05000387/LER-2020-001, 0l for Susquehanna Steam Electric Station Unit 1 Re Automatic Reactor Scram Due to Main Turbine Trip Caused by an Electrical Ground Path in the B Main Transformer
| ML21026A253 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 01/26/2021 |
| From: | Cimorelli K Susquehanna, Talen Energy |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| PLA-7898 LER 2020-001-0l | |
| Download: ML21026A253 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iv)(B), System Actuation |
| 3872020001R00 - NRC Website | |
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Kevin Cimorelli Site Vice President Attn: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Susquehanna Nuclear, LLC 769 Salem Boulevard Berwick, PA 18603 Tel. 570.542.3795 Fax 570.542.1504 Kevin.Cimorelli@TalenEnergy.com SUSQUEHANNA STEAM ELECTRIC STATION LICENSEE EVENT REPORT 50-387 /2020-001-01 UNIT 1 LICENSE NO. NPF-14 PLA-7898 TALEN~
ENERGY 10 CPR 50.73 Docket No. 50-387 Attached is Licensee Event Report (LER) 50-387/2020-001-0l. The LER supplement reports an event involving an automatic scram due to a main turbine trip. The condition is being reported in accordance with 10 CPR 50.73(a)(2)(iv)(A) as an event that resulted in an automatic actuation of the Reactor Protection System (including a reactor scram).
There were no actual consequences to the health and safety of the public as a result of this event.
This letter contains no new or revised regulatory commitments.
K. Cimorelli Attachment: LER 50-387/2020-001-0l Copy:
NRC Region I Mr. C. Highley, NRC Sr. Resident Inspector Ms. S. Goetz, NRC Project Manager Mr. M. Shields, PADEP/BRP January 26, 2021
Abstract
On May 3, 2020 at approximately 08:21, Susquehanna Steam Electric Station Unit 1 reactor automatically scrammed due to a main turbine trip. Both divisions of the Reactor Protection System (RPS) actuated and all control rods inserted. This event was reported by Event Notification 54691 in accordance with 10 CFR 50.72(b)(2)(iv)(B) and (b)(3)(iv)(A). This event is also reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in an automatic actuation of the RPS (including reactor scram), as well as associated isolation and actuation of other systems listed in 10 CFR 50.73(a)(2)(iv)(B).
The direct cause of the event was an electrical path from a replacement current transformer inside the main transformer to the low voltage bus causing a ground on the 24 kV System (Main Generator). The apparent cause of the ground was a current transformer with the incorrect insulation characteristics installed as a result of the wrong current transformer being supplied to Susquehanna. Corrective actions included removing the current transformer and replacing it with a bus bar.
There were no actual consequences to the health and safety of the public as a result of this event.
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CONDITIONS PRIOR TO EVENT
Unit 1 - Mode 1, approximately 76 percent Rated Thermal Power Unit 2 - Mode 1, approximately 100 percent Rated Thermal Power There were no structures, systems, or components that were inoperable at the start of the event that contributed to the event.
EVENT DESCRIPTION
On May 3, 2020 at approximately 08:21, Susquehanna Steam Electric Station Unit 1 reactor automatically scrammed due to a main turbine [EIIS System/Component Code: TA/TRB] trip. The Unit 1 Control Room received indication of a main turbine trip with both divisions of the Reactor Protection System (RPS) [EIIS System Code: JC] actuated and all control rods inserted. The Reactor Recirculation Pumps [EIIS System/Component Code: AD/P] tripped on End of Cycle Recirculation Pump Trip (EOC-RPT).
Operators subsequently maintained reactor water level at the normal operating band using the Reactor Feed Water system [EIIS System Code: SJ]. All safety systems responded properly during the event.
This event was reported by Event Notification 54691 in accordance with 10 CFR 50.72(b)(2)(iv)(B) and (b)(3)(iv)(A). This event is also reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in an automatic actuation of the RPS (including reactor scram), as well as associated isolation and actuation of other systems listed in 10 CFR 50.73(a)(2)(iv)(B).
CAUSE OF EVENT
The direct cause of the event was an electrical path from a replacement current transformer (CT7) [EIIS System/Component Code: EL/XCT] inside the main transformer to the low voltage bus causing a ground on the 24 kV System (Main Generator) [EIIS System Code: TB]. The apparent cause of the ground was a current transformer with the incorrect insulation characteristics installed as a result of the wrong current transformer being supplied to Susquehanna.
ANALYSIS/SAFETY SIGNIFICANCE
The actual consequence of this event was a Unit 1 Reactor scram. The scram did not require or result in the actuation of Emergency Core Cooling System or Reactor Core Isolation Cooling system [EllS System Code: BN] and no main steam relief valves [EllS System/Component Code: SB/RV] opened. All safety systems responded properly during the event. The condition described herein did not result in a safety system functional failure. Accordingly, this event will not be counted as a safety system functional failure in the Reactor Oversight Process Performance Indicators. There were no actual consequences to the health and safety of the public as a result of this event.
CORRECTIVE ACTIONS
Key corrective actions included:
- 1. Removed the current transformer and replaced it with bus bar under an approved engineering change.
COMPONENT FAILURE INFORMATION
Component Identification - 1X102 CT7 Component Name - Unit 1 B Main Transformer Current Transformer 7 Component Part Number - 40889-1-001 Manufacturer - Instrument Transformers Limited (ITL)
PREVIOUS OCCURRENCES
None.