Xcel's Prairie Island nuclear plant will be out of commission until January

An equipment problem at Xcel Energy's nuclear power plant near Red Wing has shut down the facility likely until January, causing a three-month outage for one of the utility's biggest power sources.

The issue at the Prairie Island plant hasn't affected electric service, but it could lead to higher fuel costs that are passed down to Xcel's customers on their monthly bills.

On Oct. 19, one of two units at the plant shut itself down after an issue between the turbine and the electric grid, said Xcel spokesman Kevin Coss. The company said repairs are underway as it replaces cabling between the unit and the substation at the plant.

In a public filing with the U.S. Nuclear Regulatory Commission, Xcel said all safety functions operated as designed when the reactor "automatically tripped," causing a loss in "non-safety related power" at both plant units.

"Prairie Island has been an extremely reliable plant for the last 50 years, providing carbon-free electricity for more than 1 million customers across the Upper Midwest," Coss said in a written statement. "With that said, all power plants experience outages from time to time, and Prairie Island is no different."

The incident happened shortly after Prairie Island's second unit had powered down Oct. 6 for scheduled refueling and maintenance, a process that happens every two years for each unit at the plant.

Xcel expected that refueling process would take about two months, but Coss said both units will stay offline until the cable replacement is completed. Xcel expects both the reactors to be up and running in January.

"As we navigate supply-chain challenges and the process of making repairs, we are taking the additional time to ensure all components of both reactors are ready to return to service and are using the opportunity to execute other maintenance work that cannot be done while units are online," Coss said.

Dave Lochbaum, a nuclear safety engineer formerly with the Union of Concerned Scientists, said the issue sounded like "an aging problem." Other plants down for that long have had issues with their electric distribution systems, he said, and often with the generator itself.

"Things do wear out," Lochbaum said.

Lochbaum said safety systems worked as they were supposed to. He said it was prudent for Xcel to look for vulnerabilities at the unit down for scheduled maintenance during the outage and said the length of the stall makes sense when considering what Xcel has to order are "specialty items."

While Prairie Island is down, Coss said Xcel is replacing the energy Prairie Island normally supplies through more production from the company's other power sources in the region, as well as purchases on the energy market.

Coss said the company can't accurately estimate any potential costs until after Xcel knows the full scope of the nuclear outage. He said any costs from obtaining replacement power are based on the value of energy Xcel sells and buys from the market — run by the regional grid operator — and what would have happened if there was no outage.

The price of replacement power does fall to customers as fuel costs are normally recovered by the company on monthly bills. However, Coss said the company plans, if approved by state regulators to return a total of $5 million per month to customers between January and September because the company's fuel costs were lower than forecast in 2023.

Xcel doesn't expect the outage at Prairie Island to change that, he said.

This is the second unplanned outage at an Xcel nuclear plant in recent months. Xcel's Monticello nuclear plant shut down Sept. 27 after an issue with pressure control valves in the turbine during scheduled testing. Xcel told federal regulators that all safety systems functioned properly and there were no environmental or health impacts. Xcel made repairs to the plant, which is now running.

Together, the aging nuclear plants are a large part of Xcel's plans for a carbon-free energy grid by 2040. Nuclear makes up roughly 28% of the utility's power supply in the upper Midwest. Xcel applied earlier this year to the federal government to extend Monticello's license for an extra 20 years after it expires in 2030. The utility hopes to extend the units at Prairie Island, too, which are licensed to operate until 2033 and 2034.

Xcel must maintain the plants — which have run since the late 1960s and early 1970s — to run them well beyond the age they were initially licensed for.