Earth is most probably one gigantic, stable nuclear molten salt reactor !
Ever wondered where all that heat from inside the Earth comes from ? As a matter of fact the planet produces an excess of ~30 TW. Together with the water thermostat made up of the ocean heat reservoir, the atmosphere blanket and the cloud cover, inner heat production enables us earthlings to enjoy stable and balmy temperatures isolated from hostile and cold space. 30TW is far away from any realistic range of natural fission with observed uranium concentrations in crust and mantle.
J. Marvin Herndon proposed that the inner core is made up of sulphides of nickel containing sufficient uranium isotopes to sustain stable breeding and fission. The key point is that concentrations, neutronics and half lives combine to make a plausible model for a nuclear heat generator lasting eons. Helium isotopes vented with vulcanic activities globally confirm that fission processes are going on at an immense scale. Electrical currents set up by fisson products in the possibly slurry outer core could be the source of the geomagnetic field. Curiously, a georeactor has also been found at Oklo in Gabon.
Model : the biggest molten fission reactor core - in Earth