estimate Large Break LOCA analyses indicated that the majority of plants had less than 2000 curves in their ul9 files; therefore theseplants 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 impact the peak cladding temperature (PCT) calculation for prior analyses.

This represents a Discretionary Change in accordance with Section 4.1.1 of WCAP-13451.

Mfected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect As discussed in the Background section, resolution of this issue does not impact the peak cladding temperature calculation for prior LBLOCA analyses, leading to an estimated peak cladding temperature impact of 0°F.

Attachment to LTR-LIS-14-98 HEAT TRANSFER MODEL ERROR CORRECTIONS Background March 17,2014 Page 6 of27 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 impact on existing LBLOCA analysis results. Correction of -these errors represents a clb11ely-related group of Non-Discretionary Changes in accordance with Section 4.1.2 of WCAP-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect 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 peak cladding temperature impact of0°F.

Attachment to LTR-LIS-14-98 CORRECTION TO HEAT TRANSFER NODE INITIALIZATION Background March 17,2014 Page 7 of27 An error was discovered in the heat transfer node initialization logic in WCOBRNTRAC 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. Mfected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect 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 peak cladding temperature impact of0°F.

Attachment to LTR-LIS-14-98 MASS CONSERVATION ERROR FIX Background March 17, 2014 Page 8 of27 It was identified that mass was not conserved in WCOBRA/TRAC one-dimensional component cells when void fraction values were calculated to 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 Changt;: in accordance with Section 4.1.2 ofWCAP-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westirighouse Realistic Large Break LOCA Evaluation l-4?del Using ASTRUM Estimated Effect . This error was observed to primarily affect the mass ort the Secondary side of the steam generator.

This* issue was judged to have a negligible impact on existing LBLOCA analysis results, leading to an estimated peal.< cladding temperature impact of 0°F.

Attachment to LTR-LIS-14-98 CORRECTION TO SPLIT CHANNEL MOMENTUM EQUATION Background March 17,2014 Page 9 of27 An error was discovered in the momentum equation calculations for split channels in WCOBRAJTRAC.

This error impacts 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 impact on existing analyses and its resolution represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451.

Mfected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect Based on the results from a matrix ofrepresentative plant calculations, it is concluded that the effect of this error on the quantities directly impacted by the momentum equation calculations for split channels (velocities, flows, etc.) is negligible, leading to an estimated peak cladding temperature impact of0°F.

Attachment to LTR-LIS-14-98 . CHANGES "TO VESSEL SUPERHEATED STEAM PROPERTIES Background . March 17,2014 Page 10 of27 Several related changes were made to the WCOBRAITRAC coding for the vessel super-heated water properties, including updating the HGAS subroutine coding to be consistent with WCAP-12945-P-A Equation 10-6, 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 changes represent a closely-related group of Non-Discretionary Changes in accordance with Section 4.1.2 ofWCAP-13451.

Mfected Evaluation Model(s) 1996 Westinghouse Best Estimat!;'l Large Break LOCA Evaluation Model *

• 2004 Westinghouse Realistic Lru.:ge Break LOCA Evaluation Model Using ASTRUM . . Estimated Effect The updates to the calculations of the superheated steam properties had generally less than 1 op impact on the resulting steam temperature values, leading to an estimated peak cladding temperature impact of 0°F.

Attachment to LTR-LIS-14-98 UPDATE TO METAL DENSITY REFERENCE TEMPERATURES Background March 17, 2014 Page 11 of27 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 to tar' metal mass was not preserved.

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

Affected Evaluation Model{s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect This change primarily impacts the reactor coolant system loop piping modeled in the large 'break coolant accident (LBLOCA) WCOBRAJTRAC models. It was judged that the effect ofthis change on the peak cladding temperature results was negligible, leading to an estimated peak cladding temperature impact of 0°F.

Attachment to DECAY HEAT MODEL ERROR CORRECTIONS Background March 17,2014 Page 12 of27 The decay heat model in the WCOBRAJTRAC code was updated to correct the erroneously coded value of the yield fraction directly from fission for Group 19 of and to include the tenn for uncertainty in the prompt energy per fission in the calculation of the decay heat power uncertainty.

