Under the United Nations classification of dangerous goods, there are different classes. There are about nine classes. All the radioactive materials fall under class 7. That's a specific class for all types of radioactive nuclear materials. That's how it works. You can have class 1, which is explosives. You have liquids. You have solids. They're all classified under the United Nations classification model.
On February 11th, 2013. See this statement in context.