CNL-18-040, Transmittal of 10 CFR 50.46 - 30-Day and Annual Report

Transmittal of 10 CFR 50.46 - 30-Day and Annual Report

ML18066A730
Person / Time
Site:	Watts Bar
Issue date:	03/07/2018
From:	Simmons P Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
CNL-18-040
Download: ML18066A730 (16)

Text

Tennessee Valley Authority, 1101 Market Street, Chattanooga, TN 37402 CNL-18-040 March 7, 2018 10 CFR 50.4 10 CFR 50.46 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Units 1 and 2 Facility Operating License NPF-90 and NPF-96 NRC Docket Nos. 50-390 and 50-391

Subject:

10 CFR 50.46 Day and Annual Report for Watts Bar Nuclear Plant Units 1 and 2

References:

1. TVA Letter to NRC, 10 CFR 50.46 Day and Annual Report for Watts Bar, Units 1 and 2, dated March 8, 2017 (ML17067A079)

2. TVA Letter to NRC, 10 CFR 50.46 Day Report for Watts Bar Nuclear Plan Unit 1, dated August 21, 2017 (ML17235A905)

The purpose of this letter is to provide the annual report of changes and errors to the calculated peak cladding temperature (PCT) for the Watts Bar Nuclear Plant (WBN) Units 1 and 2, Emergency Core Cooling System (ECCS) evaluation model. This report is required in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.46, Acceptance Criteria for Emergency Core Cooling Systems for Light-Water Nuclear Power Reactors, paragraph (a)(3)(ii).

The Tennessee Valley Authority (TVA) submitted the last 10 CFR 50.46 annual report for WBN Units 1 and 2 to the Nuclear Regulatory Commission (NRC) in Reference 1 and a subsequent 30-day report for WBN Unit 1 in Reference 2. As indicated in the enclosure, there are no changes to the current updated (net) licensing basis PCT for the WBN Unit 1 large break loss of coolant accident (LBLOCA) and the updated (net) licensing basis PCT for the WBN Unit 1 small break loss of coolant accident (SBLOCA). Similarly, there are no changes to the current updated (net) licensing basis PCT for the WBN Unit 2 LBLOCA and the updated (net) licensing basis PCT for the WBN Unit 2 SBLOCA.

U.S. Nuclear Regulatory Commission Page 2 March 7, 2018 The enclosure also serves as the 30-day report in accordance with 10 CFR 50.46(a)(3)(ii),

which states that a holder of an operating license or construction permit is required to report changes and errors affecting an ECCS evaluation model to the NRC within 30 days when the cumulative sum of the absolute magnitudes of resulting PCT changes exceeds 50°F. The licensee is also required to include with the report a proposed schedule for providing a 1

reanalysis or taking other action as may be needed to show compliance with the 10 CFR 50.46 requirements. Westinghouse performs the LOCA analysis for WBN and Westinghouse submitted a list of changes and errors to the LOCA analysis to TVA on February 15, 2018. All the submitted changes and errors result in a 0°F change in PCT, but because the accumulated changes and errors from previous years are more than 50°F (with the exception of the WBN Units 1 and 2 SBLOCA analysis), a 30-day report is required.

As presented in this report, compliance with 1O CFR 50.46 requirements is demonstrated by the calculated PCT for both WBN units remaining below the 2200°F limit. Therefore, TVA has concluded that no proposed schedule for providing a reanalysis or other action is required . No further actions are needed to show compliance with 10 CFR 50.46 requirements.

There are no regulatory commitments in this letter. Please address any questions regarding this response to Kimberly Hulvey at (423) 365-7720.

Paul Simmons Site Vice President Watts Bar Nuclear Plant

Enclosure:

Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017 cc (Enclosures):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant Division of Radiological Health - State of Tennessee

ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNITS 1 and 2 DOCKET NOs . 50-390 and 50-391 Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017 In accordance with the reporting requirements of Title 10 of the Code of Federal Regulations (10 CFR) 50.46(a)(3)(ii), the Tennessee Valley Authority (TVA) is providing the following summary of the limiting design basis loss of coolant accident (LOCA) analysis results established using the current Watts Bar Nuclear Plant (WBN) Emergency Core Cooling System (ECCS) evaluation models for WBN Units 1 and 2. This report describes the changes and errors affecting the calculated peak cladding temperatures (PCTs) since the last analysis of record was submitted to the Nuclear Regulatory Commission (NRC).

