ML25121A246
| ML25121A246 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 05/12/2025 |
| From: | Sarah Elkhiamy Division of Operating Reactors |
| To: | Rhoades D Constellation Energy Generation |
| References | |
| IR 2025001 | |
| Download: ML25121A246 (1) | |
Text
May 12, 2025 David P. Rhoades Senior Vice President Constellation Energy Generation, LLC President and Chief Nuclear Officer (CNO)
Constellation Nuclear 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
LIMERICK GENERATING STATION, UNITS 1 AND 2 - INTEGRATED INSPECTION REPORT 05000352/2025001 AND 05000353/2025001
Dear David Rhoades:
On March 31, 2025, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Limerick Generating Station, Units 1 and 2. On April 22, 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.
One finding of very low safety significance (Green) is documented in this report. This finding involved a violation of NRC requirements. We are treating this violation as a non-cited violation (NCV) consistent with Section 2.3.2 of the Enforcement Policy.
If you contest the violation or the significance or severity of the violation documented in this inspection report, you should provide a response within 30 days of the date of this inspection report, with the basis for your denial, to the U.S. Nuclear Regulatory Commission, ATTN:
Document Control Desk, Washington, DC 20555-0001; with copies to the Regional Administrator, Region 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.
D. Rhoades 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, Sarah H. Elkhiamy, Chief Operations Branch 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 SARAH ELKHIAMY Digitally signed by SARAH ELKHIAMY Date: 2025.05.12 06:41:42 -04'00'
ML25121A246 SUNSI Review Non-Sensitive Sensitive Publicly Available Non-Publicly Available OFFICE R1/DORS R1/DORS R1/DORS NAME AZiedonis SHaney SElkhiamy DATE 5/1/2025 5/1/2025 5/1/2025
Enclosure U.S. NUCLEAR REGULATORY COMMISSION Inspection Report Docket Numbers:
05000352 and 05000353 License Numbers:
NPF-39 and NPF-85 Report Numbers:
05000352/2025001 and 05000353/2025001 Enterprise Identifier: I-2025-001-0047 Licensee:
Constellation Energy Generation, LLC Facility:
Limerick Generating Station, Units 1 and 2 Location:
Sanatoga, PA 19464 Inspection Dates:
January 1, 2025 to March 31, 2025 Inspectors:
A. Ziedonis, Senior Resident Inspector L. Grimes, Resident Inspector Approved By:
Sarah H. Elkhiamy, Chief Operations Branch 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 Inadequate 50.69 Alternative Treatment of a Pipe Flaw in the Residual Heat Removal Service Water System Cornerstone Significance Cross-Cutting Aspect Report Section Mitigating Systems Green NCV 05000352,05000353/2025001-01 Open/Closed
[H.14] -
Conservative Bias 71152A The inspectors identified a Green finding with an associated non-cited violation (NCV) of Title 10 of the Code of Federal Regulations (10 CFR) 50.69(d)(2) alternative treatment requirements when Constellation did not ensure, with reasonable confidence, that the B loop of the residual heat removal service water (RHRSW) system remained capable of performing its safety-related function under design basis conditions, following the identification and monitoring of a pipe flaw in risk-informed safety class 3 (RISC-3) piping. Specifically, inspectors determined that alternative treatment procedure requirements were not followed as pipe flaw leakage progressively degraded in excess of established room flooding limits, which resulted in emergent RHRSW B loop unavailability to perform repairs.
Additional Tracking Items None.
3 PLANT STATUS Unit 1 began the inspection period at rated thermal power (RTP) and remained at or near RTP for the remainder of the inspection period.
Unit 2 began the inspection period at RTP. On March 16, 2025, the unit began coasting down due to end of cycle conditions and was at approximately 92 percent RTP at the end 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 71111.01 - Adverse Weather Protection Impending Severe Weather Sample (IP Section 03.02) (1 Sample)
(1)
The inspectors evaluated the adequacy of the overall preparations to protect risk-significant systems from severe cold weather during the week of January 20, 2025.
