ML23346A138

Regulatory Audit Summary Related to Request to Increase the Number of Tritium Producing Burnable Absorber Rods

ML23346A138
Person / Time
Site:	Watts Bar
Issue date:	01/03/2024
From:	Kimberly Green NRC/NRR/DORL/LPL2-2
To:	Jim Barstow Tennessee Valley Authority
References
EPID L-2023-LLA-0039
Download: ML23346A138 (1)

Text

January 3, 2024 Mr. James Barstow Vice President, Nuclear Regulatory Affairs and Support Services Tennessee Valley Authority 1101 Market Street, LP 4A-C Chattanooga, TN 37402-2801

SUBJECT:

WATTS BAR NUCLEAR PLANT, UNITS 1 AND 2 - REGULATORY AUDIT

SUMMARY

RELATED TO REQUEST TO INCREASE THE NUMBER OF TRITIUM PRODUCING BURNABLE ABSORBER RODS (EPID L-2023-LLA-0039)

Dear Mr. Barstow:

By letter to the U.S. Nuclear Regulatory Commission (NRC) dated March 20, 2023, Tennessee Valley Authority (TVA) submitted a license amendment request to increase the number of tritium producing burnable absorber rods that can be irradiated in the reactors at Watts Bar Nuclear Plant, Units 1 and 2.

To enhance the review of TVAs request, the NRC staff conducted an audit of supporting documents from June 12, 2023, to July 24, 2023. The staff audited the requested documents to confirm certain information relied upon in the license amendment request. A summary of the regulatory audit is enclosed.

J. Barstow The NRC staff did not identify any significant issues during the audit, nor did it identify the need for additional information related to the topic of the audit.

Sincerely,

/RA/

Kimberly J. Green, Senior Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-390 and 50-391

Enclosure:

Regulatory Audit Summary cc: Listserv

Enclosure REGULATORY AUDIT

SUMMARY

RELATED TO LICENSE AMENDMENT REQUEST REGARDING INCREASE IN NUMBER OF TRITIUM PRODUCING BURNABLE ABSORBER RODS TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNITS 1 AND 2 DOCKET NOS. 50-390 AND 50-391

1.0 BACKGROUND

A regulatory audit is a planned license or regulation-related activity that includes the examination and evaluation of docketed and non-docketed information. The audit was conducted with the intent to gain understanding, to verify information, and to identify information that will require docketing to support the basis of a licensing or regulatory decision.

By letter dated March 20, 2023 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23079A270), the Tennessee Valley Authority (TVA, the licensee) submitted a license amendment request (LAR) to the U.S. Nuclear Regulatory Commission (NRC) for Watts Bar Nuclear Plant (Watts Bar), Units 1 and 2. The proposed changes would revise Watts Bar, Units 1 and 2, Technical Specification (TS) 4.2.1, Fuel Assemblies, to increase the number of tritium producing burnable absorber rods (TPBARs) that can be irradiated in the reactors from 1,792 to 2,496. TVA also requested a supporting change to TS 5.9.6, Reactor Coolant System (RCS) PRESSURE AND TEMPERATURE LIMITS REPORT (PTLR), and approval of the new large-break loss-of-coolant accident (LOCA)-specific Tritium Producing Burnable Absorber Rod (TPBAR) stress analysis methodology to evaluate the integrity of the TPBARs for conditions expected during a LOCA.

The NRC staff performed a preliminary review of the LAR and determined that a regulatory audit would assist in the timely completion of the review. The regulatory audit was performed consistent with NRC Office of Nuclear Reactor Regulation Office Instruction LIC-111, Revision 1, Regulatory Audits, dated October 31, 2019 (ML19226A274).

2.0 AUDIT ACTIVITIES AND OBSERVATIONS The NRC staff conducted a regulatory audit that consisted of a remote audit from June 12, 2023, to June 30, 2023, that was subsequently extended to July 24, 2023. The audit plan was provided to TVA on May 25, 2023 (ML23150A247). The list of documents uploaded by the licensee in response to the NRC staffs request and examined by the audit team is provided in Section 4.0 below.

