GB2086770A

GB2086770A - Separator cascade

Info

Publication number: GB2086770A
Application number: GB7834947A
Authority: GB
Original assignee: Uranit Uran Isotopen Trennungs GmbH
Current assignee: Uranit GmbH
Priority date: 1977-10-19
Filing date: 1978-08-30
Publication date: 1982-05-19
Also published as: GB2086770B; NL190633C; DE2746871C1; NL7808732A; NL190633B

Abstract

This invention relates to a method of and a device for operating a separation cascade for the separation of gaseous mixtures, especially mixtures of isotopes into a lighter and a heavier fraction. The mixture of substances is separated in a first cascade stage 1, the lighter fraction being subjected to a plurality of enrichment (2) and depletion (3) stages, and fed to the light and heavy cascade outlets 6, 7. The mixture of substances to be separated is split into two controllable partial streams. One partial stream 5 is fed to the first stage and the other 8 or 9 to an enrichment or depletion stage adjacent to the first stage, subject to the concentration to be maintained at the heavy cascade outlet. The bulk stream to be fed is set according to the concentration of the light fraction to be maintained at the light cascade outlet. <IMAGE>

Description

SPECIFICATION Method and device for operating a separation cascade for the separation of gaseous mixtures of substances, especially mixtures of isotopes The invention relates to a method and a device for operating a separation cascade for the separation of gaseous mixtures of substances, especially mixtures of isotopes into a lighter and heavier fraction, in which the mixture of substances is separated in a first cascade stage and, with respect to the lighter fraction, several enrichment and depletion stages and fed to the light and the heavy cascade outlets.

Uranium enrichment is commonly carried out in one or more cascades. A cascade consists of a first stage, into which the mixture of substances is fed, and several enrichment and depletion stages, the different stages being composed of a multitude of separation units connected parallel, e.g., gas centrifuges. A cascade arrangement of this type is shown by way of example in the attached Fig. 1.

In view if the characteristics of centrifuges, centrifuge cascades for natural uranium enrichment are characterized by the fact that the composition of the mixture of isotopes at the light cascade outlet (product concentration P) can be controlled over a wide range by variation of the feed of the mixture of substances (cascade feed F), while the composition of the mixture of isotopes at the heavy cascade outlets (tails concentration T) changes only slightly in the process. This allows the customers' wishes with respect to different product concentrations to be met. In the figure, the feed stream is indicated by solid lines (-), the product stream by dashed lines (---), and the tails stream by dotted lines (.. .).

As a rule, centrifuge cascades are designed so that an optimum value results for the tails concentration, with given costs of separative work and natural uranium. For economic reasons it would be advantageous if, irrespective of the required product concentration, also the respective optimum tails concentration could by set in case of price fluctuations of natural uranium. This is to say that, e.g., in the case of price increases for natural uranium, the tails concentration of the lighter uranium isotope U 235 could be reduced by a corresponding margin. In this way, an increase in costs of the uranium raw material could at least partly be compensated by better exploitation of the valuable U 235 contained in it.

The invention is based on the problem to improve the operation of a separation cascade of the type described initially in such a way as to permit also a variation of the tails concentration. The measures listed in the distinguishing feature in claim 1 are proposed as a solution to this problem.

This would allow also the tails concentration to be controlled continuously. If, e.g., part of the cascade feed is fed not only to the first stage, but also to the adjacent enrichment stage, the tails concentration will contain a smaller fraction of the lighter component, while the desired product concentration can be maintained by proper setting of the bulk feed.

One embodiment of the invention is explained below by means of a schematic diagram: Fig. 2 shows a centrifuge cascade consisting of a first stage 1 and several enrichment and depletion stages 2a to 2n and 3a to 3n, respectively, which stages consist of different numbers of single centrifuges parallel or of centrifuge units combined in groups.

