2. Uranium Enrichment
Enrichment is the process that increases the percentage of one isotope found in natural uranium (Uranium 235) from about 0.7% to 3 to 5 % for nuclear reactors, and to 80% for nuclear weapons grade materials, although lower levels of enrichment will suffice.
The enrichment process produces a powder, which is pressed and fired into pellet form. These pellets are stacked into tubes, and then sealed and used in fuel rods. Many fuel rods are used in each nuclear reactor.
Numerous technologies have been developed to enrich uranium, such as gaseous-diffusion and centrifuges. All of these technologies require a large initial investment and large amounts of energy to operate.
Gaseous diffusion involves forcing uranium hexafluoride gas under pressure through a series of porous membranes or diaphragms. As Uranium 235 molecules are lighter than the Uranium 238 molecules they move faster and have a slightly better chance of passing through the pores in the membrane. The UF6 that diffuses through the membrane is thus slightly enriched, that is the amount of U235 becomes more concentrated.
The centrifuge process uses UF6 gas and again makes use of the slight difference in mass between U-235 and U-238. The gas is fed into a series of vacuum tubes, each containing a rotor one to two metre long and 15-20 cm diameter. When the rotors are spun rapidly, the heavier molecules with U-238 increase in concentration towards the cylinder's outer edge. There is a corresponding increase in concentration of U-235 molecules near the centre.
Enrichment is a large-scale industrial process and is difficult to conceal. A technique for enriching uranium with lasers is under development in Australia, which would make this process much easier and more compact.
