Nuclear Power
Tackling one of the most challenging nuclear clean-up projects
Bo Wier looks at the challenges involved to complete one of the world’s deepest nuclear clean-ups, and at some of the innovative approaches being deployed to accelerate the programme whilst minimising cost.
Bo Wier observa los retos implicados para completar una de las limpiezas nucleares más exhaustivas en el mundo y algunos de los enfoques más innovativos desplegados para acelerar el programa al tiempo que se minimizan los costes.
Bo Wier betrachtet die Herausforderungen, die eine der umfangreichsten Sanierungen von Kernenergieanlagen der Welt mit sich bringt, sowie einige der innovativen Ansätze, die eingesetzt werden, um das Programm zu beschleunigen und dabei die Kosten zu minimieren.
A
vertical shaft, excavated in the 1950s for the removal of rock spoil during construction of an undersea tunnel for the Dounreay site’s effluent discharge pipes, and
authorised in 1958 as the UK’s first Intermediate Level Waste (ILW) disposal facility, now represents one of the biggest challenges in the UK’s nuclear decommissioning portfolio. Tis major project, to decommission the shaft (and wet silo also used for ILW storage) including recovery and packaging of over 1500 tonnes of radioactive waste, is now the focus of ‘renewed emphasis’ for the new Babcock Dounreay Partnership management team at Dounreay. Te team, which is responsible for the decommissioning, demolition and clean-up of the Dounreay nuclear site (the first major closure project in the UK), having taken over in April this year, is taking the decommissioning programme at Dounreay to its interim end state, and has committed to accelerate the programme (by up to 16 years over previous estimates of two years ago) and reduce project costs by well in excess of a billion pounds. Te shaft and silo project is one of the key projects being accelerated within this programme.
Fig. 1 Up to 400 boreholes were drilled around the shaft in a boot shape.
Current status Waste disposal in the shaft (measuring up to 4.6m across and 65.4m deep) ceased following a chemical explosion in 1977, thought to have resulted from an accumulation of hydrogen. By this time most of the waste was being consigned to a nearby wet silo (a concrete lined and roofed box built just beneath the surface with an approximate storage capacity of 720m3
), which was used until 1998 as a storage facility for the site’s ILW.
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ILW consigned to the shaft and silo now comprises items of solid waste plus sludge from the pond clean-up and decomposition of some of the solid waste, and covers a broad chemical and radiological spectrum. A decision was taken in the 1990s, as a result of advances in technology, to empty the shaft and silo, and a major programme is now underway to decommission them.
Te first step (completed in 2008) was to isolate the shaft to reduce the ingress of ground water, minimising potential contamination. Up
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