Pump problem knocks Monticello nuclear plant offline, leads to fishkill


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.

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Monticello nuclear plant shuts down

Xcel Energy says its Monticello nuclear power plant automatically shut down at 11:07 a.m. Tuesday, but officials aren't sure why and a cause is being investigated, the Pioneer Press reports. All plant safety systems were functioning, officials with the Minneapolis-based utility said. The shutdown posed no danger to the public or workers, Xcel officials said. The plant is not expected to be down long.

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The safety performance of the nuclear plant in Monticello will be the subject of a public meeting Tuesday set by the U.S. Nuclear Regulatory Commission. The NRC found that the Monticello plant, owned by Xcel Energy, operated safely in 2011. The agency will also discuss its reaction to the Fukushima Daiichi disaster in Japan, including increased inspections at U.S. nuclear plants.

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A transformer lockout at the Monticello nuclear power plant prompted an automatic shutdown Friday afternoon. Xcel Energy says the malfunction interrupted non-safety-related power, but that all safety systems functioned as designed.