A fire alarm overnight at the Prairie Island nuclear plant prompted operators to shut down one of the facility's units.
Xcel Energy said in a press release the alarm went off in the unit two containment building around 4 a.m. Thursday. There is no indication of a fire, but personnel at the southeastern Minnesota plant halted service at the unit as a precaution.
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"The plant is being safely shut down. There is no release of radioactive materials as a result of this event," Xcel said.
In an update issued around 8:20 a.m., Xcel said unit two was fully shut down and operators are investigating. The company said the unit had to be shut down before crews could enter to confirm.
Unit one is operating at full power.
There is a "potential reduction" in safety at the plant, but there is no threat to public safety.
The notice is called a "notification of unusual event," and Xcel says it's the lowest of four emergency classifications established by the U.S. Nuclear Regulatory Commission.