Gaseous diffusion
Encyclopedia
Gaseous diffusion is a technology used to produce enriched uranium
by forcing gaseous uranium hexafluoride
(UF6) through semi-permeable membranes
. This produces a slight separation between the molecules containing uranium-235
(235U) and uranium-238
(238U). By use of a large cascade
of many stages, high separations can be achieved. It was the first process to be developed that was capable of producing enriched uranium in industrially useful quantities.
Gaseous diffusion was devised by Francis Simon
and Nicholas Kurti
at the Clarendon Laboratory
in 1940, tasked by the MAUD Committee
with finding a method for separating Uranium-235 from Uranium-238 in order to produce a bomb for the British Tube Alloys
project. The prototype gaseous diffusion equipment itself was manufactured by Metropolitan-Vickers
(MetroVick) at Trafford Park
, Manchester, at a cost of £150,000 for four units. This work was later transferred to the United States when the Tube Alloys project became subsumed by the later Manhattan Project
.http://www.ryhdymwynvalleyhistory.co.uk/index.php?option=com_k2&view=item&id=91:the-tube-alloys-project&Itemid=91&lang=en
. These two isotope
s are similar in many ways, except that only 235U is fissile
(capable of sustaining a nuclear chain reaction of nuclear fission
with thermal neutrons). In fact, 235U is the only naturally occurring fissile nucleus. Because natural uranium
is only about 0.72% 235U by weight, it must be enriched to a concentration of 2–5% to be able to support a continuous nuclear chain reaction when normal water is used as the moderator. The product of this enrichment process is called enriched uranium.
Gaseous diffusion is based on Graham's law
, which states that the rate of effusion
of a gas is inversely proportional to the square root of its molecular mass
. For example, in a box with a semi-permeable membrane containing a mixture of two gases, the lighter molecules will pass out of the container more rapidly than the heavier molecules. The gas leaving the container is somewhat enriched in the lighter molecules, while the residual gas is somewhat depleted. A single container wherein the enrichment process takes place through gaseous diffusion is called a diffuser
.
Uranium hexafluoride
UF6 is the only compound of uranium sufficiently volatile
to be used in the gaseous diffusion process. Fortunately, fluorine
consists of only a single isotope 19F, so that the 1% difference in molecular weights between 235UF6 and 238UF6 is due only to the difference in weights of the uranium isotopes. For these reasons, UF6 is the only choice as a feedstock
for the gaseous diffusion process. UF6, a solid at room temperature, sublimes
at 56.5 °C (133 °F) at 1 atmosphere. The triple point is at 64.05 °C and 1.5 bar. Applying Graham's Law to uranium hexafluoride:
where:
This explains the 0.4% difference in the average velocities of 235UF6 molecules over that of 238UF6 molecules.
UF6 is a highly corrosive substance. It is an oxidant and a Lewis acid which is able to bind to fluoride
, for instance the reaction of copper(II) fluoride
with uranium hexafluoride in acetonitrile
is reported to form copper(II) heptafluorouranate(VI), Cu(UF7)2. It reacts with water to form a solid compound, and is very difficult to handle on an industrial scale. As a consequence, internal gaseous pathways must be fabricated from austenitic stainless steel
and other heat-stabilized
metals. Non-reactive fluoropolymer
s such as Teflon
must be applied as a coating
to all valve
s and seals
in the system.
Barrier materials
Gaseous diffusion plants typically use aggregate barriers (porous membranes) constructed of sintered
nickel or aluminum
, with a pore size of 10–25 nanometers
(this is less than one-tenth the mean free path
of the UF6 molecule). They may also use film-type barriers, which are made by boring pores through an initially nonporous medium. One way this can be done is by removing one constituent in an alloy, for instance using hydrogen chloride
to remove the zinc
from silver-zinc (Ag-Zn).
Energy requirements
Because the molecular weights of 235UF6 and 238UF6 are nearly equal, very little separation of the 235U and 238U is effected by a single pass through a barrier, that is, in one diffuser. It is therefore necessary to connect a great many diffusers together in a sequence of stages, using the outputs of the preceding stage as the inputs for the next stage. Such a sequence of stages is called a cascade. In practice, diffusion cascades require thousands of stages, depending on the desired level of enrichment.
