CA1078326A - Method for the separation of isotopes - Google Patents

Abstract

Abstract of the Disclosure Method of separating isotopes bound to isotopic elements to form a mixture of isotope compounds such as UCl6 compounds, by selectively exciting one compound by laser radiation and separating the excited compound from the mixture of isotope compounds, contacting the separated mixture of isotope compounds with the isotopic element having a natural isotope com-position to effect an isotope exchange and replenish in the separated mixture, the isotope compound separated by selective excitation, and re-turning the replenished mixture for further treatment with laser radiation.
Method provides an economical, efficient separation of desired isotope from a mixture.

Description

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~ his invention relates to a method for the separation of isotopes of gaseous compounds, and more particularly refers to a new method for separating an isotope compound from a mixture of isotope compounds in which the element bound to the isotope is present as a mixture of isotopes in the isotope compounds, by selective excitation by means of laser radiation and subsequent chemical or physical separation of the reaction product.
The separation of isotopes of gaseous compounds by selective ex-citation, where the wavelength of the radiation required therefor corres-ponds to a rotational vibration line of the compound containing the desired isotope, is known. The process proper of separating the excited molecules from the not excited ones can be carried out here by physical means; see the German Pulished Non-Prosecuted Appl;cations DT-OS 2 312 194 and DT-OS

2 1~0 401. Separation by chemical means has also been proposed; see the German Published Non-Prosecuted Application DT-OS 1 959 767. This technique is primarily aimed at the enrichment of uranium, as this is of the greatest importance for the supply of energy and every attempt must be made to replace the present, extremely expensive enrichment processes by more economical ones.
The proposals made up to now have used UF6 as the raw material, as it has a relatively high vapor pressure. It has the further advantage that the compound partner, i.e., the fluorine, is a pure isotope element.
The rotational vibration lines which are to be chosen for the selective enrichment therefore correspond only to two isotope compounds, i.e. to those with uranium 238 and those with uranium 235.
It has also been proposed to make UC16 the basis for the isotope enrichment (British Patent 1 284 620). However, the compound partner, chlorine, is present, according to its natural occurrence, in two isotope forms, so that a multiplicity of partially overlapping spectra are present because of the multiplicity of the isotope compounds provided thereby.

