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MHD generator A magnetohydrodynamic generator ( MHD generator) is a device that transforms and into. MHD generators are different from traditional in that they operate at high temperatures without.
MHD was developed because the hot exhaust gas of an MHD generator can heat the boilers of a, increasing overall efficiency. MHD was developed as a to increase the efficiency of, especially when burning. MHD dynamos are the complement of, which have been applied to pump liquid metals and in several experimental ship engines.
An MHD generator, like a conventional generator, relies on moving a conductor through a to generate electric current. The MHD generator uses hot conductive as the moving conductor. The mechanical dynamo, in contrast, uses the motion of mechanical devices to accomplish this. MHD generators are technically practical for fossil fuels, but have been overtaken by other, less expensive technologies, such as in which a 's or 's exhaust heats to power a. Natural MHD dynamos are an active area of research in and are of great interest to the and communities, since the magnetic fields of the and are produced by these natural dynamos. Diagram of a Disk MHD generator showing current flows The third and, currently, the most efficient design is the Hall effect disc generator. This design currently holds the efficiency and energy density records for MHD generation.
A disc generator has fluid flowing between the center of a disc, and a duct wrapped around the edge. The magnetic excitation field is made by a pair of circular above and below the disk. The Faraday currents flow in a perfect dead short around the periphery of the disk. The Hall effect currents flow between ring electrodes near the center and ring electrodes near the periphery.
Another significant advantage of this design is that the magnet is more efficient. First, it has simple parallel field lines. Second, because the fluid is processed in a disk, the magnet can be closer to the fluid, and magnetic field strengths increase as the 2nd power of distance. Finally, the generator is compact for its power, so the magnet is also smaller. The resulting magnet uses a much smaller percentage of the generated power. Generator efficiency As of 1994, the 22% efficiency record for closed-cycle disc MHD generators was held by Tokyo Technical Institute.
The peak enthalpy extraction in these experiments reached 30.2%. Typical open-cycle Hall & duct coal MHD generators are lower, near 17%. These efficiencies make MHD unattractive, by itself, for utility power generation, since conventional power plants easily reach 40%. However, the exhaust of an MHD generator burning is almost as hot as the flame of a conventional steam boiler. By routing its exhaust gases into a boiler to make steam, MHD and a can convert into electricity with an estimated efficiency up to 60 percent, compared to the 40 percent of a typical coal plant. A magnetohydrodynamic generator might also be the first stage of a gas-cooled.
Economics MHD generators have not been employed for large scale mass energy conversion because other techniques with comparable efficiency have a lower lifecycle investment cost. Advances in natural gas turbines achieved similar thermal efficiencies at lower costs, by having the turbine's exhaust drive a steam plant. To get more electricity from coal, it is cheaper to simply add more low-temperature steam-generating capacity. A coal-fueled MHD generator is a type of, similar to the power cycle of a combustion turbine. However, unlike the combustion turbine, there are no moving mechanical parts; the electrically conducting plasma provides the moving electrical conductor.
The side walls and electrodes merely withstand the pressure within, while the anode and cathode conductors collect the electricity that is generated. All Brayton cycles are heat engines. Ideal Brayton cycles also have an ideal efficiency equal to ideal efficiency. Thus, the potential for high energy efficiency from an MHD generator. All Brayton cycles have higher potential for efficiency the higher the firing temperature.
While a combustion turbine is limited in maximum temperature by the strength of its air/water or steam-cooled rotating airfoils; there are no rotating parts in an open-cycle MHD generator. This upper bound in temperature limits the energy efficiency in combustion turbines. The upper bound on Brayton cycle temperature for an MHD generator is not limited, so inherently an MHD generator has a higher potential capability for energy efficiency.
U-25 In 1971 the natural-gas fired U-25 plant was completed near Moscow, with a designed capacity of 25 megawatts. By 1974 it delivered 6 megawatts of power. By 1994, Russia had developed and operated the coal-operated facility U-25, at the High-Temperature Institute of the in Moscow. U-25's bottoming plant was actually operated under contract with the Moscow utility, and fed power into Moscow's grid.
