Browns Ferry adds automated trash racks after eelgrass shut two reactors
The July 2020 intake clog derated a third unit to about 78 percent power; engineers put TVA's revenue loss at $15 million to $20 million.
Key facts
- IAEA 2026 report puts the production loss at roughly 0.5 terawatt-hours
- Cleaning takes one operator about 1.5 hours, versus three mechanics and four to six hours
- Racks arrived April 2021; system fully installed by end of July 2021
- Contractor WTR Engineering supplied the rakes; vertical rack position required post-installation tweaks
- Jellyfish shut three of six reactors at France's Gravelines plant this summer
Browns Ferry shut down two reactors and derated a third to about 78 percent power in July 2020 after a surge of nonnative eelgrass clogged the cooling water intake, said Antonio Diaz-Lucier, a system engineer at the plant.
The incident cost the Tennessee Valley Authority about $15 million to $20 million in revenue, plant engineers said, and a 2026 report from the International Atomic Energy Agency put the production loss at roughly 0.5 terawatt-hours.
New racks hold tighter spacing and push debris out
Browns Ferry replaced its trash racks with a custom system made by WTR Engineering that adds automated raking. The IAEA described the new racks as "designed with tighter bar spacing to capture more biotic fouling, increasing protection for the systems downstream." The rake drops between funnels onto guide rails, pitches its tines behind the rack bars and closes a grapple at the bottom to lift debris out rather than push it toward the traveling water screens.
Diaz-Lucier said the racks arrived in April 2021 and the system was fully installed by the end of July 2021, with WTR on site for a week or two of testing. It was running by August.
One operator cleans 18 screens in about an hour and a half
Raking the racks previously took three mechanics, a crane and two workers on a bucket four to six hours, and did not remove debris well, Diaz-Lucier said. The new system takes one operator about an hour and a half to clean all 18 screens. Because the rake swings out beyond the plant's security-protected area, the system runs only when security is watching it. The trash racks are vertical, a position WTR and other raking vendors do not recommend; Diaz-Lucier said the plant could not change that without a permit process that takes three years at the quickest.
Weekly eelgrass notices go to two dams
Browns Ferry now sends weekly eelgrass notifications and exchanges information with Guntersville Dam upstream and Wheeler Dam downstream, Diaz-Lucier said. Communication between the sites was limited before the 2020 incident. He said he does not foresee severe impacts from eelgrass with the new system in place.
