U.S. nuclear regulators are investigating a leak at an Illinois uranium plant that happened on Sunday. The facility, operated by Honeywell International Inc., produces a radioactive fuel that, when airborne, can be chemically toxic.

An inspector from the Nuclear Regulatory Commission launched a probe into the accident on Tuesday, an NRC spokesman told Reuters. He said the investigation could take up to a week.

Honeywell has said there’s no evidence that any of the leaked compound, called uranium hexafluoride, has left the site in Metropolis, a town of about 7,000 people along the Ohio River. At the facility, the uranium compound is enriched to be used as fuel for nuclear power plants. It’s the only plant to do so in the U.S.

“The plant’s emergency procedures were followed exactly as prescribed, including the engagement of our comprehensive safety systems. Among these were water cannons, which we used to contain the leak,” Jim Pritchett, the Metropolis plant manager, said in a letter Tuesday to employees.

No injuries resulted from the Oct. 26 chemical leak, which was the result of an equipment failure, the company said. The accident comes as Honeywell is battling union-backed workers over contract negotiations. More than 100 members of United Steelworkers Local 7-669 have been locked out of the Metropolis facility since August.