IR 05000352/2025004
| ML26040A086 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 02/09/2026 |
| From: | Nicole Warnek Division of Operating Reactors |
| To: | Mudrick C Constellation Energy Generation, Constellation Nuclear |
| References | |
| EAF-NMSS-2025-0219 IR 2025004 | |
| Download: ML26040A086 (0) | |
Text
February 9, 2026
SUBJECT:
LIMERICK GENERATING STATION, UNITS 1 AND 2 - INTEGRATED INSPECTION REPORT 05000352/2025004 AND 05000353/2025004 AND INDEPENDENT SPENT FUEL STORAGE INSTALLATION INSPECTION REPORT 07200065/2024001 AND EXERCISE OF ENFORCEMENT DISCRETION
Dear Christopher Mudrick:
On December 31, 2025, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Limerick Generating Station, Units 1 and 2. On January 30, 2026, the NRC inspectors discussed the results of this inspection with Michael Gillin, Site Vice President, 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.
A licensee-identified violation which was determined to be Severity Level IV is documented in this report. We are treating this violation as an NCV consistent with Section 2.3.2 of the Enforcement Policy.
The NRC identified a violation of Title 10 of the Code of Federal Regulations (10 CFR) 72.48, paragraphs (c)(1), (c)(2), and (d)(1), and provisions of 10 CFR 72.212 that resulted from a certificate of compliance (CoC) holders failure to comply with 10 CFR 72.48 for a CoC holder-generated change for the Holtec continuous basket shim multi-purpose canister variant design.
However, an Interim Enforcement Policy issued in August 2025 is applicable to this violation.
Specifically, Enforcement Policy Section 9.4, Enforcement Discretion for General Licensee Adoption of Certificate of Compliance (CoC) Holder-Generated Modifications under 10 CFR 72.48, provides enforcement discretion to not issue an enforcement action for this violation. The licensee will be expected to comply with 10 CFR 72.212 provisions after the NRC dispositions the noncompliance for a CoC holder-generated change that affects the general licensee.
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 I; the Director, Office of Enforcement; and the NRC Resident Inspector at Limerick Generating Station, Units 1 and 2.
If you disagree with a cross-cutting aspect assignment 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 I; and the NRC Resident Inspector at Limerick Generating Station, Units 1 and 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, 05000353, and 07200065 License Nos. NPF-39 and NPF-85
Enclosure:
As stated
Inspection Report
Docket Numbers:
05000352, 05000353, and 07200065
License Numbers:
Report Numbers:
05000352/2025004, 05000353/2025004, and 07200065/2024001
Enterprise Identifier: I-2025-004-0039 and I-2024-001-0105
Licensee:
Constellation Energy Generation, LLC
Facility:
Limerick Generating Station, Units 1 and 2
Location:
Sanatoga, PA
Inspection Dates:
October 1, 2025 to December 31, 2025
Inspectors:
A. Ziedonis, Senior Resident Inspector
L. Grimes, Resident Inspector
J. Kepley, Operations Engineer
A. Kostick, Health Physicist
Approved By:
Nicole S. Warnek, Chief
Projects Branch 3
Division of Operating Reactor Safety
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. A licensee-identified non-cited violation (NCV) is documented in report section: 71111.11
List of Findings and Violations
Failure to Promptly Identify Multiple Deficiencies Associated with Safety-Related Batteries Cornerstone Significance Cross-Cutting Aspect Report Section Mitigating Systems Green NCV 05000352,05000353/2025004-01 Open/Closed
[H.8] - Procedure Adherence 71111.12 The inspectors identified a Green finding and associated NCV of Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix B, Criterion XVI, Corrective Action, when Constellation did not promptly identify and correct conditions adverse to quality associated with multiple safety-related direct current battery cells on Unit 1 and Unit 2. Specifically, during the course of required periodic inspections, the licensee did not promptly identify and correct multiple battery cell deficiencies, such as corrosion on terminal post connections, seal bulge, lid cracking, and jar cracking, which resulted in urgent actions to assess operability and replace various battery system components.
Additional Tracking Items
Type Issue Number Title Report Section Status EDG EAF-NMSS-2025-0219 Noncompliance Related to a General Licensees Use of Non-Qualified Spent Fuel Casks (IEP 9.4)
60855 Closed LER 05000352/2025-002-00 LER 2025-002-00 for Limerick Generating Station, Unit 1,
Loss of Power to the 1A Reactor Protection System resulted in Multiple Invalid Primary Containment Isolations 71153 Closed
PLANT STATUS
Unit 1 began the inspection period at rated thermal power (RTP). On December 16, 2025, operators lowered thermal power to approximately 75 percent for a rod pattern adjustment and planned testing. The unit was restored to RTP on December 17, 2025, and remained at or near RTP for the remainder of the inspection period.
