Re: U-235 in Natural Uranium

[Chris Alston <alstonc@ODRGE.ODR.GEORGETOWN.EDU>]

Leo



I don't know about the "normal variability" of the percentage of U235, but 

bear in mind that the reactor at Oklo ran 2 x 10^9 years ago (" . . . for 

on the order of 10,000 years").  The isotopic ratio was then in a state of 

*enrichment*, not depletion, because the t1/2 of U235 is 7 x 10^8 y, 

whereas that of U238 is 4.5 x 10^9 y.  That's why the reactor ran, with the 

help of some moderating groundwater in the ore-bed.



You might try searching some of the DOE's lab websites, e.g., Oak Ridge, 

Argonne, INEL, Battelle, the EML.



Break a leg

cja



PS.  I thought that the definition of DU was 0.35% U235.



PPS.  The quotation above is from (surprise!!): Eisenbud, M and Gesell, T. 

Environmental Radioactivity, 4th ed., 1997.



PPPS.  Although physical evidence has only been found for the reactor in 

West Africa, it's been estimated that there could have been 100 of them.



At 09:18 AM 6/12/01 -0400, you wrote:



>Does anyone have any literature/information on the normal variability of 

>the U-235 concentration in naturally occurring uranium in ores and soils 

>i.e. 0.72% +/- ??.  I understand that the NRC considers depleted uranium 

>(DU) as uranium depleted below 0.711% U-235.  Does this then mean that 

>natural uranium does not exhibit U-235 levels this low (except in unique 

>circumstances such as the Okla natural reactor)?

>

>Thank you.

>Leo M. Lowe, PhD



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