Research and development on coated fuel particle for HTR-10

The 10MW high temperature gas cooled reactor (HTR-10) was constructed in China. The HTR-10 uses spherical all-ceramic fuel elements with TRISO type coated fuel particle. The TRISO coated fuel particle consists of a microspherical fuel kernel and coating layers of a porous pyrolytic carbon, an inner dense pyrolytic carbon, a pyrolytic silicon carbide and an outer dense pyrolytic carbon. The advanced coating technology of using a gas mixture of propylene (C3H6) and acetylene (C2H2) and the successive four-layer coating processes were developed. The relationship between the coating parameter and the properties of the coated fuel particles has been systematically investigated. The optimum coating technology was obtained. The TRISO type coated fuel particles with the properties fulfilling the design specification for the HTR-10 have been fabricated by chemical vapour deposition in a 150 mm diameter fluidized bed coating furnace. The microstructure of coated fuel particles was observed by using SEM (scanning electron microscope). The failure rate of as-fabricated coated fuel particles is 3.4 x 10-6. The result of irradiated tests, the fission gas release to birth ratio R/B is about 1 x 10-6, confirms that the quality of the coated fuel particles can meet the requirement of the safety operation for the HTR-10