Re: Decay Storage Requirements

[rkathren@tricity.wsu.edu (Ron L. Kathren)]

After 10 half-lives, the remaining activity is approximately 0.1% of the
original.  Using numbers to the base ten (eg 10 halflives and 0.1% or 10E-3)
is more convenient than dealing with the binary system.  BTW, 7 half-lives
is also sometimes used as the activity is reduced to 1/128 or approximately
1% of the orginal.

Ron Kathren

What is the scientific/technical basis for the regulatory requirement of
holding 
>radioactive wastes for a minimum of 10 half-lives prior to release.  Is
there a 
>technical reference as to why it is not 7 or even 12 for that matter.  The 
>requirement is always accompanied by the need to survey with conventional 
>instrumentation.... prior to release. For low activity wastes the 10
half-lives 
>+ surveys can be overkill. 
>
>If a researcher uses radioactivity for an experiment and does a survey of 
>his/her experiment wastes at the bench top and finds no detectable
radioactivity 
>on the materials they are not placed in the radioactive waste.  So if one
was to 
>survey wastes which are held for decay after 5 or even 7 half-lives and
finds no 
>detectable activity why can't it be released?
>
>Any technical basis for this requirement would be helpful.  
>
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