ML25128A347
| ML25128A347 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 05/12/2025 |
| From: | Renee Taylor NRC/RGN-II/DORS/PB5 |
| To: | Erb D Tennessee Valley Authority |
| References | |
| EAF-RII-2025-0052 IR 2025001 | |
| Download: ML25128A347 (1) | |
Text
EAF-RII-2025-0052 Delson Erb Vice President, OPS Support Tennessee Valley Authority 1101 Market Street, LP 4A-C Chattanooga, TN 37402-2801
SUBJECT:
WATTS BAR NUCLEAR PLANT - INTEGRATED INSPECTION REPORT 05000390/2025001 AND 05000391/2025001
Dear Delson Erb:
On March 31, 2025, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Watts Bar Nuclear Plant. On May 7, 2025, the NRC inspectors discussed the results of this inspection with Christopher Reneau, Site Vice President, and other members of your staff. The results of this inspection are documented in the enclosed report.
Three findings of very low safety significance (Green) are documented in this report. Two of these findings involved violations of NRC requirements. We are treating these violations as non-cited violations consistent with Section 2.3.2 of the Enforcement Policy.
If you contest the violations or the significance or severity of the violations documented in this inspection report, you should provide a response within 30 days of the date of this inspection report, with the basis for your denial, to the U.S. Nuclear Regulatory Commission, ATTN:
Document Control Desk, Washington, DC 20555-0001; with copies to the Regional Administrator, Region II; the Director, Office of Enforcement; and the NRC Resident Inspector at Watts Bar Nuclear Plant.
If you disagree with a cross-cutting aspect assignment or a finding not associated with a regulatory requirement in this report, you should provide a response within 30 days of the date of this inspection report, with the basis for your disagreement, to the U.S. Nuclear Regulatory Commission, ATTN: Document Control Desk, Washington, DC 20555-0001; with copies to the Regional Administrator, Region II; and the NRC Resident Inspector at Watts Bar Nuclear Plant.
May 12, 2025
D. Erb 2
This letter, its enclosure, and your response (if any) will be made available for public inspection and copying at http://www.nrc.gov/reading-rm/adams.html and at the NRC Public Document Room in accordance with Title 10 of the Code of Federal Regulations 2.390, Public Inspections, Exemptions, Requests for Withholding.
Sincerely, Ryan C. Taylor, Chief Projects Branch 5 Division of Operating Reactor Safety Docket Nos. 05000390 and 05000391 License Nos. NPF-90 and NPF-96
Enclosure:
As stated cc w/ encl: Distribution via LISTSERV Signed by Taylor, Ryan on 05/12/25
SUNSI Review X
Non-Sensitive
Sensitive X
Publicly Available
Non-Publicly Available OFFICE RII/DORS RII/DORS RII/DORS RII/DORS NAME N. Childs E. Robinson D. Hardage R. Taylor DATE 05/08/25 05/09/25 05/11/25 05/12/25
Enclosure U.S. NUCLEAR REGULATORY COMMISSION Inspection Report Docket Numbers:
05000390 and 05000391 License Numbers:
NPF-90 and NPF-96 Report Numbers:
05000390/2025001 and 05000391/2025001 Enterprise Identifier:
I-2025-001-0037 Licensee:
Tennessee Valley Authority Facility:
Watts Bar Nuclear Plant Location:
Spring City, Tennessee Inspection Dates:
January 1, 2025 to March 31, 2025 Inspectors:
D. Hardage, Senior Resident Inspector R. Wehrmann, Resident Inspector Approved By:
Ryan C. Taylor, Chief Projects Branch 5 Division of Operating Reactor Safety
2
SUMMARY
The U.S. Nuclear Regulatory Commission (NRC) continued monitoring the licensees performance by conducting an integrated inspection at Watts Bar Nuclear Plant, in accordance with the Reactor Oversight Process. The Reactor Oversight Process is the NRCs program for overseeing the safe operation of commercial nuclear power reactors. Refer to https://www.nrc.gov/reactors/operating/oversight.html for more information.
List of Findings and Violations Failure to Implement Transient Combustible Control Requirements for the Unit 1 Annulus Cornerstone Significance Cross-Cutting Aspect Report Section Initiating Events Green NCV 05000390/2025001-01 Open/Closed
[P.3] -
Resolution 71111.05 The inspectors identified a Green finding and associated non-cited violation (NCV) of Unit 1 Operating License Condition 2.F. for the licensees failure to implement the approved fire protection program as described in the Fire Protection Report. Specifically, the licensee failed to implement transient combustible material controls in the Unit 1 annulus in accordance with the Fire Protection Report and procedure NPG-SPP-18.4.7, Control of Transient Combustibles.
