Development of Advanced Cermet Waste Forms

The growing interest in the expansion of nuclear energy in the United States is widely acknowledged. While public support for the expanded use of nuclear power is relatively high, the disposition of the resulting waste remains a significant concern. A Blue Ribbon Commission on America’s Nuclear Future has recently been established at the direction of the President to examine options for the permanent disposal of high-level nuclear waste. Waste forms other than glass for high-level-waste (HLW) disposal are expected to be included in this assessment. The Oak Ridge National Laboratory has been conducting research to develop a cermet waste form for the immobilization of the HLW generated in processing of used nuclear fuel. The cermet waste form will allow emplacement of the high-radioactivity, high decay heat–generating fission products, Cs/Ba and Sr/Y, along with other oxide-forming fission products in a ceramic or oxide form, distributed within a high-thermal-conductivity metallic matrix. The metallic phase will contain those waste components that are amenable to metal formation by simple hydrogen reduction of oxides, as well as the cladding and hardware materials (e.g., Fe, Cr, Ni, and Sn). This cermet waste form (1) will improve the heat transfer characteristics and reduce the centerline temperature and/or allow for increased waste loading and higher density when compared with a glass or ceramic waste form; (2) may result in significant cost benefits through the improvements to the heat transfer from the waste during decay heat storage; and (3) may simplify or eliminate some of the currently proposed upstream separations processes. The successful deployment of such waste forms may also facilitate an option of using the decay heat during an interim storage period for process and facility heating applications. To date we have demonstrated the production of several cermet materials from simulated waste streams.