The so-called Radkowsky Thorium Reactor design is based on a heterogeneous ‘seed & blanket’ thorium fuel concept, tailored for Russian-type LWRs (VVERs)6. 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. The fuels have performed well in terms of their material properties. 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. Waste pickup is scheduled for last Tuesday of every month with the exception of when the university is closed. However, Th-232 fast fissions only one tenth as well as U-238, so there is no particular reason for using thorium in fast reactors, given the huge amount of depleted uranium awaiting use. 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. Most fission products dissolve or suspend in the salt and some of these are removed progressively in an adjacent on-line radiochemical processing unit. The reactor will operate with a power of 300 MWe using thorium-plutonium or thorium-U-233 seed fuel in mixed oxide form. …the character of thorium radioactivity is unaltered by chemical treatment… It is well established that this property [radioactivity] is the function of the atom and not of the molecule. [Back], f. Blanket fuel is designed to reach 100 GWd/t burn-up. Pressurised heavy water reactors (PHWRs) and light water reactors fuelled by natural uranium producing plutonium that is separated for use in fuels in its fast reactors and indigenous advanced heavy water reactors. Neutron moderation is tailored by the amount of graphite in the core (aiming for an epithermal spectrum). In fuel cycles involving the multi-recycle of thorium-U-233 fuels, the build up of U-234 can be appreciable. Freeman, H.F. Raab, “LWBR: A successful demonstration completed” Nuclear News, Sept 1988, pp114-116 (1988)
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). Thorium recovery from monazite usually involves leaching with sodium hydroxide at 140°C followed by a complex process to precipitate pure ThO2. Other impediments to the development of thorium fuel cycle are the higher cost of fuel fabrication and the cost of reprocessing to provide the fissile plutonium driver material. R&D into thorium fuel use in CANDU reactors continues to be pursued by Canadian and Chinese groups as part of joint studies looking at a wide range of fuel cycle options involving China's Qinshan Phase III PHWR units. 45, 71-84 (2004) [Back], 5. It decays eventually to lead-208. 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. The reflector region contained only thorium oxide at the beginning of the core life. 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. Small amounts of thorium are present in all rocks, soil, above-ground and underground water, plants, and animals. These were continuously moved through the reactor as it operated, and on average each fuel pebble passed six times through the core. Soil contains an average of around 6 parts per million (ppm) of thorium. The decay chains of natural thorium and uranium give rise to minute traces of Th-228, Th-230 and Th-234, but the presence of these in mass terms is negligible. Thorium (Th) is a radioactive metallic element that, until the 1950's, was known only by chemists and physicists. 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. The fluid circulates through a core region and then through a chemical processing circuit that removes various fission products (poisons) and/or the valuable U-233. 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). Thorium oxide has a crystalline structural similar … 4, P. 304 (July-August 2010)
There have been several significant demonstrations of the use of thorium-based fuels to generate electricity in several reactor types. 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. India’s nuclear developers have designed an Advanced Heavy Water Reactor (AHWR) specifically as a means for ‘burning’ thorium – this will be the final phase of their three-phase nuclear energy infrastructure plan (see below). Small amounts of thorium are present in all rocks, soil, water, plants, and animals. The volatile uranium hexafluoride is captured, reduced back to soluble UF4 by hydrogen gas, and finally is directed to the core to serve as fissile fuel. Thorium is a weak radioactive metal as its isotopes are highly unstable. Thorium is a naturally occurring radioactive element that was discovered in 1828 by J. J. Berzelius. In nuclear fuel, fission gas release is much lower than in UO2. Thorium is very insoluble, which is why it is plentiful in sands but not in seawater, in contrast to uranium. Thorium is a chemical element with symbol Th and atomic number 90.A radioactive actinide metal, thorium is one of only three radioactive elements that still occurs in quantity in nature as a primordial element (the other two being bismuth and uranium). Both elements have naturally occurring isotopes. The study showed that appreciable conversion to U-233 could be obtained with various thorium fuels, and that useful uranium savings could be achieved. The TMSR Research Centre has a 5 MWe MSR prototype under construction at Shanghai Institute of Applied Physics (SINAP, under the Academy). Thorite (ThSiO4) is another common thorium mineral. Fast breeder reactors (FBRs) will use plutonium-based fuel to extend their plutonium inventory. 