Oxide fuels thorium dioxide

In simple oxides, the actinides are most stable in the +4 oxidation state the dioxides, An02, are known for all elements thorium through californium. Although the properties of Th02, U02, and Pu02 are especially important in nuclear technology, complex actinide oxides (oxides with one or more metal ions in addition to an actinide) are also important since they may be found as fission products in nuclear fuels and they are models for possible matrices in which nuclear wastes will be stored. 

EINECS 215-225-1 HSDB 6364 Thoria Thorianite Thorium anhydride Thorium dioxide Thorium oxide Thorium oxide (Th02) Thorotrast Thortrast Umbrathor. Used in ceramics, gas mantles, nuclear fuel, medicine and non-silica optical glass. White crystalline powder mp = 3390 d = 10.0 insoluble in H2O carcinogen. 

As far as reprocessing in the U/Pu fuel cycle is concerned, several chemical separation techniques have been proposed and developed in the past few decades. The most efficient process to date remains the PUREX process (Plutonium and Uranium Recovery by Extraction). This process uses nitric acid HNO3 and organic solvents to dissolve and extract selectively U and Pu, resulting in two separate product streams (U on one side and Pu on the other side of the process chain). As far as reprocessing in the Th/ U fuel cycle is concerned, THOREX (Thorium Oxide Recovery by Extraction) technology must be used, also based on dissolution in nitric acid and solvent extraction (however, with special care for the extraction of Pa, for the separa-tion of U and U, and for the dissolution of thorium dioxide in pure nitric acid). 

Considering chemical structures of ceramic fuels, these fuels can be categorized as oxide fuels, carbide fuels, and nitride fuels. Oxide fuels such as UO2, mixed oxide (MOX), and thorium dioxide (Th02) have low thermal conductivities compared to carbide and nitride fuels. Hence, from the heat transfer point of view, oxide fuels can also be identified as low thermal conductivity fuels. On the other hand, carbide (eg, UC and UC2) and nitride (eg, UN) fuels are identified as high thermal conductivity fuels. Table 18.3 lists basic properties of these fuels at 0.1 MPa and 25°C. 

Carbides of the Actinides, Uranium, and Thorium. The carbides of uranium and thorium are used as nuclear fuels and breeder materials for gas-cooled, graphite-moderated reactors (see Nuclearreactors). The actinide carbides are prepared by the reaction of metal or metal hydride powders with carbon or preferably by the reduction of the oxides uranium dioxide [1344-57-6] UO2 tduranium octaoxide [1344-59-8], U Og, or thorium... 

The basic nuclear reactor fuel materials used today are the elements uranium and thorium. Uranium has played the major role for reasons of both availability and usability. It can be used in the form of pure metal, as a constituent of an alloy, or as an oxide, carbide, or other suitable compound. Although metallic uranium was used as a fuel in early reactors, its poor mechanical properties and great susceptibility to radiation damage excludes its use for commercial power reactors today. The source material for uranium is uranium ore, which after mining is concentrated in a "mill" and shipped as an impure form of the oxide UjO (yellow cake). The material is then shipped to a materials plant where it is converted to uranium dioxide (UO2), a ceramic, which is the most common fuel material used in commercial power reactors. The UO2 is formed into pellets and clad with zircaloy (water-cooled reactors) or stainless steel (fast sodium-cooled reactors) to form fuel elements. The cladding protects the fuel from attack by the coolant, prevents the escape of fission products, and provides geometrical integrity. 

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