The last 1500 tonnes of hazardous liquid sodium has been drained from the prototype fast reactor (PFR) at Dounreay, marking an important milestone in the operation to make the site safe.

In a task which has taken eight years to complete, the material has been transferred from the base of the reactor' vessel and is now being destroyed in a purpose-built chemical treatment plant that extracts the radioactivity and converts the sodium to common salt that can be discharged to the sea.

PFR was the second fast reactor to be built at Dounreay. It was completed in 1974 and operated till 1994 but is now part of the £2.9m Dounreay decommissioning programme which is scheduled to be completed by 2032.

The liquid sodium metal was used as the coolant to transfer the heat from the reactor core. Its removal means the decommissioning team can now "steam-clean" the last traces of sodium from the pipework, making it safe to begin dismantling the entire system.