Zippe-type centrifuge
Encyclopedia
The Zippe-type centrifuge is a device designed to collect Uranium-235
. It was developed in the Soviet Union
by a team of 60 Austrian and German scientists captured after World War II
, working in detention. The centrifuge is named after the team's lead experimenter, Gernot Zippe
.
consists of three isotope
s; the majority (99.274 percent) is U-238
, while approximately 0.72 percent is U-235 and the remaining 0.0055 percent is U-234. If natural uranium is enriched
to contain 3 percent U-235
, it can be used as fuel for light water
nuclear reactor
s. If it is enriched to contain 90 percent Uranium-235, it can be used for nuclear weapon
s.
Enriching uranium
is difficult because the isotopes are practically identical in chemistry and very similar in weight: U-235 is only 1.26% lighter than U-238. Separation efficiency in a centrifuge depends on weight difference. Separation of uranium isotopes requires a centrifuge
that can spin at 1,500 revolutions per second
(90,000 RPM
). If we assume a rotor diameter of 20 cm (actual rotor diameter is likely to be less), this corresponds to a linear speed of greater than Mach 2 (Mach 1 = 340 m/s). For comparison, automatic washing machine
s operate at only about 12 to 25 revolutions per second during the spin cycle (720-1500 rpm), while turbines in automotive turbocharger
s can run up to around 150,000 - 200,000 rpm (2500 - 3333 revolutions per second).
A Zippe-type centrifuge has a hollow, cylindrical rotor
filled with gas
eous uranium in the form of its hexafluoride
. A pulsating magnetic field
at the bottom of the rotor, similar to that used in an electric motor
, is able to spin it quickly enough that the U-238 is thrown towards the edge. The lighter U-235 collects near the centre. The bottom of the gaseous mix is heated, producing convection currents that move the U-238 down. The U-235 moves up, where scoops collect it. Each centrifuge has one inlet and two output lines (corresponding to the heavy and the light fractions).
At the high speed of rotation, the gas is compressed close to the wall of the rotor. The rotor can be almost a meter in length (diameter is likely to be less than 10 cm) and a temperature gradient of 300C between the top and bottom of the rotor produces a very strong convection current. In addition, very strong coriolis forces produced add to the separation efficiency.
To reduce friction, the rotor spins in a vacuum
. A magnetic bearing
holds the top of the rotor steady, and the only physical contact is the needle-like bearing
that the rotor sits on. The three gas lines must be concentric with the axis and the seal is very important.
After the scientists were released from Soviet captivity in 1956, Gernot Zippe
was surprised to find that engineers in the West were years behind in their centrifuge technology. He was able to reproduce his design at the University of Virginia
in the United States
, publishing the results, even though the Soviets had confiscated his notes. Dr. Zippe left the United States when he was effectively barred from continuing his research: The Americans classified the work as secret, requiring him to become an American citizen (he refused), return to Europe, or abandon his research. He returned to Europe where, during the 1960s, he and his colleagues made the centrifuge more efficient by changing the material of the rotor from aluminum
to a stronger alloy called maraging steel
, which allowed higher speed. This improved centrifuge design is used by the commercial company Urenco
to produce enriched uranium fuel for nuclear power stations.
The exact details of advanced Zippe-type centrifuges are closely guarded secrets, but the efficiency of the centrifuges is improved by making them longer, and increasing their speed of rotation. To do so, even stronger materials, such as carbon fiber
reinforced composite material
s are used, and various techniques are used to avoid forces causing destructive vibrations, including the use of flexible "bellows" to allow controlled flexing of the rotor, as well as careful speed control to ensure that the centrifuge does not operate for very long at speeds where resonance
is a problem.
The Zippe-type is difficult to build successfully, and requires carefully machined parts. To give some idea of the precision required, it was reported in 2006 that the tiny amount of material deposited in fingerprints on Iran
's prototype centrifuges were enough to cause the machines to shatter. However, compared to other enrichment methods, it is much cheaper and can be used in relative secrecy. This makes it ideal for covert nuclear-weapons programs and possibly increases the risk of nuclear proliferation
. Centrifuge cascades
also have much less material held in the machine at any time, unlike gaseous diffusion plants
.
, a Pakistan
i engineer
, admitted to operate a smuggling ring responsible for supplying at least three countries with Zippe-type centrifuges.