There was substantial interest in Russia in developing a coal-powered disc generator. See also.
Close-up of a replica of the core of the at the Nuclear fuel is a substance that is used in nuclear power stations to produce heat to power. Heat is created when nuclear fuel undergoes. Most nuclear fuels contain heavy elements that are capable of nuclear fission, such as uranium-235 or plutonium-239. When the unstable nuclei of these atoms are hit by a slow-moving neutron, they split, creating two daughter nuclei and two or three more. These neutrons then go on to split more nuclei. This creates a self-sustaining that is controlled in a, or uncontrolled in a. The processes involved in mining, refining, purifying, using, and disposing of nuclear fuel are collectively known as the.
Not all types of nuclear fuels create power from nuclear fission; and some other elements are used to produce small amounts of nuclear power by in and other types of. Nuclear fuel has the highest of all practical fuel sources.
The thermal conductivity of zirconium metal and uranium dioxide as a function of temperature UOX is a black solid. It can be made by reacting nitrate with a base to form a solid (ammonium uranate). It is heated (calcined) to form U 3O 8 that can then be converted by heating in an / mixture (700 °C) to form UO 2.
The UO 2 is then mixed with an organic binder and pressed into pellets, these pellets are then fired at a much higher temperature (in H 2/Ar) to the solid. The aim is to form a dense solid which has few pores. The thermal conductivity of uranium dioxide is very low compared with that of zirconium metal, and it goes down as the temperature goes up.
Corrosion of uranium dioxide in water is controlled by similar processes to the of a metal surface. Main article: Mixed oxide, or MOX fuel, is a blend of and natural or which behaves similarly (though not identically) to the enriched uranium feed for which most were designed. MOX fuel is an alternative to low enriched uranium (LEU) fuel used in the which predominate generation. Some concern has been expressed that used MOX cores will introduce new disposal challenges, though MOX is itself a means to dispose of surplus plutonium.
Reprocessing of commercial nuclear fuel to make MOX was done in the (England). As of 2015, MOX fuel is made in France (see ), and to a lesser extent in Russia (see ), India and Japan. China plans to develop (see ) and reprocessing. The, was a U.S. Proposal in the to form an international partnership to see spent nuclear fuel reprocessed in a way that renders the plutonium in it usable for nuclear fuel but not for.
Reprocessing of spent commercial-reactor nuclear fuel has not been permitted in the United States due to nonproliferation considerations. All of the other reprocessing nations have long had nuclear weapons from military-focused 'research'-reactor fuels except for Japan.Normally, with the fuel being changed every three years or so, about half of the Pu-239 is 'burned' in the reactor, providing about one third of the total energy. It behaves like U-235 and its fission releases a similar amount of energy. The higher the burn-up, the more plutonium in the spent fuel, but the lower the fraction of fissile plutonium. Typically about one percent of the used fuel discharged from a reactor is plutonium, and some two thirds of this is fissile (c. 50% Pu-239, 15% Pu-241). Worldwide, some 70 tonnes of plutonium contained in used fuel is removed when refueling reactors each year.
Metal fuel Metal fuels have the advantage of a much higher heat conductivity than oxide fuels but cannot survive equally high temperatures. Metal fuels have a long history of use, stretching from the in 1946 to many test and research reactors. Metal fuels have the potential for the highest fissile atom density. Metal fuels are normally alloyed, but some metal fuels have been made with pure uranium metal. Uranium alloys that have been used include uranium aluminum, uranium zirconium, uranium silicon, uranium molybdenum, and uranium zirconium hydride. Any of the aforementioned fuels can be made with plutonium and other actinides as part of a closed nuclear fuel cycle.
Metal fuels have been used in water reactors and liquid metal fast breeder reactors, such as. TRIGA fuel fuel is used in TRIGA (Training, Research, Isotopes, ) reactors. The TRIGA reactor uses UZrH fuel, which has a prompt negative, meaning that as the temperature of the core increases, the reactivity decreases—so it is highly unlikely for a meltdown to occur.
