[ RadSafe ] Natural Uranium / Depleted Uranium

[Dan W McCarn]

Hi Bernard:

Not all "natural" uranium is leached aggressively, which would provide for a
U-234 / U-238 ratio equal to their isotopic ratios assuming that the deposit
is in secular equilibrium which is not always the case.

To some degree, this depends on the manner of processing & recovery of the
natural uranium ores.  When U-238 decays, the alpha recoil damages the
crystal structure of uraninite / coffinite allowing the progeny U-234 to be
more easily leached from the surface of the mineral than the secular
equilibrium ratios would suggest.  This sometimes occurs when weak leaching
solutions are used to lixiviate uranium ores either in situ or ex situ. The
234/238 ratios can also be used to interpret U mobilization in natural
systems. 

The result is that the alpha activity of products leached under these
conditions is significantly increased due to the increased amount of U-234.

There was a French/Cogema paper on this subject given at the IAEA in 1998 or
1999 dealing with the elevated U-234 caused by weakly-leached ores and the
various problems caused by elevated U-234 in the nuclear fuel cycle.  I'll
try to find the reference.

D. McCarn, Geologist
Albuquerque & Houston


-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On Behalf
Of Bernard L. Cohen
Sent: Thursday, December 14, 2006 13:24
To: Michael McNaughton
Cc: Flanigan, Floyd; radsafe at radlab.nl
Subject: Re: [ RadSafe ] Pepto-Bismol

Natural uranium should have the same alpha activity from U-238 and U-234 
(they are in secular equilibrium).. The enrichment process takes U-235 
from 0.7% to about 3.5% so the DU should have 1/5 as much U-235 as 
natural uranium. Enrichment shoud remove a  somewhat larger fraction of 
U-234 (it is lower in mass) than of U-235, so the U-234 alpha activity 
in DU should be somewhat less than 20% of that in natural uranium. Even 
if it was 20%, it would be 0.2/ (1+0.2) = 17% of the total alpha 
activity. How can it be as much as 28%?

Michael McNaughton wrote:

> According to figure 2.2 of DOE-STD-1136-2004, about 28% of the total 
> alpha activity of DU is U-234.
>
> At 06:01 PM 12/13/2006, John R Johnson wrote:
>
>> What do you mean by "pure depleted uranium"? Producing U-238 without 
>> U-234 is very difficult.
>
>
> Mike McNaughton
> Los Alamos National Lab.
> email: mcnaught at LANL.gov or mcnaughton at LANL.gov
> phone: 505-667-6130; page: 505-664-7733