Failure to Identify a Failure Mechanism for Inlet Dampers not Opening Challenged 2A-A EDG Operability Cornerstone Significance Cross-Cutting Aspect Report Section Mitigating Systems Green NCV 05000390,05000391/2024004-01 Closed EAF-RII-2025-0052
[P.2] -
Evaluation 71111.12 NRC inspectors identified a Green finding and associated non-cited violation of 10 CFR 50, Appendix B, Criterion V, Instructions, Procedures, and Drawings, for the licensee's failure to identify the failure mechanism affecting performance of emergency diesel generator (EDG) intake damper sections as required by quality-related procedure NPG-SPP-22.300, "Corrective Action Program." Specifically, the licensee's performance of the same corrective actions subsequent to repetitive failures across a variety of the same components reasonably indicated that the equipment or part failure mechanism of multiple damper sections was not identified, which is required by NPG-SPP-22.300, Revision 25. This resulted in the 2A-A EDG being declared inoperable due to the failure of multiple damper sections on November 8, 2024.
Degradation of Main Generator Current Transformer 152C Causes Automatic Turbine and Reactor Trip Cornerstone Significance Cross-Cutting Aspect Report Section Initiating Events Green FIN 05000390/2025001-02 Open/Closed None (NPP) 71153
3 A self-revealed Green finding was identified when the licensee failed to properly classify main generator current transformers (CTs) as critical components in accordance with NPG-SPP-09.18.2, Equipment Reliability Classification. Specifically, during a single point vulnerability (SPV) review, the licensee improperly reclassified CTs as non-SPVs and non-critical components which led to lack of preventive maintenance and degradation of the 152C main generator CT.
Additional Tracking Items Type Issue Number Title Report Section Status LER 05000390/2024-002-00 Unit 1, Automatic Reactor Trip Due to Main Generator Protection Relay Actuation 71153 Closed
4 PLANT STATUS Unit 1 began the inspection period at rated thermal power. On January 17, 2025, the unit tripped due to a main generator lockout. The plant was cooled down and operated the remainder of the inspection period in Mode 5.
Unit 2 operated at or near rated thermal power for the entire inspection period.
INSPECTION SCOPES Inspections were conducted using the appropriate portions of the inspection procedures (IPs) in effect at the beginning of the inspection unless otherwise noted. Currently approved IPs with their attached revision histories are located on the public website at http://www.nrc.gov/reading-rm/doc-collections/insp-manual/inspection-procedure/index.html. Samples were declared complete when the IP requirements most appropriate to the inspection activity were met consistent with Inspection Manual Chapter (IMC) 2515, Light-Water Reactor Inspection Program - Operations Phase. The inspectors performed activities described in IMC 2515, Appendix D, Plant Status, observed risk-significant activities, and completed onsite portions of IPs. The inspectors reviewed selected procedures and records, observed activities, and interviewed personnel to assess licensee performance and compliance with Commission rules and regulations, license conditions, site procedures, and standards.
REACTOR SAFETY 71111.01 - Adverse Weather Protection Seasonal Extreme Weather Sample (IP Section 03.01) (1 Sample)
(1)
The inspectors evaluated readiness for seasonal extreme weather conditions prior to the onset of seasonal cold temperatures for the following systems:
Unit 1 and Unit 2 residual heat removal (RHR) and Unit 1 and Unit 2 auxiliary feedwater (AFW), on January 2, 2025 71111.04 - Equipment Alignment Partial Walkdown Sample (IP Section 03.01) (4 Samples)
The inspectors evaluated system configurations during partial walkdowns of the following systems/trains:
(1)
Unit 1 RHR system with the 'B' train in operation for shutdown cooling in Mode 5 with loops filled on January 27, 2025 (2)
Unit 2 safety injection system A train on February 19, 2025 (3)
Unit 2 120V AC vital power system 2-II with vital inverter 0-II aligned to vital instrument power board 2-II and vital inverter 2-II out of service for emergent maintenance on March 3, 2025 (4)
Unit 1 AFW - A train on March 19, 2025
5 71111.05 - Fire Protection Fire Area Walkdown and Inspection Sample (IP Section 03.01) (5 Samples)
The inspectors evaluated the implementation of the fire protection program by conducting a walkdown and performing a review to verify program compliance, equipment functionality, material condition, and operational readiness of the following fire areas:
(1)
Emergency diesel generator (EDG) building elevation 742' 2A-A EDG room, 2B-B EDG room, pipe gallery and corridor, and lube oil storage room on January 21, 2025 (2)
Intake pumping station on January 23, 2025 (3)
Unit 1 and Unit 2 6.9kV shutdown board rooms, auxiliary building elevation 757', on February 11, 2025 (4)
Unit 1 annulus after demobilization for containment integrated leak rate testing on March 5, 2025 (5)
Unit 1 lower containment on March 26, 2025 Fire Brigade Drill Performance Sample (IP Section 03.02) (1 Sample)
(1)
The inspectors evaluated the onsite fire brigade training and performance during an unannounced fire drill on March 7, 2025.
