05000049/LER-2021-001, Reactor Scram Due to Main Power Transformer Failure
| ML21355A306 | |
| Person / Time | |
|---|---|
| Site: | 05000049 |
| Issue date: | 12/15/2021 |
| From: | Karaba P Exelon Generation Co LLC |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| 21-0065 LER 2021-001-00 | |
| Download: ML21355A306 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 0492021001R00 - NRC Website | |
text
Exelon Generation December 15, 2021 SVPLTR # 21-0065 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Unit 3 Renewed Facility Operating License No. DPR-25 NRC Docket No. 50-249 Dresden Nuclear Power Station 6500 North Dresden Road Morris, IL 60450 10 CFR 50.73
Subject:
Licensee Event Report 249/2021-001-00, Reactor Scram due to Main Power Transformer Failure Enclosed is Licensee Event Report 249/2021-001-00, Reactor Scram due to Main Power Transformer Failure.
- There are no regulatory commitments contained in this submittal.
Should you have any questions concerning this letter, please contact Mr. Duane Avery, acting Regulatory Assurance Manager, at (815) 416-2804.
Site Vice President Dresden Nuclear Power Station
Enclosure:
Licensee Event Report 249/2021-001-00 CC:
Regional Administrator - NRC Region Ill NRC Senior Resident Inspector-Dresden Nuclear Power Station
Abstract
On October 16, 2021 at 0428 CDT, an automatic reactor protection system actuation occurred due to failure of the main power transformer. The safety significance of this event was minimal. All control rods inserted to their full-in position. Following the reactor scram, all systems operated as expected.
The cause of this event was due to a sudden, unanticipated, catastrophic failure of the main power transformer high voltage oil impregnated paper bushing. The cause of the bushing failure has not yet been determined. A root cause investigation and failure analyses are ongoing. Results of the root cause report and failure analyses will be provided in a supplemental report.
Corrective actions included replacement of the failed main power transformer. Other corrective actions will be provided in a supplemental report.
This event is being reported in accordance with 10 CFR 50. 73(a)(2)(iv)(A), an event that resulted in automatic actuation of a system listed in paragraph 10 CFR 50. 73(a)(2)(iv)(B), specifically the reactor protection system including reactor scram.
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor, 2957 megawatts thermal rated core power Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
A. CONDITIONS PRIOR TO EVENT
Unit: 3 Reactor Mode: 1 Event Date: October 16, 2021 Mode Name: Power Operation
B. DESCRIPTION OF EVENT
Event Time: 0428 CDT Power Level: 100%
SEQUENTIAL NUMBER 001 REV NO.
00 On October 16, 2021, at 0428 CDT, an automatic reactor protection system [JC] actuation occurred due to failure of the main power transformer (MPT) [EL]. All control rods [AA] inserted to their full-in position.
Following the reactor scram, all systems operated as expected.
The MPT experienced a phase-to-ground fault. There is no evidence of a plant event or grid event as the initiator. There were no alarms indicative of a transformer failure as a precursor to the failure.
Additionally, a dissolved gas analysis of the transformer oil sample performed two hours prior to the event revealed no alert nor degrading trend.
The MPT "A" phase high voltage bushing, lightning arrester, and control cabinet suffered catastrophic damage. Ancillary components and equipment of the transformer suffered various degrees of damage.
As a result of a fire associated with the MPT failure, an Unusual Event was declared due to a fire in the protected area not extinguished in less than 60 minutes. The Unusual Event was terminated at 0709 CDT.
The transformer was replaced with a transformer of a different design and a different manufacturer.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A), an event that resulted in automatic actuation of a system listed in paragraph 1 O CFR 50. 73(a)(2)(iv)(B), specifically the reactor protection system including reactor scram.
C. CAUSE OF EVENT
The cause of the event was due to a sudden, unanticipated, catastrophic failure of the MPT high voltage oil impregnated paper bushing.
Additional cause(s) of the transformer and bushing failure is under investigation and will be reported in a supplemental report.
D. SAFETY ANALYSIS
SEQUENTIAL NUMBER 001 REV NO.
00 The safety significance of this event was determined to be minimal based upon the availability of the required systems to
- 1) Shutdown the reactor and maintain it in a safe shutdown condition,
- 2) Remove residual heat,
- 3) Control the release of radioactive material, or
- 4) Mitigate the consequences of an accident.
There were no safety consequences impacting plant or public safety as a result of this event. There was no loss of safety function for this event.
E. CORRECTIVE ACTIONS
Corrective actions included replacement of the failed MPT with a transformer of a different design and from a different manufacturer.
Additional corrective action(s) will be developed during the ongoing root cause investigation.
F. PREVIOUS OCCURRENCES
The most recent transformer failure at Dresden was in April 2014 (LER 05000237/2014-002-02). During that event the Unit 2 MPT failed due to an internal fault with the most probable cause determined to be a combination of insulation issues. The event resulted in the main turbine tripping and a reactor scram.
The transformer was replaced with a transformer of a different design and a different manufacturer.
G. COMPONENT FAILURE DATA
I Device I Manufacturer I Model I SIN I Type I
I Main Power Transformer I Siemens IELIN I 1731659 I TDQ-A27D9K-99 I Page_3_ of _3_