A Geological Disposal Facility is a posh name for an underground dump for High-Level nuclear waste.

The world has been looking for a way to dispose of used fuel rods from nuclear power stations and dismantled nuclear warheads. The current thinking is that the safest means of disposal is to bury it deep underground and leave it there for thousands of years while the material degrades naturally.

Some of these materials have a half-life of more that 10,000 years

The surface site alone takes up at least 1 square kilometre. up to 1000 metres below will be a network of tunnels occupying more than 13 Square Kilometres. You can find out more from RWM's webpage