Fluidised-bed Chemical Vapour Deposition Process

Fluidised-bed CVD is a special technique to coat nuclear-fuel particles for high-temperature gas-cooled nuclear reactors which was developed in the late 1950s. This technique has also been used in other applications, such as the production of biomedical components (e.g. heart valves deposited by pyrolysis carbon) and some special functional coatings on ceramic particles. 

Vacuum Covers for Yarn Feed and Collection Apparatus 

In practice the minimum gas flow velocity is used, which corresponds to the critical pressure drop required for fluidisation. If the particle size is larger than 100 pm, then the minimum gas velocity (umf) is calculated by the following equation [65]  

If the size of particles is smaller than 100 pm, then the minimum gas velocity is 

The buffer layer is a low-density pyrocarbon layer. The density is less than 1.05 g em 3 and the thickness is 95 20 pm. This layer is deposited with C2H2 as the reactant gas. Due to the relatively low density, the buffer layer can provide the void volume for the gaseous fission products and fuel swelling as well as the accommodation for the kernel dimensional change. 

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