Thorium Ceramic Fuels

Farkas, M.S., Storhok, V.W, Pardue, W.M., Smith, R.A., Veigel, N.D., Miller,N.E., Wright, T.R., Bames, R.H., Chubb, W., Lemmon, A. W., Berry, W.E., Rough, F.A, Fuel and Fertile Materials -Uranium Metal and Alloys - Plutonium - Thorium - Metal-Ceramic Fuels - Coated-Paiticle Fuel Materials - Uranium and Thorium Oxides - Uranium Carbides, Nitrides, Phosphides, Sulfides and Arsenides - Fuel-Water Reactions , Reactor Mater., 9(3), 151-165 (1966) (Assessment, Electr. Prop., Meehan. Prop., Phys. Prop., Transport Phenomena, 77)... 

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. 

Thorium is used to make ceramics, lantern mantles, and metals used in the aerospace industry and in nuclear reactions. Thorium can also be used as a fuel for generating nuclear energy. More than 30 years ago thorium oxides were used in hospitals to make certain kinds of diagnostic x-ray photographs. Further information on the properties and uses of thorium can be found in Chapters 3 and 4 of this profile. 

The high-temperature gas-cooled reactor (HTGR) is a thermal reactor that produces desired steam conditions. Helium is used as the coolam. Graphite, with its superior high temperature properties, is used as the moderator and structural material. The fuel is a mixture of enriched uranium and thorium in the form of carbide particles clad with ceramic coatings. 

Thorium dioxide Th02 is the form in which thorium is proposed for use as reactor fuel for light-water, heavy-water, and liquid-metal fast-breeder reactors. It is a stable ceramic that can be... 

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. 

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. 

The VHTR has two typical reactor configurations, namely the pebble bed type and the prismatic block type. Although the shape of the fuel element for two configurations are different, the technical basis for both configuration is same, such as the TRISO-coated particle fuel in the graphite matrix, foil ceramic (graphite) core structure, helium coolant, and low power density, in order to achieve high outlet temperature and the retention of fission production inside the coated particle under normal operation condition and accident condition. The VHTR can support alternative fuel cycles such as U—Pu, Pu, mixed oxide (MOX), and U—thorium (Th). 

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