Uranium oxide fuel, chemical system

Fuel. The nuclear fuel cycle starts with mining of the uranium ore, chemical leaching to extract the uranium, and solvent extraction with tributyl phosphate to produce eventually pure uranium oxide. If enriched uranium is required, the uranium is converted to the gaseous uranitim hexafluoride for enrichment by gaseous diffusion or gas centrifuge techniques, after which it is reconverted to uranium oxide. Since the CANDU system uses natural uranium, I will say no more about uranium enrichment although, as I m sure you appreciate, it is a major chemical industry in its own right. 

The fuel was a mixture of oxides of thorium and uranium-235 (THUD fuel), a material expected to have high physical and chemical stability in a reactor atmosphere, and to offer possibilities of breeding in a boiling water power system. Small cylinders of this mixture were pressed, sintered and stacked inside aluminum to form a fuel pin 60 inches long and -q inch ta diameter. Two versions of this fuel were available in quantity, the first having a thorium to uranium-235 atomic ratio of 25 1 the second an atomic ratio of 50 1. ... 

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