Nuclear Fuel Cycle

Laser Isotope Separation

AVLIS (Atomic Vapor Laser Isotope Separation):

• Uranium metal is evaporated at ~2,300 degrees C in a vacuum chamber
• Tuned lasers selectively excite and ionise $^{235}$U atoms (at 591.5 nm, then UV at 310 nm)
• The ionised $^{235}$U atoms are collected on negatively charged plates
• Offers near-complete separation in a single step, with very low energy consumption (~300 kWh/SWU)
• Not yet proven at industrial scale due to insufficient laser power

MLIS (Molecular Laser Isotope Separation):

• Uses UF₆ as the feed (not metallic uranium)
• Infrared lasers selectively dissociate $^{235}$UF₆ to $^{235}$UF₅, which precipitates and can be filtered from the gas
• Developed at Los Alamos National Laboratory; experimental results not yet published

Electromagnetic Separation — The Calutron

The Calutron was developed at Oak Ridge, Tennessee during the Manhattan Project (1942-45). It is essentially a large-scale mass spectrometer: uranium is ionised and the ions are accelerated through a magnetic field, which causes them to travel in circular paths. The lighter $^{235}$U ions follow a tighter curve and can be collected separately from the heavier $^{238}$U ions.

The Calutron was extraordinarily expensive and slow, but it was the method used to produce the first highly enriched uranium for nuclear weapons. The Oak Ridge facility included electromagnetic separation (Y-12 plant), thermal diffusion, and the enormous gaseous diffusion plant (K-25). The gas diffusion plant enriched uranium to about 7%, and the Calutrons completed the enrichment to ~90% for weapons use. Only enough HEU for one weapon was produced by June 1945.

Historical Note: The Oak Ridge K-25 gaseous diffusion plant, constructed 1942-45, covered 20 hectares and was the largest industrial building in the world at that time, with the world’s largest electricity generating station built next door.

Gas Nozzle (Aerodynamic Separation)

UF₆ mixed with a light carrier gas (H₂ or He) at a ratio of 1:19 is injected at supersonic speed into a specially designed nozzle. The curvature of the nozzle creates a pressure gradient that separates the isotopes. The reported separation factor is ~1.015, requiring approximately 500 stages for 3% enrichment. Developed experimentally by Becker in Germany.