Материал: Апсе ENVIRONMENTAL PROTECTION 2014

The following conditions should be satisfied for successful implementation of the laser-induced isotope separation:

1.The energy spectrum of the excited electronic levels must contain a line belonging to one isotope only, and this line must be sufficiently far from other spectral lines of the desirable isotope and from all spectral lines of other isotopes.

2.Physical or chemical processes must be found which are able to separate the excited and non-excited uranium-containing components.

3.Laser-induced impact on the isotopic composition to be separated must be a main excitation mechanism, not inter-atomic or intermolecular collisions.

4.High-efficiency lasers must be developed and finely tuned to the appropriate wavelength.

Presently, the following two laser isotope separation technologies are under intense development and demonstration, namely atomic vapor laser isotope separation (AVLIS) and molecular laser isotope separation (MLIS).

The AVLIS-technology has been developed at the Lawrence Livermore National Laboratory (USA). The AVLIS technology includes the following stages:

1. Vacuum evaporation of uranium atoms at very high temperature ( 23000C). Beam of accelerated electrons knocks uranium atoms out of

uranium-rhenium alloy.

2. Irradiation by xenon laser (λ 3780 Å, ultraviolet range). are selectively excited.

3.Irradiation by krypton laser (λ 3500 Å, ultraviolet range). The excited 235U atoms are selectively ionized.

4.Collection of 235U ions on an electrically charged plate.

The MLIS-technology has been developed at the Los Alamos National Laboratory (USA). The MVLIS technology includes the following stages:

1. Expansion of gaseous uranium hexafluoride – hydr ogen composition through a hypersonic nozzle. As a result, uranium hexafluoride

cools down to about 30 K but it does not condense.

2. Irradiation by infrared laser (λ 1,6·105 Å). Molecules of are selectively excited.

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3. Irradiation by ultraviolet laser (l~3,08·104 Å). The excited molecules of 235UF6 are selectively dissociated with the formation of uranium pentafluoride 235UF5 and free fluorine:

2 × 235 UF6 ® 2 × 235 UF5 + F2 .

Uranium pentafluoride 235UF5 precipitates from the gas flow as a fine powder (so called, “laser snow”) that can be e asily collected.

The single-stage enrichment factors are very high for both laser technologies of uranium enrichment. They cover the range from 3 to 15, according to different experimental studies. Such high-efficiency technologies make it possible to use even the waste materials from GDand GC-processes containing about 0,2% 235U for production of reactorgrade uranium (about 3% 235U) by a single enrichment stage.

1.2.7. Chemical methods of isotope separation

The chemical methods of isotope separation are based on the preferential stability of certain isotopes in various immiscible chemical compounds. The isotope exchange reactions can occur, if two different chemical compounds of one multi-isotope chemical element enter into a contact. The isotope exchange reactions lead to the concentration of isotopes in those compounds where they can be more stable.

The following conditions must be satisfied for feasibility of the chemical isotope separation technologies:

1.The contacting compounds must be chemically stable together.

2.The contacting compounds must be separated by a relatively simple means (for example, organic and inorganic substances).

3.It is desirable for the chemical element to be of different valences in two contacting compounds.

The following examples of the chemical isotope separation are presented below:

1.Boron enrichment with isotope 10B:

BF3 + BF3O(CH3)2 ® 11BF3 + 10BF3O(CH3)2 ,

i.e. isotope 10B passes into the organic compound.

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Orbital radius R and angular frequency of spiral rotation can be derived from the following relationships:

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