TVA submitted the last 10 CFR 50.46 annual report for WBN Units 1 and 2 to the NRC in Reference 1 and a subsequent 10 CFR 50.46 30-Day Report for WBN Unit 1 in Reference 22.

Table 1 lists the changes and errors in the large break LOCA (LBLOCA) analysis for WBN Unit 1 since the analysis of record (AOR) and the associated effect on PCT. Table 2 lists the changes and errors in the small break LOCA (SBLOCA) analyses for WBN Unit 1 since the AOR and the associated effect on PCT. The changes that were not previously identified in Reference 1 and 22 are described in the notes to Tables 1 and 2.

Table 3 lists the changes and errors in the LBLOCA analysis for WBN Unit 2 since the AOR and the associated effect on PCT. Table 4 lists the changes and errors in the SBLOCA analyses for WBN Unit 2 since the AOR and the associated effect on PCT. The changes that were not previously identified in Reference 1 are described in the notes to Tables 3 and 4.

The updated (net) licensing basis PCT for the LBLOCA and SBLOCA remain unchanged for WBN Units 1 and 2 from the last annual report.

This report also serves as the 30-day report in accordance with 10 CFR 50.46(a)(3)(ii), which states that a holder of an operating license or construction permit is required to report changes and errors affecting an ECCS evaluation model to the NRC within 30 days when the cumulative sum of the absolute magnitudes of resulting PCT changes exceeds 50°F. The licensee is also required to include with the report, a proposed schedule for providing a reanalysis or taking other action as may be needed to show compliance with the 10 CFR 50.46 requirements. Westinghouse performs the LOCA analysis for WBN; Westinghouse submitted a list of changes and errors to the LOCA analysis to TVA on February 15, 2018. All the submitted changes and errors result in a 0°F change in PCT, but because the accumulated changes and errors from previous years are more than 50F, a 30-day report is required.

As presented in this report, compliance with 10 CFR 50.46 requirements is demonstrated by the calculated PCT for both WBN units remaining below the 2200°F limit. Therefore, TVA has concluded that no proposed schedule for providing a reanalysis or other action is required.

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ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNITS 1 and 2 DOCKET NOs . 50-390 and 50-391 Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017 Table 1 Watts Bar Unit 1 LBLOCA Reflood 1 Reflood 2 PCT PCT PCT PCT Note Reference Year Description (°F) (°F) (°F) (°F) 1998 BE LBLOCA AOR PCT 1656 --- 1892 --- --- 3 1999 Vessel Channel DX Error 56 56 -4 4 --- 4 2000 Increased Accumulator Room Temperature 4 4 4 4 --- 4 Evaluation 2000 1.4% Uprate Evaluation 12 12 12 12 --- 4 2000 Accumulator Line/Pressurizer Surge Line -37 37 -131 131 --- 4 Data Evaluation 2000 MONTECF Decay Heat 4 4 4 4 --- 5 Uncertainty Error 2001 WBN Specific LBLOCA Vessel Geometry Input 0 0 0 0 --- 6 Errors 2003 Input Error Resulting in 60 60 0 0 --- 7 Incomplete Solution Matrix 2003 Tavg Bias Error 8 8 8 8 --- 7 2004 Increased Stroke Time for 0 0 0 0 --- 8 ECCS Valves 2004 Revised Blowdown Heatup 5 5 5 5 --- 8 Uncertainty Distribution 2006 Replacement Steam

-50 50 -10 10 --- 9 Generators (D3 to 68AXP) 2006 HOTSPOTTM Fuel 0 0 65 65 --- 9 Relocation Error 2012 PMID/PBOT Violation 20 20 20 20 --- 10, 11 Evaluation 2012 TCD and Peaking Factor 114 114 15 15 --- 10, 11 Burndown E 2 of 14

ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNITS 1 and 2 DOCKET NOs . 50-390 and 50-391 Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017 Table 1 Watts Bar Unit 1 LBLOCA Reflood 1 Reflood 2 PCT PCT PCT PCT Note Reference Year Description (°F) (°F) (°F) (°F) 2013 WCOBRA/TRACTM History 0 0 0 0 --- 12 File Dimension Error 2013 General Code Maintenance 0 0 0 0 --- 13 TM 2013 HOTSPOT Burst Temperature Calculation for 0 0 0 0 --- 13 ZIRLOTM Cladding 2013 HOTSPOTTM Iteration Algorithm for Calculation 0 0 0 0 --- 13 Initial Fuel Pellet Average Temperature 2013 WCOBRA/TRACTM Automated Restart Process 0 0 0 0 --- 13 Logic Error 2013 Rod Internal Pressure 0 0 0 0 --- 13 Calculation Error 2013 Elevations for Heat Slab 0 0 0 0 --- 14 Temperature Initialization 2013 Heat Transfer Model Error 0 0 0 0 --- 14 Corrections 2013 Correction to Heat Transfer 0 0 0 0 --- 14 Node Initialization 2013 Mass Conservation Error Fix 0 0 0 0 --- 14 2013 Correction to Split Channel 0 0 0 0 --- 14 Momentum Equation Heat Transfer Logic 2013 Correction for Rod Burst 0 0 0 0 --- 14 Calculation Changes to Vessel 2013 Superheated Steam 0 0 0 0 --- 14 Properties Update to Metal Density 2013 0 0 0 0 --- 14 Reference Temperatures E 3 of 14

ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNITS 1 and 2 DOCKET NOs . 50-390 and 50-391 Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017 Table 1 Watts Bar Unit 1 LBLOCA Reflood 1 Reflood 2 PCT PCT PCT PCT Note Reference Year Description (°F) (°F) (°F) (°F)

Decay Heat Model Error 2013 0 0 0 0 --- 14 Corrections Correction to the Pipe Exit 2013 0 0 0 0 --- 14 Pressure Drop Error WCOBRA/TRAC File 2013 0 0 0 0 --- 14 Dimension Error Correction Revised Heat Transfer 2013 -40 40 -85 85 --- 14 Multiplier Distributions 2013 HOTSPOT Burst Strain Error 20 20 70 70 --- 15 General Computer Code 2014 Maintenance 0 0 0 0 --- 20 Revised Uncertainty in 2014 LBLOCA Monte Carl 0 0 0 0 --- 20 Simulations 2016 General Code Maintenance 0 0 0 0 --- 1 2016 Clad Oxidation Calculation 0 0 0 0 --- 1 LOTIC2 Net Free Volume 2016 Direction of Conservatism 0 0 0 0 --- 1 and Ice Melt Condition LOTIC2 Calculation of the 2016 Thermodynamic Properties 0 0 0 0 --- 1 of Air Increased Safety Injection 2016 Time Delay with Offsite 0 0 0 0 --- 1 Power Available Increase in ECCS pump 2017 0 0 0 0 22 injection delay time 2017 General Code Maintenance 0 0 0 0 1 ---

Entrained Liquid / Vapor 2017 Interfacial Drag Coefficient 0 0 0 0 2 ---

Calculation Inconsistency Resetting of the Transverse 2017 0 0 0 0 3 ---

Liquid Mass Flow E 4 of 14

ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNITS 1 and 2 DOCKET NOs . 50-390 and 50-391 Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017 Table 1 Watts Bar Unit 1 LBLOCA Reflood 1 Reflood 2 PCT PCT PCT PCT Note Reference Year Description (°F) (°F) (°F) (°F)

Updated (net) licensing basis PCT 1832

--- --- 1865 ---

AOR PCT + PCT Cumulative sum of PCT changes --- 430 --- 433

---

PCT Notes

1. Various changes have been made to enhance the usability of codes and to streamline future LBLOCA 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. The nature of these changes leads to an estimated PCT impact of 0°F.

2. A numerical ramp which was used to account for the disappearance of the entrained liquid phase was applied to the entrained liquid / vapor interfacial drag coefficient. The numerical ramp was applied such that the interfacial drag coefficient used in the solution of the entrained liquid and vapor momentum equations was not consistent. WCOBRA/TRAC was updated to apply the numerical ramp prior to usage of the interfacial drag coefficient in the momentum equations, such that a consistent interfacial drag coefficient was used in the entrained liquid and vapor momentum equations. Based on the code validation results, the impact of correcting the error is estimated to have a 0°F impact on PCT.

3. In the WCOBRA/TRAC routine which evaluates the mass and energy residual error of the time step solution, the transverse liquid mass flow was found to be resetting as the liquid phase disappeared. The routine is updated to remove the resetting of the transverse liquid mass flow since the routine is to only evaluate the residual error based on the time step solution values.

Based on the code validation results and limited applicability of the logic removed, correcting the error is estimated to have a 0°F impact on PCT.

