Radiological Safety Traning for Uranium Facilities
Module 102 - The Nuclear Fuel Cycle
Reacting the UF4 with fluorine gas (F2) to form uranium hexafluoride (UF 6),
which is a volatile form ready for enrichment. The UF 6 is a solid at room
temperature but readily becomes a gas when heated above 56°C.
The enrichment process is necessary to increase the percentage of the 235U isotope in the
uranium to make it suitable for reactor fuel. Natural uranium contains 0.7% 235U.
Typically, enriched uranium contains 2-4% 235U. Other uses may require much higher
concentrations up to, or even greater than, 90% 235U. Depleted uranium, which is left
over after the enrichment process, has an abundance of about 0.2% 235U.
The methods used to enrich uranium include:
Gaseous diffusion is based on princ iples of gas laws. The UF6 gas is forced
made of a special barrier material that is porous. The 235UF6 molecules are lighter
than the 238UF6 molecules and bounce against the porous barrier more frequently.
The 235UF6 has a greater chance of passing through the barrier, resulting in a
slightly richer 235U content. It may take as many as a thousand passes to obtain
the desired degree of enrichment.
The Atomic Vaporization Laser Isotope Separation (AVLIS) involves
vaporization, selective ionization of one isotope, and subsequent electrical
separation. Currently, no DOE production plants exist which use this
The nozzle separation process is based on the different speeds of 235U and 238U
compounds when they are injected through a nozzle into a small chamber.