UPDATE AND INSULATION TESTING FOR URANIUM HEXAFLUORIDE TRANSPORT OVERPACKS UNITED STATES DEPARTMENT OF TRANSPORTATION SPECIFICATION 21PF-l

The slightly enriched product UF6 shipped from the enriching plants for the world's nuclear power plants must be protected in order to conform to domestic and international transport regulations. The principal overpack currently in use is the US Department of Transportation (DOT) Specification 21PF-l which protects Model 30 UF6 cylinders (Title 49, Code of Federal Regulations, Part 178.121, Specification 2 1 PF-1 ; Fire and Shock Resistant, Phenolic-Foam Insulated, Metal Overpack. Specification 21 PF-1 (Horizontal Loading Overpack)). Operational problems have developed from both design and lack of maintenance, resulting in the entry of water into the insulation zone. In order to minimize this water entry, design modifications are necessary to the 21PF-l overpacks. Proposed modifications for existing overpacks are to be made only after any water absorbed within the phenolic foam insulation is reduced to an acceptable level. New 21PF-l overpacks will be fabricated under an enhanced design. In both cases, proposed quality assurance/ control requirements in the fabrication, modification, use and maintenance of the overpacks are applicable to fabricators, modifiers, owners and users. Design changes are reviewed in Part I. The phenolic foam is the thermal barrier of the protective overpacks, which maintains the UF6 below its triple point in the event of exposure to elevated temperatures. Evaluation of the thermal qualities of the overpack required extensive analytical modeling correlated with experimental measurement. An experimental programme was devised to measure the thermal conductivity and heat capacity of the phenolic foam from room temperature to approximately 147S°F (l073K). The test programme, which consisted of the guarded hot plate method for thermal conductivity and drop calorimetry for heat capacity determination, is reviewed in Part II.