Pakistan's nuclear program developed the P1 and P2 centrifuges—the first two centrifuges that Pakistan deployed in large numbers. The P1 centrifuge uses an aluminum rotor, and the P2 centrifuge uses a maraging steel rotor, which is stronger, spins faster, and enriches more uranium per machine than the P1. The western sources allegedly claimed that Zippe-technology was significantly improved by a team of Pakistani scientists working in KRL when a Pakistani mathematician Dr. Tasneem M. Shah
had improvised and developed the new version of the technology.
Russian and Soviet sources dispute the account of Soviet centrifuge development given by Gernot Zippe. They cite Prof. Max Steenbeck
as the actual German scientist in charge of the German part of the Soviet centrifuge effort, which was started by German refugee Fritz Lange in the 1930s. The Soviets credit Steenbeck, Lange, Isaac Kikoin and Evgeni Kamenev with originating different valuable aspects of the design. They state Zippe was engaged in building prototypes for the project for two years from 1953. Since the centrifuge project was top secret the Soviets did not challenge any of Zippe's claims at the time.
Physics Today
page 40, September 2008
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...
. It was developed in 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....
by a team of 60 Austrian and German scientists captured after World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, working in detention. The centrifuge is named after the team's lead experimenter, Gernot Zippe
Gernot Zippe
Gernot Zippe , was a Austrian-German mechanical engineer who is widely held responsible for leading the team which developed the Zippe-type centrifuge, a centrifuge machine for the collection of 235U in Soviet Union....
.
Background
Natural uraniumUranium
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...
consists of three 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; the majority (99.274 percent) is U-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...
, while approximately 0.72 percent is U-235 and the remaining 0.0055 percent is U-234. If natural uranium is enriched
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...
to contain 3 percent U-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...
, it can be used as fuel for light water
Light water reactor
The light water reactor is a type of thermal reactor that uses normal water as its coolant and neutron moderator. Thermal reactors are the most common type of nuclear reactor, and light water reactors are the most common type of thermal reactor...
nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
s. If it is enriched to contain 90 percent Uranium-235, it can be used for nuclear weapon
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
s.
Centrifuge uranium enrichment
Enriching uranium
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...
is difficult because the isotopes are practically identical in chemistry and very similar in weight: U-235 is only 1.26% lighter than U-238. Separation efficiency in a centrifuge depends on weight difference. Separation of uranium isotopes requires a centrifuge
Centrifuge
A centrifuge is a piece of equipment, generally driven by an electric motor , that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis...
that can spin at 1,500 revolutions per second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
(90,000 RPM
Revolutions per minute
Revolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...
). If we assume a rotor diameter of 20 cm (actual rotor diameter is likely to be less), this corresponds to a linear speed of greater than Mach 2 (Mach 1 = 340 m/s). For comparison, automatic washing machine
Washing machine
A washing machine is a machine designed to wash laundry, such as clothing, towels and sheets...
s operate at only about 12 to 25 revolutions per second during the spin cycle (720-1500 rpm), while turbines in automotive turbocharger
Turbocharger
A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...
s can run up to around 150,000 - 200,000 rpm (2500 - 3333 revolutions per second).
A Zippe-type centrifuge has a hollow, cylindrical rotor
Rotor (electric)
The rotor is the non-stationary part of a rotary electric motor, electric generator or alternator, which rotates because the wires and magnetic field of the motor are arranged so that a torque is developed about the rotor's axis. In some designs, the rotor can act to serve as the motor's armature,...
filled with gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
eous uranium in the form of its 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...
. A pulsating magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
at the bottom of the rotor, similar to that used in an electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
, is able to spin it quickly enough that the U-238 is thrown towards the edge. The lighter U-235 collects near the centre. The bottom of the gaseous mix is heated, producing convection currents that move the U-238 down. The U-235 moves up, where scoops collect it. Each centrifuge has one inlet and two output lines (corresponding to the heavy and the light fractions).
At the high speed of rotation, the gas is compressed close to the wall of the rotor. The rotor can be almost a meter in length (diameter is likely to be less than 10 cm) and a temperature gradient of 300C between the top and bottom of the rotor produces a very strong convection current. In addition, very strong coriolis forces produced add to the separation efficiency.
To reduce friction, the rotor spins in a vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
. A magnetic bearing
Magnetic bearing
A magnetic bearing is a bearing which supports a load using magnetic levitation. Magnetic bearings support moving machinery without physical contact; for example, they can levitate a rotating shaft and permit relative motion with very low friction and no mechanical wear...
holds the top of the rotor steady, and the only physical contact is the needle-like bearing
Bearing (mechanical)
A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can...
that the rotor sits on. The three gas lines must be concentric with the axis and the seal is very important.
