I thought there were continuous thermo nuclear reactions going on, causing the flow of heat.. Or is it just ancient residual heat from
where the planet once formed ? I dont know
Most of the uranium is in the core.
Some core/mantle heat is generated from fission, some from the differentiation by gravity (the heavy part ssunk to the bottom), and some from gravitational interactions.
In theory generating the magnetic field should generate some heat as well, but nobody mentions it. The core rotating backwards has to generate a lot of turbulence and friction.
Estimates are about 1/3 the heat is residual from creation of the earth, about 1/3 fission and 1/3 other things.