Helikon vortex separation process
Encyclopedia
The Helikon vortex separation process is an aerodynamic uranium enrichment
process designed around a device called a vortex tube
. This method was designed and used in South Africa
for producing reactor fuel with a uranium-235
content of around 3–5%, and 80–93% enriched uranium for use in nuclear weapons
. The Uranium Enrichment Corporation of South Africa, Ltd.
, (UCOR), developed the process, operating a facility at Pelindaba
(known as the 'Y' plant) to produce hundreds of kilograms of HEU. Aerodynamic enrichment processes require large amounts of electricity and are not generally considered economically competitive because of high energy consumption and substantial requirements for removal of waste heat. The South African enrichment plant has apparently been closed.
gas and hydrogen
is injected tangentially into a tube at one end through nozzles or holes, at velocities close to the speed of sound. The tube tapers to a small exit aperture at one or both ends. This tangential injection of gas results in a spiral or vortex motion within the tube, and two gas streams are withdrawn at opposite ends of the vortex tube; centrifugal force providing the isotopic
separation. The spiral swirling flow decays downstream of the feed inlet due to friction at the tube wall. Consequently, the inside diameter of the tube is typically tapered to reduce decay in the swirling flow velocity. This process is characterized by a separating element with a very small stage cut (the ratio of product flow to feed flow) of about 1/20, and high process-operating pressures.
Due to the extremely difficult plumbing
required to link stages together, the design was developed into a cascade design technique (dubbed Helikon), in which 20 separation stages are combined into one module, and all 20 stages share a common pair of axial-flow compressors. A basic requirement for the success of this method is that the axial-flow compressors successfully transmit parallel streams of different isotopic compositions without significant mixing. A typical Helikon module consists of a large cylindrical steel vessel housing the 20 separator assemblies, along with two compressors (one mounted on each end), and two water-cooled heat exchanger
s.
Advantages of this process are a lack of criticality concerns
due to the highly diluted feedstock and suitability for batch processing. This means Helikon-type plants can be relatively small, making the technology a nuclear proliferation concern
.
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...
process designed around a device called a vortex tube
Vortex tube
The vortex tube, also known as the Ranque-Hilsch vortex tube, is a mechanical device that separates a compressed gas into hot and cold streams. It has no moving parts....
. This method was designed and used in 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...
for producing reactor fuel with a 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...
content of around 3–5%, and 80–93% enriched uranium for use in nuclear weapons
South Africa and weapons of mass destruction
From the 1960s to the 1980s, South Africa pursued research into weapons of mass destruction, including nuclear, biological, and chemical weapons. Six nuclear weapons were assembled...
. The Uranium Enrichment Corporation of South Africa, Ltd.
NECSA
The South African Nuclear Energy Corporation was established as a public company by the Republic of South Africa Nuclear Energy Act in 1999 and is wholly owned by the State...
, (UCOR), developed the process, operating a facility at Pelindaba
Pelindaba
Pelindaba is South Africa's main Nuclear Research Centre, run by The South African Nuclear Energy Corporation, and was the location where South Africa's atomic bombs of the 1970s were developed, constructed and subsequently stored...
(known as the 'Y' plant) to produce hundreds of kilograms of HEU. Aerodynamic enrichment processes require large amounts of electricity and are not generally considered economically competitive because of high energy consumption and substantial requirements for removal of waste heat. The South African enrichment plant has apparently been closed.
Process
In the vortex separation process a mixture of uranium hexafluorideUranium 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...
gas and 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...
is injected tangentially into a tube at one end through nozzles or holes, at velocities close to the speed of sound. The tube tapers to a small exit aperture at one or both ends. This tangential injection of gas results in a spiral or vortex motion within the tube, and two gas streams are withdrawn at opposite ends of the vortex tube; centrifugal force providing the isotopic
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...
separation. The spiral swirling flow decays downstream of the feed inlet due to friction at the tube wall. Consequently, the inside diameter of the tube is typically tapered to reduce decay in the swirling flow velocity. This process is characterized by a separating element with a very small stage cut (the ratio of product flow to feed flow) of about 1/20, and high process-operating pressures.
Due to the extremely difficult plumbing
Plumbing
Plumbing is the system of pipes and drains installed in a building for the distribution of potable drinking water and the removal of waterborne wastes, and the skilled trade of working with pipes, tubing and plumbing fixtures in such systems. A plumber is someone who installs or repairs piping...
required to link stages together, the design was developed into a cascade design technique (dubbed Helikon), in which 20 separation stages are combined into one module, and all 20 stages share a common pair of axial-flow compressors. A basic requirement for the success of this method is that the axial-flow compressors successfully transmit parallel streams of different isotopic compositions without significant mixing. A typical Helikon module consists of a large cylindrical steel vessel housing the 20 separator assemblies, along with two compressors (one mounted on each end), and two water-cooled heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
s.
Advantages of this process are a lack of criticality concerns
Criticality accident
A criticality accident, sometimes referred to as an excursion or a power excursion, is an accidental increase of nuclear chain reactions in a fissile material, such as enriched uranium or plutonium...
due to the highly diluted feedstock and suitability for batch processing. This means Helikon-type plants can be relatively small, making the technology a nuclear proliferation concern
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...
.
See also
- South Africa and weapons of mass destructionSouth Africa and weapons of mass destructionFrom the 1960s to the 1980s, South Africa pursued research into weapons of mass destruction, including nuclear, biological, and chemical weapons. Six nuclear weapons were assembled...
- Nuclear reprocessingNuclear reprocessingNuclear reprocessing technology was developed to chemically separate and recover fissionable plutonium from irradiated nuclear fuel. Reprocessing serves multiple purposes, whose relative importance has changed over time. Originally reprocessing was used solely to extract plutonium for producing...
- 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...
- 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...