Re: A real solution

["ruth_weiner" <ruth_weiner@email.msn.com>]

That's not correct.  Some years ago Oak Ridge published decay cuves for
spent nuclear fuel.  There is a rather sharp drop in activity around 90-1000
years (about 30 half-lives of Cs-137 and Sr-90) and another more gradual
decrease (that looks like a "bump" in the curve) where most of the
activation products have decayed away.  The activity will still be
considerably more than fresh fuel -- the ingrowth of Np-237, for example,
doesn't reach its peak until several hundred thousand years.  10,000 years
was chosen as  the "regulatory" limit for several reasons:

1.  It's 20 half lives of Am-241 and well past the decay of the nuclides
whose half-lives are around 100 years (e.g. Pu-238. t 1/2 = 87 years)
2.  It is a time period during which one may reasonably suppose that the
geology, geography, and hydrology of the earth won't have changed
drastically.
3.  One can even assume, as EPA in fact does, that human life will not be
drastically different from what it is now; that is, no more different than
our life is from life in ancient Rome.
4.  If one is forced to make a prediction, would a prediction longer than
10,000 years -- another order of magnitude -- be remotely credible?  Even
10,000 years stretches credibility.

Ruth Weiner
ruth_weiner
-----Original Message-----
From: Bob Flood <bflood@SLAC.Stanford.EDU>
To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
Date: Friday, August 18, 2000 1:47 PM
Subject: Re: A real solution


>>I am curious, though, about the composition of spent fuel (not my
>>field).  What are the shorter half-life isotopes of concern (say those
>>that will be mostly gone within 300 years) vs. the very-long half-live
>>ones, and their relative proportions?
>
>Some years ago I was told by someone whose opinions I respect that the
>oft-used 10,000 year worry period is way off and that spent fuel will decay
>to being no more radioactive than the original unirradiated fuel in about
>300 years. I have not tested this assertion and haven't seen any other
>calculations of this sort. Can anyone confirm or deny this claim? Might
>there be a reference on this?
>============================
>Bob Flood
>Dosimetry Group Leader
>Stanford Linear Accelerator Center
>bflood@slac.stanford.edu
>
>
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