Thorium fuels can be designed for both ‘pebble bed’ and ‘prismatic’ types of HTR reactors. This may include, but is not limited to the disposal of sources, LSC standards, uranium and thorium compounds. A thorium reactor is a form of nuclear energy, proposed for use as a molten salt reactor. With regard to proliferation significance, thorium-based power reactor fuels would be a poor source for fissile material usable in the illicit manufacture of an explosive device. Contact Us to ask a question, provide feedback, or report a problem. [Back], 4. The fission of a U-233 nucleus releases about the same amount of energy (200 MeV) as that of U-235. Thorium oxide (ThO2) is relatively inert and does not oxidise further, unlike UO2. Molten salt reactors: In the 1960s the Oak Ridge National Laboratory (USA) designed and built a demonstration MSR using U-233 as the main fissile driver in its second campaign. Adjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland. Data taken from Uranium 2016: Resources, Production and Demand, OECD Nuclear Energy Agency and the International Atomic Energy Agency. Thorium has 6 naturally occurring isotopes. (i) S. Şahin, etal, “CANDU Reactor as Minor Actinide / Thorium Burner with Uniform Power Density in the Fuel Bundle” Ann.Nuc.Energy. Accelerator-driven reactors: A number of groups have investigated how a thorium-fuelled accelerator-driven reactor (ADS) may work and appear. Non-destructive determination of uranium, thorium and 40K in tobacco and their implication on radiation dose levels to the human body. These were embedded in graphite ‘compacts’ that were arranged in hexagonal columns ('prisms'). All of these isotopes are unstable (radioactive), but only 232 Th is relatively stable with half-life of 14 billion years, which is comparable to the age of the Earth (~4.5×10 9 years). Projects are (or have recently been) underway in China, Japan, Russia, France and the USA. The NRX, NRU and WR-1 reactors were used, NRU most recently. The other two radioactive elements are Bismuth and Uranium. In the environment, thorium exists in combination with other minerals, such as silica. radon, radium etc.) 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. This principle applies to all the thorium-capable reactor systems. Aqueous homogeneous reactor: An aqueous homogenous suspension reactor operated over 1974-77 in the Netherlands at 1 MWth using thorium plus HEU oxide pellets. Also, uranium is abundant and cheap and forms only a small part of the cost of nuclear electricity generation, so there are no real incentives for investment in a new fuel type that may save uranium resources. [Back], g. The molten salt in the core circuit consists of lithium, beryllium and fissile U-233 fluorides (FLiBe with uranium). These neutrons are directed at a region containing a thorium fuel, eg, Th-plutonium which reacts to produce heat as in a conventional reactor. Thermal breeding with thorium requires that the neutron economy in the reactor has to be very good (ie, there must be low neutron loss through escape or parasitic absorption). In the environment, thorium exists in combination with other minerals, such as silica. It is found in small amounts in most rocks and soils. Soil commonly contains an average of about 6 parts of thorium per million parts (ppm) of soil. Before we go around throwing accusations at early nuclear scientists for using uranium instead of thorium, let’s take a quick look at how nuclear reactors operate. Ashley, S.F. The reactor will operate with a power of 300 MWe using thorium-plutonium or thorium-U-233 seed fuel in mixed oxide form. [Back], b. One isotope, 232 Th, is relatively stable, with a half-life of 1.405×10 10 years, considerably longer than the age of the Earth, and even slightly longer than the generally accepted age of the universe.This isotope makes up nearly all natural thorium, so thorium … The TMSR-SF (solid fuel) stream has only partial utilization of thorium, relying on some breeding as with U-238, and needing fissile uranium input as well. The total mass of U-233 in the core is around 600 grams. Instabile Radiumisotope sind nicht nur signifikante … Commercial and federal facilities that have processed thorium may also have released thorium to the air, water or soil. 