Monticello nuclear plant radioactive leak: A timeline

MONTICELLO, Minn. -- Late last year, a leak of hundreds of thousands of gallons of contaminated water was discovered at Xcel Energy's Monticello Nuclear Generating Plant.

There was a monthslong delay in announcing the initial leak to the public, raising questions about public safety and transparency.

Then, a second leak meant the plant had to power down. And now, Xcel Energy says the leak is fixed and the plant will reopen soon.

A lot has happened between the leak and the plant's planned reopening, including a fish kill in the Mississippi River.

Here's a timeline of events:

Nov. 22, 2022: Leak confirmed, authorities notified

Xcel Energy officials say they reported the initial leak to state officials the day the leak was confirmed.

According to state officials, 400,000 gallons of water contaminated with tritium leaked from a water pipe running between two buildings at the facility.

The state and Nuclear Regulatory Commission were notified.

Tritium is a radioactive isotope of hydrogen that occurs naturally in the environment and is a common by-product of nuclear plant operations. It emits a weak form of beta radiation that does not travel very far and cannot penetrate human skin, according to the Nuclear Regulatory Commission.

March 16, 2023: Public first informed of leak

Four months later, the public was first informed of the leak in separate press releases from Xcel Energy and the Minnesota Pollution Control Agency.

Xcel Energy officials say the leak was "fully contained on-site" and that the company has been coordinating with federal, state and local officials to clean up the leak. The company said the leak poses no threat to health and safety of the community or environment.

MORE: Xcel Energy cleaning up radioactive leak at Monticello nuclear generating plant

"To date, Xcel Energy has recovered about 25% of the tritium released and will continue recovery over the course of the next year," Xcel Energy said in the release.

The MPCA said the leak had been stopped, and that there's no evidence to indicate a risk to nearby drinking water wells.

Xcel said the facility contained the leak by diverting the water to an in-plant water treatment system, but will install a permanent solution this spring.

March 17, 2023: Regulators defend delay in notifying public

The delay in notifying the public about the November leak raised questions about public safety and transparency, but industry experts said there was never a public health threat.

"This is something that we struggle with because there is such concern with anything that is nuclear," said Victoria Mitlyng, a spokesperson with the Nuclear Regulatory Commission. "The concern is very, very understandable. That is why I want to make extra clear the fact that the public in Minnesota, the people, the community near the plant, was not and is not in danger."

RELATED: Regulators: Nuclear plant leak didn't require public notice

State officials said that while they knew of the leak in November, they waited to get more information before making a public announcement.

March 22, 2023: Monticello residents voice concerns, expert talks tritium

Monticello residents had a chance to make their voices heard as the nuclear plant near their homes tries to have its license renewed.

Xcel Energy has applied for a 20-year renewal to operate the plant that would green light it until 2050.

READ MORE: Federal officials work to reassure residents near site of Monticello nuclear plant leak

The public hearing on the matter was scheduled well before the leak was announced.

Senior health physicist with the Nuclear Regulatory Commission Valerie Myers, who is part of the cleanup, said the amount of radiation involved in the leak is negligible.

Myers says there's three times as much tritium in a hallway exit sign than in the water under the plant.

"If we look at the dose impact of something like this, it would be a fraction of a milligram. I'm talking 0.00-something milligrams. The average person will get 300 milligram in a year just from the sun, the ground, everything," Myers said.

March 24, 2023: Second leak discovered

Xcel Energy began powering down the nuclear plant after finding a new radioactive leak, coming from the temporary repair to the original leak. They said the second leak was smaller, but forced the company to take new measures.

Xcel says powering down the plant will make it easier for crews to "permanently resolve" the leak.

Xcel again said there is no threat to drinking water or the environment.

March 25, 2023: Full power down 

Xcel Energy says the plant was fully powered down around 7 a.m. on this date, allowing crews to repair the leak. 

March 27, 2023: Shutdown causes fish kill

On this date, the MPCA announced that the temporary shutdown of the facility led to a fish kill on the Mississippi River.

The Xcel Energy Monticello Nuclear Generating Plant sits close to the river. When the utility company started powering it down, it cooled the surrounding water.

RELATED: Temporary shutdown of Monticello nuclear power plant causes fish kill

State officials say the temperature change killed about 230 fish, including bass, channel catfish, carp and sucker fish.

"As part of its normal operations, warm water from the Monticello plant enters the river, which the fish get used to. The fish kill is unfortunate but not unexpected given the significant temperature change that can occur when warm water from the plant stops flowing to the river during a shut down in operations," the MPCA said.

The MPCA says the fish were not killed by tritium.

Also on this date: another open house was held at the Monticello Community Center.

March 28, 2023: Xcel Energy says leak fixed, plant to open soon

An Xcel Energy spokesperson reportedly said the leak has been repaired and the plant will return to service soon.

READ MORE: Xcel Energy says Monticello leak fixed, plant to reopen soon

According to Xcel Energy spokesman Theo Keith, the plant will return to service "in the next week," but will temporarily close in mid-April for an annual maintenance project.

Xcel says the water that leaked contained 8 curies of tritium and crews have recovered 2.56 curies, or 32%, of the tritium as of this date.