Enrichment - hdbk1113cn10127

DOE-HDBK-1113-98

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 56C.

Enrichment

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

Gaseous diffusion is based on princ iples of gas laws. The UF6 gas is forced

through converters by large compressors. The converters contain many tubes

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.

Laser Processes

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

technology.

Nozzle Separation

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.