05000391/LER-2024-001, Automatic Reactor Trip Due to Main Generator Protection Relay Actuation
| ML24087A215 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 03/27/2024 |
| From: | Anthony Williams Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| WBL-24-013 LER 2024-001-00 | |
| Download: ML24087A215 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3912024001R00 - NRC Website | |
text
W4 TENNESSEE VALLEY AUTHORITY Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 WBL-24-013 March 27, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 2 Facility Operating License No. NPF-96 NRC Docket No. 50-391 10 CFR 50.73
Subject:
Licensee Event Report 391/2024-001-00, Automatic Reactor Trip Due to Main Generator Protection Relay Actuation Pursuant to the reporting requirements of 10 CFR 50. 73, attached is the subject Licensee Event Report concerning the Automatic Reactor Trip and Reactor Protection System Actuation for Watts Bar Nuclear Plant, Unit 2, which occurred on January 27, 2024.
There are no new regulatory commitments contained in this letter. Please direct any questions concerning this matter to Jonathan Johnson, WBN Licensing Manager, at jtjohnsonO@tva.gov.
Respectfully, Anthony L.
Site Vice P Watts Bar N
U.S. Nuclear Regulatory Commission WBL-24-013 Page 2 March 27, 2024
Enclosure:
LER 391/2024-001-00, Automatic Reactor Trip Due to Main Generator Protection Relay Actuation cc (w/Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant NRC Project Manager - Region II
WBL-24-013 E1 of 1 ENCLOSURE Tennessee Valley Authority Watts Bar Nuclear Plant Unit 2 LER 391/2024-001-00, Automatic Reactor Trip Due to Main Generator Protection Relay Actuation
Abstract
On January 27, 2024 at 2141 Eastern Standard Time (EST), while Unit 2 was at 100 percent rated thermal power, Watts Bar Nuclear Plant (WBN) Unit 2 experienced an automatic reactor trip due to a main turbine trip. All control and shutdown bank rods inserted properly in response to the reactor trip. All safety systems, including the Auxiliary Feedwater (AFW) System, performed as designed and there were no complications with the trip.
The most likely cause for the main turbine trip was vibration induced wear damage from metal conduit threading and conduit edging to cable insulation, exposing conductors and subsequently causing a ground fault in the associated Current Transformer (CT) protective relay circuit. The cables connecting the current transformers to the main termination box were identified as degraded and all were replaced. A protective wrap was used on the new cables at wear locations.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A), as an automatic actuation of the Reactor Protection System (RPS) and Auxiliary Feedwater System (AFW).
Page 6 of 6 Clamp-on amp meters connected to a power quality analyzer were installed for additional online monitoring capabilities. Data has been assessed on a weekly basis with no indications of cable deficiencies.
B. Corrective Actions to Prevent Recurrence or to reduce the probability of similar events occurring in the future The root cause analysis for this event determined the following corrective actions to prevent recurrence:
- 1. Set the standard by revising the troubleshooting equipment investigation process, Corrective Action Program, and issue resolution process to incorporate common language and requirements around cause levels and failure mechanism.
- 2. Revise Leadership Culture, Site Middle Manager, and Management Review Committee training material to include discussion on failure investigation and failure mechanism.
- 3. Revise the Corporate Functional Area Management and Quality Assurance processes to require periodic assessment on personnel and leadership behaviors around failure investigations and failure mechanisms.
VII. Previous Similar Events at the Same Site
LER 391/2018-003-00 documents a unit trip that occurred on June 22, 2018 due to actuation of the main transformer differential current relay. The most probable cause of that event was attributed to an intermittent equipment failure between the neutral side current transformer of the main generator and the protection relays which led to actuation of the A phase main transformer differential current relay and subsequent trip.
LER 391/2023-002-00 documents a unit trip that occurred on June 27, 2023 due to a main turbine trip. The most likely cause for the main turbine trip was a loose terminal connection for current input into a main transformer phase differential trip relay.
VIII. Additional Information
None.
IX.
Commitments
None.