I'm excited about nuclear, but it seems like we will eventually run out of uranium fuel unless we switch to breeder reactors. Am I off on this? This is assuming that nuclear usage grows to become a larger portion of our total energy use. I see nuclear as potentially solving a lot of our problems, but it seems to have some difficulties as well.
I'm more skeptical that we can support such a large population. Right now we make heavy use of fertilizer, which is produced from natural gas and by mining phosphates. Probably we could avoid using natural gas, but this would require using more energy, so I'm not sure how sustainable this is long-term.
You're absolutely right, U235 reserves are only enough to last a couple hundred years at current consumption and exploration. We could probably sustain a long time with burner LWRs but it will require massive investment.
Breeders however (whether you go with Th-U or U-Pu fuel) both should be able to take us to at least another 10,000 present-equivalent years on a wholly nuclear powered economy.
You're also right to suspect fertilizer, I feel the same way. I've seen some of the phosphate mines around the world and it's kind of horrifying, so I'm hoping asteroid mining can fix our metal extraction problem.
I heard C-Type asteroids have plenty of phosphorus, but I'm definitely not an expert on asteroid mining. If they do, though, it will likely be enough to sustain us for quadrillions of human-years (humans * years) because the asteroid belt is just so damn massive compared to the Earth's crust.
I'm more skeptical that we can support such a large population. Right now we make heavy use of fertilizer, which is produced from natural gas and by mining phosphates. Probably we could avoid using natural gas, but this would require using more energy, so I'm not sure how sustainable this is long-term.