05000416/LER-2024-004, High Pressure Core Spray Over Frequency Relay Trip
| ML24326A363 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 11/22/2024 |
| From: | Hardy J Entergy Operations |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| GNRO2024-00037 LER 2024-004-00 | |
| Download: ML24326A363 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4162024004R00 - NRC Website | |
text
- ) entergy GNRO2024-00037 November 22, 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 2024-004-00, High Pressure Core Spray Over Frequency Relay Trip Grand Gulf Nuclear Station, Unit 1 Docket No. 50-416 Renewed License No. NPF-29 Attached is Licensee Event Report (LER) 2024-004-00, High Pressure Core Spray Over Frequency Relay Trip. This report is being submitted in accordance with 1 O CFR 50.73(a)(2)(v)(D), any event or condition that could have prevented the fulfillment of the safety function of systems that are needed to mitigate the consequences of an accident.
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 2024-004-00
GNRO2024-00037 Page 2 of 3 cc:
NRC Senior Resident Inspector Grand Gulf Nuclear Station Port Gibson, MS 39150 U.S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
G N RO2024-00037 Page 3 of 3 Attachment Licensee Event Report 2024-004-00
Abstract
On September 24, 2024, Grand Gulf Nuclear Station, Unit 1 was operating at 100 percent power with the High Pressure Core Spray (HPCS) offline for testing and all safety systems operable. At 22:04 CT, during planned surveillance testing of HPCS and the Division Ill diesel generator, the HPCS pump breaker unexpectantly tripped after the HPCS diesel generator started and powered the safety bus. The breaker performed its motor protection function and tripped due to an over-frequency indication. This resulted in a potential loss of safety function. Troubleshooting was performed, and the HPCS over-frequency relay was replaced. The system was returned to service. The cause of the trip was determined to be the failure of the over-frequency relay. The over-frequency relay was determined to be non-essential, and actions were created to remove the relay from the system. During the testing of the HPCS system, alternate ECCS systems were available to provide core cooling and injection to the reactor; therefore, there were no actual safety consequences to the event.
This report is made in accordance with 10 CFR 50. 73a(2)(v)(D) for an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.
Plant Conditions
- 2. DOCKET NUMBER YEAR 00416 2024
- 3. LEA NUMBER SEQUENTIAL NUMBER 004 REV NO.
00 At the time of the event, Grand Gulf Nuclear Station, Unit 1 was in Mode 1 at 100% power. The station was conducting planned surveillance testing on the High Pressure Core Spray (HPCS) Division Ill Emergency Diesel Generator (EDG).
Description of Event
On September 24, 2024, while performing a HPCS loss of offsite power surveillance, the Division Ill EDG started and loaded the safety bus as expected, but the HPCS pump breaker immediately tripped which resulted in a potential loss of safety function.
Reportability
This report is made in accordance with 10 CFR 50.73a(2)(v)(D) for an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. HPCS is required to be able to inject water during a loss of cooling accident.
Cause(s)
The direct cause of the event was a failure of the HPCS over-frequency relay. The HPCS original system design included an over-frequency relay that is not required. This feature has existed since construction, and its need was not evaluated after HPCS was built without the Level-8 injection valve isolation bypass signal, per the GE system design criteria.
Corrective Actions
Completed Actions:
- - Electrical Maintenance replaced the HPCS over-frequency relay.
- - A Failure Modes Analysis and a Root Cause Evaluation were performed to identify and correct the causes of the event.
Planned Actions:
- - Revise current preventative maintenance to include capacitor checks based on EPRI guidance.
- - Revise over-frequency calibration procedure to state that all installation or reinstallation of the over frequency relay is required to be with a matched capacitor.
- - Remove the over-frequency relay protection (17 AC-181) from the HPCS motor protection circuit.
Safety Significance
There were no actual safety consequences associated with this condition. The HPCS system functions as a part of the Emergency Core Cooling System (ECCS). It functions to provide and maintain an adequate coolant inventory inside the reactor vessel to limit the fuel cladding temperatures in the event of breaks in the reactor coolant pressure boundary. The system is initiated by either high pressure in the drywall or low water level in the reactor vessel. During the testing of the HPCS system, alternate ECCS systems were available to provide core cooling and injection to the reactor.
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