After the scientists were released from Soviet captivity in 1956, Gernot Zippe
Gernot Zippe
Gernot Zippe , was a Austrian-German mechanical engineer who is widely held responsible for leading the team which developed the Zippe-type centrifuge, a centrifuge machine for the collection of 235U in Soviet Union....
was surprised to find that engineers in the West were years behind in their centrifuge technology. He was able to reproduce his design at the University of Virginia
University of Virginia
The University of Virginia is a public research university located in Charlottesville, Virginia, United States, founded by Thomas Jefferson...
in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, publishing the results, even though the Soviets had confiscated his notes. Dr. Zippe left the United States when he was effectively barred from continuing his research: The Americans classified the work as secret, requiring him to become an American citizen (he refused), return to Europe, or abandon his research. He returned to Europe where, during the 1960s, he and his colleagues made the centrifuge more efficient by changing the material of the rotor from 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....
to a stronger alloy called maraging steel
Maraging steel
Maraging steels are steels which are known for possessing superior strength and toughness without losing malleability, although they cannot hold a good cutting edge. Aging refers to the extended heat-treatment process...
, which allowed higher speed. This improved centrifuge design is used by the commercial company Urenco
Urenco Group
The URENCO Group is a nuclear fuel company operating several uranium enrichment plants in Germany, Netherlands, the United Kingdom, and the United States. It supplies nuclear power stations in about 15 countries, and has a 25% share of the global market for enrichment services...
to produce enriched uranium fuel for nuclear power stations.
The exact details of advanced Zippe-type centrifuges are closely guarded secrets, but the efficiency of the centrifuges is improved by making them longer, and increasing their speed of rotation. To do so, even stronger materials, such as carbon fiber
Carbon fiber
Carbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber...
reinforced composite material
Composite material
Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...
s are used, and various techniques are used to avoid forces causing destructive vibrations, including the use of flexible "bellows" to allow controlled flexing of the rotor, as well as careful speed control to ensure that the centrifuge does not operate for very long at speeds where resonance
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
is a problem.
The Zippe-type is difficult to build successfully, and requires carefully machined parts. To give some idea of the precision required, it was reported in 2006 that the tiny amount of material deposited in fingerprints on Iran
Iran
Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...
's prototype centrifuges were enough to cause the machines to shatter. However, compared to other enrichment methods, it is much cheaper and can be used in relative secrecy. This makes it ideal for covert nuclear-weapons programs and possibly increases the risk of 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...
. Centrifuge cascades
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...
also have much less material held in the machine at any time, unlike gaseous diffusion plants
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...
.
Global usage
In 2004 Abdul Qadeer KhanAbdul Qadeer Khan
Abdul Qadeer Khan , also known in Pakistan as Mohsin-e-Pakistan , D.Eng, Sc.D, HI, NI , FPAS; more widely known as Dr. A. Q...
, a Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
i engineer
Engineer
An engineer is a professional practitioner of engineering, concerned with applying scientific knowledge, mathematics and ingenuity to develop solutions for technical problems. Engineers design materials, structures, machines and systems while considering the limitations imposed by practicality,...
, admitted to operate a smuggling ring responsible for supplying at least three countries with Zippe-type centrifuges.
Pakistan's nuclear program developed the P1 and P2 centrifuges—the first two centrifuges that Pakistan deployed in large numbers. The P1 centrifuge uses an aluminum rotor, and the P2 centrifuge uses a maraging steel rotor, which is stronger, spins faster, and enriches more uranium per machine than the P1. The western sources allegedly claimed that Zippe-technology was significantly improved by a team of Pakistani scientists working in KRL when a Pakistani mathematician Dr. Tasneem M. Shah
Tasneem M. Shah
Tasneem M. Shah, Ph.D., SI, TI, is a Pakistani scientist and a prominent mathematician who has made pioneering and instrumental research and contributions to the field of computational fluid dynamics at Dr. A. Q. Khan Research Laboratories...
had improvised and developed the new version of the technology.
