Fabrication and structural stability of ZrC-SiC double layer TRISO coated particles

Since the SiC layer reacts with the fission product Pd to form Pd2Si at high temperature, which causes corrosion, resulting in a loss of 137Cs trapping ability of TRISO coated fuel particle. ZrC is an advanced ceramic material that is more stable than SiC at high temperatures due to its high melting point. ZrC is thermally stable with no phase transition up to 2850 .deg. C, has excellent corrosion resistance to Pd, and excellent radiation resistance. ZrC coating has a low diffusion coefficient for Pd and Cs at high temperatures, which makes it easy to prevent release of fission products. ZrC coating has been studied as a structural layer of TRISO coated fuel particles. The CVD-coated ZrC layer is difficult to fabricate by precisely controlling the stoichiometry so that defects such as free carbon and carbon vacancy are easily formed in the coating layer, which is likely to cause deterioration of mechanical properties. The CVD ZrC coating layer has a low high temperature strength, which makes it difficult to guarantee the structural integrity of TRISO coated fuel particles. In this study, ZrC-SiC double coating layer was proposed as a structural layer of TRISO coated particles to compensate for disadvantages of SiC and ZrC coating. The ZrC-SiC double coating layer should be fabricated with a ZrC coating layer on the IPyC layer and a SiC coating layer coated continuously on the ZrC coating layer. Using the FBCVD, ZrC and SiC layers were continuously coated to fabricate ZrC-SiC double layer TRISO coated particle. After annealing at 1800 ° C for 2hr, the ZrC-SiC double layer coating maintained its structural integrity and did not cause peeling or breakage of the coating. In the ZrC1+x-SiC double layer coating, the free carbon was mostly present between the interface of ZrC and SiC interfaces. In the ZrC1-SiC double layer coating, ZrC and SiC were in direct contact.