[anonporridge]

I don't know if this would be any extra heat, because the radioactive material would already be decaying anyway if it was left in its natural state. Maybe the same problem where radioactive material would be left mostly underground and insulated where its heat would leak slowly.

Then again, part of the Earth's core heat comes form radioactive decay. So in a way, geothermal is an indirect form of nuclear fission.

[eru]

Nuclear power plants don't just capture the energy from natural decay.

Though the precise mechanism doesn't matter too much for my comment. Just assume I'm talking about fusion plants.