Grayson 
28
Dounreay's operators have been told to improve safety at the site after a piece of equipment toppled over and injured a worker.
The accident happened at the nuclear power complex, near Thurso in Caithness, in February.
Industry watchdog the Office for Nuclear Regulation (ONR) said the worker escaped with minor injuries, but added that it considered the incident as "significant" and "preventable".
ONR has issued Nuclear Restoration Services (NRS) with an improvement notice.
NRS said it took the protection of people and the environment "very seriously".
