05000425/LER-2020-001, Transformer Failure Leads to Main Generator Trip and Subsequent Reactor Trip
| ML21008A571 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 01/08/2021 |
| From: | Pitts D Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-20-1407 LER 2020-001-00 | |
| Download: ML21008A571 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4252020001R00 - NRC Website | |
text
._ Southern Nuclear January 8, 2021 Docket No:
50-425 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 R. Drayton Pitts Sile Vice President Voglle Units 1-2 Vogtle Electric Generating Plant - Unit 2 Licensee Event Report 2020-001-00 7821 River RD Waynesboro GA, 30830 706-848-0001 tel 706-848-3321 fax NL-20-1407 Transformer failure leads to main generator trip and subsequent reactor trip Ladies and Gentlemen:
In accordance with the requirements of 10 CFR 50.73(a)(2)(iv)(A), Southern Nuclear Operating Company is submitting the enclosed Licensee Event Report, 2020-001-00 for Vogtle Electric Generating Plant Unit 2. This letter contains no NRC commitments. If you have any questions, please contact Matthew Harn at (706) 848-1544.
Respectfully submitted, Drayton Pitts Site Vice President Vogtle 1&2 RDP/KCW Enclosure: Unit 2 Licensee Event Report 2020~001-00 Cc: Regional Administrator NRR Project Manager - Vogtle 1 & 2 Senior Resident Inspector - Vogtle 1 & 2 RType: CVC?OOO
U. S. Nuclear Regulatory Commission NL-20-1407 Page 2 Vogtle Electric Generating Plant - Unit 2 Licensee Event Report 2020~001 ~00 Transformer_failure leads to main generator trip and subsequent reactor trip Enclosure Unit 2 Licensee Event Report 2020~001 9 00
Abstract
On November 12, 2020 at approximately 1732 EST with Unit 2 in Mode 1 and 100 percent power, the reactor automatically tripped due to a main generator trip and subsequent turbine trip. The reason for the generator trip was a fault in the B-phase main step-up transformer. The trip was not complex with all systems responding normally post trip. Operations stabilized the plant in Mode 3. Decay heat was removed by the steam generators, through the steam dumps into the condenser.
Unit 1 was not affected. The operating crew performed as expected. The faulted transformer was removed from service and an installed spare transformer was placed in service.
Due to the automatic Reactor Protection System (RPS) actuation and the automatic actuation of the Auxiliary Feedwater
( FW) system, this event is being reported in accordance with 10 CFR 50.73{a)(2}(iv)(A).
A.
Event Description
On November 12, 2020 at approximately 1732 EST with Unit 2 in Mode 1 and 100 percent power, the reactor automatically tripped due to a generator trip and subsequent turbine trip. The reason for the generator trip was a fault in the B-phase main step-up transformer (XFMR), Siemens model 351-18210. This caused the generator to trip. Due to the generator and turbine trip, the reactor tripped.
There were no other Structures, Systems, or Components (SSCs) that were out of seNice that were inoperable at the beginning of the event and contributed to the event.
Due to the automatic Reactor Protection System (RPS)[JC] actuation and the automatic actuation of the Auxiliary Feedwater (AFW)[BA] system, this event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A).
B.
Cause of Event
The cause of the main step-up transformer fault was an internal fault around the Oeenergized Tap Changer (DETC). There were no previous indications that there were any issues with this transformer.
C. Safety Assessment
The main step-up transfom,ers serves no safety related purpose for U1e unit. When the transfom1er failed, all the appropriate safety systems responded as designed. The generator, turbine, reactor, and Auxiliary Feedwater system operated as expected; all the control rods fully inserted into the core. The operating crew performed as expected. The event was within the analysis of the Updated Final Safety Analysis Report Chapter 15. There was no release of radioactivity. This event did not pose a threat to the health and safety of the public. Therefore, the safety significance of this issue is very tow.
D. Corrective Actions
The faulted transformer was removed from service and the switchyard was realigned to place the spare main step-up transformer into seNice. The remaining main step-up and the spare step-up transformers were thoroughly checked while the unit was offiine to ensure that there were no abnormal indications, and none were found.
E.
Previous Similar Events
None N C FORM 366B (08-2020)