Answer to Question #11107 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
With regard to the transport of radioactive labeled packages in air transportation, I have been briefed as to limits placed on the TI, transportation index. What is lacking in the information I have received is the amount of time of exposure plays with regard to the index on the labeled packages being transported. Is distance away from the item being shipped the primary concern? Or is there a time associated with the index as well?
There is a requirement for "separation distance" between a radioactive labeled package and a person, which reduces exposure. Shippers are only required to label packages based on the surface and 1 meter radiation dose rate and whether it is transported by nonexclusive use (common carrier) or an exclusive use (contract carrier) vehicle.
If you want to read the assumptions in preparing the TIs, you can read through this 198-page document, NUREG-0170, Final Environmental Statement on the Transportation of Radioactive Material by Air and Other Modes. It provides the basis and assumptions made for the calculations that demonstrate the adequacy of the Transport Indices of those regulations to provide safety assurance.
This is the information provided on the Nuclear Regulatory Commission website:
"Labels are used to visually indicate the type of hazard and the level of hazard contained in a package. Labels rely principally on symbols to indicate the hazard.
Although the package required for transporting radioactive material is based on the activity INSIDE the package, the label required on the package is based on the radiation hazard OUTSIDE the package. Radioactive material is the only hazardous material which has three possible labels, depending on the relative radiation levels external to the package. Also, labels for radioactive material are the only ones which require the shipper to write some information on the label. The information is a number called the Transport Index (TI), which, in reality, is the highest radiation level at 1 meter from the surface of the package.
The three labels are commonly called White I, Yellow II, and Yellow III, referring to the color of the label and the Roman numeral prominently displayed. A specific label is required if the surface radiation limit and the limit at 1 meter satisfy the following requirements:
|Label||Surface Radiation Level||Radiation Level at 1 Meter|
|White I||Does not exceed 0.5 mrem/hr||Not applicable|
|Yellow II||Does not exceed 50 mrem/hr||AND||Does not exceed 1 mrem/hr|
|Yellow III||Exceeds 50 mrem/hr||OR||Exceeds 1 mrem/hr|
Since the TI is the radiation level at 1 meter, it is clear that a White I label has no TI. A Yellow II must have a TI no greater than 1, and a Yellow III may have a TI greater than 1.
Referring to the radiation limits for vehicles, it can be seen that the maximum TI for non-exclusive use vehicles (common carriers) and for exclusive use (contract carriers) open vehicles is 10. The radiation level at 1 meter from the surface of a package can exceed 10 mrem/hr only if the package is transported in an exclusive use (contract carrier) closed vehicle."