Determination of mechanical behavior of U3Si2 nuclear fuel by microindentation method

Purpose U3Si2 is under investigation as an accident tolerant fuel due to its advantageous thermo-physical properties, including; high uranium density, high thermal conductivity, and high melting temperature. However, mechanical data available for the fuel is limited. Vickers micro-indentation characterization was used to evaluate the mechanical properties of U3Si2 specimens of varying microstructure in order to determine the effect of sintering conditions on mechanical behavior. Methods A chemical etchant was applied in order to observe grain boundaries in the material. The microstructure surrounding the indentations was investigated using polarized light optical microscopy imaging, scanning electron microscopy imaging, and elemental analysis techniques. Results All U3Si2 samples cracked in a brittle manner with cracks adjacent to the indents. Cracks tend to propagate through grains rather than along grain boundaries. The Vickers hardness of the U3Si2 samples was between 414 HV and 678 HV. High porosity in the sample was associated with a lower hardness. The toughness of the samples was roughly the same amongst all U3Si2 samples, ∼1 MPa√m. Conclusions The hardness and fracture toughness of U3Si2 was found to be comparable to that of unirradiated UO2. Given that UO2 has a history of good experience in the nuclear industry, U3Si2's comparable cracking behavior and mechanical properties speak favorably for its anticipated performance in reactor.