All components of a diffusion plant
must be maintained at an appropriate temperature and pressure to assure that the UF6 remains in the gaseous phase. The gas must be compressed at each stage to make up for a loss in pressure across the diffuser. This leads to compression heating of the gas, which then must be cooled before entering the diffuser. The requirements for pumping and cooling make diffusion plants enormous consumers of electric power
. Because of this, gaseous diffusion is the most expensive method currently used for producing enriched uranium.
developed several different methods for the separation of isotopes
of uranium. Three of these methods were used sequentially at three different plants in Oak Ridge to produce the 235U for "Little Boy
" and other early nuclear weapons
. In the first step, the S-50 uranium enrichment facility used the thermal diffusion process to enrich the uranium from 0.7% up to nearly 2% 235U. This product was then fed into the gaseous diffusion process at the K-25
plant, the product of which was around 23% 235U. Finally, this material was fed into calutron
s at the Y-12
. These machines (a type of particle accelerator
or cyclotron
) employed electromagnetic isotope separation to boost the final 235U concentration to about 84%.
The preparation of UF6 feedstock for the K-25 gaseous diffusion plant was the first ever application for commercially produced fluorine, and significant obstacles were encountered in the handling of both fluorine and UF6. For example, before the K-25 gaseous diffusion plant could be built, it was first necessary to develop non-reactive chemical compound
s that could be used as coatings, lubricant
s and gasket
s for the surfaces which would come into contact with the UF6 gas (a highly reactive and corrosive substance). Scientists of the Manhattan Project recruited William T. Miller
, a professor of organic chemistry
at Cornell University
, to synthesize
and develop such materials, because of his expertise in organofluorine chemistry
. Miller and his team developed several novel non-reactive chlorofluorocarbon
polymer
s that were used in this application.
Calutrons were expensive to build and operate and inefficient. As soon as the engineering obstacles posed by the gaseous diffusion process had been overcome and the gaseous diffusion cascades began operating at Oak Ridge in 1945, all of the calutrons were shut down. The gaseous diffusion technique then became the preferred technique for producing enriched uranium.
At the time of their construction in the early 1940s, the gaseous diffusion plants were the largest buildings ever constructed. Large gaseous diffusion plants were constructed by the United States, the Soviet Union
(including a plant that is now in Kazakhstan
), the United Kingdom
, France
, China
, and South Africa
. Most of these have now closed or are expected to close, unable to compete economically with newer enrichment techniques. However some of the technology used in pumps and membranes still remains top secret, and some of the materials that were used remain subject to export controls, as a part of the continuing effort to control nuclear proliferation
.
(USEC), the Paducah Gaseous Diffusion Plant
in Kentucky is currently the only fully functioning uranium enrichment facility in the United States that employs the gaseous diffusion process. The only other such facility in the United States, the Portsmouth Gaseous Diffusion Plant
in Ohio, ceased enrichment activities in 2001. Since 2010, the Ohio site is now used mainly by AREVA
, a French conglomerate
, for the conversion of depleted UF6 to uranium oxide
.
As existing gaseous diffusion plants become obsolete, they are being replaced by second generation gas centrifuge
technology, which requires far less electric power to produce equivalent amounts of separated uranium. AREVA is replacing its Georges Besse gaseous diffusion plant with the Georges Besse II centrifuge plant. AVLIS and SILEX
are two more recently developed uranium enrichment technologies which may be utilized in the future, and are possibly already being utilized.
Enriched uranium
Enriched uranium is a kind of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99.284% 238U isotope, with 235U only constituting about 0.711% of its weight...
by forcing gaseous uranium hexafluoride
Uranium hexafluoride
Uranium hexafluoride , referred to as "hex" in the nuclear industry, is a compound used in the uranium enrichment process that produces fuel for nuclear reactors and nuclear weapons. It forms solid grey crystals at standard temperature and pressure , is highly toxic, reacts violently with water...
