I can't find the name at the moment but its a structure that has been unchanging for 1000s of years and has been evaluated as perfect for nuclear waste since th

I can't find the name at the moment but its a structure that has been unchanging for 1000s of years and has been evaluated as perfect for nuclear waste since the very early days of nuclear in the US. I think it was evaluated at about 1/5 the cost of bringing Yucca Maintain to the same standard. 'Combating climate change: The role of nuclear power' from University of University of Michigan had a number of lectures where some of this is mentioned if I remember correctly. I'm working so I don't have time at the moment.