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Re: nuclear "blast"

> What was described in Sci. Amer., and has been verified thoroughly,
> was a natural self-sustaining nuclear reaction, but NOT an explosion.
> [Note, even the time scale you mention, several thousand years, clearly
> indicates a reactor not an explosion].

> I, too, seriously doubt that a natural nuclear *explosion* could occur.
> I rather suspect that what was found in the Sahara was another example
> of a natural nuclear *reactor*.

In all the many times the Oklo reactor has been disgust on sci.geo.geology
and elsewhere on the net no one has ever mentioned a reactor in the
Sahara until now.  The only nuclear activity I know of in the Sahara
is recent and no one would call the French testing of nuclear weapons
'natural' (I digress)

The Oklo reactor was situated in what is now Gabon (West Africa), not
far from the Sahara.  I think we'll find that the reactor in the Sahara
turns out to be a slight confusion in retelling.

The following are descriptions culled from sci.geo.geology and
alt.folklore.urban over the years,  I'll trim it down a bit.

Check Scientific American Indexes maybe 10-15 years ago. They published an
interesting article called "A natural fission reaction" or "A natural
chain reaction" describing a uranium mine in south africa that contains
an eliptical body of ore that is quite depleted compared to normal U ore.
As I recall, the uranium existed at least partly in a metallic state due
the reducing atmosphere that existed around 2000Mya. It also became
super-concentrated from a sequence of at least two sedimentation and
sorting processes.

In this perhaps unique case, the superconcentration was sufficient to
establish a critical mass.


#### At about 1800 million years ago, uranium became sufficiently           
concentrated in the Oklo uranium deposit (Gabon) to become 'critical'       
i.e. in the deposit fission started. The energy produced is estimated at    
15000 MW years. Interestingly, since about 400 million years, no natural    
fission reactor may form since 235U, the fuel of the reastion, decays so    
quickly relatively to 238U, so that in young uranium ore it it so diluted as
to prevent natural fission.                                                 
a useful reference for laymen is:                                           
Cowan: A natural fission reactor. Scientific American 1976, 36-47           
more for professionals:                                                     
Lancelot et al.: The Oklo natural reactor: age and evolution studies of U-Pb
and Rb-Sr systematics. Earth Planetary Science Letters 25 (1975) 189-196.   


+The following are a few references that I found on the Oklo phenomenon  
+(out of a total of 80 references) from GEOREF in the USGS Library.      
+1)  Scientific American  July 1976, vol 235, no.1, p36-47.              
+2)  New Scientist  Nov. 9, 1972, vol 56, no 819, p 342-343.             
+3)  Geotimes  1978, vol 23, no 3, p. 27-28.                             
+4)  Geotimes  1975, vol 20, no 10, p. 14-16.                            
+5)  Interdisciplinary Science Review  1976, vol 1, no 1, p. 72-84.      
+6)  Le phenomene d'Oklo - The Oklo phenomenon.  1975,  Published by     
+      the International Atomic Energy Agency, Vienna. A series of papers
+      (mostly in French) presented at a symposium in Libreville, Gabon, 
+      June 1975.                                                        

Terry Chan

I also remember reading recently that anaerobic bacteria had been 
implicated in the process of concentrating the fissile material, 
an activity which I would assume was ultimately detrimental
to their health...

--- Derek