When started in 2005, the site's decommissioning was estimated to cost £31.5bn of the Nuclear Decommissioning Authority's then £56bn budget, which has now risen to £83bn.
The job of managing the clean-up process alone, for which a consortium led by URS-owned Washington Group and also including AMEC is preferred bidder, could be the largest-ever publicly procured contract in European history.
Sellafield's decommissioning is such a vastly expensive and time-consuming task because it is the largest and most complex of the Nuclear Decommissioning Authority-owned sites.
First opened in 1947, the Sellafield group of sites in Cumbria includes the world's first commercial nuclear power station at Calder Hall and the fire-ravaged Windscale reactors. A separate site at Capenhurst, Cumbria, is also grouped under the Sellafield umbrella.