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). Most fission products dissolve or suspend in the salt and some of these are removed progressively in an adjacent on-line radiochemical processing unit. Extracting its latent energy value in a cost-effective manner remains a challenge, and will require considerable R&D investment. The level of moderation is given by the amount of graphite built into the core. About 39% of the power will come from thorium (via in situ conversion to U-233, c. two-thirds in AHWR), and burn-up will be 64 GWd/t. When heated in air, thorium metal ignites and burns brilliantly with a white light. Babyak, L.B. Boiling (Light) Water Reactors (BWRs): BWR fuel assemblies can be flexibly designed in terms of rods with varying compositions (fissile content), and structural features enabling the fuel to experience more or less moderation (eg, half-length fuel rods). Kazimi M.S. Thorium based fuel options for the generation of electricity: Developments in the 1990s, IAEA-TECDOC-1155, International Atomic Energy Agency, May 2000 Data for reasonably assured and inferred resources recoverable at a cost of $80/kg Th or less are given in the table below, excluding some less-certain Asian figures. This was a small pebble bed reactor that operated at 15 MWe, mainly with thorium-HEU fuel. Thorium oxide (ThO2), also called thoria, has one of the highest melting points of all oxides (3300°C) and so it has found applications in light bulb elements, lantern mantles, arc-light lamps, welding electrodes and heat-resistant ceramics. It is estimated that the element This is more abundant than Uranium in the Earth’s crust. 2013-056-037-WS §401.052(d) collected by TCEQ were to be deposited into the Environmental Radiation and Perpetual Care Account. It is noteworthy for being the only U-233 fuelled reactor in the world, though it does not in itself directly support thorium fuel R&D. This is because such fuel is usable in existing reactors (with minimal modification) using existing uranium-MOX technology and licensing experience. This reactor platform, designed by Hitachi Ltd and JAEA, should be well suited for achieving high U-233 conversion factors from thorium due to its epithermal neutron spectrum. Basic development work has been conducted in Germany, India, Canada, Japan, China, Netherlands, Belgium, Norway, Russia, Brazil, the UK & the USA. [Back], 2. Key Difference – Thorium vs Uranium Both Thorium and Uranium are two chemical elements from actinide group, which have radioactive properties and function as energy sources in nuclear power plants; the key difference between Thorium and Uranium exists in their natural abundance. The fuel particles are embedded in a graphite matrix that is very stable at high temperatures. 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. They are a viable early-entry thorium platform. There is also a negative temperature coefficient of reactivity due to expansion of the fuel. More neutrons are released per neutronabsorbed in the fuel in a traditional (thermal) type of reactor Since the fission of thorium doesn't produce plutonium (one of the elements used in nuclear weapons) as a byproduct, uranium, the dual-purpose nuclear fuel took precedence. In fact, its half-life is considerably longer than the age of earth. Most people are not exposed to dangerous levels of thorium. Construction of the pilot AHWR was envisaged in the 12th plan period to 2017, for operation about 2022. 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). Thorium has the potential to be used as a fuel for generating nuclear energy. It has higher thermal conductivity and lower thermal expansion than UO2, as well as a much higher melting point. Thorium is commonly found in monazite sands (rare earth metals containing phosphate mineral). World monazite resources are estimated to be about 16 million tonnes, 12 Mt of which are in heavy mineral sands deposits on the south and east coasts of India. Since thorium is naturally present in the environment, people are exposed to tiny amounts in air, food and water. Thorium’s half-life of 14 billion years is actually longer than the age of the universe. The experience gained with component design, operation, and maintenance with clean salts makes it much easier then to move on and consider the use of liquid fuels, while gaining several key advantages from the ability to operate reactors at low pressure and deliver higher temperatures. About 1360 kg of thorium was used in some 100,000 pebbles. The possibility to breed fissile material in slow neutron systems is a unique feature for thorium-based fuels and is not possible with uranium fuels. It is a silvery-white metal at room temperature, but will readily oxidize when exposed to air, and only occurs naturally in oxidized form. It is notable that the MSR is one of the six ‘Generation IV’ reactor designs selected as worthy of further development (see information page on Generation IV Nuclear Reactors). Spallation neutrons are producedd when high-energy protons from an accelerator strike a heavy target like lead. This is occurring preeminently in China, with modest US support. High-temperature gas-cooled reactors: Thorium fuel was used in HTRs prior to the successful demonstration reactors described above. Certain MSR designsc will be designed specifically for thorium fuels to produce useful amounts of U-233. 