Unit 2 began the inspection period at RTP. On October 8, 2025, operators lowered thermal power to approximately 70 percent for a control rod pattern adjustment and planned maintenance activities. The unit was restored to RTP on October 9, 2025, and remained 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.
REACTOR SAFETY
71111.04 - Equipment Alignment
Partial Walkdown Sample (IP Section 03.01) (2 Samples)
The inspectors evaluated system configurations during partial walkdowns of the following systems/trains:
- (1) Unit 2, primary containment instrument gas system with degraded 'A' and 'B' compressors during the weeks of October 6 and 13, 2025
- (2) Unit 1, 'D' division safeguard battery following installation of a temporary seismic maintenance cart to support battery cell replacement on October 30, 2025
71111.05 - Fire Protection
Fire Area Walkdown and Inspection Sample (IP Section 03.01) (2 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) Unit 2, F-R-284, reactor enclosure cooling water heat exchanger area, fire area 64 on October 15, 2025
- (2) Units 1 and 2, F-A-542, Aux equipment room with a degraded fire detection panel during the week of October 20, 2025
71111.11A - Licensed Operator Requalification Program and Licensed Operator Performance
Requalification Examination Results (IP Section 03.03) (1 Sample)
- (1) The inspectors reviewed and evaluated the licensed operator examination failure rates for the requalification annual operating exam administered between October 10, 2025, and November 13, 2025, and the biennial written examinations administered between October 17, 2025, and November 13, 2025.
71111.11B - Licensed Operator Requalification Program and Licensed Operator Performance
Licensed Operator Requalification Program (IP Section 03.04) (1 Sample)
- (1) Biennial Requalification Written Examinations
The inspectors evaluated the quality of the licensed operator biennial requalification written examination administered the week of November 3-6, 2025 and performed a document review during the week of December 8-11, 2025. The inspection activities were separated in time due the government shutdown that was in progress during the annual operating exams administered by the licensee.
Annual Requalification Operating Tests
The inspectors evaluated the adequacy of the facility licensees annual requalification operating test.
Administration of an Annual Requalification Operating Test
The inspectors evaluated the effectiveness of the facility licensee in administering requalification operating tests required by 10 CFR 55.59(a)(2) and that the facility licensee is effectively evaluating their licensed operators for mastery of training objectives.
Requalification Examination Security
The inspectors evaluated the ability of the facility licensee to safeguard examination material, such that the examination is not compromised.
Remedial Training and Re-examinations
The inspectors evaluated the effectiveness of remedial training conducted by the licensee, and reviewed the adequacy of re-examinations for licensed operators who did not pass a required requalification examination.
Operator License Conditions
The inspectors evaluated the licensees program for ensuring that licensed operators meet the conditions of their licenses.
Control Room Simulator
The inspectors evaluated the adequacy of the facility licensees control room simulator in modeling the actual plant, and for meeting the requirements contained in 10 CFR 55.46.
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 October 8 and 9, 2025; as well as during Unit 1 surveillance testing on the D12 emergency diesel generator (EDG) and 4 kilo-volt vital bus on November 5, 2025.
Licensed Operator Requalification Training/Examinations (IP Section 03.02) (1 Sample)
- (1) The inspectors observed licensed operator training associated with an anticipated digital controls modification on December 17, 2025.
