L-18-037, Annual 10 CFR 50.46 Report of Changes to or Errors in Emergency Core Cooling System Evaluation Models

Annual 10 CFR 50.46 Report of Changes to or Errors in Emergency Core Cooling System Evaluation Models

ML18170A133
Person / Time
Site:	Beaver Valley
Issue date:	06/18/2018
From:	Bologna R FirstEnergy Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-18-037
Download: ML18170A133 (9)

Text

FENOC Beaver Valley Power Station FirstEnergy Nuclear Operating Company P.O. Box 4 Shippingport, PA 15077 Richard D. Bologna 724-682-5234 Site Vice President Fax: 724-643-8069 June 18, 2018 L-18-037 10 CFR 50.46 ATTN: Docume nt Control Desk U.S. Nuclear Regulato ry Commis sion Washing ton, DC 20555-0001 SUBJEC T:

Beaver Valley Power Station, Unit Nos. 1 and 2 Docket No. 50-334, License No. DPR-66 Docket No. 50-412, License No. NPF-73 2017 Annual 10 CFR 50.46 Report of Changes to or Errors in Emergen cy Core Cooling System Evaluatio n Models In accordan ce with Title 10 of the Code of Federal Regulations, Part 50, Section 50.46(a)(3)(ii), FirstEne rgy Nuclear Operatin g Compan y (FENOC ) hereby submits the 2017 annual report of changes to or errors in emergen cy core cooling system evaluatio n models, or in the applicati on of the models, for the Beaver Valley Power Station, Unit Nos. 1 (BVPS-1 ) and 2 (BVPS-2 ).

The attachme nts provide a summar y list and descripti on of each change to or error in the acceptab le evaluatio n models that affects the peak fuel cladding tempera ture (PCT) calculation for various loss-of-c oolant accident s, as well as the estimate d PCT effects of the change or error.

There are no regulato ry commitm ents contained in this submittal. If there are any question s or if additiona l informat ion is required, please contact Mr. Thomas A. Lentz, Manage r - Nuclear Licensing & Regulato ry Affairs, at (330) 315-681 0 .

Richard D. Bologna

Beaver Valley Power Station, Unit Nos. 1 and 2 L-18-037 Page 2 Attachments:

1. Summary of 2017 Peak Fuel Cladding Temperature (PCT) Effects for Beaver Valley Power Station (BVPS) Loss-of-Coolant Accident (LOCA) Transients

2. Descriptions of 2017 Emergency Core Cooling System (ECCS) Evaluation Model Changes or Errors cc: NRG Region I Administrator NRG Resident Inspector NRG Project Manager Director BRP/DEP Site BRP/DEP Representative

Attachment 1 L-18-037 Summa ry of 2017 Peak Fuel Cladding Temperature (PCT) Effects for Beaver Valley Power Station (BVPS) Loss-of-Coolant Accident (LOCA) Transients Page 1 of 1 Beaver Valley Power Station, Unit 1 Large Break Small Break LOCA LOCA PCT or PCT PCT or PCT Change Change Licensing Basis PCT at BEGINNING of 2017 1840°F 1895°F 2017 Activity EM Changes General Computer Code Maintenance 0°F 0°F (refer to page 1 of Attachment 2)

EM Errors Vessel Average Temperature Uncertainty 0°F 0°F (refer to page 2 of Attachment 2)

Error in Upper Plenum Fluid Volume NIA 0°F Calculation (refer to page 3 of Attachment 2)

Inconsistent Application of Numerical 0°F N/A Ramp (refer to page 4 of Attachment 2)

Inappropriate Resetting of Transverse 0°F N/A Liquid Mass Flow (refer to page 5 of Attachment 2)

Steady-State Fuel Temperature 0°F N/A Calibration Method (refer to page 6 of Attachment 2)

Licensing Basis PCT at END of 2017 1840°F 1895°F Beaver Valley Power Station, Unit 2 Large Break Small Break LOCA LOCA PCT or PCT PCT or PCT Change Change Licensing Basis PCT at BEGINNING of 2017 1839°F 1917°F 2017 Activity EM Changes General Computer Code Maintenance 0°F 0°F (refer to page 1 of Attachment 2)

EM Errors Vessel Average Temperature Uncertainty 0°F 0°F (refer to page 2 of Attachment 2)

Error in Upper Plenum Fluid Volume N/A 0°F Calculation (refer to page 3 of Attachment 2)

Inconsistent Application of Numerical 0°F NIA Ramp (refer to page 4 of Attachment 2)

Inappropriate Resetting of Transverse 0°F N/A Liquid Mass Flow (refer to page 5 of Attachment 2)

Licensing Basis PCT at END of 2017 1839°F 1917°F

Attachment 2 L-18-037 Descriptions of 2017 Emergency Core Cooling System (ECCS)

Evaluation Model Changes or Errors Page 1 of 6 GENERAL COMPUTER CODE MAINTENANCE

Background

Various changes have been made to enhance the usability of computer 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 computer 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 of WCAP-13451, "Westinghouse Methodology for Implementation of 10 CFR 50.46 Reporting," October 1992.