Correction of these errors represents a

group of Non-Discretionary Changes in accordance with Section 4.1.2 Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect These changes have a negligible impact on the calculated decay heat power, leading to an estimated peak cladding temperature impact of 0°F.

Attachment to LTR-LIS-14-98 CORRECTION TO THE PIPE EXIT PRESSURE DROP ERROR Background March 17,2014 Page 13 of27 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-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect 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 peak cladding temperature impact of0°F.

Attachment to LTR-LIS-14-98 GRID HEAT TRANSFER ENHANCEMENT CALCULATION Background March 17,2014 Page 14 of27 An issue was identified which could affect the calculation of the heat transfer at gridded elevations for Best-Estimate (BE) Large-Break Loss-of-Coolant Accident (LBLOCA) Evaluation Models (EMs). For a specific input condition, the grid heat transfer enhancement factor is calculated based on an erroneous core geometry, which can cause an over-prediction of the heat transfer coefficient at gridded elevations.

This issue has been evaluated to estimate the impact on existing LBLOCA analysis results. The resolution of this issue represents a Non-Discretionary.

Change in accordance with Section 4.1.2 of WCAP-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model

• 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect The effect described above was judged to have a negligible effect on existing LBLOCA analysis results, leading to an estimated Peak Cladding Temperature (PCT) impact of0°F.

Attachment to LTR-LIS-14-98 REVISED HEAT TRANSFER MULTIPLIER DISTRIBUTIONS Background March 17, 2014 Page 15of27 Several changes and error corrections were made to WCOBRA/TRAC and the impacts 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 02 Refill and 02 Reflood tests, 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 impact on existing analyses.

Resolution of these issues represents a closely related group of Non-Discretionary Changes in accordance with Section 4.1.2 ofWCAP-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect A plant transient calculation representative of Prairie Island Unit 1 and Unit 2 transient behavior W!l:S performed with the latest version of WCOBRA/TRAC.

Using this transient, a matrix of HOTSPOT calculations was performed to estimate the effect of the heat transfer multiplier distribution changes. Using these results and considering the heat transfer multiplier uncertainty attributes from limiting cases for Prairie Island Unit 1 and Unit 2, an estimated PCT effect of -2°F has been established for 10 CFR 50.46 reporting purposes for Prairie Island Unit 1 and Unit 2 (future RSO AOR) and an estimated PCT effect of -16°F has been established for 10 CFR 50.46 reporting purposes for Prairie Island Unit 2 (current AOR).

Attachment to LTR-LIS-14-98 ERROR IN BURST STRAIN APPLICATION Background March 17, 2014 Page 16 of27 An error in the application of the burst strain was discovered in HOTSPOT. The equation for the application of the burst strain is given as Equation 7-69 in WCAP-16009-P-A and in WCAP-12945-P-A.

The outer radius of the cladding after burst occurs should be calculated based on the burst strain, and the inner radius of the cladding should be calculated based on, the outer radius. In HOTSPOT, the burst strain is applied to the calculation of the cladding inner radius. The cladding outer radius is then calculated based on the inner radius. As such, the burst strain is incorrectly applied to the inner radius rather than the outer radius, which impacts the resulting cladding geometry at the burst elevation after burst occurs. Correction of the erroneous calculation results in thinner cladding at the burst node and more fuel relocating into the burst node, leading to an increase in the Peak Cladding Temperature (PCT) at the burst node. This issue has been evaluated to estimate the impact on existing Best-Estimate (BE) Large-Break Accident (LBLOCA) analysis results. The resolution of this issue represents a Discretionary Change in accordance with Section 4.1.2 ofWCAP-13451.

Affected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect The issue described above was evaluated based on the results of executing the most limiting plant-specific HOTSPOT runs for similar plants with a HOTSPOT version that includes the correction of this error. This resulted in an estimated PCT impact of 25°F for Prairie Island Units 1 and 2.

Attachment to LTR-LIS-14-98 CHANGES TO GRID BLOCKAGE RATIO AND POROSITY Background March 17, 2014 Page 17 of27 A change in the methodology used to calculate grid blockage ratio and porosity for Westinghouse fuel resulted in a change to the grid inputs for large break loss-of-coolant accident (LBLOCA) analyses.