71111.12 - Maintenance Effectiveness
Maintenance Effectiveness (IP Section 03.01) (1 Sample)
The inspectors evaluated the effectiveness of maintenance to ensure the following structures, systems, and components remain capable of performing their intended function:
- (1) Unit 1, 'B' and 'D' safeguard battery maintenance effectiveness, during the week of November 3, 2025
71111.15 - Operability Determinations and Functionality Assessments
Operability Determination or Functionality Assessment (IP Section 03.01) (3 Samples)
The inspectors evaluated the licensee's justifications and actions associated with the following operability determinations and functionality assessments:
- (1) Unit 1, EDG D14 following identification of a potential degraded condition on cylinder number 3 liner during the week of October 13, 2025
- (2) Unit 1, 125/250 volts direct current (VDC) division II safeguard battery 1B1 following NRC identification of degradation on cell number 5 during the weeks of October 20 and 27, 2025
- (3) Unit 2, 'B' reactor enclosure recirculation system following emergent restoration from planned maintenance in response to the unplanned inoperability of 'A' reactor enclosure recirculation system on November 19, 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) (3 Samples)
- (1) Unit 2, verification of temporary leak repair on the service water cooling line to the off-gas recombiner after-condenser during the week of October 6, 2025
- (2) Unit 1, emergency service water 'B' supply to the Unit 2 turbine enclosure cooling water heat exchanger valve HV-011-205 stroke following breaker preventive maintenance during the week of November 3, 2025
Surveillance Testing (IP Section 03.01) (1 Sample)
- (1) Unit 2, ST-6-047-200-2, "Scram Discharge Volume Exercise Test," on October 10, 2025
Inservice Testing (IST) (IP Section 03.01) (1 Sample)
- (1) Unit 2, ST-6-061-200-2, "Liquid Radwaste Valve Test," on December 4, 2025
OTHER ACTIVITIES - BASELINE
71151 - Performance Indicator Verification The inspectors verified licensee performance indicators submittals listed below:
MS10: Cooling Water Support Systems (IP Section 02.09) (2 Samples)
- (1) Unit 1, for the period of October 1, 2024 through September 30, 2025
- (2) Unit 2, for the period of October 1, 2024 through September 30, 2025
BI01: Reactor Coolant System (RCS) Specific Activity Sample (IP Section 02.10) (2 Samples)
- (1) Unit 1, for the period of October 1, 2024 through September 30, 2025
- (2) Unit 2, for the period of October 1, 2024 through September 30, 2025
BI02: RCS Leak Rate Sample (IP Section 02.11) (2 Samples)
- (1) Unit 1, for the period of October 1, 2024 through September 30, 2025
- (2) Unit 2, for the period of October 1, 2024 through September 30, 2025
OR01: Occupational Exposure Control Effectiveness Sample (IP Section 02.15) (1 Sample)
- (1) Unit 1, for the period of October 1, 2024 through September 30, 2025 Unit 2, for the period of October 1, 2024 through September 30, 2025 PR01: Radiological Effluent Technical Specifications/Offsite Dose Calculation Manual Radiological Effluent Occurrences (RETS/ODCM) Radiological Effluent Occurrences Sample (IP Section 02.16) (1 Sample)
- (1) Unit 1, for the period of October 1, 2024 through September 30, 2025 Unit 2, for the period of 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) The inspectors reviewed Constellation's evaluation and corrective actions in response to a jacket water (JW) leak on EDG D12, documented in Issue Reports 4899077 and 4900670
71152S - Semiannual Trend Problem Identification and Resolution
Semiannual Trend Review (Section 03.02) (1 Sample)
- (1) The inspectors reviewed the licensees corrective action program for potential adverse trends that might be indicative of a more significant safety issue.
===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 352-2025-002-00, "Loss of Power to the 1A Reactor Protection System Resulted in Multiple Invalid Primary Containment Isolations" (Agencywide Documents Access and Management System (ADAMS) Accession No. ML25224A176). The inspection conclusions associated with this LER are documented in this report under Inspection Results Section 71153. This LER is closed.
OTHER ACTIVITIES
- TEMPORARY INSTRUCTIONS, INFREQUENT AND ABNORMAL
60855 - Operation of an Independent Spent Fuel Storage Installation
Inspections were conducted using the appropriate portions of the 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 IMC 2690, Inspection Program for Storage of Spent Reactor Fuel and Reactor-Related Greater-than-Class C Waste at Independent Spent Fuel Storage Installations (ISFSI) and for 10 CFR Part 71 Transportation Packagings."
Operation of an Independent Spent Fuel Storage Installation (1 Sample)
- (1) The inspectors conducted a periodic in-office follow-up that focused on the review of the general licensees (GLs) implementation of the 10 CFR 72.48 process and associated corrective actions related to independent spent fuel storage installation activities. The review included:
- 10 CFR 72.48 Evaluations and Screenings: Reviewed the GLs 10 CFR 72.48 process and associated evaluation associated with the adoption of the continuous basket shim (CBS) variant.
- Corrective Action Program: Reviewed condition reports related to the design change of the CBS variant.
INSPECTION RESULTS
Enforcement Discretion Enforcement Action EAF-NMSS-2025-0219: Noncompliance Related to a General Licensees Use of Non-Qualified Spent Fuel Casks (IEP 9.4)60855
Description:
Holtec International (also referred to as the CoC [Certificate of Compliance]
holder) implemented a design change to its multi-purpose canister fuel basket, known as the CBS variant, which altered the structural configuration from welded to bolted shims. This change resulted in a departure from the method of evaluation (MOE) described in the final safety analysis report (FSAR) used to establish the design basis for tip-over events. Holtec did not fully evaluate the cumulative impact of the MOE changes or apply them consistently with the licensing basis. As a result, the NRC issued three Severity Level IV violations to Holtec for noncompliance with 10 CFR 72.48 requirements (see U.S. Nuclear Regulatory Commission Inspection Report 07201014/2022-201, Holtec International, ML23145A175; and Holtec International, Inc. - Notice of Violation; The U.S. Nuclear Regulatory Commission Inspection Report No. 07201014/2022-201, ML24016A190).
