[meteorite-list] Earths core

From: Marc D. Fries <m.fries_at_meteoritecentral.com>
Date: Mon Aug 9 10:25:20 2004
Message-ID: <1102.>


   A quick two cents... It makes sense that the heaviest elements will
sink to the center of a planetary body, and that far more than enough
would accumulate to sustain a nuclear reaction. The problem that nags
at me is - how to moderate the reactor? In a nuclear reactor,
moderator rods (graphite, I think...) are used to slow down fission
neutrons enough that they can be absorbed by the fuel to sustain the
reaction. Recall that the first nuclear reactor, under the stadium in
Chicago, was composed of fissile material encased in graphite moderator
blocks. The "natural reactors" in uranium deposits in Africa show
signs that they only operated during periods of heavy rainfall -
groundwater perculating through the deposits would act as a moderator
and allow the deposit to sustain a nuclear reaction.
   So - what would act as a moderator in the core of a planet? I'm going
way out on a limb here, but I bet that groundwater is right out...!

   Is it possible that a reactor in the core would simply be large enough
to self-moderate? Any nuclear engineers out there care to have a shot
at this?


> Hi.
> Just been reading an interesting article in 'New scientist' (this
> weeks).
> It is about the centre of the Earth (i.e the core) , apparently there is
> simply far too much heat to be explained by the conventional 'still
> molten since it formed' theory (or from gravitation actions).
> One theory that is being taken seriously is that fissile radioactive
> elements (These being the heaviest elements) would sink into the core
> mixture) and start a nuclear chain reaction, so the extra heat could be
> generated from nuclear processes. Scientists are looking for the tell
> tale anti neutrino's that could indicate nuclear reactions going on.
> They point out that natural nuclear reactors exist on earth already, in
> area's where uranium is sufficiently concentrated in the rock, it has
> undergone fission.
> If this where the case, there ought to be similar processes going on
> other planetary bodies (indeed this might explain why mars still appears
> to have volcanism when it shouldn't really have, for it's size?).
> My question:
> Would we not expect to find iron meteorites with nuclear reaction
> by-products or even higher than normal un-reacted radioisotope
> concentrations - if this were feasible?
> Or is it a case of Asteroids being too small to differentiate enough for
> the heavier elements to collect in sufficient quantities?
> Maybe we just haven't had a sample of 'inner core' yet, and somewhere
> out there are chunks of natural reactor!!
> Best,
> Mark Ford
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Marc D. Fries, Ph.D.
Postdoctoral Research Associate
Carnegie Institution of Washington
Geophysical Laboratory
5251 Broad Branch Rd. NW
Washington, DC 20015
PH:  202 478 7970
FAX: 202 478 8901
Received on Mon 09 Aug 2004 10:25:10 AM PDT

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