Grid inputs affect heat transfer in the core during a LBLOCA. This change represents a Non-Discretionary Change in accordance with Section 4.1.2 ofWCAP-13451.

Mfected Evaluation Model(s) 1996 Westinghouse Best Estimate Large Break LOCA Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect The updates to the methodology to calculate grid blockage ratio and porosity used as input in Westinghouse LBLOCA models resulted in a negligible change to heat transfer in the core for the fuel type used in Prairie Island Unit 1 and Unit 2. The estimated penalty associated with the changes is 0°F for 10 CPR 50.46 reporting purposes.

Attachment to LTR-LIS-14-98 March 17,2014 Page 18 of27 INITIAL FUEL PELLET AVERAGE TEMPERATURE UNCERTAINTY CALCULATION Background In the Automated Statistical Treatment of Uncertainty Method (ASTRUM) Best-Estimate (BE) Break Loss-of-Coolant Accident (LBLOCA) Evaluation Model (EM), uncertainties are applied to the gap heat transfer coefficient and pellet thermal conductivity to capture the uncertainty in the initial fuel pellet average temperature.

This approach was compared to the initial fuel pellet average temperature uncertainties predicted by the PAD code at beginning-of-life conditions and found to be conservative in Section 25-4-2-4 of WCAP-12945-P-A.

However, the initial fuel pellet average temperature uncertainty range analyzed at higher burnups in the ASTRUM EM is much wider than the uncertainty range predicted by the PAD code, which may result in excessively low or high analyzed initial fuel pellet average temperatures.

This issue has been evaluated to estimate the impact on existing ASTRUM LBLOCA analysis results. The' resolution of this issue represents a Non-Discretionary Change in accordance with Section 4.1.2 ofWCAP-13451.

Affected Evaluation Model(s) 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect The issue described above is judged to have either no effect or a negligible effect on existing LBLOCA analysis results, leading to an estimated Peak Cladding Temperature (PCT) impact of0°F.

Attachment to LTR-LIS-14-98 SBLOCTA CLADDING STRAIN REQUIREMENT FOR FUEL ROD BURST March 17,2014 Page 19 of27 Background An error was discovered in the minimum local strain required for burst for ZIRL01 cladding in the SBLOCT A code. The coding does not enforce reaching the minimum percent local strain threshold prior to calculating fuel rod burst. However, a review of licensing basis analyses revealed no instances of this error impacting calculated results. Resolution of this issue represents a Non-Discretionary Change to the Evaluation Model as described in Section 4.1.2 ofWCAP-13451.

Affected Evaluation Model(s) 1985 Westinghouse Small Break LOCA Evaluation Model with NOTRUMP Estimated Effect Based on a review of current licensing basis ru;talyses, and the phenomena and physips of a small break LOCA transient, it is concluded that this error has a negligible.

effect on small break LOCA analysis results, leading to an estimated Peak Cladding Temperature (PCT) impact of 0°F. 1 ZIRLO is a registered trademark of Westinghouse Electric Company LLC, its affiliates and/or its subsidiaries in the United States of America and may be registered in other countries throughout the world. All rights reserved.

Unauthorized use is strictly prohibited.

Other names may be trademarks of their respective owners Attachment to LTR-LIS-14-98 March 17,2014 Page 20 of27 PRAIRIE ISLAND UNIT 2 EARLIER CONTAINMENT SPRAY ACTUATION TIME DUE TO. DEGRADED FAN COOLER HEAT REMOVAL CAPACITY Background During the installation of the replacement steam generators (RSGs) at Prairie Island Unit 2, fan coolers were damaged, resulting in a degraded heat removal capacity.

Due to the design of the Prairie Island emergency core cooling system (ECCS), a complete interruption in high head safety injection (HHSI) flows can occur during the switchover to sump recirculation for the small break loss-of-coolant accident (SBLOCA) transient.

The Prairie Island analysis-of-record (AOR) uses containment pressurization calculations to determine the time when the containment sprays would actuate for the smaller break sizes (1.5-inch and 2-inch breaks). This ultimately dictates the time to switch to ECCS sump recirculation and therefore the flow interruption.

