To add to what other commenters have said, apart from the weapons proliferation issues, enriching uranium is very expensive. U-235 only makes up about 0.72% o

To add to what other commenters have said, apart from the weapons proliferation issues, enriching uranium is very expensive. U-235 only makes up about 0.72% of natural uranium, the rest of it being U-238. Running a reactor on low enriched uranium is much more cost effective, although reactor designs that can run on LEU can be less safe, like Chernobyls RBMK design.