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ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNITS 1 and 2 DOCKET NOs . 50-390 and 50-391 Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017 Table 2 Watts Bar Unit 1 SBLOCA SBLOCA SBLOCA Year Description PCT l PCT l Note Reference

(°F) (°F) 2006 SBLOCA AOR PCT 1132 --- --- 16 NOTRUMP-EMTM Evaluation of Fuel 2013 0 0 --- 13 Pellet TCD 2014 General Computer Code Maintenance 0 0 --- 20 2014 Fuel Rod Gap Conductance Error 0 0 --- 20 2014 Radiation Heat Transfer Model Error 0 0 --- 20 SBLOCTA Pre-DNB Cladding Surface 2014 0 0 --- 20 Heat Transfer Coefficient Calculation 2014 Evaluation of 8-inch Axial Blankets 0 0 --- 20 2015 General Computer Code Maintenance 0 0 --- 21 Auxiliary Feedwater (AFW) 2015 Temperature Increase During Cold 0 0 --- 21 Leg Recirculation Plant-Specific Upper Head Geometric 2016 0 0 --- 1 Data Increased Containment Spray Flow 2016 Rate and Reduced RWST Useable 0 0 --- 1 Volume 2017 General Code Maintenance 0 0 1

---

Upper Plenum Fluid Volume 2017 0 0 2 Reduction ---

Updated (net) licensing basis PCT

--- AOR PCT + PCT 1132 --- --- ---

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ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNITS 1 and 2 DOCKET NOs . 50-390 and 50-391 Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017 Table 2 Watts Bar Unit 1 SBLOCA SBLOCA SBLOCA Year Description PCT l PCT l Note Reference

(°F) (°F)

Cumulative sum of PCT changes

--- 0 --- ---

--- PCT Notes:

1. Various changes have been made to enhance the usability of codes and to streamline future LBLOCA 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. The nature of these changes leads to an estimated PCT impact of 0°F.

2. An error was found in the fluid volume calculation in the upper plenum where the support column outer diameter was being used instead of the inner diameter. The correction of this error lead to a reduction in the upper plenum fluid volume used in the SBLOCA analyses. The corrected values represent a less than 1% change in the total reactor coolant system (RCS) fluid volume. The differences in the upper plenum fluid volume are relatively minor and have been evaluated to have a negligible effect on SBLOCA analysis results, leading to an estimated PCT impact of 0°F.

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ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNITS 1 and 2 DOCKET NOs . 50-390 and 50-391 Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017 Table 3 Watts Bar Unit 2 LBLOCA Year LBLOCA LBLOCA Description Note Reference PCT (°F) PCT (°F) 2013 LBLOCA AOR PCT 1766 --- --- 17 Elevations for Heat Slab 2013 0 0 --- 19 Temperature Initialization Heat Transfer Model Error 2013 0 0 --- 19 Corrections Correction to Heat Transfer Node 2013 0 0 --- 19 Initialization 2013 Mass Conservation Error Fix 0 0 --- 19 Correction to Split Channel 2013 0 0 --- 19 Momentum Equation Heat Transfer Logic Correction for 2013 0 0 --- 19 Rod Burst Calculation Changes to Vessel Superheated 2013 0 0 --- 19 Steam Properties Update to Metal Density Reference 2013 0 0 --- 19 Temperatures 2013 Decay Heat Model Error Corrections 0 0 --- 19 Correction to the Pipe Exit Pressure 2013 0 0 --- 19 Drop Error WCOBRA/TRAC File Dimension 2013 0 0 --- 19 Error Correction Revised Heat Transfer Multiplier 2013 -55 55 --- 19 Distributions Initial Fuel Pellet Average 2013 Temperature Uncertainty Calculation 0 0 --- 19 2013 HOTSPOT Burst Strain Error 0 0 --- 15 Cold Leg Accumulator Injection 2014 Lines Hydraulic Resistance 0 0 --- 2 Changes E 8 of 14

ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNITS 1 and 2 DOCKET NOs . 50-390 and 50-391 Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017 Table 3 Watts Bar Unit 2 LBLOCA Year LBLOCA LBLOCA Description Note Reference PCT (°F) PCT (°F)

General Computer Code 2014 Maintenance 0 0 --- 20 Errors in Decay Group Uncertainty 2014 Factors 0 0 --- 20 Treatment of Burnup Effects on 2014 Thermal Conductivity Degradation 0 0 --- 20 2016 General Code Maintenance 0 0 --- 1 2016 Clad Oxidation Calculation 0 0 --- 1 Use of Steam Tables in Upper Head 2016 0 0 --- 1 Fluid Temperature Calculations Lower Support Plate Heat 2016 0 0 --- 1 Conductor Surface Area LOTIC2 Net Free Volume Direction 2016 of Conservatism and Ice Melt 0 0 --- 1 Condition LOTIC2 Calculation of the 2016 0 0 --- 1 Thermodynamic Properties of Air 2017 General Code Maintenance 0 0 1 ---