(UF6) through semi-permeable membranes
Semipermeable membrane
A semipermeable membrane, also termed a selectively permeable membrane, a partially permeable membrane or a differentially permeable membrane, is a membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally specialized "facilitated diffusion".The rate of...
. This produces a slight separation between the molecules containing uranium-235
Uranium-235
- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...
(235U) and uranium-238
Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...
(238U). By use of a large cascade
Cascade (chemical engineering)
In chemical engineering, a cascade is a plant consisting of several similar stages with each processing the output from the previous stage. Cascades are most commonly used in isotope separation, distillation and other separation or purification processes....
of many stages, high separations can be achieved. It was the first process to be developed that was capable of producing enriched uranium in industrially useful quantities.
Gaseous diffusion was devised by Francis Simon
Francis Simon
Sir Francis Simon, born Franz Eugen Simon , was a German and later British physical chemist and physicist who devised the method, and confirmed its feasibility, of separating the isotope Uranium-235 and thus made a major contribution to the creation of the atomic bomb.-Early life:He was born to a...
and Nicholas Kurti
Nicholas Kurti
Professor Nicholas Kurti FRS was a Hungarian-born physicist who lived in Oxford, UK, for most of his life. In his era, he was one of the leading experimental physicists....
at the Clarendon Laboratory
Clarendon Laboratory
The Clarendon Laboratory, located on Parks Road with the Science Area in Oxford, England , is part of the Physics Department at Oxford University...
in 1940, tasked by the MAUD Committee
MAUD Committee
The MAUD Committee was the beginning of the British atomic bomb project, before the United Kingdom joined forces with the United States in the Manhattan Project.-Frisch & Peierls:...
with finding a method for separating Uranium-235 from Uranium-238 in order to produce a bomb for the British Tube Alloys
Tube Alloys
Tube Alloys was the code-name for the British nuclear weapon directorate during World War II, when the development of nuclear weapons was kept at such a high level of secrecy that it had to be referred to by code even in the highest circles of government...
project. The prototype gaseous diffusion equipment itself was manufactured by Metropolitan-Vickers
Metropolitan-Vickers
Metropolitan-Vickers, Metrovick, or Metrovicks, was a British heavy electrical engineering company of the early-to-mid 20th century formerly known as British Westinghouse. Highly diversified, they were particularly well known for their industrial electrical equipment such as generators, steam...
(MetroVick) at Trafford Park
Trafford Park
Trafford Park is an area of the Metropolitan Borough of Trafford, in Greater Manchester, England. Located opposite Salford Quays, on the southern side of the Manchester Ship Canal, it is west-southwest of Manchester city centre, and north of Stretford. Until the late 19th century it was the...
, Manchester, at a cost of £150,000 for four units. This work was later transferred to the United States when the Tube Alloys project became subsumed by the later Manhattan Project
Manhattan Project
The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...
.http://www.ryhdymwynvalleyhistory.co.uk/index.php?option=com_k2&view=item&id=91:the-tube-alloys-project&Itemid=91&lang=en
Background
Of the 33 known radioactive primordial nuclides, two of them (235U and 238U) are isotopes of uraniumIsotopes of uranium
Uranium is a naturally occurring radioactive element that has no stable isotopes but two primordial isotopes that have long half-life and are found in appreciable quantity in the Earth's crust, along with the decay product uranium-234. The average atomic mass of natural uranium is 238.02891 u...
. These two isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
s are similar in many ways, except that only 235U is fissile
Fissile
In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. By definition, fissile materials can sustain a chain reaction with neutrons of any energy. The predominant neutron energy may be typified by either slow neutrons or fast neutrons...
(capable of sustaining a nuclear chain reaction of nuclear fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
with thermal neutrons). In fact, 235U is the only naturally occurring fissile nucleus. Because natural uranium
Natural uranium
Natural uranium refers to refined uranium with the same isotopic ratio as found in nature. It contains 0.7 % uranium-235, 99.3 % uranium-238, and a trace of uranium-234 by weight. In terms of the amount of radioactivity, approximately 2.2 % comes from uranium-235, 48.6 % uranium-238, and 49.2 %...
is only about 0.72% 235U by weight, it must be enriched to a concentration of 2–5% to be able to support a continuous nuclear chain reaction when normal water is used as the moderator. The product of this enrichment process is called enriched uranium.
