High humidity inside the containment of unit 1 is believed to have set off a fire alarm at Pennsylvania's Beaver Valley nuclear plant over the weekend, causing operators to declare an unusual event until workers could confirm that there was not actually smoke in the building.
The smoke alarm activated at 9:20 p.m., Saturday. According to a report filed with the Nuclear Regulatory Commission, instrumentation showed an elevated dew point inside containment while temperature and pressure were unchanged. The plant did not call the fire department but notified the Nuclear Regulatory Commission and local emergency management agencies because the status of the alarm could not be confirmed within 15 minutes. The plant cancelled the unusual event declaration at 2:05 a.m. after a containment entry confirmed there had not been a fire. The unit did not power down during the event, and both of the reactors remained at full power on Monday.
An NRC spokesman later told the Ellwood City Ledger that FirstEnergy believes the false alarm was caused by moisture from the lifting of a relief valve while an accumulator tank was being filled.