Normally, the uranium hexafluoride (us6) mixture to be separated is fed to the first stage 1 through pipe-lines 4 and 5 and separated into lighter and heavier mixtures, whereupon the lighter mixture is fed to the first enrichment stage 2a and the heavier mixture is fed to the first depletion stage 3a, etc. The number and size of the stages are chosen so that a product is obtained at the light cascade outlet 6 whose U 235 concentration may be set between, e.g., 1% and 4%, with the U 235 concentration remaining more or less constant, e.g., at 0.25% at the heavy cascade outlet 7.

If, for the reasons mentioned above, the U 235 tails concentration at the heavy cascade outlet 7 is to be reduced, for example, at least part of the mixture of substances to be fed is branched off to pipelines 8 and fed to the first enrichment stage 2a. This in a way increases the number of depletion stages. In the other case, at least a partial stream is fed to the first depletion stage 3a through pipeline 9. The control valves 10, 11 and 12 and the pressure sensors 13, 14 and 15 can be used to set and to monitor partial streams continuously.

Given the proper centrifuge characteristics, this method allows the tails concentration to be continuously varied, e.g., for a product concentration of 2.5% U 235 specified by the client, between 0.2% and 0.3% of U 235 without sizable losses in separate work.

1. A method of operating a separation cascade for the separation of gaseous mixtures of substances, especially mixtures of isotopes into a lighter and a heavier fraction, in which the mixture of substances is separated in a first cascade stage and, with respect to the lighter fraction, several enrichment and depletion stages and fed to the light and the heavy cascade outlets, with the mixture of substances to be separated being split into two controllable partial (5 and 8 or 5 and 9),

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Method and device for operating a separation cascade for the separation of gaseous mixtures of substances, especially mixtures of isotopes The invention relates to a method and a device for operating a separation cascade for the separation of gaseous mixtures of substances, especially mixtures of isotopes into a lighter and heavier fraction, in which the mixture of substances is separated in a first cascade stage and, with respect to the lighter fraction, several enrichment and depletion stages and fed to the light and the heavy cascade outlets. Uranium enrichment is commonly carried out in one or more cascades. A cascade consists of a first stage, into which the mixture of substances is fed, and several enrichment and depletion stages, the different stages being composed of a multitude of separation units connected parallel, e.g., gas centrifuges. A cascade arrangement of this type is shown by way of example in the attached Fig. 1. In view if the characteristics of centrifuges, centrifuge cascades for natural uranium enrichment are characterized by the fact that the composition of the mixture of isotopes at the light cascade outlet (product concentration P) can be controlled over a wide range by variation of the feed of the mixture of substances (cascade feed F), while the composition of the mixture of isotopes at the heavy cascade outlets (tails concentration T) changes only slightly in the process. This allows the customers' wishes with respect to different product concentrations to be met. In the figure, the feed stream is indicated by solid lines (-), the product stream by dashed lines (---), and the tails stream by dotted lines (.. .). As a rule, centrifuge cascades are designed so that an optimum value results for the tails concentration, with given costs of separative work and natural uranium. For economic reasons it would be advantageous if, irrespective of the required product concentration, also the respective optimum tails concentration could by set in case of price fluctuations of natural uranium. This is to say that, e.g., in the case of price increases for natural uranium, the tails concentration of the lighter uranium isotope U 235 could be reduced by a corresponding margin. In this way, an increase in costs of the uranium raw material could at least partly be compensated by better exploitation of the valuable U 235 contained in it. The invention is based on the problem to improve the operation of a separation cascade of the type described initially in such a way as to permit also a variation of the tails concentration. The measures listed in the distinguishing feature in claim 1 are proposed as a solution to this problem. This would allow also the tails concentration to be controlled continuously. If, e.g., part of the cascade feed is fed not only to the first stage, but also to the adjacent enrichment stage, the tails concentration will contain a smaller fraction of the lighter component, while the desired product concentration can be maintained by proper setting of the bulk feed. One embodiment of the invention is explained below by means of a schematic diagram: Fig. 2 shows a centrifuge cascade consisting of a first stage 1 and several enrichment and depletion stages 2a to 2n and 3a to 3n, respectively, which stages consist of different numbers of single centrifuges parallel or of centrifuge units combined in groups. Normally, the uranium hexafluoride (us6) mixture to be separated is fed to the first stage 1 through pipe-lines 4 and 5 and separated into lighter and heavier mixtures, whereupon the lighter mixture is fed to the first enrichment stage 2a and the heavier mixture is fed to the first depletion stage 3a, etc. The number and size of the stages are chosen so that a product is obtained at the light cascade outlet 6 whose U 235 concentration may be set between, e.g., 1% and 4%, with the U 235 concentration remaining more or less constant, e.g., at 0.25% at the heavy cascade outlet 7. If, for the reasons mentioned above, the U 235 tails concentration at the heavy cascade outlet 7 is to be reduced, for example, at least part of the mixture of substances to be fed is branched off to pipelines 8 and fed to the first enrichment stage 2a. This in a way increases the number of depletion stages. In the other case, at least a partial stream is fed to the first depletion stage 3a through pipeline 9. The control valves 10, 11 and 12 and the pressure sensors 13, 14 and 15 can be used to set and to monitor partial streams continuously. Given the proper centrifuge characteristics, this method allows the tails concentration to be continuously varied, e.g., for a product concentration of 2.5% U 235 specified by the client, between 0.2% and 0.3% of U 235 without sizable losses in separate work. CLAIMS