Affected Evaluation Model(s)

1. 1996 Westinghouse Best-Estimate Large Break Loss of Coolant Accident (LOCA)

Evaluation Model (Applicable to BVPS-2)

2. 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using Automated Statistical Treatment of Uncertainty Method (ASTRUM)

(Applicable to BVPS-1)

3. 1985 Westinghouse Small Break LOCA Evaluation Model with NOTRUMP (Applicable to BVPS-1 and BVPS-2)

Estimated Effect The nature of these changes leads to an estimated peak cladding temperature (PCT) impact of 0°F for both BVPS-1 and BVPS-2.

Attachment 2 L-18-037 Page 2 of 6 VESSEL AVERAGE TEMPERATURE UNCERTAINTY

Background

A hysteresis issue was identified for plants with Weed Resistance Temperature Detectors (RTDs) supplied to Westinghouse, which resulted in an additional uncertainty of +0.1 °F bias (indicated higher than actual) that applies to the reactor coolant system (RCS) average temperature accident analysis initial condition uncertainty. This discrepancy has been evaluated for impact on existing large and small break LOCA analysis results, and its resolution represents a non-discretionary change in accordance with Section 4.1.2 of WCAP-13451.

Affected Evaluation Model(s)

1. 1985 Westinghouse Small Break LOCA Evaluation Model with NOTRUMP (Applicable to BVPS-1 and BVPS-2)

2. 1996 Westinghouse Best-Estimate Large Break LOCA Evaluation Model (Applicable to BVPS-2)

3. 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM (Applicable to BVPS-1)

Estimated Effect This issue was evaluated as having a negligible impact on existing large and small break LOCA analysis results, leading to an estimated PCT impact of 0°F for both BVPS-1 and BVPS-2.

Attachment 2 L-18-037 Page 3 of 6 ERROR IN THE UPPER PLENUM FLUID VOLUME CALCULATION

Background

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 Appendix K small break LOCA analyses. The corrected value represents a less than 1

percent change in the total RCS fluid volume and will be incorporated on a forward

-fit basis, based on the evaluated impact on the current licensing basis analysis results.

This change represents a non-discretionary change in accordance with Section 4.1.2 of WCAP-13451.

Affected Evaluation Model(s)

1. 1985 Westinghouse Small Break LOCA Evaluation Model with NOTRUMP (Applicable to BVPS-1 and BVPS-2)

Estimated Effect The differences in the upper plenum fluid volume are relatively minor and have been evaluated to have a negligible effect on small break LOCA analysis results, leading to an estimated PCT impact of 0°F for BVPS-1 and BVPS-2.

Attachment 2 L-18-037 Page 4 of 6 INCONSISTENT APPLICATION OF NUMERICAL RAMP APPLIED TO THE ENTRAINED LIQUID/VAPOR INTERFACIAL DRAG COEFFICIENT

Background

A numerical ramp, which was used to account for the disappearance of the entraine d

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 interfac ial drag coefficient was used in the entrained liquid and vapor momentum equations.

This item represents a non-discretionary change in accordance with Section 4.1.2 of WCAP-13451.

Affected Evaluation Model(s)

1. 1996 Westinghouse Best-Estimate Large Break LOCA Evaluation Model (Applicable to BVPS-2)

2. 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRU M

(Applicable to BVPS-1)

Estimated Effect Based on the code validation results, the impact of correcting the error is estimated to have a 0°F impact on PCT for both BVPS-1 and BVPS-2.

Attachment 2 L-18-037 Page 5 of 6 INAPPROPRIATE RESETTING OF TRANSVERSE LIQUID MASS FLOW

Background

In the WCOBRA/TRAC routine, which evaluates the mass and energy residual error of the time step solution, the transverse liquid mass flow is reset as the liquid phase disappears. 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.

This item represents a non-discretionary change in accordance with Section 4.1.2 of WCAP-13451.

Affected Evaluation Model{s)

1. 1996 Westinghouse Best-Estimate Large Break LOCA Evaluation Model (Applicable to BVPS-2)

2. 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM (Applicable to BVPS-1)

Estimated Effect 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 for both BVPS-1 and BVPS-2.

Attachment 2 L-18-037 Page 6 of 6 STEADY-STATE FUEL TEMPERATURE CALIBRATION METHOD

Background

In the ASTRUM best-estimate (BE) large break LOCA evaluation model, the steady-state fuel pellet temperature calibration method involves solving for the hot gap width 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 defined by Table 12-6 of WCAP-16009-P/NP-A, "Realistic Large-Break LOCA Evaluation Methodology Using the Automated Statistical Treatment of Uncertainty Method (ASTRUM)," January 2005.

This issue has been evaluated to estimate the impact on ASTRUM BE large break LOCA 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)

1. 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM (Applicable to BVPS-1)

Estimated Effect 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 for BVPS-1.