05000259/LER-2020-001, Re Manual Reactor Shutdown of Two Units on Decreasing Condenser Vacuum Due to Eel Grass Intrusion
| ML20260H103 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 09/16/2020 |
| From: | Bono S Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2020-001-00 | |
| Download: ML20260H103 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2592020001R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Decatur, Alabama 35609-2000 September 16, 2020 10 CFR 50.73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Browns Ferry Nuclear Plant, Units 1 and 2 Renewed Facility Operating License Nos. DPR-33 and DPR-52 NRC Docket Nos. 50-259 and 50-260
Subject:
Licensee Event Report 50-259/2020-001 Manual Reactor Shutdown of Two Units on Decreasing Condenser Vacuum due to Eel Grass Intrusion The enclosed Licensee Event Report (LER) provides details of the manual reactor shutdown of two units on decreasing condenser vacuum due to eel grass intrusion. The Tennessee Valley Authority is submitting this report in accordance with Title 10 CFR 50.73(a)(2)(iv)(A), as any event or condition that resulted in a manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B).
There will be a supplement to this LER to provide additional time to complete the root cause evaluation.
There are no new regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact J. L. Paul, Site Licensing Manager, at (256) 729-2636.
Respectfully, S. M. Bono Site Vice President Enclosure: Licensee Event Report 50-259/2020-001 Manual Reactor Shutdown of Two Units on Decreasing Condenser Vacuum due to Eel Grass Intrusion cc (w/ Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant NRC Project Manager - Browns Ferry Nuclear Plant p
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Abstract
On July 20, 2020, at approximately 0955 Central Daylight Time (CDT), the Unit 1 control room received the traveling screen differential pressure high alarm. Assistant Unit Operators dispatched to the condenser circulating water (CCW) system forebay reported large masses of eel grass. The influx of eel grass resulted in fouling of the trash racks and traveling water screens for all three units which reduced the CCW flows during this event.
As a result of degrading condenser vacuum on Unit 2, operators manually scrammed the reactor at 1325 CDT. On July 21, 2020, as Unit 1 condenser vacuum continued to degrade to the turbine trip setpoint, the Unit 1 operators manually scrammed the reactor at 0435 CDT.
The direct cause of the manual reactor shutdowns was degraded main condenser vacuum.
There will be a supplement to this Licensee Event Report to provide additional time to complete the root cause evaluation.
A. Immediate Corrective Actions
- 1. Actions were taken to rake trash racks, clean traveling water screens, and reduce reactor power.
- 2. An Operations Decision-Making Issue (ODMI) evaluation was developed to provide critical thinking and additional guidance for unit restart. The ODMI evaluation included actions such as assessing CCW system health, increased monitoring, and increased staffing for harvester operation & trash rack cleaning.
B. Corrective Actions to Prevent Recurrence or to reduce the probability of similar events occurring in the future There will be a supplement to this Licensee Event Report to provide additional time to complete the root cause evaluation.
VII. Previous Similar Events at the Same Site
A search of BFN Licensee Event Reports (LERs) for Units 1, 2, and 3 within the last three years identified no LERs associated with biofouling at the CCW system intake.
In 2019, eel grass growth and breakaway resulting in accumulation in the forebay became a new problem for BFN and the generational risk was quickly identified. Evaluation of this issue and resultant actions are being tracked by CR 1563233.
VIII. Additional Information
There is no additional information.
IX.
Commitments
There are no new commitments.