Why doesn't all the Uranium sink to the bottom of Earth?

I sometimes have research ideas that I think are cool, but that don’t make sense for me to pursue. I generally just make a note of them and move on. This is the 28th post in a series describing some of the ideas I’ve accumulated.

Why doesn’t all the Uranium sink to the bottom of Earth?

What’s the idea?

Uranium is denser than iron. Why hasn’t it all fallen to the center of the Earth? Does it preferentially alloy with lighter elements, or something else?

Why is this important?

It’s just weird, and feels like there ought to be an answer. There might be a known answer, but I haven’t found it. There was some discussion of this idea in the 1990s, including considering if there could be a small actinide ball inside the primary Nickel-Iron core which could produce lots of heat and make the early Earth more geologically active than it is today.

How can I get started?

I’d start with a literature review. I didn’t spend long looking into this, and it’s entirely plausible that there’s a known answer.