ML20196L862

NRR E-mail Capture - Watts Bar Nuclear Plant, Units 1 and 2 - Request for Additional Information Regarding Request to Implement the Full Spectrum LOCA Methodology

ML20196L862
Person / Time
Site:	Watts Bar
Issue date:	07/14/2020
From:	Michael Wentzel NRC/NRR/DORL/LPL2-2
To:	Wells R Tennessee Valley Authority
References
L-2020-LLA-0005
Download: ML20196L862 (7)

Text

From: Wentzel, Michael Sent: Tuesday, July 14, 2020 8:40 AM To: Wells, Russell Douglas Cc: Green, Kimberly

Subject:

Watts Bar Nuclear Plant, Units 1 and 2 - Request for Additional Information Regarding Request to Implement the FULL SPECTRUM' LOCA Methodology (EPID L-2020-LLA-0005)

Attachments: NON-PROPRIETARY - Request for Additional Information Regarding Request to Implement the FULL SPECTRUM LOCA Methodology (EPID L-2020-LLA-0005).pdf

Dear Mr. Wells,

By application dated January 17, 2020 (Agencywide Documents Access and Management System Accession No. ML20017A338), Tennessee Valley Authority (TVA) submitted a license amendment request for the Watts Bar Nuclear Plant, Units 1 and 2 (WBN). The proposed changes would: revise WBN Units 1 and 2 Technical Specification (TS) 5.9.5, Core Operating Limits Report, to replace the loss-of-coolant accident (LOCA) analysis evaluation model references with reference to the FULL SPECTRUM' Loss-of-Coolant Accident (FSLOCA') Evaluation Model analysis applicable to WBN Units 1 and 2, with replacement steam generators; revise the WBN Unit 2 Operating License Condition 2.C(4) to reflect the implementation of the FSLOCA Evaluation Model methodology; and, revise WBN Unit 1 TS 4.2.1, Fuel Assemblies, to delete discussion of Zircalloy fuel rods. TVA is also requesting approval of the new LOCA-specific Tritium Producing Burnable Absorber Rod (TPBAR) stress analysis methodology to evaluate the integrity of the TPBARs for conditions expected during a large break LOCA (LBLOCA).

The U.S. Nuclear Regulatory Commission (NRC) staff is reviewing your submittal and has identified areas where additional information is needed to complete its review.

A draft request for additional information (RAI) was previously transmitted to you via BOX due to the proprietary nature of some of the requests. At your request, a clarification call was held on July 13, 2020, to clarify the NRC staffs requests. As a result of the clarification call, changes were made to RAI.

The redacted, non-proprietary version of the RAI is attached. The version containing proprietary information will be transmitted to you via the NRCs BOX - Enterprise File Synchronization and Sharing service.

As requested in your email to Kim Green, dated July 8, 2020, a response to the attached RAI (non-proprietary) is requested no later than 45 days from the clarification call held on July 13, 2020.

The NRC staff considers that timely responses to RAIs help ensure sufficient time is available for staff review and contribute toward the NRCs goal of efficient and effective use of staff resources. If circumstances result in the need to revise the requested response date, please Kim Green at (301) 415-1627 or via email at Kimberly.Green@nrc.gov.

Sincerely, Michael Wentzel, Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing

Office of Nuclear Reactor Regulation Hearing Identifier: NRR_DRMA Email Number: 676 Mail Envelope Properties (DM6PR09MB578479F35BB376E019DF12A9E7610)

Subject:

Watts Bar Nuclear Plant, Units 1 and 2 - Request for Additional Information Regarding Request to Implement the FULL SPECTRUM' LOCA Methodology (EPID L-2020-LLA-0005)

Sent Date: 7/14/2020 8:40:09 AM Received Date: 7/14/2020 8:40:09 AM From: Wentzel, Michael Created By: Michael.Wentzel@nrc.gov Recipients:

"Green, Kimberly" <Kimberly.Green@nrc.gov>

Tracking Status: None "Wells, Russell Douglas" <rdwells0@tva.gov>

Tracking Status: None Post Office: DM6PR09MB5784.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 2539 7/14/2020 8:40:09 AM NON-PROPRIETARY - Request for Additional Information Regarding Request to Implement the FULL SPECTRUM LOCA Methodology (EPID L-2020-LLA-0005).pdf 90609 Options Priority: Normal Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:

