Fabrication and characterization of silicon nitride-based inert matrix fuels sintered with magnesium silicates

The effects of sintering additives of magnesium silicates, i.e. enstatite (MgSiO3), steatite (MgSiO3) and forsterite (Mg2SiO4), on the sintering behaviors and characteristics of the silicon nitride ceramics-based inert matrix fuels (IMFs) were experimentally investigated. Fabrication tests and characterizations of Si3N4-based IMFs with the sintering additives were carried out using cerium oxide (CeO2) to represent minor actinide oxides. Sintered bodies were characterized in terms of their densities and thermal conductivities. In addition, a solubility test with hot nitric acid was carried out for evaluation of applicability to the existing reprocessing technology. The densification of sintered bodies was enhanced by using additives of magnesium silicates at relatively low sintering temperature. In particular, the relative density of Si3N4-based IMFs with Mg2SiO4 was above 90% at 1723 K. The thermal conductivities of Si3N4-based IMFs varied according to sintering temperature, and for the IMFs sintered at 1923 K were above 34 W/m K. The solubility test results revealed that only grain boundary phases in Si3N4-based IMFs can be dissolved into hot nitric acid.

► We proposed a new concept for the densification of Si3N4-based inert matrix fuels.
► We investigated the effect of magnesium silicates additives.
► High density of the fuels was achieved at relatively low sintering temperature.
► The thermal conductivities of fuels varied according to additives.
► The fuels properties depended on the amount of MgO in magnesium silicates.