We've got 300k years of fissile material, at current usage rates, which is only a small fraction of our current energy usage. If we magically went to 100% nuclear fission for energy (which is not reasonable for personal transportation, at least), and continued to increase energy consumption per business as usual (developed economies not reducing, and developing economies rapidly catching up to developed usage per capita), then it would not last nearly as long, by 2 orders of magnitude. Also I think that estimate imagines efficient breeder reactors and "complete burning" of the material, and does not take into account our current incredibly wasteful techniques of using 5% of the available energy and burying the rest in an unrecoverable mountain sludge.
I know that a few thousand years still feels like a long time, but with nuclear fission, it is truly the most non-renewable resource, being formed only in stellar explosions. Let's put aside the science fiction of asteroid mining nuclear fuel for now; I think a reasonable argument could be made to not spend nuclear fuel for our primary energy needs. If we have dreams of ever being able to do mass interstellar travel, nuclear material is the only fuel we have so far with reasonable energy density for the speeds and distances involved. (Of course some will say "nuclear fusion" or "light sails", to which I say, we should defer mass consumption of fissile material until we have a reasonable expectation that those methods are viable).
I know that a few thousand years still feels like a long time, but with nuclear fission, it is truly the most non-renewable resource, being formed only in stellar explosions. Let's put aside the science fiction of asteroid mining nuclear fuel for now; I think a reasonable argument could be made to not spend nuclear fuel for our primary energy needs. If we have dreams of ever being able to do mass interstellar travel, nuclear material is the only fuel we have so far with reasonable energy density for the speeds and distances involved. (Of course some will say "nuclear fusion" or "light sails", to which I say, we should defer mass consumption of fissile material until we have a reasonable expectation that those methods are viable).