Processing of Graphite Reactor Fuels Containing Coated Particles and Ceramics

Potential processing methods for graphite-matrix nuclear reactor fuels which contain coated particles and/or ceramics are discussed. Both nonaqueous and aqueous processing methods are being developed. Fuels containing either uncoated or carbon-coated particles generally are first burned in oxygen at 800–1200 C to eliminate the graphite as CO₂ and convert the uranium, thorium and other metallic constituents of the fuel to their respective oxides. The combustion ash (oxides) can then either be treated by a nonaqueous volatility method or be dissolved or leached in a suitable aqueous reagent in preparation for decontamination and recovery of the fuel by solvent extraction. In the Fluoride Volatility and Chloride Volatility methods, the constituents of the ash are converted to the respective halides; decontamination and recovery is then achieved by selective volatilization in the fluoride volatility method and, possibly, with chloride volatility. The chlorides can also be dissolved in water in preparation for solvent extraction. Fuel particles coated with such materials as Al₂O₃, BeO and SiC can be separated from the graphite matrix by a variety of methods other than burning; for example, disintegration of the fuel in boiling 90% HNO₃ or anodic disintegration in dilute nitric acid. Special methods are then required for recovery of the fuel.