The containment pressurization calculations are impacted by the degraded fan coolers and result in an earlier containment spray actuation time. This change represents a Discretionary Change to the Evaluation Model as described at Section 4.1.2 ofWCAP-13451.

Affected Evaluation Model(s) 1985 Westinghouse Small BreakLOCA Evaluation Model with NOTRUMP Estimated Effect When considering the reduced heat transfer capability of the fan coolers for the 1.5-inch and 2-inch breaks, the containment spray pumps actuate earlier than modeled in the AOR but the interruption in ECCS flow during the switchover to sump recirculation still occurs after the 'Core has recovered.

There is sufficient RCS inventory during the flow interruption such that additional, post-switchover core uncovery would not occur. Therefore, this issue is estimated as a 0°F PCT impact on the Prairie Island Unit 2 SBLOCA analysis with the RSGs installed.

• Attachment to March 17, 2014 Page 21 of27 Westinghouse LOCA Peak Clad Temperature Summary for ASTRUM Best Estimate Large Break Plant Name: Utility Name: Revision Date: Prairie Island Unit I Xcel Energy, Inc 2/27/2014 Analysis Information EM: ASTRUM Analysis FdH: . SGTP(%): 11/30/2007 1.77 Limiting Break Split FQ: 2.5 Fuel: 422 Vantage+ 10 Notes: LICENSING BASIS PCT PCT ASSESSMENTS (Delta PCT) A. PRIOR ECCS MODEL ASSESSMENTS I . Evaluation of Fuel Pellet Thennal Conductivity Degradation and Peaking Factor Burn down B. PLANNED PLANT MODIFICATION EVALUATIONS 1 . None C. 2013 ECCS MODEL ASSESSMENTS I . Revised Heat Transfer Multiplier Distributions 2 . Error in Burst Strain Application D. OTHER* I . None LICENSING BASIS PCT + PCT ASSESSMENTS Clad Temp eF) 1765 227 0 -2 25 0 PCT== 2015

• It is recommended that the licensee detennine ifthese PCT allocations should be considered with respect to I 0 CPR 50.46 reporting requirements.

Reference Ref. 1 2 3 4 I . WCAP-16890-P, Revision 1, "Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for the Prairie Island Nuclear Plant Unit 1 Using ASTRUM Methodology," June 2008. Notes: 2 . LTR-LIS-12-414, "Prairie Island Units 1 and 2, 10 CPR 50.46 Notification and Reporting for Fuel Pellet Thenna\ Conductivity Degradation and Peaking Factor Burndown," September 20, 2012. 3 . LTR-LIS-13-366, Revision 1, "Prairie Island Units I and 2 10 CFR 50.46 Report for Revised Heat Transfer Multiplier Distributions," August 2013. 4 . "Prairie Island Units I and 2 10 CFR 50.46 Report for the HOTSPOT Burst Strain Error Correction," January 2014. (a) This evaluation credits peaking factor bumdown, see Reference

2. Notes (a)

Attachment to LTR-LIS-14-98 Westinghouse LOCA Peak Clad Temperature Summary for Appendix K Small Break Plant Name: Utility Name: Revision Date: Prairie Island Unit 1 Xcel Energy, Inc 2/27/2014 Analysis Information EM: NOTRUMP Analysis FdH: FQ: 2.5 Fuel: 422 Vantage+ SGTP (%): Notes: Zirlo (14Xl4), Framatome RSG 1/21/2008 1.77 10 Limiting Break March 17,2014 Page22 of27 3 inch Clad Temp (OF) Ref. Notes LICENSING BASIS Analysis-Of-Record PCT PCT ASSESSMENTS (Delta PCT) A. PRIOR ECCS MODEL ASSESSMENTS I . None B. PLANNED PLANT MODIFICATION EVALUATIONS I . None C. 2013 ECCS MODEL ASSESSMENTS I . None D. OTHER* I

• None LICENSING BASIS PCT + PCT ASSESSMENTS 959 0 0 0 0 PCT== 959

• It is recommended that the licensee detennine iflhese PCT allocations should be considered with respect to I 0 CPR 50.46 reporting requirements.

