ML25349A002
| ML25349A002 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 12/15/2025 |
| From: | Matt Young Division of Operating Reactors |
| To: | Carr E Dominion Energy |
| References | |
| IR 2025003 | |
| Download: ML25349A002 (0) | |
Text
December 15, 2025 Eric S. Carr Chief Nuclear Officer and President - Nuclear Operations and Contracted Energy Dominion Energy, Inc.
Innsbrook Technical Center 5000 Dominion Blvd.
Glen Allen, VA 23060-6711
SUBJECT:
MILLSTONE POWER STATION, UNITS 2 AND 3 - INTEGRATED INSPECTION REPORT 05000336/2025003 AND 05000423/2025003
Dear Eric Carr:
On September 30, 2025, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Millstone Power Station, Units 2 and 3. On December 3, 2025, the NRC inspectors discussed the results of this inspection with Mark Goolsbey, Director, Nuclear Operations, 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 make 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.
One Severity Level IV violation without an associated finding is documented in this report. We are treating this violation as a non-cited violation (NCV) consistent with Section 2.3.2 of the Enforcement Policy.
No NRC-identified or self-revealing findings were identified during this inspection.
E. Carr 2
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 I; the Director, Office of Enforcement; and the NRC Resident Inspector at Millstone Power Station, Units 2 and 3.
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, Matt R. Young, Chief Projects Branch 2 Division of Operating Reactor Safety Docket Nos. 05000336 and 05000423 License Nos. DPR-65 and NPF-49
Enclosure:
As stated cc w/ encl: Distribution via LISTSERV MATTHEW YOUNG Digitally signed by MATTHEW YOUNG Date: 2025.12.15 08:30:34 -05'00'
ML25349A002 SUNSI Review Non-Sensitive Sensitive Publicly Available Non-Publicly Available OFFICE RI/DORS RI/DORS RI/DORS NAME BPinson NMentzer MYoung DATE 12/11/2025 12/11/2025 12/11/2025
Enclosure U.S. NUCLEAR REGULATORY COMMISSION Inspection Report Docket Numbers:
05000336 and 05000423 License Numbers:
DPR-65 and NPF-49 Report Numbers:
05000336/2025003 and 05000423/2025003 Enterprise Identifier: I-2025-003-0045 Licensee:
Dominion Energy Nuclear Connecticut, Inc.
Facility:
Millstone Power Station, Units 2 and 3 Location:
Waterford, CT Inspection Dates:
July 01, 2025 to September 30, 2025 Inspectors:
E. Bousquet, Resident Inspector D. Antonangeli, Resident Inspector E. Chen, Reactor Inspector N. Eckhoff, Health Physicist P. Finney, Senior Resident Inspector J. Kepley, Operations Engineer A. Kostick, Health Physicist N. Mentzer, Senior Project Engineer S. Veunephachan, Senior Health Physicist Approved By:
Matt R. Young, Chief Projects Branch 2 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 Millstone Power Station, Units 2 and 3, 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 Main Steam Safety Valve Lift Setpoint Exceeds Technical Specification Allowable Value, Closure of LER 05000336/2024-002-00 and 05000336/2024-002-01 Cornerstone Severity Cross-Cutting Aspect Report Section Not Applicable Severity Level IV NCV 05000336/2025003-01 Open/Closed Not Applicable 71153 A self-revealed Severity Level IV NCV of Technical Specification (TS) 3.7.1.1 was identified when Dominion discovered, through as-found surveillance testing, that two main steam safety relief valves (MSSVs) had lift pressure setpoints that were not within TS lift setting tolerance of +/- 3 percent.
Additional Tracking Items Type Issue Number Title Report Section Status LER 05000336/2024-002-00 LER 2024-002-00 for Millstone Power Station, Unit 2, Two Main Steam Safety Valves Failed To Lift Within the Acceptance Criteria Resulting in a Condition Prohibited by Technical Specifications 71153 Closed LER 05000336/2024-002-01 LER 2024-002-01 For Millstone, Unit 2, Two Main Steam Safety Valves Failed To Lift Within The Acceptance Criteria Resulting In A Condition Prohibited By Technical Specifications 71153 Closed