When the GL chooses to adopt a change the CoC holder made pursuant to a CoC holder's change authority under 10 CFR 72.48 (referred to herein as a CoC holder-generated change), the GL must perform a separate review using the requirements of 10 CFR 72.48(c).
Accordingly, when the GL chooses to adopt a CoC holder-generated change, and that change results in a non-conforming cask, there is a violation of 10 CFR 72.48 and certain provisions of 10 CFR 72.212 by the GL, in addition to a CoC holder violation of 10 CFR 72.48. As it relates to the adoption of the CBS variant casks, the GL failed to recognize the noncompliance with 10 CFR 72.48 requirements made by the CoC holders design change and subsequently loaded the CBS variant casks.
Corrective Actions:
The GL entered this into its corrective action program with actions to restore compliance with the 10 CFR 72.212 provisions that require each cask to conform to the terms, conditions, and specifications of a CoC or an amended CoC listed in 72.214.
Corrective Action References: AR 04762683
Enforcement:
Significance/Severity: This violation was dispositioned in accordance with Section 9.4, Enforcement Discretion for General Licensee Adoption of CoC Holder-Generated Changes Under 10 CFR 72.48, of the NRCs Enforcement Policy.
Specifically, as stated in the Policy, the NRC will exercise enforcement discretion and not issue an enforcement action to a GL, for a noncompliance with the requirements of paragraphs (c)(1) and
- (2) and (d)(1) of 10 CFR 72.48 and with provisions of 10 CFR 72.212 that require GLs to ensure use of casks that conform to the terms, conditions and specifications of a CoC listed in 10 CFR 72.214, when the noncompliance results from a CoC holders failure to comply with 10 CFR 72.48 for a CoC holder-generated change.
Violation:
10 CFR 72.48 (c)(1) requires, in part, that a licensee or certificate holder may make changes in the facility or spent fuel storage cask design as described in the FSAR (as updated), without obtaining:
- (ii) CoC amendment submitted by the certificate holder pursuant to § 72.244 if:
- (c) The change, test, or experiment does not meet any of the criteria in paragraph (c)(2) of this section.
10 CFR 72.48(c)(2) requires, in part, that a GL shall request that the certificate holder obtain a CoC amendment, prior to implementing a proposed change, if the change would: (viii) Result in a departure from an MOE described in the FSAR used in establishing the design bases or in the safety analyses.
10 CFR 72.48(d)(1) requires, in part, that the licensee shall have a written evaluation which provides the bases for the determination that the change does not require a CoC amendment pursuant to 10 CFR 72.48(c)(2).
10 CFR 72.212(b)(3) requires, in part, a GL must ensure that each cask used by the GL conforms to the terms, conditions, and specifications of a CoC or an amended CoC listed in 10 CFR 72.214.
Contrary to the above, in August 2023, the GL loaded the first CBS design variant and failed to maintain records of changes in the spent fuel storage cask design made pursuant to 10 CFR 72.48(c) that include a written evaluation which provided the bases for the determination that the change did not require a CoC amendment. The GL failed to request that the certificate holder obtain a CoC amendment, prior to implementing a proposed change, if the change would: (viii) result in a departure from an MOE described in the FSAR used in establishing the design bases or in the safety analyses. Further, the GL failed to ensure each cask conformed to the terms, conditions, and specifications of a CoC or amended CoC listed in 10 CFR 72.214.
Basis for Discretion: When a GL chooses to adopt a CoC holder-generated change, and that change results in a non-conforming cask, there is a violation of 10 CFR 72.48 and certain provisions of 10 CFR 72.212 by the GL, in addition to a CoC holder violation of 10 CFR 72.48.
And, when a GL chooses to adopt a CoC holder-generated change without performing a separate 10 CFR 72.48 analysis, the GL is in violation of 10 CFR 72.48. These requirements could lead to enforcement actions being issued against both the GL's 10 CFR 72.48 program (as well as certain 10 CFR 72.212 violations) and the CoC holder's 10 CFR 72.48 program for changes that originated with the CoC holder. The NRC has concluded that this enforcement approach would be inconsistent with efficiency, which is one of the NRC's Principles of Good Regulation, and NRC's mission of efficient and reliable oversight.
