Re: Activity of waste

[mcnaught@lanl.gov (Mike McNaughton)]

>Just a guess, but most of the U238 that's around was separated from Ra226 at
>the U mills. The Ra will then re-ingrow. Note that the half-lives of U238 and
>its daughters "above" Ra in the decay chain are, in order and very rounded:
>5E9y, 24d, 1m, 7h, 2E5y, 8E4y.
>
>chris alston

This thread refers to the graph on page 34 of the June issue of Physics Today.

My tentative conclusion is that the calculation of Ra-226 in radioactive
waste included ingrowth of U-234. However, I think this is incorrect. U-234
is concentrated during the enrichment process (because it is similar to
U-235). Ra-226 will come into secular equilibrium in about 10,000 years,
and then decrease as the U-234 decreases.

Pb-210 is still a puzzle. This should be in secular equilibrium with Ra-226
after about 100 years, unless the calculation includes diffusion of Rn-222.

It would be good to confirm this possible error with whoever did the
calculation. Similar graphs have appeared in so many publications, that it
would be good to confirm if there is an error.

"Shlala gashle" (Zulu greeting, meaning "Stay safe")
mike (mcnaught@LANL.GOV)