Reference I . LTR-LIS-08-158, "Transmittal of Future Prairie Island Units I and 2 PCT Summaries," February 2008. Notes: None Attachment to LTR-LIS-14-98 March 17,2014 Page 23 of27 Westinghouse LOCA Peak Clad Temperature Summary for ASTRUM Best Estimate Large Break Plant Name: Utility Name: Revision Date: Prairie Island Unit 2 Xcel Energy, Inc 2/27/2014 Analysis Information EM: ASTRUM (2004) Analysis Date: FQ: 2.5 FdH: Fuel: 422 Vantage+ SGTP(%): Notes: 11130/2007 1.77 10 Limiting Break Size: Split Clad Temp (OF) Ref. LICENSING BASIS Analysis-Of-Record PCT PCT ASSESSMENTS (Delta PCT) A. PRIOR ECCS MODEL ASSESSMENTS I . Evaluation of Fuel Pellet Thennal Conductivity Degradation and Peaking Factor Bumdown B. PLANNED PLANT MODIFICATION EVALUATIONS I . None C. 2013 ECCS MODEL ASSESSMENTS I . Revised Heat Transfer Multiplier Distributions 2 . Error in Burst Strain Application D. OTHER* I . None LICENSING BASIS PCT + PCT ASSESSMENTS 1765 227 0 -2 25 0 PCT= 2015

• It is recommended that the licensee detennine ifthese PCT allocations should be considered with respect to I 0 CFR 50.46 reporting requirements.

2 3 4 Notes (a), (b) References I . WCAP-17783-P, "Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for Prairie Island Units 1 and 2 with Replacement Steam Generators Using ASTRUM Methodology," June 2013. Notes: 2 . LTR-LTS-12-414, "Prairie Island Units I and 2, 10 CFR 50.46 Notification and Reporting for Fuel Pellet Thennal Conductivity Degradation and Peaking Factor Bumdown," September 20, 2012. 3 , LTR-LIS-13-366, Revision 1, "Prairie Island Units I and 2 10 CFR 50.46 Report for Revised Heat Transfer Multiplier Distributions," August 2013. 4 . LTR-LIS-14-50, "Prairie Island Units I and 2 I 0 CFR 50.46 Report for the HOTSPOT Burst Strain Error Correction," January 2014. (a) This evaluation credits peaking factor bumdown, see Reference

2. (b) The reporting text and line item originally identified for Unit 1 in Reference 2 is applicable to Unit 2 with RSGs.

Attachment to LTR-LIS-14-98 March 17,2014 Page 24 of27 Westinghouse LOCA Peale Clad Temperature Summary for ASTRUM Best Estimate Large Break Plant Name: Prairie Island Unit 2 Xcel Energy, Inc 2/27/2014 OSG Utility Name: Revision Date: Analysis Information EM: ASTRUM (2004) FQ: 2.5 Fuel: 422 Vantage+ Notes: Analysis Date: FdH: SGTP(%): 11/30/2007 1.77 25 Limiting Break Size: Split Clad Temp (DF) Ref. LICENSING BASIS Analysis-Of-Record PCT PCT ASSESSMENTS (Delta PCT) A. PRIOR ECCS MODEL ASSESSMENTS I . Evaluation of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Bumdown B. PLANNED PLANT MODIFICATION EVALUATIONS I . None C. 2013 ECCS MODEL ASSESSMENTS I . Revised Heat Transfer Multiplier Distributions D. OTHER* I

• None LICENSING BASIS PCT + PCT ASSESSMENTS 16:L3 340 0 -16 0 PCT= 1947

• It is recommended that the licensee determine if these PCT allocations should be considered with respect to 10 CFR 50.46 reporting requirements.

References 2 3 Notes (a) I . WCAP-16891-P, "Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for the Prairie Island Nuclear Plant Unit 2 Using ASTRUM Methodology," June 2008. Notes: 2 . LTR-LIS-12-414, "Prairie Island Units I and 2, 10 CPR 50.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Bumdown," September 20, 2012. 3 . LTR-LIS-13-366, Revision I, "Prairie Island Units I and 2 10 CFR50.46 Report for Revised Heat Transfer Multiplier Distributions," August 2013. (a) This credits peaking factor bumdown, see Reference

2.

