05000391/LER-2023-002, Automatic Reactor Trip Due to Main Generator Protection Relay Actuation
| ML23236A544 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 08/24/2023 |
| From: | Anthony Williams Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| WBL-23-037 LER 2023-002-00 | |
| Download: ML23236A544 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3912023002R00 - NRC Website | |
text
W4 TENNESSEE VALLEY AUTHORITY Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 WBL-23-037 August24, 2023 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 391/2023-002-00, 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 June 27, 2023.
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.
Anthony L. Williams IV Site Vice President Watts Bar Nuclear Plant
U.S. Nuclear Regulatory Commission WBL-23-037 Page 2 August 24, 2023 Enclosure: LER 391/2023-002-00, 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
ENCLOSURE Tennessee Valley Authority Watts Bar Nuclear Plant Unit 2 LER 391/2023-002-00, Automatic Reactor Trip Due to Main Generator Protection Relay Actuation
Abstract
On June 27, 2023 at approximately 1626 Eastern Daylight-Saving Time (EDT), while both units were at 100% 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 a loose terminal connection for current input into a main transformer phase differential trip relay. A design change was implemented to relocate the differential trip signal such that the one out of two taken twice logic and circuit protection is maintained.
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).
Page 5 of 5 VI.
Corrective Actions
This event was entered into the TVA Corrective Action Program and is being tracked under Condition Report 1864894.
A. Immediate Corrective Actions
Operations personnel promptly stabilized the plant in Mode 3. Troubleshooting and field inspections identified the associated loose connection and corrected it.
B. Corrective Actions to Prevent Recurrence or to reduce the probability of similar events occurring in the future Design change WBN-23-040 was issued to relocate the 287T differential trip signal from the 252 current transformer (CT) loop to the 251 CT loop through relays RLY-244-S300G3/1 and 2-RLY-244-M3425A/2 such that the one out of two taken twice logic and circuit protection is maintained. Terminal connection tightness was verified on all other 287T relay current inputs.
Additionally, preventive maintenance change requests are being processed to add wire termination checks to associated relay calibration activities.
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.
VIII. Additional Information
None.
IX.
Commitments
None.