Nuclear fuel refers to any substance, typically fissile material, which is used by nuclear power stations or other nuclear devices to generate energy.
128-638: Springfields is a nuclear fuel production installation in Salwick , near Preston in Lancashire , England ( grid reference SD468315 ). The site is currently operated by Springfields Fuels Limited, under the management of Westinghouse Electric UK Limited , on a 150-year lease from the Nuclear Decommissioning Authority . Since its conversion from a munitions factory in 1946, it has previously been operated and managed by
256-579: A critical mass . During the early stages of research, animals were used to study the effects of radioactive substances on health. These studies began in 1944 at the University of California at Berkeley's Radiation Laboratory and were conducted by Joseph G. Hamilton. Hamilton was looking to answer questions about how plutonium would vary in the body depending on exposure mode (oral ingestion, inhalation, absorption through skin), retention rates, and how plutonium would be fixed in tissues and distributed among
384-422: A fertile material . Twenty-two radioisotopes of plutonium have been characterized, from Pu to Pu. The longest-lived are Pu, with a half-life of 80.8 million years; Pu, with a half-life of 373,300 years; and Pu, with a half-life of 24,110 years. All other isotopes have half-lives of less than 7,000 years. This element also has eight metastable states , though all have half-lives less than
512-458: A multiplication factor (k eff ) larger than one, which means that if the metal is present in sufficient quantity and with an appropriate geometry (e.g., a sphere of sufficient size), it can form a critical mass . During fission, a fraction of the nuclear binding energy , which holds a nucleus together, is released as a large amount of electromagnetic and kinetic energy (much of the latter being quickly converted to thermal energy). Fission of
640-450: A nuclear chain reaction , leading to applications in nuclear weapons and nuclear reactors . Plutonium-240 has a high rate of spontaneous fission , raising the neutron flux of any sample containing it. The presence of plutonium-240 limits a plutonium sample's usability for weapons or its quality as reactor fuel, and the percentage of plutonium-240 determines its grade ( weapons-grade , fuel-grade, or reactor-grade). Plutonium-238 has
768-414: A vacuum or an inert atmosphere to avoid reaction with air. At 135 °C the metal will ignite in air and will explode if placed in carbon tetrachloride . Plutonium is a reactive metal. In moist air or moist argon , the metal oxidizes rapidly, producing a mixture of oxides and hydrides . If the metal is exposed long enough to a limited amount of water vapor, a powdery surface coating of PuO 2
896-406: 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 electrochemical processes to the galvanic corrosion of a metal surface. While exposed to the neutron flux during normal operation in the core environment,
1024-432: A fuel would be so expensive it is likely that the fuel would require pyroprocessing to enable recovery of the N. It is likely that if the fuel was processed and dissolved in nitric acid that the nitrogen enriched with N would be diluted with the common N. Fluoride volatility is a method of reprocessing that does not rely on nitric acid, but it has only been demonstrated in relatively small scale installations whereas
1152-508: A half-life of 87.7 years and emits alpha particles . It is a heat source in radioisotope thermoelectric generators , which are used to power some spacecraft . Plutonium isotopes are expensive and inconvenient to separate, so particular isotopes are usually manufactured in specialized reactors. Producing plutonium in useful quantities for the first time was a major part of the Manhattan Project during World War II that developed
1280-453: A kernel of UO X fuel (sometimes UC or UCO), which has been coated with four layers of three isotropic materials deposited through fluidized chemical vapor deposition (FCVD). The four layers are a porous buffer layer made of carbon that absorbs fission product recoils, followed by a dense inner layer of protective pyrolytic carbon (PyC), followed by a ceramic layer of SiC to retain fission products at elevated temperatures and to give
1408-431: A kilogram of plutonium-239 can produce an explosion equivalent to 21,000 tons of TNT (88,000 GJ ). It is this energy that makes plutonium-239 useful in nuclear weapons and reactors . The presence of the isotope plutonium-240 in a sample limits its nuclear bomb potential, as Pu has a relatively high spontaneous fission rate (~440 fissions per second per gram; over 1,000 neutrons per second per gram), raising
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#17327718952091536-463: A large range of temperatures (over 2,500 kelvin wide) at which plutonium is liquid, but this range is neither the greatest among all actinides nor among all metals, with neptunium theorized to have the greatest range in both instances. The low melting point as well as the reactivity of the native metal compared to the oxide leads to plutonium oxides being a preferred form for applications such as nuclear fission reactor fuel ( MOX-fuel ). Alpha decay ,
1664-426: A limited pressure range. These allotropes, which are different structural modifications or forms of an element, have very similar internal energies but significantly varying densities and crystal structures . This makes plutonium very sensitive to changes in temperature, pressure, or chemistry, and allows for dramatic volume changes following phase transitions from one allotropic form to another. The densities of
1792-605: A number of different organisations including the United Kingdom Atomic Energy Authority and British Nuclear Fuels . Fuel products are produced for the UK's nuclear power stations and for international customers. The site has been making nuclear fuels since the mid-1940s. The site is notable for being the first nuclear plant in the world to produce Magnox fuel for a commercial power station ( Calder Hall ). The four main activities carried out on
