ML25272A158

Regulatory Audit Summary Regarding License Amendment Request to Use Online Monitoring (EPID L-2024-LLA-0147) - Non-Proprietary

ML25272A158
Person / Time
Site:	Sequoyah, Watts Bar
Issue date:	11/20/2025
From:	Kimberly Green NRC/NRR/DORL/LPL2-2
To:	Erb D Tennessee Valley Authority
References
EPID L-2024-LLA-0147
Download: ML25272A158 (0)

Text

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION November 20, 2025 Mr. Delson C. Erb Vice President, OPS Support Tennessee Valley Authority 1101 Market Street, LP 4A-C Chattanooga, TN 37402-2801

SUBJECT:

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

SUMMARY

REGARDING LICENSE AMENDMENT REQUEST TO USE ONLINE MONITORING (EPID L-2024-LLA-0147)

Dear Mr. Erb:

By letter dated November 4, 2024, the Tennessee Valley Authority (TVA) submitted a license amendment request (LAR) for Renewed Facility Operating License Nos. DPR-77 and DPR-79 for Sequoyah Nuclear Plant, Units 1 and 2 (Sequoyah), respectively, and Facility Operating License Nos. NPF-90 and NPF-96 for Watts Bar Nuclear Plant (Watts Bar), Units 1 and 2, respectively. The proposed amendments would revise some definitions in Sequoyah, Units 1 and 2, and Watts Bar, Units 1 and 2, Technical Specification (TS) 1.1, Definitions, and add new TS 5.5.19, Online Monitoring Program, (Sequoyah) and TS 5.7.2.24, Online Monitoring Program (Watts Bar), to permit the use of an NRC-approved online monitoring (OLM) methodology as the technical basis to switch from time-based surveillance frequency for channel calibrations to a condition-based calibration frequency based on OLM results.

The Nuclear Regulatory Commission (NRC) staff reviewed TVAs LAR and determined that a regulatory audit would assist in the timely completion of the LAR review. The NRC staff conducted a regulatory audit that consisted of a remote audit from June 17 - August 7, 2025.

The audit plan was provided to Ms. Hulvey of your staff by letter dated February 27, 2025. The audit plan included a list of items to be provided on an electronic portal. The staff audited these documents and held discussions with members of TVA on the LAR relevant to the NRC staffs review. As a result of the audit, no requests for additional information were issued. A summary of the audit is enclosed.

The NRC staff has determined that enclosure 1 contains proprietary information pursuant to Title 10 of the Code of Federal Regulations Section 2.390, Public inspections, exemptions, request for withholding. Proprietary text will be contained within double brackets (( this is proprietary text )). Accordingly, the staff has prepared a redacted version, which is provided as enclosure 2.

to this letter contains proprietary information. When separated from enclosure 1, this document is DECONTROLLED.

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION If you have questions, please contact me at 301-415-1627 or via email at Kimberly.Green@nrc.gov.

Sincerely,

/RA/

Kimberly J. Green, Sr. Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos.: 50-327, 50-328, 50-390, and 50-391

Enclosures:

1. Proprietary Audit Summary

2. Non-Proprietary Audit Summary cc: Listserv w/o enclosure 1

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION ENCLOSURE 2 (NON-PROPRIETARY)

SEQUOYAH NUCLEAR PLANT, UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328 WATTS BAR NUCLEAR PLANT, UNITS 1 AND 2 DOCKET NOS. 50-390 AND 50-391 REGULATORY AUDIT

SUMMARY

RELATED TO LICENSE AMENDMENT REQUEST TO REVISE TECHNICAL SPECIFICATIONS TO USE ONLINE MONITORING Proprietary information pursuant to Title 10 of the Code of Federal Regulations Section 2.390 has been redacted from this document.

Redacted information is identified by blank space enclosed within (( double brackets )).

