Zippe-type centrifuge
The Zippe-type centrifuge is a
Background
Natural
Centrifuge uranium enrichment
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 (note this applies only to uranium metal). Centrifuges need to work with a gas rather than a solid, and the gas used here is uranium hexafluoride. The relative mass difference between 235UF6 and 238UF6 is less than 0.86%. On the other hand, separation efficiency in a centrifuge depends on absolute mass 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 (as in some modern centrifuges[3]), this would correspond to a centripetal acceleration of around 900,000 x g[4] (around 42 times the max speed of a standard, lab benchtop microcentrifuge[5] and between 0.9 to 9 times the max speed of a standard lab ultracentrifuge[6]) or a linear speed of greater than Mach 2 in air (Mach 1 = sound velocity, in air ca. 340 m/s) and much more in UF6. For comparison, automatic washing machines operate at only about 12 to 25 revolutions per second (720–1500 rpm) during the spin cycle, while turbines in automotive turbochargers can run up to around 2500–3333 revolutions per second (150,000–200,000 rpm).[7][8]
A Zippe-type centrifuge
Quantitatively, the radial pressure (or density) distribution can be given by[9]
where p is the pressure, r the variable radius and R its maximum, M the molecular mass, ω the angular velocity, k the Boltzmann constant and T the temperature. (This equation is similar to the barometric formula.) Writing this equation for both isotopes and dividing, gives the (r-dependent) isotope ratio. It only contains ΔM (not the relative mass difference ΔM/M) in the exponent. The radial enrichment factor then results by dividing through the initial isotope ratio. To calculate the total enrichment in a countercurrent centrifuge of height H, one has to add a factor of H/(R√2) in the exponent.
According to Glaser,[3] early centrifuges had rotor diameters of 7.4 to 15 cm and lengths of 0.3 to 3.2 m, and the peripheral speed was 350 to 500 m/s. The modern centrifuge TC-21 of Urenco has a diameter of 20 cm and a length of more than 5 m, spinning with 770 m/s. Centrus (formerly Usec) plans a centrifuge with 60 cm diameter, 12 m height and 900 m/s peripheral speed.
A countercurrent of the gas is stimulated either mechanically or (less preferred) by a temperature gradient between the top and bottom of the rotor. With a countercurrent-to-feed ratio of 4, Glaser[3] calculates a separation factor of 1,74 for a TC-21 centrifuge of 5 m height. Lowering this ratio (by increasing the feed) decreases the separation factor but increases the throughput and thus the productivity.
To reduce friction, the rotor spins in a vacuum. Part of the rotor with the near-by housing acts as a molecular pump, which maintains the vacuum. A magnetic bearing holds the top of the rotor steady, and the only physical contact (necessary only during start-up) is the conical jewel bearing on which the rotor sits.[1][9] Both bearings contain measures for damping vibrations. The three gas lines enter the rotor on its axis.
After the scientists were released from Soviet captivity in 1956,
The exact details of advanced Zippe-type centrifuges are closely guarded secrets. For example, the efficiency of the centrifuges is improved by increasing their speed of rotation. To do so, stronger materials, such as
The Zippe-type centrifuge is difficult to build successfully and requires carefully machined parts. However, compared to other enrichment methods, it is much cheaper and is faster to set up, consumes much less energy and requires little area for the plant. Therefore it can be built in relative secrecy. This makes it ideal for covert nuclear-weapons programs and increases the risk of nuclear proliferation.[3] Centrifuge cascades also have much less material held in the machine at any time than gaseous diffusion plants.
Global usage
Pakistan's atomic bomb program developed the P1 and P2 centrifuges based on early designs of Urenco;[3] the first two centrifuges that Pakistan deployed in larger numbers but reduce it after 1981 based on estimation require for critical mass. The P1 centrifuge uses an aluminum rotor, and the P2 centrifuge uses a maraging steel rotor,[3] which is stronger, spins faster, and enriches more uranium per machine than the P1. In Pakistan, the Zippe-type centrifuge had a local designation and was known as Centrifuge Khan (after Abdul Qadeer Khan).: 151 [10]
Russian sources dispute the account of Soviet centrifuge development given by Gernot Zippe. They cite Max Steenbeck as the 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, 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.[2]
Zippe-type centrifuge facilities
- Khan Research Laboratories in Pakistan
- National Enrichment Facility of Los Alamos National Laboratory in the United States
- Urenco Group in Great Britain, the Netherlands, and Germany
- Russia (where it is called Kamenev centrifuge)
See also
- Gas centrifuge
- Ultracentrifuge
- Magnetic levitation
- Thrust bearing
- German nuclear weapon project
- Germany and weapons of mass destruction
- Pakistan and weapons of mass destruction
- Netherlands and weapons of mass destruction
- Forced labor of Germans in the Soviet Union
- Russian Alsos
- Stuxnet
References
- ^ Broad, William J. (2004-03-23). "Slender and Elegant, It Fuels the Bomb". The New York Times. Retrieved 2009-10-23.
- ^ a b Oleg Bukharin, Oleg. Russia’s Gaseous Centrifuge Technology and Uranium Enrichment Complex Archived January 11, 2014, at the Wayback Machine 2004.
- ^ S2CID 27062236.
- ^ "Calculation of Centripetal Force". Wolfram Alpha. Retrieved 29 April 2023.
- ^ "Benchtop Centrifuges". ThermoFisher Scientific. ThermoFisher Scientific. Retrieved 29 April 2023.
- ^ "Thermo Scientific Sorvall MTX/MX Plus Series Micro-ultracentrifuge Rotor Guide" (PDF). ThermoFisher Scientific. Retrieved 29 April 2023.
- ^ How A Turbo Works
- ^ HowStuffWorks "How Turbochargers Work"
- ^ a b c d e Wolfang Ehrfeld, Ursula Ehrfeld, Anreicherung von Uran-235, Gmelin Handbuch der Anorganischen Chemie. 8.Aufl.System-Nr.55: U-Uran. Erg.Bd.A2: Isotope. By C. Keller. Ed.: K.-C. Buschbeck, C. Keller. Berlin, Heidelberg, New York: Springer 1980
- ISBN 978-0-8047-8480-1.
External links
- The Zippe Type - The Poor Man's Bomb, BBC Radio 4, 19 May 2004
- Tracking the technology, Nuclear Engineering International, 31 August 2004
- Slender and Elegant, It Fuels the Bomb, The New York Times, 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 page 40, September 2008
- Long-term Energy Security Interests of the United States: Hearing Before the Congressional Subcommittee on Economic Stabilization, December 11, 1990 page 140, Subcommittee on Economic Stabilization (United States House Committee on Banking, Finance and Urbain Affaires)