Doesn't Uranium after it's been used turn into some other radioactive element or there's some means to turn it into a fuel source again. I think someone mentioned that we have enough radioactive material on the planet to cover our energy needs for the next 200,000 years if you take into account lower level nuclear fuel sources like Thorium and the like.
No, not really. After
235U fissions, you have waste isotopes like strontium and cesium that are radioactive but not fissile. What you can do is to design the reactor so that the neutrons from the fission can be captured by other elements. This causes transmutation into a target isotope, hopefully one with economic value. We do this all the time to make medical isotopes. But making fissile materials this way (a breeder reactor, like Fermi built at Oak Ridge) is controversial because there is a fear that it makes nuclear weapons easier to make and harder to control.
In a traditional breeder reactor,
238U is transmuted to
239Pu, which is fissile and can be used for fuel. The transmutation of thorium to
233U is also promising since thorium is a relatively common element, but it hasn't yet been shown to be a viable process.
The problem with nuclear power is not that people are using it to generate electricity. The problem is people complaining about the byproducts and the problem of byproducts would not be there if we a a global community agreed to say ship all our hazardous nuclear waste somewhere to be reconstituted into usable fuel again.
Only the fissile byproducts are usable as fuel. It's possible for a reactor to produce more fuel than it consumes, but a lot of other materials get irradiated and simply become (high or low level) nuclear waste. Those do need to be disposed somehow, but for the most part reprocessing isn't even part of the plan now, which is unfortunate.