A mechanical problem led to a brief outage at Xcel Energy's nuclear plant in Monticello this week. And while the company assured the Nuclear Regulatory Commission that the health and safety of the public was never in any danger, that was not the case for some of the fish in the Mississippi River outside the plant.
When the plant went offline, its normally balmy discharge water suddenly went cold. Xcel reported that it counted 59 dead fish after the incident.
An official with the Department of Natural Resources tells the Star Tribune the water temperature during nuclear plant outages can drop from 65 degrees down to 40 degrees. The DNR tells the newspaper the dead fish in Monticello were bass, crappies, sunfish, catfish, and carp.
A similar unplanned shutdown at the plant in January of 2014 left about 2,000 fish dead.
What happened in the Monticello plant?
The workings of a nuclear plant are a mystery to most of us, but Xcel's filing describes a Residual Heat Removal pump and the sudden closure of its suction isolation valves. Ultimately, "this was determined to be from an invalid signal on the Reactor Pressure Vessel (RPV) suction interlock," the company told regulators.
Xcel says the shutdown that was triggered went smoothly and safety was not compromised. Rules required that part of the plant's operations (the Residual Heat Removal system) be limited for 24 hours after the incident.
Wildlife and nuclear plants
The warm water discharged from power plants keeps rivers from freezing over and in many cases becomes a magnet for wildlife.
In Florida, for example, manatees are drawn to the discharge canals of power plants, which mimic the warm-water springs of their natural habitat.
Probably the best-known example in Minnesota is near the site of this week's fishkill. For years, trumpeter swans – a bird that had once vanished from Minnesota – have wintered on the Mississippi outside Xcel's Monticello nuclear plant.
A neighbor who became known as "the Swan Lady" put out food for them for 25 years, and that tradition has continued even after Sheila Lawrence's 2011 death from cancer.