1920-491: A powder that is pyrophoric . It is radioactive and can accumulate in bones , which makes the handling of plutonium dangerous. Plutonium was first synthesized and isolated in late 1940 and early 1941, by deuteron bombardment of uranium-238 in the 1.5-metre (60 in) cyclotron at the University of California, Berkeley . First, neptunium-238 ( half-life 2.1 days) was synthesized, which then beta-decayed to form
2048-624: A properly designed reactor. Two such reactor designs are the prismatic-block gas-cooled reactor (such as the GT-MHR ) and the pebble-bed reactor (PBR). Both of these reactor designs are high temperature gas reactors (HTGRs). These are also the basic reactor designs of very-high-temperature reactors (VHTRs), one of the six classes of reactor designs in the Generation IV initiative that is attempting to reach even higher HTGR outlet temperatures. TRISO fuel particles were originally developed in
2176-768: A reactor is plutonium, and some two thirds of this is fissile (c. 50% Pu , 15% Pu ). 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 Clementine reactor 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, uranium zirconium hydride (UZrH), and uranium zirconium carbonitride. Any of
2304-454: A reduction mechanism similar to FeO 4 , PuO 4 can be stabilized in alkaline solutions and chloroform . Metallic plutonium is produced by reacting plutonium tetrafluoride with barium , calcium or lithium at 1200 °C. Metallic plutonium is attacked by acids , oxygen , and steam but not by alkalis and dissolves easily in concentrated hydrochloric , hydroiodic and perchloric acids . Molten metal must be kept in
2432-493: A relatively short half-life, U decays to Np, which decays into Pu. Finally, exceedingly small amounts of plutonium-238, attributed to the extremely rare double beta decay of uranium-238, have been found in natural uranium samples. Due to its relatively long half-life of about 80 million years, it was suggested that plutonium-244 occurs naturally as a primordial nuclide , but early reports of its detection could not be confirmed. Based on its likely initial abundance in
2560-507: A second. Pu has been found in interstellar space and it has the longest half-life of any non-primordial radioisotope. The main decay modes of isotopes with mass numbers lower than the most stable isotope, Pu, are spontaneous fission and alpha emission , mostly forming uranium (92 protons ) and neptunium (93 protons) isotopes as decay products (neglecting the wide range of daughter nuclei created by fission processes). The main decay mode for isotopes heavier than Pu, along with Pu and Pu,
2688-867: A similar design to the CANDU but built by German KWU was originally designed for non-enriched fuel but since switched to slightly enriched fuel with a U content about 0.1 percentage points higher than in natural uranium. 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. Magnox (magnesium non-oxidising) reactors are pressurised, carbon dioxide –cooled, graphite - moderated reactors using natural uranium (i.e. unenriched) as fuel and Magnox alloy as fuel cladding. Working pressure varies from 6.9 to 19.35 bars (100.1 to 280.6 psi) for
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#17327718952092816-452: A small percentage of the U in the fuel absorbs excess neutrons and is transmuted into U . U rapidly decays into Np which in turn rapidly decays into Pu . The small percentage of Pu has a higher neutron cross section than U . As the Pu accumulates the chain reaction shifts from pure U at initiation of the fuel use to a ratio of about 70% U and 30% Pu at the end of
2944-409: A solid called ammonium diuranate , (NH 4 ) 2 U 2 O 7 . This is then heated ( calcined ) to form UO 3 and U 3 O 8 which is then converted by heating with hydrogen or ammonia to form UO 2 . The UO 2 is mixed with an organic binder and pressed into pellets. The pellets are then fired at a much higher temperature (in hydrogen or argon) to sinter the solid. The aim is to form
3072-476: 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 CANFLEX 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
3200-399: A typical spent fuel assembly still exceeds 10,000 rem/hour, resulting in a fatal dose in just minutes. Two main modes of release exist, the fission products can be vaporised or small particles of the fuel can be dispersed. 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
3328-404: A way as to ensure low contamination with non-radioactive carbon (not a common fission product and absent in nuclear reactors that don't use it as a moderator ) then fluoride volatility could be used to separate the C produced by producing carbon tetrafluoride . C is proposed for use in particularly long lived low power nuclear batteries called diamond batteries . Much of what
3456-399: Is beta emission , forming americium isotopes (95 protons). Plutonium-241 is the parent isotope of the neptunium series , decaying to americium-241 via beta emission. Plutonium-238 and 239 are the most widely synthesized isotopes. Pu is synthesized via the following reaction using uranium (U) and neutrons (n) via beta decay (β ) with neptunium (Np) as an intermediate: Neutrons from
3584-490: Is plutonocene . Computational chemistry methods indicate an enhanced covalent character in the plutonium-ligand bonding. Powders of plutonium, its hydrides and certain oxides like Pu 2 O 3 are pyrophoric , meaning they can ignite spontaneously at ambient temperature and are therefore handled in an inert, dry atmosphere of nitrogen or argon. Bulk plutonium ignites only when heated above 400 °C. Pu 2 O 3 spontaneously heats up and transforms into PuO 2 , which
3712-730: Is a means to dispose of surplus plutonium by transmutation . Reprocessing of commercial nuclear fuel to make MOX was done in the Sellafield MOX Plant (England). As of 2015, MOX fuel is made in France at the Marcoule Nuclear Site , and to a lesser extent in Russia at the Mining and Chemical Combine , India and Japan. China plans to develop fast breeder reactors and reprocessing. The Global Nuclear Energy Partnership
3840-485: Is a radioactive actinide metal whose isotope , plutonium-239 , is one of the three primary fissile isotopes ( uranium-233 and uranium-235 are the other two); plutonium-241 is also highly fissile. To be considered fissile, an isotope's atomic nucleus must be able to break apart or fission when struck by a slow moving neutron and to release enough additional neutrons to sustain the nuclear chain reaction by splitting further nuclei. Pure plutonium-239 may have