Technology
Scientific basisGaseous diffusion is based on Graham's law
Graham's law
Graham's law, known as Graham's law of effusion, was formulated by Scottish physical chemist Thomas Graham in 1846. Graham found experimentally that the rate of effusion of a gas is inversely proportional to the square root of the mass of its particles...
, which states that the rate of effusion
Effusion
In physics, effusion is the process in which individual molecules flow through a hole without collisions between molecules. This occurs if the diameter of the hole is considerably smaller than the mean free path of the molecules...
of a gas is inversely proportional to the square root of its molecular mass
Molecular mass
The molecular mass of a substance is the mass of one molecule of that substance, in unified atomic mass unit u...
. For example, in a box with a semi-permeable membrane containing a mixture of two gases, the lighter molecules will pass out of the container more rapidly than the heavier molecules. The gas leaving the container is somewhat enriched in the lighter molecules, while the residual gas is somewhat depleted. A single container wherein the enrichment process takes place through gaseous diffusion is called a diffuser
Diffuser (thermodynamics)
A diffuser is the mechanical device that is designed to control the characteristics of a fluid at the entrance to a thermodynamic open system. Diffusers are used to slow the fluid's velocity and to enhance its mixing into the surrounding fluid...
.
Uranium hexafluoride
UF6 is the only compound of uranium sufficiently volatile
Volatility (chemistry)
In chemistry and physics, volatility is the tendency of a substance to vaporize. Volatility is directly related to a substance's vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure.The term is primarily...
to be used in the gaseous diffusion process. Fortunately, fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
consists of only a single isotope 19F, so that the 1% difference in molecular weights between 235UF6 and 238UF6 is due only to the difference in weights of the uranium isotopes. For these reasons, UF6 is the only choice as a feedstock
Raw material
A raw material or feedstock is the basic material from which a product is manufactured or made, frequently used with an extended meaning. For example, the term is used to denote material that came from nature and is in an unprocessed or minimally processed state. Latex, iron ore, logs, and crude...
for the gaseous diffusion process. UF6, a solid at room temperature, sublimes
Sublimation
Sublimation may refer to:* Sublimation , the change from solid to gas without entering liquid phase* Sublimation , the transformation of emotions* Sublimation , a music album by Canvas Solaris-See also:...
at 56.5 °C (133 °F) at 1 atmosphere. The triple point is at 64.05 °C and 1.5 bar. Applying Graham's Law to uranium hexafluoride:
where:
- Rate1 is the rate of effusion of 235UF6.
- Rate2 is the rate of effusion of 238UF6.
- M1 is the molar massMolar massMolar mass, symbol M, is a physical property of a given substance , namely its mass per amount of substance. The base SI unit for mass is the kilogram and that for amount of substance is the mole. Thus, the derived unit for molar mass is kg/mol...
of 235UF6 = 235.043930 + 6 × 18.998403 = 349.034348 g·mol−1 - M2 is the molar mass of 238UF6 = 238.050788 + 6 × 18.998403 = 352.041206 g·mol−1
This explains the 0.4% difference in the average velocities of 235UF6 molecules over that of 238UF6 molecules.
UF6 is a highly corrosive substance. It is an oxidant and a Lewis acid which is able to bind to fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
, for instance the reaction of copper(II) fluoride
Copper(II) fluoride
Copper fluoride is an inorganic compound with the chemical formula CuF2. It is a white or green, crystalline, hygroscopic solid. It has a rutile-type crystal structure similar to other fluorides of chemical formulae MF2.-Uses:...
with uranium hexafluoride in acetonitrile
Acetonitrile
Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture...
is reported to form copper(II) heptafluorouranate(VI), Cu(UF7)2. It reacts with water to form a solid compound, and is very difficult to handle on an industrial scale. As a consequence, internal gaseous pathways must be fabricated from austenitic stainless steel
Austenitic stainless steel
Austenitic steels have austenite as their primary phase . These are alloys containing chromium and nickel , structured around the Type 302 composition of iron, 18% chromium, and 8% nickel. Austenitic steels are not hardenable by heat treatment...
