Dounreay has clocked up more than three million man-hours without a lost-time accident.
The site reached the milestone at the end of May, 278 days since the last LTA.
The previous best was 2.7 million man-hours, or 232 days, recorded in 2006/07.
A lost-time accident is an injury sustained by a worker that keeps them off work for more than three days.
UKAEA, parent body of Dounreay Site Restoration, donates £2500 to the Dounreay Communities Fund for every month worked without a LTA.