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION REGULATORY AUDIT

SUMMARY

RELATED TO LICENSE AMENDMENT REQUEST TO REVISE TECHNICAL SPECIFICATIONS TO USE ONLINE MONITORING TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT, UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328 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 application dated November 4, 2024 (Agencywide Documents Access and Management System Accession No. ML24309A061), pursuant to Section 50.90 of Title 10 of the Code of Federal Regulations (10 CFR), the Tennessee Valley Authority (TVA) submitted a license amendment request (LAR) to amend Facility Operating License Nos. DPR-77 and DPR-79 for Sequoyah Nuclear Plant, Units 1 and 2 (SQN or Sequoyah), respectively, and NPF-90 and NPF-96 for Watts Bar Nuclear Plant, Units 1 and 2 (WBN or Watts Bar), respectively. The proposed amendments would revise Sequoyah and Watts Bar Technical Specification (TS) 1.1, Use and Application Definitions, and add new Sequoyah TS 5.5.19 and new Watts Bar TS 5.7.2.24, Online Monitoring Program, to permit the use of an online monitoring methodology (OLM) as the technical basis to switch from time-based surveillance frequency for channel calibrations to a condition-based calibration frequency based on OLM results.

As the NRC staff performed its review of the LAR, it was 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 remotely from June 17 - August 7, 2025. The remote audit was conducted using the Certrec portal. An audit plan was provided to TVA on February 27, 2025 (ML25052A088). The list of information uploaded by TVA in response to the

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION NRC staffs request and examined by the audit team is provided in section 4.0 below. The list of audit questions sent to TVA is provided in section 5.0 below.

TVA staff and Analysis and Measurement Services Corporation (AMS) staff supported the audit by providing remote access via Certrec, an internet-based electronic reading room, to requested reports and by making appropriate staff with detailed knowledge of AMS-TR-0720R1 available for discussions with the NRC staff.

A summary of the audit discussions is provided below.

Audit Call, June 17, 2025 TVA addressed questions 1-7 listed in section 5.0.

Licensee Response:

1. TVA discussed, for both SQN and WBN, plant specific examples related to the measurement and test equipment (M&TE) being proposed to support OLM. They described the components related to the measurement loop and how their uncertainties were determined, starting from the sensor all the way through the devices used to provide inputs to the plant computer and data historian that captures the measurement. Discussions were held regarding the accuracy of the plant computer to support the OLM detection for flagging a transmitter for a calibration check, which is the point at which the final drift measurement is determined. TVA personnel described how the process computer analog to digital resolution plays a large role in determining the process computer uncertainty for the measurement that was being taken at the end of the loop.

2. TVA also elaborated on the discussion above by describing the measurement loop configurations of plant safety equipment and M&TE, providing plant loop schematics to illustrate these configurations, the components used for each plant, and their related transmitter group being proposed to support OLM.

3. TVA confirmed that there was a transposition error observed by the NRC staff on document SQN2308R0 (OLM Analysis Methods and Limits). They noted that this will be addressed in an update to the report.

4. TVA confirmed that within Section 3.6, Step 8, found in document WBN2303R0 (OLM Analysis Methods and Limits), the amount of redundant analog computer points for WBN, Units 1 and 2, was not properly reflected. TVA noted that this will be addressed in an update to the report. In addition, TVA confirmed that the values found in the calculation and tables in WBN2303R0 are correct.

5. TVA confirmed that the information found in Section 3.10, Step 8, of the document WBN2303R0 (OLM Analysis Methods and Limits) had an incorrect number of redundant sensors for WBN, Unit 1, and would be addressed in a later update to address the information and table calculations. In addition, TVA confirmed that for WBN, Unit 2, the redundant sensors, calculations and table have the correct values.

6. TVA confirmed that there was an incorrect reflection of the redundancy of the number of sensors used in document WBN2303R0 (OLM Analysis methods and Limits), Section 3.1, Step 3 for WBN, Unit 1, on the Process Estimate Uncertainty (PEU) term, and the associated table calculations, both of which would be corrected in an update to the report.

For WBN, Unit 2, the associated redundancy of the number of sensors was confirmed to be correct.

