Optimization of preparation process and study on the properties and microstructures of nuclear natural graphite powder for HTR pebble fuel elements

Abstract

Nuclear natural graphite powder (NNGP) is the key and main component in the matrix graphite (MG) of pebble fuel elements for high temperature gas-cooled reactors (HTRs). In this study, a modified lab-scale powder preparation process of NNGP proposed for the first time would contribute to a more efficient and lower energy-consumption preparation system. The optimized NNGP was successfully prepared by the modified process, whose properties and microstructures were comprehensively investigated. The results indicated that the optimized NNGP possessed a lower specific surface area, a higher graphitization degree and fewer structural defects. MG pebbles manufactured by the optimized NNGP exhibited higher crush strength and thermal conductivity, a lower corrosion rate, as well as better thermal stability during heat treatment. This indicated that the modified NNGP was conducive to improving the integrity and safety of MG pebbles.