3968-403: Is a silvery-gray actinide metal that tarnishes when exposed to air, and forms a dull coating when oxidized . The element normally exhibits six allotropes and four oxidation states . It reacts with carbon , halogens , nitrogen , silicon , and hydrogen . When exposed to moist air, it forms oxides and hydrides that can expand the sample up to 70% in volume, which in turn flake off as
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4096-475: Is able to release xenon gas, which normally acts as a neutron absorber ( Xe is the strongest known neutron poison and is produced both directly and as a decay product of I as a fission product ) and causes structural occlusions in solid fuel elements (leading to the early replacement of solid fuel rods with over 98% of the nuclear fuel unburned, including many long-lived actinides). In contrast, molten-salt reactors are capable of retaining
4224-498: 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 Advanced Test Reactor (ATR) at Idaho National Laboratory , and the nuclear research reactor at
4352-410: 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
4480-596: 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 thermal conductivity of uranium dioxide
4608-566: Is formed into pellets and inserted into Zircaloy tubes that are bundled together. The Zircaloy tubes are about 1 centimetre (0.4 in) in diameter, and the fuel cladding gap is filled with helium gas to improve heat conduction 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 m (13 ft) long. In PWR fuel bundles, control rods are inserted through
4736-429: Is formed. Also formed is plutonium hydride but an excess of water vapor forms only PuO 2 . Plutonium shows enormous, and reversible, reaction rates with pure hydrogen, forming plutonium hydride . It also reacts readily with oxygen, forming PuO and PuO 2 as well as intermediate oxides; plutonium oxide fills 40% more volume than plutonium metal. The metal reacts with the halogens , giving rise to compounds with
4864-460: Is in its α ( alpha ) form . This allotrope is about as hard and brittle as gray cast iron . When plutonium is alloyed with other metals, the high-temperature δ allotrope is stabilized at room temperature, making it soft and ductile. Unlike most metals, it is not a good conductor of heat or electricity . It has a low melting point (640 °C, 1,184 °F) and an unusually high boiling point (3,228 °C, 5,842 °F). This gives
4992-450: Is known about uranium carbide is in the form of pin-type fuel elements for liquid metal fast reactors during their intense study in the 1960s and 1970s. Recently there has been a revived interest in uranium carbide in the form of plate fuel and most notably, micro fuel particles (such as tristructural-isotropic particles). The high thermal conductivity and high melting point makes uranium carbide an attractive fuel. In addition, because of
5120-426: Is likely that Hahn and Strassmann were aware that plutonium-239 should be fissile. However, they did not have a strong neutron source. Element 93 was reported by Hahn and Strassmann, as well as Starke, in 1942. Hahn's group did not pursue element 94, likely because they were discouraged by McMillan and Abelson's lack of success in isolating it when they had first found element 93. However, since Hahn's group had access to
5248-413: Is low; it is affected by porosity and burn-up. The burn-up results in fission products being dissolved in the lattice (such as lanthanides ), the precipitation of fission products such as palladium , the formation of fission gas bubbles due to fission products such as xenon and krypton and radiation damage of the lattice. The low thermal conductivity can lead to overheating of the center part of
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5376-435: Is responsible for directional covalent bonds in molecules and complexes of plutonium. Plutonium can form alloys and intermediate compounds with most other metals. Exceptions include lithium, sodium , potassium , rubidium and caesium of the alkali metals ; and magnesium , calcium, strontium , and barium of the alkaline earth metals ; and europium and ytterbium of the rare earth metals . Partial exceptions include
5504-414: Is roughly as strong and malleable as aluminium. In fission weapons, the explosive shock waves used to compress a plutonium core will also cause a transition from the usual δ phase plutonium to the denser α form, significantly helping to achieve supercriticality . The ε phase, the highest temperature solid allotrope, exhibits anomalously high atomic self-diffusion compared to other elements. Plutonium
5632-402: Is stable in dry air, but reacts with water vapor when heated. Crucibles used to contain plutonium need to be able to withstand its strongly reducing properties. Refractory metals such as tantalum and tungsten along with the more stable oxides, borides , carbides , nitrides and silicides can tolerate this. Melting in an electric arc furnace can be used to produce small ingots of
5760-544: Is unusual for metals. This trend continues down to 100 K , below which resistivity rapidly decreases for fresh samples. Resistivity then begins to increase with time at around 20 K due to radiation damage, with the rate dictated by the isotopic composition of the sample. Because of self-irradiation, a sample of plutonium fatigues throughout its crystal structure, meaning the ordered arrangement of its atoms becomes disrupted by radiation with time. Self-irradiation can also lead to annealing which counteracts some of
5888-404: Is used in U.S. Navy weapons stored near ship and submarine crews, due to its lower radioactivity. Plutonium-238 is not fissile but can undergo nuclear fission easily with fast neutrons as well as alpha decay. All plutonium isotopes can be "bred" into fissile material with one or more neutron absorptions , whether followed by beta decay or not. This makes non-fissile isotopes of plutonium
6016-429: Is usually listed as watt/kilogram, or milliwatt/gram. In larger pieces of plutonium (e.g. a weapon pit) and inadequate heat removal the resulting self-heating may be significant. At room temperature, pure plutonium is silvery in color but gains a tarnish when oxidized. The element displays four common ionic oxidation states in aqueous solution and one rare one: The color shown by plutonium solutions depends on both
