Xcel cleans up radioactive water at Minnesota plant

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A ruptured pipe at Xcel Energy’s nuclear power plant in Monticello leaked about 400,000 gallons of water containing radioactive tritium, and the utility is working to clean up the contaminated plume, state regulators said Thursday.

Both Xcel and the Minnesota Pollution Control Agency said there was no risk to drinking water from the spill, which was traced to a pipe connecting two buildings across a space of just half an inch. The leak was first reported to state and federal regulators on Nov. 22, 2022. The source was found on Dec. 19 and patched shortly after, according to the MPCA.

Xcel and the state are actively managing the site to ensure that an underground tritium plume doesn’t begin to float beyond the site, including into the nearby Mississippi River, said Kirk Koudelka, an assistant commissioner with MPCA. Water is pumped from wells on site to both remove the contamination and control underground flow. Xcel pays for sampling, pumping and temporary treatment, Koudelka said.

“Our goal is to remove the source, the contamination that’s down there, as much as possible,” he said.

Once the leak was discovered, Xcel began diverting the water to an in-plant water treatment system – a step that continues today.

“We were able to contain it so that no more water was leaking,” said Christopher Clark, president of Xcel for Minnesota. Clark estimated the restoration work would take about a year; the company does not yet have a cost estimate.

Koudelka said the MPCA announced the vulnerability nearly three months after it was patched because “we now have enough information to be able to share it with a larger group.”

When first discovered, high levels of tritium in groundwater were reported to the Nuclear Regulatory Commission, which released the “non-emergency” report the next day in its public list of nuclear events. The list said the source of the tritium was being investigated.

Tritium is a mildly radioactive form of hydrogen that occasionally occurs in nature but is more common in human activities such as nuclear power generation, according to the NRC’s website. Tritium is sometimes deliberately released from power plants under NRC rules.

Like regular hydrogen, the odorless, colorless gas can react with oxygen to create water, known as tritiated water. According to the Environmental Protection Agency, it is used in some scientific works, including as a tracer in biochemical research. The EPA has a limit on the amount of tritium that can be present in drinking water — 20,000 picocuries per liter — to protect people from radiation.

“We are well above the EPA standard of 20,000 picocuries per liter,” Clark said. In water directly under the plant, the number of picocuries per liter ran into the millions.

However, those high levels are quickly reduced as tritium dilutes in groundwater. “This does not pose a public health or drinking water problem,” Clark said. The company is monitoring the plume in two dozen wells.

Tritiated water can’t harm someone just through proximity, said Daniel Huff, assistant health protection commissioner in the Minnesota Department of Health. The only way a person can be exposed to radiation is by drinking it or inhaling it, he said.

People are regularly exposed to small amounts of radiation from medical procedures and even activities such as sunbathing or flying in an airplane, Huff said. But the health effects are cumulative, making it important to limit contact where possible.

“The public’s exposure to a nuclear power plant should be zero,” Huff said.

In a statement, the city of Monticello indicated that its drinking water was not affected and that the leak occurred outside of the area where it draws groundwater for municipal wells.

Xcel said it would examine the pipe that caused the leak to understand how it failed.

Tritium levels from the Monticello leak are well below safety thresholds set by the NRC, and the plant is not breaking the rules, said Viktoria Mitlyng, a spokeswoman for the NRC. Tritium leaks, she added, “are not uncommon for nuclear power plants.”

Leaks are a problem for aging plants because tritium mixes so easily in water, said Edwin Lyman, director of nuclear safety at the Union of Concerned Scientists. So anywhere water could escape from a nuclear power plant, so could tritium, he said.

There have been accidental tritium releases at several power plants over the years.

Xcel checked groundwater near the Monticello plant for tritium long before the recent spill, and in 2009 it found tritium levels of 21,300 picocuries per liter in a newly dug well at Monticello, according to a report from MPR.

The company typically samples water from 18 wells, ranging from every month to every year, according to a January Xcel filing with the NRC. A well in Monticello has had elevated tritium levels since 2009.

There was already a more dilute plume of tritium before the spill, Xcel said in the NRC filing. “The plume appears to be stationary under the turbine building.” The tritium “migrated” through the concrete floor of the turbine building, the filing said.

Despite that spill, the highest level of tritium found by Xcel since 2016 was less than half the federal drinking water limit, the filing said.

In 2012, Xcel released 27 liters of tritium-contaminated water from the Prairie Island Nuclear Power Plant near Red Wing after a leak in the condenser system. That leak reportedly contained 15,000 picocuries per liter of tritium.

In 2019, Xcel announced plans to extend the life of the Monticello plant by at least ten years beyond 2030, when the current NRC license expires. Two months ago, the company filed a formal application with the NRC to extend Monticello’s licenses for another 20 years.

The tritium leak “has some implications for their license renewal,” Lyman said. Managing an aging facility is “clearly one of the most important issues”.

The Monticello factory opened in 1971, although Xcel has spent tens of millions of dollars over the years to keep the factory up to date.

The company says extending the lifespans of both Monticello and Prairie Island by 20 years is critical to meeting a new state law mandating completely carbon-free electricity by 2040. Federal licenses for Prairie Island’s two reactors are expiring. ​in 2033 and 2034.

2023 Star Stand.
Distributed by Tribune Content Agency, LLC.

Quote: Xcel cleans up radioactive water at Minnesota plant (2023, March 17) Retrieved March 19, 2023 from https://phys.org/news/2023-03-xcel-radioactive-minnesota.html

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