Backup diesel generators are powering one of the two nuclear reactors at the Byron Station facility in northern Illinois. Unit Two came offline yesterday after it inexplicably lost power. The facility's operator, Exelon, declared the incident an "unusual event" - the lowest of four emergency status declarations set by the Nuclear Regulatory Commission.
Fire crews were called to the site, about 25 miles outside of Rockford, as smoke was seen from the top of the facility building, according to WREX-TV. But the NRC told the Chicago Tribune the smoke was from a transformer and fire crews didn't find a fire.
Exelon says workers vented steam to help the reactor cool off, which is part of their emergency response process. AP reports the steam came from plant turbines, not the reactor itself, but Exelon notes tritium was released in the steam, which is radioactive; both the NRC and Exelon say radiation levels are safe and there's no harm to the public. There's a brief Q-and-A about the steam release at the Christian Science Monitor.
Now investigators are examining whether equipment failed in the plant's electrical switchyard, triggering the shutdown, according to Exelon, which explains the switchyard transmits power both ways between the electrical grid and the nuclear plant.