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. 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). These were continuously moved through the reactor as it operated, and on average each fuel pebble passed six times through the core. The pioneering research & development in the nuclear domain was performed with the purpose of creating nuclear weapons. And because of the complexity of problems listed below, thorium reactors are far more expensive than uranium fueled reactors. Thorium recovery from monazite usually involves leaching with sodium hydroxide at 140°C followed by a complex process to precipitate pure ThO2. Thorium exists in nature in a single isotopic form – T… Consumer products with radioactive components or emissions: Smoke detectors: most smoke detectors available for home use contain americium-241, a radioactive … it contains. The blanket around the core will have uranium as well as thorium, so that further plutonium (particularly Pu-239) is produced as well as U-233. Pebble bed reactor development builds on German work with the AVR and THTR and is under development in China (HTR-10, and HTR-PM). Epub 2015 May 4. et al, 2004, Thorium-based Transmuter Fuels for Light Water Reactors, INL, Nuclear Technology 147, July 2004 Natural thorium is a mixture of radioactive isotopes, predominantly the very long-lived thorium-232 (1.40 × 10 10-year half-life), the parent of the thorium radioactive decay series. 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. Thorium is a naturally occurring, radioactive substance. U-233 contained in spent thorium fuel contains U-232 which decays to produce very radioactive daughter nuclides and these create a strong gamma radiation field. Thorium is a weak radioactive element of the actinide series. [Back], 1. There are similar problems in recycling thorium itself due to highly radioactive Th-228 (an alpha emitter with two-year half life) present. Together, the seed and blanket have the same geometry as a normal VVER-100 fuel assembly (331 rods in a hexagonal array 235 mm wide). Man-made thorium isotopesisotopeA form of an element that has the same number of protons but a different number of neutrons in the nucleus, giving it a different atomic mass. There is potential application to Enhanced Candu 6 (EC6) and ACR-1000 reactors fueled with 5% plutonium (reactor grade) plus thorium. AECL had a Thoria Roadmap R&D project. These were embedded in annular graphite segments (not pebbles). Thorium is a naturally-occurring, slightly radioactive metal discovered in 1828 by the Swedish chemist Jons Jakob Berzelius, who named it after Thor, the … The blanket circuit contains a significant amount of thorium tetrafluoride in the molten Li-Be fluoride salt. Taesin Chung, The role of thorium in nuclear energy, Uranium Industry Annual 1996, Energy Information Administration, DOE/EIA-0478(96) p.ix-xvii (April 1997) 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. Occasionally, household items may be found with thorium in them, such as some older ceramic wares in which uranium and thorium were used in the glaze. Furthermore, heavy water reactors (especially CANDU) are well established and widely-deployed commercial technology for which there is extensive licensing experience. The small amount of thorium left in the body will enter the bloodstream and be deposited in the bones where it may remain for many years. The physical properties of thorium are similar to that of lead. 