Most cores that use this fuel are 'high leakage' cores where the excess leaked neutrons can be utilized for research. TRIGA fuel was originally designed to use highly enriched uranium, however in 1978 the U.S. Department of Energy launched its Reduced Enrichment for Research Test Reactors program, which promoted reactor conversion to low-enriched uranium fuel. A total of 35 TRIGA reactors have been installed at locations across the USA.
A further 35 reactors have been installed in other countries. Actinide fuel In a, the minor actinides produced by neutron capture of uranium and plutonium can be used as fuel. Metal actinide fuel is typically an alloy of zirconium, uranium, plutonium, and. It can be made inherently safe as thermal expansion of the metal alloy will increase neutron leakage. Molten plutonium Molten plutonium, alloyed with other metals to lower its melting point and encapsulated in tantalum, was tested in two experimental reactors, LAMPRE I and LAMPRE II, at LANL in the 1960s. 'LAMPRE experienced three separate fuel failures during operation.' Ceramic fuels fuels other than oxides have the advantage of high heat conductivities and melting points, but they are more prone to than oxide fuels and are not understood as well.
Uranium nitride. Main article: This is often the fuel of choice for reactor designs that produces, one advantage is that UN has a better than UO 2. Uranium nitride has a very high melting point.
This fuel has the disadvantage that unless was used (in place of the more common ) that a large amount of would be generated from the nitrogen by the (n,p). As the required for such a fuel would be so expensive it is likely that the fuel would have to be reprocessed by to enable the 15N to be recovered. It is likely that if the fuel was processed and dissolved in that the nitrogen with 15N would be diluted with the common 14N. Uranium carbide. Main article: Much of what is known about uranium carbide is in the form of pin-type fuel elements for during their intense study during the 1960s and 1970s. However, recently there has been a revived interest in uranium carbide in the form of plate fuel and most notably, micro fuel particles (such as TRISO particles). The high thermal conductivity and high melting point makes uranium carbide an attractive fuel.
In addition, because of the absence of oxygen in this fuel (during the course of irradiation, excess gas pressure can build from the formation of O 2 or other gases) as well as the ability to complement a ceramic coating (a ceramic-ceramic interface has structural and chemical advantages), uranium carbide could be the ideal fuel candidate for certain such as the. Liquid fuels. This section does not any. Unsourced material may be challenged and. (July 2013) Liquid fuels are liquids containing dissolved nuclear fuel and have been shown to offer numerous operational advantages compared to traditional solid fuel approaches. Liquid-fuel reactors offer significant safety advantages due to their inherently stable 'self-adjusting' reactor dynamics.
This provides two major benefits: - virtually eliminating the possibility of a run-away reactor meltdown, - providing an automatic load-following capability which is well suited to electricity generation and high temperature industrial heat applications. Another major advantage of the liquid core is its ability to be drained rapidly into a passively safe dump-tank. This advantage was conclusively demonstrated repeatedly as part of a weekly shutdown procedure during the highly successful 4 year ORNL MSRE program.
Another huge advantage of the liquid core is its ability to release xenon gas which normally acts as a neutron absorber and causes structural occlusions in solid fuel elements (leading to early replacement of solid fuel rods with over 98% of the nuclear fuel unburned, including many long lived actinides). In contrast Molten Salt Reactors (MSR) are capable of retaining the fuel mixture for significantly extended periods, which not only increases fuel efficiency dramatically, but also incinerates the vast majority of its own waste as part of the normal operational characteristics. Molten salts Molten salt fuels have nuclear fuel dissolved directly in the molten salt coolant., such as the (LFTR), are different from molten salt-cooled reactors that do not dissolve nuclear fuel in the coolant. Molten salt fuels were used in the LFTR known as the, as well as other liquid core reactor experiments. The liquid fuel for the molten salt reactor was a mixture of lithium, beryllium, thorium and uranium fluorides: LiF-BeF 2-ThF 4-UF 4 (72-16-12-0.4 mol%).
