Thorium (Th), radioactive chemical element of the actinoid series of the periodic table, atomic number 90; it is a useful nuclear reactor fuel. Thorium is used to make ceramics, welding rods, camera and telescope lenses, fire brick, heat resistant paint and metals used in the aerospace industry, as well as in nuclear reactions. It is fueled by the uranium-233 isotope that is taken from the element thorium. Thorium oxide has a crystalline structural similar … Certain MSR designsc will be designed specifically for thorium fuels to produce useful amounts of U-233. Therefore 232 Th belongs to primordial … Indian heavy water reactors (PHWRs) have for a long time used thorium-bearing fuel bundles for power flattening in some fuel channels – especially in initial cores when special reactivity control measures are needed. Thorium (chemical symbol Th) is a naturally occurring radioactive metal found at trace levels in soil, rocks, water, plants and animals. Summary: Thorium is a naturally occurring, radioactive substance. The China Academy of Sciences in January 2011 launched an R&D program on LFTR, known there as the thorium-breeding molten salt reactor (Th-MSR or TMSR), and claimed to have the world's largest national effort on it, hoping to obtain full intellectual property rights on the technology. And importantly, BWRs are a well-understood and licensed reactor type. Fast breeder reactors (FBRs) will use plutonium-based fuel to extend their plutonium inventory. It could therefore be used in fast molten salt and other Gen IV reactors with uranium or plutonium fuel to initiate fission. gtag('js', new Date());
Research into the use of thorium as a nuclear fuel has been taking place for over 50 years, though with much less intensity than that for uranium or uranium-plutonium fuels. The system remains subcritical ie, unable to sustain a chain reaction without the proton beam. The most common source of thorium is the rare earth phosphate mineral, monazite, which contains up to about 12% thorium phosphate, but 6-7% on average. In the closed fuel cycle, the driver fuel required for starting off is progressively replaced with recycled U-233, so that on reaching equilibrium 80% of the energy comes from thorium. The other two radioactive elements are Bismuth and Uranium. For export, India has also designed an AHWR300-LEU which uses low-enriched uranium as well thorium in fuel, dispensing with plutonium input. The USA produced about 2 tonnes of U-233 from thorium during the ‘Cold War’, at various levels of chemical and isotopic purity, in plutonium production reactors. Instabile Radiumisotope sind nicht nur signifikante … It is formed by the radioactive decay of uranium. If ingested, thorium typically leaves the body through feces and urine within several days. More neutrons are released per neutronabsorbed in the fuel in a traditional (thermal) type of reactor Construction of the pilot AHWR was envisaged in the 12th plan period to 2017, for operation about 2022. [Back], 6. The 40 MWe Peach Bottom HTR in the USA was a demonstration thorium-fuelled reactor that ran from 1967-74.2 It used a thorium-HEU fuel in the form of microspheres of mixed thorium-uranium carbide coated with pyrolytic carbon. Light water reactors: The feasibility of using thorium fuels in a PWR was studied in considerable detail during a collaborative project between Germany and Brazil in the 1980s5. Thorium based fuel options for the generation of electricity: Developments in the 1990s, IAEA-TECDOC-1155, International Atomic Energy Agency, May 2000
A key finding from thorium fuel studies to date is that it is not economically viable to use low-enriched uranium (LEU – with a U-235 content of up to 20%) as a fissile driver with thorium fuels, unless the fuel burn-up can be taken to very high levels – well beyond those currently attainable in LWRs with zirconium cladding. Earlier proposals for ADS reactors required high-energy and high-current proton beams which are energy-intensive to produce, and for which operational reliability is a problem. Spallation neutrons are producedd when high-energy protons from an accelerator strike a heavy target like lead. For example, uranium has thirty-seven different isotopes, including uranium-235 and uranium-238. In this case, a high-enery proton beam directed at a heavy target expels a number of spallation particles, including neutrons. All thorium fuel concepts therefore require that Th-232 