05000366/LER-2025-002, A Emergency Diesel Generator Inoperable Due to Inadvertent Overspeed Trip
| ML25143A260 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 05/23/2025 |
| From: | Coleman J Southern Nuclear Operating Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NL-25-0200 LER 2025-002-00 | |
| Download: ML25143A260 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3662025002R00 - NRC Website | |
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._ Southern Nuclear May 23, 2025 Docket No.:
50-366 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Regulatory Affairs Edwin I. Hatch Nuclear Plant Licensee Event Report 2025-002-00 3535 Colonnade Parkway Binningham, AL 35243 Tel. 205 992 5000 NL-25-0200 2A Emergency Diesel Generator Inoperable Due to Inadvertent Overspeed Trip Ladies and Gentlemen:
In accordance with the requirements of 10 CFR 50.73(a)(2)(i)(B) and 10 CFR 50.73(a)(2)(v)(D),
Southern Nuclear Operating Company hereby submits the enclosed Licensee Event Report.
This letter contains no NRC commitments. If you have any questions, please contact the Hatch Licensing Manager, Jimmy Collins, at 912.453.2342.
Respectfully submitted, Cr;~~
Jamie M. Coleman Regulatory Affairs Director Southern Nuclear Operating Co., Inc.
JMC/JMH Enclosure: LER 2025-002-00 Cc:
Regional Administrator, Region II NRR Project Manager - Hatch Senior Resident Inspector - Hatch RTYPE: CHA02.004
Enclosure to NL-25-0200 LER 2025-002-00 Edwin I. Hatch Nuclear Plant Licensee Event Report 2025-002-00 2A Emergency Diesel Generator Inoperable Due to Inadvertent Overspeed Trip Enclosure LER 2025-002-00
Abstract
The 2A Emergency Diesel Generator (EDG) unexpectedly tripped during a test on 2/13/2025, due to its emergency overspeed switch (EOS) falsely signaling an overspeed condition. An initial investigation and operability review found no firm evidence suggesting that the 2A EDG was unable to perform its safety function prior to the trip. Subsequently, the EOS was replaced, the 2A EDG successfully completed its operability surveillance on 2/15/2025, and the original EOS was sent off for failure analysis.
On 3/26/2025, at 14:53 EDT, Unit 2 was operating at approximately 22 percent power in MODE 1 when results from the failure analysis of the EOS for the 2A EDG were received. Contrary to the findings of the initial investigation and operability review, the analysis revealed that the condition experienced with the EOS during the 2/13/2025 test most likely caused the 2A EDG to be inoperable longer than allowed by Technical Specifications (TS). Additionally, during the time period the 2A EDG was inoperable, the 1 B EDG was tagged out in support of planned maintenance for the standby plant service water pump resulting in two EDGs being inoperable for Unit 2 longer than allowed by TS. Having two EDGs inoperable for the same unit resulted in an event or condition that could have prevented the fulfillment of a safety function needed to mitigate the consequences of an accident.
EVENT DESCRIPTION
050 052 I
- 2. DOCKET NUMBER
- 3. LER NUMBER 00366 I
YEAR SEQUENTIAL REV NUMBER NO.
~-I 002 1-G The 2A Emergency Diesel Generator (EOG) (EIIS: DG) unexpectedly tripped during a test on 2/13/2025, due to its emergency overspeed switch (EOS) falsely signaling an overspeed condition. An initial investigation and operability review found no firm evidence suggesting that the 2A EOG was unable to perform its safety function prior to the trip. Subsequently, the EOS was replaced, the 2A EOG successfully completed its operability surveillance on 2/15/2025, and the original EOS was sent off for failure analysis.
On 3/26/2025, at 14:53 EDT, Unit 2 was operating at approximately 22 percent power in MODE 1 when results from the failure analysis of the EOS for the 2A EOG were received. Contrary to the findings of the initial investigation and operability review, the analysis revealed that the condition experienced with the EOS during the 2/13/2025 test most likely caused the 2A EOG to be inoperable from 6/6/2024, the date the EOS was installed, to when the 2A EOG successfully completed its operability surveillance on 2/15/2025, which is longer than allowed by Technical Specifications {TS) 3.8.1.B.
Additionally, while reviewing the 2A EOG EOS trip event, it was discovered that the 1 B EOG {EIIS: DG) was tagged out for eighteen hours and forty-nine minutes in support of planned maintenance for the standby plant service water pump on 6/21/2024, during the same time the 2A EOG was inoperable. The overlapping time of the inoperabilities of the 2A EOG and the 1 B EOG resulted in two EDGs being inoperable for Unit 2 longer than allowed by TS 3.8.1.F. Having two EDGs inoperable for the same unit resulted in an event or condition that could have prevented the fulfillment of a safety function needed to mitigate the consequences of an accident.
FAILED COMPONENTS Name: Emergency Overspeed Switch (EOS)
Master Parts List Number: N/A; the EOS is a subcomponent of the 2A EOG (2R43S001A)
Manufacturer: Honeywell Model: BZE6-RQ Type: Limit Switch
EVENT CAUSE ANALYSIS
Analysis showed that a loose retaining nut on the EOS impacted switch operation and caused the EOS to falsely signal an overspeed condition during the 2/13/2025 test. The EOS installed near the actuation point also contributed to the inadvertent trip of the 2A EOG.
SAFETY ASSESSMENT
There were no actual safety consequences as a result of these events. However, while the 2A EOG was inoperable, both the 2C EOG and the 1 B swing EOG remained operable for Unit 2, except when TS surveillances were performed and when the 1 B EOG was required to be tagged out for eighteen hours and forty-nine minutes on 6/21/24 in support of planned maintenance for the standby plant service water pump. Due to the 2A EOG being inoperable longer than allowed by TS and the overlapping time of the inoperabilities of the 2A EOG and the 1 B EOG, resulting in two EDGs being inoperable for Unit 2 longer than allowed by TS, the completion times of TS 3.8.1.B and TS 3.8.1.F were not met. Additionally, the completion time associated with TS 3.8.1.H to be in MODE 3 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> was also not met. Therefore, these events are reportable as conditions prohibited by TS per 10 CFR 50.73(a)(2)(i)(B). Additionally, having the 2A EDG and the 18 EDG simultaneously inoperable on the same unit is a condition that could have prevented the fulfillment of a safety function needed to mitigate the consequences of an accident and is, therefore, reportable per 10 CFR 50.73(a)(2)(v)(D).
CORRECTIVE ACTIONS
- 2. DOCKET NUMBER 00366 18-1
- 3. LER NUMBER SEQUENTIAL NUMBER 002 REV NO.
1-G The EOS was replaced and the 2A EOG successfully completed its operability surveillance on 2/15/2025. An extent-of-condition was conducted for the remaining EDGs. Two additional retaining nuts were found loose and subsequently corrected. Although two retaining nuts were found loose, the EOS's were installed in a position that would not result in the inoperablity of the EDGs. Additionally, procedures will be revised to capture installation guidance for the EOS.
PREVIOUS SIMILAR EVENTS
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