Reactor at Earth's Core?

An anonymous submitter sent in this story suggesting that uranium in the Earth's core may be acting as a giant breeder reactor, generating a large amount of heat and perhaps being responsible for the Earth's magnetic field.

Comments

it's not quite as bizarre as it may seem

[g4dget]

People have thought for a long time that radioactive decay contributes to warming of the earth's core. That was also considered to be the source of the He3 that still can be found in volcanic vents.

The question is just how much of a chain reaction there is. I guess traditionally, the assumption was "not much". But it seems quite plausible that uranium might concentrate and actually start a significant chain reaction.

Re:What if that Reator Blew Up!

[Bonker]

Concerns about global warming aside, the Earth's external temperature has fluctuated *wildly* during the 4 or 5 billion years our planet has been around. At times, such as when the atmosphere wasn't made primarily of oxygen for example, it has been much colder or hotter. Assuming that our planet's core does indeed act like a breeder reactor, something so slight as global warming is not going to significantly affect it.

Primary Literature

[Wayne Hoxsie]

As usual, the pop science publications do this little justice. The primary literature is published by the Proceedings of the National Academy of Sciences and is published online at: http://www.pnas.org/cgi/content/full/98/20/11085 and certainly makes the case sound more convincing.

The article at EV world doesn't didn't, to my dismay, discuss the electro-magnetic implications at all. It sounded like a stretch to me to conflate geomagnetism with a nuclear process.

Only if you don't read it carefully

[texchanchan]

Re, ...the article authours propose no mechanism for their magical solid-state fission reactor to turn on and off...

Yes, they do:

"One might imagine instances in which the rate of production of [neutron-absorbing] fission products exceeds their rate of removal by gravitationally driven diffusion," Herndon wrote in a recent paper on the subject. If so, he explained, "the power output of the geo-reactor would decrease and the reactor might eventually shut down, thereby diminishing and ultimately shutting down the Earth's magnetic field."

Over time, as the lighter elements moved away from the uranium core, the reactor would restart.

Also, re Without a really strong mechanism operating to separate it out and concentrate it, it's going to remain a trace impurity in other ores, and not a ball at the center of the Earth.

There is such a mechanism. Everyone agrees that the core is iron. How did that happen, when the Earth coalesced from random rocky materials? The same way. If iron, why not uranium? From the article:

...over time, solid uranium particles would rain out from Earth's fluid core at high temperatures. Because of their high density, they could collect at the very center of the Earth.

Gravitational fractioning of elements.

[Christopher Thomas]

Without a really strong mechanism operating to separate it out and concentrate it, it's going to remain a trace impurity in other ores, and not a ball at the center of the Earth.

There is such a mechanism. Everyone agrees that the core is iron. How did that happen, when the Earth coalesced from random rocky materials? The same way. If iron, why not uranium?

Iron is plentiful. Enough of it was present for gross gravitational effects to be enough to separate it from lighter ores within solution.

Uranium is far, far less plentiful, and so would tend to remain dissolved.

There are no "grains" to migrate, as you suggest - uranium would be mixed in as impurities on an atomic level, literally dissolved in other metals and metal oxides.

Re:Gravity effect wrong?

[alienmole]

But at the center of the earth gravity is a much weaker force.

True, but the pressure of the material above the center, which is attracted towards the core, is very strong. That's what causes the earth's core to be dense - gravity creates pressure.

Is there a point just outside the center of the earth where gravity would actually pull you *UP*, since the bulk of the earth's mass lays above you?

No. The Earth is roughly spheroid, remember? The "center" of the Earth for the purposes of this discussion is the center of gravity, which is the net gravitational effect of all of Earth's atoms at any point. At the center of gravity, those forces cancel out. But anywhere other than that, the net force is towards the center of gravity.