05000458/LER-2023-006, Automatic Reactor Scram Due to a Turbine Trip Following a Disconnect Failure at Switchyard
| ML24039A130 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 02/08/2024 |
| From: | Crawford R Entergy Operations |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RBG-48275 LER 2023-006-00 | |
| Download: ML24039A130 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4582023006R00 - NRC Website | |
text
entergy RBG-48275 Randy Crawford Manager Regulatory Assurance 225-381-4177 10 CFR 50.73 February 8, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
Licensee Event Report 50-458 / 2023-006-00, Automatic Reactor Scram Due to a Turbine Trip Following a Disconnect Failure at Switchyard River Bend Station - Unit 1 NRC Docket Nos. 50-458 Renewed Facility Operating License No. NPF-47 In accordance with 1 O CFR 50.73, enclosed is the subject Licensee Event Report.
This document contains no commitments.
Should you have any questions, please contact Mr. Randy Crawford, Regulatory Assurance Manager, at 225-381-4177.
Respectfully, Randy Crawford RC/db
Enclosure:
cc:
Licensee Event Report 50-458 / 2023-006-00, Automatic Reactor Scram Due to a Turbine Trip Following a Disconnect Failure at Switchyard NRC Region IV Regional Administrator - Region IV NRC Senior Resident Inspector - River Bend Station Entergy Operations, Inc., 5485 U.S. Highway 61 N. St. Francisville, LA 70775
Enclosure RBG-48275 Licensee Event Report 50-458 / 2023-006-00, Automatic Reactor Scram Due to a Turbine Trip Following a Disconnect Failure at Switchyard
1
Abstract
On December 13, 2023, at 01 :02 CST, with River Bend Station, Unit 1, operating in Mode 1 at 100% power, a turbine trip signal resulted in an automatic reactor scram. All control rods fully inserted and there were no complications. All systems responded as designed.
The turbine trip signal was caused by a switchyard disconnect that was not properly seated in the saddle of the disconnect fingers, which resulted in an open circuit condition on the output of the main generator.
Following a trip of the Reactor Feedwater System due to a Reactor Feedwater Heating isolation, Reactor Core Isolation Cooling was utilized to maintain reactor vessel inventory. The Reactor Feedwater System was restarted once the Reactor Feedwater Heating isolation signal was reset. Reactor water level control was transitioned back to the Reactor Feedwater System.
This report is made pursuant to 10 CFR 50. 73(a)(2)(iv)(A), any event or condition that resulted in manual or automatic actuation of the Reactor Protection System.
EVENT DESCRIPTION
- 2. DOCKET NUMBER
- 3. LEA NUMBER YEAR SEQUENTIAL REV NUMBER NO, 458 2023 006 00 On December 13, 2023, at 01 :02 CST, River Bend Station (RBS), Unit 1, was operating in Mode 1 at 100% power when a turbine trip signal resulted in an automatic reactor scram. All control rods fully inserted and there were no complications. All systems responded as designed.
Following the scram, the Reactor Feedwater System (FWS) [SJ] tripped on low suction pressure caused by isolations to both trains of Reactor Feedwater Heating [SJ]. At 01 :08 CST, reactor water level control was transitioned to the Reactor Core Isolation Cooling (RCIC) [BN] system to maintain inventory of the reactor vessel. At 01 :10 CST, Reactor Feedwater System Pump B (FWS-P1 B) [SJ] was restarted. At 01 :14 CST, reactor water level control was transitioned back to FWS and RCIC was secured. Reactor pressure was maintained by the Turbine Bypass Valves (JI).
This event was reported under 10 CFR 50.72(b)(2)(iv)(B), as any event or condition that results in actuation of the Reactor Protection System (RPS) when the reactor is critical and 10 CFR 50.72(b)(3)(iv)(A) Specified System Actuation as result of Group 3 isolations (EN 56887).
This report is made pursuant to 10 CFR 50.73(a)(2)(iv)(A), any event or condition that resulted in manual or automatic actuation of the Reactor Protection System.
EVENT CAUSE
The cause of the turbine trip signal was due to a Generator Side Disconnect [DISC] switch failing as a result of not being fully seated in the saddle of the disconnect fingers. This created a hotspot that melted the pads to the point where the cable connections faulted between the disconnect and the triad jumper cable to the next length of bus work. The damaged disconnects resulted in an open circuit condition on the output of the Main Generator.
After further investigation, it was determined that the disconnects were not properly seated in the saddle of the disconnect fingers because of personnel error. During the closing of the disconnects following maintenance activities, the disconnects were locked in a partially closed position. The movable members were closed, but not all the way to their mechanical stops.
SAFETY ASSESSMENT
There were no actual Nuclear or Radiological safety consequences due to this event. Thus, this event was of minimal significance to the health and safety of the public. The plant response to this event was bounded by the Updated Safety Analysis Report analysis of a Main Turbine Trip with Steam Bypass Valves/Pressure Regulators in service.
CORRECTIVE ACTIONS
- 2. DOCKET NUMBER
- 3. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO.
458 2023 006 00 Establish the expectation for the RBS Switchyard Coordinator or a Subject Matter Expert to be engaged for reference or oversight on all work being performed at the switchyard by RBS personnel.
Communicate with the Operations Department that only qualified electrical switchyard workers will be allowed to operate disconnects at the switchyard going forward.
Procedure revisions are planned to track the following (tracked by Corrective Action Process):
Add guidance to ensure only qualified switchyard workers operate disconnects.
Add guidance to ensure thermography is performed after closing disconnects to verify the disconnects are functioning as designed.
PREVIOUS SIMILAR OCCURRENCES None Energy Industry Identification System (EIIS) codes are identified in the text as [XX]. River Bend equipment codes are identified as (XX). Page _3_ of _3_