3 PLANT STATUS Unit 2 operated at or near rated thermal power for the entire inspection period.
Unit 3 began the inspection period at rated thermal power. On July 31, 2025, the unit shut down for a planned maintenance outage and returned to rated thermal power on August 5, 2025. On August 14, 2025, the unit lowered power to approximately 18 percent for maintenance on the C reactor coolant pump and returned to rated thermal power on August 16, 2025. On September 28, 2025, the unit lowered power to approximately 72 percent, and subsequently, returned to rated thermal power in response to notification by ISO New England that offsite power line 371 was being removed from service. The unit remained at or near rated thermal power 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, 'B' high pressure safety injection system from the refueling water storage tank header to the containment penetration, March 6, 2025 This sample was completed in the first quarter of 2025, but due to an administrative error it was not documented in the Millstone Power Station, Units 2 and 3, integrated inspection report 05000336/2025001 and 05000423/2025001. (ADAMS Accession No. ML25125A114)
(2)
Unit 2, 'B' emergency diesel generator (EDG) fuel oil system, July 16, 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:
4 (1)
Unit 2, 'B' EDG room (fire area A-16), July 16, 2025 (2)
Unit 2, service water intake structure (fire areas I-1A, I-1B, I-1C), July 21, 2025 71111.12 - Maintenance Effectiveness Maintenance Effectiveness (IP Section 03.01) (4 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)
Unit 2 'A' vital chiller (X-169A) (WO53203464719), August 8, 2025 (2)
Unit 3, site fire water valve replacement for Millstone License Renewal involving tagging of multiple pumps and significant valve leakby, August 11, 2025 (3)
Unit 3, A1 evaluation associated with increased leakage for Unit 3 'C' reactor coolant pump seal, August 25, 2025 (4)
Unit 3, review of east switchgear room air conditioning unit filter replacement preventive maintenance activity (RE608034), September 15, 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 3, increased risk due to the emergent through-wall leak on service water piping inside the enclosure tube originally identified on May 20, 2025 (2)
Unit 3, site fire water valve replacement for Millstone License Renewal involving tagging of multiple pumps and significant valve leakby, August 11, 2025 (3)
Unit 2, Yellow probabilistic risk assessment (PRA) risk due to reserve station service transformer out of service along with switchyard north bus maintenance outage associated with breaker 15G-1T-2 installation, August 25, 2025 71111.15 - Operability Determinations and Functionality Assessments Operability Determination or Functionality Assessment (IP Section 03.01) (1 Sample)
The inspectors evaluated the licensee's justifications and actions associated with the following operability determinations and functionality assessments:
(1)
Unit 2, operability determination for direct current (DC) switchgear following failure of vital DC switchgear chiller (X-169A) per CR1297232, July 29, 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:
5 Surveillance Testing (IP Section 03.01) (2 Samples)
(1)
Unit 2, SP-2613N, "'B' EDG 18 Month Surveillance from Safety Injection Actuation System Start," Work Orders (WOs) 53203441516 and 53203441512, July 15, 2025 (2)
Unit 2, SP-2402PD, "Channel 'D' SPEC 200 Safety Parameters Functional Test," WO 53203442217, July 23, 2025 Inservice Testing (IST) (IP Section 03.01) (2 Samples)
(1)
Unit 3, SP-3608.2, "Safety Injection Pump 'B' Cooling Pump Comprehensive IST,"
and SP-3630E.2, "Safety Injection Pump 'B' Quarterly IST," July 22, 2025 (2)
Unit 3, 3610A.2, "Residual Heat Removal Pump 3RHS*P1B Operational Readiness Test," July 30, 2025 Reactor Coolant System Leakage Detection Testing (IP Section 03.01) (1 Sample)
(1)
Unit 3, elevated unidentified leakage due to degraded 'D' reactor coolant pump seal, March 5, 2025 This sample was completed in the first quarter of 2025, but due to an administrative error it was not documented in the Millstone Power Station, Units 2 and 3, integrated inspection report 05000336/2025001 and 05000423/2025001. (ADAMS Accession No. ML25125A114)
RADIATION SAFETY 71124.05 - Radiation Monitoring Instrumentation Walkdowns and Observations (IP Section 03.01) (5 Samples)
The inspectors evaluated the following radiation detection instrumentation during plant walkdowns:
(1)
Unit 3, area radiation monitor 3RMS-RM12 (2)
AMS-4 air monitor SN #13187 (3)
Unit 3, primary auxiliary building 24' Sirius 5AB (4)
Unit 2, resin drum (-45') area radiation monitor (RM-9813)
(5)
Unit 2, drum decontamination area (RM-7892)
Calibration and Testing Program (IP Section 03.02) (10 Samples)
The inspectors evaluated the calibration and testing of the following radiation detection instruments:
(1)
Fixed pump air sampler SN #5587 (2)
Eberline RO-40 SN #1350 (3)
Ludlum 2241 SN #234904 (4)
Rad-eye GX SN #602 (5)
Ludlum 177 SN #208722 (6)
SAM12 SN #144 (7)
Amp-100 SN #5003-010 (8)
Tele-pole SN #6618-035
6 (9)
Victoreen air monitor 808B SN #1207 (10)
Eberline RO-20 SN #1165 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 3, vent high gas 3HVR*RE10A2 (2)
Unit 2, vent normal gas RM-8132B OTHER ACTIVITIES - BASELINE 71152A - Annual Follow-up Problem Identification and Resolution Annual Follow-up of Selected Issues (Section 03.03) (3 Samples)
The inspectors reviewed the licensees implementation of its corrective action program related to the following issues:
(1)
Unit 3, 'C' reactor coolant pump seal degradation including seal leakage, oscillating differential stage pressure, (CR1296419), August 25 - September 5, 2025 (2)
Unit 3, service water enclosure tube maintenance activity risk assessment and management (CR1292867), September 30, 2025 (3)
Unit 2, failure of 2-CH-432 and 2-CH-433 to close during check valve surveillance testing (CR1271772 and CR1271962), September 30, 2025 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 05000336/2024-002-00, Unit 2, Two Main Steam Safety Valves Failed To Lift Within the Acceptance Criteria Resulting in a Condition Prohibited by Technical Specifications (ADAMS Accession No. ML24331A015) and supplement 05000336/2024-002-01 (ADAMS Accession No. ML25079A251): The inspection conclusions associated with these LERs are documented in this report under Inspection Results Section 71153. These LERs are closed.