Since this violation meets the conditions of the NRC's Enforcement Policy Section 9.4, "Enforcement Discretion for General Licensee Adoption of Certificate of Compliance Holder-Generated Changes under 10 CFR 72.48" (ML25224A097), and the GL has entered the noncompliance into the corrective action program, the NRC is exercising enforcement discretion by not issuing an enforcement action for this violation.
Licensee-Identified Non-Cited Violation 71111.11B This violation of very low safety significance was identified by the licensee and has been entered into the licensee corrective action program and is being treated as an NCV, consistent with Section 2.3.2 of the Enforcement Policy.
Violation:
A licensee-identified Severity Level IV NCV of 10 CFR 55.25, "Incapacitation Because of Disability or Illness," was identified when Constellation did not notify the NRC within 30 days of a change to one licensed reactor operator's (RO) medical condition. 10 CFR 55.25 requires that if, during the term of the license, the licensee develops a permanent physical or mental condition that causes the licensee to fail to meet the requirements of § 55.21 of this part, the facility licensee shall notify the Commission, within 30 days of learning of the diagnosis, in accordance with § 50.74(c). For conditions for which a conditional license (as described in § 55.33(b) of this part) is requested, the facility licensee shall provide medical certification on Form NRC 396 to the Commission (as described in § 55.23 of this part).
Specifically, a licensed operator developed a medical condition which resulted in the facility notifying the NRC of a change in the ROs license conditions and temporary restriction from performing licensed duties. The licensee notified the NRC of this change in medical condition on October 7, 2024. In response, the NRC required the licensee to notify the NRC prior to the RO resuming licensed duties and that the NRC must agree that his condition is satisfactory and receive an updated NRC Form 396, signed by the operator, along with medical evidence that he is able to return to work. Contrary to that requirement, the licensee did not notify the NRC until the following year on October 9, 2025, after the RO had been performing licensed duties since December 2024 and continued to perform these duties for several months.
Significance/Severity: Severity Level IV. This violation was screened as traditional enforcement in accordance with IMC 0612, Appendix B, "Issue Screening," because it involved the failure to notify the NRC of a change in licensed activities, and assigned a Severity Level IV because it fits the Severity Level IV example of Enforcement Policy Section 6.4.d.1, "Violation Examples: Licensed Reactor Operators." Specifically, this section states:
"Severity Level IV violations involve, for example d.1.(c) an individual operator who did not meet ANSI/ANS 3.4, Section 5, as certified on NRC Form 396, 'Certification of Medical Examination by Facility Licensee,' required by 10 CFR 55.23, due to an incomplete medical examination, but was subsequently found to meet the health requirements for licensing." No cross-cutting aspect was assigned because the violation was processed using traditional enforcement
Corrective Action References: AR 04896963 Failure to Promptly Identify Multiple Deficiencies Associated with Safety-Related Batteries Cornerstone Significance Cross-Cutting Aspect Report Section Mitigating Systems
Green NCV 05000352,05000353/2025004-01 Open/Closed
[H.8] - Procedure Adherence 71111.12 The inspectors identified a Green finding and associated NCV of 10 CFR Part 50, Appendix B, Criterion XVI, Corrective Action, when Constellation did not promptly identify and correct conditions adverse to quality associated with multiple safety-related direct current battery cells on Unit 1 and Unit 2. Specifically, during the course of required periodic inspections, the licensee did not promptly identify and correct multiple battery cell deficiencies, such as corrosion on terminal post connections, seal bulge, lid cracking, and jar cracking, which resulted in urgent actions to assess operability and replace various battery system components.
Description:
The safeguard battery system consists of four divisions per unit to provide independent electrical power to certain safety-related plant loads vital for safe shutdown.
Divisions I and II consist of two 60-cell banks per division, and each division is capable of supplying 125 VDC or 250 VDC. Divisions III and IV supply 125 VDC and consist of 60 cells per division. Each cell is rated for approximately two volts and is connected in series to achieve the required voltage for each division. Technical Requirements Manual (TRM) section 4.8.2.1 contains maintenance requirements for the safeguard batteries, including verification that cell terminal connections are free of corrosion or exhibit satisfactory resistance, voltage, and electrolyte level; and also that cells show no visual indication of physical damage or abnormal deterioration, or is evaluated through an engineering evaluation as having no impact to cell functionality.
