05000458/LER-2020-002, Manual Reactor Scram Due to Reactor Recirculation Pump Trip
| ML20293A475 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 10/19/2020 |
| From: | Vercelli S Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBG-48048 LER 2020-002-00 | |
| Download: ML20293A475 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4582020002R00 - NRC Website | |
text
Entergy Operations, Inc.
Entergy 61 N St. Francisville, LA 70775 Tel 225-381-4374 Steve Vercelli Site Vice President 10 CFR 50.73 RBG-48048 October 19, 2020 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
Licensee Event Report 50-458 I 2020-02-00, Manual Reactor Scram Due to Reactor Recirculation Pump Trip River Bend Station Unit 1 NRC Docket Nos. 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, Regulatory Assurance Manager, at 225-381-4177.
Respectfully, S PVIblj
Enclosure:
Licensee Event Report 50-458 I 2020-02-00, Manual Reactor Scram Due to Reactor Recirculation Pump Trip 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-48048 Licensee Event Report 50-458 I 2020-02-00, Manual Reactor Scram Due to Reactor Recirculation Pump Trip
Abstract
On August 21 2020 at 0908 CT, River Bend Station (RBS) was operating at 100% reactor power when Reactor Recirculation Pump B tripped. At 0918 CT, a manual reactor scram was inserted at 67% reactor power after receiving indications of flux oscillations on the Period Based Detection System (PBDS) and Average Power Range Monitors (APRMs). All control rods fully inserted and there were no complications. All systems responded as designed.
This report is made in accordance with 10 CFR 50.73(a)(2)(iv)(A) for the manual reactor trip.
EVENT DESCRIPTION
On August 21, 2020 at 0908 hours0.0105 days <br />0.252 hours <br />0.0015 weeks <br />3.45494e-4 months <br /> CT the Reactor Recirculation Pump B tripped. Power lowered to approximately 66%
and operators entered GOP-0004, Single Loop Operation, and AOP-0024, Thermal Hydraulic Stability Controls.
At 0911 hours0.0105 days <br />0.253 hours <br />0.00151 weeks <br />3.466355e-4 months <br /> extraction steam isolated, leading to lowering level in the 3rd point Feedwater Heater B which caused Heater Drain Pump C to trip on low heater level. This condition led to colder Feedwater temperature being sent to the Reactor. At 0913 hours0.0106 days <br />0.254 hours <br />0.00151 weeks <br />3.473965e-4 months <br /> recirculation flow was lowered to maintain recirculation loop A flow in accordance with Single Loop Operations and Technical Requirement 3.4.1.1.1. The operators began inserting control rods at 0916 hours0.0106 days <br />0.254 hours <br />0.00151 weeks <br />3.48538e-4 months <br /> due to unexpected entry into the Restricted Region of the power to flow map as directed by AOP-0024.
While inserting control rods, alarms were received for Division 1 Period Based Detection System Hi Decay Ratio, Division 2 Period Based Detection System Hi Decay Ration alarm, and Division 2 Period Based Detection System Hi-Hi Decay Ratio. APRM power was observed fluctuating between 62% and 68%.
The Licensed Operator manually tripped the reactor due to indication of rising counts on PBDS.
SAFETY ASSESSMENT
The actual consequence was the initiation of a manual SCRAM. All core responses were as expected and the RBS power to flow map continued to meet the licensing acceptance criteria parameters. There were no actual consequences to general safety of the public, nuclear safety, industrial safety and radiological safety for this event.
EVENT CAUSE
While in single loop operation, slow response of the high-level dump valve, due to debris identified in the air relays, led to low water level in the 3rd point B heater. The low water level in the 3rd point B heater resulted in the trip of the C Heater Drain Pump resulting in colder Feedwater temperature being sent to the Reactor. This condition, combined with being in the Restricted Region of the power to flow map, led to power oscillations.
CORRECTIVE ACTION TO PREVENT RECURRENCE:
- Implement a modification to install air filters upstream of the regulator feeding the positioner to each of the affected AOVs.
- Complete dynamic tuning of the Feedwater Heater Drain System control valves to reduce unnecessary cycling of the AOVs to improve response to changing level demands in the various heaters.
PREVIOUS SIMILAR EVENTS
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