An exploration of measuring lower-length-scale structures in nuclear materials: Thermal conductivity of U-Mo fuel particle

The feasibility of utilizing the suspended bridge method, which was originally developed for one-dimensional or nearly-one-dimensional nanomaterials, to measure the thermal conductivity of lower-length-scale structures in nuclear materials is explored in this study. Nanoribbon specimens of stainless steel SS304, representing materials with well-known thermal conductivity, and atomized U-Mo alloy particles used in dispersion fuels for research reactors, representing new nuclear materials with limited thermal conductivity data reported, were made using focused ion beam (FIB). The contact thermal resistance was corrected by measuring a series of specimens with different bridge lengths. The measured thermal conductivity of SS304 was found to be consistent with that reported for bulk samples. The thermal conductivity of U-Mo particles measured using the suspended bridge method was also analyzed and compared with literature data of monolithic U-Mo alloys. Ab initio molecular dynamics (AIMD) was used to quantitatively demonstrate that the reduced specimen size only has marginal effects on the measured thermal conductivity compared to the bulk specimens. The novel concept of utilizing the suspended bridge method in nuclear material research is proven and future work is discussed.