FWIW, fissible material that's used with current technology is actually running out, with a similar timeline to oil. Fission is not an infinite energy source, despite appearances to the contrary. It's also not an cheap as one might hope.
If fuel were serious concern for cost, real searching for it would find much more.
And even with current technologies and reactors there are many ways to extend this, if you are willing to mix in some more highly enriched materials.
Eating up the absurd amount of nukes the US still has for example would be helpful.
And of course no society that actually bet on nuclear would still be using that fuel cycle in any serious way.
This is just the typical fear mongering that people use for all technologies they don't like, "Not enough lithium for EV".
Fuel reprocessing employed by France uses all of U235 + generates and burns plutonium. Fast reactors, which exist in small numbers in Russia, etc, take it up by another two orders of magnitude