William Thompson, the first baron Kelvin worked out that the Earth was around 20 to 400 million years old, based on the rate of cooling from an assumed molten state. This would imply that the Earth's primordial heat would already be essentially lost, so you could argue the answer is zero (assuming Kelvin's calculation remains reasonable). However once energy is "thermalised" it loses any memory of where it is from, which makes that answer questionable.
[I assume that by "radiative heating" you mean heating from radioctive decay in the mantle, rather than radiative heating of the surface by the sun. There is also the Kelvin-Helmholtz heating from the iron sinking to form the core, but presumably that is finished now?]