Not much in the way of neutron moderators so far below the Earth's surface, so I'd be skeptical. Now, natural radioactive decay of Uranium, etc, are a huge fac

Not much in the way of neutron moderators so far below the Earth's surface, so I'd be skeptical. Now, natural radioactive decay of Uranium, etc, are a huge factor in keeping the Earth's core warm. It's just that nuclear chain reactions where one atom's decay sets off the next that isn't believed to be a factor.