An electrical insulator in a switchyard may be to blame for a power outage and reactor trip at the Byron nuclear plant Monday.
Unit 2 at the Illinois plant shut down from full power just after 11 a.m. when external power to the reactor was cut. Smoke was seen coming from a faulted station auxiliary transformer but no fire was reported, according to an event report from the Nuclear Regulatory Commission. Backup diesel power started, and natural circulation cooldown ensued, assisted by auxiliary feedwater pumps and atmospheric steam releases.
According to a statement from the company, the reactor is in stable condition, with neighboring unit 1 continuing to operate normally. Nonetheless, the power failure prompted plant owner Exelon to declared an unusual event, the lowest of the NRC’s emergency declarations. The steam vented into the atmosphere, while not from the primary coolant loop that passes through the core, contained tritium at levels Exelon said do not pose a risk to public health.
Company officials were quoted as saying they had traced the source of the external power failure to a specific insulator at a switchyard. Byron is located near Rockford, Ill., north of Chicago and uses two Westinghouse pressurized water reactors built in 1980s that produce more than 1,100 megawatts each.