IR 05000413/2025004

Integrated Inspection Report 05000413/2025004 and 05000414/2025004

ML26028A165
Person / Time
Site:	Catawba
Issue date:	01/29/2026
From:	Robert Williams NRC/RGN-II/DORS/EB1
To:	Huecker J Duke Energy Carolinas
References
IR 2025004
Download: ML26028A165 (0)

Text

SUBJECT:

CATAWBA NUCLEAR STATION - INTEGRATED INSPECTION REPORT 05000413/2025004 AND 05000414/2025004

Dear Jonathan Huecker:

On December 31, 2025, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Catawba Nuclear Station. On January 14, 2026, the NRC inspectors discussed the results of this inspection with Blaine Peters, Plant Manager, and other members of your staff.

The results of this inspection are documented in the enclosed report.

One finding of very low safety significance (Green) is documented in this report. This finding involved a violation of NRC requirements. We are treating this violation as a non-cited violation (NCV) consistent with Section 2.3.2 of the Enforcement Policy.

If you contest the violation or the significance or severity of the violation 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 Catawba Nuclear Station.

January 29, 2026 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, Robert E. Williams, Jr., Chief Projects Branch 1 Division of Operating Reactor Safety Docket Nos. 05000413 and 05000414 License Nos. NPF-35 and NPF-52

Enclosure:

As stated

Inspection Report

Docket Numbers:

05000413 and 05000414

License Numbers:

NPF-35 and NPF-52

Report Numbers:

05000413/2025004 and 05000414/2025004

Enterprise Identifier:

I-2025-004-0022

Licensee:

Duke Energy Carolinas, LLC

Facility:

Catawba Nuclear Station

Location:

York, South Carolina

Inspection Dates:

October 1, 2025, to December 31, 2025

Inspectors:

D. Rivard, Senior Resident Inspector

A. Wang, Resident Inspector

M. Kennard, Senior Operations Engineer

Approved By:

Robert E. Williams, Jr., Chief

Projects Branch 1

Division of Operating Reactor Safety

SUMMARY

The U.S. Nuclear Regulatory Commission (NRC) continued monitoring the licensees performance by conducting an integrated inspection at Catawba Nuclear Station, 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 Correct Through Wall Leak in Letdown Piping at Vent Valve Cornerstone Significance Cross-Cutting Aspect Report Section Initiating Events Green NCV 05000414/2025004-01 Open/Closed None (NPP)71111.12 A self-revealed Green finding and associated non-cited violation (NCV) of 10 CFR Part 50,

Appendix B, Criterion XVI, "Corrective Action," was identified when the licensee failed to correct a condition adverse to quality. Specifically, the licensee failed to implement corrective actions to address the vibration of letdown line components, including vent and drain valves, which resulted in pressure boundary through wall leakage at vent valve 2NV-951.

Additional Tracking Items

Type Issue Number Title Report Section Status LER 05000414/2025-004-00 LER 2025-004-00 for Catawba Nuclear Station,

Unit 2, Through Wall Leak in Letdown Piping 71111.12 Closed

PLANT STATUS

Unit 1 operated at or near RTP for the entire inspection period.

Unit 2 began the inspection period shut down for scheduled refueling outage, C2R27. The unit was returned to rated thermal power (RTP) on October 9, 2025, and operated at or near RTP for the remainder of the 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 on-site 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.

71111.04 - Equipment Alignment

Partial Walkdown Sample (IP Section 03.01) (1 Sample)

The inspectors evaluated system configurations during partial walkdowns of the following systems/trains:

(1) Nuclear service water system alignment to the nuclear service water pond for 2B nuclear service water pump testing on October 16, 2025

Complete Walkdown Sample (IP Section 03.02) (1 Sample)

(1) The inspectors evaluated system configurations during a complete walkdown of the Unit 1 auxiliary feedwater system on November 21 and 25, 2025.