OFFICIAL USE ONLY PROPRIETARY INFORMATION REQUEST FOR ADDITIONAL INFORMATION TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNITS 1 AND 2 DOCKET NOS. 50-390 AND 50-391 FULL SPECTRUM' LOCA METHODOLOGY FOR LOSS-OF-COOLANT ACCIDENT ANALYSIS AND NEW LOCA-SPECIFIC TRITIUM PRODUCING BURNABLE ABSORBER ROD STRESS ANALYSIS METHODOLOGY By application dated January 17, 2020 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20017A338), pursuant to Section 50.90 of Title 10 of the Code of Federal Regulations (10 CFR), Tennessee Valley Authority (TVA) submitted a license amendment request (LAR) for the Watts Bar Nuclear Plant, Units 1 and 2 (WBN). The proposed changes would: revise WBN Units 1 and 2 Technical Specification (TS) 5.9.5, Core Operating Limits Report, to replace the loss-of-coolant accident (LOCA) analysis evaluation model references with reference to the FULL SPECTRUM' Loss-of-Coolant Accident (FSLOCA') Evaluation Model analysis applicable to WBN Units 1 and 2, with replacement steam generators; revise the WBN Unit 2 Operating License Condition 2.C(4) to reflect the implementation of the FSLOCA Evaluation Model methodology; and, revise WBN Unit 1 TS 4.2.1, Fuel Assemblies, to delete discussion of Zircalloy fuel rods. TVA is also requesting approval of the new LOCA-specific Tritium Producing Burnable Absorber Rod (TPBAR) stress analysis methodology to evaluate the integrity of the TPBARs for conditions expected during a large break LOCA (LBLOCA).

The U.S. Nuclear Regulatory Commission (NRC) staff has been auditing several analyses documents that were not provided as part of the LAR. The documents listed below were made available to the NRC staff as part of its audit request (ADAMS Accession No. ML20120A021) via an online portal (i.e., CERTEC electronics library).

1. WCAP-18429-P Revision 0, Watts Bar Units 1 and 2 TPBAR Structural Integrity Analysis for the Large Break Loss of Coolant Accident (LBLOCA), Westinghouse, March 2019.

2. TTP-1-3101 Revision 1, Development of a Metric for Evaluation of TPBAR Structural Integrity During LBLOCA Event, Westinghouse/TVA/PNNL, April 2019

3. PNNL-TTP-1-3123, Revision 1, Tritium Technology Program Stainless Steel Burst Stress Curve Evaluation, PNNL/TVA, March 2020.

4. PNNL TTP-3-714 Revision 0, Thermal Creep Rupture Model Development for lOC Behavior of TPBARs, PNNL/TVA, March 2020.

5. PNNL TTP-3-721 Revision 1, High Temperature Fracture Models for Assessment of TPBAR Cladding Survivability During LOCA, PNNL/TVA, April 2020.

6. Application to Implement the FULL SPECTRUM LOCA (FSLOCA) Methodology for Loss-of-Coolant Accident (LOCA) Analysis," and New LOCA-specific Tritium Producing Burnable Absorber Rod Stress Analysis Methodology (WBN-TS-19-04) (LAR)

OFFICIAL USE ONLY PROPRIETARY INFORMATION

OFFICIAL USE ONLY PROPRIETARY INFORMATION As a result of the NRC staffs audit of these documents and review of the LAR, the staff requests the following additional information.

SFNB RAI 1 Section 4.2.2 of Enclosure 1 of the LAR summarizes the LOCA-specific TPBAR cladding stress analysis methodology to determine the potential TPBAR cladding mechanical rupture under LBLOCA temperature and differential pressure conditions. The stress analysis of the TPBAR following an LBLOCA is performed assuming conditions as calculated using the WCOBRA/TRAC-TF2 (WCT-TF2) code, the thermal-hydraulic code associated with the FSLOCA Evaluation Model.

(a) Provide details of reactor vessel, core, loop, emergency core cooling, and safety injection (SI) models used in the WCOBRA/TRAC-TF2 (WCT-TF2) code. The response should include the location of TPBARs with respect to location of fuel rods, hot assembly, guide tube, instrumentation tube, and burnable poison.

