Isotope Separator. Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes. E.g., separating natural uranium into enriched uranium and depleted uranium. This is a crucial process
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Isotope Separator • Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes. E.g., 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 also required for the creation of uranium based nuclear weapons
While in general chemical elements can be purified through chemical processes, • Isotopes of the same element have nearly identical chemical properties, which makes this type of separation impractical, except for separation of deuterium. • Enrichment unit is weight percent
Natural U • Natural uranium (NU) refers to uranium with the same isotopic ratio as found in nature. • It contains 0.7% U235, 99.3% U238, and a trace of U234 by weight. • In terms of the amount of radioactivity, approximately 2.2% comes from U235, 48.6% U238, and 49.2% U234.
NU can be used to fuel both low- and high-power reactors. Graphite moderated reactors and heavy water moderated reactors have been fueled with natural uranium in the pure metal (U) or uranium dioxide (UO2) ceramic forms
Enriched U • Enriched uranium is a type of U in which the % composition of U235 has been increased through the process of isotope separation. • U235 is the only nuclide existing in nature (in any appreciable amount) that is fissile with thermal neutrons. • The International Atomic Energy Agency [IAEA] attempts to monitor and control enriched uranium supplies and processes in its efforts to ensure nuclear power generation safety and curb nuclear weapons proliferation. • ~2000 tonnes of highly EU in the world
Slightly enriched uranium (SEU) has a 235U concentration of 0.9% to 2%. • Reprocessed uranium (RepU) - fuel typically contains slightly more U-235 than natural U • Low-enriched uranium (LEU) has a lower than 20% concentration of 235U. • Highly enriched uranium (HEU) has a greater than 20% concentration of 235U or 233U
The very first uranium bomb, Little Boy dropped on Hiroshima in 1945, used 64 kilograms of 80% enriched uranium. A billet of highly enriched uranium metal
Depleted U • Depleted uranium (DU / Q-metal / depletalloy / D-38) is U with a lower content of the fissile isotope U235 than natural uranium. • Uses of DU take advantage of its very high density of 19.1 g/cm3 (68.4% denser than lead).
Apps: • Civilian uses include counterweights in aircraft, radiation shielding in medical radiation therapy and industrial radiography equipment and containers used to transport radioactive materials. • Military uses include defensive armor plating and armor-piercing projectiles. Most DU arises as a byproduct of the production of Enriched U.
Potential long-term health effects? • The actual level of acute and chronic toxicity of DU is also a point of medical controversy. • Estimated DU stocks until 2008 (tonnes): 1,188,273 • Safety and environmental issues: in steel cylinders.
Back to - Isotope Separator [IS] • Isotope separation / U Enrichment is it difficult? If so, then why? • It is difficult because two isotopes of the same elements have very nearly identical chemical properties, and can only be separated gradually using small mass differences. • 235U is only 1.26% lighter than 238U. • Also, U is rarely separated in its atomic form, but instead as a compound (235UF6 is only 0.852% lighter than 238UF6.)
A cascade of identical stages produces successively higher concentrations of 235U. • Each stage passes a slightly more concentrated product to the next stage and returns a slightly less concentrated residue to the previous stage.
IS – commercial methods • 1st generation – gaseous diffusion • 2nd gen – gas centrifuge [which consumes only 2% to 2.5% as much energy as gaseous diffusion] – energy-efficient! • 3rd gen – not yet
It is ok for light isotopes n • those for which small quantities are needed. • For nuc reactor - NO
1. Diffusion tech for Isotope sep. • Gaseous diffusion is a technology used to produce enriched uranium by forcing gaseous uranium hexafluoride (hex) through semi-permeable membranes. • This produces a slight separation between the molecules containing 235U and 238U. Permeable – porous / leaky
Throughout the Cold War, gaseous diffusion played a major role as a U enrichment technique. • As of 2008, ~33% of enriched uranium production is by this process. • But is now an obsolete technology that is steadily being replaced by the later generations of technology, as the diffusion plants reach their ends-of-life.
2. Centrifuge tech for Isotope sep. • The gas centrifuge process uses a large number of rotating cylinders in series and parallel formations. • Each cylinder's rotation creates a strong centrifugal force so that the heavier gas molecules containing 238U move toward the outside of the cylinder and the lighter gas molecules rich in 235U collect closer to the center.
It requires much less energy [6~10 times less] to achieve the same separation than the older gaseous diffusion process. Gas centrifuge techniques produce about 54% of the world's enriched uranium. Need large amounts of units in parallel – as the flow rate per stage is much lower than that of gaseous diffusion. • Though since 1940s, recent to get popularity!
Others… • The Zippe centrifuge is an improvement on the standard gas centrifuge, the primary difference being the use of heat. • Laser techniques: Laser processes promise lower energy inputs, lower capital costs. • Aerodynamic processes • Electromagnetic isotope separation • Plasma separation process • Chemical methods