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Re: RE: Origination, Assumptions, Restrictions for Use ofUranium SA Calc
Bruce,
Your good words are appreciated but it also would be helpful to know the source of the information. Are these actual measurement results or are they estimates?
In principle, of course, the specific activity of U-238 is about 0.336 microcuries/gm and the specific activity of U-235 is about 2.161 microcuries/gm. Natural U mass is essentially all U-238 with 0.92 percent U-235 plus enough U-234 to give the same activity as the U-238. Thus the specific U activity of natural U should be about 0.682 microcuries/gm. Part 20 gives the value as 0.677 which is reasonable agreement.
The total U activity increases with enrichment (i.e. replacing U-238 with U-235) but the change is not simple because the U-234 content is expected to increase faster than that of U-235. My recollection of the source of the Part 20 formula is foggy to say the least but I believe the formula is a fit to measurements made long ago (enrichment by Gaseous Diffusion, of course). As the formula predicts, the U activity is expected to be largely from U-234 and the predicted 62 microcuries/gm for 90 percent enrichment does not seem outrageous; in fact, this value is close to the result obtained by assuming that essentially all the U-234 from the feed material is in the enriched U.
As you say, the activity depends on the enrichment plant and the process used.
Of course, this all is based on the assumption that the starting point is natural uranium; all bets are off if recycled U is addressed. That gets into U-236 and all that.
Charlie Willis
caw@nrc.gov
>>> "Manninen, Bruce S." <manninenb@lmus.com> 01/21 1:55 PM >>>
The enriched uranium specific activity formula in 10 CFR20 App B generally
underpredicts the specific activity between 1 to 20% U-235 and above 93%
U-235, and overpredicts the specific activity at assays less than natural
uranium. At assays below 20% U-235, the use of the formula can result in an
error that may exceed 40%. For very highly enriched uranium (>93% U-235),
use of the formula may result in underprediction of the specific activity by
much as 50%. The actual specific activity of any enriched uranium depends
on the U-234% and will vary depending on what plant produced the enriched
uranium and when.
Only my opinion,
Bruce Manninen
manninenb@lmus.com
> -----Original Message-----
> From: Redmond, Randy R. (RXQ) [SMTP:RXQ@ornl.gov]
> Sent: Thursday, January 21, 1999 8:15 AM
> To: Multiple recipients of list
> Subject: Origination, Assumptions, Restrictions for Use of Uranium SA
> Calc
>
> All,
>
> I have been unable to locate the origin/good documentation of the
> uranium
> gaseous diffusion process specific activity formula:
>
> Specific Activity = [0.4 + 0.38 (enrichment) + 0.0034 (enrichment)^2]
> E-6.
>
>
> The formula can be found in the Health Physics Manual of Good Practices
> for
> Uranium Facilities and 10 CFR 20, App. B. What I'm really interested in
> is: (1) how accurate is the formula; and, (2) is it applicable to
> enrichments < 0.71 - 10 CFR 20, App. B implies it is good only for
> enrichments > 0.72.
>
> Any help and prodding in the right direction is appreciated.
>
> Randy Redmond
> Lockheed Martin Energy Systems
> P.O. Box 2009
> Bldg. 9769, MS 8081
> Oak Ridge, TN 37831-8081
> Email: rxq@cosmail3.ctd.ornl.gov
> Phone: 423-574-5640
> Fax: 423-576-6047
>
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