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Transportation : Types of Transportation Casks
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Radioactive materials are grouped, for transportation purposes, according to quantity of radioactive material shipped, its physical form, its specific radioactivity, the energy of its emissions, and the half life (the specific radioactivity is related to the half-life), as regulated by the Nuclear Regulatory Commission (NRC) and the Department of Transportation. These factors determine the type of packaging used for transportation. No matter what type of packaging is used, the external radiation dose rate is limited to an amount that results in at most about 0.2% of background radiation to any member of the general public. Three different types of packaging are used: Industrial Packages, Type A Containers and Type B Containers.
Industrial Packages
Very low specific activity materials like slightly contaminated tools and other solid objects, mine waste, some medical and research radioisotopes, and waste from soil cleanup are transported as low-specific activity materials. The quantitative criteria for low-specific activity classification are described in the cited regulations. Low-specific activity material can be transported in ordinary strong industrial packaging appropriate to the physical nature of the material.
Type A Containers
Type A containers are small packages (about the size of a pint container) that contain low levels of radioactive material and are designed and tested to withstand the rigors of routine transportation, such as exposure to rain, rough handling, and slight mishaps, but not necessarily of transportation accidents. Since the radioactive material content is low, the hazard is low even if the container is badly damaged in an accident. All packaging is leak-tested and transported liquids are packaged to contain any spills, in the same manner as any transported hazardous liquid (e.g., acid in glass bottles). The NRC certifies Type A packages. Materials transported in type A packages are radioisotopes from the medical world, the industry, agriculture and research.
Type B Casks
Very radioactive material like irradiated (spent) nuclear fuel is transported in Type B casks, certified by the NRC to withstand severe accident conditions as well as conditions of normal transportation. Type B packages may have 10 inches of lead shielding to protect the environment from radiation, and weigh a ton.
These accident conditions include a drop of 30 feet onto an unyielding surface, a drop onto a metal pin 6 inches in diameter; engulfing fire at 1480°F that lasts half an hour; and immersion in water for eight hours. "Withstanding" these conditions means that in accident producing these conditions, a container will not release more than the allowed amount of its radioactive contents.
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