内容摘要：Generating nuclear power requires moving spent radioactive fuel safely over thousands of miles from

Generating nuclear power requires moving spent radioactive fuel safely over thousands of miles from reactor sites for reprocessing or disposal. To ensure that this is being carried out with the minimum of risks, Sandia National Laboratories (SNL) recently completed a nuclear "triathlon" that involved moving a simulated cargo of spent fuel rods over 14,500 miles to record the stress and jolts that fuel undergoes in transit.

According to SNL, up to 2,600 tonnes of spent fuel is produced by the reactors that supply the United States with 20 percent of its electricity. Transporting this fuel is a serious and delicate operation because it not only involves containing the fuel rods in line with the strict regulations of the International Atomic Energy Agency (IAEA), but it must also be done in a way that reassures the public that every possible precaution is being taken.

For over 30 years, the consignments have been stored in 125-tonne Type B casks, which contain up to about 24 tonnes of used fuel in the form of fuel rod assemblies. These consist of rectangular bundles of zirconium rods stuffed with fuel pellets of enriched uranium 235 or plutonium. The casks are forged out of solid steel with heavily gasketed steel hatches held on by specially reinforced pins that can withstand 100 tonnes of force each. When loaded and sealed, these casks are so strong that they can take a direct hit at their weakest point by a 100 tonne diesel locomotive traveling at 100 mph (160 km/h) and still come away with little more than scratches and superficial dents.

The problem today is that the fuel rods themselves are very fragile. Sitting inside the intense radioactive environment of a critical nuclear reactor for several years, the metal cladding of the rods becomes very brittle and the assemblies require careful handling if they're not to shatter. A similar problem occurs in any routine transportation of fuel rods, where repeated strains place them in danger of unexpectedly snapping.