71111.07A - Heat Exchanger/Sink Performance Annual Review (IP Section 03.01) (1 Sample)
The inspectors evaluated readiness and performance of:
(1)
A-A main control room chiller during component outage March 9 - 15, 2025, under WO 123621065 71111.11Q - Licensed Operator Requalification Program and Licensed Operator Performance Licensed Operator Performance in the Actual Plant/Main Control Room (IP Section 03.01) (1 Sample)
(1)
The inspectors observed and evaluated licensed operator performance in the control room during a Unit 1 reactor shutdown on January 17, 2025.
Licensed Operator Requalification Training/Examinations (IP Section 03.02) (1 Sample)
(1)
The inspectors observed and evaluated a cycle 25-1 crew simulator exam involving a steam generator tube rupture scenario on March 20, 2025 (SEG # 3-OT-SRE-2501AL).
6 71111.12 - Maintenance Effectiveness Maintenance Effectiveness (IP Section 03.01) (2 Samples)
The inspectors evaluated the effectiveness of maintenance to ensure the following structures, systems, and components (SSCs) remain capable of performing their intended function:
(1)
D-A essential raw cooling water (ERCW) pump failure to start documented in condition report (CR) 1995665 on March 1, 2025 (2)
B Train ERCW strainer oil leak documented in CR 1994222 with repairs under work order (WO) 124336550 on March 3, 2025 Quality Control (IP Section 03.02) (1 Partial)
The inspectors evaluated the effectiveness of maintenance and quality control activities to ensure the following SSCs remain capable of performing their intended function:
(1)
(Partial) oil dispensing room, and diesel generator building oil storage room 71111.13 - Maintenance Risk Assessments and Emergent Work Control Risk Assessment and Management Sample (IP Section 03.01) (4 Samples)
The inspectors evaluated the accuracy and completeness of risk assessments for the following planned and emergent work activities to ensure configuration changes and appropriate work controls were addressed:
(1)
Unit 1 and 2, week of January 12 - 18, 2025, including protected equipment reviews for scheduled maintenance on 120V vital inverter 1-III, 1A RHR pump and emergent maintenance on Unit 2 main generator to switchyard tie breaker PCB-5048 (2)
Unit 2 elevated risk due to power supply alert and emergent repairs to 1-III vital inverter, January 21 - 22, 2025 (3)
Unit 1 and 2, week of March 2 - 8, 2025, including protected equipment reviews for Unit 1 shutdown defense-in-depth and for emergent maintenance on 120V Vital Inverter 2-II and the 'A' main control room chiller (4)
Unit 1 and 2, week of March 17 - 21, 2025, including protected equipment reviews for Unit 1 shutdown defense-in-depth and emergent work on the A-A MCR chiller and the emergent repairs to the125V vital DC distribution panel 5B 71111.15 - Operability Determinations and Functionality Assessments Operability Determination or Functionality Assessment (IP Section 03.01) (6 Samples)
The inspectors evaluated the licensee's justifications and actions associated with the following operability determinations and functionality assessments:
(1) 2B centrifugal charging pump (CCP) elevated reactor coolant system (RCS) leakage with pump in service on January 15, 2025
7 (2) 2B-B traveling water screen elevated oil leakage on January 22, 2025 (3)
Unit 1 reactor coolant pump #3, overdue flywheel exam as documented in CR 1986833, on January 22, 2025 (4)
ERCW pipe snubber misalignment as documented in CR 1982351, on January 29, 2025 (5)
Emergency diesel generator lube oil storage room less than 40 degrees as documented in CR 1988711, on January 30, 2025 (6)
Foamy oil in the 1A-A RHR pump motor oil sight glasses as documented in CR 1990739, on February 9, 2025 71111.18 - Plant Modifications Temporary Modifications and/or Permanent Modifications (IP Section 03.01 and/or 03.02) (1 Sample 1 Partial)
The inspectors evaluated the following temporary or permanent modifications:
(1)
(Partial) 480V EBR HVAC procedurally controlled temporary modification (2)
Procedure change to 0-SOI-31.01 to incorporate a temporary modification 71111.20 - Refueling and Other Outage Activities Refueling/Other Outage Sample (IP Section 03.01) (1 Sample)
(1)
The inspectors evaluated Unit 1 main generator forced outage activities from January 17 to March 31, 2025.