On September 5, 2025, inspectors identified corrosion buildup on the terminal post connections of Unit 1, division II bank 2 (1B2) cell #19. Constellation documented this under IR 4895576 and created a work request (WR) on September 10 to clean the corrosion. On October 24, during a subsequent walkdown of both banks of the Unit 1, division II batteries, inspectors noted the corrosion on cell #19 had not yet been cleaned and also identified significant corrosion buildup on bank 1B1 cell #5. Constellation subsequently cleaned the 1B2 cell #19 corrosion on October 27. For 1B1 cell #5, Constellation documented the condition under IR 4908536, performed cell voltage and resistance readings in accordance with TRM 4.8.2.1a to support the initial operability screening, and prioritized expedited replacement of the cell post connection hardware in lieu of cleaning due to concerns with the significant corrosion buildup. On November 21, Constellation entered a two-hour technical specification (TS) limiting condition for operation (LCO) action statement under 3.8.2.1.c to jumper out 1B1 cell #5, install a temporary seismic battery rack, and perform the post connection hardware replacement.
The inspectors performed a corrective action program review and noted 1B1 cell #5 was previously written up for corrosion under IR 4685761 on June 20, 2023, and IR 4857423 on April 15, 2025. The 2025 IR was closed to a WR that cleaned the corrosion on April 16 and recommended monitoring for more frequent excessive buildup which might require future cell replacement. The inspectors performed a review of completed battery inspections since April 15, 2025, and determined that no additional IRs or work activities were generated for 1B1 cell #5 until inspectors identified significant corrosion buildup on October 24, 2025. Specifically, the inspectors reviewed Constellation procedure ST-6-095-912-1, Div I 125/250 VDC 1B1D101/1B2D101 Safeguard Battery Quarterly Inspection, revision 44, completed May 8 and August 7, 2025, and noted that step 4.3.4 required an IR if cell terminals or connectors exhibited corrosion. In addition, the inspectors noted that ST-6-095-905-1, Unit 1 Safeguard Battery Weekly Inspection, revision 24, was performed multiple times from April 15 to October 24, and step 4.3.1.6 required notification to maintenance to ensure TRM 4.8.2.1a.1 (clean corrosion) is met. While the weekly surveillance test did not contain specific guidance to generate an IR when cell terminals or connections exhibited corrosion, procedure PI-AA-120, Issue Identification and Screening Process, revision 13, step 4.3.4 required generating an IR when an equipment deficiency was identified.
On October 28, 2025, during the performance of weekly surveillance test inspections, Constellation identified cracked lids on multiple Unit 1, division IV (1D) safeguards battery cells and documented the condition under IR 4909737. Additionally, Constellation identified a vertical cell jar crack extending well below the liquid electrolyte level on 1D cell #18, with evidence of electrolyte weepage, and documented this in IR 4909735. In response to the cracked cell jar, Constellation performed a formal operability evaluation under Engineering Change 646123, which included vendor seismic testing of a bounding cracked cell. On October 30, Constellation entered two-hour TS LCO action statement under 3.8.2.1.c to jumper out 1D cell #18, install a seismic battery rack, and perform single cell replacement. The inspectors performed a corrective action program review and noted 1D cell #18 was previously written up for a cracked lid under IR 4899593 on September 22, 2025. Inspectors reviewed pictures from the September 22 IR, and noted the same cell jar crack below the electrolyte level was present as was later documented on October 28, but was not discussed in the September 22 IR, and therefore not evaluated in the operability screening. The inspectors therefore determined the delay in identification of a cracked battery cell jar below the electrolyte level was another example of not promptly identifying a battery cell deficiency.
On November 5, 2025, inspectors performed a walkdown of the Unit 1, division I batteries, and identified corrosion on the terminal connections of 1B1 cells 49 and 59. Constellation documented this condition under IR 4912250 and subsequently cleaned the battery cell terminals on November 6. The inspectors noted earlier the day on November 5, prior to the NRC walkdown, electrical maintenance completed an annual battery inspection and cleaning under Work Order 5597032 and maintenance procedure M-095-007, Maintenance of Battery Rack and Cells, revision 4, but did not identify the corrosion on cells 49 and 59 despite direction in procedure step 5.3.7 to generate an IR if corrosion is found, and step 5.4.2 to clean the corrosion. Additionally, operators had performed the weekly ST-6-095-905-1 during the previous nights shift, and did not identify the corrosion on cells 49 and 50.
Between November 24 and December 14, 2025, Constellation documented two additional IRs (4916778 and 4921112) capturing deficiencies associated with 66 safeguard battery cells across Units 1 and 2, such as positive plate growth, seal distortion, and cracked lids. The IRs included an evaluation that the physical damage and abnormal deterioration had no impact on cell functionality, as directed by TRM 4.8.2.1. The inspectors noted that many of the deficiencies appeared to have been present for extended periods of time without any previous IRs written against them.