6144-529: The C concentration will be too low for use in nuclear batteries without enrichment. Nuclear graphite discharged from reactors where it was used as a moderator presents the same issue. Liquid fuels contain 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
6272-464: The Cigar Lake Mine uranium deposit ranges from 2.4 × 10 to 44 × 10 . These trace amounts of Pu originate in the following fashion: on rare occasions, U undergoes spontaneous fission, and in the process, the nucleus emits one or two free neutrons with some kinetic energy. When one of these neutrons strikes the nucleus of another U atom, it is absorbed by the atom, which becomes U. With
6400-472: The Cold War is a nuclear-proliferation and environmental concern. Other sources of plutonium in the environment are fallout from many above-ground nuclear tests, which are now banned . Plutonium, like most metals, has a bright silvery appearance at first, much like nickel , but it oxidizes very quickly to a dull gray, though yellow and olive green are also reported. At room temperature plutonium
6528-459: The Manhattan Project , for developing an atomic bomb. The three primary research and production sites of the project were the plutonium production facility at what is now the Hanford Site ; the uranium enrichment facilities at Oak Ridge, Tennessee ; and the weapons research and design lab, now known as Los Alamos National Laboratory , LANL. The first production reactor that made Pu was
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#17327718952096656-512: The University of Massachusetts Lowell Radiation Laboratory . 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
6784-404: The liquid fluoride thorium reactor (LFTR), this fuel salt is also the coolant; in other designs, such as the stable salt reactor , the fuel salt is contained in fuel pins and the coolant is a separate, non-radioactive salt. There is a further category of molten salt-cooled reactors in which the fuel is not in molten salt form, but a molten salt is used for cooling. Molten salt fuels were used in
6912-502: The r-process in supernovae and colliding neutron stars ; when nuclei are ejected from these events at high speed to reach Earth, Pu alone among transuranic nuclides has a long enough half-life to survive the journey, and hence tiny traces of live interstellar Pu have been found in the deep sea floor. Because Pu also occurs in the decay chain of Pu, it must thus also be present in secular equilibrium , albeit in even tinier quantities. Minute traces of plutonium are usually found in
7040-509: The 18 to 24 month fuel exposure period. Mixed oxide , or MOX fuel , is a blend of plutonium and natural or depleted uranium which behaves similarly (though not identically) to the enriched uranium feed for which most nuclear reactors were designed. MOX fuel is an alternative to low enriched uranium (LEU) fuel used in the light water reactors which predominate nuclear power generation. Some concern has been expressed that used MOX cores will introduce new disposal challenges, though MOX
7168-504: 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 the lower neutron absorption in their heavy water moderator compared to light water), however, some newer concepts call for low enrichment to help reduce the size of the reactors. The Atucha nuclear power plant in Argentina,
7296-469: The 6d and 5f subshells is very low. The size of the 5f shell is just enough to allow the electrons to form bonds within the lattice, on the very boundary between localized and bonding behavior. The proximity of energy levels leads to multiple low-energy electron configurations with near equal energy levels. This leads to competing 5f 7s and 5f 6d 7s configurations, which causes the complexity of its chemical behavior. The highly directional nature of 5f orbitals
7424-537: The LFTR known as the Molten Salt Reactor Experiment, 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 operating temperature of 705 °C in the experiment, but could have operated at much higher temperatures since
7552-541: The Solar System, present experiments as of 2022 are likely about an order of magnitude away from detecting live primordial Pu. However, its long half-life ensured its circulation across the solar system before its extinction , and indeed, evidence of the spontaneous fission of extinct Pu has been found in meteorites. The former presence of Pu in the early Solar System has been confirmed, since it manifests itself today as an excess of its daughters, either Th (from
7680-479: The TRISO particle more structural integrity, followed by a dense outer layer of PyC. TRISO particles are then encapsulated into cylindrical or spherical graphite pellets. 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 1600 °C, and therefore can contain the fuel in the worst of accident scenarios in
7808-526: The US and an additional 35 in other countries. In a fast-neutron reactor , 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 minor actinides . It can be made inherently safe as thermal expansion of the metal alloy will increase neutron leakage. Molten plutonium, alloyed with other metals to lower its melting point and encapsulated in tantalum ,
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#17327718952097936-856: The United Kingdom as part of the Dragon reactor project. The inclusion of the SiC as diffusion barrier was first suggested by D. T. Livey. The first nuclear reactor to use TRISO fuels was the Dragon reactor and the first powerplant was the THTR-300 . Currently, TRISO fuel compacts are being used in some experimental reactors, such as the HTR-10 in China and the high-temperature engineering test reactor in Japan. In
8064-519: The United States, spherical fuel elements utilizing a TRISO particle with a UO 2 and UC solid solution kernel are being used in the Xe-100 , and Kairos Power is developing a 140 MWE nuclear reactor that uses TRISO. In QUADRISO particles a burnable neutron poison ( europium oxide or erbium oxide or carbide ) layer surrounds the fuel kernel of ordinary TRISO particles to better manage
8192-484: The X-10 reactor. Information from CP-1 was also useful to Met Lab scientists designing the water-cooled plutonium production reactors for Hanford. Construction at the site began in mid-1943. In November 1943 some plutonium trifluoride was reduced to create the first sample of plutonium metal: a few micrograms of metallic beads. Enough plutonium was produced to make it the first synthetically made element to be visible with