The remote audit was conducted using an online portal and teleconferencing capabilities. The purpose of the audit was to (1) gain a better understanding of the calculations, analyses, and bases underlying the LAR and confirm the NRC staffs understanding of the LAR, and (2) identify any information that would be required from the licensee to be provided on the docket for the NRC to render a staff finding to support the safety evaluation.

The NRC staff examined several of the documents identified in Section 4.0 below and held an audit entrance call with members of TVA on June 5, 2023.

At the conclusion of the audit, the NRC staff determined that no additional information would be needed for the staff to complete the review of the LAR.

2.1 Observations Regarding Impacts on the Core 2.1.1 ATWS Analysis and Post-LOCA Subcriticality Verification TVA Audit Response Form, CNL-22-2022, indicated that the anticipated transient without scram (ATWS) analysis and post-LOCA sub-criticality verification analysis were both performed in CN-WATTS-200 based on models documented in CN-WATTS-199. These analyses show positive margins to the bounding Reload Safety Analysis Checklist analysis as per approved WCAP-9272 methodology.

CN-WATTS-200 summarizes the following calculations:

Reactivity coefficients moderator temperature coefficient (MTC) and Reactivity coefficients MTC power range Reactivity coefficients End of Cycle MTC Reactivity coefficients Doppler Beta effective Trip reactivity shape Trip reactivity vs power FH vs power Rod withdrawal from subcritical Rod misalignment (rod out of position)/Single rod withdrawal Rod withdrawal at power Locked rotor Rod ejection Shutdown margin Hot zero power (HZP) Steamline break melt criteria.

Hot full power (HFP) Steamline break ATWS MTC LOCA reflood LOCA long term subcriticality with hot leg switchover Doppler defect Maximum FQ for Doppler rod centerline TVA explained that dropped rod analysis was not explicitly calculated for the LAR to increase the maximum number of TPBAR to 2,496 rods. This is due in part to the dropped rod event not being explicitly requested as part of the plant-specific interface issues required to be addressed for amendment requests related to tritium production cores (NUREG-1672, Section 5.1). TVA indicated that the dropped rod analysis historically has never been challenged. Watts Bar Unit 1 Cycle 19 and Unit 2 Cycle 5 show an excess of 20 percent positive margin. TVA stated that the dropped rod margin will continue to be calculated on a cycle-by-cycle basis to ensure sufficient positive margin exists to the safety limit.

The purpose of CN-WATTS-199 calculation is to document the core loading pattern (CLP),

equilibrium ANC9 model, and data files for the 2,496 TPBAR project at Watts Bar. The calculation documents the CLP for the 18-month 2,496 TPBAR equilibrium model presented as Watts Bar Unit 1, Cycle 22.

The staff noted that the following computer codes were used:

ANC CORPIX WPOST ALPHA PARAGON NEXrun NEXpre NEXlink This calculation contains the following figures:

1. Various Unit 1 Cycle 22 Axial Designs

2. WATTS BAR Unit 1 Cycle 22 Reference Core Pattern

3. WATTS BAR Unit 1 Cycle 22 Control Rod and Shutdown Rod Locations

4. WATTS BAR Unit 1 Cycle 22 Incore Detector Locations

5. WATTS BAR Unit 1 Cycle 22 Burnable Absorber and Source Rod Locations

6. WATTS BAR Unit 1 Cycle 22 TPBAR Number and Linear Loadings

7. WATTS BAR Unit 1 Cycle 22 Region and Fuel Assembly IDS

8. WATTS BAR Unit 1 Cycle 22 Various Fuel Assembly Configurations

9. WATTS BAR Unit 1 Cycle 22 Various Fuel Assembly and Components 2.1.2 Compliance with Departure from Nucleate Boiling Criterion The NRC staff audited Calculation CN-WATTS-209, which documents the thermal-hydraulic (T-H) evaluation of a 2,496 TPBAR core, as well as the compilation of licensing documentation needed to support the proposed increase in the number of TPBARs.

The NRC staff identified compliance with the departure from nucleate boiling (DNB) criterion as an interface issue for which plant-specific information would be required in the licensees submittal. This criterion requires the demonstration that DNB will not occur on the most limiting fuel rod on at least a 95 percent probability at a 95 percent confidence levels. For the Watts Bar 2496 Tritium Production core, the normal T-H DNB related reload analyses were performed using VIPRE-01 (Reference 1).

