Isotope Separator

1. 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.

2. 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

3. 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

4. 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.

5. 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

6. 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

7. ??% U235

8. 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

9. 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

10. 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).

11. 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.

12. The DU penetrator of a 30 mm round

13. 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.

14. 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.)

15. 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.

16. 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

17. Mass spectrograph

18. It is ok for light isotopes n • those for which small quantities are needed. • For nuc reactor - NO

19. 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

23. 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.

24. 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.

25. 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!

29. Cascade of gas centrifuges used to produce enriched U.

30. 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