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION

7. TVA highlighted differences found from similar work performed for another licensee by the vendor, related to uncertainty terms being utilized and generated for the parity band calculation. TVA noted that this would be explained in an update to the associated report for WBN.

Audit Call, June 23, 2025 In responding to Question 1 (see section 5.0), TVA provided additional details on the associated uncertainty terms related to the M&TE used for monitoring drift. This included conversations on the conservative aspect of the data used to generate the provided calculations for establishing the OLM limits in accordance with the AMS topical report (TR). TVA provided an updated calculation using realistic process computer vendor data to support their M&TE uncertainty.

NRC staff observations regarding each of the audited reports are provided below:

AMS Report SYA2307R0, OLM Amenable Transmitters Report for Sequoyah Units 1 and 2, August 2024, and AMS Report WBR2302R0, OLM Amenable Transmitters Report for Watts Bar Units 1 and 2, August 2024 These reports address Steps 1 through 6 of Section 11.1.1 of the TR for the transmitters in Watts Bar, Units 1 and 2, and Sequoyah, Units 1 and 2, that are to be included in the OLM program. It identifies groups of pressure, level, and flow transmitters for each unit that qualify to be entered into the respective plants proposed OLM program.

AMS Report SYA2308R0, OLM Analysis Methods and Limits Report for Sequoyah Units 1 and 2, September 2024, and AMS Report WBR2303R0, OLM Analysis Methods and Limits Report for Watts Bar Units 1 and 2, September 2024 These reports address Steps 7 through 8 of Section 11.1.1 of the TR AMS-TR-0720R2-A for the transmitters in Sequoyah, Units 1 and 2, and Watts Bar, Units 1 and 2, that are to be included in the proposed OLM program. The NRC staff observed greater values for uncertainties associated with the M&TE in certain configurations and transmitter groups. This led to a conversation on the recommended practice for the uncertainty associated with the plant process computer that is included as part of the proposed M&TE, to account for uncertainties associated with the digital system accuracy term.

On August 8, 2025, TVA provided a response to the audit portal addressing Question 8 (see section 5.0 below). TVA had generated an updated calculation of the plant computer accuracy term when addressing Question 1. Using this updated calculation, TVA emphasized that there were no cases where computer plant accuracy term would be larger to the OLM limit being measured. In addition, TVA demonstrated, using the methodology identified in the International Society of Automation (ISA) Recommended Practice 67.04.02, Annex H, the uncertainty terms described therein to be accounted for as part of their calculations for the proposed M&TE. TVA emphasized that given that the uncertainty of the plant computer that was calculated in their response to Question 1 of this audit is smaller than the OLM limit in all cases, there would not be masking of the drift measurement.

Based on TVAs response, the NRC staff notes that TVA has demonstrated that the magnitude of the uncertainty estimates for the plant process computer and other M&TE used to monitor for

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION drift of the instrument channels in the OLM program appear to be reasonably low enough to enable reliable measurement of the drift of these channels as they approach the OLM limits.

AMS Report SYA2309R0, OLM Drift Monitoring Program Report for Sequoyah Units 1 and 2, August 2024, and AMS Report WBR2304R0, OLM Drift Monitoring Program Report for Watts Bar Units 1 and 2, August 2024 These documents provide the steps to be followed to implement OLM for transmitter drift monitoring in accordance with TR AMS-TR-0720R2-A for Sequoyah, Units 1 and 2, and Watts Bar, Units 1 and 2. The steps described in the document are intended to be repeated at each operating cycle to identify the transmitters that should be scheduled for a calibration check.

Following the steps in this document will ensure that OLM data is properly acquired, qualified, analyzed, interpreted, reported, and documented.

AMS Procedure OLM2201R0, Procedure for Online Monitoring Data Retrieval, Revision 0, December 2022 This is a test procedure for retrieving OLM data from the plant historian using the AMS Bridge software. It provides general steps that are followed when retrieving OLM data, not specific to Sequoyah Units, 1 and 2, or Watts Bar, Units 1 and 2.

