Ameren Missouri officials declared an "Alert" at the Callaway Nuclear Plant near Fulton at 10:56 a.m. on Sunday and exited the emergency status at 5:37 p.m.
An Alert means events have occurred, or may occur, which could significantly reduce the overall level of safety at the plant. Company officials claim the Alert at the Mid-Missouri facility did not impact plant personnel safety or pose a hazard to the public.
Ameren issued this explanation: "Sunday's Alert at the Callaway plant was due to a potentially hazardous atmosphere from a refrigerant leak in one of two rooms containing redundant air conditioning equipment that cools the control room. The other air conditioner remained in service throughout the event. Repair plans are underway for the affected equipment. There are no threats to plant personnel or the public. The plant remains on line operating safely."
Company officials said there was no release of radioactivity to the environment "above normal operating limits." The utility notified the appropriate federal, state and local agencies about the incident.
An Alert is the second least serious of four emergency classifications established by the U.S. Nuclear Regulatory Commission (NRC) for nuclear power plants. It is more significant than an "Unusual Event," but less serious than a "Site Area Emergency" or "General Emergency."