It had a peak of 705 °C in the experiment, but could have operated at much higher temperatures, since the boiling point of the molten salt was in excess of 1400 °C. Aqueous solutions of uranyl salts The (AHRs) use a solution of or other uranium salt in water. Historically, AHRs have all been small, not large power reactors. An AHR known as the Medical Isotope Production System is being considered for production of medical isotopes. Common physical forms of nuclear fuel. See also: Uranium dioxide (UO 2) powder is compacted to cylindrical pellets and sintered at high temperatures to produce ceramic nuclear fuel pellets with a high density and well defined physical properties and chemical composition. A grinding process is used to achieve a uniform cylindrical geometry with narrow tolerances.
Such fuel pellets are then stacked and filled into the metallic tubes. The metal used for the tubes depends on the design of the reactor. Stainless steel was used in the past, but most reactors now use a which, in addition to being highly corrosion-resistant, has low neutron absorption.
The tubes containing the fuel pellets are sealed: these tubes are called fuel rods. The finished fuel rods are grouped into fuel assemblies that are used to build up the core of a power reactor. Cladding is the outer layer of the fuel rods, standing between the coolant and the nuclear fuel. It is made of a -resistant material with low for, usually or in modern constructions, or with small amount of aluminium and other metals for the now-obsolete. Cladding prevents radioactive fission fragments from escaping the fuel into the coolant and contaminating it. PWR fuel assembly (also known as a fuel bundle) This fuel assembly is from a pressurized water reactor of the nuclear-powered passenger and cargo ship.
Designed and built by the Babcock & Wilcox Company. PWR fuel (PWR) fuel consists of cylindrical rods put into bundles. A uranium oxide ceramic is formed into pellets and inserted into tubes that are bundled together. The Zircaloy tubes are about 1 cm in diameter, and the fuel cladding gap is filled with gas to improve the conduction of from the fuel to the cladding. There are about 179-264 fuel rods per fuel bundle and about 121 to 193 fuel bundles are loaded into a reactor core. Generally, the fuel bundles consist of fuel rods bundled 14×14 to 17×17. PWR fuel bundles are about 4 meters long.
In PWR fuel bundles, control rods are inserted through the top directly into the fuel bundle. The fuel bundles usually are enriched several percent in 235U. The uranium oxide is dried before inserting into the tubes to try to eliminate moisture in the ceramic fuel that can lead to corrosion and hydrogen embrittlement.
The Zircaloy tubes are pressurized with helium to try to minimize pellet-cladding interaction which can lead to fuel rod failure over long periods. BWR fuel In (BWR), the fuel is similar to PWR fuel except that the bundles are 'canned'. That is, there is a thin tube surrounding each bundle. This is primarily done to prevent local from affecting neutronics and thermal hydraulics of the reactor core.
In modern BWR fuel bundles, there are either 91, 92, or 96 fuel rods per assembly depending on the manufacturer. A range between 368 assemblies for the smallest and 800 assemblies for the largest U.S. BWR forms the reactor core.
Each BWR fuel rod is backfilled with helium to a pressure of about three atmospheres (300 kPa). CANDU fuel bundles Two ('CANada Deuterium Uranium') fuel bundles, each about 50 cm long, 10 cm in diameter. CANDU fuel CANDU fuel bundles are about a half meter long and 10 cm in diameter.
They consist of sintered (UO 2) pellets in zirconium alloy tubes, welded to zirconium alloy end plates. Each bundle is roughly 20 kg, and a typical core loading is on the order of 4500-6500 bundles, depending on the design. Modern types typically have 37 identical fuel pins radially arranged about the long axis of the bundle, but in the past several different configurations and numbers of pins have been used. The bundle has 43 fuel elements, with two element sizes. It is also about 10 cm (4 inches) in diameter, 0.5 m (20 in) long and weighs about 20 kg (44 lb) and replaces the 37-pin standard bundle. It has been designed specifically to increase fuel performance by utilizing two different pin diameters. Current CANDU designs do not need enriched uranium to achieve criticality (due to their more efficient ), however, some newer concepts call for low enrichment to help reduce the size of the reactors.
