Despite initial thoughts that the buildings in Dungeness would use a pile type foundation a closer inspection of planning proposals and case study example of the Reactor building for Dungeness B suggest slabs are favoured. The case study suggest the selection of the slab is as a result of sub-soil (typically sand) and very deep mud rock base which sits 30m below ground level. Slabs can be allowed to flex as the earth below moves. Moreover the raft is of carefully designed to balance the 3 primary loads of the 2 reactors and the fuel handling unit, ensure equilibrium of the slab.
The notion of the buildings sitting on slabs rather than a piled foundation connecting to the bed rock reinforces (pardon the pun) the notion that the earth below the ground plan is in flux.
Source: Design Applications of Raft Foundations – By J. A. Hemsley