Re: Use of unsealed thorium

[joseph guido <jguido@poky.srv.net>]

Does anyone had any experiance with the developement of release limits (surface contamination) 
for Thorium.  Specifically when does the Th-natural limit apply as opposed to developing a limit 
based on isotopic contributions for each of the Thorium isotopes.  

I know this may seem to be an obvious one, but ... I am working a Thorium remediation project at 
a site which had produced a Mg-Th alloy.  The decomissioning plan is pre-written (~5 years ago) 
and establishes a surface contamination release limit of 26 dpm/100 cm2 for gross alpha (based 
upon an assumed 3:1 ratio of Th-230 to Th-232 and inventory weighted isotope specific release 
limits).

Does this seem like an overkill to anyone else?  Any experience with release limits for similiar 
cases are appreciated.

Also... I seem to remember that there was a MPC published for Th-natural, however, my current 
(1995) copy of 10 CFR 20 does not show a DAC for anything but individual Thorium isotopes. Any 
history on this?

joe guido
joseph_guido@radian.com