Introductory Nuclear Reactor Dynamics
Less-common fuel forms Various other nuclear fuel forms find use in specific applications, but lack the widespread use of those found in BWRs, PWRs, and CANDU power plants. Many of these fuel forms are only found in research reactors, or have military applications. A magnox fuel rod Magnox fuel are pressurised, –cooled, - reactors using (i.e. Unenriched) as fuel and as fuel cladding.
Working pressure varies from 6.9 to 19.35 for the steel pressure vessels, and the two reinforced concrete designs operated at 24.8 and 27 bar. Magnox alloy consists mainly of with small amounts of and other metals—used in cladding unenriched metal fuel with a non-oxidising covering to contain fission products. Magnox is short for Magnesium non- oxidising.
This material has the advantage of a low capture cross-section, but has two major disadvantages:. It limits the maximum temperature, and hence the thermal efficiency, of the plant. It reacts with water, preventing long-term storage of spent fuel under water. Magnox fuel incorporated cooling fins to provide maximum heat transfer despite low operating temperatures, making it expensive to produce.
Nuclear Reactor Dynamics
While the use of uranium metal rather than oxide made reprocessing more straightforward and therefore cheaper, the need to reprocess fuel a short time after removal from the reactor meant that the fission product hazard was severe. Expensive remote handling facilities were required to address this danger. TRISO fuel particle which has been cracked, showing the multiple coating layers TRISO fuel Tristructural- isotropic (TRISO) fuel is a type of micro fuel particle. It consists of a fuel kernel composed of (sometimes or UCO) in the center, coated with four layers of three materials. The four layers are a porous buffer layer made of carbon, followed by a dense inner layer of (PyC), followed by a ceramic layer of to retain fission products at elevated temperatures and to give the TRISO particle more structural integrity, followed by a dense outer layer of PyC.
TRISO fuel particles are designed not to crack due to the stresses from processes (such as differential thermal expansion or fission gas pressure) at temperatures up to and beyond 1600 °C, and therefore can contain the fuel in the worst of accident scenarios in a properly designed reactor. Two such reactor designs are the (PBR), in which thousands of TRISO fuel particles are dispersed into graphite pebbles, and the prismatic-block gas-cooled reactor (such as the ), in which the TRISO fuel particles are fabricated into compacts and placed in a graphite block matrix. Both of these reactor designs are (HTGRs). These are also the basic reactor designs of (VHTRs), one of the six classes of reactor designs in the that is attempting to reach even higher HTGR outlet temperatures. TRISO fuel particles were originally developed in the United Kingdom as part of the project.
The inclusion of the SiC as diffusion barrier was first suggested by D. The first nuclear reactor to use TRISO fuels was the Dragon reactor and the first powerplant was the. Currently, TRISO fuel compacts are being used in the experimental reactors, the in China, and the in Japan. Spherical fuel elements utilizing a TRISO particle with a and solid solution kernel are being used in the in the United States. QUADRISO Particle QUADRISO fuel In QUADRISO particles a ( or or ) layer surrounds the fuel kernel of ordinary TRISO particles to better manage the excess of reactivity.
If the core is equipped both with TRISO and QUADRISO fuels, at beginning of life neutrons do not reach the fuel of the QUADRISO particles because they are stopped by the burnable poison. After irradiation, the poison depletes and neutrons stream into the fuel kernel of QUADRISO particles inducing fission reactions. This mechanism compensates fuel depletion of ordinary TRISO fuel. In the generalized QUADRISO fuel concept the poison can eventually be mixed with the fuel kernel or the outer pyrocarbon.
The QUADRISO concept has been conceived. RBMK reactor fuel rod holder 1 – distancing armature; 2 – fuel rods shell; 3 – fuel tablets. RBMK fuel RBMK reactor fuel was used in -designed and built -type reactors.
This is a low-enriched uranium oxide fuel. The fuel elements in an RBMK are 3 m long each, and two of these sit back-to-back on each fuel channel, pressure tube.
Reprocessed uranium from Russian VVER reactor spent fuel is used to fabricate RBMK fuel. Following the Chernobyl accident, the enrichment of fuel was changed from 2.0% to 2.4%, to compensate for control rod modifications and the introduction of additional absorbers. CerMet fuel CerMet fuel consists of ceramic fuel particles (usually uranium oxide) embedded in a metal matrix.
