05000458/LER-2025-006, For River Bend Station, Potential Loss of Safety Function of Control Building Chillers Due to a Valve Mispositioned
| ML25293A255 | |
| Person / Time | |
|---|---|
| Site: | River Bend  (NPF-047) |
| Issue date: | 10/20/2025 |
| From: | Mccoy J Entergy Operations |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RBG-48377 LER 2025-006-00 | |
| Download: ML25293A255 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 4582025006R00 - NRC Website | |
text
Jack McCoy Manager Regulatory and Emergency Planning River Bend Station 225-381-3310 Entergy Operations, Inc., 5485 U.S. Highway 61N. St. Francisville, LA 70775 RBG-48377 10 CFR 50.73 October 20, 2025 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
Licensee Event Report 50-458 / 2025-006-00, Potential Loss of Safety Function of Control Building Chillers Due to a Valve Mispositioned River Bend Station - Unit 1 NRC Docket Nos. 50-458 Renewed Facility Operating License No. NPF-47 In accordance with 10 CFR 50.73, enclosed is the subject Licensee Event Report.
This document contains no commitments.
Should you have any questions, please contact Mr. Jack McCoy, Regulatory and Emergency Planning Manager, at 225-381-3310.
Respectfully, JM/hpk
Enclosure:
Licensee Event Report 50-458 / 2025-006-00 cc:
NRC Region IV Regional Administrator - Region IV NRC Senior Resident Inspector - River Bend Station NRC Office of Nuclear Security and Incident Response Digitally signed by Jack McCoy DN: cn=Jack McCoy, o=Manager Regulatory and Emergency Preparedness, ou=Entergy/ River Bend,
email=jmccoy1@entergy.com Date: 2025.10.20 10:46:56 -05'00' Jack McCoy
Enclosure RBG-48377 Licensee Event Report 50-458/2025-006-00
- 11. This Report is Submitted Pursuant to the Requirements of 10 CFR §:
(Check all that apply) 10 CFR Part 20 20.2203(a)(2)(vi) 10 CFR Part 50 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 73.1200(a) 20.2201(b) 20.2203(a)(3)(i) 50.36(c)(1)(i)(A) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 73.1200(b) 20.2201(d) 20.2203(a)(3)(ii) 50.36(c)(1)(ii)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 73.1200(c) 20.2203(a)(1) 20.2203(a)(4) 50.36(c)(2) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x) 73.1200(d) 20.2203(a)(2)(i) 10 CFR Part 21 50.46(a)(3)(ii) 50.73(a)(2)(v)(A) 10 CFR Part 73 73.1200(e) 20.2203(a)(2)(ii) 21.2(c) 50.69(g) 50.73(a)(2)(v)(B) 73.77(a)(1)(i) 73.1200(f) 20.2203(a)(2)(iii) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C) 73.77(a)(2)(i) 73.1200(g) 20.2203(a)(2)(iv) 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D) 73.77(a)(2)(ii) 73.1200(h) 20.2203(a)(2)(v) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii)
Other (Specify here, in abstract, or in NRC 366A).
Abstract
On August 23, 2025, at 1433 CDT, River Bend Station, Unit 1 (RBS) was operating in Mode 1 at 100% reactor power, a post maintenance test was being performed on Division II Control Building Chilled Water System Chiller B (HVK-CHL1B). During this test, Division I Control Building Chilled Water System (HVK) was declared Inoperable as a result of HVK Chiller A (HVK-CHL1A) failing to start.
HVK-CHL1A failed to start due to the HVK Low Side Isolation Valve, HVK-FTY5B-V2L, being in the closed position.
The closed isolation valve prevented a low flow signal from the transmitter and render Division I of the HVK Chillers, HVK-CHL1A and HVK-CHL1C, inoperable. Operations immediately alternated back to HVK-CH1B, with HVK-CH1C in standby.
