An investigation has been launched following a fire at the Dounreay nuclear plant in Caithness.
Fire alarms alerted the site's firefighters to the blaze at the Prototype Fast Reactor (PFR) at about 0040 BST on Friday.
The fire involved sodium which had earlier been removed from pipe work and stored in a small tented enclosure.
Dounreay Site Restoration Limited (DSRL) said the fire was extinguished.
The company, which is leading the decommissioning of the site, said radioactivity had not been a concern during what it described as an "industrial event".
One person who was in the building when the fire broke out left the scene immediately.
DSRL said the tented area involved was "the size of a small bathroom".
The sodium was transferred to metal drums and layered with graphex, a fire suppressing material.
DSRL said: "No-one was injured. Fire damage was confined to the tented enclosure, the bags and a wooden barrier.
"Work in the localised area has been halted pending an investigation into the cause. The rest of PFR decommissioning is unaffected."