One option for the long-term disposition of excess weapons plutonium involves vitrification, which entails combining the plutonium with radioactive high-level wastes and glass frit in a melter and then filling small stainless steel “cans” with the molten mixture. Several of these cans are then placed on a “rack” within larger stainless steel canisters, which are subsequently filled with molten high-level waste glass (HLWG) for security against theft. This disposition alternative is referred to as the “Can-in-Canister” option . Of particular concern is the ability of the molten HLWG to flow around the Pu-cans and their support structure to form a proliferation barrier. The canister filling process is investigated experimentally using room temperature model fluids as well as molten HLWG surrogates. Also, analytical results obtained from thermal models and detailed simulations show the role of heat transfer on the temperature distribution within the HLWG, and consequently on the strongly temperature dependent viscosity of the HLWG and its ability to flow and fill the canister.
Creep fracture behavior has been studied in Al-Mg and Al-Mg-Mn alloys undergoing solute-drag creep and in microduplex stainless steel undergoing both solute-drag creep and superplastic deformation. Failure in these materials is found to be controlled by two mechanisms, neck formation and cavitation. The mechanism of creep fracture during solute-drag creep in Al-Mg is found to change from necking-controlled fracture to cavitation controlled fracture as Mn content is increased. Binary Al-Mg material fails by neck formation during solute-drag creep, and cavities are formed primarily in the neck region due to high hydrostatic stresses. Ternary alloys of Al-Mg- Mn containing 0.25 and 0.50 wt % Mn exhibit more uniform cavitation, with the 0.50 Mn alloy clearly failing by cavity interlinkage. Failure in the microduplex stainless steel is dominated by neck formation during solute-drag creep deformation but is controlled by cavity growth and interlinkage during superplastic deformation. Cavitation was measured at several strains, and found to increase as an exponential function of strain. An important aspect of cavity growth in the stainless steel is the long latency time before significant cavitation occurs. For a short latency period, cavitation acts to significantly reduce ductility below that allowed by neck growth alone. This effect is most pronounced in materials with a high strain-rate sensitivity, for which neck growth occurs very slowly.