The nuclear station, about 60 km northwest of Minneapolis, was fully powered down at around 07:00 on Saturday to fix the leaky pipe discovered last week, Xcel Energy spokesman Theo Keith said.
“Crews have already repaired the leak, which did not pose any risks to public health, safety, or the environment,” Keith said. “The pipe was confirmed as the only source of the leak.”
The station will return to service in the next week, but will temporarily close in mid-April for an annual maintenance project.
In November, a leak was discovered of 1.5 million litres of water containing tritium. There was a months-long delay in announcing the initial leak that raised questions about public safety and transparency, but Xcel said there was no public health threat and no water leaked into the nearby Mississippi River.
Tritium 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 far and cannot penetrate human skin, according to the US Nuclear Regulatory Commission.
Last week, the new leak was found coming from a temporary repair to the original leak, the company said. Chris Clark, president of Xcel Energy for Minnesota, North Dakota and South Dakota, said the new leak also posed no risk to the public or the environment.
Monticello’s 628-MW boiling water reactor unit, supplied by General Electric, began commercial operation in 1971.