Attachment to LTR-LIS-14-98 March 17,2014 Page 25 of27 Westinghouse LOCA Peak Clad Temperature Summary for Appendix K Small Break Plant Name: Utility Name: Revision Date: Prairie Island Unit 2 Xcel Energy, Inc 2/27/2014 Analysis Information EM: NOTRUMP Analysis Date: 1/21/2008 1.77 Limiting Break Size: 3 inch FQ: 2.5 FdH: Fuel: 422 Vantage+ SGTP (%): 10 Notes: Zirlo (14Xl4), ARE.V A RSG LICENSING BASIS PCT PCT ASSESSMENTS (Delta PCT) A. PRIOR ECCS MODEL ASSESSMENTS 1 . None B. PLANNED PLANT MODIFICATION EVALUATIONS 1

• None C. 2013 ECCS MODEL ASSESSMENTS I

• None D. OTHER* I . None LICENSING BASIS PCT + PCT ASSESSMENTS Clad Temp (DF) 959 0 0 0 0 PCT= 959

• It is recommended that the licensee detennine if these PCT allocations should be considered with respect to I 0 CFR 50.46 reporting requirements.

References I , LTR-LIS-08-158, "Transmittal of Future Prairie Island Units 1 and 2 PCT Summaries," February 2008. Ref. 1, 2 2 . LTR-LIS-13-274, "Prairie Island Units I and 2, 10 CFR 50.46 Summary Sheets for the Evaluation to Support the Unit 2 Installation of AREVA Model 56/19 Replacement Steam (RSGs)," June 2013. Notes: (a) The Unit I AOR is applicable to Unit 2 with the RSGs installed.

Notes a Attachment to March 17,2014 Page 26 of27 Westinghouse LOCA Peak Clad Temperature Summary for Appendix K Small Break Plant Name: Utility Name: Revision Date: Prairie Island Unit 2 Xcel Energy, Inc 2/27/2014 Analysis Information EM: NOTRUMP FQ: 2.5 Fuel: Notes: 422 Vantage+ Zirlo (14X14) Analysis Date: FdH: . SGTP(%): 1/21/2008 1.77 25 OSG Limiting Break Size: 2 inch Clad Temp (DF) Ref. Notes LICENSING BASIS PCT PCT ASSESSMENTS (Delta PCT) A. PRIOR ECCS MODEL ASSESSMENTS 1 . None B. PLANNED PLANT MODIFICATION EVALUATIONS 1 . None C. 2013 ECCS MODEL ASSESSMENTS 1 .None D. OTHER* 1 . None LICENSING BASIS PCT + PCT ASSESSMENTS 965 0 0 0 0 PCT= 965

• It is recommended that the licensee detennine ifthese PCT allocations should be considered with respect to 10 CFR 50.46 reporting requirements.

References I

• LTR-LIS-08-158, "Trnnsmittal ofFuture Prairie Island Units 1 and 2 PCT Summaries," February 2008. Notes: None 1 Attachment to 10 CFR 50.46 Reporting SharePoint Site Check: EMs applicable to Prairie Island: Realistic Large Break-ASTRUM (2004) Appendix K Small Break-NOTRUMP 2013 Issues Transmittal Letter Issue Description LTR-LIS-13-219 10 CFR 50.46 Report for the Initial Fuel Pellet Average Temp. Uncert. Calculation LTR-LIS-13-346 10 CFR 50.46 Notification and Reporting for WCOBRA-TRAC Changes and Error Corrections LTR-LIS-13-366, Prairie Island Units 1 and 2 10 CFR 50.46 Report for Revised Rev.1 Heat Transfer Multiplier Distributions LTR-LIS-14-50 Prairie Island Units 1 and 2 10 CFR 50.46 Report for the HOTSPOT Burst Strain Error Correction LTR-LIS-13-274 Prairie Island Units 1 and 2 10 CFR 50.46 Summary Sheets for the Evaluation to Support the Unit 2 Installation of AREV A Model56/19 Replacement Steam Generators (RSGs) March 17,2014 Page27 of27