05000416/LER-2024-005, Loss of Seal Steam Controller Power Resulted in Manual Reactor Shutdown
| ML25009A011 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 01/09/2025 |
| From: | Hardy J Entergy Operations |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| GNRO2025-00002 LER 2024-005-00 | |
| Download: ML25009A011 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4162024005R00 - NRC Website | |
text
S) entergy GNRO2025-00002 January 9, 2025 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Entergy Operations, Inc.
P.O. Box 756 Port Gibson, Mississippi 39150 Jeffery A. Hardy Manager Regulatory Assurance Grand Gulf Nuclear Station Tel: 802-380-5124 10 CFR 50.73
SUBJECT:
Grand Gulf Nuclear Station, Unit 1 Licensee Event Report 2024-005-00, Loss of Seal Steam Controller Power Resulted in Manual Reactor Shutdown Grand Gulf Nuclear Station, Unit 1 Docket No. 50-416 Renewed License No. NPF-29 Attached is Licensee Event Report (LER) 2024-005-00, Loss of Seal Steam Controller Power Resulted in Manual Reactor Shutdown. This report is being submitted in accordance with 10 CFR 50.73(a)(2)(iv)(A). for events or conditions that resulted in the manual or automatic actuation of the reactor protection system.
This letter contains no new Regulatory Commitments. Should you have any questions concerning the content of this letter, please contact me at 802-380-5124.
Sincerely, 9A~
JAH/saw Attachments: Licensee Event Report 2024-005-00
GNRO2025-00002 Page 2 of 3 cc:
NRG Senior Resident Inspector Grand Gulf Nuclear Station Port Gibson, MS 39150 U.S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
GNRO2025-00002 Page 3 of 3 Attachment Licensee Event Report 2024-005-00
Abstract
On November 10, 2024, at 0337 CST, Grand Gulf Nuclear Station, Unit 1 was operating at 100 percent power with all safety systems operable. A failed power supply resulted in a loss of seal steam controller power and led to a degraded condenser vacuum which resulted in a manual reactor shutdown. All control rods were fully inserted with no complications. Following initial scram response, a group 1 containment isolation signal resulted in the closure of all main steam isolation valves at 0545 CST. Later, an automatic Reactor Protection System actuation occurred at 0620 CST while in MODE 3 while all control rods were inserted.
The cause of the loss of seal steam controller power was determined to be a failed power supply, 1 N21 K602B which had exceeded its expected life. The 1 N21 K602B power supply was replaced, and seal steam control was returned to service.
This report is made in accordance with 10 CFR 50.73(a)(2)(iv)(A) for events or conditions that resulted in the manual or automatic actuation of the reactor protection system.
Plant Conditions
- 2. DOCKET NUMBER YEAR 00416 2024
- 3. LEA NUMBER SEQUENTIAL NUMBER 005 REV NO.
00 At the time of the event, Grand Gulf Nuclear Station, Unit 1 was in Mode 1 at 100% power, and all safety systems were operable.
Description of Event
On November 10, 2024, at 0337 CST, a power supply failure resulted in a loss of seal steam controller power and led to a degraded condenser vacuum which resulted in a manual reactor shutdown. All control rods fully inserted, and there were no complications.
Following initial scram response, a group 1 containment isolation signal resulted in the closure of all main steam isolation valves at 0545 CST. This signal was due to the continued degradation of the condenser vacuum post-trip. An automatic RPS actuation occurred while in MODE 3 with all control rods currently inserted at 0620 CST.
Following the second actuation of the reactor protection system (RPS), pressure was controlled by safety relief valves and reactor core isolation cooling was used to maintain water level.
Reportability
This report is made in accordance with 10 CFR 50.73(a)(2)(iv)(A) for events or conditions which resulted in the manual or automatic actuation of the RPS.
Cause(s)
The direct cause of the 1 N21 K602B power supply failure was aged components exceeding their expected life.
The root cause of the event was the determination of the life expectancy of the power supplies with electrolytic capacitors was incorrectly designed using the in-service date as the starting criteria; however, electrolytic capacitors begin degrading upon manufactured date. Starting the life expectancy for this power supply from the in-service date as opposed to manufactured date resulted in the power supply being installed with a projected life expectancy of 10 years when the component already had 6 years of shelf life and only 4 years of remaining life expectancy.
Corrective Actions
Completed Actions:
- - The seal steam power supply 1 N21 K602B was replaced, and seal steam control was restored.
Planned Actions:
- - Revise maintenance procedure to include steps which guide actual full age determination and evaluation of power supplies. This will include a signature requirement for Maintenance to contact Supply Chain, and it will require initiating a Condition Report to document and evaluate the power supply age prior to being installed.
Safety Significance
There were no actual safety consequences associated with this condition. Plant systems responded as designed and the unit was brought to Mode 3 by Control Room Operators.
Previous Similar Events
None identified. Page 2 of 2