1. A method of operating a separation cascade for the separation of gaseous mixtures of substances, especially mixtures of isotopes into a lighter and a heavier fraction, in which the mixture of substances is separated in a first cascade stage and, with respect to the lighter fraction, several enrichment and depletion stages and fed to the light and the heavy cascade outlets, with the mixture of substances to be separated being split into two controllable partial (5 and 8 or 5 and 9), one partial stream (5) being fed to the first stage (1) and the other (8 and 9, respectively) to an enrichment or depletion stage (2 and 3, respectively) adjacent to the former, subject to the concentration to be maintained at the heavy cascade outlet (7), while the bulk stream (4) to be fed is set according to the concentration of the light fraction to be maintained at the light cascade outlet (6).

2. A centrifuge cascade device for carrying out the method claimed in claim 1, to separate a gaseous isotope mixture into a lighter and a heavier fraction, said device comprising a first cascade stage and several enrichment and depletion stages, three feed lines (5, 8, 9) being connected in parallel and equipped with flow control valves (10, 11, 12) for feeding the mixture of substances, one of said feed lines leading to the first cascade stage (1), and the two others to one enrichment and one depletion stage (2, 3), the enrichment and depletion stages to which the feed lines are connected being adjacent to the first cascade stage.

2. Device for implementation of the method as claimed in claim 1 with three fed lines (5, 8, 9) connected parallel and equipped with flow control valves (10, 11, 12) for feeding the mixture of substances, one of which leads to the first cascade stage (1), the two others to one enrichment and one depletion stage (2, 3).

CLAIMS (3 Oct 1980)

1. A method of operating a separation cascade for the separation of gaseous mixtures of isotopes into a lighter and a heavier fraction, in which the mixture of substances is separated in a first cascade stage (1) and, with respect to the lighter fraction, several enrichment and depletion cascade stages, and fed to the light and the heavy cascade outlets, with the mixture (4) of substances to be separated being split into two controllable partial streams (5 and 8 or 5 and 9), one partial stream (5) being fed to the first stage (1) and the other (8 and 9, respectively) to an enrichment or depletion stage (2 and 3, respectively) adjacent to the former, subject to the desired concentration to be maintained at the heavy cascade outlet (7), while the flow rate of the mixture (4) to be separated is set according to the desired concentration of the light fraction to be maintained at the light cascade outlet (6).