Exelon Nuclear says steam is being vented at its Byron Generating Station to reduce pressure. Plant operators say the unit is safe.
They declared an unusual event at 10:18 a.m. Monday, when Unit 2 shut down after losing power from an off-site source. They say the facility's generators are providing power to equipment.
Officials say Byron Station is designed to vent steam in the event of a power loss. They say the steam contains low levels of tritium, a radioactive isotope, but not at unsafe levels.
Officials say engineers are investigating why the unit lost offsite power. Unit 1 continues to operate normally.
Byron Generating Station is about 95 miles (152 kilometers) northwest of Chicago.
