Preparation of ZrC coating in TRISO fuel particles by precise transportation of solid precursor and its microstructure evolution

Very-high-temperature gas-cooled reactors (VHTRs) with outlet temperatures above 1273 K show higher thermal efficiencies, which require fuel elements to operate at higher temperatures. In such situations, the conventional silicon carbide (SiC) coatings in TRISO particles might not be able to adapt to such high temperatures, and zirconium carbide (ZrC) can function as a potential fission product barrier material. For ZrC coating, controlling the stoichiometric ratio is a key challenge in the preparation process in fluidized bed. In this paper, a novel solid precursor feeding mode was proposed, combining quantitative powder feeding with cold transport. By controlling the powder feeding rate of ZrCl4 and the flow rate of propylene, the C/Zr atomic ratio in ZrC coating was controlled accurately. ZrC coatings with different stoichiometric ratios were successfully prepared via fluidized-bed chemical vapor deposition (FB-CVD). The ZrC coatings were subjected to high temperature heat treatment for different times from 2473 to 2673 K under argon atmosphere and the microstructure and property evolutions after high-temperature heat treatment were investigated. The deposition mechanism of ZrC coating was proposed.