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Re: Comments on NRC Soil Limits
Re: NRC soil screening limits
1. NRC soil screening limits are just that screening. If you are less than this, you are OK and no t other thought is needed.
2. The basis is the screening code D&D. This code and its description and user manual are on the web. Start at the NRC's web page www.nrc.gov.
3. NCRP Report 129 discusses screening limits for soil and factors relevant to site-specific studies.
4. There are other codes out there. RESRAD is probably the most widely used. I have it on my computer in addition to D&D.
5. The real problem is not screening but dealing with irregular finite areas well below the land area needed to support an agricultural path and hardly likely to support a resuspension path. How do you do realistic modeling?
6. Do not comment to me over RADSAFE. I am just a manager these days. The NRC website
devoted to decommissioning invites comments on all the posted guidance. Comment at public nmeetings. Please just don't grouse. Help us make to technically correct.
Carl Paperiello,CHP
>>> "Oldewage, Hans D" <HDOLDEW@sandia.gov> 12/8/1999 12:21:32 PM >>>
The NRC should consider the following for the proposed uranium numbers:
First, look at the radionuclides used in the uranium runs. It is important
to differentiate between "natural" or unprocessed uranium, and uranium that
has been separated from its daughter products, since the majority of the
radionuclides in the two chains aren't going to grow back to any appreciable
level for a hundred thousand years or so (give or take some millennia).
At Sandia, we don't deal much with uranium contamination where the entire
chain is in equilibrium (and I don't know if the NRC would face this often
either). Most of our uranium contamination is depleted uranium, so the
activity is dominated by U-238 and the first couple of short-lived daughter
products (Th-234 and Pa-234m), plus a little U-234 and U-235. Without the
bottom part of the chain (especially the Ra-226), the 25 mrem/year soil
limit should be considerably higher (>100 pCi U-238 per gram) for a
"generic" site. I don't know, but I'd imagine the numbers are similar for
enriched uranium (except for the uranium isotope of interest).
Also, I doubt if you can reliably distinguish 0.5 pCi/g (U-238) of
unprocessed uranium contamination, or 0.6 or 0.7 pCi/g of Ra-226, from their
natural concentrations. At least around here, the natural concentrations
can vary by at least these amounts depending on the soil type.
The other radionuclide that looks very low is Sr-90, although not as far off
as the uranium numbers. It doesn't make sense that Sr-90 should be less
than 1/2 the Co-60 number, since the inhalation dose conversion factors are
similar, and there is essentially no external dose pathway ( a significant
factor for Co-60). My guess is they used the class Y dose conversion factor
for inhalation, but this is only appropriate for one compound (SrTiO3,
according to FGR 11), and probably shouldn't be used in determining a
generic limit.
And to paraphrase another commenter, none of these numbers are any good if
there isn't a reasonable method of detection in the field. It isn't good
enough that it can be detected in a lab, if you can't figure out where to
take a sample. The entire process needs to be considered in establishing
these levels.
On the plus side - at least there is progress in establishing generic
limits. I would like to see DOE follow suit. With some of the above
considerations, it would be a significant improvement over the current
process, which is equally complex for every site regardless of the magnitude
of the problem.
Just my opinions (and with luck, a few facts).
=====================
Hans Oldewage
Sandia National Laboratories
505-845-7728
hdoldew@sandia.gov
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