Both reactors at Exelon Corp.'s nuclear power plant in Braidwood have shut down, and the company is looking for the source of the problem.
Exelon spokesman Marshall Murphy and Nuclear Regulatory Commission spokesman Scott Burnell both say the situation isn't a safety concern. The Braidwood Generating Station is about 50 miles southwest of Chicago.
Murphy says the power-generating units shut down early Monday.
Steam is being vented from the plant to reduce pressure in its steam generators.
The NRC spokesman says that noise is loud and can be heard by people in the area.
"As this happened overnight, we understand our neighbors may have heard the venting steam and we want to make sure they know there is no cause for concern. We appreciate their patience," Braidwood Station Site Vice President Amir Shahkarami said in a statement, according to the Chicago Tribune.
The company isn't sure when the 2,300-megawatt plant will start up again.
Burnell says NRC inspectors are at the plant.