Uranium is found naturally in a variety of forms. The atoms of the element 92 protons but they can have varying numbers of neutrons, creating different isotopes with varying properties. U-235, a designation formed from the sum of 92 protons plus 143 neutrons, is the isotope prized for reactors and bombs – but it makes up only 0.7 percent of mined uranium, nearly all of which is the heavier U-238, with three extra neutrons.To generate electricity, the concentration of U-235 must be increased to between 3 and 5 percent. It must be refined to levels above 80 percent to create the core of an atom bomb. This is called Uranium Enrichment. The two most popular production techniques require uranium, in a processed form known as “yellow cake”, to be converted into a gas called uranium hexafluoride (UF-6) before enrichment.
Diffusion Method:
- When gaseous uranium hexafluoride is pumped through a porous barrier, the lighter molecules formed with U-235 atoms traverse the pores at a quicker rate those bearing U-238.
- This is like smaller grains of sand passing through a sieve more easily than larger ones. The process has to be repeated about 1,400 times to get U-235 at a concentration of 3 percent of the UF-6.
Centrifuge Method:
- Used by Iran. Like the diffusion process, the centrifuge method exploits the slight difference in mass between U-235 and U-238. Uranium hexafluoride gas is fed into a cylindrical centrifuge.
- It spins at supersonic speeds, causing the heavier U-238 to move towards the cylinder’s outer edge while U-235 collects around the centre. By separating the outer and inner layers and repeating the process many times the concentration of U-235 in the mixture is increased.