First, mining uranium is not exactly environmentally friendly and those involved in the mining process are at a considerably higher risk of lung and non-lung cancers.
Second, it takes about 10 metric tons of raw uranium to make enough low enriched uranium to generate 400 million kilowatt-hours of electricity. If you take known reserves, and estimated undiscovered reserves, we only have 200ish years worth at current energy demands.
Energy demands increase over time, for example we are generating 4x the energy we were in the early 1970s and more and more people are being able to afford electronic devices, if you go adding electric vehicles in worthwhile numbers you'll see a rapid spike as well so if we switched the entire world over to uranium based power, we might have 50 years worth.
Even if you then use the waste from those reactors, via a different process like YC funded Oklo Inc is attempting to do using nuclear waste as an energy source, you still might only buy the world a century of clean nuclear energy.