(b) (( )).

Provide justification for this assumption.

(c) TVA states that the TPBAR figure-of-merit (for rapid burst failure mode and thermal creep rupture node) calculation is performed (( )).

Provide the rationale for this assumption.

SFNB RAI 2 TVA has submitted a detailed analysis for high temperature failure model for TPBAR cladding during LOCA. TPBAR failure modes analyzed are the thermal creep rupture failure and rapid burst failure modes. For the thermal creep rupture and cladding burst failure analyses, provide responses to the following:

(a) Describe the five sets of experimental bursts tests performed by Pacific Northwest National Laboratory (PNNL). Describe how these experiments simulate the TPBAR thermal creep rupture failure.

(b) Describe the details of the cladding burst rupture model used in the TPBAR failure analysis.

(c) Provide details of the cladding creep rupture model and the procedure to develop the time to rupture curves.

(d) Describe how the burst and creep burst curves are used to determine the TPBAR failure assessment. The response should include the criteria to determine cladding failure.

SFNB RAI 3 TVA states that a statistical approach similar to the that used in FSLOCA Evaluation Model to demonstrate compliance with 10 CFR 50.46 acceptance criteria is used for the LOCA-specific TPBAR stress analysis. The figures-of-merit (FOM) are related to (1) rupture due to primary and bending stress and (2) rupture due to creep damage. Provide the following information Official Use Only - Proprietary Information

OFFICIAL USE ONLY PROPRIETARY INFORMATION related to stress evaluation metric that is capable of directly processing results from FSLOCA analysis:

(a) Provide a list of input parameters and derived parameters that are used in the calculation of stress intensities. Also list the assumptions and range of validity for the metric.

(b) Describe the primary and secondary stresses and their components that are considered in the development of the TPBAR structural model.

(c) Explain how the stress intensities are derived based on the American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section III, Subsection NG.

(d) Describe how allowable stress limits are calculated for burst stress, end plug stress, and creep damage stress. Provide justification for the selection of allowable stress that results in TPBAR stress failure.

SFNB RAI 4 Section 4.2.2 of Enclosure 1 of the LAR specifies values for the acceptance criteria that ensure TPBAR structural integrity as listed in Table 4.3.2-1.

(a) Provide the basis or justification for the criterion values listed in Table 4.3.2-1.

(b) Table 4.3.2-1 indicates that criterion values reflect the correction of the error in gamma energy redistribution uncertainty. Please explain how the error in gamma distribution uncertainty is determined and how the corrections are made in the safety factor for offsite power available (OPA) and loss of offsite power (LOOP).

SFNB RAI 5

((

))

SFNB RAI 6 WCAP-18429-P and other documents viewed during the audit, and the LAR indicate that a statistical approach similar to the that used in the FSLOCA Evaluation Model to demonstrate compliance with 10 CFR 50.46 acceptance criteria is used for the LOCA-specific TPBAR stress analysis. Section 4.2.2 of the LAR indicates that a Monte Carlo style uncertainty analysis to construct the FOM related to TPBAR structural integrity is performed. The NRC staff could not identify any documents where the details of either the statistical approach or Monte Carlo style uncertainty analysis for the TPBAR structural integrity analysis were provided.

Provide details of the statistical approach and/or the Monte Carlo style uncertainty analyses where tolerance limits are constructed for the figures-of-merit related to the TPBAR structural integrity. The response should include sampling size and their origin, type of statistical Official Use Only - Proprietary Information

OFFICIAL USE ONLY PROPRIETARY INFORMATION distribution of samples, (( )), analysis methods and other attributes to statistical approach.

SNSB RAI 1 In Enclosures 3 and 4 to the LAR, in response to Limitation and Condition 12, TVA states that a bounding plant-specific dynamic pressure loss from the steam generator secondary-side to the main steam safety valves was modeled in the Watts Bar Units 1 and 2 analysis. Provide the value used for the bounding plant-specific analysis and a brief explanation for why it is a way to adequately account for the pressure loss.

SNSB RAI 2 In Enclosures 3 and 4 to the LAR, TVA states that inboard grid deformation due to combined LOCA and seismic loads is not calculated to occur for Watts Bar Units 1 and 2. Discuss how TVA came to this determination.

Official Use Only - Proprietary Information