Iran has agreed to ship 2.65 tons of low-enriched uranium to Turkey in exchange for the right to receive 265 pounds of 20 percent enriched uranium a year later from Russia and France. Iran has entered into and reneged on similar agreements in the past, so no one knows if the swap will actually happen. But, assuming the Iranians are on the level, how will the Russians and the French ship 265 pounds of enriched uranium to Tehran?
Probably in a tractor-trailer. In the United States, Western Europe, and Asia, most radioactive material is shipped by truck. Trains are more popular within Russia, but the cross-border shipment to Iran is more likely to happen over the roads. Two-hundred-sixty-five pounds of enriched uranium takes up a little less space than your average office copier and is only slightly more dangerous if you keep adequate space between the 60-by-6-by-1-centimeter plates. (The actual uranium, a compressed disk of black granules, is encased inside a zinc alloy jacket.) Uranium-235 is always emitting neutrons here and there. As long as there aren't too many other U-235 atoms in the vicinity, the neutrons drift off harmlessly. Pack too much nuclear fuel in a small space, though, and you might see a spontaneous chain reaction. As a security measure, shipping containers include plenty of neutron-absorbing spacers and a thick layer of shock-absorbing material to prevent a gob of uranium from forming in the event of a crash. A chain reaction is unlikely, however, as there are thousands of nuclear fuel shipments worldwide every year and there has never been a nuclear reaction during transport.
Under World Nuclear Transport Institute guidelines, nuclear shipping containers must pass a series of bruising tests before taking to the road, rails, sea, or air. Quality inspectors drop the containers from 30 feet onto a concrete surface, then subject them to a compressive force equal to five times their own weight for 24 hours. Testers drop a 13-pound bar onto the cylinders from three feet. The canister is thrust into a fire for 30 minutes, then immersed in 50 feet of water for eight hours. Each ordeal is followed by a test to make sure the container hasn't gotten too leaky. Unfortunately, not all nuclear shipping companies belong to the WNTI, and the I nternational A tomic E nergy A gency lacks the authority to enforce its own, similar container-testing requirements. So we can't be sure that there aren't substandard nuclear shipping containers out there.
While governments aren't too keen to disclose the measures that are taken to protect the shipments from criminals, many provide armed security, require security clearances for drivers, and closely monitor the shipments using GPS. As with container quality, though, there is no enforcement mechanism to punish states with lax security.
A couple hundred pounds of unused nuclear fuel doesn't emit enough radiation to endanger a trucker, even if he hauls it 1,500 miles in his Lada. Spent fuel is significantly more dangerous. In a nuclear reactor, enriched uranium decays into forms of iodine, cesium, cobalt, and plutonium that produce far more radiation than the original fuel. To put the difference into perspective, consider that nuclear-power-plant technicians keep fresh fuel in ordinary storage rooms, while they submerge the spent stuff in pools lined with steel-reinforced concrete for about a decade, then move it into tornado-proof casks.
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Explainer thanks Scott Burnell and David McIntyre of the Nuclear Regulatory Commission.