ML25356A125
| ML25356A125 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 12/22/2025 |
| From: | Nicole Warnek Division of Operating Reactors |
| To: | Mudrick C Constellation Energy Generation, Constellation Nuclear |
| References | |
| IR 2025003 | |
| Download: ML25356A125 (0) | |
Text
December 22, 2025 Christopher H. Mudrick Senior Vice President and Chief Nuclear Officer Constellation Energy Generation, LLC President Constellation Nuclear 200 Energy Way, KSA-3N Kennett Square, PA 19348
SUBJECT:
LIMERICK GENERATING STATION, UNITS 1 AND 2 - INTEGRATED INSPECTION REPORT 05000352/2025003 AND 05000353/2025003
Dear Christopher Mudrick:
On September 30, 2025, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Limerick Generating Station, Units 1 and 2. On December 4, 2025, the NRC inspectors discussed the results of this inspection with William Levis, Plant Manager, and other members of your staff. The results of this inspection are documented in the enclosed report.
Due to the temporary cessation of government operations, which commenced on October 1, 2025, the NRC began operating under its Office of Management and Budget-approved plan for operations during a lapse in appropriations. Consistent with that plan, the NRC operated at reduced staffing levels throughout the duration of the shutdown. However, the NRC continued to perform critical health and safety functions and made progress on other high-priority activities associated with the ADVANCE Act and Executive Order 14300. On November 13, 2025, following the passage of a continuing resolution, the NRC resumed normal operations. However, due to the 43-day lapse in normal operations, the Office of Nuclear Reactor Regulation granted the Regional Offices an extension on the issuance of the calendar year 2025, third quarter integrated inspection reports normally issued by November 15, 2025, to December 31, 2025. The NRC will resume the routine cycle of issuing inspection reports on a quarterly basis beginning with the calendar year 2025, fourth quarter integrated inspection reports, which will be issued 45 days after the fourth quarter ends on December 31, 2025.
No findings or violations of more than minor significance were identified during this inspection.
C. Mudrick 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, Nicole S. Warnek, Chief Projects Branch 3 Division of Operating Reactor Safety Docket Nos. 05000352 and 05000353 License Nos. NPF-39 and NPF-85
Enclosure:
As stated cc w/ encl: Distribution via LISTSERV NICOLE WARNEK Digitally signed by NICOLE WARNEK Date: 2025.12.22 12:21:11 -05'00'
ML25356A125 SUNSI Review Non-Sensitive Sensitive Publicly Available Non-Publicly Available OFFICE RI/DORS RI/DORS RI/DORS NAME AZiedonis SHaney NWarnek DATE 12/22/2025 12/22/2025 12/22/2025
Enclosure U.S. NUCLEAR REGULATORY COMMISSION Inspection Report Docket Numbers:
05000352 and 05000353 License Numbers:
NPF-39 and NPF-85 Report Numbers:
05000352/2025003 and 05000353/2025003 Enterprise Identifier: I-2025-003-0039 Licensee:
Constellation Energy Generation, LLC Facility:
Limerick Generating Station, Units 1 and 2 Location:
Sanatoga, PA 19464 Inspection Dates:
July 1, 2025 to September 30, 2025 Inspectors:
A. Ziedonis, Senior Resident Inspector L. Grimes, Resident Inspector B. Edwards, Health Physicist N. Harmon, Health Physicist A. Kostick, Health Physicist Approved By:
Nicole S. Warnek, Chief Projects Branch 3 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 Limerick Generating Station, Units 1 and 2, 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 No findings or violations of more than minor significance were identified.
Additional Tracking Items None.
3 PLANT STATUS Unit 1 began the inspection period at rated thermal power (RTP). On September 6, 2025, operators lowered thermal power to approximately 75 percent for a rod pattern adjustment and planned maintenance activities. The unit was restored to RTP on September 7, 2025, and remained at or near RTP for the remainder of the inspection period.
Unit 2 operated at or near RTP for the duration 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.