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 common emergency service water (ESW) system with normal service water partially isolated and the 'A' ESW pump in-service during the week of February 18, 2025 (2)
Unit common 'B' standby gas system following maintenance on February 20, 2025 (3)
Unit 2 emergency diesel generators (EDGs) on February 28, 2025
4 71111.05 - Fire Protection Fire Area Walkdown and Inspection Sample (IP Section 03.01) (4 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, fire area 64, reactor enclosure cooling water heat exchanger area on January 7, 2025 (2)
Unit 1 F-PCLSF-001, pre-fire plan strategy for 5-line facility following fire brigade response on January 15, 2025 (3)
Unit 2 F-D-315A, fire area 83, D21 EDG and fuel oil-lube oil tank room on February 28, 2025 (4)
Unit 2 F-T-460, fire area 109, battery room on March 24, 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 Unit 1 loss of drywell chilled water on January 21, 2025, and during a Unit 2 removal of 6A feedwater heater from service on February 7, 2025.
Licensed Operator Requalification Training/Examinations (IP Section 03.02) (1 Sample)
(1)
The inspectors observed and evaluated licensed operator requalification training in the simulator on February 10, 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 (SSCs) remain capable of performing their intended function:
(1)
Unit 2 reactor enclosure fan elevated vibrations during the week of January 13, 2025 71111.13 - Maintenance Risk Assessments and Emergent Work Control Risk Assessment and Management Sample (IP Section 03.01) (5 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 common emergent work following the 'A' control room emergency filtration air system supply damper failure during the week of January 13, 2025
5 (2)
Unit 2 elevated risk during planned reactor core isolation coolant (RCIC) testing on February 12, 2025 (3)
Unit 2 emergent work following an unexpected test condition associated with the high-pressure coolant injection turbine exhaust line vacuum breakers during the week of March 3, 2025 (4)
Unit common elevated risk during the planned unavailability of the 'B' loop of RHRSW for pipe leak repairs during the weeks of March 17 and 24, 2025 (5)
Unit 2 elevated risk with the RCIC system unavailable for planned maintenance on March 31, 2025 71111.15 - Operability Determinations and Functionality Assessments Operability Determination or Functionality Assessment (IP Section 03.01) (5 Samples)
The inspectors evaluated the licensee's justifications and actions associated with the following operability determinations and functionality assessments:
(1)
Unit common 'B' ESW loop following the identification of a pinhole leak during the week of February 18, 2025 (2)
Unit common 'A' ESW loop following the identification of a pinhole leak during the week of February 18, 2025 (3)
Unit 1 rod position indication system following control rod indication issues on February 24, 2025 (4)
Unit 1 'N' safety relief valve following identification of elevated tailpipe temperature during the week of March 10, 2025 (5)
Unit 1 standby liquid control system following repetitive low suction temperature alarms during the week of March 10, 2025 71111.18 - Plant Modifications Temporary Modifications and/or Permanent Modifications (IP Section 03.01 and/or 03.02)
(1 Sample)
The inspectors evaluated the following temporary or permanent modifications:
(1)
Unit common 'A' ESW loop isolation valve 50.69 categorization change during the week of February 24, 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) (4 Samples)
(1)
Unit 1 'A' residual heat removal (RHR) suppression pool spray valve stroke time testing following planned maintenance activities during the week of January 27 and February 3, 2025 (2)
Unit 2 D21 EDG fast-start testing following planned maintenance on February 6, 2025 (3)
Unit 1 core spray system following planned maintenance on February 20, 2025
6 (4)
Unit 1 high-pressure coolant injection system response time testing following planned maintenance during the week of March 17, 2025 Surveillance Testing (IP Section 03.01) (3 Samples)
(1)
ST-6-049-230-1, Unit 1 RCIC system pump, valve, and flow (PV&F) test on March 14, 2025 (2)