AMS Procedure OLM2202R1, Procedure for Performing Online Monitoring Data Qualification and Analysis, Revision 1, August 2024 This is a procedure outlining the general steps that are followed when performing OLM data analysis of the data being retrieved. It provides general steps that are followed when analyzing OLM data, not specific to Sequoyah, Units 1 and 2, or Watts Bar, Units 1 and 2.

AMS Report SYA2310R0, OLM Noise Analysis Program Report for Sequoyah Units 1 and 2, August 2024, and AMS Report WBR2305R0, OLM Noise Analysis Program Report for Watts Bar Units 1 and 2, August 2024 This document provides the steps that must be followed to implement noise analysis for assessment of transmitter dynamic failure modes. The steps described are to be repeated at each operating cycle at Sequoyah, Units 1 and 2, and Watts Bar, Units 1 and 2, for a minimum of one transmitter on a staggered basis in each redundant group which has a response time requirement as outlined to identify its dynamic failure modes. The steps outlined in this document will ensure that proper noise analysis equipment is used, and data is properly acquired, qualified, analyzed, interpreted, reported, and documented.

AMS Procedure NPS1501R0, Procedure for Noise Data Collection from Plant Sensors, Revision 0, March 2015 This procedure provides guidelines for the collection of noise data to determine the dynamic performance characteristics of sensors and systems in nuclear power plants and other processes. This procedure is used for on-line data acquisition from a wide variety of sensors and systems while the plant is operating at any mode that provides adequate signal amplitudes for analysis.

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION AMS Procedure NAR2201R1, Procedure for Performing Dynamic Failure Mode Assessment Using Noise Analysis, Revision 1, August 2024 This procedure provides general guidelines for performing dynamic failure mode assessment using the noise analysis method. This is a generic document not specific to Sequoyah, Units 1 and 2, or Watts Bar, Units 1 and 2.

The NRC staff held an audit exit call with members of TVA and AMS on July 21, 2025. Based on the audit activities, the NRC staff determined no additional information is needed on the docket, and the staff can complete its review.

3.0 AUDIT PARTICIPANTS NRC TVA Gilberto Blas Russ Wells Fred OBrien Joyce Artis David Rahn Isaac Chandler Aaron Armstrong Shawna Hughes Tarico Sweat Amber Aboulfaida Kim Green AMS Greg Morton Brent Shumaker Caleb Crosby 4.0 DOCUMENTS PROVIDED IN ELECTRONIC READING ROOM Item #

Audit Item 1

AMS Report SYA2307R0, OLM Amenable Transmitters Report for Sequoyah Units 1 and 2, August 2024 2

AMS Report WBR2302R0, OLM Amenable Transmitters Report for Watts Bar Units 1 and 2, August 2024 3

AMS Report SYA2308R0, OLM Analysis Methods and Limits Report for Sequoyah Units 1 and 2, September 2024 4

AMS Report WBR2303R0, OLM Analysis Methods and Limits Report for Watts Bar Units 1 and 2, September 2024 5

AMS Report SYA2309R0, OLM Drift Monitoring Program Report for Sequoyah Units 1 and 2, August 2024 6

AMS Report WBR2304R0, OLM Drift Monitoring Program Report for Watts Bar Units 1 and 2, August 2024 7

AMS Procedure OLM2201R0, Procedure for Online Monitoring Data Retrieval, Revision 0, December 2022 8

AMS Procedure OLM2202R1, Procedure for Performing Online Monitoring Data Qualification and Analysis, Revision 1, August 2024

OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION Item #

Audit Item 9

AMS Report SYA2310R0, OLM Noise Analysis Program Report for Sequoyah Units 1 and 2, August 2024 10 AMS Report WBR2305R0, OLM Noise Analysis Program Report for Watts Bar Units 1 and 2, August 2024 11 AMS Procedure NPS1501R0, Procedure for Noise Data Collection from Plant Sensors, Revision 0, March 2015 12 AMS Procedure NAR2201R1, Procedure for Performing Dynamic Failure Mode Assessment Using Noise Analysis, Revision 1, August 2024 5.0 LIST OF AUDIT QUESTIONS

1.