71111.24 - Testing and Maintenance of Equipment Important to Risk The inspectors evaluated the following testing and maintenance activities to verify system operability and/or functionality:
Post-Maintenance Testing (IP Section 03.01) (5 Samples)
(1) vital inverter 1-III repairs, due to failure documented in CR 1986372, under WO 12584294 on January 25, 2025 (2) 2B-B traveling water screen repairs under WOs 125012738, 125088340, and 125089939, on January 28, 2025 (3)
H-B ERCW pump post maintenance testing under WO 124101426, on February 14, 2025 (4) 1B-B CCP seal replacement under WO 1250115071, on February 20, 2025 (5)
D-A ERCW pump under WO 125157486, on February 25, 2025 Surveillance Testing (IP Section 03.01) (5 Samples)
(1) 2A containment spray pump quarterly test per 2-SI-72-901-A, on January 28, 2025 (2) 1A-A EDG surveillance test per 0-SI-82-17-A, "184 Day Fast Start and Load Test DG 1A-A," on January 29, 2025 (3) 2-SI-0-53.1-B, "Remote Transfer Switch Verification Performance - Train B," on March 3, 2025
8 (4) 1B-B EDG surveillance test per 0-SI-82-17-B, "184 Day Fast Start and Load Test DG 1B-B," on March 5, 2025 (5) 1-SI-0-703, "Containment Integrated Leak Rate Test," on WO 123765008 71114.06 - Drill Evaluation Required Emergency Preparedness Drill (1 Sample)
(1)
On February 25, 2025, the inspectors evaluated an emergency preparedness drill which included high vibrations in the #1 reactor coolant pump, resulting in seal failure and a loss of coolant accident that led to a safety injection and Alert declaration. This was followed by an EDG voltage regulator failure, loss of a shutdown board, phase B actuation, and failure of a containment spray pump discharge valve resulting in an increase in containment pressure that required a Site Area Emergency declaration.
Lastly, a containment penetration leak into the annulus and evidence of fuel failure resulted in a General Emergency declaration.
OTHER ACTIVITIES - BASELINE 71152A - Annual Follow-up Problem Identification and Resolution Annual Follow-up of Selected Issues (Section 03.03) (1 Sample)
The inspectors reviewed the licensees implementation of its corrective action program related to the following issues:
(1)
CR 1970157, NRC resident question on WBN definition of "Loops NOT filled" in TS 3.4.7/3.4.8 71153 - Follow Up of Events and Notices of Enforcement Discretion Event Report (IP Section 03.02) (1 Sample)
The inspectors evaluated the following licensee event reports (LERs):
(1)
LER 05000390/2024-002-00, Unit 1 Automatic Reactor Trip Due to Main Generator Protection Relay Actuation (ADAMS Accession No. ML24249A175). The inspection conclusions associated with this LER are documented in this report under Inspection Results Section 71153. This LER is Closed.
Personnel Performance (IP Section 03.03) (1 Sample)
(1)
The inspectors evaluated an uncomplicated reactor trip on Unit 1 due to a main generator lockout, and the licensees performance on January 17, 2025.
9 INSPECTION RESULTS Failure to Implement Transient Combustible Control Requirements for the Unit 1 Annulus Cornerstone Significance Cross-Cutting Aspect Report Section Initiating Events Green NCV 05000390/2025001-01 Open/Closed
[P.3] -
Resolution 71111.05 The inspectors identified a Green finding and associated NCV of Unit 1 Operating License Condition 2.F. for the licensees failure to implement the approved fire protection program as described in the Fire Protection Report. Specifically, the licensee failed to implement transient combustible material controls in the Unit 1 annulus in accordance with the Fire Protection Report and procedure NPG-SPP-18.4.7, Control of Transient Combustibles.
==
Description:==
Description:
On December 2, 2024, inspectors identified transient combustible materials outside of closed metal containers, in excess of the fire hazard analysis limits for the Unit 1 annulus. CR 1976195, which documented the condition, was closed on February 19, 2025, stating that all scaffold and housekeeping were cleaned and removed from the Unit 1 annulus.
However, during a walkdown on March 5, 2025, inspectors identified transient combustible materials in the Unit 1 annulus, outside of closed metal containers and in excess of the fire hazard analysis limits for the area. The inspectors observed that a significant amount of the transient combustibles previously identified and documented in CR 1976165, remained in the Unit 1 annulus. The licensee initiated CR 1996761 to document the transient combustible materials.
Licensee procedure NPG-SPP-18.4.7 Section 3.4.2 describes the Unit 1 annulus as a Risk Level 1 Fire Area, and states:
"Risk Level 1 Fire Areas must meet the following requirements: Staging or storing of transient combustible materials, outside of closed metal containers, is not allowed in Fire Risk Level 1 Fire Areas, unless: Transient Combustible Permit /
Evaluation, with appropriate compensatory measure or engineering evaluation, is performed for any transient combustible material introduced to these areas that are not either A. In-Use and constantly attended (as defined by this procedure) or B. Staged/stored in a closed metal container."
Further, the Fire Protection Report Part-II, "Fire Protection Plan," Section 10, "Control of Combustibles, states:
"Combustible Control Zones (CCZs) are established at WBN to strictly control or prohibit the placement of transient combustibles. Transient combustibles brought into CCZs require an evaluation in accordance with site administrative procedures CCZs are shown on the compartmentation drawings (Figures II-27A through II-46A excluding 37A)."
