WBL-21-050, CFR 50.46 - 30-Day Event Report

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CFR 50.46 - 30-Day Event Report
ML21301A130
Person / Time
Site: Watts Bar Tennessee Valley Authority icon.png
Issue date: 10/28/2021
From: Anthony Williams
Tennessee Valley Authority
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
WBL-21-050
Download: ML21301A130 (8)
v • d • e


Text

Post Office Box 2000, Spring City, Tennessee 37381

WBL-21-050

October 28, 2021

10 CFR 50.4 10 CFR 50.46

U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 0001

Watts Bar Nuclear Plant, Unit 2 Facility Operating License No. NPF-96 NRC Docket No. 50-391

Subject:

10 CFR 50.46 Day Report for Watts Bar Nuclear Unit 2

Reference:

TVA Letter to NRC, WBL-21-009, 10 CFR 50.46 Annual Report for Watts Bar Nuclear Plant Units 1 and 2, dated March 4, 2021 (ML21063A176)

In accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.46, "Acceptance Criteria for ECCS for Light-Water Nuclear Power Reactors," paragraph (a)(3)(ii), the purpose of this letter is to provide the 30-day report of changes in the emergency core cooling system (ECCS) evaluation model for the Watts Bar Nuclear Plant (WBN) Unit 2. 10 CFR 50.46 requires that a holder of an operating license is required to report significant changes and errors affecting an ECCS evaluation model to the NRC within 30 days when the cumulative sum of the absolute magnitudes of resulting peak cladding temperature (PCT) changes exceeds 50°F. This report is the result of the implementation of a Reactor Coolant System (RCS) average temperature (T avg) window and results in a 0°F change in PCT. Because the accumulated changes and errors in the large-break loss of coolant accident (LBLOCA) analysis from previous years are greater than 50°F (Reference),

a 30-day report is required in accordance with 10 CFR 50.46(a)(3)(ii). The change to the T avg operating window was implemented on WBN Unit 2 on September 30, 2021.

The enclosure to this letter provides the 30-day report of significant changes to WBN Unit 2 and describes the nature and the estimated effect on the limiting ECCS analysis of changes since the referenced letter for WBN Unit 2.

ENCLOSURE

Watts Bar Nuclear Plant Unit 2, 10 CFR 50.46 30-Day Report

In accordance with the reporting requirements of Title 10 of the Code of Federal Regulations (10 CFR) 50.46(a)(3)(ii), Tennessee Valley Authority (TVA) is providing the following 30-day report of changes in the emergency core cooling system (ECCS) evaluation model for the Watts Bar Nuclear Plant (WBN) Unit 2. 10 CFR 50.46 requires that a holder of an operating license is required to report significant changes and errors affecting an ECCS evaluation model to the NRC within 30 days when the cumulative sum of the absolute magnitudes of resulting peak cladding temperature (PCT) changes exceeds 50°F. This report is the result of the implementation of a Reactor Coolant System (RCS) average temperature (Tavg) window and results in a 0°F change in PCT. Because the accumulated changes and errors in the large-break loss of coolant accident (LBLOCA) analysis from previous years are greater than 50°F, a 30-day report is required in accordance with 10 CFR 50.46(a)(3)(ii). The change to the Tavg operating window was implemented on WBN Unit 2 on September 30, 2021.

TVA submitted the last 10 CFR 50.46 annual report for WBN Units 1 and 2 to the Nuclear Regulatory Commission in Reference 1 of this Enclosure.

Table 1 lists the changes and errors in the large break LOCA (LBLOCA) analysis for WBN Unit 2 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 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 1 and 2.

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

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.

WBL-21-050 E 1 of 6 ENCLOSURE

Table 1 Watts Bar Unit 2 LBLOCA

Year Description LBLOCA LBLOCA PCT (°F) PCT (°F) Note Reference 2013 LBLOCA AOR PCT 1766 - - - - - - 6

2013 Elevations for Heat Slab Temperature Initialization 0 0 - - - 8

2013 Heat Transfer Model Error Corrections 0 0 - - - 8

2013 Correction to Heat Transfer Node Initialization 0 0 - - - 8

2013 Mass Conservation Error Fix 0 0 - - - 8

2013 Correction to Split Channel Momentum Equation 0 0 - - - 8

2013 Heat Transfer Logic Correction for Rod Burst Calculation 0 0 - - - 8

2013 Changes to Vessel Superheated Steam Properties 0 0 - - - 8

2013 Update to Metal Density Reference Temperatures 0 0 - - - 8

2013 Decay Heat Model Error Corrections 0 0 - - - 8

2013 Correction to the Pipe Exit Pressure Drop Error 0 0 - - - 8

2013 WCOBRA/TRAC File Dimension Error Correction 0 0 - - - 8

2013 Revised Heat Transfer Multiplier Distributions -55 55 - - - 8

Initial Fuel Pellet Average 2013 Temperature Uncertainty Calculation 0 0 - - - 8

2013 HOTSPOT Burst Strain Error 0 0 - - - 5 Cold Leg Accumulator Injection 2014 Lines Hydraulic Resistance 0 0 - - - 4 Changes

2014 General Computer Code Maintenance 0 0 - - - 9

WBL-21-050 E 2 of 6 ENCLOSURE

Table 1 Watts Bar Unit 2 LBLOCA

Year Description LBLOCA LBLOCA PCT (°F) PCT (°F) Note Reference

2014 Errors in Decay Group Uncertainty Factors 0 0 - - - 9

2014 Treatment of Burnup Effects on Thermal Conductivity Degradation 0 0 - - - 9 2016 General Code Maintenance 0 0 - - - 11 2016 Clad Oxidation Calculation 0 0 - - - 11 Use of Steam Tables in Upper 2016 Head Fluid Temperature 0 0 - - - 11 Calculations 2016 Lower Support Plate Heat Conductor Surface Area 0 0 - - - 11 LOTIC2 Net Free Volume Direction 2016 of Conservatism and Ice Melt 0 0 - - - 11 Condition 2016 LOTIC2 Calculation of the Thermodynamic Properties of Air 0 0 - - - 11

