Optimization of Sintering Parameters for Nitride Transmutation Fuels

Abstract

One mission of the Advanced Fuel Cycle Initiative (AFCI) is to develop transmutation fuels (i.e. fuels capable of having their transuranic elements transmuted to a shorter-lived isotopes) in order to close the nuclear fuel cycle, thereby reducing: the U.S. inventory of civilian plutonium, the waste stored in geologic repositories, and the cost of nuclear waste management. Actinide mononitrides are potential transmutation fuel materials due to favorable properties such as high melting point, excellent thermal conductivity, high fissile density, suitability towards reprocessing, and good radiation tolerance'. In order to avoid the difficulties of working with actinide bearing materials, we have performed a processing study on ZrN. ZrN is isostructural (i.e. NaCl structure) with actinide nitrides, and is therefore a good surrogate compound. Furthermore, ZrN is a diluent in so-called non-fertile fuels, i.e. containing no uranium. The effects of sintering were investigated by varying both the sintering atmosphere and temperature in order to determine the effect on important properties such as density and nitrogen stoichiometry. The density and stoichiometry values were then compared to hardness and microstructure on similar samples. The results of these studies are presented in the context of the various issues associated with the design and fabrication of actinide-bearing nitride fuel forms.