REACTOR SAFETY 71111.04 - Equipment Alignment Partial Walkdown Sample (IP Section 03.01) (3 Samples)
The inspectors evaluated system configurations during partial walkdowns of the following systems/trains:
(1)
Unit 2, reactor core isolation cooling (RCIC) system with the high pressure coolant injection (HPCI) system unavailable on July 23, 2025 (2)
Unit 2, 'B' and 'D' trains of the core spray system on August 21, 2025 (3)
Units 1 and Unit 2, Class 1E 125 volts direct current power distribution system during the week of September 1, 2025 Complete Walkdown Sample (IP Section 03.02) (1 Sample)
(1)
The inspectors evaluated system configurations during a complete walkdown of the Units 1 and 2, residual heat removal service water and spray pond make-up system alignment during the weeks of July 21 and 29, 2025.
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:
4 (1)
Unit 2, F-R-179, RCIC pump room, fire area 56, on July 1, 2025 (2)
Units 1 and 2, F-A-542, auxiliary equipment room, fire area 25, in response to fire system impairment 23146, on July 21, 2025 (3)
Units 1 and 2, F-S-001 and F-S-002, spray pond pump structure, fire areas 122 and 123, on July 25, 2025 (4)
Units 1 and 2, F-R-202, service water pipe tunnel room 202, fire area 75, on July 30, 2025 (5)
Unit 2, F-D-315-A, 'D21' emergency diesel generator (EDG) room and fuel oil and lube oil tank room, rooms 315A and 316A, fire area 83, on July 31,2025 Fire Brigade Drill Performance Sample (IP Section 03.02) (2 Samples)
(1)
The inspectors evaluated the onsite fire brigade training and performance during an unannounced fire drill on August 26, 2025.
(2)
The inspectors evaluated the onsite fire brigade training and performance during an unannounced fire drill on September 9, 2025.
71111.07A - Heat Exchanger/Sink Performance Annual Review (IP Section 03.01) (1 Sample)
The inspectors evaluated readiness and performance of:
(1)
Units 1 and 2, 'A' emergency service water (ESW) flow balance test on September 9 and 10, 2025 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 main control room during a planned Unit 1 power reduction for a rod pattern adjustment and maintenance activities on September 6 and 7, 2025.
Licensed Operator Requalification Training/Examinations (IP Section 03.02) (2 Samples)
(1)
The inspectors observed and evaluated licensed operator classroom system training associated with the digital modification project on August 15, 2025.
(2)
The inspectors observed and evaluated licensed operator training in the digital glasstop simulator on September 25, 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:
5 (1)
Unit 1, 'D12' EDG planned maintenance effectiveness during the week of July 14, 2025 (2)
Unit 1, 'B' residual heat removal (RHR) system outage window during the week of September 15, 2025 (3)
Unit 1, 'D12' EDG emergent maintenance effectiveness in response to a jacket water leak during the weeks of September 16 and 22, 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 remains capable of performing its intended function:
(1)
Unit 1, scram discharge volume level switch and float chamber assembly emergent maintenance during the weeks of September 1 and 8, 2025 71111.13 - Maintenance Risk Assessments and Emergent Work Control Risk Assessment and Management Sample (IP Section 03.01) (3 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 2, risk assessment in response to the discovery of an overdue surveillance test associated with the channel 'E' calibration and functional check of the scram discharge volume high water level on July 17, 2025 (2)
Units 1 and 2, elevated risk during grid emergencies and 'D11' EDG planned maintenance during the week of July 28, 2025 (3)
Unit 1, emergent work controls and associated plant risk following an electrical fault while closing in the 'B' balance-of-plant battery charger 480-volt breaker on August 21 and 22, 2025 71111.15 - Operability Determinations and Functionality Assessments Operability Determination or Functionality Assessment (IP Section 03.01) (4 Samples)
The inspectors evaluated the licensee's justifications and actions associated with the following operability determinations and functionality assessments:
(1)
Units 1 and 2, 'B' control enclosure chiller following unplanned trip during the week of June 30, 2025 (2)
Units 1 and 2, 'A' north stack radiation monitor functionality following loss of sample flow with 'B' north stack radiation monitor and wide range area monitor inoperable on August 4, 2025 (3)
Unit 1, HPCI system following the identification of unexpected stop valve movement during planned testing during the weeks of August 11 and 18, 2025 (4)
Units 1 and 2, ESW following the identification of a pipe leak during the weeks of August 11 and 18, 2025
6 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)
Unit 2, RCIC system barometric condenser condensate pump following corrective maintenance on July 1, 2025 (2)
Unit 2, 'A' RHR train comprehensive pump test following planned maintenance during the week of July 13, 2025 (3)
Unit 1, 'D12' EDG fast start test run following planned maintenance on July 18, 2025 (4)
Unit 1, HPCI turbine overspeed mechanism operability test following corrective maintenance on August 18, 2025 (5)
Units 1 and 2, 'A' ESW following temporary pipe clamp installation in manhole 214 on September 3, 2025 Surveillance Testing (IP Section 03.01) (2 Samples)
(1)
Unit 2, ST-6-052-231-2, "'A' Loop Core Spray Pump, Valve and Flow Test," on August 28, 2025 (2)
Unit 2, ST-6-055-231-2, "HPCI Pump Comprehensive Test" on September 17, 2025 Inservice Testing (IST) (IP Section 03.01) (1 Sample)
(1)
Unit 1, ST-6-048-231-1, "Standby Liquid Control Pump A/B/C Comprehensive Test,"
during the week of July 14, 2025 Diverse and Flexible Coping Strategies (FLEX) Testing (IP Section 03.02) (1 Sample)
(1)
Units 1 and 2, 'A' FLEX diesel generator loaded run on July 22, 2024 71114.06 - Drill Evaluation Required Emergency Preparedness Drill (1 Sample)
(1)
The inspectors observed and evaluated the adequacy of an emergency preparedness drill on August 5, 2025.
Additional Drill and/or Training Evolution (1 Sample)
The inspectors observed and evaluated:
(1)
A training evolution involving licensed operator requalification with associated emergency action level entry on September 22, 2025 RADIATION SAFETY 71124.05 - Radiation Monitoring Instrumentation
7 Walkdowns and Observations (IP Section 03.01) (5 Samples)
The inspectors evaluated the following radiation detection instrumentation during plant walkdowns:
(1)
Canberra Fast Scan Whole Body Counter (2)
Chemistry Canberra High Purity Germanium Counter (DET-1)
(3)
Chemistry Tri-Carb Liquid Scintillation Counter (LSC-1)
(4)
Control Room Emergency Ventilation System Radiation Monitor (RY-26-007A)
(5)
AMS4 at 5' line entrance SN#0013541 Calibration and Testing Program (IP Section 03.02) (10 Samples)
The inspectors evaluated the calibration and testing of the following radiation detection instruments:
(1)
Thermo AMS 4, SN#1004 (2)
Cronos-11 Large Article Monitor SN#336050 (3)
MGP DRM-2 SN#12711261 (4)
Ludlum Model 177 SN#337237 (5)
MGP Telepole SN#078238 (6)
Eberline AMS-4 SN#882/02565 (7)
Ludlum Model 177 SN#334048 (8)
Unit 2 General Atomic RD-23 Drywell Post LOCA Radiation Monitor #RY-026-291B (9) 41' Line RCA Exit PM-12 Portal Monitor SN#338000 (10) 41' Line RCA Exit Small Article Monitor (SAM) SN#335002 Effluent Monitoring Calibration and Testing Program Sample (IP Section 03.03) (2 Samples)
The inspectors evaluated the calibration and maintenance of the following radioactive effluent monitoring and measurement instrumentation:
(1)
Unit 2 Service Water Radiation Monitor #RE-26-210 (2)
Wide Range Accident Monitor 71124.07 - Radiological Environmental Monitoring Program Environmental Monitoring Equipment and Sampling (IP Section 03.01) (1 Sample)
(1)
The inspectors evaluated environmental monitoring equipment and observed collection of environmental samples.
Radiological Environmental Monitoring Program (IP Section 03.02) (1 Sample)
(1)
The inspectors evaluated the implementation of the licensees radiological environmental monitoring program.
8 Groundwater Protection Initiative Implementation (IP Section 03.03) (1 Sample)
(1)
The inspectors evaluated the licensees implementation of the Groundwater Protection Initiative program to identify incomplete or discontinued program elements.
