Nuclear is very sustainable. With enrichment, the world's known uranium supplies (5.5 million tons) would last about 30,000 years at present usage rates, if used with fast breeder reactors. The NEA estimates that's a sixth of what's out there. Obviously this doesn't go as far if you scale it up 10-100x, but in addition, there's about 4.5 billion tons dissolved in seawater.
This is just the uranium, not even touching the thorium. And once we get to this point, there is uranium on the Moon and Mars. The waste-management problem is harder in the political sense than the engineering sense.
This is just the uranium, not even touching the thorium. And once we get to this point, there is uranium on the Moon and Mars. The waste-management problem is harder in the political sense than the engineering sense.