The technology is very new at the commercial scale, NREL emphasizes, and needs to be developed for safety and best practices. In the MSBR, the reactor-grade U-233 bred in the secondary circuit needs to be removed, or it will fission there and contaminate that circuit with ‘hot’ fission products. The UF6 is reduced and added to the fuel stream. Graphite as moderator is chemically compatible with the fluoride salts. Seaborg Technologies in Denmark has a thermal-epithermal single fluid reactor design for 50 MWt pilot unit with a view to 250 MWt commercial modular units fuelled by spent LWR fuel and thorium. The rate of damage increases with temperature, which is a particular problem with MSRs at 700°C. This allows the operator to maintain temperatures in a useful range, yet avoids exceeding temperatures that the the metal constructing the reactor can withstand. While similar to the gas-cooled HTR it operates at low pressure (less than 1 atmosphere) and higher temperature, and gives better heat transfer than helium. Multiple pumps and six heat exchangers allow for redundancy. MSFRs have a negative void coefficient in the salt and a negative thermal reactivity feedback, so can maintain a high power density with passive safety. Ho M.K.M., Yeoh G.H., & Braoudakis G., 2013, Molten Salt Reactors, in Materials and processes for energy: communicating current research and technological developments, ed A.Mendez-Vilas, Formatex Research Centre, Merle-Lucotte, E. et al 2009, Minimising the fissile inventory of the Molten Salt Fast Reactor, Advances in Nuclear Fuel Management IV (ANFM 2009), American Nuclear Society, Merle-Lucotte, E. et al 2007, The Thorium molten salt reactor: launching the thorium cycle while closing the current fuel cycle, ENC 2007, Forsberg, C.W., Peterson, P.F., Zhao, H.H. Since the 2002 Generation IV selection process, significant changes in design philosophy have taken place, according to a 2015 report by Energy Process Developments Ltd (EPD). During the 1960s, the USA developed the molten salt breeder reactor concept at the Oak Ridge National Laboratory, Tennessee (built as part of the wartime Manhattan Project). MSRs would normally operate at much higher temperatures than LWRs – up to at least 700°C, and hence have potential for process heat. A molten salt reactor also converts heat to electricity, but in this case the fuel does not come in the form of pellets. 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. Compact Molten Salt Reactor Their aim is to make small reactors which they can mass produce in a central location and transport to customers. The 10 MWt TMSR-SF1 will have TRISO fuel in 60mm pebbles, similar to HTR-PM fuel, and deliver coolant at 650°C and low pressure. The first fluid fueled reactors were built during the Manhattan project. While NaCl has good nuclear, chemical and physical properties, its high melting point means it needs to be blended with MgCl2 or CaCl2, the former being preferred in eutectic, and allowing the addition of actinide trichlorides. See also Lithium paper. A slightly different type of MSR can consume the uranium/plutonium waste from solid-fueled reactors as fuel. This itself is not a radical departure when the fuel is solid and fixed. Some U-232 is also formed via Pa-232 along with Th-233, and a decay product of this is very gamma active. The aim is to develop both the thorium fuel cycle and non-electrical applications in a 20-30 year timeframe. Core temperature is 500-600°C, at atmospheric pressure. In August 2016 Southern Nuclear Operating Company signed an agreement to work with X-energy to collaborate on development and commercialization of their respective small reactor designs. In the thorium breeder version of SSR-U, thorium would be in the coolant salt and the U-233 produced is progressively dissolved in bismuth at the bottom of the salt pool. But extending the concept to dissolving the fissile and fertile fuel in the salt certainly represents a leap in lateral thinking relative to nearly every reactor operated so far. The aluminium smelting industry provides substantial experience in managing them safely. The Fuji MSR is a 100-200 MWe graphite-moderated design to operate as a near-breeder with ThF4-UF4 fuel salt and FLiBe coolant at 700°C. A recent report from the National Renewable Energy Lab (NREL) found that molten salt tanks had experienced leaks that required costly full drainage and refilling for repairs. The original objectives of the MSRE were achieved by March 1965, and the U-235 campaign concluded. The fuel-salt is a eutectic of low-enriched (2-4%) uranium-235 fuel (as UF4) and a fluoride carrier salt – likely sodium rubidium fluoride with potential to change to FLiBe – at atmospheric pressure. Once the desired level of U-233 is achieved, the bismuth with uranium is taken out batch-wise, and the mixed-isotope uranium is chlorinated to become fuel. It plans advanced experimental and numerical techniques, to deliver a breakthrough in nuclear safety and optimal waste management, and to create a consortium of stakeholders. How we test gear. Canada-based Terrestrial Energy has designed the Integral MSR. Lithium used in the salt must be fairly pure Li-7, since Li-6 produces tritium when (readily) fissioned by neutrons. Laboratory Director Argonne National Laboratory Gear-obsessed editors choose every product we review. Uranium floats in a stabilizing bath of melted fluoride salts inside this container. The Generation IV international Forum (GIF) mentions 'salt processing' as a technology gap for MSRs, putting the initial focus clearly on burners rather than breeders. This means that lithium must be enriched beyond its natural 92.5% Li-7 level to minimise tritium production. There are difficulties with plutonium and other TRU fluorides in fluoride solvents. A 100 MWt demonstration pebble bed plant with open fuel cycle is planned by about 2025. A 2 MWt pilot plant is envisaged, and eventually 2225 MWt commercial plants. Primary reactivity control is using the secondary coolant salt pump or circulation which changes the temperature of the fuel salt in the core, thus altering reactivity due to its strong negative reactivity coefficient. What is there to melt down then? The refuelling interval is 2.5 to 4 years depending on fuel configuration. There are active molten salt plants like Crescent Dunes in Nevada, which