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, for the period of July 1, 2024 through June 30, 2025 (2)
Unit 2, for the period of July 1, 2024 through June 30, 2025 IE04: Unplanned Scrams with Complications (USwC) Sample (IP Section 02.03) (2 Samples)
(1)
Unit 1, for the period of July 1, 2024 through June 30, 2025 (2)
Unit 2, for the period of July 1, 2024 through June 30, 2025 MS09: Residual Heat Removal Systems (IP Section 02.08) (2 Samples)
(1)
Unit 1, for the period of July 1, 2024 through June 30, 2025 (2)
Unit 2, for the period of July 1, 2024 through June 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)
The inspectors reviewed Constellation's evaluation and corrective actions in response to the Unit 1 'B' RHR minimum flow valve delayed closure response documented in issue report (IR) 4855353.
INSPECTION RESULTS Observation: Low Pressure Coolant Injection Past Operability Evaluated in Response to Inspector Question 71152A The inspectors performed a review of Constellation's evaluation and corrective actions in response to the Unit 1 'B' RHR minimum flow valve failure to close in a timely manner during logic system functional testing (LSFT), as documented in IR 4855353. Specifically, with the
'B' train of RHR declared inoperable and unavailable during the test, the minimum flow valve took greater than 10 minutes (exact time unknown) to close in response to a close signal. Inspectors noted that stroke time requirements for this motor operated valve were removed following implementation of Limerick's fourth in-service test (IST) interval in 2020, as permitted under the American Society of Mechanical Engineers (ASME) operation and
9 maintenance (OM) Code Case OMN-1, Revisions 1 and 2; Regulatory Guide 1.192, Revisions 3, 4 and 5; and NUREG-1482, Revisions 3 and 4. Inspectors also noted that historical stroke times for this valve were less than 30 seconds. Constellation paused the test with 'B' RHR remaining inoperable and unavailable, and performed simple troubleshooting that determined the most likely cause of the delayed response was attributed to oxidized contacts on a particular relay in the actuation circuit. In addition, Constellation determined that the contact oxidation was most likely cleared during subsequent valve closure strokes during simple troubleshooting. Constellation resumed and completed LSFT, declared 'B' RHR operable, and subsequently replaced the relay in a timely manner to ensure continued reliability of the system. Inspectors noted that Constellation determined the LSFT test was satisfactorily completed because there was no specific closure time requirement associated with the minimum flow valve.
The inspectors reviewed updated final safety analysis report (UFSAR) and noted the RHR minimum flow valves were designed to close when the low pressure coolant injection (LPCI) discharge valves opened, as described in UFSAR section 7.3.1.1.1.4.7 (LPCI actuated devices) and table 7.3-4 (minimum flow sensor range), and further noted the LPCI injection valve maximum opening time was described in UFSAR table 6.3-1 to be 64 seconds. Based on this design basis information, the inspectors questioned whether the 'B' LPCI train was capable of performing its safety function during the period of time when the relay was oxidized and causing a subsequent delay in the closure response of the minimum flow valve. In response, Constellation created assignment 5 to IR 4855353 and performed an engineering evaluation that determined the 'B' RHR pump had sufficient flow margin capability, given the associated emergency diesel generator (D12) governor setting at the time, to perform its required LPCI injection function with the minimum flow valve failed in a fully open condition. In addition, Constellation sent the relay for failure analysis and created an action to review the results under assignment 4 to IR 4855353. Lastly, while the IST program did not require periodic stroke timing of the RHR minimum flow valves, Constellation revised the IST Basis document for the RHR minimum flow valves to remove the statement that there was no licensing basis stroke time associated with the valves, given the UFSAR information noted above by the inspectors.
The inspectors did not identify any performance deficiencies associated with the issue described above, but noted Constellation missed an opportunity to review the past operability and reportability aspects prior to questioning by the inspectors.
EXIT MEETINGS AND DEBRIEFS The inspectors verified that no proprietary information was retained or documented in this report.
On December 4, 2025, the inspectors presented the integrated inspection results to William Levis, Plant Manager, and other members of the licensee staff.
On August 21, 2025, the inspectors presented the Exit Debrief for IP 71124.05 Radiation Monitoring Instrumentation inspection results to William Levis, Plant Manager, and other members of the licensee staff.
On September 25, 2025, the inspectors presented the NRC IP 71124.07 REMP Exit Debrief inspection results to William Levis, Plant Manager, and other members of the licensee staff.