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. Various groups are evaluating the option of using thorium fuels in an advanced reduced-moderation BWR (RBWR). It is estimated that the element This is more abundant than Uranium in the Earth’s crust. 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. 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+). The first five of these have all entered into operational service at some point. [Back], d. Spallation is the process where nucleons are ejected from a heavy nucleus being hit by a high energy particle. For example, uranium has thirty-seven different isotopes, including uranium-235 and uranium-238. Contact Us to ask a question, provide feedback, or report a problem. [Back], b. High levels of actinide destruction may also be achieved in carefully designed thorium fuels in these conditions. 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. Radiat Prot Dosimetry. Although this confers proliferation resistance to the fuel cycle by making U-233 hard to handle and easy to detect, it results in increased costs. 2. Kamini is water cooled with a beryllia neutron reflector. In some, the radioactive material is a working part of the product. 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. So it is possible, for example, to design thorium-plutonium BWR fuels that are tailored for ‘burning’ surplus plutonium. 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). The blanket circuit contains a significant amount of thorium tetrafluoride in the molten Li-Be fluoride salt. These are continually removed in on-line reprocessing, though this is more complex than for the uranium-plutonium fuel cycle. K.P. Fissile drive fuel could be LEU, plutonium, or recycled uranium from LWR. The U.S. tried for 50 years to create thorium reactors, without success. When pure, thorium is a silvery white metal that retains its lustre for several months. Epub 2015 May 4. Pressurised (Light) Water Reactors (PWRs): Viable thorium fuels can be designed for a PWR, though with less flexibility than for BWRs. This still includes many dangerous alpha and beta emitters, and isotopes with extremely long half-lives, including iodine-129 (half-life of 15.7 … Thorium’s half-life of 14 billion years is actually longer than the age of the universe. India is focusing and prioritizing the construction and commissioning of its fleet of 500 MWe sodium-cooled fast reactors in which it will breed the required plutonium which is the key to unlocking the energy potential of thorium in its advanced heavy water reactors. Babyak, L.B. 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. If not properly controlled, wind and water can introduce the tailings into the wider environment. Test irradiations have been conducted on a number of different thorium-based fuel forms. Protactinium – a neutron absorber – is not a major problem in the blanket salt. [Back], e. The core of the Shippingport demonstration LWBR consisted of an array of seed and blanket modules surrounded by an outer reflector region. These small amounts of thorium contribute to the weak background radiation for such substances. Both elements are in the actinide series of the f block of the periodic table of elements. The only fissile driver options are U-233, U-235 or Pu-239. Perhaps most notable is the ‘ADTR’ design patented by a UK group. This may include, but is not limited to the disposal of sources, LSC standards, uranium and thorium compounds. 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. 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. In this regard it is similar to uranium-238 (which transmutes to plutonium-239). ), die es enthält, etwa zehnmal radioaktiver als das reine Thorium-232-Metall. Thorium is a naturally occurring, radioactive substance. it contains. In general, naturallyÂ occurring thorium exists as Th-232, Th-230Â or Th-228. Furthermore, heavy water reactors (especially CANDU) are well established and widely-deployed commercial technology for which there is extensive licensing experience. These neutrons are directed at a region containing a thorium fuel, eg, Th-plutonium which reacts to produce heat as in a conventional reactor. Certain MSR designsc will be designed specifically for thorium fuels to produce useful amounts of U-233. Commercial and federal facilities that have processed thorium may also have released thorium to the air, water or soil. Also, there is a huge amount of surplus DU available for use when more FNRs are commercially available, so thorium has little or no competitive edge in these systems.  