A radiation leak at Three Mile Island, the site of the worst nuclear accident in US history, has sent home about 150 workers, the Nuclear Regulatory Commission reported Sunday.

"They had an airborne radiological contamination alarm," NRC spokeswoman Diane Screnci told AFP. "They evaluated all the workers, a handful of workers -- I don't have a precise number -- had contamination. They since have been decontaminated," she said.

About 150 people work in the building where the leak occurred.

Screnci said what she called a "leak... happened at 4:00 pm Saturday (2100 GMT) and they resumed work in the contaminated building" near Middletown, Pennsylvania.

"There was no impact on public health safety and it does not appear to have an impact on the workers," she said adding that "this kind of incident occurs once in a while."

So far, "they don't know the origin of the contamination," Screnci said. "There were a lot of activities going on at the time and when the alarm sounded. The engineers are working to determine what the cause was."

"It's a minor incident," she said stressing it was "under control."

Three Mile Island suffered a major accident in 1979, with the core of a reactor partially melting down.

Since then no new nuclear power plants have been built in the United States.

Nuclear energy supplies 20 percent of power in the United States with 104 reactors, while 50 percent comes from coal burning plants.

The rest is from natural gas, oil and renewable sources such as hydroelectric power as well as solar and wind power.