Re: Yucca Mountain

[erollins <erollins@conterra.com>]

Bob Flood wrote:
> 
> >QUESTION: Is a time span of 10,000 years realistic?  Why should it be
> >designed to last for such a long and unforeseeable time period?
> 
> I've heard it said, but I have never tried to verify by my own calculations,
> that a standard mix of spent fuel (mixed fission products) will decay to
> about the same total activity per unit volume as the original uranium ore in
> about 300 years. Has anyone done this calculation? If this is true, wouldn't
> it be reasonable to require protection only until the radioactivity levels
> are no worse than when they started?
> 
> Bob Flood
> Unless otherwise noted, all opinions are mine alone.
> (415) 926-3793
> bflood@slac.stanford.edu

We have recently performed performance assessments to support closure of high level waste tanks at a DOE facility.  The 
isotopes that contributed most of the potential dose through the groungwater pathway during the 10,000 year period of 
interest were Tc-99 and Se-76.  The NRC has also focused on I-129.  All of these isotopes have very long halflives and remain 
long after the 10,000 years considered.

What I am interested in, due to their very low specific activity, is it physically possible to consume sufficient quantities 
of these materials to receive a significant dose?  Some years ago, I performed back-of-the-envelope calculations for I-129 
and came to the conclusion that it was not possible.  Does anyone have references regarding this conclusion?