One of our FAQs.
Q. Surely if you bury nuclear waste deep enough, it should be safe, after all gravity pulls it downwards and not up?
A. Gravity would work to keep nuclear waste, or anything sufficiently heavy buried, and away from the surface, but at the proposed depth of the repository (200-1000 metres), pressure is much stronger than gravity and able to overcome it. Because of this, fluids and gases often want to migrate upwards towards the surface, just as oil often gushes out of a deep well without being pumped.
If you would like to find out more about the geological issues please follow this link. Professor Stuart Haszeldine’s MRWS response to the 2012 Consultation.