Maybe some other life form could have one after enough time has passed, but we can’t bootstrap ourselves a second time.
(Edit: to be clear, I’m agreeing with you.)
That's probably what someone said in the middle ages when they finished deforesting Scotland.
We still have nuclear. There's an obscene amount of energy in it. It's just not attractive while we still have other "easy" options.
If you know that radioactive isotopes exist, it sounds like steampunk, 1850s, level tech could build a power plant, but perhaps not a bomb.
https://www.reddit.com/r/worldbuilding/comments/57peek/can_y...
I don’t think it’s that hard to build a vessel full of warm radioactive pebbles to boil water.
Sorting ore by chemical element, and then making a fluid / gas / solution of the fuel element to sort by isotope mass in a centrifuge may or may not be doable for “blacksmith” level technology, though. Hard to say.