Characterization of Oxidic Fuel Debris Simulants with Different Compositions and Heat Treatments for Evaluation of Airborne Release During Fuel Debris Retrieval

抄録

From the standpoint of minimizing radiation exposure to both workers and the general public, it is imperative to gain a comprehensive understanding of the characteristics exhibited by the dust dispersed during the process of fuel debris retrieval. The dispersion behavior of dust is thought to be associated with material properties, simulated fuel debris samples were made with the intention of evaluating material properties. These were made dense enough to be suitable for such an evaluation and were exposed to high temperatures similar to those experienced by the actual fuel debris.

A series of simulated fuel debris samples were prepared by mixing uranium dioxide (UO₂) and zirconium dioxide (ZrO₂) in four different ratios (100:0, 90:10, 40:60, 15:85). Subsequently, the mixtures were subjected to sintering at 1700 °C, resulting in the production of pellet-shaped samples. Then the samples were observed under a scanning electron microscope coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), underwent X-ray diffraction (XRD) analysis. Additionally, the grain size, density, Young’s modulus, Vickers hardness, the oxygen-to-uranium (O/U) ratio were evaluated. Furthermore, fracture toughness was calculated from the obtained data. The observed phases in the samples followed the pseudo-binary equilibrium phase diagram of UO₂ and ZrO₂, with some variations noted upon additional heating at 2400 °C. In this study, two main trends in the changes in material properties, other than grain size and O/U ratio as a function of the composition ratio were identified. A significant discontinuity was observed at higher ZrO₂ ratios. These observations indicate that the properties of the samples are influenced by the primary matrix component.