The staff verified that the reload analyses in CN-WATTS-209 included the following T-H evaluations, which were previously included and summarized in the December 20, 2017, LAR for the 1,792 TPBAR core (ML17354B282):

An axial power shape study was performed to assure that the limiting power distributions used in design would still be valid in the presence of the TPBAR. This study compares power shapes resulting from depletion during operation of the cycles to reference shapes used as the basis for Thermal-hydraulic design analyses.

The Steamline Break with Rod Withdrawal at Power transient was analyzed to demonstrate the continued acceptability of the Departure from Nucleate Boiling Ratio (DNBR)

Zero Power Hypothetical Steamline Break was analyzed to demonstrate that the DNBR design basis was met.

The staff noted that Calculation CN-WATTS-209 concluded that the axial power shape comparison has assured that the current safety analysis for Watts Bar would remain bounding and the TPBARs would not present any excessive power distribution changes beyond those, which are already bounded within the thermal-hydraulic design bases.

It also concluded that the presence of TPBARs in the reload core design did not challenge the DNB criterion. To verify this, an explicit check of the DNB criterion was included in the cycle-specific reload safety evaluation performed for each Watts Bar reload core.

These conclusions are the same as the ones reached for the 1,792 TPBAR core, and were previously documented in the December 20, 2017, LAR (ML17354B282).

2.1.3 Core Neutronic Design In Audit Item 2, the staff requested to view documents and calculations related to the neutron fluence determination (ML23150A247). During an audit call, the staff clarified that it was seeking documents that show how the nuclear core design is modeled and what the impacts are on the vessel fluence with respect to increasing the number of TPBARs to 2,496, and how the increase in TPBARs affects other poisons. TVA explained that the effects on poisons can be answered in two parts: (1) the TPBAR loading with respect to other integral fuel burnable absorbers (IFBA) and (2) the TPBAR loading with respect to the critical boron concentration. TVA referred the staff to the CN-WATTS-199 calculation. The NRC staff examined the core design details and the figures that show the placement of the discrete and integral poisons within the reactor core and within the individual assemblies. The staff confirmed that the numbers and patterns of IFBA/TPBAR combinations are consistent with prior operating cycles and no new patterns were developed.

2.1.4 Poison and Boron Concentration The CN-WATTS-199 calculation also provides the steady-state depletion parameters for the 2,496 TPBAR equilibrium model. The NRC staff examined the depletion parameters including boron concentration for equilibrium model for the cycle of operation. The staff verified that the boron letdown (critical boron concentration vs. cycle exposure) is consistent with prior operating cycles as well as previous licensing submittals.

2.2 Observations Regarding Control Room Dose Calculations The staff audited the following documents:

TVA Calculation WBNAPS3077, Revision 019, Offsite and Control Room Operator Doses due to a Main Steam Line Break, dated January 15, 2023 TVA Calculation WBNTSR008, Revision 020, Control Room Operator and Offsite Doses due to a Steam Generator Tube Rupture, dated January 9, 2023 TVA Calculation WBNTSR009, Revision 018, Control Room Operator and Offsite Doses from a Fuel Handling Accident, dated December 20, 2022 These documents describe TVAs site-specific design basis analyses for control room dose following the TPBAR increase per Interface Issue 5, Control Room Habitability Systems of NUREG-1672, Section 2.6.1. The staff verified that the licensees analyses for the accidents evaluated by these calculations are consistent with approaches previously approved by the NRC as described in the licensees final safety analysis report.

2.3 Observations Regarding the Tritium Bioassay Program The NRC staff audited the following TVA documents to verify the tritium bioassay program:

TVA NPG Standard Department Procedure RCDP-7, Revision 0011, Bioassay and Internal Dose Program, dated July 22, 2021 TVA NPG Standard Programs and Processes Procedure NPG-SPP-05.1, Revision 0016, Radiological Controls, dated September 13, 2022 TVA Watts Bar Nuclear Plant, Units 0, 1, and, 2, Radiological Control Instruction RCI-137, Revision 0009, Radiation Protection Tritium Control Program, dated December 14, 2021.

The staff verified that TVA will continue to have a tritium bioassay program in place as a part of its radiation protection and control program.