Corrective Actions:
The licensee generated IRs for all of the deficiencies described above, evaluated the issues for any operability impacts, and performed various corrective-type maintenance activities commensurate with the priority and significance of each issue.
Corrective Action References: IRs 4895576, 4908536, 4909735, 4912250, 4916778, and 4921112
Performance Assessment:
Performance Deficiency: The inspectors determined that not promptly identifying and correcting safeguard battery deficiencies such as terminal connection corrosion, physical damage, and abnormal deterioration, in accordance with TRM section 4.8.2.1 as well as multiple station procedures as noted above, was reasonably within Constellations ability to foresee and correct, and that further degradation of several battery cells should have been prevented. Therefore, the inspectors determined this constituted a performance deficiency.
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. Specifically, the failure to promptly identify and correct corrosion, physical damage, and abnormal deterioration on multiple safeguard battery cells adversely affected the battery system reliability, resulted in additional licensee actions to ensure functional capability of two cells, and resulted in the unavailability of two battery system divisions to urgently replace degraded components.
Significance:
The inspectors assessed the significance of the finding using IMC 0609, Appendix A, The Significance Determination Process (SDP) for Findings At-Power.
Specifically, using Exhibit 2, Mitigating Systems, the finding was determined to be of very low safety significance, or Green, because the deficiencies did not affect the design or qualification of the batteries, and the degraded conditions did not represent a loss of PRA function of any trains or systems.
Cross-Cutting Aspect:
H.8 - Procedure Adherence: Individuals follow processes, procedures, and work instructions. Specifically, the inspectors determined that the cause of Constellation not promptly identifying and correcting the safety-related battery deficiencies was attributed to not following station procedures.
Enforcement:
Violation: 10 CFR Part 50, Appendix B, Criterion XVI, Corrective Action, requires, in part, that measures shall be established to assure that conditions adverse to quality, such as failures, malfunctions, deficiencies, deviations, defective material and equipment, and nonconformances are promptly identified and corrected.
Contrary to the above, from May 8, 2025 (estimated) to December 14, 2025, Constellation did not assure that conditions adverse to quality of the Units 1 and 2 safeguard batteries were promptly identified and corrected. Specifically, Constellation did not promptly identify and correct multiple safeguard battery deficiencies such as terminal connection corrosion, physical damage, and abnormal deterioration, which resulted in adverse impacts to the safety-related batteries.
Enforcement Action:
This violation is being treated as an NCV, consistent with Section 2.3.2 of the Enforcement Policy.
Minor Performance Deficiency 71152A Failure to Generate a New IR or Update an Existing WR for EDG JW Leakage
Minor Performance Deficiency: The inspectors performed a problem identification and resolution annual inspection sample to review Constellations identification, evaluation, and corrective actions associated with a JW leak on the D12 EDG. During the review, inspectors identified that Constellation did not write a new IR, nor update an existing WR, for repetitive (at least 5) JW expansion tank low level alarms between August 13, 2025, and August 26, 2025. Inspectors noted that on each occasion, operators performed the required JW tank make-up via manual alignment of the demineralized water system. Additionally, inspectors noted that on each occasion, operators referenced, but did not update, open WR 1594457 from previous IR 4882809 (written July 17, 2025) capturing an issue where D12 JW leakage was stopped following a planned maintenance window by closing a quarter-turn drain valve that leads to the common D12 JW drain line. Inspectors noted that the associated WR 1594457 was created to correct slight misalignment of the mechanical stop on the quarter-turn drain valve, because the slight open condition was not previously recognized. On September 18, 2025, following receipt of a subsequent JW expansion tank low level alarm, operators investigated and identified a JW leak of 6 milliliters per minute (mL/min) from the D12 common JW drain line, which was documented in IR 4899077. Operators determined that the 6 mL/min leak rate would amount to 12.2 mL/min with the JW system pressurized in-service, and that D12 EDG remained OPERABLE due to the JW leak rate remaining below the allowable 14.75 mL/min leak rate without credit for manual make-up over the 7-day EDG mission time, as determined under Engineering Technical Evaluation 202873-01. Operators subsequently added IR 4899077 to the priority work list and stopped the JW leak on September 22, 2025.
The inspectors reviewed PI-AA-120, Issue Identification and Screening Process, revision 13, and determined that the repetitive examples of JW expansion tank low level alarms between August 13 and August 26, 2025, would have required either an update to the existing WR per step 4.1.5, or the generation of a new IR per step 4.1.5 or 4.3.4. The inspectors determined that not meeting required steps of PI-AA-120 constituted a performance deficiency.
Constellation documented this NRC-identified issue in IR 4930703.