8320-401: 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 Generation IV reactors such as the gas-cooled fast reactor . While
8448-490: The advantage of avoiding dealing directly with the highly reactive plutonium metal. Trace amounts of plutonium-238, plutonium-239, plutonium-240, and plutonium-244 can be found in nature. Small traces of plutonium-239, a few parts per trillion , and its decay products are naturally found in some concentrated ores of uranium, such as the natural nuclear fission reactor in Oklo , Gabon . The ratio of plutonium-239 to uranium at
8576-519: 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 light-water reactors and liquid metal fast breeder reactors , such as Experimental Breeder Reactor II . TRIGA fuel is used in TRIGA (Training, Research, Isotopes, General Atomics ) reactors. The TRIGA reactor uses UZrH fuel, which has a prompt negative fuel temperature coefficient of reactivity , meaning that as
8704-416: The alpha decay pathway) or xenon isotopes (from its spontaneous fission ). The latter are generally more useful, because the chemistries of thorium and plutonium are rather similar (both are predominantly tetravalent) and hence an excess of thorium would not be strong evidence that some of it was formed as a plutonium daughter. Pu has the longest half-life of all transuranic nuclides and is produced only in
8832-424: The application of the new fuel-cladding material systems for various types of ATF materials. The aim of the research is to develop nuclear fuels that can tolerate loss of active cooling for a considerably longer period than the existing fuel designs and prevent or delay the release of radionuclides during an accident. This research is focused on reconsidering the design of fuel pellets and cladding, as well as
8960-399: The background neutron levels and thus increasing the risk of predetonation . Plutonium is identified as either weapons-grade , fuel-grade, or reactor-grade based on the percentage of Pu that it contains. Weapons-grade plutonium contains less than 7% Pu. Fuel-grade plutonium contains 7%–19%, and power reactor-grade contains 19% or more Pu. Supergrade plutonium , with less than 4% of Pu,
9088-420: The boiling point of the molten salt was in excess of 1400 °C. The aqueous homogeneous reactors (AHRs) use a solution of uranyl sulfate or other uranium salt in water. Historically, AHRs have all been small research reactors, not large power reactors. The dual fluid reactor (DFR) has a variant DFR/m which works with eutectic liquid metal alloys, e.g. U-Cr or U-Fe. Uranium dioxide (UO 2 ) powder
9216-420: The chain-reaction. This mechanism compensates for the accumulation of undesirable neutron poisons which are an unavoidable part of the fission products, as well as normal fissile fuel "burn up" or depletion. In the generalized QUADRISO fuel concept the poison can eventually be mixed with the fuel kernel or the outer pyrocarbon. The QUADRISO concept was conceived at Argonne National Laboratory . RBMK reactor fuel
9344-504: The complicated phase diagram are not entirely understood. The α form has a low-symmetry monoclinic structure, hence its brittleness, strength, compressibility, and poor thermal conductivity. Plutonium in the δ ( delta ) form normally exists in the 310 °C to 452 °C range but is stable at room temperature when alloyed with a small percentage of gallium , aluminium , or cerium , enhancing workability and allowing it to be welded . The δ form has more typical metallic character, and
9472-510: The coolant and contaminating it. Besides the prevention of radioactive leaks this also serves to keep the coolant as non-corrosive as feasible and to prevent reactions between chemically aggressive fission products and the coolant. For example, the highly reactive alkali metal caesium which reacts strongly with water, producing hydrogen, and which is among the more common fission products. Pressurized water reactor (PWR) fuel consists of cylindrical rods put into bundles. A uranium oxide ceramic
9600-427: The different allotropes vary from 16.00 g/cm to 19.86 g/cm . The presence of these many allotropes makes machining plutonium very difficult, as it changes state very readily. For example, the α form exists at room temperature in unalloyed plutonium. It has machining characteristics similar to cast iron but changes to the plastic and malleable β ( beta ) form at slightly higher temperatures. The reasons for
9728-434: The established PUREX process is used commercially for about a third of all spent nuclear fuel (the rest being largely subject to a "once through fuel cycle"). All nitrogen-fluoride compounds are volatile or gaseous at room temperature and could be fractionally distilled from the other gaseous products (including recovered uranium hexafluoride ) to recover the initially used nitrogen. If the fuel could be processed in such
9856-496: 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. During reactor operation, neutron irradiation of the poison causes it to "burn up" or progressively transmute to non-poison isotopes, depleting this poison effect and leaving progressively more neutrons available for sustaining
9984-407: 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 actinides and fission products within the uranium dioxide crystal lattice . The radiation hazard from spent nuclear fuel declines as its radioactive components decay, but remains high for many years. For example 10 years after removal from a reactor, the surface dose rate for
10112-412: 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
10240-440: The fatigue effects as temperature increases above 100 K. Unlike most materials, plutonium increases in density when it melts, by 2.5%, but the liquid metal exhibits a linear decrease in density with temperature. Near the melting point, the liquid plutonium has very high viscosity and surface tension compared to other metals. Plutonium normally has six allotropes and forms a seventh (zeta, ζ) at high temperature within
10368-594: The first atomic bombs. The Fat Man bombs used in the Trinity nuclear test in July 1945, and in the bombing of Nagasaki in August 1945, had plutonium cores . Human radiation experiments studying plutonium were conducted without informed consent , and several criticality accidents , some lethal, occurred after the war. Disposal of plutonium waste from nuclear power plants and dismantled nuclear weapons built during