INSPECTION RESULTS Observation: Risk Assessment and Management During Maintenance Activities 71152A Inspectors completed a review of the licensee's corrective actions associated with risk screening for maintenance activities, such as the temporary removal of the Unit 3 service water enclosure tube hatch flood barrier to support service water pipe inspections. The inspectors reviewed multiple work orders that performed this maintenance activity during at power and shutdown configurations and noted the activity was screened as low risk.
The inspectors reviewed "Operational Risk Assessment," WM-AA-201, and determined activities that have the potential to cause uncontrolled flooding through defeating flood control
7 equipment should be screened as medium risk. However, the licensee provided evidence that during the short durations the maintenance activity was performed at power, there was a continuous flood watch and contingency measures in place to reinstall the flood barrier.
Therefore, the inspectors determined the performance deficiency was minor because it did not adversely affect the initiating events 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 contingency measures in place would have prevented the impact of a service water flooding initiating event.
The inspectors reviewed "Shutdown Risk Management," OU-AA-200, and noted potential flood hazards are considered in the shutdown risk review checklist. The inspectors challenged the qualitative risk assessment and the licensee performed a quantitative risk assessment (PRA-MPS3-RA.038 Revision 0) which concluded the risk was low as long as the activity is completed within approximately 51 days. The inspectors noted in all work orders reviewed the maintenance activity was complete and restored within 51 days.
The licensee restored the service water enclosure tube hatch flood barrier following maintenance activities and documented planned corrective actions (CR1292867) to review and revise risk assessment procedures and general operating procedures, as necessary, and to clarify guidance for assessing and managing risk associated with maintenance activities.
Main Steam Safety Valve Lift Setpoint Exceeds Technical Specification Allowable Value, Closure of LER 05000336/2024-002-00 and 05000336/2024-002-01 Cornerstone Severity Cross-Cutting Aspect Report Section Not Applicable Severity Level IV NCV 05000336/2025003-01 Open/Closed Not Applicable 71153 A self-revealed Severity Level IV NCV of Technical Specification (TS) 3.7.1.1 was identified when Dominion discovered, through as-found surveillance testing, that two main steam safety relief valves (MSSVs) had lift pressure setpoints that were not within TS lift setting tolerance of +/- 3 percent.
==
Description:==
With the plant in MODE 1 at 100 percent rated thermal power on October 1, 2024, set pressure testing of Unit 2 MSSVs was conducted per plant procedures.
Two of the valves did not meet the as-found acceptance criteria of +/- 3 percent within setpoint. Technical Specification (TS) Table 4.7-1 allows a +/- 3 percent setpoint tolerance (allowable value) on the as-found lift setting for operability. During this testing, the MSSVs are operable provided that the actual as-found lift settings are within +/- 3 percent of the required lift setting. A footnote to Table 4.7-1 required that the lift setting be within +/-1 percent of the required lift setting following testing (as-left).
The as-found lift pressures for the two valves exceeded the +/- 3 percent TS allowable values and were, therefore, inoperable. The test result for 2-MS-249 was 4 percent below the nameplate set pressure of 1000.3 psig, or 10.2 psi outside of the acceptance range. The test result for 2-MS-251 was 3.3 percent below the nameplate set pressure of 1020.3 psig, or 3.0 psi outside of the acceptance range. Dominion promptly declared each valve inoperable.