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~0783Z6 Selective separation is therefore possible only in part. It is therefore also proposed in the British Patent to replace the chlorine of natural composition in the UC16 by only one chlorine isotope. For reasons of economy, however, this must be recovered after the first separation step is carried out, and returned to the starting materials.
A relatively complicated process is therefore necessary, requiring an extremely large amount of technical facilities and therefore does not meet the requirement of maximum economy, mentioned at the outset.
It is accordingly an object of the invention to provide an efficient, economical method for separating isotopes from a mixture of isotope compounds, in which both compound partners occur in the form of several isotopes.
With the foregoing and other objects in view, there is provided in accordance with the invention, a method of separating isotopes which are bound to isotopic elements and form with the latter a mixture of isotope compounds by subjecting the mixture of isotope compounds to laser radiation to selectively excite one isotope compound and separating the excited compound from the mixture of isotope compounds by chemical reaction or physical means, which includes contacting the mixture of isotope compounds after separation of the excited compound, with the isotopic element having a natural isotope composition to effect an isotope exchange between the bound isotopic element in the separated mixture of isotope compounds and the isotopic element having a natural isotopic composition to replenish in the separated mixture the isotope compound which had been separted by selective excitation, and returning the replenished mixture of isotope compounds for further treatment with laser radiation to selectively separ-ate one isotope compound.
The mixture of isotope compounds after separation of the excited compounds, and the isotopic element having a natural isotope composition are heated to maintain them in the gaseous phase and facilitate isotope exchange between the bound isotopic element in the separated mixture and the isotopic element, the resultant mixture then cooled to condense the isotope compounds in the resultant mixture, and the non-condensed gaseous isotopic element in the resultant mixture separated from the condensed isotope compounds.
In a specific embodiment., the mixture of isotope compounds subjected to laser radiation have the formula UC16 and the uranium isotopes in the mixture of isotope compounds are U 35 and U 3 , and the bound chlorine in the mixture of isotope compound are C135 and C137 in the quantitative proportion of about 76:24.
In a more specific embodiment of the invention, the mixture of UC16 isotope compounds after separation of the excited UC16 compound, and chlorine containing C135 and C137 in the quantitative proportion of about 76:24 are heated to a temperature between about 120 to 200 C to effect an isotope exchange between the chlorine in the separated UC16 isotope compounds and the chlorine having C135 and C137 in the quantitative pro-portion of about 76:24, cooling the resultant mixture after isotope ex-change to a temperature between about 20 to 70 to convert the gaseous UC16 in the resultant mixture to solid UC16, and separating the noncondensed gaseous chlorine from the solid UC16.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in the method for the separation of isotopes, it is nevertheless not intended to be l;m;ted to the details shown, since various modifications may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The invention, however, together with additional objects and 1(~783~:6 advantages thereof will be best understood from the following description when read in connection with the accompanying drawing.
The attached drawing diagrammatically illustrates a method in accordance with the invention of separating an isotope compound from a mixture of compounds and replenishing the mixture with the isotope compound.
In accordance with the invention, after selective excitation, known per se, of only one given isotope compound, the remainder of the compound mixture is brought into contact, after separation of the reaction product, with a separately supplied quantity of the compound partner with natural isotope composition to make an isotope exchange possible. The compound mixture after it has been subjected to isotope exchange is returned to run through the separation apparatus again where one compound is excited and separated from the mixture. This means that the natural isotope composition of the reaction partner is substantially restored and the uranium compound which is to be excited selectively, is present again for renewed passage through the separation apparatus.
The natural composition of chlorine consists of the isotope C135 and C137 in the quantitative proportion 76:24. Most of the UC16 is there-fore present as U 3 C155 C137. The natural equilibrium distribution of C135 and C137 in the compound UC16 is given in the following table:
U C165 Frequency 18,6%
Frequency 36,1 %
U C1435 C1237 Frequency 29,2 %
U C1335 C137 Frequency 12,6 %
U C1325 C147 Frequency 3,3 %
U C135 C137 Frequency 0,4 %
U C1637 Frequency 0,02%
The compound U 35 C1355 C137 therefore occurs approximately 90 times more frequently than U 35 C1357 C13 If, for example, only the U 3 ~078326 C157 C135 absorbs selectively, this means that according to the present state of the art, only 4 % of the U 35 can be excited and separated. This corresponds to a depletion from 0.71 % to 0.702 % of the natural uranium.
As this is not sufficient, the depleted uranium would have to be fed to the separation apparatus according to the British Patent mentioned very often before the desired degree of depletion is reached.
According to the present invention, the rest of the UC16 compounds remaining after the selective separation is treated in such a manner that the selectively excitable compound U 35 C157 C135 is again present in substantially the original percent based on the quantity of remaining U 35 in the UC16- For this purpose, the remaining UC16 coming from the separation apparatus is heated together with chlorine of natural isotope composition so that an isotope exchange takes place in accordance with the functional equation UC16~ UC14 + C12 and the natural mixture of UC16 molecules can therefore adjust itself again.
This method can also be applied, for example, to the compound U (BH4)4, except that the isotope exchange is carried out here with diborane.
An operating cycle of the method according to the invention will be described in connection with the attached figure. me raw material UC16 is in the supply vessel 1. It flows in the gaseous state through the separation apparatus 2, in which the isotope mixture is excited selectively by a laser beam 21. The separation of the excited molecules is accomp-lished by chemical or physical means in the apparatus 3, from where they are passed on to the collecting tank 31. The non-excited and therefore, not separated molecules get to the isotope equalization section 4, which is equipped with a heatin~ system 41 which may be a steam jacket or a plurality of pipes through which a heating fluid flows to heat by indirect heat exchange the mixture in section 4. Into this apparatus, chlorine 1~783'~6 gas of natural isotope composition is simultaneously introduced from the supply vessel 5. The heating of the mixture in this apparatus is preferably set at a temperature of 120 to 200 C at which temperature the mixture of isotope compounds and chlorine are in gaseous phase and isotope exchange between the chlorine in the compounds and the gaseous chlorine is effected. After isotope exchange in chamber 4, the gas mixture of UC16 and chlorine is discharged from chamber 4 and directed alternately to the vessels 6 and 7 wherein the gas mixture is cooled to 20 to 70 C.
Cooling the gas mixture causes the gaseous UC16 to condense, i.e. reduce in volume, and precipitate as solid UC16, while the chlorine remains in gaseous form. The non-condensed chlorine released from vessels 6 and 7 is condensed in tank 8. When a sufficient quantity of solid UC16 has collected in the vessel 6, the line is switched to vessel 7 for separating, and vessel 6 is heated by any suitable means such as a steam jacket to the temperature needed to evaporate the UC16. The evaporated UC16 com-pounds from vessels 6 and 7, which have now been brought back substantially to their original isotope composition, is fed fia the line 9 to the sep-aration apparatus proper 2, where the specific isotope compound now pre-sent again in the mixture of U~16 compounds is excited selectively by laser beam 21 and these excited molecules are separated out in the ap-paratus 3. This cycle is then repeated until the depletion of the ori-ginally supplied quantity of UC16 of the one uranium isotope, e.g., U 35, has reached the desired degree. Then, a further quantity, as fresh charge, of UC16 of the original isotope composition is fed to the separation apparatus 2 from the supply vessel 1.
Isotope exchange, which is used in this method, require relatively little energy and the means required for its technical implementation are practically negligible in view of the known excitation and separation devices 2 and 3. This method can be used, of course, with other isotope separation processes. 6

