5 July 2012 Last updated at 23:47 ET

Dounreay nuclear waste to be stored in 'big holes'

Tonnes of rock are being removed from a site at Dounreay

What have been described as the two biggest man-made holes in Caithness are being dug to store tonnes of low-level radioactive waste from Dounreay.

The larger of the two vaults involves the excavation of about 200,000 cubic metres of rock.

The stores, being constructed at a cost of £100m, are separated by a spine of rock nine metres wide at the top.

The waste will include paper, rags, tools, glass, concrete and clothing contaminated by radioactivity.

Once inside the store it will be monitored for 300 years.

After that period of time the radioactivity will have decayed by 95%.

Dounreay, an experimental nuclear power complex built in the 1950s, is being demolished and the site cleaned up.

The first phase of the work close to the nuclear power plant is being done by Graham Construction.