Entrained Liquid / Vapor Interfacial 2017 Drag Coefficient Calculation 0 0 2 ---

Inconsistency Resetting of Transverse Liquid 2017 0 0 3 ---

Mass Flow Steady State Fuel Temperature 2017 0 0 4 ---

Calibration non-Conservatisms Updated (net) licensing basis PCT

--- --- --- ---

(AOR PCT + PCT) 1711 Cumulative sum of PCT changes

--- --- 55 --- ---

PCT E 9 of 14

ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNITS 1 and 2 DOCKET NOs . 50-390 and 50-391 Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017 Notes:

1. Various changes have been made to enhance the usability of codes and to streamline future LBLOCA 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. The nature of these changes leads to an estimated PCT impact of 0°F.

2. A numerical ramp which was used to account for the disappearance of the entrained liquid phase was applied to the entrained liquid / vapor interfacial drag coefficient. The numerical ramp was applied such that the interfacial drag coefficient used in the solution of the entrained liquid and vapor momentum equations was not consistent. UCOBRA/TRAC was updated to apply the numerical ramp prior to usage of the interfacial drag coefficient in the momentum equations, such that a consistent interfacial drag coefficient was used in the entrained liquid and vapor momentum equations. Based on the code validation results, the impact of correcting the error is estimated to have a 0°F impact on PCT.

3. In the WCOBRA/TRAC routine which evaluates the mass and energy residual error of the time step solution, the transverse liquid mass flow was found to be resetting as the liquid phase disappeared. The routine is updated to remove the resetting of the transverse liquid mass flow since the routine is to only evaluate the residual error based on the time step solution values.

Based on the code validation results and limited applicability of the logic removed, correcting the error is estimated to have a 0°F impact on PCT.

4. In the Automated Statistical Treatment of Uncertainty Method (ASTRUM) Best-Estimate (BE)

LBLOCA Evaluation Model (EM), the steady-state fuel pellet temperature calibration method involves solving for the hot gap width (AGFACT) to calibrate the fuel temperature for each fuel rod.

In some infrequent situations, small non-conservatisms can occur in the calibration process such that the resulting fuel pellet temperature will be slightly lower than intended and outside the acceptable range of the methodology. A review of licensing basis analyses concluded that the potential non-conservatisms in the fuel pellet temperature calibration did not occur for the limiting analysis cases. Therefore, an estimated PCT impact of 0°F is assigned for 10 CFR 50.46 reporting purposes.

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ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNITS 1 and 2 DOCKET NOs . 50-390 and 50-391 Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017 Table 4 Watts Bar Unit 2 SBLOCA Year Description SBLOCA SBLOCA Note Reference PCT (°F) PCT (°F) 2010 SBLOCA AOR PCT 1184 --- --- 18 Cold Leg Accumulator Injection 2014 Lines Hydraulic Resistance 0 0 --- 2 Changes General Computer Code 2014 Maintenance 0 0 --- 20 2014 Fuel Rod Gap Conductance Error 0 0 --- 20 2014 Radiation Heat Transfer Model Error 0 0 --- 20 SBLOCTA Pre-DNB Cladding 2014 Surface Heat Transfer Coefficient 0 0 --- 20 Calculation General Computer Code 2015 Maintenance 0 0 --- 21 AFW Temperature Increase During 2015 Cold Leg Recirculation 0 0 --- 21 Plant-Specific Upper Head 2016 Geometric Data 0 0 --- 1 2016 Reduced RWST Useable Volume 0 0 --- 1 2017 Increased SI injection time delay 0 0 1 ---

2017 General Code Maintenance 0 0 2 ---

Upper Plenum Fluid Volume 2017 Reduction 0 0 3 ---

Updated (net) licensing basis PCT

--- --- --- ---

(AOR PCT + PCT) 1184 Cumulative sum of PCT changes

--- PCT 0 0 --- ---

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ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNITS 1 and 2 DOCKET NOs . 50-390 and 50-391 Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017

Notes

1. An increase in the safety injection (SI) delay time representing the time between reaching the low pressurizer pressure SI setpoint and full flow being delivered to the cold legs. The delay time has been increased from 27.0 to 37.0 seconds. The SBLOCA analysis methodology assumes a loss of offsite power coincident with reactor trip; therefore, the delay time includes emergency diesel generator start time and sequencing, ECCS pump start-up, and any required valve alignment changes. An additional 10 seconds of delay time has a negligible impact on the total make-up mass provided by the ECCS and the total change in reactor coolant system mass during the event. As such, this change is concluded to have an estimated PCT impact of 0°F.