Russian and Soviet sources dispute the account of Soviet centrifuge development given by Gernot Zippe. They cite Prof. Max Steenbeck
Max Steenbeck
Max Christian Theodor Steenbeck was a German physicist who worked at the Siemens-Schuckertwerke in his early career, during which time he invented the betatron in 1934. He was taken to the Soviet Union after World War II , and he contributed to the Soviet atomic bomb project...
as the actual German scientist in charge of the German part of the Soviet centrifuge effort, which was started by German refugee Fritz Lange in the 1930s. The Soviets credit Steenbeck, Lange, Isaac Kikoin and Evgeni Kamenev with originating different valuable aspects of the design. They state Zippe was engaged in building prototypes for the project for two years from 1953. Since the centrifuge project was top secret the Soviets did not challenge any of Zippe's claims at the time.
See also
- Isotope separationIsotope separationIsotope 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...
- 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...
- UltracentrifugeUltracentrifugeThe ultracentrifuge is a centrifuge optimized for spinning a rotor at very high speeds, capable of generating acceleration as high as 2,000,000 g . There are two kinds of ultracentrifuges, the preparative and the analytical ultracentrifuge...
- Magnetic levitationMagnetic levitationMagnetic levitation, maglev, or magnetic suspension is a method by which an object is suspended with no support other than magnetic fields...
- Thrust bearingThrust bearingA thrust bearing is a particular type of rotary bearing. Like other bearings they permit rotation between parts, but they are designed to support a high axial load while doing this.Thrust bearings come in several varieties....
- German nuclear energy projectGerman nuclear energy projectThe German nuclear energy project, , was an attempted clandestine scientific effort led by Germany to develop and produce the atomic weapons during the events involving the World War II...
- Germany and weapons of mass destructionGermany and weapons of mass destructionThough Germany is one of the most technologically advanced countries in the world, since World War II it has generally refrained from using this technology to outfit its own armed forces with weapons of mass destruction , although it participates in the NATO nuclear weapons sharing arrangements and...
- Pakistan and weapons of mass destructionPakistan and weapons of mass destructionPakistan began focusing on nuclear weapons development in January 1972 under the leadership of Prime Minister Zulfiqar Ali Bhutto, who delegated the program to the Chairman of PAEC Munir Ahmad Khan...
- Forced labor of Germans in the Soviet UnionForced labor of Germans in the Soviet UnionForced labor of Germans in the Soviet Union was considered by the Soviet Union to be part of German war reparations for the damage inflicted by Nazi Germany on the Soviet Union during World War II. German civilians in Eastern Europe were deported to the USSR after World War II as forced laborers...
- Russian AlsosRussian AlsosThe Russian Alsos was an operation which took place in early 1945 in Germany, Austria, and Czechoslovakia, and whose objectives were the exploitation of German atomic related facilities, intellectual materials, materiel resources, and scientific personnel for the benefit of the Soviet atomic bomb...
- Gernot ZippeGernot ZippeGernot Zippe , was a Austrian-German mechanical engineer who is widely held responsible for leading the team which developed the Zippe-type centrifuge, a centrifuge machine for the collection of 235U in Soviet Union....
- Abdul Qadeer KhanAbdul Qadeer KhanAbdul Qadeer Khan , also known in Pakistan as Mohsin-e-Pakistan , D.Eng, Sc.D, HI, NI , FPAS; more widely known as Dr. A. Q...
- StuxnetStuxnetStuxnet is a computer worm discovered in June 2010. It initially spreads via Microsoft Windows, and targets Siemens industrial software and equipment...
External links
- The Zippe Type - The Poor Man's Bomb, BBC Radio 4BBC Radio 4BBC Radio 4 is a British domestic radio station, operated and owned by the BBC, that broadcasts a wide variety of spoken-word programmes, including news, drama, comedy, science and history. It replaced the BBC Home Service in 1967. The station controller is currently Gwyneth Williams, and the...
, 19 May 2004 - Tracking the technology, Nuclear Engineering International, 31 August 2004
- Slender and Elegant, It Fuels the Bomb, The New York TimesThe New York TimesThe New York Times is an American daily newspaper founded and continuously published in New York City since 1851. The New York Times has won 106 Pulitzer Prizes, the most of any news organization...
, March 23, 2004 - The Gas Centrifuge and Nuclear Proliferation, Marvin Miller, October 22, 2004
- The gas centrifuge and nuclear weapons proliferation, Houston G. Wood, Alexander Glaser, and R. Scott Kemp,
Physics Today
Physics Today
Physics Today, created in 1948, is the membership journal of the American Institute of Physics. It is provided to 130,000 members of twelve physics societies, including the American Physical Society...
page 40, September 2008