Molten salts fuel salt, metallic materials

The excellent insulating and dielectric properties of BN combined with the high thermal conductivity make this material suitable for a huge variety of applications in the electronic industry [142]. BN is used as substrate for semiconductor parts, as windows in microwave apparatus, as insulator layers for MISFET semiconductors, for optical and magneto-optical recording media, and for optical disc memories. BN is often used as a boron dopant source for semiconductors. Electrochemical applications include the use as a carrier material for catalysts in fuel cells, electrodes in molten salt fuel cells, seals in batteries, and BN coated membranes in electrolysis cells for manufacture of rare earth metals [143-145]. 

Electrochemical applications of a-BN include its use as carrier material for catalysts in fuel cells [297], as a constituent of electrodes in molten salt fuel cells [298, 299], as anticracking particles in the electrolyte for molten carbonate fuel cells [300, 301], and in seals for insulating terminals of Li/FeS batteries from the structural case [302], A BN-coated membrane is used in an electrolysis cell for the manufacture of high-purity rare earth metals from salt melts [381]. A porous boron nitride layer is applied to the upper outer surface of the electrolyte tube in sodium-sulfur batteries [303], and ceramic boron nitride separators are used in liquid fuel cells and batteries [304, 305]. Boron nitride powder may be included in the electrolyte of electrolytic capacitors for high-frequency utilization [306]. 

Molten Carbonate Fuel Cell. The electrolyte ia the MCFC is usually a combiaation of alkah (Li, Na, K) carbonates retaiaed ia a ceramic matrix of LiA102 particles. The fuel cell operates at 600 to 700°C where the alkah carbonates form a highly conductive molten salt and carbonate ions provide ionic conduction. At the operating temperatures ia MCFCs, Ni-based materials containing chromium (anode) and nickel oxide (cathode) can function as electrode materials, and noble metals are not required. 

Molten Carbonate Fuel Cell The electrolyte in the MCFC is a mixture of lithium/potassium or lithium/sodium carbonates, retained in a ceramic matrix of lithium aluminate. The carbonate salts melt at about 773 K (932°F), allowing the cell to be operated in the 873 to 973 K (1112 to 1292°F) range. Platinum is no longer needed as an electrocatalyst because the reactions are fast at these temperatures. The anode in MCFCs is porous nickel metal with a few percent of chromium or aluminum to improve the mechanical properties. The cathode material is hthium-doped nickel oxide. 

It is usual to operate an aqueous-medium fuel cell under pressure at temperatures well in excess of the normal boiling point, as this gives higher reactant activities and lower kinetic barriers (overpotential and reactant diffusion rates). An alternative to reliance on catalytic reduction of overpotential is use of molten salt or solid electrolytes that can operate at much higher temperatures than can be reached with aqueous cells. The ultimate limitations of any fuel cell are the thermal and electrochemical stabilities of the electrode materials. Metals tend to dissolve in the electrolyte or to form electrically insulating oxide layers on the anode. Platinum is a good choice for aqueous acidic media, but it is expensive and subject to poisoning. 

The tetrahalides are the thorium halides of greatest practical importance. The tetrafluoride ThF4 is the preferred starting material for large-scale production of thorium metal (Sec. 10.4). ThF4 has been proposed as fertile material in the fuel mixture of the molten-salt reactor. The tetraiodide has been used as feed material in the iodide process for making very pure thorium metal (Sec. 10.4). 

The second edition of this handbook contains some new and updated information including chapters on liquid metal cooled fast reactors, liquid fueled molten salt reactors, and small modular reactors that have been added to the first section on reactors. In the second section, a new chapter on fuel cycles has been added that presents fuel cycle material generally and from specific reactor types. In addition, the material in the remaining chapters has been reviewed and updated as necessary. The material in the third section has also been revised and updated as required with new material in the thermodynamics chapter and economics chapters, and also includes a chapter on the health effects of low level radiation. 

The two types of high temperature fuel cell are quite different from each other (Table 6). The molten carbonate fuel cell, which operates at 650°C, has a metal anode (nickel), a conducting oxide cathode (e.g. lithiated NiO) and a mixed Li2C03/K2C03 fused salt electrolyte. Sulphur attack of the anode, to form liquid nickel sulphide, is a severe problem and it is necessary to remove H2S from the fuel gas to <1 ppm or better. However, CO is not a poison. Other materials science problems include anode sintering and degradation, corrosion of cell components and evaporation of the electrolyte. Work continues on this fuel cell in U.S.A. and there is some optimism that the problem will be solved within 10 years. 

Because of the small reactivity margin available for breeding in a thermal reactor, the use of the thorium cycle has mainly been associated with reactors with very good neutron economy based on low parasitic absorption, such as the high-temperature gas-cooled reactor, where graphite is used in place of metal for the fuel cladding, or heavy water reactors, with very low moderator absorption. A special case is the molten salt breeder reactor, where circulation of the fissile and fertile materials allows continuous removal not only of Pa but also of fission products. 

For high-temperature operations, materials, and fuels are key technologies. There is a century of large-scale experience in the use of fluoride molten salts. Aluminum is made by electrolysis of a mixture of bauxite and sodium aluminum fluoride salts at 1000 C in large graphite baths. Fluoride salts are compatible with graphite fuels. A smaller nuclear experience base exists with molten fluoride salts in molten salt reactors. Nickel alloys such as modified Hastelloy-N have been qualified for service to 750 C. A number of metals and carbon-carbon composites have been identified for use at much higher temperatures however, these materials have not yet been fully developed or tested for such applications. 

This book will introduce the materials considered for the different structural components of the Generation IV systems, under high doses of irradiation such as fuel cladding, wrapper tubes, internal structures, lower doses such as pressure vessel, or no irradiation such as the power conversion systems. It will deal with the behavior in the different environments encountered, liquid metals, molten salts, supercritical water, and gas, as well as the behavior under mechanical stress and irradiation. Subsequently, the different classes of materials for in-core and out-of-core applications will be discussed. 

Gas diffusion electrode — (also gas fed electrode) Electrode employed in fuel cells, - electrolysers, and - sensors. The electrode is a porous body prepared in various ways from a variety of materials [i]. Hydrophilic electrodes are mostly made from metals (e.g., nickel). The material is finely dispersed (e.g., by the Raney process) and manufactured into a sheet or plate. Depending on the wetting properties and the pore size, large pores will be wetted and subsequently filled by the electrolyte solution (or molten electrolyte salt), fine pores are not filled... 

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