The NRC staff also audited TVA Records and Information Management System (RIMS) T71220525801, Validation of GELC and QWATA used to Develop Interface Issue 14 for the 2496 LAR, dated November 15, 2022, to review the computer code inputs/outputs that implement the Offsite Dose Calculation Manual methodology for calculating liquid and gaseous doses.

The NRC staff audited TVA RIMS T71230227803, Watts Bar Nuclear 2,496 TPBAR LAR, Methodology used to Demonstrate Compliance with 40 CFR 190, dated February 27, 2023, to review how the site complies with the Environmental Protection Agencys regulatory requirements in 40 CFR 190 of the per-site annual dose equivalent limits of 25 mrem whole body, 75 mrem thyroid, and 25 mrem to any other organ to a member of the public.

The NRC staff audited TVA Calculation TI534, Revision 013, Annual Routine Radioactive Airborne Releases from the Operation of One Unit, dated December 27, 2022, to review how the site calculates total annual routine gaseous effluent releases. This information is used in TVA RIMS T71220525801, referenced above, in calculation of dose from gaseous effluent releases.

The NRC staff also audited TVA Calculation WBNTSR093, Revision 015, Liquid Radioactive Waste Releases, dated December 27, 2022, to review how the site calculates total annual routine liquid effluent releases. This information is used in TVA RIMS T71220525801, referenced above, in calculation of doses from liquid effluent releases.

2.4 Observations Regarding Quality Assurance for TPBARs The NRC staff audited the last audit report and annual evaluation of TVAs two suppliers for the TPBARs: (1) Battelle - Pacific Northwest National Laboratory (PNNL) and (2) Westinghouse Government Services, LLC (WGS). The purpose of the NRC staffs audit was to confirm there have been no changes to TVAs quality oversight of these suppliers as documented in the NRC staffs Safety Evaluation Report dated May 22, 2019 (ML183478330).

In Section 4.0, Technical Evaluation, of LAR (ML23079A270), TVA stated, in part, that [t]here are no substantive changes to Interface Issues 2, Procurement and Fabrication Issuesas described in Reference 4.0-2 and they remain applicable to this LAR. Reference 4.0-2 is TVAs application to the NRC requesting a revision to Technical Specification 4.2.1, Fuel Assemblies, and Watts Bar Units 1 and 2 Technical Specifications Related to Fuel Storage (ML17354B282).

The NRC staff verified that there have been no changes made in how TVA provides the required quality oversight of its two suppliers for the TPBARs. The only change observed by the NRC staff in the audited documents was the change in the name of one of the suppliers from WesDyne International, LLC to WGS.

Reference:

1. WCAP-14565-P-A/WCAP-15306-NP-A, VIPRE-01 Modeling Qualification for Pressurized Water Reactor Non-LOCA Thermal-Hydraulic Safety Analysis, October 1999 3.0 AUDIT PARTICIPANTS NRC Kim Green Mathew Panicker David Garmon Bill Rautzen Yamir Diaz-Castillo TVA Russ Wells James Fitzsimmons Tim Lorentz Mark Burzynski Doug Pollock James Poole Stuart Rymer David Sumego Jon Talbott Steven Woods Carla Borrelli Korrie Yetzer Pacific Northwest National Laboratory Robert Montgomery Gary Wolfram Westinghouse Eric Husser Sargent and Lundy Megan Langerman Aleksandar Milicevic Robert Young 4.0 DOCUMENTS PROVIDED IN ELECTRONIC READING ROOM

1.

Westinghouse Electric Company, LLC, CN-WATTS-200, Revision 0, Watts Bar 2496 TPBAR Core WARP Automation, dated May 28, 2021

2.

Westinghouse Electric Company, LLC, CN-WATTS-199, Revision 0, Watts Bar 2496 TPBAR Core Loading Plan, Equilibrium Model and CD File Generation - Deliverable Attachment, dated April 21, 2021

3.

Westinghouse Electric Company, LLC, CN-WATTS-209, Revision 0, T/H Analysis of 2496 TPBAR Program, dated April 1, 2022

4.

Westinghouse Electric Company, LLC, WATM-REAC-CN-AA-000001, Revision 0, Development of a RAPTOR-M3G Model for Watts Bar Units 1 & 2 Extended Beltline Fluence, dated May 5, 2022 (Westinghouse Proprietary Class 2)

5.

