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18 March 2010

Answer to Question #6767 Submitted to "Ask the Experts"

Category: Radioactive Waste Disposal

The following question was answered by an expert in the appropriate field:

Please clarify the meaning of this statement in a community newspaper: "One of the greatest hazards to residents comes from the trucking of highly toxic, radioactive material through our streets. Besides long-term radioactive contamination caused by radiation from the trucks, a criticality could occur if enriched uranium came into contact with water in a serious road accident." Does the reference to the contamination from the truck mean (1) that any material, liquid or solid, which is loaded into the truck after the radioactive material is removed becomes radioactive as well and (2) that the truck itself is now radioactive and therefore poses a serious health risk to the people who come in contact with it?

To be blunt, there is so much misinformation in the brief statement from the newspaper you sent, it is difficult to know where to begin. Without knowing the nature of the material being shipped through your community, I can't speak definitively to the risk of long-term contamination. However, in my experience, shipments of radioactive material are subjected to intense scrutiny and rigorous inspections. This should include surveys of the trucks before, during, and after transport of their cargo. The purpose of such surveys is to ensure that no radioactive contamination has resulted. Assuming that such surveys are properly conducted, the risk of contamination, especially to levels that would pose a hazard, is pretty remote.

The statement also mentions enriched uranium. Accepting the accuracy of this statement for the moment—though I have grave suspicions about it—a criticality is highly unlikely even if such material were to come into contact with water. Water, or some other suitable moderator, is one ingredient required to cause a criticality but others include sufficient quantities of fissile material (like enriched uranium) and, importantly, a very specific arrangement of the fissile material and moderator known as a critical geometry. It is highly unlikely that (1) highly enriched uranium (suitable for achieving criticality) is being shipped through your community, (2) sufficient quantities to achieve a criticality are being shipped together, (3) an accident would occur such that enriched uranium would come into contact with water or some other moderator (in no small part because the transport containers for such material are designed to withstand high-speed impacts and high-temperature fires), and finally that (4) a critical geometry would be achieved by chance in an accident scenario.

I hope this helps ease your concerns.

Brant Ulsh, PhD, CHP

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