See more of the story

Xcel Energy is temporarily shutting down its Monticello nuclear power plant after discovering that a new quantity of radioactive water from a leak had reached the groundwater.

The company in a news release Thursday night reported it to be a "small amount" of new leakage, expected to be in the "hundreds of gallons" range. The original leak reported last week was about 400,000 gallons.

The plant will begin shutting down Friday in order to more quickly repair the water leak, which contains tritium, a mildly radioactive form of hydrogen. The company does not expect it to affect customers' electric service due to powering down early, according to Xcel's news release. The timeline for resuming operation at the plant is not yet determined.

Kevin Coss, an Xcel spokesman, said the company voluntarily closed the plant. "We were not told to do so by regulators at the state or federal level," he said.

The spill was first reported to state and federal regulators on Nov. 22. The source was found Dec. 19 and patched soon after, according to the Minnesota Pollution Control Agency (MPCA).

Xcel implemented a short-term solution to capture leaking water and reroute it into the plant for reuse. It was designed to prevent new tritium from entering the groundwater until a replacement pipe could be installed during a regularly scheduled refueling outage in mid-April.

But on Wednesday, monitoring equipment indicated a small amount of new contaminated water had reached the groundwater, and that, over the past two days, the solution was no longer capturing 100% of the leaking fluid, the release stated.

The company said the monitoring wells show the leaked water remains contained onsite and has not been detected beyond the facility or in local drinking water.

The company said the new leakage does not pose any risk to health or the environment. The Minnesota Pollution Control Agency issued a statement late Thursday saying state agencies "have no evidence at this point to indicate a current or imminent risk to the public and will continue to monitor groundwater samples."

The company has recovered about 32% of the total leaked tritium, and said it would continue recovery over the next year.

Tritium occurs occasionally in nature but more commonly from human activities such as nuclear power generation, according to the Nuclear Regulatory Commission's website. Tritium is at times intentionally released from power plants under NRC rules.

Members of the public with questions about the leak or the plant powering down can attend one of two open houses at the Monticello Community Center at 505 Walnut St. on Friday from 10 a.m. to 1 p.m. and Monday from 5 to 8 p.m.