Westinghouse Electric Company, LLC, WAT-REAC-CN-AA-000001, Revision 0, Watts Bar Unit 1 Extended Beltline Fluence Analysis for the Core Design with 2,496 Tritium-Producing Burnable Absorber Rods, dated May 11, 2022 (Westinghouse Proprietary Class 2)

6.

Westinghouse Electric Company, LLC, WBT-REAC-CN-AA-000001, Revision 0, Evaluation of Watts Bar Unit 2 Pressure Vessel Fluence for 2496 TPBAR Implementation Project, dated May 13, 2022 (Westinghouse Proprietary Class 2)

7.

WCAP-18769-NP, Revision 1, Watts Bar Units 1 & 2 Reactor Vessel Integrity Evaluations for the 2496 TPBAR Implementation Project, dated February 2023

8.

TVA RIMS T71220525801, Validation of GELC and QWATA used to Develop Interface Issue 14 for the 2496 LAR, dated November 15, 2022

9.

TVA RIMS T71230227803, Watts Bar Nuclear 2,496 TPBAR LAR, Methodology used to Demonstrate Compliance with 40 CFR 190, dated February 27, 2023

10.

TVA Calculation TI534, Revision 013, Annual Routine Radioactive Airborne Releases from the Operation of One Unit, dated December 27, 2022

11.

TVA Calculation WBNAPS3077, Revision 019, Offsite and Control Room Operator Doses due to a Main Steam Line Break, dated January 15, 2023

12.

TVA Calculation WBNTSR008, Revision 020, Control Room Operator and Offsite Doses due to a Steam Generator Tube Rupture, dated January 9, 2023

13.

TVA Calculation WBNTSR009, Revision 018, Control Room Operator and Offsite Doses from a Fuel Handling Accident, dated December 20, 2022

14.

TVA Calculation WBNTSR080, Revision 014, Control Room Operator and Offsite Doses due to a Loss of AC Power, dated January 15, 2023

15.

TVA Calculation WBNTSR093, Revision 015, Liquid Radioactive Waste Releases, dated December 27, 2022

16.

TVA NPG Standard Department Procedure RCDP-7, Revision 0011, Bioassay and Internal Dose Program, dated July 22, 2021

17.

TVA NPG Standard Programs and Processes Procedure NPG-SPP-05.1, Revision 0016, Radiological Controls, dated September 13, 2022

18.

TVA Watts Bar Nuclear Plant, Units 0, 1, & 2, Radiological Control Instruction RCI-137, Revision 0009, Radiation Protection Tritium Control Program, dated December 14, 2021

19.

Letter from Talbott, J.T., Tennessee Valley Authority, to Borey, N., Battelle - Pacific Northwest National Laboratory, TVA Sequoyah and Watts Bar Nuclear Plants - Design, Procurement, Fabrication, and Test & Inspection Activities for Tritium Production and Associated Safety Related Components - TVA Supplier Audit 2020V-12, dated August 27, 2020

20.

Letter from Talbott, J.T., Tennessee Valley Authority, to Greifenkamp, T., Westinghouse Government Services, TVA Sequoyah and Watts Bar Nuclear Plants Audit of Tritium Producing Burnable Absorber Rod (TPBAR) Fabrication - TVA Supplier Audit 2021V-13, dated September 5, 2021

21.

2022 Supplier Annual Evaluation for Battelle - Pacific Northwest National Laboratory

22.

2022 Supplier Annual Evaluation for Westinghouse Government Services

23.

TVA WBN TPBAR LAR Audit Response Form, CNL-22-002, dated June 7, 2023

ML23346A138 NRR-058 OFFICE NRR/DORL/LPLII2/PM* NRR/DORL/ LPLII2/LA NRR/DSS/SFNB/BC NRR/DRA/ARCB/BC NAME KGreen RButler SKrepel KHsueh (SMeighan for)

DATE 12/6/23 12/21/23 12/7/23 12/7/23 OFFICE NRR/DRO/IQVB/BC NRR/DORL/ LPLII2/BC NRR/DORL/ LPLII2/PM NAME KKavanagh DWrona KGreen DATE 8/7/23 1/2/24 1/3/24