Evaluating quantitative 3-D image analysis as a design tool for low enriched uranium fuel compacts for the transient reactor test facility: A preliminary study

Abstract

3-D image analysis when combined with a non-destructive examination technique such as X-ray computed tomography (CT) provides a highly quantitative tool for the investigation of a material's structure. In this investigation 3-D image analysis and X-ray CT were combined to analyze the microstructure of a preliminary sub-sized fuel compact for the Transient Reactor Test Facility's low enriched uranium conversion program to assess the feasibility of the combined techniques for use in the optimization of the fuel block fabrication process.The quantitative image analysis focused on determining the size and spatial distribution of the surrogate fuel particles and the size, shape, and orientation of voids within the compact. Additionally, the maximum effect of microstructural features on heat transfer through the carbonaceous matrix of the preliminary compact was estimated.The surrogate fuel particles occupied 0.8% of the compact by volume with a log-normal distribution of particle sizes with a mean diameter of 39μm and a standard deviation of 16μm. Roughly 39% of the particles had a diameter greater than the specified maximum particle size of 44μm suggesting that the particles agglomerate during fabrication. The local volume fraction of particles also varies significantly within the compact, although uniformities appear to be evenly dispersed throughout the analysed volume. The voids produced during fabrication were on average plate-like in nature with their major axis oriented perpendicular to the compaction direction of the compact. Finally, the microstructure, mainly the large preferentially oriented voids, may cause a small degree of anisotropy in the thermal diffusivity within the compact. α∥/α⊥, the ratio of thermal diffusivities parallel to and perpendicular to the compaction direction are expected to be no less than 0.95 with an upper bound of 1.