1) The isotope paradox is not as paradoxical as a giant nuclear explosion blasting debris into orbit.
2) I'm a broadly-trained Geophysicist with a Ph.D. in mantle Convection and solid-earth geophysics, so I'm as close to an 'expert" as you'll get in a hurry
3) In the sense of the Gabon Okla natural reactor, no, but within the body of the earth - unlikely.

of course, nobody can rule anything out, totally, but when people go from one concept (Gaiai- Selene) and then extend it to highly improbable planetary pairs like Venus and mercury, they are clearly disconnected from reality.

When you throw-in variations in the laws of physics, you're well into looney-land.