A huge seasonal mayfly hatch last week shut down offsite power to one of the two power lines serving DTE Energy’s Fermi 2 1200-MW nuclear plant in Michigan on Lake Erie. The event at a switchyard supplying power to the plant caused the plant’s backup diesel generators to kick in, keeping power to the plant.
The Toledo Blade quoted plant spokesman Stephen Tait, “That occurred after a large hatch of mayflies overnight. Many of those mayflies landed on equipment, which caused arcing or a short on the equipment and the loss of power on one of our lines.”
The annual summer mayfly hatch is a well-known problem. Tait said the plant this time of year dims the lighting to deter the mayflies from gathering. In 1990, the Nuclear Regulatory Commission reported that an accumulation of dead mayflies at the Tennessee Valley Authority’s Browns Ferry plant clogged roof drains and let water into the room housing the backup generators. The NRC said, “A short downpour of rain came and dead mayflies clogged the drain screens allowing water to enter the diesel generator building. One of the six clogged drain screens was subsequently removed and all of the water on the diesel generator building roof drained off.”
Mayflies are aquatic insects in the Ephemeroptera order. They are a sign of good water quality, as they do not survive in polluted water. But when they emerge in late June and early July to breed and live for only a day in enormous numbers, attracted by light, they can hinder highways, cover buildings, and become a nuisance.
The Toledo newspaper noted, “Their numbers have been so thick along Lake Erie, the Detroit River, and Lake St. Clair that they sometimes show up on weather radar and have been known to leave roadways dangerously slick.”
They are also a delight to fly fishermen and women, who use artificial lures to angle for trout and bass.
Can mayflies cause serious damage to power plants? Very unlikely, by all accounts. But they can make life difficult in places where even seemingly minor problems require vigilance and response.
— Kennedy Maize