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a method of separating isotopes which are bound to isotopic elements and form with the latter a mixture of isotope compounds by subjecting the mixture of isotope compounds to laser radiation to selec-tively excite one isotope compound and separating the excited compound from the mixture of isotope compounds by chemical reaction or physical means, the improvement which comprises contacting said mixture of isotope compounds after separation of said excited compound, with the isotopic element having a natural isotope composition to effect an isotope exchange between the bound isotopic element in said separated mixture of isotope compounds and said isotopic element having a natural isotopic composition to replenish in said separated mixture said isotope compound which had been separated by selective excitation, and returning said replenished mixture of isotope compounds for further treatment with laser radiation to selectively separate one isotope compound.

2. Method according to claim 1, wherein said mixture of isotope compounds subjected to laser radiation have the formula UCl6 and wherein the uranium isotopes in said mixture of isotope compounds are U 35 and U238, and wherein the bound chlorine in said mixture of isotope compounds are Cl35 and Cl37 in the quantitative proportion of about 76:24.

3. Method according to claim 1, wherein said mixture of isotope compounds after separation of said excited compound, and said isotopic element having a natural isotope composition are heated to maintain them in the gaseous phase and facilitate isotope exchange between the bound isotopic element in said separated mixture and said isotopic element, the resultant mixture then cooled to condense the isotope compounds in the resultant mixture, and the non-condensed gaseous isotopic element in the resultant mixture separated from the condensed isotope compounds.

4. Method according to claim 2, wherein said mixture of UCl6 isotope compounds after separation of the excited UCl6 compound, and chlorine containing Cl35 and Cl37 in the quantitative proportion of about 76:24 are heated to a temperature between about 120 to 200° C to effect an isotope exchange between the chlorine in said separated UCl6 isotope compounds and said chlorine having Cl35 and Cl37 in the quantitative pro-portion of about 76:24, cooling the resultant mixture after isotope exchange to a temperature between about 20 to 70 C to convert the gaseous UCl6 in the resultant mixture to solid UCl6, and separating the non-con-densed gaseous chlorine from the solid UCl6.