2-MS-249 was retested following adjustment until it had two successive tests with results meeting the required set pressure "as-left" test acceptance criteria of +/- 1 percent, and 2-MS-251 was retested without adjustment, until two consecutive tests were within the required "as-left" +/- 1 percent criteria. Based on two successive, acceptable as-left tests,
8 Dominion declared both valves operable.
Test scope expansion was required and all other MSSVs were tested on the A main steam header. All as-found lift settings associated with the expanded test scope were found to be within +/- 3 percent of their set pressures. Additionally, two valves on the B main steam header were tested and found to be within the acceptable +/- 3 percent acceptance criteria.
As described in NUREG-1022, Event Report Guidelines 10 CFR 50.72 and 50.73, a similar discrepancy in multiple valves is an indication that the discrepancies may have occurred at some point during the operating cycle and were, therefore, likely inoperable for greater than the TS allowed outage time of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, this condition was reportable under 10 CFR 50.73(a)(2)(i)(B), "any operation or condition prohibited by the plant's TSs." Dominion submitted LER 05000336/2024-002-00, Two Main Steam Safety Valves Failed to Lift Within the Acceptance Criteria Resulting in a Condition Prohibited by Technical Specifications, (ADAMS Accession Number ML24331A015) and supplement 05000336/2024-002-01 (ADAMS Accession Number ML25079A251) for this event.
Although the as-found lift pressure for both valves was low and outside the TS allowable band, the as-found setpoints remained bounded by the accident analysis, as described in the Final Safety Analysis Report (FSAR). Therefore, the valves safety function to limit the secondary system pressure from exceeding the limit of 110 percent of design pressure was not affected.
Corrective Actions: 2-MS-249 was adjusted and retested successfully. 2-MS-251 did not require adjustment, and was retested successfully. Dominion established actions to retest both valves in the next refueling outage.
Corrective Action References: CRs 1270647 and 1270649.
Performance Assessment: The NRC determined this violation was not reasonably foreseeable and preventable by the licensee and therefore is not a performance deficiency.
Specifically, setpoint drift is a recognized valid phenomenon that can occur despite routine testing and maintenance.
Enforcement: Traditional Enforcement is being used to disposition this violation with no associated Reactor Oversight Process performance deficiency per Section 3.10 of the Enforcement Manual.
Severity: The inspector assessed the severity of the violation using Section 6.1 of the Enforcement Policy and determined the significance is appropriately characterized as Severity Level IV, due to the low potential safety consequences. Specifically, both valves as-found lift pressures remained below the FSAR limit of 110 percent of main steam system design pressure, and would not have resulted in increased offsite dose during design basis events that credit the valves to limit offsite dose.
Violation: Millstone Unit 2 TS Limiting Condition for Operation 3.7.1.1 states, in part, All main steam line code safety valves shall be OPERABLE with lift settings as specified in Table 4.7-
- 1. With one or more main steam line code safety valves per steam generator inoperable, the TS Condition 3.7.1.1.a Required Action is to reduce thermal power within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> to less than or equal to the applicable percent of rated thermal power in Table 3.7-1, and reduce the power level-high trip setpoint in accordance with Table 3.7-1 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />, otherwise, be in hot standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, and hot shutdown within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
9 Contrary to the above, during the operating cycle spanning July 2023 until October 2024, Millstone Unit 2 operated with two inoperable MSSVs and failed to take the action required by TS 3.7.1.1. Similar discrepancies in two (multiple) valves is an indication that the discrepancies may have arisen over a period of time; therefore, it is reasonable to conclude the condition existed during the operating cycle prior to testing on October 1, 2024.
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 December 3, 2025, the inspectors presented the integrated inspection results to Mark Goolsbey, Director, Nuclear Operations, and other members of the licensee staff.
On July 17, 2025, the inspectors presented the 71124.05 instrumentation inspection results to Mike Wynn, Radiation Protection Manager, and other members of the licensee staff.
10 DOCUMENTS REVIEWED Inspection Procedure Type Designation Description or Title Revision or Date 71111.12 Calculations MP-CALC-000-98-107 Minimum Required Flow from Alternate Cooling Source 88F to the EDG Heat Exchangers for Bounding/1950 KW Electrical Load with Tube Plugged: 10 Air Cooler, 19 Lube Oil Cooler, 11 Jacket Water Cooler 0
Corrective Action Documents Resulting from Inspection CR1301792 Maintenance Manager Override of RTE Rejection for RTE-PM-25-088531 09/23/25 Procedures ER-AA-102 Preventive Maintenance Program 18 MP-PROC-OPS-SP 2610BS TDAFP Tests, Shutdown 005 71111.13 Work Orders 53203460467 71152A Corrective Action Documents CR1274590 SP 2601J Changes Recommended for Non-Intrusive Testing of 2-CH-432 and 2-CH-433 10/31/2024 Procedures WM-AA-20 Risk Assessment of Maintenance Activities 3