Can the earth's magnetic field be generated by heat from a natural nuclear reactor? I've come upon Dr. J. Marvin Herndon's theory that the earth's magnetic field is generated by a hot nuclear reactor operating in the center of the earth. This is backed by various papers, some of them peer reviewed:
http://www.nuclearplanet.com/Herndon%27s%20Nuclear%20Georeactor.html
His theory purports to explain various anomalies such as the high level of He3 in basalt in Hawaii and their dependency with time. A recent Herndon arXiv paper is:
Uniqueness of Herndon's Georeactor: Energy Source and Production Mechanism for Earth's Magnetic Field
http://arxiv.com/abs/0901.4509
His papers suggest that the natural reactors sometimes seen in uranium deposits must also occur at the center of the earth. He says that the conventional explanation for the earth's magnetic field fails because the Rayleigh number for the core is inappropriate as far as determining whether convection exists.
Since this is not accepted geology, what are the problems with the theory?
 A: KamLAND Borexino has set moderately strict limits of the total power of a central geo-reactor. See for instance Geo-neutrino: Experiments (pdf link) a talk by one of my colleagues. (Jalena notes that Borexino's limit is the strongest one going, but KamLAND was the leader for a while.)
The upper extreme of these limits is less than half the total geological power, but quite non-trivial. The bottom goes all the way to zero.
There is also a recent paper (that I have yet to read) on a variation of this idea: The KamLAND-experiment and Soliton-like Nuclear Georeactor. Part 1. Comparison of Theory with Experiment.
I've no idea, how the rest of these ideas stand.
A: This theory has been around a while.  The one problem I see is that in order to get a uranium reactor running you need a fair concentration of U235.  The core of the Earth most likely does not have that.  There might be a low level or very subcritical amount of fission which goes on in the core of the Earth.  However, I suspect this is not larger than the amount of energy produced by strong and weak nuclear decay processes.
