05000458/LER-2021-002, Automatic Reactor Scram Due to Turbine Control System Communication Fault
| ML21152A033 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 05/28/2021 |
| From: | Karenina Scott Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBG-48095 LER 2021-02-00 | |
| Download: ML21152A033 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4582021002R00 - NRC Website | |
text
Entergy Operations, Inc.
Entergy St. Francisville, LA 70775 Tel 225-381-4374 Kent Scott Site Vice President 10 CFR 50.73 RBG-48095 May 28, 2021 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
Licensee Event Report 50-458 I 2021-02-00, Automatic Reactor Scram due to Turbine Control System Communication Fault River Bend Station Unit 1 NRC Docket No. 50-458 Renewed Facility Operating License No. NPF-47 In accordance with 10 CFR 50.73, enclosed is the subject Licensee Event Report. This document contains no commitments. If you have any questions, please contact Mr. Tim Schenk at 225-381-4177.
Respecifully, KCSIdmw
Enclosure:
Licensee Event Report 50-458 I 2021-02-00, Automatic Reactor Scram due to Turbine Control System Communication Fault cc:
NRC Regional Administrator
- - Region IV NRC Project Manager
- - River Bend Station NRC Senior Resident Inspector
- - River Bend Station Louisiana Department of Environmental Quality Public Utility Commission of Texas
Enclosure RBG-48095 Licensee Event Report 50-458 I 2021-02-00, Automatic Reactor Scram due to Turbine Control System Communication Fault
Abstract
On April 2, 2021 at 1017 CT, River Bend Station was operating at 86% reactor power when a turbine trip signal caused a Main Turbine trip and an automatic reactor scram. All control rods fully inserted and there were no complications. All systems responded as designed.
The Main Turbine trip and reactor scram were caused by a random, spurious communication error within the Ovation Turbine Control System. The condition was repaired by replacing a communication module in the remote panel.
EVENT DESCRIPTION
On April 2,2021 at 1017 CT, while operating at 86% reactor power, a random, spurious communication error within the Ovation Turbine Control System (referred to as Ovation) (JJ) caused a Main Turbine (TA) trip and an automatic reactor scram. All control rods fully inserted and there were no complications. All systems responded as designed.
Following the scram, reactor pressure was maintained by the Turbine Bypass Valves (JI) and reactor water level was maintained by the Feedwater (SJ) system.
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 when the reactor is critical and 10 CFR 50.72(b)(3)(iv)(A) Specified System Actuation as a result of expected post scram level 3 isolations. (EN 55169)
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.
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. Post scram reactor level and pressure control functioned as expected.
EVENT CAUSE
This event was caused by a remote communications module that erroneously sent a turbine front standard manual pushbutton trip signal by making the normally energized input appear de-energized.
Investigation into this event identified that communication errors were coming into Ovation from a remote panel following RF-21. These communication errors were causing random, spurious alarms to come in on Ovation. The condition was not detected because the Ovation alarms did not last long enough to trigger a main control room annunciator and there was no procedural guidance to periodically review the Ovation alarm log. After the faulty remote communication module was replaced, system operation returned to normal. This was also determined to be a single point vulnerability.
CORRECTIVE ACTIONS
The defective remote communication module was replaced.
A temporary modification was installed to eliminate the Front Standard Ovation push button inputs (single point vulnerability) as Turbine trip signals.
Procedure revisions are planned to provide the following (tracked by Corrective Action Process):
Improved Ovation system shutdown and restoration instructions. (Prevents damage to modules)
Improved guidance for Ovation alarm monitoring.
Direction to place Ovation controllers in service before Turbine shell and chest warming to allow monitoring prior to plant startup.
PREVIOUS SIMILAR EVENTS
None