RE: Georeactor

["Franta, Jaroslav" <frantaj@AECL.CA>]

Dale,



The questions you raise below have been addressed numerous times in various

publications, including the Dutch paper I referenced in my initial post of

this thread (ie. http://www.nuclearplanet.com/0404046.pdf ).

I quote:

"Calculations at Oak Ridge National Laboratory (Hollenbach and Herndon,

2001) show that a

planetary-scale nuclear reactor can operate over the lifetime of the Earth

as a breeder reactor"

The paper is also available through a link at the nuclearplanet.com web

site, at http://www.pnas.org/cgi/reprint/98/20/11085.pdf



Regarding the uranium question,

" The possibility of a nuclear georeactor is linked to the state of

oxidation in the deep interior of the Earth. Herndon has convincing

arguments for a state of oxidation like an enstatite chondrite, different

from the more oxidised, ordinary chondrites considered by Birch. 

As a consequence of the highly reduced state some so-called lithophile

elements including some Si, Mg, Ca, U and possibly Th occur in part of the

core. These elements, tending to be incompatible in an iron alloy, are

expected to precipitate at relative high temperatures. Due to their density

MgS and CaS will float to the core-mantle boundary, whereas uranium sulphide

(US) and nickel silicide will sink to the Earth's centre.

At pressures that prevail in the core, U and Th, being high-temperature

precipitates and the densest substances would tend to concentrate in the

Earth core by the action of gravity. In that process it will ultimately form

a fissionable, critical mass. Fission produces less (half) dense fission

products that tend to separate from the more dense actinides. In this way a

critical reactor condition can maintain. "



This is again from the Dutch paper. 



Several of Herndon's papers on this subject are available in pdf format on

the nuclearplanet.com web site.



Also, according to a recent paper in Nature (vol.427, 505 - 509, 5 February

2004); 

Mixing, volatile loss and compositional change during impact-driven

accretion of the Earth

ALEX N. HALLIDAY

<snip> "....impacting core material did not always mix efficiently with the

silicate portions of the Earth before being added to the Earth's core.

"<snip>



Thanks for your interest.



Jaro



http://www.cns-snc.ca/branches/quebec/quebec.html



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-----Original Message-----

From: daleboyce@charter.net [mailto:daleboyce@charter.net]

Sent: Friday April 16, 2004 11:00 AM

To: radsafe@list.vanderbilt.edu

Subject: Georeactor





Jaro,



Thanks for the reply.  I accept that the directional/delayed coincidence

method would work.  Pretty neat trick.  However, I'm having problems

accepting the premise of a georeactor in the core for the following reasons:



Uranium is not expected to concentrate in the core like the platinum metals

such as iridium.  It's chemical properties cause it to fractionate into the

crust.  The earth's crust contains about 1.4 ppm of uranium on average while

meteorites contain about 0.008 ppm. Meteorites are thought to better

represent the mantle/core. See for example:



http://www.uic.com.au/nip78.htm



I also see a problem with the physics.  The U238 decay chain releases about

52 MeV per decay(8 alphas and several betas).  A U235 fission releases about

200 MeV.  So for the U235 fission to reach the energy output of the U238

decay chain the fission rate would have to be 25% of the U238 decay rate.

Since U235 is about 0.7% of uranium present day, the partial half-life due

to fission would have to be about 1.6E8 years to reach the energy output of

the U238 decay chain. This is more than 4 times shorter than the physical

half-life of U235. Without breeding all of the U235 would have been burned

up in fission by now.



Given today's natural abundances, the ratios of fission cross section in

U235 vs. the capture cross section in U238 are such that the fission and

capture rates are similar depending on the neutron spectrum. So in earlier

times the fission rate would have exceeded the capture rate until the U235

abundance reached a balance with the breeding rate.  Without doing a lot

more calculating I can't say this would save the possibility.  I would say

that it would be very fortuitous if it did, and one would expect that

U235/U238 ratios would be different from the crustal material we observe

today.



I found a reference online (which I failed to bookmark) that estimated the

average heat loss from the earth to be 70 to 80 milliwatts per square meter.

This is a difficult number to measure BTW since noon insolation reaches 1 kW

per square meter, temperature gradients are hard to characterize. The earth

is about 5E14 m^2 so we need about 4E13 watts 40 (TW) to match this heat

loss, less power is needed since it is thought that the earth is cooling.



If I plug in the concentrations from uranium given above to various parts of

the earth's structure I come up with way too much heat from the U238 chain

using crustal concentration, and too little power using meteoritic

concentration. The lower mantle makes up almost half the earth's mass, and

should have an intermediate concentration of uranium. Oh and I forgot to add

in thorium and potassium which contribute as well, and fractionate in a

similar way to uranium.



Dale