Advanced Csic Composites for High-Temperature Nuclear Heat Transport with Helium, Molten Salts, and Sulfur-Iodine Thermochemical Hydrogen Process Fluids

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Advanced CSiC Composites for High-Temperature Nuclear Heat Transport with Helium, Molten Salts, and Sulfur-Iodine Thermochemical Hydrogen Process Fluids (A Review)

A Ramesh
Assistant Professor
Department of Mechanical Engineering
Government Engineering College, Thrissur, Kerala, India
ramesh_gec71@rediffmail.com
Ph: 9447422303

Shillin K S
Department of Mechanical Engineering
Government Engineering College, Thrissur, Kerala, India shillin.ks@gmail.com Ph: 9995733157

Abstract
This present paper discusses the use of liquid-silicon-impregnated (LSI) carbon-carbon composites for the development of compact and inexpensive heat exchangers, piping, vessels and pumps capable of operating in the temperature range of 800 to 1100°c with high-pressure helium, molten fluoride salts, and process fluids for sulfur-iodine thermochemical hydrogen production. LSI composites have several potentially attractive features, including ability to maintain nearly full mechanical strength to temperatures approaching 1400°c, inexpensive and commercially available fabrication materials, and the capability of simple forming, machining and joining of carbon-carbon performs, which permits the fabrication of highly complex component geometries. LSI C/C-SiC composites are a potentially promising material for high-temperature heat exchangers and other flow-loop components. Potentially inexpensive and simple fabrication methods exit for compact plate-type heat exchangers. Carbon coating by CVI or CVD provides a route toward very low corrosion rates with molten fluoride salts, and because carbon is not wetted by noble metals, precipitation and fouling performance may also be good with molten salts. Extensive work has examined approaches to make carbon-carbon composites resistant to oxidation at high temperatures. Some of these approaches may provide acceptable barriers for use with process fluids for sulfur-iodine thermochemical production of hydrogen, making LSI C/C-SiC composite an interesting candidate material for the nuclear thermochemical production of hydrogen. In the near term, these materials may prove to be attractive for use with a molten-salt intermediate loop for the demonstration of hydrogen production with gas-cooled high temperature reactor. In the longer term, these materials could be attractive for use with the molten salt cooled Advanced HighTemperature Reactor, molten salt reactors, and fusion power plants.

1.Introduction
Molten salt reactors (MSRs) are liquid-fueled reactors that can be used for burning actinides, producing electricity, producing hydrogen, and producing fissile fuels (breeding). Fissile, fertile, and fission products are dissolved in a high-temperature, molten fluoride salt with a very high boiling temperature (~1400ºC). Two reactors were successfully built and operated in the 1950s and 1960s. A detailed conceptual design of a 1000 MW(e) reactor was developed. There is renewed interest in MSRs because of changing goals and new technologies. Three technologies, partly or fully developed since the 1970s, have been identified that may dramatically improve the economics and viability of MSRs: Brayton helium power cycles, compact heat exchangers, and carbon-carbon composites. A schematic of an MSR is shown in Fig.. The fluoride molten salt with dissolved fissile, fertile, and fission isotopes flows through a reactor core moderated by unclad graphite to a primary heat exchanger, where the heat is transferred to a secondary molten salt coolant. The fuel salt then flows back to the reactor core. The fission heat is deposited directly in the molten fuel. In traditional MSR designs, the liquid fuel salt enters the reactor vessel at 565EC and exits at 705EC and 1 atmosphere (coolant boiling point: -1400EC). The reactor and primary system are constructed of modified Hastelloy-N or a similar alloy to provide corrosion resistance to the molten salt. Volatile fission...
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