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. The thorium fuel cycle is sometimes promoted as having excellent non-proliferation credentials. In the closed cycle, the driver fuel required for starting off is progressively replaced with recycled U-233, so that an ever-increasing energy share in the fuel comes from the thorium component. Burn-ups of 150 GWd/t were achieved. Freeman, H.F. Raab, “LWBR: A successful demonstration completed” Nuclear News, Sept 1988, pp114-116 (1988) 4, P. 304 (July-August 2010) Registered office: Tower House, 10 Southampton Street, London, WC2E 7HA, United Kingdom, Reuse of World Nuclear Association Content, Uranium 2016: Resources, Production and Demand, A Competitive Thorium Fuel Cycle for Pressurized Water Reactors of Current Technology, Thorium fuel utilization: Options and trends, Thorium based fuel options for the generation of electricity: Developments in the 1990s, Revisiting the Thorium-Uranium Nuclear Fuel Cycle, Background, Status, and Issues Related to the Regulation of Advanced Spent Nuclear Fuel Recycle Facilities. 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. Both elements undergo alpha decay slowly. Particularly in a molten salt reactor, the equilibrium fuel cycle is expected to have relatively low radiotoxicity, being fission products only plus short-lived Pa-233, without transuranics. Although thorium advocates say that thorium reactors produce little radioactive waste, they simply produce a different spectrum of waste to those from uranium-235. Newly-formed U-233 forms soluble uranium tetrafluoride (UF4), which is converted to gaseous uranium hexafluoride (UF6) by bubbling fluorine gas through the salt (which does not chemically affect the less-reactive thorium tetrafluoride). Almost 25 tonnes of thorium was used in fuel for the reactor, much of which attained a burn-up of about 170 GWd/t. In some, the radioactive material is a working part of the product. A 2007 NRC report quotes a breeding ratio of 1.01. Thorium is a weakly radioactive chemical element from actinide series with symbol Th and atomic number 90. Even though PWRs are not the perfect reactor in which to use thorium, they are the industry workhorse and there is a lot of PWR licensing experience. 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. et al, 2012, Thorium fuel has risks, Nature 492: 31-33, 6 Dec 2012 When pure, thorium is a silvery white metal that retains its lustre for several months. It is fueled by the uranium-233 isotope that is taken from the element thorium. A U-233 nucleus yields more neutrons, on average, when it fissions (splits) than either a uranium-235 or plutonium-239 nucleus. The fuel comprised small particles of uranium oxide (1 mm diameter) coated with silicon carbide and pyrolytic carbon which proved capable of maintaining a high degree of fission product containment at high temperatures and for high burn-ups. Various groups are evaluating the option of using thorium fuels in an advanced reduced-moderation BWR (RBWR). The Truth Behind the Rumors. a. Neutron absorption by Th-232 produces Th-233 which beta-decays (with a half-life of about 22 minutes) to protactinium-233 (Pa-233) – and this decays to U-233 by further beta decay (with a half-life of 27 days). It did not reach its later stages which would have involved trial irradiations of thorium-plutonium fuels in the Angra-1 PWR in Brazil, although preliminary Th-fuel irradiation experiments were performed in Germany. Minerals such as monazite, thorite, and thorianite are rich in thorium and may be mined for the metal. The technical difficulty of using molten salts is significantly lower when they do not have the very high activity levels associated with them bearing the dissolved fuels and wastes. Thorium is three times … In February 2018 a third batch of Th-MOX fuel pellets commenced testing. TRISO particles will be with both low-enriched uranium and thorium, separately. Both chemical elements are used in nuclear power plants and nuclear weapons. Perhaps most notable is the ‘ADTR’ design patented by a UK group. gtag('js', new Date()); The fuel contained 2.6 % of high fissile-grade plutonium (86% Pu-239) and the fuel achieved about 20 GWd/t burnup. The pure form of thorium is air-stable, and it can retain its luster for many months. It is inherently unstable; all of its isotopes are radioactive. The TMSR Research Centre has a 5 MWe MSR prototype under construction at Shanghai Institute of Applied Physics (SINAP, under the Academy). In July 2009 a second phase agreement was signed among AECL, the Third Qinshan Nuclear Power Company (TQNPC), China North Nuclear Fuel Corporation and the Nuclear Power Institute of China to jointly develop and demonstrate the use of thorium fuel and to study the commercial and technical feasibility of its full-scale use in Candu units such as at Qinshan. Near-term goals