Figures II-39A and II-40A show that the Unit 1 annulus is a CCZ and contains a note which states "CCZ - Combustible Control Zone, Transient Combustibles not allowed in this area without adequate compensatory measures."
10 The licensee entered the condition discovered on December 2, 2024, as an adverse condition in the corrective action program (CR 1976195) but failed to ensure that the transient combustibles were removed from the area until March 5, 2025, when identified by NRC inspectors. The inspectors also noted that the license had not performed an engineering evaluation of transient combustibles introduced into the area.
Corrective Actions: The licensee documented the transient combustibles in CRs 19676195 and 1996761. The area was restored to compliance on March 5, 2025. CR 2001949 has been initiated to address any additional actions needed.
Corrective Action References: CR 1976195, CR 1996761, and CR 2001949 Performance Assessment:
Performance Deficiency: Failure to ensure that transient combustibles in the Unit 1 annulus were controlled in accordance with the requirements of the Fire Protection Report and NPG-SPP-18.4.7 was a performance deficiency within the licensee's ability to foresee and prevent.
Specifically, transient combustibles were identified in the Unit 1 annulus on December 2, 2024, and entered into the licensee's corrective action program as an adverse condition, but the licensee failed to ensure that either the transient combustibles were removed, or an engineering evaluation was performed.
Screening: The inspectors determined the performance deficiency was more than minor because it was associated with the Protection Against External Factors attribute of the Initiating Events cornerstone and adversely affected the cornerstone objective to limit the likelihood of events that upset plant stability and challenge critical safety functions during shutdown as well as power operations. Specifically, the fire loading was not within the fire hazard analysis limits, moreover these transient combustible materials were stored in a combustible control zone, which is specifically credited to ensure separation of the redundant trains without compensatory measures or engineering evaluation and required subsequent additional evaluation. This issue is similar to example 4.j. of IMC 0612 Appendix E.
Significance: The inspectors assessed the significance of the finding using IMC 0609 Appendix F, Fire Protection and Post - Fire Safe Shutdown SDP. Specifically, Step 1.3.1-A was screened per IMC 0609 APP F Attachment 2, and it was determined that the Degradation Rating did not meet any of the High Degradation examples; therefore, Step 1.3.1-A Question: was answered Yes - Screen to Green.
Cross-Cutting Aspect: P.3 - Resolution: The organization takes effective corrective actions to address issues in a timely manner commensurate with their safety significance. Specifically, the licensee documented initial discovery of the transient combustibles in the Unit 1 annulus as CR 1976195, but closed out the CR without ensuring compliance had been restored.
Enforcement:
Violation: Watts Bar Unit 1 Operating License Condition 2.F. states, in part: "TVA shall implement and maintain in effect all provisions of the approved fire protection program as described in the Fire Protection Report for the facility, as approved in Appendix FF of Section 3.5 of Supplement 18 and Supplement 29 of the SER (NUREG-0847)."
Fire Protection Report Part-II, Section 10 states: "Combustible Control Zones (CCZs) are established at WBN to strictly control or prohibit the placement of transient combustibles.
Transient combustibles brought into CCZs require an evaluation in accordance with site
11 administrative procedures.
NPG-SPP-18.4.7, Section 3.4.2 defines the Unit 1 annulus as a Risk Level 1 Fire Area, and states: "Risk Level 1 Fire Areas must meet the following requirements: Staging or storing of transient combustible materials, outside of closed metal containers, is not allowed in Fire Risk Level 1 Fire Areas, unless: Transient Combustible Permit/Evaluation, with appropriate compensatory measure or engineering evaluation, is performed for any transient combustible material introduced to these areas that are not either A. In-Use and constantly attended (as defined by this procedure) or B. Staged/stored in a closed metal container."
Contrary to the above, from December 2, 2024, to March 5, 2025, the licensee failed to implement the approved fire protection program as described in the Fire Protection Report.
Specifically, the licensee failed to prevent the introduction of transient combustibles into the Unit 1 annulus without evaluation and permit as required by the Fire Protection Report and NPG-SPP-18.4.7.
Enforcement Action: This violation is being treated as a non-cited violation, consistent with Section 2.3.2 of the Enforcement Policy.
Failure to Identify a Failure Mechanism for Inlet Dampers not Opening Challenged 2A-A EDG Operability Cornerstone Significance Cross-Cutting Aspect Report Section Mitigating Systems Green NCV 05000390,05000391/2024004-01 Closed EAF-RII-2025-0052
[P.2] -
Evaluation 71111.12 NRC inspectors identified a Green finding and associated non-cited violation of 10 CFR 50, Appendix B, Criterion V, Instructions, Procedures, and Drawings, for the licensee's failure to identify the failure mechanism affecting performance of emergency diesel generator (EDG) intake damper sections as required by quality-related procedure NPG-SPP-22.300, "Corrective Action Program." Specifically, the licensee's performance of the same corrective actions subsequent to repetitive failures across a variety of the same components reasonably indicated that the equipment or part failure mechanism of multiple damper sections was not identified, which is required by NPG-SPP-22.300, Revision 25. This resulted in the 2A-A EDG being declared inoperable due to the failure of multiple damper sections on November 8, 2024.