10496-504: The first self-sustaining chain reaction in a graphite and uranium pile known as CP-1 . Using theoretical information garnered from the operation of CP-1, DuPont constructed an air-cooled experimental production reactor, known as X-10 , and a pilot chemical separation facility at Oak Ridge. The separation facility, using methods developed by Glenn T. Seaborg and a team of researchers at the Met Lab, removed plutonium from uranium irradiated in
10624-568: The first transuranic element neptunium after the planet Neptune , and suggested that element 94, being the next element in the series, be named for what was then considered the next planet, Pluto . Nicholas Kemmer of the Cambridge team independently proposed the same name, based on the same reasoning as the Berkeley team. Seaborg originally considered the name "plutium", but later thought that it did not sound as good as "plutonium". He chose
10752-491: The fission of uranium-235 are captured by uranium-238 nuclei to form uranium-239; a beta decay converts a neutron into a proton to form neptunium-239 (half-life 2.36 days) and another beta decay forms plutonium-239. Egon Bretscher working on the British Tube Alloys project predicted this reaction theoretically in 1940. Plutonium-238 is synthesized by bombarding uranium-238 with deuterons (D or H,
10880-403: The fuel being changed every three years or so, about half of the Pu is 'burned' in the reactor, providing about one third of the total energy. It behaves like U and its fission releases a similar amount of energy. The higher the burnup , the more plutonium is present in the spent fuel, but the available fissile plutonium is lower. Typically about one percent of the used fuel discharged from
11008-403: 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 density variations 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
11136-853: The fuel mixture for significantly extended periods, which increases fuel efficiency dramatically and incinerates the vast majority of its own waste as part of the normal operational characteristics. A downside to letting the Xe escape instead of allowing it to capture neutrons converting it to the basically stable and chemically inert Xe , is that it will quickly decay to the highly chemically reactive, long lived radioactive Cs , which behaves similar to other alkali metals and can be taken up by organisms in their metabolism. Molten salt fuels are mixtures of actinide salts (e.g. thorium/uranium fluoride/chloride) with other salts, used in liquid form above their typical melting points of several hundred degrees C. In some molten salt-fueled reactor designs, such as
11264-408: The fuel of choice for reactor designs that NASA produces. One advantage is that uranium nitride has a better thermal conductivity than UO 2 . Uranium nitride has a very high melting point. This fuel has the disadvantage that unless N was used (in place of the more common N ), a large amount of C would be generated from the nitrogen by the (n,p) reaction . As the nitrogen needed for such
11392-406: The fuel rods, standing between the coolant and the nuclear fuel. It is made of a corrosion -resistant material with low absorption cross section for thermal neutrons , usually Zircaloy or steel in modern constructions, or magnesium with small amount of aluminium and other metals for the now-obsolete Magnox reactors . Cladding prevents radioactive fission fragments from escaping the fuel into
11520-540: The fuel. Accident tolerant fuels (ATF) are a series of new nuclear fuel concepts, researched in order to improve fuel performance under accident conditions, such as loss-of-coolant accident (LOCA) or reaction-initiated accidents (RIA). These concerns became more prominent after the Fukushima Daiichi nuclear disaster in Japan, in particular regarding light-water reactor (LWR) fuels performance under accident conditions. Neutronics analyses were performed for
11648-407: The general formula PuX 3 where X can be F , Cl , Br or I and PuF 4 is also seen. The following oxyhalides are observed: PuOCl, PuOBr and PuOI. It will react with carbon to form PuC , nitrogen to form PuN and silicon to form PuSi 2 . The organometallic chemistry of plutonium complexes is typical for organoactinide species; a characteristic example of an organoplutonium compound
11776-564: The highest atomic number known to occur in nature. Trace quantities arise in natural uranium deposits when uranium-238 captures neutrons emitted by decay of other uranium-238 atoms. The heavy isotope plutonium-244 has a half-life long enough that extreme trace quantities should have survived primordially (from the Earth's formation) to the present, but so far experiments have not yet been sensitive enough to detect it. Both plutonium-239 and plutonium-241 are fissile , meaning they can sustain
11904-596: The human body due to the 550 atmospheric and underwater nuclear tests that have been carried out, and to a small number of major nuclear accidents . Most atmospheric and underwater nuclear testing was stopped by the Limited Test Ban Treaty in 1963, which of the nuclear powers was signed and ratified by the United States, United Kingdom and Soviet Union . France would continue atmospheric nuclear testing until 1974 and China would continue atmospheric nuclear testing until 1980. All subsequent nuclear testing
12032-468: The interactions between the two. Used nuclear fuel is a complex mixture of the fission products , uranium , plutonium , and the transplutonium metals . 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 platinum group metals such as palladium . Also the fuel may well have cracked, swollen, and been heated close to its melting point. Despite
12160-473: The introduction of additional absorbers. 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. Plate-type fuel has fallen out of favor over the years. Plate-type fuel
12288-531: The letters "Pu" as a joke, in reference to the interjection "P U" to indicate an especially disgusting smell, which passed without notice into the periodic table. Alternative names considered by Seaborg and others were "ultimium" or "extremium" because of the erroneous belief that they had found the last possible element on the periodic table . Hahn and Strassmann, and independently Kurt Starke , were at this point also working on transuranic elements in Berlin. It
