> Main point is that "200 year supply" is not all that impressive. Demand growth can dominate that rapidly. Sure. But if we keep exponentially increasing energ

> Main point is that "200 year supply" is not all that impressive. Demand growth can dominate that rapidly. Sure. But if we keep exponentially increasing energy usage, at some point we'll boil the oceans. And long before that we would have wrecked the earths ecosystem. So I'm assuming that the exponential increase in energy usage will stop at some point. The 120000 year figure I arrived at in my previous post included a factor of 100 increase over current usage. Even if we add another factor of 100 increase (a total of a factor of 10000 increase over current usage!), we'd still have fuel for 1200 years, surely more than enough to get fusion working. > When coal was first becoming a mainstream fuel in the US, reserves were estimated as sufficient for 1 million years. Current estimates are for about 100-250 years (latter from BP's Annual Statistical Review for 2019). Demand increased somewhat, and consequences emerged. Now 150 years into the million we're phasing out coal as quickly as possible. Sure, but ~200 years ago our understanding of geology was quite rudimentary compared to today. And yes, starting from more or less zero we did exponentially increase usage for a couple of centuries. I don't think it's realistic to continue at the same exponential rate for several centuries more, regardless of where the energy comes from (maybe in the far future if humanity starts to look at interstellar travel we would have a usage for such truly stupendous amounts of energy). Furthermore, we're not phasing out coal because we're running out of it, but due to climate/pollution/economics. From a climate perspective, it unfortunately seems we have more than enough coal left to wreck the climate if we would burn all of it. > Breeders, thorium (a breeder fuel), and uranium seawater extraction are possible but have proved challenging or limited to date. The main reason is economics. Uranium is currently just so cheap that it doesn't make economic sense to deploy breeder reactors and reprocessing yet. And without volume deployment, they remain expensive and underdeveloped compared to the current once-through cycle. However, there is no question whether the technology works. It does. Earlier in the nuclear age (say 1950-1970 or so), uranium was believed to be scarce, isotope enrichment by gas diffusion was very expensive and energy consuming, and we believed the world would soon be powered by atomic energy. So a lot of effort was made to develop breeder reactor and reprocessing technology. However, all of this turned out to be incorrect. Uranium turned out to be quite plentiful, centrifuges made enrichment a lot cheaper, and nuclear power expansion ground to a standstill. But the earlier R&D showed that the technology is viable, so if uranium prices would start to drastically increase, the option to deploy breeders at scale still exists.