High temperature thorium fueled reactor

A second type of GCR used the pebble bed concept with helium as a coolant. The uranium and thorium fuel was imbedded in graphite spheres and cooled with helium. The high temperature thorium fueled reactor (THTR) operated between 1985 and 1989 in Germany. It produced 760 MWt and 307 MWe. The thorium in the fuel pellets was used to breed Two GCR power plants have been operated in the United States. The first was Peach Bottom Unit 1, which provided 40 MWe. The second was the Fort St. Vrain reactor, which provided 330 MWe. 

The search for a liquid for use at high temperatures and low pressures in a fluid-fueled reactor led to the choice of either fluorides or chlorides because of the requirements of radiation stability and solubility of appreciable quantities of uranium and thorium. The chlorides (based on the isotope) are most suitable for fast reactor use, but the low thermal-neutron absorption cross section of fluorine makes the fluorides a uniquely desirable choice for a high-temperature fluid-fueled reactor in the thermal or epithermal neutron region. 

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. 

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... 

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 carbides (ThC, ThC2) and uranium carbides (UC, UC2) exhibit metallic properties, but in other properties differ significantly from the carbides of the subgroups of the IVth, Vth and Vlth groups of the periodic table. Their hardnesses are substantially lower (see Table 5.6-1), they are pyrophoric and are easily hydrolyzed in water or weak aeids. Their only economic importance is as carbidie fuels in nuelear technology, particularly for high temperature and breeder reactors which are currently in the evaluation phase. 

The dicatbide, either by itself, mixed with uranium dicarbide, or in solid solution with uranium dicarbide, is used as fuel material in some versions of high-temperature gas-cooled reactors. Like uranium carbides, the thorium carbides react rapidly with water or moist air and must be protected from moisture in storage and fuel fabrication. 

Thorium makeup requirements for one reactor system, the HTGR (high-temperature gas-cooled reactor), may be estimated from Fig. 3.33. A 1000-MWe HTGR requires 7.4 MT of thorium as feed pet year. Reprocessing recovers 6.8 MT, which can be recycled after storage for 20 to 30 years to permit excess Th to decay. The net thorium consumption of a 1000-MWe reactor then is 0.6 MT/year. Thus, the 441,000 MT of U.S. ThOa thorium reserves listed in Table 6.14 would provide thorium fuel for... 

The LS-VHTR uses the same type of coated-particle graphite-matrix fuel that has been successfully used in high-temperature gas-cooled reactors such as the Peach Bottom Reactor, the Fort St. Viain Reactor (FSVR), the Arbeitsgemeinshaft Versuchsreaktor (AVR), and the Thorium High-Temperature Reactor (THTR). At this time, graphite-based fuels have been demonstrated to be compatible with only two coolants helium and fluoride salts. 

A standard fuel cycle of high temperature gas cooled reactors could be used as basic option for the FBNR. A variety of alternative fuel cycle options could be used according to the demand. These include a plutonium burner mode using plutonium-thorium oxide fuel and a closed fuel cycle based on U-Th. 

Experience of the Th -U cycle was first obtained in the Indian Point boiling water reactor, where the first core, loaded in 1962, contained pellets of urania-thoria mixture. The main interest, however, has centered on its use in the high-temperature gas-cooled reactor (HTGR), and thorium has been employed as fertile material both in the prismatic fuel elements of the Dragon reactor in the United Kingdom and the Peach Bottom reactor in the United States, and in the spherical elements of the pebble-bed AVR in West Germany. There is also a possibility of adopting the thorium cycle in the... 

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. 

The research and development work on high temperature gas cooled reactors in China started in 1970s [XVII-1-3]. Initially, the work was focused on gas cooled breeders using thorium fuel cycle. The R D and design work was carried out for a helium cooled thorium breeder of 100-MW output, using spherical fuel elements. The activities included ... 

MSR developments in Russia on the Molten Salt Actinide Recycler and Transmuter aim to be used as efficient burners of transuranic waste from spent UOX and MOX LWR fuel without any uranium and thorium support and also with it. Other advanced reactor concepts are being studied, which use the liquid salt technology as a primary coolant for fluoride salt-cooled high-temperature reactors, and coated particle fuels similar to high-temperature gas-cooled reactors. 

Nuclear Applications. Use of the nitrides of uranium-235 and thorium as fuels and breeders in high temperature reactors has been proposed (see Nuclearreactors). However, the compounds most frequently used for this purpose are the oxides and carbides. Nitrides could be useful in high... 

The Arbeitsgemeinschaft Versuchsreaktor (AVR) and Thorium High-Temperature Reactor (THTR-300) were both helium-cooled reactors of the pebble-bed design [29,42,43]. The major design parameters of the AVR and THTR are shown in Table 10. Construction started on the AVR in 1961 and full power operation at 15MW(e) commenced in May 1967. The core of the AVR consisted of approximately 100,000 spherical pebble type fuel elements (see Section 5). The pebble bed was surrounded by a cylindrical graphite reflector and structural carbon... 

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