This event is reportable in accordance with 10 CFR 50.73(a)(2)(v)(A) and 10 CFR 50.73(a)(2)(v)(D) as an event that could have prevented the fulfillment of the safety function of structures or systems that are needed to shut down the reactor and maintain it in a safe shutdown condition and mitigate the consequences of an accident.
Event Description
On August 23, 2025, at 1433 CDT, River Bend Station, Unit 1 (RBS) was operating in Mode 1 at 100% reactor power, a post maintenance test was being performed on Division II Control Building Chilled Water System Chiller B (HVK-CHL1B) [VI:CHU].
During this test, while transferring operation from HVK Chiller B (HVK-CHL1B) to HVK Chiller A (HVK-CHL1A), HVK-CHL1A failed to start. Division I Control Building Chilled Water System (HVK) was declared Inoperable. The inoperability of Division I and II Control Building Chilled Water Systems could have prevented the fulfillment of a safety function.
HVK-CHL1A failed to start due to the HVK Low Side Isolation Valve, HVK-FTY5B-V2L, being in the closed position. The closed isolation valve prevented a low flow signal from the transmitter and render Division I of the HVK Chillers, HVK-CHL1A and HVK-CHL1C, inoperable. Operations immediately alternated back to HVK-CH1B, with HVK-CH1C in standby.
Limiting Conditions for Operation (LCO) 3.7.3, Control Room Air Conditioning System Condition A (One control room AC subsystem inoperable) and 3.7.7, Control Building Air Conditioning System Condition A (one control building air conditioning subsystem inoperable) was entered.
After further investigation, it was determined that Instrument and Control (I&C) Technicians manipulated HVK-FTY5B-V2L to the closed position earlier that day during performance of a work order to fill and vent transmitters on the Control Building Chiller 1B. The I&C Technicians failed to document the change of valve position as required by EN-MA-157, Maintenance Configuration Control, therefore the valve was not returned to its proper position (i.e., open).
Event Cause
The direct cause of this event was due to the misposition of HVK-FTY5B-V2L that resulted in the valve being left in the closed position by I&C Technicians.
The causal factor was determined to be that the workers failed to stop work and notify supervision when a potential issue was encountered. The workers did not utilize EN-MA-157, Maintenance Configuration Control, before manipulating a valve. The workers failed to identify potential error traps and failed to utilize human performance tools as required by EN-HU-102, Human Performance Traps & Tools.
Safety Assessment
Dedicated operator actions had been established to maintain the safety function for the HVK system in the event that the standby chiller doesnt start and the previously running chiller doesnt start when alternating divisions of control building chilled water as a planned evolution. Safety function is maintained if a chiller is started within 23 minutes, which is the Environmental Design Criteria limitation. The safety significance of this event is low based on temperatures in the areas cooled by the HVK systems remained below maximum environmental design criteria and actions taken by Operations.
Corrective Actions
Completed:
- - Maintenance Department held a stand-down for a standards reset.
- - Maintenance Department maintained 100% Supervisor job oversight for 2 weeks following the event.Page 3 of 3(04-02-2024)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 04/30/2027
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER River Bend Station, Unit 1 050 00458 YEAR SEQUENTIAL NUMBER REV NO.
052 2025 006 00 In Progress:
- - Performance management actions will be used to reinforce the behaviors with the individuals to prevent recurrence.
- - Performance of observations to ensure human performance standards for procedure use and adherence are being observed and coached.
Previous Occurrences
One similar event was reported in LER 050/458-2020-001-00. The plant operating at 100 percent power, a post modification test was performed on Division I Control Building Chilled Water System Chiller A (HVK-CHL1A). During the test, both Division I and Division II Control Building Chilled Water Systems (HVK) were declared Inoperable resulting in a condition that could have prevented fulfillment of a safety function. The event occurred while transferring from operation of HVK-CHL1B to HVK-CHL1A as part of the test. The failure of HVK-CHL1A was attributed to a trip on a Phase Reversal alarm within the digital control logic, during post modification testing.
NOTE: Energy Industry Identification System component function identifier and system name of each component or system referred to in the LER are annotated as (**XX**) and [XX], respectively.