ST-6-011-231-0, Unit common 'A' ESW PV&F on February 27, 2025 (3)
ST-6-012-232-0, Unit common 'B' RHRSW PV&F test on March 16 and 17, 2025 Inservice Testing (IST) (IP Section 03.01) (1 Sample)
(1)
ST-6-051-233-2, Unit 2 'C' RHR PV&F test on February 14, 2024 OTHER ACTIVITIES - BASELINE 71151 - Performance Indicator Verification The inspectors verified licensee performance indicators submittals listed below:
IE03: Unplanned Power Changes per 7000 Critical Hours Sample (IP Section 02.02)
(2 Samples)
(1)
Unit 1 for the period of January 1, 2024 through December 31, 2024 (2)
Unit 2 for the period of January 1, 2024 through December 31, 2024 MS07: High-Pressure Injection Systems (IP Section 02.06) (2 Samples)
(1)
Unit 1 for the period of January 1, 2024 through December 31, 2024 (2)
Unit 2 for the period of January 1, 2024 through December 31, 2024 MS08: Heat Removal Systems (IP Section 02.07) (2 Samples)
(1)
Unit 1 for the period of January 1, 2024 through December 31, 2024 (2)
Unit 2 for the period of January 1, 2024 through December 31, 2024 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 the adequacy of Constellation's evaluation and corrective actions in response to a pipe flaw identified in the 'B' loop of the RHRSW system.
7 INSPECTION RESULTS Inadequate 50.69 Alternative Treatment of a Pipe Flaw in the RHRSW System Cornerstone Significance Cross-Cutting Aspect Report Section Mitigating Systems Green NCV 05000352,05000353/2025001-01 Open/Closed
[H.14] -
Conservative Bias 71152A The inspectors identified a Green finding with an associated NCV of 10 CFR 50.69(d)(2) alternative treatment requirements when Constellation did not ensure, with reasonable confidence, that the B loop of the RHRSW system remained capable of performing its safety-related function under design basis conditions, following the identification and monitoring of a pipe flaw in RISC-3 piping. Specifically, inspectors determined that alternative treatment procedure requirements were not followed as pipe flaw leakage progressively degraded in excess of established room flooding limits, which resulted in emergent RHRSW B loop unavailability to perform repairs.
==
Description:==
On September 6, 2024, operators identified a visible water mist, estimated to be 6 feet in length and quantified at approximately 0.11 gallons per minute (gpm), emanating from a small hole in the weld of a two-inch branch connection drain line on a 20-inch pipe header associated with the B loop of RHRSW. This section of RHRSW pipe (HBC-183) was designed to American Society of Mechanical Engineers Code Class III requirements, and is considered a moderate energy fluid system (maximum operating temperature of 200 degrees Fahrenheit [F]) and maximum operating pressure of 275 pounds per square inch gauge (psig), with a design maximum operating pressure of 160 psig, and a maximum pressure of 190 psig at pump shutoff head and 70 degrees F. The inspectors noted that Constellation re-categorized this piping as RISC-3 (safety-related, low safety significance) in accordance with 10 CFR 50.69, as specified in LG-5069-012-003, RHRSW System 10 CFR 50.69 Categorization Document, Revision 2.
In response to the leak, operators wrote Issue Report 4799631 and performed an immediate determination that the B loop of RHRSW remained OPERABLE in accordance with guidance contained in OP-LG-108-115-1000, SRO Operability Determination Aid, Revision 9,, American Society of Mechanical Engineers Class 3, RISC-3 piping Categorized IAW 10 CFR 50.69. Attachment 1, page 3, note 1 describes the process for use of the attachment as alternative treatment of RISC-3 piping flaws under 10 CFR 50.69(d)(2) for purposes of immediate operability determinations. The inspectors reviewed Attachment 1 and noted several conditions were required to be met in order for the immediate operability determination to apply under alternative treatment, including:
- 1. The degradation mechanism must be readily discernable through visual inspections (such as a pinhole through-wall leak); and
- 2. pertinent operating experience must exist with the degradation mechanism on the system, including that the most probable cause is localized corrosion whereby the actual flaw size is not expected to grow significantly, or leakage rise significantly.