12416-488: The metal oxide ; the oxides are used rather than the metals themselves because the oxide melting point is much higher than that of the metal and because it cannot burn, being already in the oxidized state. Uranium dioxide is a black semiconducting solid. It can be made by heating uranyl nitrate to form UO 2 . This is then converted by heating with hydrogen to form UO 2 . It can be made from enriched uranium hexafluoride by reacting with ammonia to form
12544-449: The metal without the need for a crucible. Cerium is used as a chemical simulant of plutonium for development of containment, extraction, and other technologies. Plutonium is an element in which the 5f electrons are the transition border between delocalized and localized; it is therefore considered one of the most complex elements. The anomalous behavior of plutonium is caused by its electronic structure. The energy difference between
12672-420: The neutron cross section of carbon is low, during years of burnup, the predominantly C will undergo neutron capture to produce stable C as well as radioactive C . Unlike the C produced by using uranium nitrate, the C will make up only a small isotopic impurity in the overall carbon content and thus make the entirety of the carbon content unsuitable for non-nuclear uses but
12800-400: The new element with atomic number 94 and atomic weight 238 (half-life 88 years). Since uranium had been named after the planet Uranus and neptunium after the planet Neptune , element 94 was named after Pluto , which at the time was also considered a planet. Wartime secrecy prevented the University of California team from publishing its discovery until 1948. Plutonium is the element with
12928-448: The nuclei of heavy hydrogen ) in the following reaction: where a deuteron hitting uranium-238 produces two neutrons and neptunium-238, which decays by emitting negative beta particles to form plutonium-238. Plutonium-238 can also be produced by neutron irradiation of neptunium-237 . Plutonium isotopes undergo radioactive decay, which produces decay heat . Different isotopes produce different amounts of heat per mass. The decay heat
13056-454: The oxidation state and the nature of the acid anion . It is the acid anion that influences the degree of complexing —how atoms connect to a central atom—of the plutonium species. Additionally, the formal +2 oxidation state of plutonium is known in the complex [K(2.2.2-cryptand)] [Pu Cp″ 3 ], Cp″ = C 5 H 3 (SiMe 3 ) 2 . A +8 oxidation state is possible as well in the volatile tetroxide PuO 4 . Though it readily decomposes via
13184-517: 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 International Nuclear Safety Center the thermal conductivity of uranium dioxide can be predicted under different conditions by a series of equations. Plutonium Plutonium is a chemical element ; it has symbol Pu and atomic number 94. It
13312-486: The possibility of a runaway reactor meltdown, and providing an automatic load-following capability which is well suited to electricity generation and high-temperature industrial heat applications. In some liquid core designs, the fuel can 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 Molten-Salt Reactor Experiment from 1965 to 1969. A liquid core
13440-410: The reactor. Stainless steel was used in the past, but most reactors now use a zirconium alloy 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
13568-473: The refractory metals chromium , molybdenum , niobium , tantalum, and tungsten, which are soluble in liquid plutonium, but insoluble or only slightly soluble in solid plutonium. Gallium, aluminium, americium, scandium and cerium can stabilize δ-phase plutonium for room temperature. Silicon , indium , zinc and zirconium allow formation of metastable δ state when rapidly cooled. High amounts of hafnium , holmium and thallium also allows some retention of
13696-412: The release of a high-energy helium nucleus, is the most common form of radioactive decay for plutonium. A 5 kg mass of Pu contains about 12.5 × 10 atoms. With a half-life of 24,100 years, about 11.5 × 10 of its atoms decay each second by emitting a 5.157 MeV alpha particle. This amounts to 9.68 watts of power. Heat produced by the deceleration of these alpha particles makes it warm to
13824-490: The site are: At its peak the site employed 4000 people, but reduced demand and increased automation saw this fall to about 800 by 2020. In December 2022 Westinghouse received a £13 million grant from the UK government to explore the development of Uranium Conversion Services at the site. Protests have been held at the site against the production of nuclear waste. In the 1980s there were also protests against apartheid, due to
13952-496: The smallest and 800 assemblies for the largest BWR in the U.S. form the reactor core. Each BWR fuel rod is backfilled with helium to a pressure of about 3 standard atmospheres (300 kPa). Canada deuterium uranium fuel (CANDU) fuel bundles are about 0.5 metres (20 in) long and 10 centimetres (4 in) in diameter. They consist of sintered (UO 2 ) pellets in zirconium alloy tubes, welded to zirconium alloy end plates. Each bundle weighs roughly 20 kilograms (44 lb), and
14080-587: The steel pressure vessels, and the two reinforced concrete designs operated at 24.8 and 27 bars (24.5 and 26.6 atm). Magnox alloy consists mainly of magnesium with small amounts of aluminium and other metals—used in cladding unenriched uranium metal fuel with a non-oxidising covering to contain fission products. This material has the advantage of a low neutron capture cross-section, but has two major disadvantages: Magnox fuel incorporated cooling fins to provide maximum heat transfer despite low operating temperatures, making it expensive to produce. While
14208-416: The stronger cyclotron at Paris at this point, they would likely have been able to detect plutonium had they tried, albeit in tiny quantities (a few becquerels ). The chemistry of plutonium was found to resemble uranium after a few months of initial study. Early research was continued at the secret Metallurgical Laboratory of the University of Chicago . On August 20, 1942, a trace quantity of this element
