Earth's core and mantle could be nuclear fission reactor

Geophysicist J. Marvin Herndon and nuclear engineer Daniel F. Hollenbach believe that the earth's core could contain billions of nuclear fission reactions.

A Washington Post article discusses their theory:

Is Earth's Core a Nuclear Reactor?

The view held by most Earth scientists is that iron and nickel migrated downward, taking with them all the trace elements that readily combine with these metals. The rest of the trace elements, including uranium, combined with oxygen to form oxides that remained in the Earth's mantle and crust.

These scientists use common meteorites as their model, but Herndon used a rare meteorite with a small amount of oxygen as his example, arguing that the uranium would remain metallic and, as the heaviest element in nature, would migrate to the Earth's core, forming a sphere about five miles in diameter -- a natural nuclear fission reactor.

"It's a self-sustaining critical reaction," said nuclear engineer Daniel F. Hollenbach of Oak Ridge National Laboratory, a longtime collaborator of Herndon's until the two parted ways last year. "Depending on how much it fissions, that's the power."

Hollenbach explained that the core would be composed primarily of two uranium isotopes. Atoms of the isotope U235 would split, giving up neutrons, which would be absorbed by the isotope U238, transforming it into an isotope of plutonium -- Pu239. The numbers signify the number of protons and neutrons in the atomic nucleus, known as the atomic weight.

This reaction, the same produced in some nuclear power plants, eventually creates radioactive waste isotopes much lighter than uranium. These migrate upward and outward from the core, "like fizz from a soft drink," Hollenbach said. The heat from the reaction is what drives the Earth's magnetic field.

It is an intriguing theory and it is backed up by the fact that a self-sustaining natural nuclear fission reaction is known to have occurred before on earth:

Natural nuclear fission reaction

A natural nuclear fission reactor is a uranium deposit where analysis of isotope ratios has shown that self-sustaining nuclear chain reactions have occurred. The existence of this phenomenon was discovered in 1972 by French physicist Francis Perrin. The conditions under which a natural nuclear reactor could exist were predicted in 1956 by P. Kuroda[1]. The conditions found at Oklo were very similar to what was predicted.

At the only known location, three ore deposits at Oklo in Gabon, sixteen sites have been discovered so far at which self-sustaining nuclear fission reactions took place approximately 1.5 billion years ago, and ran for a few hundred thousand years, averaging 100 kW of power output during that time.

Geological Situation in Gabon leading to natural nuclear fission reactors

1. Nuclear reactor zones

2. Sandstone

3. Uranium ore layer

4. Granite

If this theory is correct, it would mean that the two greatest sources of energy on earth, geothermal and solar radiation, are both produced by nuclear reactions; a nuclear fusion reaction in the sun, and nuclear fission reactions in the deep earth.