If efficient, safe and low cost fast breeders become available, you don't need thorium or sea extraction. Just transmute the vast quantities of U238 that have b

If efficient, safe and low cost fast breeders become available, you don't need thorium or sea extraction. Just transmute the vast quantities of U238 that have been stockpiled as depleted uranium into fissionable Plutonium 239 and run reactors on that for decades. Large nations have about one milion tons of depleted Uranium, in oxide or hexaflouride form, that's about 1 trillion megawatt-days, enough for 150 years of current energy consumption, or decades of geometric increases of energy use. Only then we need to go after existing proven mineral reserves, and only after that, maybe at the turn of the 22nd century, we would need to ponder sea water extraction.