Molecular laser isotope separation
Encyclopedia
Molecular laser isotope separation (MLIS) is a method of isotope separation
, where specially tuned lasers
are used to separate isotope
s of uranium
using selective ionization of hyperfine transitions of uranium hexafluoride
molecules. It is similar to AVLIS
. Its main advantage over AVLIS is low energy consumption and use of uranium hexafluoride instead of vaporized uranium.
MLIS was conceived in 1961 at the Los Alamos National Laboratory
.
MLIS operates in cascade
setup, like the gaseous diffusion
process. Instead of vaporized uranium as in AVLIS the working medium of the MLIS is uranium hexafluoride
which requires a much lower temperature to vaporize. The UF6 gas is mixed with a suitable carrier gas (a noble gas
including some hydrogen
) which allows the molecules to remain in the gaseous phase after being cooled by expansion through a supersonic Laval nozzle. A scavenger gas (e.g. methane
) is also included in the mixture to bind with the fluorine atoms after they are dissociated from the UF6 and inhibit their recombination with the enriched UF5 product. In the first stage the expanded and cooled stream of UF6 is irradiated with an infrared
laser
operating at the wavelength
of 16 µm. The mix is then irradiated with another laser, either infrared or ultraviolet, whose photons are selectively absorbed by the excited 235UF6, causing its photolysis to 235UF5 and fluorine
. The resultant enriched UF5 forms a solid which is then separated from the gas by filtration or a cyclone separator. The precipitated UF5 is relatively enriched with 235UF5 and after conversion back to UF6 it is fed to the next stage of the cascade to be further enriched.
The laser for the excitation is usually a carbon dioxide laser
with output wavelength shifted from 10.6 µm to 16 µm; the photolysis laser may be a excimer laser
operating at 308 nm, however infrared lasers are mostly used in existing implementations.
The process is considerably complex in that many mixed complexes of UFx are formed contaminating the product, with many technical difficulties. United States
, France
, United Kingdom
, Germany
and South Africa
reported termination of their MLIS programs, however Japan has a small scale program in operation.
The Commonwealth Scientific and Industrial Research Organisation in Australia has developed the SILEX pulsed laser separation process. GE, Cameco and Hitachi are currently involved in developing it for commercial use. Silex information
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...
, where specially tuned lasers
Tunable laser
A tunable laser is a laser whose wavelength of operation can be altered in a controlled manner. While all laser gain media allow small shifts in output wavelength, only a few types of lasers allow continuous tuning over a significant wavelength range....
are used to separate 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 of uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
using selective ionization of hyperfine transitions of 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...
molecules. It is similar to AVLIS
AVLIS
AVLIS Is an acronym which stands for atomic vapor laser isotope separation and is a method by which specially tuned lasers are used to separate isotopes of uranium using selective ionization of hyperfine transitions....
. Its main advantage over AVLIS is low energy consumption and use of uranium hexafluoride instead of vaporized uranium.
MLIS was conceived in 1961 at the Los Alamos National Laboratory
Los Alamos National Laboratory
Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...
.
MLIS operates in 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....
setup, like the gaseous diffusion
Gaseous diffusion
Gaseous diffusion is a technology used to produce enriched uranium by forcing gaseous uranium hexafluoride through semi-permeable membranes. This produces a slight separation between the molecules containing uranium-235 and uranium-238 . By use of a large cascade of many stages, high separations...
process. Instead of vaporized uranium as in AVLIS the working medium of the MLIS is 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...
which requires a much lower temperature to vaporize. The UF6 gas is mixed with a suitable carrier gas (a noble gas
Noble gas
The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity...
including some hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
) which allows the molecules to remain in the gaseous phase after being cooled by expansion through a supersonic Laval nozzle. A scavenger gas (e.g. methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
) is also included in the mixture to bind with the fluorine atoms after they are dissociated from the UF6 and inhibit their recombination with the enriched UF5 product. In the first stage the expanded and cooled stream of UF6 is irradiated with an infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
operating at the wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
of 16 µm. The mix is then irradiated with another laser, either infrared or ultraviolet, whose photons are selectively absorbed by the excited 235UF6, causing its photolysis to 235UF5 and 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...
. The resultant enriched UF5 forms a solid which is then separated from the gas by filtration or a cyclone separator. The precipitated UF5 is relatively enriched with 235UF5 and after conversion back to UF6 it is fed to the next stage of the cascade to be further enriched.
The laser for the excitation is usually a carbon dioxide laser
Carbon dioxide laser
The carbon dioxide laser was one of the earliest gas lasers to be developed , and is still one of the most useful. Carbon dioxide lasers are the highest-power continuous wave lasers that are currently available...
with output wavelength shifted from 10.6 µm to 16 µm; the photolysis laser may be a excimer laser
Excimer laser
An excimer laser is a form of ultraviolet laser which is commonly used in the production of microelectronic devices , eye surgery, and micromachining....
operating at 308 nm, however infrared lasers are mostly used in existing implementations.
The process is considerably complex in that many mixed complexes of UFx are formed contaminating the product, with many technical difficulties. United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, 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...
, 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...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
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...
reported termination of their MLIS programs, however Japan has a small scale program in operation.
The Commonwealth Scientific and Industrial Research Organisation in Australia has developed the SILEX pulsed laser separation process. GE, Cameco and Hitachi are currently involved in developing it for commercial use. Silex information
See also
- Nuclear powerNuclear powerNuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...
- 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...
- Gaseous diffusionGaseous diffusionGaseous diffusion is a technology used to produce enriched uranium by forcing gaseous uranium hexafluoride through semi-permeable membranes. This produces a slight separation between the molecules containing uranium-235 and uranium-238 . By use of a large cascade of many stages, high separations...
- Gas centrifugeGas centrifugeA 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...
- CalutronCalutronA 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,...
- AVLISAVLISAVLIS Is an acronym which stands for atomic vapor laser isotope separation and is a method by which specially tuned lasers are used to separate isotopes of uranium using selective ionization of hyperfine transitions....
- CRISLA
External links
- Laser isotope separation uranium enrichment
- Reed J. Jenson, O’Dean P. Judd, and J. Allan Sullivan Separating Isotopes with Lasers Los Alamos Science v4, 1982.
- Article in New York Times (August 20, 2011) regarding General Electric's plans to build a commercial laser enrichment facility in Wilmington, North Carolina, USA. http://www.nytimes.com/2011/08/21/science/earth/21laser.html