and other heat-stabilized
Austempering
Austempering is an isothermal heat treatment that is applied to ferrous metals, most notably steel and ductile iron. In steel it produces a lower bainite microstructure whereas in cast irons it produces a structure of acicular ferrite and high carbon, stabilized austenite known as ausferrite. It is...
metals. Non-reactive fluoropolymer
Fluoropolymer
A fluoropolymer is a fluorocarbon based polymer with multiple strong carbon–fluorine bonds. It is characterized by a high resistance to solvents, acids, and bases.-History:Fluoropolymers were accidentally discovered in 1938 by Dr. Roy J...
s such as Teflon
Polytetrafluoroethylene
Polytetrafluoroethylene is a synthetic fluoropolymer of tetrafluoroethylene that finds numerous applications. PTFE is most well known by the DuPont brand name Teflon....
must be applied as a coating
Coating
Coating is a covering that is applied to the surface of an object, usually referred to as the substrate. In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wetability, corrosion resistance, wear resistance, and scratch resistance...
to all valve
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
s and seals
Seal (mechanical)
A mechanical seal is a device which helps join systems or mechanisms together by preventing leakage , containing pressure, or excluding contamination...
in the system.
Barrier materials
Gaseous diffusion plants typically use aggregate barriers (porous membranes) constructed of sintered
Sintering
Sintering is a method used to create objects from powders. It is based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it occurs much faster at higher temperatures. In most sintering processes, the powdered material is held in a mold and then heated to a temperature...
nickel or aluminum
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
, with a pore size of 10–25 nanometers
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
(this is less than one-tenth the mean free path
Mean free path
In physics, the mean free path is the average distance covered by a moving particle between successive impacts which modify its direction or energy or other particle properties.-Derivation:...
of the UF6 molecule). They may also use film-type barriers, which are made by boring pores through an initially nonporous medium. One way this can be done is by removing one constituent in an alloy, for instance using hydrogen chloride
Hydrogen chloride
The compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...
to remove the zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
from silver-zinc (Ag-Zn).
Energy requirements
Because the molecular weights of 235UF6 and 238UF6 are nearly equal, very little separation of the 235U and 238U is effected by a single pass through a barrier, that is, in one diffuser. It is therefore necessary to connect a great many diffusers together in a sequence of stages, using the outputs of the preceding stage as the inputs for the next stage. Such a sequence of stages is called a cascade. In practice, diffusion cascades require thousands of stages, depending on the desired level of enrichment.
All components of a diffusion plant
Chemical plant
A chemical plant is an industrial process plant that manufactures chemicals, usually on a large scale. The general objective of a chemical plant is to create new material wealth via the chemical or biological transformation and or separation of materials. Chemical plants use special equipment,...
must be maintained at an appropriate temperature and pressure to assure that the UF6 remains in the gaseous phase. The gas must be compressed at each stage to make up for a loss in pressure across the diffuser. This leads to compression heating of the gas, which then must be cooled before entering the diffuser. The requirements for pumping and cooling make diffusion plants enormous consumers of electric power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...
. Because of this, gaseous diffusion is the most expensive method currently used for producing enriched uranium.
History
Scientists working on the Manhattan Project in Oak Ridge, TennesseeOak Ridge, Tennessee
Oak Ridge is a city in Anderson and Roane counties in the eastern part of the U.S. state of Tennessee, about west of Knoxville. Oak Ridge's population was 27,387 at the 2000 census...
developed several different methods for the separation of isotopes
Isotope separation
Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes, for example separating natural uranium into enriched uranium and depleted uranium. This is a crucial process in the manufacture of uranium fuel for nuclear power stations, and is...
of uranium. Three of these methods were used sequentially at three different plants in Oak Ridge to produce the 235U for "Little Boy
Little Boy
"Little Boy" was the codename of the atomic bomb dropped on Hiroshima on August 6, 1945 by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul Tibbets of the 393rd Bombardment Squadron, Heavy, of the United States Army Air Forces. It was the first atomic bomb to be used as a weapon...
