Scotland's environment secretary has called for a full investigation after a radioactive leak was found at the former Dounreay power station.
The leak was discovered during a routine operation of the plant which is destroying the liquid metal used as the coolant in the Dounreay Fast Reactor (DFR).
Monitoring systems detected drips of caustic liquor from pipework in a shielded cell. Dounreay Site Restoration Limited (DSRL) said the plant was immediately shut down and the leak isolated and stopped.
The Scottish Environment Protection Agency (Sepa) said no material had been released into the environment and that the leak was "minor".
Environment Secretary Richard Lochhead said the Scottish Government was in close contact with Sepa over the incident.
He said: "I have also been briefed by senior management at Dounreay and have been assured that this is a very minor leak that was spotted quickly and contained within the plant. As no uncontrolled release of radioactive effluent has occurred outside the plant there is no direct role for Sepa.
"The Scottish Government expects this matter to be investigated fully by the operator - Dounreay Site Restoration Limited and regulator - the Office for Nuclear Regulation.
"It is important that all those involved make information available on an open, transparent and regular basis, principles that are especially important where the nuclear industry is concerned and I conveyed this point to Dounreay's management."
Dounreay's nuclear reactor was shut down in 1994 and work to decommission the site in Caithness has been under way since then. It was the only plant in Britain to use liquid metal instead of gas or water in the cooling circuits.
DSRL said it will work with the Office for Nuclear Regulation to conduct an investigation into the reasons for the leak. It said there was no release of radioactivity to the environment and no harm to the workers.