Evaluation of physical properties of simulated plutonium inert matrix fuel of varying densities with thermal shock experiments

The concept of inert matrix fuel (IMF) has been proposed to reduce the worldwide growing stockpiles of plutonium oxide (PuO2). Small disks of a simulated IMF were synthesized by a low-temperature fabrication route not exceeding 1050degC. The samples on a silicon carbide (SiC) base possessed theoretical densities (TD) ranging from 68% to 80%. Therefore coarse and fine SiC particles were mixed with a liquid polymer precursor that yielded a one-to-one Si-to-C ratio. Five weight percent of ceria (CeO2) were added to act as a surrogate for PuO2. The specimen received thermal shocks up to 900 K by applying the water-quenching method. The mechanical properties: Vickers hardness, fracture strength and fracture toughness were determined and compared to the published data of other IMF, UO2 and MOX fuels. Although the fuel possessed a significantly lower density, the mechanical properties proved to be adequate when compared to conventional UO2 fuel. The temperature shock resistance of the fabricated fuel was found to be exceptionally good. XRD analyses indicated a chemical reaction between CeO2 and the applied polymer precursor during the sintering process. A crystalline compound, namely a cerium oxysilicate was detected. (author)