Fuel for high temperatures

Fig. 2. Fuel for high temperature gas-cooled reactor. Fissile material is coated with carbon and siHcon carbide, fertile material with carbon. Particles mixed...

Uranium carbide UC (UC2 and U2C also exist) has a melting point of about 2300 °C and is an important nuclear fuel for high-temperature reactors. It is prepared by reduction of UO2 with carbon, followed by pressing and sintering. It can also be made by hot pressing of mixtures of uranium metal powder with graphite at 1000 to 1100 °C. A mixed carbide with ThC is manufactured in the form of spheroids by melting. As the product is hydrolyzed on exposure to air, it is coated with a protective carbon layer. 

M. T. Simnad, L. R. Zumwalt, eds., Materials and Fuels for High Temperature Nuclear Energy Applications, MIT Press, Cambridge, MA, 1964. 

At the beginning of the 1980s, the interest in DMFC arose and methanol was used as fuel for high-temperature fuel cells [12]. Nowadays, PEM fuel cells with Nafion as electrolyte appear to be well suited for the direct oxidation of methanol. There are, however, some major problems in adapting a PEMFC to operate with methanol. The catalytic material of the anode has to be improved in order to avoid the loss of activity because of the formation of by-products. As in the case of a PEMFC using hydrogen from a reformer as fuel, a method to improve the anodic material is the use of Pt-Ru or Pt-Ru-Sn mixtures [8]. A particular problem of the DMFC is cross-diffusion of methanol through the electrolyte. 

VAIDYA, V.N., Coated particle fuels for high temperature reactors - Indian, programme, Technical Meeting on Current Status and Future Prospects of Gas Cooled Reactor Fuels (Paper presented at IAEA Meeting, Vienna, Austria, 2004). SATHIYAMOORTHY, D., BARC, Personal communication. 2004-2005. PRASAD, C.S.R., BARC, Personal communication based on a report on hydrogen production, submitted to the Ministry for Non-conventional Energy Sources, India, 2004-2005. 

Cigolotti V, McPhail S, Moreno A (2009) Non-conventional fuels for high-temperature fuel cells status and issue. ASME J Fuel CeU Sci Tech 6(2)... 

Oak Ridge National Laboratory, November 2008. Deep Bum Development of Transuranic Fuel for High-Temperature Helium-Cooled Reactors. ORNL/TM-2008/205. 

For high temperature fuel ceUs, there is stiU a strong need to develop lower cost materials for ceU components. In the case of SOFCs, improved fabrication processes and materials that permit acceptable performance in fuel ceUs at lower operating temperatures are also highly desirable. 

Fluidized-bed CVD was developed in the late 1950s for a specific application the coating of nuclear-fuel particles for high temperature gas-cooled reactors. PI The particles are uranium-thorium carbide coated with pyrolytic carbon and silicon carbide for the purpose of containing the products of nuclear fission. The carbon is obtained from the decomposition of propane (C3H8) or propylene... 

Sol-gel techniques have been successfidly applied to form fuel cell components with enhanced microstructures for high-temperature fuel cells. The apphcations were recently extended to synthesis of hybrid electrolyte for PEMFC. Although die results look promising, the sol-gel processing needs further development to deposit micro-structured materials in a selective area such as the triple-phase boundary of a fuel cell. That is, in the case of PEMFC, the sol-gel techniques need to be expanded to form membrane-electrode-assembly with improved microstructures in addition to the synthesis of hybrid membranes to get higher fuel cell performance. 

Table 11 Composition, molecular weight, stoichiometric air-to-fuel ratio (.y), net heat of complete combustion (Ahc T), and maximum possible stoichiometric yields of major products (jitmax) for high temperature polymers... 

H2 production for fuel cell (high temperature solid fuel cell and molten carbonate) is also possible. 

Carbon Monoxide. Carbon monoxide, a fuel in high-temperature cells (MCFC and SOFC), is preferentially absorbed on noble metal catalysts that are used in low-temperature cells (PAFC and PEFC) in proportion to the hydrogen-to-CO partial pressure ratio. A particular level of carbon monoxide yields a stable performance loss. The coverage percentage is a function of temperature, and that is the sole difference between PEFC and PAFC. PEFC cell limits are < 50 ppm into the anode major U.S. PAFC manufacturers set tolerant limits as < 1.0% into the anode MCFC cell limits for CO and H20 shift to H2 and C02 in the cell as the H2 is consumed by the cell reaction due to a favorable temperature level and catalyst. 

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