71111.05 - Fire Protection

Fire Area Walkdown and Inspection Sample (IP Section 03.01) (1 Sample)

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 area:

(1) Fire area 51, Unit 1 exterior doghouse on November 25, 2025

71111.11A - Licensed Operator Requalification Program and Licensed Operator Performance

Requalification Examination Results (IP Section 03.03) (1 Sample)

The licensee completed the annual requalification operating examinations and biennial written examinations required to be administered to all licensed operators in accordance with Title 10 of the Code of Federal Regulations 55.59(a)(2), "Requalification Requirements," of the NRC's "Operator's Licenses." The inspector performed an in-office review of the overall pass/fail results of the individual operating examinations, the crew simulator operating examinations, and the biennial written examinations in accordance with IP 71111.11, "Licensed Operator Requalification Program and Licensed Operator Performance." These results were compared to the thresholds established in Section 3.03, "Requalification Examination Results," of IP 71111.11.

(1) The inspectors reviewed and evaluated the licensed operator examination failure rates for the requalification annual operating exam administered on August 14, 2025, and the biennial written exam completed on August 16, 2024.

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 auxiliary feedwater flow balancing and reactor startup following Unit 2 refueling outage on October 4, 2025.

Licensed Operator Requalification Training/Examinations (IP Section 03.02) (1 Sample)

(1) The inspectors observed and evaluated crew performance evaluation 2507A conducted in the plant reference simulator on November 13, 2025.

71111.12 - Maintenance Effectiveness

Maintenance Effectiveness (IP Section 03.01) (3 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) Nuclear condition report (NCR) 02567300, for base metal flaw and through wall leak upstream of letdown system vent valve (2NV-951) on October 16 and 17, 2025

(2) Catawba Units 1 and 2 maintenance rule evaluation as required by 10 CFR 50.65(a)(3) as contained in NCR 02555944 Assignment 05 on October 24, 2025

(3) NCR 2530230, loss of 2A offsite power on October 28, 2025

Quality Control (IP Section 03.02) (1 Sample)

The inspectors evaluated the effectiveness of maintenance and quality control activities to ensure the following SSC remained capable of performing its intended function:

(1) Emergency diesel generator fuel oil sample failures on acceptance parameter for lubricity as documented in NCRs 02544121, 02551674, 02554669 and 02556424

71111.13 - Maintenance Risk Assessments and Emergent Work Control

Risk Assessment and Management Sample (IP Section 03.01) (1 Sample)

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) Work order (WO) 20753527 to replace power supply #1 in 2B train solid state protection system while adhering to the requirements of Selected Licensing Commitment 16.7-16, "Reactor Trip Breaker and Solid State Protection System (SSPS) Logic Train Out of Service Commitments"

71111.15 - Operability Determinations and Functionality Assessments

Operability Determination or Functionality Assessment (IP Section 03.01) (5 Samples)

The inspectors evaluated the licensee's justifications and actions associated with the following operability determinations and functionality assessments:

(1) NCR02567313, containment air return fan damper (2ARF-D-4) open delay failed to meet surveillance requirement acceptance criteria

(2) NCR 02570871, risk assessment for Mode 3 entry with Unit 2 loss of ability to operate turbine driven auxiliary feed pump trip throttle valve (2SA-145) from control room

(3) NCR 02572460, Unit 2 solid state protection system train B power supply #1 failure

(4) NCR 02573442, power range nuclear instrument 2N43 declared inoperable due to an axial flux difference alarm

(5) NCR 02579802, Unit 2 2A auxiliary feed system sump pump and associated check valve 2WL-838 failure

71111.18 - Plant Modifications

Temporary Modifications and/or Permanent Modifications (IP Section 03.01 and/or 03.02) (1 Sample)

The inspectors evaluated the following temporary or permanent modifications:

(1) EC 424095, 2A hot leg resistance temperature detector replacement - rescale 2A Thot-average signal

71111.20 - Refueling and Other Outage Activities

Refueling/Other Outage Sample (IP Section 03.01) (1 Sample)

