Survey on isotope effects and separation technologies

This paper is a review of the main industrial processes and physical principles used for stable isotope separation on a production scale. It will be restricted to 'classical' industrial technologies. Roughly speaking, only three types of technologies have been contemplated for today's production (apart from uranium enrichment, outside the scope of this review). 1. Chemical exchange processes for the lighter isotopes (D, T, 7 Li, 10 B, 13 C, 15 N, 17 O). Operating processes such as exchange distillation and liquid-gas chemical exchange are based on isotope mass-differences in the free energy (vapour pressures, vibration frequencies) of molecular species.. Insight into statistical thermodynamics gives low enrichment factors (α ≤ 1.05), which have generally a (Δm/m2) ratio dependency. Although needing thousands of repetitive elementary operations, those low cost processes are well suited for large capacity production. Modern trends are now in solid-liquid chromatographic columns: polymer-crown complexes with large macro-cyclic rings have topological ability to pick up boron, lithium, or cesium isotopes. Detritiation (on a small scale) with palladium solid-gas interface is a special case. 2. Thermal Diffusion process for the production of light rare gases (3 He, 22 Ne, 36 Ar, 86 Kr). While having a low separation factor for each stage, this process is still of topical interest for production of the rare gases, with a high purity degree, and of 13 C H4 at the gram level of yearly production. 3. Ultra Gas Centrifuge (G.C.) for medium and heavy nuclei des. This process is based on an increase of a small mass diffusion flux by a pressure gradient. Several counter-current thermal diffusion effects are added to reach higher separation factors (α ∼ 1.5). The whole process results in a Δm dependency. That allowed low cost units to separate xenon as well as metallic isotopes. The trend at Oak-Ridge and at the Kurchatoff-Institute is to replace the electromagnetic technique by G.C. for kilogram production of germanium, chromium, zinc or tungsten isotopes. For the near future, repercussions of laser research may occur in stable isotope production. Laser multistep AVLIS is a selective process developed for the nuclear fuel. Besides enriching 235 U or depleting 242 Pu it may succeed as a powerful process for the separation of rare-earth absorbers, such as 157 Gd or 167 Er. G.C. could hardly be applied to the f-elements given that the volatility of the possible feed (diketonate) is very low. Ion Cyclotron Resonance could be a challenger if active research were resumed. Infrared multiphoton dissociation (IRMPD) has shown high separation factor and yield capacity, for several light species like boron tribromine, halogenated hydrocarbons, or silicon halides. Infrared tuning flexibility with a free electron-laser is a prerequisite to industrial developments. Single photon dissociation with ultraviolet wavelength was proven to be an efficient way to produce 13 C from formaldehyde: enrichment factors higher than 35 have been reached at Saclay. (authors)