Screening:
The inspectors determined the performance deficiency was minor. The inspectors determined this issue did not adversely impact any of the cornerstone objectives. Specifically, the potential delay in identifying a JW leak from the common drain line due to not writing a new IR nor updating the existing did not result in EDG inoperability.
Minor Performance Deficiency 71153 Inadequate Component Classification in Accordance with the Preventive Maintenance Program
Minor Performance Deficiency: The inspectors reviewed the work group evaluation (WGE)associated with IR 4872773, in response to a loss of 120 volts alternating current power to the Unit 1 A reactor protection system (RPS) distribution panel 1A-Y160, which occurred on June 13, 2025. Initial investigation by Constellation revealed that an underfrequency protective relay experienced an apparent spurious actuation, which resulted in the opening of one of two in-series main supply breakers to the 1A-Y160 panel. As a result of the event, Unit 1 experienced a half-scram condition, a half nuclear steam supply shut-off system (NSSSS)group 1 isolation, and multiple nuclear steam supply shut-off system single-channel isolations, thereby resulting in LER 2025-002-00 due to an invalid RPS actuation that resulted in containment isolation valve actuation signals in more than one system. In response to the event, Constellation performed a failure analysis of the protective relay and did not identify any failed components. The WGE noted that this relay was functionally tested every two years during refueling outages, in accordance with TS Surveillance Requirement 4.8.4.3, with no adverse trend in relay performance. The WGE discussed the corrective action that was completed to replace the relay and created several additional assignments, including assignment 6 to Engineering to review the protective relay preventive maintenance strategy.
The inspectors reviewed the WGE and discussed the event with Operations and Engineering personnel. The inspectors noted IR 4792069 was written August 6, 2024, as a result of a fleetwide Generation Risk Reduction initiative, and included assignment 9 to re-evaluate the equipment classification of various components associated with the RPS distribution panels, including the protective relays. Inspectors noted this assignment was not completed at the time of the June 13, 2025, event. Following the event, Engineering re-evaluated the RPS protective relay equipment classification under assignment 9 of IR 4792069 and determined the RPS protective relays were required to be classified as critical components in accordance with ER-AA-200-1001, as opposed to the previous classification as non-critical. Inspectors reviewed and discussed the change in equipment classification with Engineering, as well as WGE assignment 6 to review the protective maintenance strategy, and noted that no changes in preventive maintenance actions were required, mainly due to the once-per-two-year functional testing that was already occurring. Inspectors reviewed the vendor manual associated with the underfrequency relay that experienced the spurious trip and noted that there were no time-based replacement recommendations from the vendor. Additionally, the inspectors noted Constellations WGE reviewed operating experience associated with other similar relay styles throughout the industry and did not identify any adverse performance trends that would warrant changes to the preventive maintenance strategy.
The inspectors determined that not performing an appropriate equipment classification for the RPS underfrequency protective relay, in accordance with ER-AA-200, Preventive Maintenance Program, revision 7, step 4.1.3, constituted a performance deficiency.
Screening:
The inspectors determined the performance deficiency was minor. The inspectors determined this issue did not adversely impact any of the cornerstone objectives. Specifically, the inspectors did not identify any information that would indicate the misclassification of the relay resulted in the apparent spurious actuation. As an additional data point, the resultant plant level impact from the relay actuation did not result in any associated power changes on the unit, and resulted in a half scram condition - which is similar to several minor examples in IMC 0612, Appendix E, Examples of Minor Issues.
EXIT MEETINGS AND DEBRIEFS
The inspectors verified that no proprietary information was retained or documented in this report.
- On January 30, 2026, the inspectors presented the integrated inspection results to Michael Gillin, Site Vice President, and other members of the licensee staff.
DOCUMENTS REVIEWED
Inspection
Procedure
Type
Designation
Description or Title
Revision or
Date
71111.11A Miscellaneous
25 Exam Results for 71111.11A
71111.11B Miscellaneous
OP-AA-105-101 - Administrative Process For NRC License
and Medical Requirements
Sim Testing results Load Release 2024-01
Sim Testing results Load Release 2024-02
Sim Testing results Load Release 2025-01
Open and Closed Simulator SWRs
RT-6-000-994-0, Rev. 27 - VERIFICATION OF OPERATOR
QUALIFICATIONS
LOR 2025 week 4 Biennial written exam
LOR 2025 Scenario Guides:
SEG-2160E REV 2
SEG5005E REV 7
SEG-7008E REV 3
SEG 3006E REV 11
JPM-LOJPM3134 REV 0
JPM-LOJPM3074 REV 2
JPM-LOJPM3044 REV 2
JPM-LOJPM 3041 REV 0