An electrical fault is believed to be the cause of an overnight alert within the Prototype Fast Reactor complex at Dounreay.
At 0245hrs today, a smoke detector went into alarm inside the complex. As the site fire brigade responded, a further five detectors inside the complex went into alarm.
An extensive search of the facility was carried out by fire personnel, supported by colleagues from Highlands and Islands Fire Brigade.
No fire was detected and personnel were stood down at 0535hrs.
An investigation is now being carried out to determine the cause of the
alarms. Burn-out of an electrical component is suspected.
All smoke detectors have been reset and all safety systems in the facility continue to function as normal.
Additional radiological monitoring was carried out as a precaution. None was detected.
The Prototype Fast Reactor closed down in 1994. It was defuelled between 1994 and 1996, and is now midway through its decommissioning and demolition.