CASTOR containers, filled with processed radioactive waste, sit at a temporary storage facility in Gorleben, Germany, after the long train trip from France.
The CASTOR railroad cars and containers are extremely strong—but some level of risk remains with the transport of nuclear waste, Bunn said.
"What happens if an accident happens that is worse than [the casks] were designed to cope with—a higher-speed accident or a very hot fire?" he asked. "That's the safety issue.
"The security issue is an attack," Bunn continued. "What if somebody takes a rocket-propelled grenade and uses it to penetrate one of those canisters?
"Some studies show that you could do that and spread a little bit of radiation. And if the train happens to be going through an urban area at the time, you could get some nasty human doses."
(Related: "Idaho, U.S. Battle Over Nuclear Waste Dump.")