(1) The inspectors evaluated refueling outage C2R27 activities from September 3, 2025, to October 5, 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 (PMT) (IP Section 03.01) (5 Samples)

(1) PT/2/A/4200/023 B, "NC PORV and Air Supply Stroke Test," for pressurizer power operated relief valve (PORV) air supply check valve (2VI-367) leakage repair, on September 30, 2025

(2) PT/2/A4250/003 C, "Turbine Driven Auxiliary Feedwater Pump #2 Performance Test,"

following loss of ability to operate turbine driven auxiliary feed pump trip throttle valve (2SA-145) from control room, on October 4, 2025

(3) WO 20747276 for 2B letdown orifice outlet vent (2NV-951) valve replacement, on October 5, 2025

(4) WO 20067119, Unit 1 letdown pressure control valve (1NV-148) failed to control letdown system pressure due to a failure of the valve actuator, on December 3, 2025

(5) WO 20765397 and WO 20765398 for 2A auxiliary feed system sump pump and associated check valve repair, on December 17, 2025.

Surveillance Testing (IP Section 03.01) (1 Sample)

(1) PT/2/A/4200/009, "Engineered Safety Features Actuation Periodic Test," 13.1, "Train A ESF Test," performed on September 7 and 8, 2025

Ice Condenser Testing (IP Section 03.01) (1 Sample)

(1) MP/0/A/7150/005, "Ice Basket Weight Determination," and inspections performed under WO 20705059 throughout Unit 2 refueling outage

OTHER ACTIVITIES - BASELINE

71151 - Performance Indicator Verification The inspectors verified licensee performance indicators submittals listed below:

IE01: Unplanned Scrams per 7000 Critical Hours Sample (IP Section 02.01) (2 Samples)

(1) Unit 1 (October 1, 2024, through September 30, 2025)

(2) Unit 2 (October 1, 2024, through September 30, 2025)

MS05: Safety System Functional Failures (SSFFs) Sample (IP Section 02.04) (2 Samples)

(1) Unit 1 (October 1, 2024, through September 30, 2025)

(2) Unit 2 (October 1, 2024, through September 30, 2025)

BI01: Reactor Coolant System (RCS) Specific Activity Sample (IP Section 02.10) (2 Samples)

(1) Unit 1 (October 1, 2024, through September 30, 2025)

(2) Unit 2 (October 1, 2024, through September 30, 2025)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) NCR 02302424, 1A emergency diesel generator #3 con-rod bearing found rotated

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 report (LER):

(1) LER 05000414/2025-004-00, Through Wall Leak in Letdown Piping (ADAMS Accession No. ML25307A221). The inspection conclusions associated with this LER are documented in this report under Inspection Results Section 71111.12. This LER is closed.

INSPECTION RESULTS

Failure to Correct Through Wall Leak in Letdown Piping at Vent Valve Cornerstone Significance Cross-Cutting Aspect Report Section Initiating Events Green NCV 05000414/2025004-01 Open/Closed None (NPP)71111.12 A self-revealed Green finding and associated NCV of 10 CFR Part 50, Appendix B, Criterion XVI, "Corrective Action," was identified when the licensee failed to correct a condition adverse to quality. Specifically, the licensee failed to implement corrective actions to address the vibration of letdown line components, including vent and drain valves, which resulted in pressure boundary through wall leakage at vent valve 2NV-951.

Description:

On September 5, 2025, during containment boric acid walkdowns, the licensee discovered through wall leakage at the weld on the pipe elbow upstream of valve 2NV-951.

Vent valve 2NV-951 is a 1-inch valve that is socket welded to the 3-inch letdown line in a cantilever configuration. The valve is used for ensuring that the associated piping is vented for containment penetration leak rate testing.

The inspectors noted that the site had previous challenges associated with fatigue failure of socket welded components on the Unit 2 letdown line and that there was a general awareness of industry challenges with fatigue failures of socket welded components.