==
Description:==
On November 8, 2024, while performing rounds on the 2A-A EDG, an operator discovered three inlet damper sections, 2-MTR-30-444A-A, 2-MTR-30-444B-A, and 2-MTR-30-444D-A, had failed to open with an exhaust fan for the 2A-A EDG running.
Each EDG has four inlet damper sections and at least two damper sections are required to be open to support EDG operability in accordance with licensee procedures. The basis of this procedural requirement is licensee calculation EPMAMP081789. Appendix E, Section 9.0, Conclusion, states in part, failure of three of the four dampers causes the pressure loss to exceed the capability of the fan, causing possible unstable fan operation and exceeding the motor allowable horsepower during a LOOP.
Based on the above, the operators declared the 2A-A EDG inoperable on November 8, 2024, at 0715. The licensee entered this issue into the corrective action program as CR 1971401
12 and generated a minor maintenance work order to repair the damper sections.
A review of the licensee's corrective action program revealed that additional EDG damper failures had occurred in the 2024 calendar year:
The 2A-A EDG experienced the following damper failures:
1.
March 13, 2024, (CR 1916514) when two sections failed to open, condition closed to WO 2.
May 15, 2024, (CR 1931587) when one section failed to open, condition closed to WO 3.
August 14, 2024, (CR 1950860) when one section failed to open, condition closed to WO 4.
October 17, 2024, (CR 1966168) when two sections failed to open, condition closed to WO The 2B-B EDG experienced the following damper failures:
1.
June 10, 2024, (CR 1936490) one section failed to open, condition closed to WO 2.
September 18, 2024, (no CR identified) one damper failed to open 3.
October 23, 2024, (CR 1967644) two sections failed to open, and a third section was not fully open, condition closed to WO The 1B-B EDG experienced the following damper failures:
1.
October 8, 2024, (CR 1964560) one damper section failed to open, condition closed to WO The defined work scope in each of these minor maintenance work orders was to:
Troubleshoot damper intake linkage (for the appropriate fan) and lubricate pivot points and linkages as required to correct issue. These work orders lubricated pivot linkage points on each damper intake and stroked each damper several times. Revision 25 of NPG-SPP-22.300, Corrective Action Program, became effective on June 27, 2024, and added a requirement that cause evaluations identify the failure mechanism. Specifically, NPG-SPP-22.300, Section 3.4.2, "Corrective Action Development," paragraph B.1 prescribes that licensee staff create at least one action to correct the adverse condition, which includes an action to address the equipment or part failure mechanism. The CRs for the damper failures noted after June 27, 2024, occurred between August 14 and November 8, 2024, and did not identify the equipment or part failure mechanism.
Corrective Actions: On November 8, 2024, at 18:06, the 2A-A EDG was declared operable after repair and testing of damper sections 2-MTR-30-444B-A and 2-MTR-30-444D-A. The licensee documented issues related to the EDG dampers in the corrective action program, including trend reviews of damper failures (CR 1967949 and CR 1971736) and damper failure analysis (CR 1966168).
Corrective Action References: CR 1966168, CR 1967949, and CR 1971736 Performance Assessment:
Performance Deficiency: The licensees failure to identify the failure mechanism affecting performance of EDG intake damper sections as required by quality-related procedure NPG-SPP-22.300 is a performance deficiency. Specifically, multiple damper failures occurred over a one-year period where the failure mechanism of the dampers was not identified and corrected. This directly resulted in the 2A-A EDG being declared inoperable.
13 Screening: The inspectors determined the performance deficiency was more than minor because it was associated with the Equipment Performance attribute of the Mitigating Systems cornerstone and adversely affected the cornerstone objective to ensure the availability, reliability, and capability of systems that respond to initiating events to prevent undesirable consequences. The damper failures degraded the ability of the EDG HVAC system to provide adequate intake air flow to the EDG room, which challenged the reliability of the associated EDG. This led to the licensee declaring the 2A-A EDG inoperable on November 8, 2024.
Significance: The inspectors assessed the significance of the finding using IMC 0609 Appendix A, The Significance Determination Process (SDP) for Findings At-Power. The inspectors screened the significance of the finding using Exhibit 2 of IMC 0609 Appendix A for the mitigating systems cornerstone and determined that a detailed risk evaluation was required because the failure of the ventilation dampers represented the loss of function of equipment designated as risk-significant for greater than three days. A detailed risk evaluation was performed by a regional Senior Reactor Analyst using Systems Analysis Programs for Hands-on Integrated Reliability Evaluations (SAPHIRE) Version 8.2.11 and NRC Watts Bar Standardized Plant Analysis Risk (SPAR) model Version 8.80. The SPAR model was adjusted to add the ventilation equipment to the fault trees for the EDG rooms.
