Floc Storage Tanks

‘Floc’ is a sludge like material which is classed as intermediate level waste. It is currently being retrieved from storage tanks at Sellafield and being processed and encapsulated in cement before being stored in modern fit-for-purpose stores pending long term disposal.

Floc Storage Tanks
Floc Storage Tanks


The Floc Storage Tanks at Sellafield are a series of ten concrete tanks built in the 1950s. Liquid effluents produced as a result of reprocessing operations were historically held in these large concrete tanks.

Although the overlying layer of liquid was discharged to the sea as liquid waste, the remaining floc stayed in the tanks. More than 99% of the radioactivity was contained in this floc – which remained in the tanks. The tanks operated until the mid-1990s when the Low Active Effluent Treatment plants came on stream.

The tanks are now over fifty years old and are unsuitable for indefinite storage of the waste.

Arrangements have been made to treat this intermediate level radioactive waste and encapsulate it in cement. In order to do this the sludges from the tanks must first be resuspended with water and then transferred into a buffer store from which they will be fed into the Low Active Effluent Treatment plants for processing and encapsulation.

Although emptying a tank takes a matter of weeks, processing the material from each tank will take approximately two years.

Once treated in the Enhanced Actinide Removal Plant at Sellafield, the material will be further processed through an ultra filtration system, before being sent to the Waste Packaging and Encapsulation Plant as intermediate level waste for storage.