Specifically, in 2003, the licensee documented a leak caused by fatigue failure of piping at vent valve 2NV-950 in NCR 01420620. Actions were taken to repair the leak at 2NV-950 by using a butt weld to replace the failed socket weld. An evaluation of the event considered eliminating vent and drain valves to reduce the number of socket welded components on the letdown line, but due to the requirements of containment leak rate testing, the licensee was unable to do so. The site also generated a corrective action to evaluate vibrational data on the letdown line, including the associated vent and drain valves. However, several vent and drain valves were not analyzed due to challenges with accessibility (this included valve 2NV-951). Despite the licensee recognizing vibration-induced fatigue failure in socket welded piping, with licensee documents referencing industry operating experience including NRC Information Notice 98-45, Cavitation Erosion of Letdown Line Orifices Resulting In Fatigue Cracking of Pipe Welds, and EPRI TR-107455, Vibration Fatigue of Small Bore Socket Weld Joints, the licensee did not generate any additional actions to monitor or correct this deficiency.

The licensee submitted an 8-hour non-emergency notification in accordance with 10 CFR 50.72(b)(3)(ii)(A), as well as associated LER 050000414/2025-004-00, "Through Wall Leak in Letdown Piping," in accordance with 10 CFR 50. 73(a)(2)(ii)(A), for a condition of the nuclear power plant, including its principal safety barriers, being seriously degraded.

Corrective Actions: The licensee implemented a design change during the repair of the 2NV-951 line. Measures were taken to reduce susceptibility to fatigue failure, which included reducing the weight of 2NV-951 and utilizing 2:1 tapered welds. The licensee also initiated actions to evaluate a flow orifice design change to minimize pressure pulsations and vibration.

Corrective Action Reference: NCR 02567300

Performance Assessment:

Performance Deficiency: The licensee's failure to correct vibration-induced fatigue issues on the letdown line in accordance with 10 CFR Part 50, Appendix B, Criterion XVI, was a performance deficiency.

Screening: The inspectors determined the performance deficiency was more than minor because it was associated with the Design Control 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 failure to correct vibration-induced fatigue issues with letdown line socket welds resulted in pressure boundary leakage at vent valve 2NV-951.

Significance: The inspectors assessed the significance of the finding using IMC 0609 Appendix A, The Significance Determination Process (SDP) for Findings At-Power. Using IMC 0609, "Initial Characterization of Findings," and IMC 0609, Appendix A, "The Significance Determination Process for Findings At-Power," Exhibit 1, "Initiating Events Screening Questions," the inspectors determined the finding to be of very low safety significance (Green) because all questions were answered no. Specifically, the leakage from the 2NV-951 valve line was within the capacity of normal reactor coolant system makeup sources.

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:

Violation: 10 CFR Part 50, Appendix B, Criterion XVI, Corrective Action, requires, in part, that measures be established to ensure conditions adverse to quality, such as failures, malfunctions, deficiencies, deviations, defective material and equipment, and nonconformances are corrected. Contrary to the above, from 2003, to September 19, 2025, the licensee failed to establish measures to ensure a condition adverse to quality associated with letdown line vibration-induced fatigue was corrected. Specifically, the licensee did not evaluate all socket welded components on the letdown line for vibration-induced fatigue failure as identified in NCR 01420620, which resulted in pressure boundary leakage at vent valve 2NV-951.

Enforcement Action: This violation is being treated as a non-cited violation, consistent with Section 2.3.2 of the Enforcement Policy.

EXIT MEETINGS AND DEBRIEFS

The inspectors verified no proprietary information was retained or documented in this report.

• On January 14, 2026, the inspectors presented the integrated inspection results to Blaine Peters, Plant Manager, and other members of the licensee staff.

THIRD PARTY REVIEWS Inspectors reviewed the Nuclear Safety Review Board report that was issued in October 2025.

DOCUMENTS REVIEWED

Inspection

Procedure

Type

Designation

Description or Title

Revision or

Date

71111.15

Corrective Action

Documents

2579624