The inspectors reviewed Constellations immediate determination of operability and determined the conditions were met. Following the immediate determination, Attachment 1 directs engineering to provide adequate documentation to support reasonable confidence to permit continued operation under the original operability assessment. The inspectors noted that Constellation engineering provided technical evaluation EC 642390, which supported the immediate determination of operability, and established a pipe flaw leakage limit of 0.48 gpm
8 based on room flooding limits in the Unit 1 B RHR pump room given the RHR system mission time. Constellation determined there was considerable leakage margin available for RHRSW system operability (approximately 100 gpm).
The inspectors noted that from September 6 through November 20, 2024, pipe flaw leakage progressively increased to approximately 6.2 gpm, as measured during operator rounds, with one revision to EC 642390 increasing the allowable leakage to 4.8 gpm. On December 6, 2024, engineering completed Revision 2 to EC 642390, thereby increasing the allowable leakage to 8.7 gpm. On December 16, 2024, leakage experienced a step increase after the B RHRSW pump was placed in-service for quarterly testing. The pump was promptly secured, and leakage was measured at 10.6 gpm. Based on the measured leakage exceeding the allowable limit of EC 642390, Revision 2, several Unit 1 B RHR modes were declared inoperable due to RHRSW leakage into the room, with the most limiting condition for operation being entry into a 72-hour technical specification shutdown action statement. The B loop of RHRSW was subsequently isolated, which resulted in entry into an additional 72-hour technical specification shutdown action statement. All limiting conditions for operation were subsequently extended to 30 days using the risk-informed completion time program. A housekeeping clamp was installed over the flaw location on December 20, 2024, which rendered leakage into the room as negligible with the B RHRSW pump in-service during PMT for the clamp. The housekeeping clamp design included a manual drain valve which supported periodic leakage monitoring (measured at 17.85 gpm with the pump in-service during PMT). A new leakage limit of 50 gpm through the manual drain valve was established, and Constellation re-assessed planning actions for permanent leak repairs.
The inspectors reviewed Constellations alternative treatment actions under 10 CFR 50.69, in response to the progressive increase in leakage as described above. The inspectors reviewed OP-LG-108-115-1000, Attachment 1, and noted the section for immediate operability determinations stated that if the conditions of the immediate operability determination cannot be met, declare the piping inoperable until repairs are completed and PMT activities satisfied. The inspectors noted that during the approximate two-and-a-half-month period of progressively increasing leakage from 0.11 gpm to 6.2 gpm, Constellation revised the leakage limit on two separate occasions by reducing margin to the allowable room flooding limit but never re-evaluated the original conditions of the immediate determination that the flaw was localized and not expected to grow significantly, nor leakage rise significantly. The inspectors determined that had the original localized pinhole assumptions been re-evaluated, repair activities could have reasonably been planned in advance of incurring emergent safety system inoperability and unavailability. Additionally, while Constellation did originally perform ultrasonic testing in the vicinity of the pipe flaw to inform the immediate determination of a localized pipe flaw, no ultrasonic testing data was recorded, and no evaluation of allowable wall thickness or corrosion rate was performed at any point from initial flaw discovery through the monitored increase in leakage to 6.2 gpm.
Finally, the inspectors noted that Limerick station procedure OP-LG-108-115-1000,, was equivalent to fleet procedure OP-AA-108-115, Operability Determinations, Revision 28, Attachment 6. The inspectors further noted that OP-AA-108-115, step 4.1.16, required re-evaluation of operability following a change in condition. While step 4.1.16 was separate from the alternative treatment procedure attachment, the inspectors noted this step was an additional option available to Constellation as a re-evaluation tool in lieu of the self-imposed alternative treatment requirement to declare the piping inoperable when conditions of the immediate determination cannot be met. However, the inspectors
9 noted this step was not performed for this issue, as the original determination of a pinhole leak condition was never re-evaluated.