has experienced setbacks that reduce its overall efficiency from a desired 50 percent to just 20 percent. After a 20 MWt demonstration reactor, the envisaged first commercial plant will be 1250 MWt/550 MWe running at 44% thermal efficiency with 650°C in the primary loop, using a steam cycle. Secondary coolant is FLiNaK to Brayton cycle, and for passive decay heat removal, separate auxiliary loops go to air-cooled radiators. Decay heat removal can be by convection. TMSR commercial deployment is anticipated in the 2030s. It is also known as the Fluoride High Temperature Reactor (FHR). The salts concerned as primary coolant, mostly lithium-beryllium fluoride and lithium fluoride, remain liquid without pressurization from about 500°C up to about 1400°C, in marked contrast to a PWR which operates at about 315°C under 150 atmospheres pressure. The operating temperature is 700°C with FLiBe primary coolant and three integral heat exchangers. PuCl3 in NaCl has been well researched. (It is an intermediate product in producing U-233 and is a major neutron absorber.) Up to this temperature, satisfactory structural materials are available. We may earn commission if you buy from a link. Actinides are fully recycled and remain in the reactor until they fission or are converted to higher actinides which do so. A 300 MWe demonstration plant was envisaged, the SSR-W300 wasteburner. Much of the interest today in reviving the MSR concept relates to using thorium (to breed fissile uranium-233), where an initial source of fissile material such as plutonium-239 needs to be provided. It would proceed to a continuous process of recycling salt, uranium and thorium, with online separation of fission products and minor actinides. LiF however can carry a higher concentration of uranium than FLiBe, allowing less enrichment. * Fuel salt melting point 434°C, coolant salt melting point 455°C. The hot molten salt in the primary circuit can be used with secondary salt circuit or secondary helium coolant generating power via the Brayton cycle as with HTR designs, with potential thermal efficiencies of 48% at 750°C to 59% at 1000°C, or simply with steam generators. Molten Salt Reactor Rendering – the IMSR ® Core-unit. Heat is transferred to a secondary salt circuit and thence to steam or process heat. The first is to design simpler, less ambitious, molten salt reactors that do not breed new fuel, do not require online fuel reprocessing and which use the well-established enriched uranium fuel cycle. For molten salt reactor designs to succeed, political support and military dollars may again be necessary. The three nuclides (Li-7, Be, F) are among the few to have low enough thermal neutron capture cross-sections not to interfere with fission reactions. The nitty gritty results of experiments like this are critical to building a wider understanding of molten salt, especially when corrosion and other unanticipated engineering issues have been cited as one of the major obstacles to the technology by the NREL. Molten salt reactors (MSRs) use molten fluoride salts as primary coolant, at low pressure. Molten salt reactors, as a class, include both burners and breeders in fast or thermal spectra, using fluoride or chloride salt-based fuels and a range of fissile or fertile consumables. 2004, An advanced molten salt reactor using high-temperature reactor technology, American Nuclear Society, LeBlanc, D, 2009, Molten Salt Reactors: a new beginning for an old idea, Nuclear Engineering & Design 2010, Elsevier, Transatomic Power Corp., technical white paper, March 2014, Ignatiev, V & Feynberg, O, Kurchatov Inst, Molten Salt Reactor: overview and perspectives, OECD 2012, Appendix 6.0 Molten Salt Reactor, Generation IV Nuclear Energy Systems Ten-Year Program Plan – Fiscal Year 2007, Department of Energy Office of Nuclear Energy (September 2007), Hargraves, R & Moir, R, 2010, Liquid Fluoride Thorium Reactors, American Scientist 98, Fluoride-Salt-Cooled High-Temperature Reactors (FHRs) for Base-Load and Peak Electricity, Grid Stabilization, and Process Heat, Forsberg, Hu, Peterson, Sridharan, 2013, MIT, Wong, C & Merrill, B, 2004, Relevant MSRE and MSR Experience, ITER TBM Project Meeting at UCLA, 23-25 February 2004. “The models we want to generate with this data would be a great asset for engineers trying to design molten salt reactors,” Khaykovich concludes. Stable Salt Reactors would be safer than conventional plants because they ditch uranium fuel rods for a molten salt that can't react violently to any situation. A molten salt reactor (MSR) is a class of nuclear fission reactor in which the primary nuclear reactor coolant and/or the fuel is a molten salt mixture. In industrial applications molten fluoride salts (possibly simply cryolite – Na-Al fluoride) are a preferred interface fluid in a secondary circuit between the nuclear heat source and any chemical plant. However, the concept is not new, as outlined below. Two methods of tritium stripping are being evaluated, and also tritium storage. SINAP has two streams of TMSR development – solid fuel (TRISO in pebbles or prisms/blocks) with once-through fuel cycle, and liquid fuel (dissolved in fluoride coolant) with reprocessing and recycle. Kirk Sorensen has been a leader in promoting thorium energy, molten salt nuclear reactors and the liquid fluoride thorium reactor. Two versions were promoted in late 2018: SSR-W and, about two years behind developmentally, the SSR-U. A range of sizes from 110 to 2700 MWt are under consideration. The SAMOFAR (Safety Assessment of the Molten Salt Fast Reactor) project, based in the Netherlands and funded by the European Commission, aims to prove the safety concepts of the MSFR in breeding mode from thorium. The basic design is not a fast neutron reactor, but with some moderation by the graphite is epithermal (intermediate neutron speed) and breeding ratio is less than 1. The company had to withdraw some exaggerated claims concerning actinide burn-up made in MIT Technology Review in 2016. Are under consideration salt thermal expansion that reactor power levelled off at 9 MWt any... Neutron Source ( SNS ) rate of damage increases with temperature, satisfactory structural materials are.. Are intended to reach 850° to 1000°C, using materials yet to be piped around the system and.... 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