An encoding error in an alert and notification system set off a pair of inadvertent siren blasts at the Cooper Nuclear Station on June 4, Nebraska Public Power District officials said Wednesday.
NPPD and a third-party vendor reviewed the incident and found the alarm parameters had been adjusted prior to a new piece of equipment being installed, causing the alarm to trip during a routine test at the plant situated on the Missouri River near Brownville.
At the time, NPPD said there was no problem at the plant nor was there a threat to area residents. The plant did not receive any calls during the event.
The tone that issued from the plant during the false alarm was for fires, different than the tone Cooper uses during tests and would in the event of an actual emergency.
A spokesman said the alarm and notification system is now working as intended.