" and other early nuclear weapons
Gun-type fission weapon
Gun-type fission weapons are fission-based nuclear weapons whose design assembles their fissile material into a supercritical mass by the use of the "gun" method: shooting one piece of sub-critical material into another...
. In the first step, the S-50 uranium enrichment facility used the thermal diffusion process to enrich the uranium from 0.7% up to nearly 2% 235U. This product was then fed into the gaseous diffusion process at the K-25
K-25
K-25 is a former uranium enrichment facility of the Manhattan Project which used the gaseous diffusion method. The plant is located in Oak Ridge, Tennessee, on the southwestern end of the Oak Ridge Reservation.-History:...
plant, the product of which was around 23% 235U. Finally, this material was fed into calutron
Calutron
A calutron is a mass spectrometer used for separating the isotopes of uranium. It was developed by Ernest O. Lawrence during the Manhattan Project and was similar to the cyclotron invented by Lawrence. Its name is a concatenation of Cal. U.-tron, in tribute to the University of California,...
s at the Y-12
Y-12 National Security Complex
The Y-12 National Security Complex is a United States Department of Energy National Nuclear Security Administration facility located in Oak Ridge, Tennessee, near the Oak Ridge National Laboratory...
. These machines (a type of particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
or cyclotron
Cyclotron
In technology, a cyclotron is a type of particle accelerator. In physics, the cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicularly to the direction of a uniform magnetic field, i.e. a magnetic field of constant magnitude and direction...
) employed electromagnetic isotope separation to boost the final 235U concentration to about 84%.
The preparation of UF6 feedstock for the K-25 gaseous diffusion plant was the first ever application for commercially produced fluorine, and significant obstacles were encountered in the handling of both fluorine and UF6. For example, before the K-25 gaseous diffusion plant could be built, it was first necessary to develop non-reactive chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
s that could be used as coatings, lubricant
Lubricant
A lubricant is a substance introduced to reduce friction between moving surfaces. It may also have the function of transporting foreign particles and of distributing heat...
s and gasket
Gasket
thumb|sright|250px|Some seals and gaskets1. [[o-ring]]2. fiber [[Washer |washer]]3. paper gaskets4. [[cylinder head]] [[head gasket|gasket]]...
s for the surfaces which would come into contact with the UF6 gas (a highly reactive and corrosive substance). Scientists of the Manhattan Project recruited William T. Miller
William T. Miller
William T. Miller was a professor of organic chemistry at Cornell University. His experimental research included investigations into the mechanism of addition of halogens, especially fluorine, to hydrocarbons...
, a professor of organic chemistry
Organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...
at Cornell University
Cornell University
Cornell University is an Ivy League university located in Ithaca, New York, United States. It is a private land-grant university, receiving annual funding from the State of New York for certain educational missions...
, to synthesize
Chemical synthesis
In chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions...
and develop such materials, because of his expertise in organofluorine chemistry
Organofluorine chemistry
Organofluorine chemistry describes the chemistry of organofluorine compounds, organic compounds that contain the carbon–fluorine bond. Organofluorine compounds find diverse applications ranging from oil- and water-repellents to pharmaceuticals, refrigerants and reagents in catalysis...
. Miller and his team developed several novel non-reactive chlorofluorocarbon
Chlorofluorocarbon
A chlorofluorocarbon is an organic compound that contains carbon, chlorine, and fluorine, produced as a volatile derivative of methane and ethane. A common subclass are the hydrochlorofluorocarbons , which contain hydrogen, as well. They are also commonly known by the DuPont trade name Freon...
polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
s that were used in this application.
Calutrons were expensive to build and operate and inefficient. As soon as the engineering obstacles posed by the gaseous diffusion process had been overcome and the gaseous diffusion cascades began operating at Oak Ridge in 1945, all of the calutrons were shut down. The gaseous diffusion technique then became the preferred technique for producing enriched uranium.
