Nuclear Regulatory Commission Region III spokeswoman Viktoria Mitlyng said two diesel generators are running at the facility, which lost power to its 1,136-megawatt unit, one of two at the site. The second unit, a 1,164-megawatt unit, was operating at full power, the Chicago Tribune reported.
Mitlyng said workers at the Exelon Corp. plant about two hours northwest of Chicago reported seeing smoke from a transformer following the outage. No fire was found.
Steam was released from the plant and was being monitored for tritium levels, fire officials said.