include preparing nuclear-grade ThF4 and ThO2 and testing them in a MSR. In this case, a high-enery proton beam directed at a heavy target expels a number of spallation particles, including neutrons. Thorium is a silvery metal with radioactive properties that was discovered in 1828 by Jöns Jakob Berzelius (a Swedish chemist) and was named after Thor (the famous Norse god of thunder). Production of all actinides is lower than with conventional fuel, and negative reactivity coefficient is enhanced compared with U-Pu MOX fuel. As of 2020, however, no site or construction schedule for the demonstration unit has been announced. Thorium: occurrences, geological deposits and resources, by F.H.Barthel & H.Tulsidas, URAM 2014 conference, IAEA. Herring, J.S. High-Temperature Gas-Cooled Reactors (HTRs): These are well suited for thorium-based fuels in the form of robust ‘TRISO’ coated particles of thorium mixed with plutonium or enriched uranium, coated with pyrolytic carbon and silicon carbide layers which retain fission gases. So it is possible, for example, to design thorium-plutonium BWR fuels that are tailored for ‘burning’ surplus plutonium. These are continually removed in on-line reprocessing, though this is more complex than for the uranium-plutonium fuel cycle. The density of thorium is 11.7 grams per cubic centimeter. A third stream of fast reactors to consume actinides from LWRs is planned. The reflector region contained only thorium oxide at the beginning of the core life. Difficulties lie with the reliability of high-energy accelerators and also with economics due to their high power consumption. This uranium can be selectively removed as uranium hexafluoride (UF6) by bubbling fluorine gas through the salt. Separated U-233 is always contaminated with traces of U-232 which decays (with a 69-year half-life) to daughter nuclides such as thallium-208 that are high-energy gamma emitters. “German Brazilian Program of Research and Development on Thorium Utilization in PWRs”, Final Report, Kernforschungsanlage Jülich, 1988. Although thorium is not fissile, it can be bred in a nuclear reactor to the fissile isotopeU-233, and so has potential as a nuclear fuel source. Thorium is a naturally occurring radioactive metal that is found in soil, rock, and water. It is not abundant, but major supplies are in sands rich in monazite. (See also information page on India). 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). K.P. Most of the natural thorium exists in isotope form as Th-232. B. Radon, Radium usw. While closed fuel cycle is possible, this is not required or envisaged, and the used fuel, with about 8% fissile isotopes can be used in light water reactors. 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. It is formed by the radioactive decay of uranium. Advanced heavy water reactors (AHWRs) will burn thorium-plutonium fuels in such a manner that breeds U-233 which can eventually be used as a self-sustaining fissile driver for a fleet of breeding AHWRs. Thorium provides a much more fuel efficient process than uranium, coal, oil, natural gas, and any renewable source. 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. These small amounts of thorium contribute to the weak background radiation for such substances. Uranium, with a half-life of 4.5 billion years, is a better clock than thorium, Frebel says. Accelerator Driven Reactors (ADS): The sub-critical ADS system is an unconventional nuclear fission energy concept that is potentially ‘thorium capable’. !-- Global site tag (gtag.js) - Google Analytics --> Chapter 336 - Radioactive Substance Rules Rule Project No. Commercially, monazite is recovered as a by-product of the processing of titanium-bearing heavy-mineral sands. Thorium (Th) is a radioactive metallic element that, until the 1950's, was known only by chemists and physicists. There are natural and man-made forms of thorium, all of which are radioactive. However, when it is contaminated with the oxide, thorium slowly tarnishes in air, becoming grey and eventually black. The only fissile driver options are U-233, U-235 or Pu-239. Thorium is solid under normal conditions. This fuel is promoted as a means to improve power profiles within commercial reactors. Four commercial thorium reactors were constructed, all of which failed. The so-called Radkowsky Thorium Reactor design is based on a heterogeneous ‘seed & blanket’ thorium fuel concept, tailored for Russian-type LWRs (VVERs)6. gtag('config', 'G-HND9DCLLLL'); The use of thorium as a new primary energy source has been a tantalizing prospect for many years. 