Xcel Energy reported another, smaller, spill of radioactive water last weekend at its Monticello, Minn. nuclear plant, about 40 miles northwest of the Twin Cities.
Crews have been pumping and storing water from the ground at the plant since a faulty pipe caused a leak of about 400,000 gallons of water contaminated with tritium in November. Xcel temporarily shut down the plant and repaired the leak in March.
On Monday, the company notified the Minnesota state duty officer that 300 to 600 gallons of pumped groundwater had overflowed a holding tank and returned to the ground. Xcel spokesperson Kevin Coss said the water — about an hour’s worth of pumping — will be recollected.
Overall, the Minneapolis-based utility said it’s made “substantial” progress in recovering the contaminated groundwater. It has now pumped over 1.1 million gallons of water and has recovered more than half of the tritium released, Coss said.
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Tritium is a mildly radioactive form of hydrogen that occurs naturally in the atmosphere and during nuclear power production. It can be hazardous, but only when consumed in large quantities.
Coss also said the concentration of tritium in the groundwater has declined. The highest measurement, directly under the plant near the leak, was about 5 million picocuries per liter. That’s dropped to below 1.5 million picocuries per liter, he said.
The U.S. Environmental Protection Agency considers 20,000 picocuries per liter to be safe for drinking water. State officials have said the contamination has not left the plant site, and does not pose a threat to any public or private drinking water wells.
The U.S. Nuclear Regulatory Commission will hold its annual public meeting in Monticello to discuss the plant's safety performance.
The NRC determined the plant operated safely in 2022, and said all inspection findings and performance indicators were of very low safety significance. More significant findings can trigger increased federal oversight and increased inspections.
Xcel is seeking federal approval to continue operating the Monticello plant beyond its current license, which expires in 2030. It’s also requesting to store additional radioactive nuclear waste at the plant.