Six contracts involving almost 30 companies and potentially worth up to £400m have been announced as part of the decommissioning of Dounreay.
The site of Britain's former centre of nuclear fast reactor research and development, near Thurso, is being demolished and cleaned up.
The new contracts include dealing with the 1950s-built shaft, which plunges 65.4m (214.5ft) below ground.
Radioactive waste was disposed there from 1959 until the late 1970s.
An explosion in the shaft ended the practice in 1977.
Colourful myths surround the site, including claims that a former worker dropped his mother-in-law's ashes inside to comply with her wish to be scattered somewhere unusual.
An unwanted car was also said to have been disposed of at the structure, which is 4.6m (15ft) wide in places.
'Real and visible signs'
The newly announced contracts, which are initially for up to four years and could be extended for an additional three years, also cover the demolition of laboratories, waste pits and the silo.
The silo is described as being like a swimming pool with a concrete roof. It was also used for the disposing of radioactive waste.
Companies working on the contracts will retrieve waste from the different sites, repackage the waste for consignment at modern waste facilities.
Stephen Adamson, head of commercial services at Dounreay, said: "This agreement will deliver real and visible signs of progress towards achieving our mission.
"It is about forming long-term partnerships so that the successful companies can work alongside our own Dounreay staff, ensuring a first-class team combining the best site skills and experience with the wider industry knowledge and innovation that the supply chain can offer."
The projects are being delivered by DSRL on behalf of the Nuclear Decommissioning Authority.
The organisations, each involving a number of companies, appointed to the decommissioning services framework contracts are AECOM E&C UK and Dounreay Decommissioning Framework Alliance.
Also the Dounreay Wood Alliance, Jacobs UK, Nuclear Decommissioning Ltd and Nuvia.