Is There a Uranium Reactor on Earth?

Uranium ore is no longer rich enough for a natural vision reactor to happen. We have to make it richer in this special kind of uranium, hence the famous centrifuges used to make nuclear fuel. But i guess it could have happened in other parts of the earth, not just in africa. Like there could have been other reactors that we don't know about yet. And there could be reactors happening in other planets, perhaps, or in other part of the galaxy.