???Selection of MDA for Volumetric Contamination

[James G. Barnes <mail15077@pop.net>]

Good afternoon,

First a discussion, then a question:

DOE and NRC define the "radioactive" condition as "any detectable radioactive 
material."  Detectability is determined by the efficiency of the counter, 
background levels of that counter, and the total number of events detected by 
the system (directly related to count time).  These factors are generally 
expressed as a system's Minimum Detectable Activity, Lower Limit of Detection, 
or similar expression of the capability of a system.

If one has material with low levels of radioactive contamination, one would not 
detect it with an R-02 ion chamber, might detect it with a micro-R meter, and 
almost certainly would detect it with a GeLi system.  Thus the "any detectable" 
criteria is highly dependent on the instrument selected to perform the 
analysis.  In addition, the MDA of a GeLi system can be manipulated by 
manipulating the count times (the longer the count time, the lower the MDA).  
Thus, "any detectable" appears to be a moving target.  With significant 
processing costs dependent on a binary "clean"/"radioactive" status, the 
setting of the MDA has significant cost/benefit impact; too low an MDA 
engenders unnecessary disposal expense; too high an MDA could be challenged as 
technically unsupportable.

This sets the stage for the question(s).

Q1:  What process should be followed in establishing a counter's MDA for the 
purpose of releasing volumetrically contaminated materials from controls, i.e. 
how does one make the decision that the MDA is "low enough."  [Regulatory 
references would be appreciated]

Q2:  What are some typical MDAs currently in use for release of materials such 
as soil, water, etc.

Q3:  What level of validation is needed for establishing these values 
(documented derivation placed in file, regulatory concurrence, license 
amendment, etc.)


Thanks,

James Barnes, CHP
Radiation Safety Officer
Rocketdyne Division; Boeing North American

mail15077@pop.net