Silicon carbide corrosion in high-temperature gas-cooled reactor fuel particles

The silicon carbide (SiC) layer in Triso-coated high-temperature reactor fuel particles is occasionally attacked during irradiation by fission products generated within the kernel material. Investigations to define the cause of the SiC corrosion included ceramographic, microradiographic, and microanalytical studies on irradiated and unirradiated coated particles of various kernel compositions. The results of these studies showed that the presence of chlorine within the particle, in combination with certain metallic fission products or uranium, can lead to corrosion of the SiC layer. These results provided the basis for establishing a model that relates the transport of fission products as volatile metal chlorides and their chemical reaction with the SiC coating. In addition, this model is consistent with the fact that under the influence of a thermal gradient, corrosive attack of the SiC occurs on the cooler side of the particle. The correlation between the occurrence of SiC corrosion during irradiation and heavy-metal transport observed in thermal gradient annealing studies of unirradiated particles of the same batch constitutes the basis for a new method for quality control