Thermal stability of fission gas bubble superlattice in irradiated U-10Mo fuel

To investigate the thermal stability of the fission gas bubble superlattice, a key microstructural feature in both irradiated U-7Mo dispersion and U-10Mo monolithic fuel plates, a focused ion beam-transmission electron microscopy (FIB-TEM) sample of irradiated U-10Mo fuel with a local fission density of 3.5 × 1021 fissions/cm3 was used for an in-situ heating TEM experiment. The temperature of the heating holder was raised at a ramp rate of approximately 10 °C/min up to ∼700 °C, kept at that temperature for about 34 min and further increased to 850 °C with a reduced rate of 5 °C/min. The result shows a high thermal stability of the fission gas bubble superlattice. The implication of this observation on the fuel microstructural evolution and performance under irradiation is discussed.