Introduction and History.

In the earliest days of reprocessing operations on the Sellafield site, the Sludge Storage Tanks formed a key part of the systems for cleaning up the site’s liquid effluents. The legacy of these operations was that until recently the 50 year old tanks held over 4500m (approx 1.1m US Gallons) of actinide rich sludge containing some 2000TBq (approx 55000 Ci) which required retrieval and treatment for long term safe storage. To enable this retrieval and treatment a significant programme of work, costing in excess of £120m, has been delivered to bring the plant as far as possible to a modern nuclear standard and provide the capability to recover and treat the sludge. To date, this programme of work has resulted in over 1500m of sludge being recovered, emptying the oldest tank within the complex. Over 1000m of this sludge containing some 760TBq alpha activity has been encapsulated in cement generating a long-term stable wasteform, thereby immobilising over one third of the plants nuclear inventory. This paper describes the project work undertaken and the operating experience gained in retrieving and treating the waste.