is first irradiated in a reactor to provide the necessary neutron dosing to produce protactinium-233. The Pa-233 that is produced can either be chemically separated from the parent thorium fuel and the decay product U-233 then recycled into new fuel, or the U-233 may be usable ‘in-situ’ in the same fuel form, especially in molten salt reactors (MSRs). A TMSR-LF fast reactor optimized for burning minor actinides is to follow. Thorium oxide (ThO2) is relatively inert and does not oxidise further, unlike UO2. Not only are unstable radium isotopes significant radioactivity emitters, but as the next stage in the decay chain they also generate radon, a heavy, inert, naturally occurring … However, the primary reason that American researchers and the China Academy of Sciences/ SINAP are working on solid fuel, salt-cooled reactor technology is that it is a realistic first step. Kazimi M.S. These were embedded in graphite ‘compacts’ that were arranged in hexagonal columns ('prisms'). Thorium fuel cycles offer attractive features, including lower levels of waste generation, less transuranic elements in that waste, and providing a diversification option for nuclear fuel supply. The ultimate energy output from U-233 (and hence indirectly thorium) depends on numerous fuel design parameters, including: fuel burn-up attained, fuel arrangement, neutron energy spectrum and neutron flux (affecting the intermediate product protactinium-233, which is a neutron absorber). The consortium comprises the DOE's Idaho National Laboratory and the Nuclear Engineering & Science Center at Texas A&M University with Clean Core Thorium Energy (CCTE). Adjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland. The pure form of thorium is air-stable, and it can retain its luster for many months. In fuel cycles involving the multi-recycle of thorium-U-233 fuels, the build up of U-234 can be appreciable. In 1998 India detonated a very small device based on U-233 called Shakti V. However, the production of U-233 inevitably also yields U-232 which is a strong gamma-emitter, as are some decay products such as thallium-208 ('thorium C'), making the material extremely difficult to handle and also easy to detect. In the environment, thorium exists in combination with other minerals, such as silica. The thorium-fuelled MSR variant is sometimes referred to as the Liquid Fluoride Thorium Reactor (LFTR), utilizing U-233 which has been bred in a liquid thorium salt blanket.g. Such fuels can be irradiated for very long periods and thus deeply burn their original fissile charge. More Fuel efficient. Neutron moderation is tailored by the amount of graphite in the core (aiming for an epithermal spectrum). A small amount of thorium-plutonium fuel was irradiated in the 60 MWe Lingen BWR in Germany in the early 1970s. The RBWR is based on the ABWR architecture but has a shorter, flatter pancake-shaped core and a tight hexagonal fuel lattice to ensure sufficient fast neutron leakage and a negative void reactivity coefficient. Main source of radioactivity is the use of thorium oxide (up to 30% by weight) as a component of the glass used in the lens elements. In the seed and blanket regions, the fuel pellets contained a mixture of thorium-232 oxide (ThO2) and uranium oxide (UO2) that was over 98% enriched in U-233. Four commercial thorium reactors were constructed, all of which failed. The UK operated the 20 MWth Dragon HTR from 1964 to 1973 for 741 full power days. et al, 2012, Thorium fuel has risks, Nature 492: 31-33, 6 Dec 2012
Small amounts of thorium are present in all rocks, soil, water, plants, and animals.Soil contains an average of about 6 parts of thorium per million parts of soil (6 ppm). It is found in small amounts in most rocks and soils, where it is about three times more abundant than uranium. Safety is achieved with a freeze plug which if power is cut allows the fuel to drain into subcritical geometry in a catch basin. Perhaps most notable is the ‘ADTR’ design patented by a UK group. Consumer products with radioactive components or emissions: Smoke detectors: most smoke detectors available for home use contain americium-241, a radioactive element. The blanket circuit contains a significant amount of thorium tetrafluoride in the molten Li-Be fluoride salt. Freeman, H.F. Raab, “LWBR: A successful demonstration completed” Nuclear News, Sept 1988, pp114-116 (1988), (ii) J.C. Clayton, “The Shippingport Pressurized Water Reactor