Re: Global Warming (NUCLEAR)

[Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>]

Your questions, Joel, would be easier to answer if each
radioactive isotope decayed into a stable produce. But
spent nuclear fuel is composed of isotopes whose products
are also radioactive. There are many natural decay chains
in spent fuel. The hallf-lives of daughters may be either
shorter or longer than those of parents.

I have a chart in front of me which shows, for example,
that the amount of Am-242 (T=16 hrs) in spent fuel
remains essentially constant for about 50,000 years.
For Am-241 (T=243 yrs) the amount increases by more
than one order of magnitude during the first 200 years
and at t=2000 yrs it becomes essentially the same as at
t=0. After that it goes down rapidly at its own rate.
There is nothing unknown or unpredictable about
this but it is not just a simple exp(-t/T) decay of each
isotope.

The most troublesome are Cs and Sr, (T=30 years or so)
because they are water soluble. They are hard to destroy
(small cross sections for neutron-induced reactions). That
is why transmuted spent fuel must be protected for about
500 years. Fortunately we know how to build containers
which can be counted upon for hundreds of years. After
that time the remains of preprocessed material are not
more radioactive than the uranium ore in a typical mine.
Ludwik Kowalski

"RAUBER, JOEL" wrote:

> Ludwik,
>
> You bring up an interesting thought (issue), speaking as a non-nuclear
> physicist.  It always seems strange why there is such a worry about very
> long lived radio-isotopes,  If it has a half-life of say 1,000,000 years,
> the isotope can not be very active (or else its half-life would be much
> shorter).  And if its not very active, how dangerous is it?
>
> I realize that there is a middle range of half-lifes that must be the
> worrisome ones.  Very active isotopes only have to be stored a short period
> of time before they are no longer dangerous.  In you opinion, what are the
> range of half-lifes that are the most worrisome?
>
> No doubt I am simplifying greatly and would appreciate responses on the
> over-simplification as well.
>
> I'm also considering only danger from radiactive properties of the
> substances and not their chemical toxicological properties (which are of
> course a factor as well).