For Watts Bar and Sequoyah plants, there are multiple cases where the Measurement Channel Uncertainty (MCU), which consists of the measurement and test equipment as part of the loop to obtain data, is greater than the established OLM limit. Being able to detect the drift to compare to the established OLM limit is how a transmitter is flagged for calibration for that specific transmitter under review. For these cases, the uncertainty of the MCU is greater than the OLM limit that is being monitored to see if the drift exceeds the established OLM limit. How would this scenario impact OLM detection for flagging a transmitter, and under this scenario are you able to utilize OLM using the M&TE equipment being proposed? The calculations for the provided example in Pg. 47 the AMS-TR-0720R2-A, and the representation in Figure 7.5, appear to show a reasonable relationship between OLM and MCU (i.e., MCU is much smaller than the OLM limit). In the application, there are instances where the MCU is greater than the OLM limit. Please explain how this situation is consistent with the topical report and associated assumptions.

2.

For the transmitters being included for OLM, can you provide each configuration that details the components from sensor to the plant computer or endpoint, that captures all items in the loop throughout the signal path? Can you provide loop schematics or schematic diagrams that capture all components of the signal path used for OLM?

3.

Document SYA2308R0 (OLM Analysis Methods and Limits), states ((

)) Is this data copied from the calculations in Section 3 of the document, or is this information transposed separately when listed in Table 4.4, for example ((

)).

4.

Document WBR2303R0 (OLM Analysis Methods and Limits) Section 3.6, Step 8, states

((

)). Does the 2 redundant sensor Analog stipulation apply to both Units and is this captured when calculating the OLM Limit dependent variables, for example the Process Estimate Uncertainty (PEU) in Tables 3.12 and 3.13.

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5.

Please provide the calculations made to generate the OLM Limits for Watts Bar, Unit 2, Reactor Coolant System Pressure Wide Range (Document 2BR2303R0) per Table 3.21.

6.

Document WBR2303R0 (OLM Analysis methods and Limits), Section 3.1, Step 3, states

((

)) Is this redundant sensor amount specific to the Eagle values or Analog Values and is this captured when calculating the OLM Limit dependent variables, for example the Process Estimate Uncertainty (PEU) in Table 3.1 and 3.2.

Please provide the calculations for Tables 3.1 and 3.2.

7.

Per staff understanding, the parity band calculation seems to be dependent on the Sensor Reference Accuracy (SRA). Are there cases where a parity band is set to a non-zero value when the associated SRA is set to zero, such as the case of Table 3.11 in document (WBR2303R0 OLM Analysis methods and Limits).

8.

Tennessee Valley Authority (TVA) wants to use Measurement and Test Equipment (M&TE), which includes the plant computer, to collect data and check if a transmitter is in need of calibration. They plan to measure how much each transmitters readings change over time or drift and compare these to a set Online Monitoring (OLM) limit. For certain cases, the drift being measured is very small. However, the documents referenced in the LAR state that the uncertainties associated with the proposed M&TE to measure these changes can be large.

Please explain how TVA has determined that the M&TE being proposed, which includes the plant process computer, is capable of reliably measuring the instrument channel drift with an accuracy that will not mask the drift being measured given the associated uncertainty in these configurations. For example, describe how the proposed M&TE, inclusive of digital signal conversion and algebraic presentation, is sufficiently accurate to reliably measure the drift in the transmitters included in the OLM program to support the decision making (for example, see ISA Recommended Practice 67.04.02, Annex H).

ML25272A045 (Package)

ML25272A057 (Proprietary)

ML25272A158 (Non-Proprietary)

NRR-058 OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DRO/IQVB/BC NAME KGreen ABaxter KKavanagh DATE 11/13/2025 11/14/2025 11/17/2025 OFFICE NRR/DEX/EICB/BC(A)

NRR/DORL/LPL2-2/BC NRR/DORL/LPL2-2/PM NAME SDarbali DWrona KGreen DATE 11/14/2025 11/19/2025 11/20/2025