14336-560: 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. That is, they can be used as a neutron source . 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. There are 35 TRIGA reactors in
14464-449: The top directly into the fuel bundle. The fuel bundles usually are enriched several percent in U. 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. In boiling water reactors (BWR),
14592-402: The touch. Pu due to its much shorter half life heats up to much higher temperatures and glows red hot with blackbody radiation if left without external heating or cooling. This heat has been used in radioisotope thermoelectric generators (see below). The resistivity of plutonium at room temperature is very high for a metal, and it gets even higher with lower temperatures, which
14720-410: The unaided eye. The nuclear properties of plutonium-239 were also studied; researchers found that when it is hit by a neutron it breaks apart (fissions) by releasing more neutrons and energy. These neutrons can hit other atoms of plutonium-239 and so on in an exponentially fast chain reaction. This can result in an explosion large enough to destroy a city if enough of the isotope is concentrated to form
14848-412: The use of uranium imported from Namibia. Manufacturing is scheduled to continue until 2023. Decommissioning activities have so far resulted in 87 buildings on the site having been fully demolished. A Clean Energy Technology Park (CETP) has been set up to encourage new companies to operate on the site. Nuclear fuel For fission reactors, the fuel (typically based on uranium ) is usually based on
14976-407: The use of uranium metal rather than oxide made nuclear 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 issue. Tristructural-isotropic (TRISO) fuel is a type of micro-particle fuel. A particle consists of
15104-542: The various organs. Hamilton started administering soluble microgram portions of plutonium-239 compounds to rats using different valence states and different methods of introducing the plutonium (oral, intravenous, etc.). Eventually, the lab at Chicago also conducted its own plutonium injection experiments using different animals such as mice, rabbits, fish, and even dogs. The results of the studies at Berkeley and Chicago showed that plutonium's physiological behavior differed significantly from that of radium. The most alarming result
15232-448: The δ phase at room temperature. Neptunium is the only element that can stabilize the α phase at higher temperatures. Plutonium alloys can be produced by adding a metal to molten plutonium. If the alloying metal is reductive enough, plutonium can be added in the form of oxides or halides. The δ phase plutonium–gallium alloy (PGA) and plutonium–aluminium alloy are produced by adding Pu(III) fluoride to molten gallium or aluminium, which has
15360-564: Was a U.S. proposal in the George W. Bush administration 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 nuclear weapons. Reprocessing of spent commercial-reactor nuclear fuel has not been permitted in the United States due to nonproliferation considerations . All other reprocessing nations have long had nuclear weapons from military-focused research reactor fuels except for Japan. Normally, with
15488-476: Was conducted underground. Enrico Fermi and a team of scientists at the University of Rome reported that they had discovered element 94 in 1934. Fermi called the element hesperium and mentioned it in his Nobel Lecture in 1938. The sample actually contained products of nuclear fission , primarily barium and krypton . Nuclear fission, discovered in Germany in 1938 by Otto Hahn and Fritz Strassmann ,
15616-500: Was created directly by the bombardment but decayed by beta emission with a half-life of a little over two days, which indicated the formation of element 94. The first bombardment took place on December 14, 1940, and the new element was first identified through oxidation on the night of February 23–24, 1941. A paper documenting the discovery was prepared by the team and sent to the journal Physical Review in March 1941, but publication
15744-624: Was delayed until a year after the end of World War II due to security concerns. At the Cavendish Laboratory in Cambridge , Egon Bretscher and Norman Feather realized that a slow neutron reactor fuelled with uranium would theoretically produce substantial amounts of plutonium-239 as a by-product. They calculated that element 94 would be fissile, and had the added advantage of being chemically different from uranium, and could easily be separated from it. McMillan had recently named
15872-426: Was isolated and measured for the first time. About 50 micrograms of plutonium-239 combined with uranium and fission products was produced and only about 1 microgram was isolated. This procedure enabled chemists to determine the new element's atomic weight. On December 2, 1942, on a racket court under the west grandstand at the University of Chicago's Stagg Field, researchers headed by Enrico Fermi achieved
16000-400: Was tested in two experimental reactors, LAMPRE I and LAMPRE II, at Los Alamos National Laboratory in the 1960s. LAMPRE experienced three separate fuel failures during operation. Ceramic fuels other than oxides have the advantage of high heat conductivities and melting points, but they are more prone to swelling than oxide fuels and are not understood as well. Uranium nitride is often
16128-400: Was that there was significant deposition of plutonium in the liver and in the "actively metabolizing" portion of bone. Furthermore, the rate of plutonium elimination in the excreta differed between species of animals by as much as a factor of five. Such variation made it extremely difficult to estimate what the rate would be for human beings. During World War II the U.S. government established
16256-579: Was unknown at the time. Plutonium (specifically, plutonium-238) was first produced, isolated and then chemically identified between December 1940 and February 1941 by Glenn T. Seaborg , Edwin McMillan , Emilio Segrè , Joseph W. Kennedy , and Arthur Wahl by deuteron bombardment of uranium in the 60-inch (150 cm) cyclotron at the Berkeley Radiation Laboratory at the University of California, Berkeley . Neptunium-238
16384-557: Was used in Soviet -designed and built RBMK -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
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