It is hypothesized that this type of fuel is what is used in United States Navy reactors. This fuel has high heat transport characteristics and can withstand a large amount of expansion. ATR Core The at uses plate-type fuel in a clover leaf arrangement. The blue glow around the core is known as. Plate-type fuel Plate-type fuel has fallen out of favor over the years.
Plate-type fuel is commonly composed of enriched uranium sandwiched between metal cladding. Plate-type fuel is used in several research reactors where a high neutron flux is desired, for uses such as material irradiation studies or isotope production, without the high temperatures seen in ceramic, cylindrical fuel.
It is currently used in the (ATR) at, and the nuclear research reactor at the. Sodium-bonded fuel Sodium-bonded fuel consists of fuel that has liquid sodium in the gap between the fuel slug (or pellet) and the cladding. This fuel type is often used for sodium-cooled liquid metal fast reactors. It has been used in EBR-I, EBR-II, and the FFTF. The fuel slug may be metallic or ceramic. The sodium bonding is used to reduce the temperature of the fuel. Main article: Used nuclear fuel is a complex mixture of the, and the.
In fuel which has been used at high temperature in power reactors it is common for the fuel to be heterogeneous; often the fuel will contain nanoparticles of metals such as. Also the fuel may well have cracked, swollen, and been heated close to its melting point. Despite the fact that the used fuel can be cracked, it is very insoluble in water, and is able to retain the vast majority of the and within the. Oxide fuel under accident conditions. Main article: Post-Irradiation Examination (PIE) is the study of used nuclear materials such as nuclear fuel.
It has several purposes. It is known that by examination of used fuel that the failure modes which occur during normal use (and the manner in which the fuel will behave during an accident) can be studied.
In addition information is gained which enables the users of fuel to assure themselves of its quality and it also assists in the development of new fuels. After major accidents the core (or what is left of it) is normally subject to PIE to find out what happened.
One site where PIE is done is the ITU which is the EU centre for the study of highly radioactive materials. Materials in a high-radiation environment (such as a reactor) can undergo unique behaviors such as swelling and non-thermal creep. If there are nuclear reactions within the material (such as what happens in the fuel), the stoichiometry will also change slowly over time. These behaviors can lead to new material properties, cracking, and fission gas release. The of is low; it is affected by and burn-up. The burn-up results in being dissolved in the (such as ), the precipitation of fission products such as, the formation of fission gas due to fission products such as and and radiation damage of the lattice.
The low thermal conductivity can lead to overheating of the center part of the pellets during use. The porosity results in a decrease in both the thermal conductivity of the fuel and the swelling which occurs during use. According to the the thermal conductivity of uranium dioxide can be predicted under different conditions by a series of equations. The bulk of the fuel can be related to the thermal conductivity Where ρ is the bulk density of the fuel and ρ td is the theoretical density of the. Then the thermal conductivity of the porous phase ( K f) is related to the conductivity of the perfect phase ( K o, no porosity) by the following equation.
Note that s is a term for the shape factor of the holes. K f = K o(1 − p/1 + ( s − 1) p) Rather than using the traditional methods such as, the, or, it is common to use where a small disc of fuel is placed in a furnace. After being heated to the required temperature one side of the disc is illuminated with a laser pulse, the time required for the heat wave to flow through the disc, the density of the disc, and the thickness of the disk can then be used to calculate and determine the thermal conductivity. Λ = ρC p α. λ. ρ.
C p. α If t 1/2 is defined as the time required for the non illuminated surface to experience half its final temperature rise then. Α = 0.1388 L 2/ t 1/2. L is the thickness of the disc For details see Radioisotope decay fuels Radioisotope battery.
Main article: The terms, nuclear battery and radioisotope battery are used interchangeably to describe a device which uses the radioactive decay to generate electricity. These systems use that produce low energy beta particles or sometimes alpha particles of varying energies. Low energy beta particles are needed to prevent the production of high energy penetrating radiation that would require heavy shielding. Radioisotopes such as, and have been used., and have been tested. There are two main categories of atomic batteries: thermal and non-thermal. The non-thermal atomic batteries, which have many different designs, exploit charged and. Install windows 8 on surface rt.