It is considered to be "fertile", due to its ability to be converted into a fissile material from neutron absorption and later nuclear decay. (See also information page on India). Actinides are less-readily formed than in fuel with atomic mass greater than 235. Non-destructive determination of uranium, thorium and 40K in tobacco and their implication on radiation dose levels to the human body. Some of the bred-in U-233 is converted to U-234 by further neutron absorption. This fuel is promoted as a means to improve power profiles within commercial reactors. It also used thorium-HEU fuel in the form of microspheres of mixed thorium-uranium carbide coated with silicon oxide and pyrolytic carbon to retain fission products. The high cost of fuel fabrication (for solid fuel) is due partly to the high level of radioactivity that builds up in U-233 chemically separated from the irradiated thorium fuel. Thorium (Th), radioactive chemical element of the actinoid series of the periodic table, atomic number 90; it is a useful nuclear reactor fuel. A third stream of fast reactors to consume actinides from LWRs is planned. et al, 2004, Thorium-based Transmuter Fuels for Light Water Reactors, INL, Nuclear Technology 147, July 2004
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. 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. TRISO particles will be with both low-enriched uranium and thorium, separately. Kazimi M.S. 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. Thorium is weakly radioactive, has a high melting point, and is available with more abundance than uranium as an element. It is formed by the radioactive decay of uranium. This reactor operates very close to criticality and therefore requires a relatively small proton beam to drive the spallation neutron source. Adjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland. 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. It is a silvery-white metal at room temperature, but will readily oxidize when exposed to air, and only occurs naturally in oxidized form. In each assembly 30 of the fuel pins will be Th-U-233 oxide, arranged in concentric rings. Fuel needs to be in heterogeneous arrangements in order to achieve satisfactory fuel burn-up. 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. 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. This is occurring preeminently in China, with modest US support. It is found in small amounts in most rocks and soils, where it is about three times more abundant than uranium. In some, the radioactive material is a working part of the product. Thorium-plutonium oxide (Th-MOX) fuels for LWRs are being developed by Norwegian proponents (see above) with a view that these are the most readily achievable option for tapping energy from thorium. chemical element. 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). Thorium is very insoluble, which is why it is plentiful in sands but not in seawater, in contrast to uranium. Thorium is a naturally occurring, radioactive substance.
Germany operated the Atom Versuchs Reaktor (AVR) at Jülich for over 750 weeks between 1967 and 1988. This design flexibility is very good for being able to come up with suitable heterogeneous arrangements and create well-optimised thorium fuels. As of 2020, however, no site or construction schedule for the demonstration unit has been announced. Although thorium advocates say that thorium reactors produce little radioactive waste, they simply produce a different spectrum of waste to those from uranium-235. Projects are (or have recently been) underway in China, Japan, Russia, France and the USA. [Back], g. The molten salt in the core circuit consists of lithium, beryllium and fissile U-233 fluorides (FLiBe with uranium). It could therefore be used in fast molten salt and other Gen IV reactors with uranium or plutonium fuel to initiate fission. The level of moderation is given by the amount of graphite built into the core. The fission of a U-233 nucleus releases about the same amount of energy (200 MeV) as that of U-235. Accelerator-driven reactors: A number of groups have investigated how a thorium-fuelled accelerator-driven reactor (ADS) may work and appear. et al, 2012, Thorium fuel has risks, Nature 492: 31-33, 6 Dec 2012
If you’ve heard that Fiestaware is highly radioactive then you should know that it isn’t a myth. 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. And because of the complexity of problems listed below, thorium reactors are far more expensive than uranium fueled reactors. Most people are not exposed to dangerous levels of thorium. Commercially, monazite is recovered as a by-product of the processing of titanium-bearing heavy-mineral sands. “German Brazilian Program of Research and Development on Thorium Utilization in PWRs”, Final Report, Kernforschungsanlage Jülich, 1988. Safety is achieved with a freeze plug which if power is cut allows the fuel to drain into subcritical geometry in a catch basin. The pure form of thorium is air-stable, and it can retain its luster for many months. Pebble bed reactor development builds on German work with the AVR and THTR and is under development in China (HTR-10, and HTR-PM). HE 1523-0901 also contains thorium, another radioactive element that is useful in age-dating of stars. In Norway, Thor Energy is developing and testing a thorium-bearing fuel for use in existing nuclear power plants. 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.