An investigation has been launched into a radioactive leak which was contained in a sealed cell at the Dounreay nuclear plant in Caithness.
Decommissioning at Dounreay is scheduled to take 30 years
A routine check of a small storage vessel found that 4.5 litres of liquid waste had spilled inside the cell, which is designed to contain a leak.
Management said there was no exposure to the environment or staff.
However, bosses said it underlined the importance of accelerating the £2.9bn clear up of the site.
The decommissioning of the United Kingdom Atomic Energy Authority-run site is expected to take 30 years.