Gas-cooled reactors

Gas-cooled reactors have been extensively developed in the United Kingdom and have also been used in several other countries. Current designs of gas-cooled reactor use an indirect closed cycle, as illustrated in Fig. 6.19. Carbon dioxide at a pressure of around 600 psi (42 kg cmis pumped through the core of the reactor and then to a heat exchanger (boiler) with water as the secondary coolant. The steam produced in the heat exchanger is used to drive the turbine. 

Carbon dioxide has the advantages of low cost and low neutron absorption cross section. The use of gas as coolant permits much higher core 

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The metal is a source of nuclear power. There is probably more energy available for use from thorium in the minerals of the earth s crust than from both uranium and fossil fuels. Any sizable demand from thorium as a nuclear fuel is still several years in the future. Work has been done in developing thorium cycle converter-reactor systems. Several prototypes, including the HTGR (high-temperature gas-cooled reactor) and MSRE (molten salt converter reactor experiment), have operated. While the HTGR reactors are efficient, they are not expected to become important commercially for many years because of certain operating difficulties. 

Coal can be processed to H2 by heat from a high temperature, gas-cooled reactor at a process efficiency of 60—70%. Process steps are coal hquefaction, hydrogasification of the Hquid, and steam reforming of gaseous products (179). 

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

As previously stated, uranium carbides are used as nuclear fuel (145). Two of the typical reactors fueled by uranium and mixed metal carbides are thermionic, which are continually being developed for space power and propulsion systems, and high temperature gas-cooled reactors (83,146,147). In order to be used as nuclear fuel, carbide microspheres are required. These microspheres have been fabricated by a carbothermic reduction of UO and elemental carbon to form UC (148,149). In addition to these uses, the carbides are also precursors for uranium nitride based fuels. 

The large physical size of the later Magnox stations, such as Wylfa, led to the development of the more compact advanced gas-cooled reactor (AGR) design [31] that could utilize the standard turbine generator units available in the UK, Stainless-steel clad, enriched uranium oxide fuel can tolerate higher temperatures... 

Fig. 4. A typical advanced gas-cooled reactor graphite core (Hinkley Point B under construction) [11].

In support of the development of graphite moderated reactors, an enormous amount of research has been conducted on the effects of neutron irradiation and radiolytic oxidation on the structure and properties of graphites. The essential mechanisms of these phenomena are understood and the years of research have translated into engineering codes and design practices for the safe design, construction and operation of gas-cooled reactors. 

Strizak, J.P. The effect of volume on the tensile strength of several nuclear-grade graphites. In Proceeding of the IAEA Specialists meeting on the Status of Graphite Development for Gas Cooled Reactors, IAEA-TECHDOC-690, IAEA, Vienna, 1993, pp. 233 240. 

Status of and Prospects for Gas-Cooled Reactors, IAEA Teeh Report No. 235, IAEA, Vienna, 1984. 

Malinauskus, A.P., de Nordwall, H.J., Dyer, F.F., Wichner, R.P., Martin, W.J. and Kolb, J.O., Fission product behavior during operation of the second Peach Bottom core. In Proceeding of the Symposium on Gas-Cooled Reactors with Emphasis on Advanced Systems, Vol. 1, IAEA-SM-200/50, IAEA, Vienna, 1976, pp. 237 249. 

Roedig, M., Status of HTR development in Germany. In Proceedings of the Specialists Meeting on The status of graphite development for gas cooled reactors, IAEA-TECDOC-690, Pub. IAEA, Vienna, 1993, 40 43. 

Kelly, B.T., The effect of radiolytic oxidation on the graphite moderator brick strength in advanced gas-cooled reactors, Nucl. Energy, 1984, 24(3), 265 272. 

Proceedings of a IAEA Specialists Meeting on the Status of Graphite for GAS Cooled Reactors, Tokai-mura, Japan, 1993... 

Cladding. The Magnox reactors get their name from the magnesium-aluminium alloy used to clad the fuel elements, and stainless steels are used in other gas-cooled reactors. In water reactors zirconium alloys are the favoured cladding materials. 

In the nuclear engineering field special magnesium-base alloys are extensively used as canning materials for uranium in gas-cooled reactors. 

In common with magnesium and zirconium the metal has little tendency to capture neutrons, and there was promise that a significant industrial use would arise in nuclear engineering, but after extensive trial in gas cooled reactors, its ultimate commercial employment in that context was also deemed inappropriate. 

In the gas-cooled reactor, reaction.between the coolant and the moderator results in formation of a proportion of carbon monoxide in the atmosphere. This gas can be carburising to nickel-base alloys but the results of tests in which CO2 was allowed to react with graphite in the furnace indicate that the attack on high-nickel alloys is slight, even at moderately high temperatures and is still mainly due to simple oxidation. 

AGR, advanced gas-cooled reactor PWR, pressurised water reactor... 

Other newer designs include the advanced, gas-cooled reactor (AGR), Canadian deuterium reactor (CANDUR), sodium-cooled reactor (SCR), sodium-heated reactor (SHR), and fast breeder reactor (FBR). These reactors employ either natural or enriched uranium fuels that may be modified in some way (e.g., graphite-moderated fuels). 

Morpholine is still the standard by which other amines are compared for pH control, and AMP has commonly been employed to control carbon steel boiler tube erosion-corrosion problems in European gas-cooled reactor stations. 

ABMA ACH AGR AMP AMP American Boiler Manufacturers Association aluminum chlorhydrate advanced gas-cooled reactor aminotri-(methylenephosphonic acid) 2-amino-2-methyl-l-propanol, AKA isobutanolamine... 

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