2. Various changes have been made to enhance the usability of codes and to streamline future LBLOCA 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. The nature of these changes leads to an estimated PCT impact of 0°F.

3. An error was found in the fluid volume calculation in the upper plenum where the support column outer diameter was being used instead of the inner diameter. The correction of this error lead to a reduction in the upper plenum fluid volume used in the SBLOCA analyses. The corrected values represent a less than 1% change in the total RCS fluid volume. The differences in the upper plenum fluid volume are relatively minor and have been evaluated to have a negligible effect on SBLOCA analysis results, leading to an estimated PCT impact of 0°F.

E 12 of 14

ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNITS 1 and 2 DOCKET NOs . 50-390 and 50-391 Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017

References:

1. TVA Letter to NRC, 10 CFR 50.46 Day and Annual Report for Watts Bar, Units 1 and 2, dated March 8, 2017 (ML17067A079)

2. TVA letter to NRC, CNL-15-034, 10 CFR 50.46 Day Report for Watts Bar, Unit 2 dated February 6, 2015 (ML15037A725)

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

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

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

6. TVA letter to NRC, Watts Bar Nuclear Plant (WBN) Unit 1 - Emergency Core Cooling System (ECCS) Evaluation Model Changes - Annual Notification and Reporting for 2001, dated April 3, 2002 (ML021070404)

7. TVA letter to NRC, Watts Bar Nuclear Plant (WBN) Unit 1 - Emergency Core Cooling System (ECCS) Evaluation Model Changes Day Report and Revised Annual Notification and Reporting for 2003, dated April 19, 2004 (ML041130196)

8. TVA letter to NRC, Watts Bar Nuclear Plant (WBN) Unit 1 - Emergency Core Cooling System (ECCS) Evaluation Model Changes - Annual Notification and Reporting for 2004, dated April 9, 2005 (ML051120164)

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

10. TVA letter to NRC, Supplement to 10 CFR 50.46 Day Special Report, dated February 13, 2013 (ML13046A002)

11. TVA letter to NRC, 10 CFR 50.46 Day Special Report, dated October 18, 2012 (ML12296A254)

12. TVA letter to NRC, 10 CFR 50.46 Day Report for Watts Bar Unit 1, dated March 19, 2013 (ML13080A405)

13. TVA letter to NRC, 10 CFR 50.46 Day and Annual Report for 2012, dated April 25, 2013 (ML13120A005)

14. TVA letter to NRC, 10 CFR 50.46 - 30 day Report for Watts Bar, Unit 1, dated August 28, 2013 (ML13267A034)

15. TVA letter to NRC, CNL-14-035, 10 CFR 50.46 - 30 day Report for Watts Bar, Units 1 and 2, dated February 28, 2014. (ML14064A431)

16. WTV-RSG-06-015, LOCA & Non-LOCA Analysis Summary for Replacement Steam Generator, February 2006 E 13 of 14

ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNITS 1 and 2 DOCKET NOs . 50-390 and 50-391 Watts Bar Nuclear Plant, 10 CFR 50.46 30-Day and Annual Report for 2017

17. WCAP-17093-P, Revision 1, Best Estimate Analysis of the Large Break Loss of Coolant Accident for the Watts Bar Unit 2 Nuclear Plant Using the ASTRUM Methodology, June 2013

18. WBT-D-1460, Final Small Break LOCA Summary Report for WBN Unit 2, January 2010

19. TVA letter to NRC, Watts Bar Nuclear Plant, Unit 2 - Emergency Core Cooling System Evaluation Model Changes - 30 Day Report - 10 CFR 50.46 Notification, dated August 28, 2013.(ML13246A076)

20. TVA letter to NRC, CNL-15-053, 10 CFR 50.46 Day and Annual Report for Watts Bar, Units 1 and 2, dated March 30, 2015 (ML15098A124)

21. TVA letter to NRC, CNL-16-057, 10 CFR 50.46 - Annual Report for Watts Bar, Units 1 and 2, dated March 18, 2016 (ML16081A248)

22. TVA letter to NRC, 10 CFR 50.46 Day Report for Watts Bar Nuclear Plant Unit 1, dated August 21, 2017 (ML17235A905)

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