[ RadSafe ] Isotopic Concentrations of Uranium VersusU-235Enrichment

[Dan W McCarn]

Dear Doug & Leo:

You ask an even more interesting question than you might have imagined
because not all produced "natural" uranium has equal activities of U234 -
U238.  George Capus published a paper in IAEA TECDOC 1396 in 2004 which
discusses both natural spatial disequilibrium of U234 / U238 in active
roll-front sandstone deposits in Wyoming as well as differences in isotopic
concentration by mining method.  In this case, he points-out the high U234
to U238 ratios of uranium produced by sulfuric acid ISL mining in Central
Asia.  Because of alpha recoil, the U234 is dislocated from the mineral
matrix making it more easily leached.  In active roll-front deposits, this
causes a higher U234 / U238 ratio near the leading edge of the roll-front,
and a lover U234 / U238 ratio near the trailing edge.

I think that the increased U234 to U238 ratios from sulfuric acid ISL mining
has something to do with the reactive chemistry and change in differential
transmissivity of the deposits as they are being mined, but I can't prove
that yet.

Take a look at George's paper.  His concern was related to product
specification prior to enrichment.

Best!

Dan ii

--

Dan W McCarn, Geologist
8, Le Buisson Sainte-Anne
78860 Saint-Nom-la-Bretèche, France
+33.(0).1.74.09.03.09 (Home)
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-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On Behalf
Of Douglas Minnema
Sent: Friday, December 05, 2008 22:32
To: radsafe at radlab.nl; llowe at senes.ca
Subject: Re: [ RadSafe ] Isotopic Concentrations of Uranium
VersusU-235Enrichment

Leo,

It's a long story, but I must be brief as I'm recovering from shoulder
surgery and only have one hand to type.

In general, the problem is that most of the enriched uranium in the DOE
complex was from recycled uranium that had been run through reactors,
processing plants, and enrichment plants multiple times.  Since some of the
other isotopes tended to follow the U-235 through the enrichment, then one
ended up with a potentially wide range of isotopic mixes for any one value
of U-235 enrichment.  This was especially an issue with U-234, which was a
major constituent of the radiation dose even though it was a minor
constituent of the isotopic mix.  Therefore, the handbook could only provide
graphs and general examples but couldn't be specific.  But as you can
imagine, the U-235 enrichment value was the only "important" value for the
DOE at the time.

Doug Minnema

>>> "Leo M. Lowe - SENES Consultants Limited" <llowe at senes.ca> 12/05/08 3:34
PM >>>
Hello,

DOE-STD-1136-2004 (Guide of Good Practices for Occupational 
Radiological Protection in Uranium Facilities) gives an equation for 
the specific activity of uranium (Ci/g) as a function of U-235 
percent enrichment.   However, it does not provide a parameterization 
of the isotopic abundances. A graph (Figure 2-2) does show the 
percent of the total activity for individual isotopes but I am 
interested in equations for the abundances, rather than having to 
read values off the graph.

Does anyone has a cite for this information  i.e. Bq/g or Ci/g for 
each uranium isotope versus % U-235 mass enrichment (by the gaseous 
diffusion method).

Feel free to respond directly to me.

Regards,

Leo M. Lowe, Ph.D., P.Phys.

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