Nuclear fuel is mined however the current waste stockpiles hidden around the world still contain significant fissile material which can be repurposed as fuel when in the correct reactor. Some new (not widely commercialised) reactor technologies 'burn' fissile material. These reactors are really interesting as they reduce the amound of waste evolved from the process which is a significant cost to operators and countries to process store and secure over millennia.
Equally there are 'breeder' reactors which generate more fuel than they consume. These were not pursued commercially only because more Uranium was found in the 60's.
Some really interesting and new challenges in the energy industry – for me nuclear has a place in providing out increasing energy baseline. New nuclear needs momentum, particularly stable governments and good engineers – it is a world away from the experimental era of the 50's to 80's where mistakes were made (Chernobyl) which are inexcusable from an environmental point of view.
Lets get behind it and do it right!