Flexible Coping Strategy (FLEX) implementation was enabled in the SPAR model for Station Blackout (SBO) scenarios. A conditional analysis was performed to evaluate the risk increase due to the failure of the ventilation intake dampers for the Unit 2 A-train EDG. A condition exposure period of 11 days was used for the analysis. The dominant sequences involved weather-related loss of offsite power (LOOP) initiating events. The LOOP was accompanied by common mode failure of the EDG ventilation dampers and random failure of the turbine-driven auxiliary feedwater pump with failure to recover offsite and emergency power sources prior to core damage. The estimated change in risk was mitigated by the relatively short exposure period of the finding. The analysis determined that the increase in core damage frequency (CDF) and large early release frequency (LERF) was less than 1E-06/year for delta-CDF and less than 1E-07/year for delta-LERF, representing a finding of very low safety significance (Green).
Cross-Cutting Aspect: P.2 - Evaluation: The organization thoroughly evaluates issues to ensure that resolutions address causes and extent of conditions commensurate with their safety significance. Following multiple damper failures, the licensee performed corrective actions that restored short-term functionality. However, the licensee failed to perform a thorough evaluation to identify the failure mechanism as required by NPG-SPP-22.300.
Enforcement:
Violation: 10 CFR 50, Appendix B, Criterion V, requires, in part that, activities affecting quality shall be prescribed by documented instructions, procedures, or drawings, of a type appropriate to the circumstances and shall be accomplished in accordance with these instructions, procedures, or drawings.
Quality-related procedure NPG-SPP-22.300, Revision 25, Section 3.4.2, paragraph B.1 prescribes that, for an adverse condition entered in the corrective action program, licensee staff create at least one action in the action plan to correct the adverse condition, which includes an action that addresses the equipment or part failure mechanism.
Contrary to the above, from August 14 to November 8, 2024, the licensee failed to accomplish activities affecting quality in accordance with an existing procedure appropriate to
14 the circumstances. Specifically, the licensees performance of the same corrective actions subsequent to repetitive failures across a variety of the same components reasonably indicated that these actions were not correcting the identified adverse condition as prescribed by NPG-SPP-22.300. This ultimately resulted in the inoperability of the 2A-A EDG.
Enforcement Action: This violation is being treated as a non-cited violation, consistent with Section 2.3.2 of the Enforcement Policy.
Degradation of Main Generator Current Transformer 152C Causes Automatic Turbine and Reactor Trip Cornerstone Significance Cross-Cutting Aspect Report Section Initiating Events Green FIN 05000390/2025001-02 Open/Closed None (NPP) 71153 A self-revealed Green finding was identified when the licensee failed to properly classify main generator current transformers (CTs) as critical components in accordance with NPG-SPP-09.18.2, Equipment Reliability Classification. Specifically, during a single point vulnerability (SPV) review, the licensee improperly reclassified CTs as non-SPVs and non-critical components which led to lack of preventive maintenance and degradation of the 152C main generator CT.
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Description:==
On July 8, 2024, at 1521 EDT while operating at 100% rated thermal power, Watts Bar Unit 1 received an actuation of the 187-G, C phase differential current relay. This relay actuation locked out the main generator which tripped the main turbine and the reactor. All control and shutdown bank rods inserted properly in response to the reactor trip.
All safety systems, including the auxiliary feedwater system, actuated in response to the trip as expected. There were no complications with the trip.
Post trip testing showed the 152 C phase CT, which provides input to the 187-G relay, to have indications of degradation that would have led to the relay actuation. The 152 C phase CT had been in service since 1996. Post trip testing also showed that an additional CT on phase B was degraded and another CT on phase A was potentially degraded. Testing of the generator protective system examined the integrity of the circuit cables, junction boxes, connections and relays and found no other indication of faults that would have led to the plant trip. The direct cause of the plant trip was determined to be the unexpected failure of the 152C current transformer.
Prior to 2013, the System 244 (Transformer Switchyard) CTs were classified as High Critical SPVs. In 2013, during an SPV review for System 244, the licensee reclassified CTs as non-SPVs and non-critical components due to a low risk of failure. This decision led to a lack of preventive maintenance and no replacement strategy for the CTs. Based on industry input the life of the CT 152C is between 25 and 40 years. Current transformer 152C had been installed for 28 years and no maintenance or testing had been performed to ensure the health of the CT.
Corrective Actions: The licensee replaced 152 loop CTs with the old 151 loop CTs. New ABB CTs were installed in the 151 loop and 15E B-phase. Post maintenance testing was completed, and the unit was returned to power. The licensee performed an extent of condition on both units' main generator protective systems and identified SPVs and reclassified the
15 components as critical. The licensee has adopted preventive maintenance strategies in accordance with industry best practices for the identified critical components.