These designs include the, the, and the. The thermal atomic batteries on the other hand, convert the heat from the radioactive decay to electricity. These designs include thermionic converter, thermophotovoltaic cells, alkali-metal thermal to electric converter, and the most common design, the radioisotope thermoelectric generator. Radioisotope thermoelectric generators.
Inspection of RTGs before launch A ( RTG) is a simple which converts heat into from a radioisotope using an array of. Has become the most widely used fuel for RTGs, in the form of. It has a half-life of 87.7 years, reasonable energy density, and exceptionally low gamma and neutron radiation levels. Some Russian terrestrial RTGs have used; this isotope has a shorter half-life and a much lower energy density, but is cheaper. Early RTGs, first built in 1958 by the, have used. This fuel provides phenomenally huge energy density, (a single gram of polonium-210 generates 140 watts thermal) but has limited use because of its very short half-life and gamma production, and has been phased out of use for this application. Main article: Fusion fuels include ( 2H) and ( 3H) as well as ( 3He).
Many other elements can be fused together, but the larger electrical charge of their nuclei means that much higher temperatures are required. Only the fusion of the lightest elements is seriously considered as a future energy source. Fusion of the lightest atom, 1H, as is done in the Sun and stars, has also not been considered practical on Earth. Although the energy density of fusion fuel is even higher than fission fuel, and fusion reactions sustained for a few minutes have been achieved, utilizing fusion fuel as a net energy source remains only a theoretical possibility.
First-generation fusion fuel Deuterium and tritium are both considered first-generation fusion fuels; they are the easiest to fuse, because the electrical charge on their nuclei is the lowest of all elements. The three most commonly cited nuclear reactions that could be used to generate energy are: 2H + 3H → (14.07 MeV) + 4He (3.52 MeV) 2H + 2H → (2.45 MeV) + 3He (0.82 MeV) 2H + 2H → (3.02 MeV) + 3H (1.01 MeV) Second-generation fusion fuel Second-generation fuels require either higher confinement temperatures or longer confinement time than those required of first-generation fusion fuels, but generate fewer neutrons. Neutrons are an unwanted byproduct of fusion reactions in an energy generation context, because they are absorbed by the walls of a fusion chamber, making them radioactive. They cannot be confined by magnetic fields, because they are not electrically charged. This group consists of deuterium and helium-3. The products are all charged particles, but there may be significant side reactions leading to the production of neutrons. 2H + 3He → (14.68 MeV) + 4He (3.67 MeV) Third-generation fusion fuel.
Main article: Third-generation fusion fuels produce only charged particles in the primary reactions, and side reactions are relatively unimportant. Since a very small amount of neutrons is produced, there would be little induced radioactivity in the walls of the fusion chamber. This is often seen as the end goal of fusion research. 3He has the highest Maxwellian reactivity of any 3rd generation fusion fuel. However, there are no significant natural sources of this substance on Earth.
3He + 3He → 2 + 4He (12.86 MeV) Another potential aneutronic fusion reaction is the proton- reaction: + 11B → 3 4He (8.7 MeV) Under reasonable assumptions, side reactions will result in about 0.1% of the fusion power being carried by neutrons. With 123 keV, the optimum temperature for this reaction is nearly ten times higher than that for the pure hydrogen reactions, the energy confinement must be 500 times better than that required for the D-T reaction, and the power density will be 2500 times lower than for D-T.
See also. (PDF) from the original on 2016-10-21. Retrieved 2016-06-04. (PDF) from the original on 2016-04-15. Retrieved 2013-11-11. The Babcock & Wilcox Company.
'The Dragon Project origins, achievements and legacies'. World Nuclear Association. September 2009. Retrieved 2010-01-27.
External links PWR fuel. BWR fuel.
CANDU fuel. TRISO fuel. QUADRISO fuel. CERMET fuel. Plate type fuel.
TRIGA fuel. Fusion fuel.