and Light Water Breeder Reactor” Westinghouse Bettis Atomic Power Laboratory WAPD-T-3007 (October 1993). The European Framework Program has supported a number of relevant research activities into thorium fuel use in LWRs. radon, radium etc.) Uranium and Thorium are radioactive elements. There is no international or standard classification for thorium resources and identified thorium resources do not have the same meaning in terms of classification as identified uranium resources. B. Radon, Radium usw. Thorium is a naturally occurring, radioactive substance. Thorium (symbol Th, atomic number90) is a radioactivechemical element. Dozens of test irradiations have been performed on fuels including: mixed ThO2-UO2, (both LEU and HEU), and mixed ThO2-PuO2, (both reactor- and weapons-grade). Closed thorium fuel cycles have been designed4 in which PHWRs play a key role due to their fuelling flexibility: thoria-based HWR fuels can incorporate recycled U-233, residual plutonium and uranium from used LWR fuel, and also minor actinide components in waste-reduction strategies. Thorium 232, which alone makes up nearly all natural thorium, is the most common isotope of thorium in the nature.This isotope has the longest half-life (1.4 x 10 10 years) of all isotopes with more than 83 protons. The 300 MWe Thorium High Temperature Reactor (THTR) at Hamm-Uentrop in Germany operated with thorium-HEU fuel between 1983 and 1989, when it was shut down due to technical problems. Mixed thorium-plutonium oxide (Th-Pu MOX) fuel is an analog of current uranium-MOX fuel, but no new plutonium is produced from the thorium component, unlike for uranium fuels in U-Pu MOX fuel, and so the level of net consumption of plutonium is high. Phone Radiation Safety at 512-471-1496 for disposal information.
Thorium (Th-232) is not itself fissile and so is not directly usable in a thermal neutron reactor. Accelerator-driven reactors: A number of groups have investigated how a thorium-fuelled accelerator-driven reactor (ADS) may work and appear. SINAP has two streams of MSR development – solid fuel (TRISO in pebbles or prisms/blocks) with once-through fuel cycle, and liquid fuel (dissolved in FLiBe coolant) with reprocessing and recycle. The thorium-HEU fuel was circulated in solution with continuous reprocessing outside the core to remove fission products, resulting in a high conversion rate to U-233. Fuel rods containing thorium additive (Th-Add) and also thorium MOX (with Pu) fuel rods were tested in a five-year irradiation trial that started in April 2013 at the Halden test reactor. Although thorium advocates say that thorium reactors produce little radioactive waste, they simply produce a different spectrum of waste to those from uranium-235. 1. It is inherently unstable; all of its isotopes are radioactive. Design of the seed fuel rods in the centre portion draws on experience of Russian naval reactors. Thorium is a naturally occurring, radioactive substance. This principle applies to all the thorium-capable reactor systems. Projects are (or have recently been) underway in China, Japan, Russia, France and the USA. In the environment, thorium exists in combination with other minerals, such as silica. Monazite is extracted in India, Brazil, Vietnam and Malaysia, probably less than 10,000 t/yr, but without commercial rare earth recovery, thorium production is not economic at present. Thorium recovery from monazite usually involves leaching with sodium hydroxide at 140°C followed by a complex process to precipitate pure ThO2. The International Atomic Energy Agency (IAEA) and the OECD Nuclear Energy Agency (NEA) joint publication Uranium 2016: Resources, Production and Demand (often referred to as the Red Book) gives a figure of 6.2 million tonnes of total known and estimated resources (the 2018 edition of the same publication did not provide estimates of thorium resources). The amounts are usually very small and pose little health hazard. There is potential application to Enhanced Candu 6 (EC6) and ACR-1000 reactors fueled with 5% plutonium (reactor grade) plus thorium. Noteworthy studies and experiments involving thorium fuel include: Heavy water reactors: Thorium-based fuels for the ‘Candu’ PHWR system have been designed and tested in Canada at AECL's Chalk River Laboratories for more than 50 years, including the irradiation of ThO2-based fuels to burn-ups to 47 GWd/t.
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