Corrective Action References: CR 1942549 Performance Assessment:
Performance Deficiency: The reclassification of CT 152C from critical to non-critical during the 2013 SPV review for system 244 was a performance deficiency. Specifically, NPG-SPP-09.18.2, Revision 1, required, in part, that if the failure of a component will cause a reactor trip it will be classified as CC1 (critical). Contrary to this requirement, the Plant Health Committee approved removal of the CT 152C SPV/critical classification on March 4, 2013.
Screening: The inspectors determined the performance deficiency was more than minor because it was associated with the Equipment Performance attribute of the Initiating Events cornerstone and adversely affected the cornerstone objective to limit the likelihood of events that upset plant stability and challenge critical safety functions during shutdown as well as power operations. Specifically, the reclassification of CT 152C from critical to non-critical removed the rigorous process of setting up its preventive maintenance strategy in accordance with TVA procedures with system engineering ownership. This ultimately led to failure of CT 152C while in service and a reactor trip.
Significance: The inspectors assessed the significance of the finding using IMC 0609 Appendix A, The Significance Determination Process (SDP) for Findings At-Power. Using Exhibit 1, "Initiating Events Screening Questions," Section B, "Transient Initiators," the inspectors determined the finding screened as Green because it did not cause the loss of mitigation equipment relied upon to transition the plant from the onset of the trip to a stable shutdown condition.
Cross-Cutting Aspect: Not Present Performance. No cross-cutting aspect was assigned to this finding because the inspectors determined the finding did not reflect present licensee performance.
Enforcement: Inspectors did not identify a violation of regulatory requirements associated with this finding.
EXIT MEETINGS AND DEBRIEFS The inspectors verified no proprietary information was retained or documented in this report.
On May 7, 2025, the inspectors presented the integrated inspection results to Christopher Reneau, Site Vice President, and other members of the licensee staff.
16 DOCUMENTS REVIEWED Inspection Procedure Type Designation Description or Title Revision or Date 71111.01 Procedures 0-PI-OPS-1-FP Freeze Protection 0043 1-SOI-74.01 Residual Heat Removal System Revision 27 71111.04 Procedures 2-SOI-235.06 120V AC Vital Power System 2-II Revision 8 Calculations EPMDOM012990 Combustible Loading Data 158 CR 1976195 NRC Identified - U1 Annulus Cleanliness 12/02/2025 CR 1996761 NRC Discrepancies found during U1 Annulus walkdown 03/05/2025 Corrective Action Documents Resulting from Inspection CR 2000355 NRC Identified Portable heater for 5th Vital Battery Room on plastic step stool 03/19/2025 AUX-0-757-02 Pre-fire Plan Auxiliary Building 757.0 elevation 5
AUX-0-757-03 Pre-fire Plan Auxiliary Building 757.0 elevation 4
DGB-0-742-01 Pre-Fire Plan Diesel Generator Building Elevation 742.0 4
IPS-0-711-01 Pre-Fire Plan Intake Pumping Station Elevations 711.0 and 722.0 2
IPS-0-728-01 Pre-Fire Plan Intake Pumping Station Elevation 728.0 and 741.0 3
RXN-1-702-1 Reactor Building Elevation 702 Pre-Fire Plan 3
71111.05 Fire Plans RXN-1-713-1 Reactor Building Elevation 713 Pre-Fire Plan 2
Watts Bar Daily Operational Focus Report 1/21/2025 Miscellaneous Watts Bar Daily Operational Focus Report 1/22/2025 0-PI-OPS-20.0 Emergency Electrical Power Curtailment 004 71111.13 Procedures NPG-SPP-07.1.6 On Line Work Control Power System Alerts / Offsite Power 0015 Calculations N36704A Piping Analysis Calculation No. N3-67-04A 22 CR 1985001 Elevated RCS leakage observed during performance of 2-SI-68-32 with 2B CCP in service 01/15-2025 Corrective Action Documents CR 1986955 Oil Leaking on 2B-B TWS 01/23/2025 71111.15 Drawings 0-47W845-1 Mechanical Flow Diagram Raw Cooling Water System 29 71111.18 Procedures 0-SOI-30.07 Shutdown Board Rooms HVAC el 757 & 772 0027
17 Inspection Procedure Type Designation Description or Title Revision or Date NPG-SPP-09.4 10 CFR 50.59 Evaluations of Changes, Tests, and Experiments.
0019 CR 1986503 Unit 1 Lower Ice Condenser Rice Paper Missing 01/21/2025 CR 1986853 Ice Stalagmites in lower Ice 01/22/2025 CR 1986871 Water on floor near Loop 1 CRDM cooler 01/22/2025 71111.20 Corrective Action Documents Resulting from Inspection CR 2002249 NRC identified items in Unit 1 Containment 03/27/2025 71152A Corrective Action Documents CR 198942 Enhancements to Procedures and TS Bases from information in CR 1970157 02/03/2025