Re: DOT regulations, Specific Activity

[larsongr@ornl.gov (Greg Larson)]

One of the key points associated with the DOT definition of 'specific
activity' (49 CFR 173.403) is the fact that the definition contains 2 parts:

1) Part 1 of the definition is associated with the standard specific
activity definition that we are all familiar with and that is converting
the activity of a specific radionuclide into its mass.  As stated in 49
CFR, "...the activity of the radionuclide per unit mass of that
radionuclide."  This portion of the definition is used to find, for
instance, how many grams of U235 you may have.
2) Part 2 of the definition refers to the specific activity of the material
that is contaminated.  As stated in 49 CFR, "...The specific activity of a
material in which the radionuclide is essentially uniformily distributed is
the activity per unit mass of the material."  This portion of the
definition is used to determine if the material exceeds 70 Bq/gm.  In
essence, from my use and application of the DOT regulations for a number of
years, this was also one of the factors behind the split of SCO and LSA
determinations.

One of the responses to this issue that I read indicated that you could
package a source in a heavy container and use the weight of the container
to cause the material to be less than 70 Bq/gm.  If you look at the Part 2
of the definition of specific activity it is clear that you can not use
this approach.  The specific activity is determined over the mass of the
material that is contaminated and if this is greater than 70 Bq/gm then DOT
considers it radioactive material.

This same line of thought applies to SCO materials.  With SCO, the
radioactive material is on the external or internal surfaces of an object.
This means the specific activity is determined only over the unit mass of
the material that is contaminated.  Which means that one can not use the
total mass of the SCO object, only that portion on the surface that is
contaminated in order to determine if the object is radioactive per DOT.
For this same reason, one can not look at this SCO object from the LSA
perspective and use the weight of the material that does not contain the
radioactive material to lower your specific activity to qualify as LSA and
not avoid the SCO subtype determination.

Also as Charles Smith has stated, this is only DOT's defintion of
radioactive material and is to be used strictly for transportation purposes
over public highways.  The whole purpose of the DOT regulations is to
ensure public safety during transport.  Because a material is not DOT
radioactive does not mean that it is NOT radioactive.  Other regulations
will apply when there is detectable radioactivity contained within the
material.

Thanks,

Greg Larson
Oak Ridge National Laboratory
Radioactive Solid Waste Operations Group
Waste Acceptance and Tracking Supervisor
Phone:  (423) 241-3273
E-mail:  larsongr@ornl.gov