05000416/LER-2023-002, Reactor Scram Due to Generator Stator Fault to Ground
| ML24044A193 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  (NPF-029) |
| Issue date: | 02/13/2024 |
| From: | Hardy J Entergy Operations |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| GNRO2024-00004 LER 2023-002-00 | |
| Download: ML24044A193 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4162023002R00 - NRC Website | |
text
- } entergy GNRO2024-00004 February 13, 2024 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 2023-002-00, Reactor Scram due to Generator Stator Fault to Ground Grand Gulf Nuclear Station, Unit 1 Docket No. 50-416 Renewed License No. NPF-29 Attached is Licensee Event Report (LER) 2023-002-00, Reactor Scram due to Generator Stator Fault to Ground. This report is being submitted in accordance with 1 O CFR 50.73(a)(2)(iv)(A),
any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B).
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,
~~
JAH/saw Attachments: Licensee Event Report 2023-002-00
GNRO2024-00004 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
GNRO2024-00004 Page 3 of 3 Attachment Licensee Event Report 2023-002-00
Abstract
On December 16, 2023, Grand Gulf Nuclear Station was operating at 81 percent power following a planned sequence exchange and no critical work activities were in progress. At 0346, all three in service main generator protective relays measured an increase in voltage across the secondary of the neutral grounding transformer which resulted in a main generator lockout and subsequent main turbine trip and automatic reactor scram. The direct cause of the main generator lockout was a generator stator fault to ground. A root cause was not identified. Actions have been created to ensure the generator bushings are clean and the solenoid contactors are replaced.
All control rods fully inserted, there were no complications and all plant systems responded as designed. No radiological releases occurred due to this event. There were no consequences to the safety of the public, nuclear safety, industrial safety, or radiological safety. This report is made in accordance with 10 CFR 50.73{a)(2)(iv)(A), for any event or condition that resulted in manual or automatic actuation of the Reactor Protection System.
PLANT CONDITIONS
- 2. DOCKET NUMBER I
416
- 3. LER NUMBER REV NO.
1-0 During the event, Grand Gulf Nuclear Station (GGNS) was in Mode 1, 81 percent power following a planned sequence exchange. There were no critical work activities in progress, and there were no inoperable safety-related systems at the time of the event.
DESCRIPTION OF EVENTS On December 16, 2023, GGNS was operating at 81 percent power following a planned sequence exchange and no critical work activities were in progress. At 0346, all three in service main generator protective relays measured an increase in voltage across the secondary of the neutral grounding transformer. This voltage increased to approximately 30V (3240V primary) which was above the 59N (90 percent Stator Ground Fault) function trip setpoint of 8.566V (928.6V primary). All relays tripped after a built-in three second delay which initiated a main generator lockout and subsequent main turbine trip and reactor scram.
All control rods fully inserted, and all plant systems responded as designed. Reactor water level was maintained by main feedwater and condensate. Reactor pressure was maintained by the main turbine bypass valves. No radiological releases occurred.
REPORT ABILITY The automatic Reactor Protection System (RPS) actuation was initially reported to the NRC as a 4-hour report per 10 CFR 50.72(b)(2)(iv)(B) on December 16, 2023 (EN 56894). This report is made in accordance with 10 CFR 50.73(a)(2)(iv)(A) for any event or condition that resulted in manual or automatic actuation of any system listed in paragraph 10 CFR
- 50. 73(a)(2)(iv)(B).
CAUSE
The Direct Cause of the RPS actuation was Generator Stator fault to ground resulting in a main generator lockout and reactor scram. A root cause was not identified.
CORRECTIVE ACTIONS
Immediately following the event, a turbine and generator cooldown was performed to allow testing of the generator stator windings, the isophase bus and the neutral grounding transformer. Additionally, all components associated with the main generator terminal voltages were tested for insulation resistance to ensure no ground is present. Corrective actions are being enacted to ensure that preventative maintenance is in place to clean the main generator bushings and replace the seal oil drain regulator tank solenoid contactors.
SAFETY SIGNIFICANCE
The reactor trip system responded as expected to the automatic trip signal. There was no failure of any function that would have prevented fulfillment of actions necessary to shutdown the reactor and maintain it in a safe shutdown condition, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident. All systems required to bring the plant to MODE 3 responded correctly. All safety related emergency core cooling systems were operable and available during the SCRAM. There was no loss of safety function for this event. There were no safety consequences impacting plant or public safety because of this event.
PREVIOUSLY SIMILAR EVENTS LER 2020-003: On May 25,2020, at 0433, GGNS experienced an automatic reactor scram due to a main turbine trip. Page 2
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