It's only radiation power in the way of the sun being our main heat source which slows our planet's cooling. Which is of course one huge fusion reactor. And if

It's only radiation power in the way of the sun being our main heat source which slows our planet's cooling. Which is of course one huge fusion reactor. And if you were outside the protection of our magnetosphere and atmosphere its radiation would actually be pretty dangerous even at this distance. The earth's core is just still hot from when it was formed. It's not being heated by an internal nuclear reaction.