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. It converts to fissile U-235 (the naturally occuring fissile isotope of uranium) and this somewhat compensates for this neutronic penalty. In fuel cycles involving the multi-recycle of thorium-U-233 fuels, the build up of U-234 can be appreciable. 35, 690-703 (2008), (ii) J. Yu, K, Wang, R. Sollychin, etal, “Thorium Fuel Cycle of a Thorium-Based Advanced Nuclear Energy System” Prog.Nucl.Energy. 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). In nuclear fuel, fission gas release is much lower than in UO2. The heat energy released during fission is utilized to eva… The fuel supply for a thorium reactor is 99% less radioactive than the fuel supply for a uranium reactor. This reactor produced 33 billion kWh over 1349 equivalent full-power days with a capacity factor of 74%. Thorium is a naturally occurring, radioactive substance. You can safely handle it without protection from radioactivity. Thorium (symbol Th, atomic number90) is a radioactivechemical element. An expert panel appointed by CNNC unanimously recommended that China consider building two new Candu units to take advantage of the design's unique capabilities in utilizing alternative fuels. Nevertheless, the thorium fuel cycle offers energy security benefits in the long-term – due to its potential for being a self-sustaining fuel without the need for fast neutron reactors. Three distinct trial irradiations have been performed on thorium-plutonium fuels, including a test pin loaded in the Obrigheim PWR over 2002-06 during which it achieved about 38 GWd/t burnup. Actinides are less-readily formed than in fuel with atomic mass greater than 235. 45, 71-84 (2004) [Back], 5. Steward, “Final Summary Report on the Peach Bottom End-of-Life Program”, General Atomics Report GA-A14404, (1978) [Back], 3. It has a high burn-up to 55 GWd/t. 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. It is not possible to design viable thorium-based PWR fuels that convert significant amounts of U-233. Soil contains an average of around 6 parts per million (ppm) of thorium. However, nations have finally understood the safety aspects of thorium … chemical element. Thorium is a naturally-occurring, slightly radioactive metal discovered in 1828 by the Swedish chemist Jons Jakob Berzelius, who named it after Thor, the Norse god of thunder. Most findings from this study remain relevant today. The 2014 ‘Red Book’ suggested that extraction of thorium as a by-product of rare earth elements (REE) recovery from monazite seems to be the most feasible source of thorium production at this time. [Back], d. Spallation is the process where nucleons are ejected from a heavy nucleus being hit by a high energy particle. Chinese production is unknown. 12th Indian Nuclear Society Annual Conference 2001 conference proceedings, vol 2 (lead paper) SINAP sees molten salt fuel being superior to the TRISO fuel in effectively unlimited burn-up, less waste, and lower fabricating cost, but achieving lower temperatures (600°C+) than the TRISO fuel reactors (1200°C+). Despite these merits, the commercialization of thorium fuels faces some significant hurdles in terms of building an economic case to undertake the necessary development work. 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 … In this regard it is similar to uranium-238 (which transmutes to plutonium-239). Research reactor ‘Kamini’: India has been operating a low-power U-233 fuelled reactor at Kalpakkam since 1996 – this is a 30 kWth experimental facility using U-233 in aluminium plates (a typical fuel-form for research reactors). A large vein deposit of thorium and rare earth metals is in Idaho. As the fuel operates the U-233 content gradually increases and it contributes more and more to the power output of the fuel. Design of the seed fuel rods in the centre portion draws on experience of Russian naval reactors. Monazite is found in igneous and other rocks but the richest concentrations are in placer deposits, concentrated by wave and current action with other heavy minerals. Many of these early trials were able to use high-enriched uranium (HEU) as the fissile ‘driver’ component, and this would not be considered today. function gtag(){dataLayer.push(arguments);} Glass containing thorium oxide has both a high refractive index and wavelength dispersion, and is used in high quality lenses for cameras and scientific instruments.