Steam, containing low levels of radioactive tritium, was being vented out into the air to help reduce the pressure within the reactor.
Of interest and awaiting answers:
- NRC spokeswoman said - Smoke was seen from an onsite station transformer but no evidence of a fire was found when the plant’s fire brigade responded.
- Exelon spokesman Paul Dempsey said there is “no reason we can pinpoint right now” for the power loss.
In April 2011 the NRC conducted special inspections of backup water pumps at the Byron and Braidwood generating stations after inspections raised concerns about whether the pumps would be able to cool the reactors if the normal system wasn’t working. Exelon Corporation initially said the pumps would work but later concluded they wouldn’t.