The BBC's Colin Blane reports (0'37')

The Energy Minister, John Battle, said in a House of Commons written answer that it would be safest to place the material in sealed storage above ground.

The shaft was sealed more than 20 years ago but is still leaking radioactivity.

It was confirmed that the shaft contains about 1,000 cubic metres of intermediate-level waste, and some 4kg of plutonium and 100kg of uranium.

Professor Ian Fell of Newcastle University tells BBC News 24 there could still be some surprises ahead (19')

The work is expected to cost between �215m and �355m and will take up to 25 years to complete but anti-nuclear campaigners say it is imperative the contaminated waste is disposed of quickly.

Lorraine Mann, from Scotland Against Nuclear Dumping, said there was a real danger that the ground around the shaft will give way soon.

Dr Patrick Green of Friends of the Earth talks about the difficulties involved in the clean-up (13')

Campaigners fear a repeat of an explosion in the shaft in 1977 which official reports said had been caused by "a chemical reaction" between the cocktail of dumped materials.

Although experts said the blast had not caused "significant damage", pictures released to the BBC in October 1996 suggested the explosion was extremely powerful.

The blast blew a 12.5 tonne concrete plug four metres to one side. Shattered concrete was thrown some 60 metres beyond the perimeter fence and scaffolding poles were propelled up to 75 metres onto the foreshore.

Documents obtained by the BBC for a documentary on Dounreay last year showed that after the explosion, highly radioactive contamination was found around the waste shaft, some of it well outside the boundary fence of the nuclear plant.

During routine monitoring of the site in the weeks following the blast, contamination of the roads was around 100 times higher than normal, the programme reported.