At the time of their construction in the early 1940s, the gaseous diffusion plants were the largest buildings ever constructed. Large gaseous diffusion plants were constructed by the United States, the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
(including a plant that is now in Kazakhstan
Kazakhstan
Kazakhstan , officially the Republic of Kazakhstan, is a transcontinental country in Central Asia and Eastern Europe. Ranked as the ninth largest country in the world, it is also the world's largest landlocked country; its territory of is greater than Western Europe...
), the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, and South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. Most of these have now closed or are expected to close, unable to compete economically with newer enrichment techniques. However some of the technology used in pumps and membranes still remains top secret, and some of the materials that were used remain subject to export controls, as a part of the continuing effort to control nuclear proliferation
Nuclear proliferation
Nuclear proliferation is a term now used to describe the spread of nuclear weapons, fissile material, and weapons-applicable nuclear technology and information, to nations which are not recognized as "Nuclear Weapon States" by the Treaty on the Nonproliferation of Nuclear Weapons, also known as the...
.
Current status
As of 2008, gaseous diffusion plants in the United States and France generated 33% of the world's enriched uranium. Operated by the United States Enrichment CorporationUnited States Enrichment Corporation
The United States Enrichment Corporation, a subsidiary of USEC Inc. , is a corporation that contracts with the United States Department of Energy to produce enriched uranium for use in nuclear power plants.-History:...
(USEC), the Paducah Gaseous Diffusion Plant
Paducah Gaseous Diffusion Plant
The Paducah Gaseous Diffusion Plant is a facility located in McCracken County, Kentucky, near Paducah, Kentucky, that produces enriched uranium, for nuclear power plants. The plant is now operated by United States Enrichment Corporation, a subsidiary of USEC Incorporated, a publicly traded...
in Kentucky is currently the only fully functioning uranium enrichment facility in the United States that employs the gaseous diffusion process. The only other such facility in the United States, the Portsmouth Gaseous Diffusion Plant
Portsmouth Gaseous Diffusion Plant
The Portsmouth Gaseous Diffusion Plant is a facility located in Scioto Township, Pike County, Ohio, just south of Piketon, Ohio that previously produced enriched uranium, including weapons-grade uranium, for the United States Atomic Energy program and U.S. nuclear weapons program...
in Ohio, ceased enrichment activities in 2001. Since 2010, the Ohio site is now used mainly by AREVA
Areva
AREVA is a French public multinational industrial conglomerate headquartered in the Tour Areva in Courbevoie, Paris. AREVA is mainly known for nuclear power; it also has interests in other energy projects. It was created on 3 September 2001, by the merger of Framatome , Cogema and...
, a French conglomerate
Conglomerate (company)
A conglomerate is a combination of two or more corporations engaged in entirely different businesses that fall under one corporate structure , usually involving a parent company and several subsidiaries. Often, a conglomerate is a multi-industry company...
, for the conversion of depleted UF6 to uranium oxide
Uranium oxide
Uranium oxide is an oxide of the element uranium.The metal uranium forms several oxides:* Uranium dioxide or uranium oxide * Uranium trioxide or uranium oxide...
.
As existing gaseous diffusion plants become obsolete, they are being replaced by second generation gas centrifuge
Gas centrifuge
A gas centrifuge is a device that performs isotope separation of gases. A centrifuge relies on the principles of centripetal force accelerating molecules so that particles of different masses are physically separated in a gradient along the radius of a rotating container.A prominent use of gas...
technology, which requires far less electric power to produce equivalent amounts of separated uranium. AREVA is replacing its Georges Besse gaseous diffusion plant with the Georges Besse II centrifuge plant. AVLIS and SILEX
Silex Process
SILEX is an acronym for Separation of Isotopes by Laser Excitation , a technology developed in the 1990s for isotope separation to produce enriched uranium using lasers....
are two more recently developed uranium enrichment technologies which may be utilized in the future, and are possibly already being utilized.
See also
- Fick's laws of diffusion
- Molecular diffusion
- Nuclear fuel cycleNuclear fuel cycleThe nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in...
- Thomas Graham (chemist)Thomas Graham (chemist)Thomas Graham FRS was a nineteenth-century Scottish chemist who is best-remembered today for his pioneering work in dialysis and the diffusion of gases.- Life and work :...