2017 General Code Maintenance 0 0 - - - 12 Entrained Liquid / Vapor Interfacial 2017 Drag Coefficient Calculation 0 0 - - - 12 Inconsistency 2017 Resetting of Transverse Liquid Mass Flow 0 0 - - - 12

2017 Steady State Fuel Temperature Calibration non-Conservatisms 0 0 - - - 12

2018 Vapor Temperature Resetting 0 0 - - - 3 2019 Core Barrel Heat Slab Error 0 0 - - - 2 2019 General Code Maintenance 0 0 - - - 2

2019 Removal of the Vessel Interfacial Heat Transfer Limit 0 0 - - - 2

2021 Tavg Window 0 0 1 - - -

Updated (net) licensing basis

- - - PCT 1711 - - - - - - - - -

(AOR PCT + PCT)

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

WBL-21-050 E 3 of 6 ENCLOSURE

Table 2 Watts Bar Unit 2 SBLOCA

Year Description SBLOCA PCT SBLOCA Note Reference

(°F) PCT

(°F) 2010 SBLOCA AOR PCT 1184 - - - - - - 7 Cold Leg Accumulator Injection 2014 Lines Hydraulic Resistance 0 0 - - - 4 Changes

2014 General Computer Code Maintenance 0 0 - - - 9

2014 Fuel Rod Gap Conductance Error 0 0 - - - 9

2014 Radiation Heat Transfer Model Error 0 0 - - - 9 SBLOCTA Pre-DNB Cladding 2014 Surface Heat Transfer Coefficient Calculation 0 0 - - - 9

2015 General Computer Code Maintenance 0 0 - - - 10

2015 AFW Temperature Increase During Cold Leg Recirculation 0 0 - - - 10

2016 Plant-Specific Upper Head Geometric Data 0 0 - - - 11

2016 Reduced RWST Useable Volume 0 0 - - - 11 2017 Increased SI injection time delay 0 0 - - - 12 2017 General Code Maintenance 0 0 - - - 12

2017 Upper Plenum Fluid Volume Reduction 0 0 - - - 12

2018 UO2 Fuel Pellet Heat Capacity 0 0 - - - 3 2021 Tavg Window 0 0 2 - - -

Updated (net) licensing basis

- - - PCT 1184 - - - - - - - - -

(AOR PCT + PCT)

Cumulative sum of PCT

- - - changes PCT - - - 0 - - - - - -

WBL-21-050 E 4 of 6 ENCLOSURE

Notes:

1. Westinghouse performed an evaluation to support the implementation of a T avg operating range on the LBLOCA analysis. The results showed that the high T avg (588.2°F) condition was limiting compared to the low Tavg condition (581.2°F) permitted by the T avg operating range. Therefore, the estimated PCT impact for the Tavg window implementation is 0°F.
2. Westinghouse performed an evaluation to support the implementation of T avg operating range on the SBLOCA analysis. The Tavg window changed from a nominal 588.2°F to a range of 581.2°F -

588.2°F, and additionally, the evaluation considered +/-6°F for T avg uncertainties. The Tavg window has been evaluated for the NOTRUMP Evaluat ion Model (NOTRUMP-EM) SBLOCA analysis basis considering the original steam generators (OSGs). The estimated effect of the T avg window implementation for Watts Bar Unit 2 with the OSGs was qualitatively evaluated to be a 0°F peak cladding temperature impact.

WBL-21-050 E 5 of 6 ENCLOSURE

References:

1. TVA Letter to NRC, WBL-21-009, 10 CFR 50.46 Annual Report for Watts Bar Nuclear Plant Units 1 and 2, dated March 4, 2021 (ML21063A176)
2. TVA Letter to NRC, WBL-20-007, 10 CFR 50.46 Day and Annual Report for Watts Bar Nuclear Plant Units 1 and 2, dated March 5, 2020 (ML20065F821)
3. TVA Letter to NRC, WBL-19-019, 10 CFR 50.46 Day and Annual Report for Watts Bar Nuclear Plant Units 1 and 2, dated March 7, 2019 (ML19066A046)
4. TVA letter to NRC, CNL-15-034, 10 CFR 50.46 Day Report for Watts Bar, Unit 2 dated February 6, 2015 (ML15037A725)
5. 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)
6. WCAP-17093-P, Revision 1, Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for Watts Bar Unit 2 Nuclear Plant Using the ASTRUM Methodology, June 2013
7. WBT-D-1460, Watts Bar Unit 2 (WBT) SBLOCA A nalysis: Final Transmittal of Analysis Summary Report, January 21, 2010
8. 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)
9. 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)
10. TVA letter to NRC, CNL-16-057, 10 CFR 50.46 - Annual Report for Watts Bar Nuclear Plant Units 1 and 2, dated March 18, 2016 (ML16081A248)
11. TVA Letter to NRC, 10 CFR 50.46 Day and Annual Report for Watts Bar Nuclear Plant Units 1 and 2, dated March 8, 2017 (ML17067A079)
12. TVA Letter to NRC, CNL-18-040, 10 CFR 50.46 Day and Annual Report for Watts Bar Nuclear Plant Units 1 and 2, dated March 7, 2018 (ML18066A730)

WBL-21-050 E 6 of 6

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