Corrective Actions: In response to leakage exceeding the allowable room flooding limit, Constellation isolated the leak and installed a housekeeping clamp over the pipe flaw location on December 20, 2024, under EC 643199. The clamp design included a ball valve which supported periodic leakage monitoring while Constellation expedited planning actions for permanent leak repairs. Subsequently, during the week of March 24, 2025, Constellation removed the housekeeping clamp and installed a welded plate over the pipe flaw, under Work Order 5592268.
Corrective Action References: Issue Reports 4799631, 4812913, 4822061, 4822078, 4824058, 4825340 Performance Assessment:
Performance Deficiency: The inspectors determined there was a performance deficiency because Constellation did not meet the self-imposed alternative treatment standards in accordance with Attachment 6 of OP-AA-108-115, Operability Determinations, Revision 28, as well as the regulatory requirement outlined in 10 CFR 50.69(d)(2), following a change in conditions associated with flaw in RISC-3 piping; and because the issue of concern (unplanned safety system inoperability and unavailability) was reasonably within Constellations ability to foresee and correct, and should have been prevented.
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, Constellation did not adequately re-evaluate changing conditions of a pipe flaw in the B loop of RHRSW, which resulted in unplanned inoperability of multiple modes of Unit 1 B RHR, as well as the emergent unavailability of the B loop of RHRSW.
Significance: The inspectors assessed the significance of the finding using IMC 0609, Appendix A, The Significance Determination Process for Findings At-Power. The inspectors screened the finding as having very low safety significance (i.e., Green) because, for Exhibit 2 (Mitigating Systems), the finding did not represent a condition requiring a detailed risk evaluation (i.e., all mitigating systems questions were answered No). Specifically, all probabilistic risk assessment mission times for both RHR and RHRSW would have been met assuming worst-case leakage measured through the manual drain valve during PMT following housekeeping clamp installation on December 20, 2024.
Cross-Cutting Aspect: H.14 - Conservative Bias: Individuals use decision making practices that emphasize prudent choices over those that are simply allowable. A proposed action is determined to be safe in order to proceed, rather than unsafe in order to stop. Specifically, the inspectors determined that Constellation assumed that periodic leakage monitoring was allowable under the original assumptions of the pinhole flaw, instead of prioritizing repairs or re-evaluation of the flaw conditions.
Enforcement:
Violation: 10 CFR 50.69(d)(2) requires, for purposes of alternative treatment, that the licensee shall ensure, with reasonable confidence, that RISC-3 SSCs remain capable of
10 performing their safety-related functions under design basis conditions.
OP-AA-108-115, Operability Determinations, Revision 28, Attachment 6, requires for a RISC-3 pipe flaw that the prompt operability evaluation provides reasonable confidence to permit continued operation under the original operability assessment; and if conditions of the original operability assessment change, Attachment 6 requires the piping be declared inoperable until repairs are completed.
Contrary to the above, Constellation did not ensure, with reasonable confidence, that the B loop of RHRSW remained capable of performing its safety-related function under design basis conditions following the identification and monitoring of a pipe flaw in RISC-3 piping, and did not declare the piping inoperable to perform repairs after conditions of the immediate operability determination were not met. Specifically, as periodic leakage monitoring detected an increase from 0.1 gpm to 6.2 gpm between September 6 and November 20, 2024, Constellation did not re-evaluate conditions of the original operability assessment that assumed the degradation mechanism was discernable through visual inspection and that the flaw size was not expected to grow significantly, nor did Constellation declare the piping inoperable until repairs could be completed. Consequently, on December 16, 2024, pipe flaw leakage increased beyond established room flooding limits, resulting in the emergent unavailability of the B RHRSW system loop when it was isolated for repairs.
Enforcement Action: This violation is being treated as an NCV, consistent with Section 2.3.2 of the Enforcement Policy.
EXIT MEETINGS AND DEBRIEFS The inspectors verified that no proprietary information was retained or documented in this report.
On April 22, 2025, the inspectors presented the integrated inspection results to William Levis, Plant Manager, and other members of the licensee staff.