EP0008273A1 - A process for treating effluent gases arising from the reprocessing of irradiated nuclear fuels - Google Patents

A process for treating effluent gases arising from the reprocessing of irradiated nuclear fuels Download PDF

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Publication number
EP0008273A1
EP0008273A1 EP79400556A EP79400556A EP0008273A1 EP 0008273 A1 EP0008273 A1 EP 0008273A1 EP 79400556 A EP79400556 A EP 79400556A EP 79400556 A EP79400556 A EP 79400556A EP 0008273 A1 EP0008273 A1 EP 0008273A1
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Prior art keywords
xenon
krypton
mixture
argon
stage
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German (de)
French (fr)
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EP0008273B1 (en
EP0008273B2 (en
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Jacques Duhayon
Jean-Pierre Goumondy
Alain Leudet
Jean-Claude Rousseau
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Commissariat a lEnergie Atomique CEA
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/028—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of noble gases
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/02—Treating gases
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
    • F25J2205/40—Processes or apparatus using other separation and/or other processing means using hybrid system, i.e. combining cryogenic and non-cryogenic separation techniques
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
    • F25J2205/82—Processes or apparatus using other separation and/or other processing means using a reactor with combustion or catalytic reaction
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/40—Air or oxygen enriched air, i.e. generally less than 30mol% of O2
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2215/00—Processes characterised by the type or other details of the product stream
    • F25J2215/34—Krypton
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2215/00—Processes characterised by the type or other details of the product stream
    • F25J2215/36—Xenon
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S62/00—Refrigeration
    • Y10S62/923—Inert gas
    • Y10S62/925—Xenon or krypton

Definitions

  • the present invention due to the work of Mr. Alain LEUDET of the Society of CHEMICAL STUDIES and of Messrs Jacques DUHAYON, Jean-Pierre GOUMONDY and Jean-Claude ROUSSEAU of the ATOMIC ENERGY COMMISSIONER, relates to a process for the treatment of a mixture of air with rare gases, in particular xenon and krypton, and more particularly for treatment of gaseous effluents originating from the reprocessing of irradiated nuclear fuels, such treatment also having the aim of recovering the xenon that these mixtures contain.
  • Gaseous effluents from plants for the reprocessing of irradiated fuels consist essentially of air, the oxygen content of which can be lower than the natural content, of rare gases such as xenon and krypton, and generally contain vapor of water, carbon dioxide, traces of hydrocarbons, and also nitrogen oxides whose presence is due to the dissolution of fuels carried out in a nitric medium.
  • this preconcentration step is carried out, after catalytic reduction of all the oxygen in the mixture with hydrogen, by concentration of the rare gases in a fraction of the nitrogen. by cryogenic distillation. Then the mixture of krypton and xenon in nitrogen is then subjected to another cryogenic distillation to separate the krypton and the nitrogen from the xenon.
  • This process has the drawback that, given the low solubility of xenon in liquid nitrogen, blockages occur in the distillation columns which are due to crystallization of the xenon.
  • this preconcentration is carried out by removing all of the nitrogen from the mixture and part of the oxygen by cryogenic distillation.
  • the mixture of krypton and xenon concentrated in oxygen then obtained is first subjected to a step of catalytic reduction of oxygen with hydrogen, then to a cryogenic distillation step to separate the krypton from the xenon.
  • This method has, compared to the preconcentration process in nitrogen, the advantage that the solubility of xenon is much higher in liquid oxygen than in liquid nitrogen.
  • ozone is formed in the boiler of the distillation column; this presence of ozone creates the risk of explosion.
  • the subject of the present invention is precisely a process for the treatment, in particular of gaseous effluents originating from the reprocessing of irradiated fuels, which overcomes the drawbacks mentioned above; in fact, during the implementation of the process considered, there is no formation of ozone, and therefore no risk of explosion; as for the problems of crystallization of xenon, they can easily be avoided.
  • the process according to the invention is characterized in that it comprises a step of concentrating the rare gases in solution in liquid argon, by cryogenic distillation of the light gases, and mainly nitrogen, from the liquefied mixture .
  • this method further comprises, after said concentration step, a step of recovering xenon by cryogenic distillation of the other gas or gases from the concentrated and liquefied mixture.
  • the applicant has studied the behavior of xenon from the point of view of solubility in three cryogenic solvents, namely oxygen, nitrogen and argon.
  • the applicant studied what was the maximum pressure such that the solid-liquid-vapor xenon-solvent balance could exist. It was therefore important, to avoid any risk of crystallization of the xenon, to operate the preconcentration step at a pressure higher than this remarkable pressure mentioned above.
  • the applicant has researched and discovered that for an oxygen-xenon system, this remarkable pressure is 17 bars absolute, that for an argon-xenon system, this remarkable pressure is 18.5 bars absolute, and that for a nitrogen-xenon system , this remarkable pressure would be notably higher, for example, of the order of 35 bar absolute.
  • the subject of the invention is also a process for treating effluent gases originating from the reprocessing of irradiated nuclear fuels, consisting of a mixture containing at least xenon and radioactive krypton in the air, characterized in that it essentially comprises and successively a first stage of elimination of possible impurities such as hydrocarbons, nitrogen oxides, carbon dioxide, water vapor, a second stage of concentration of xenon and krypton in solution in argon liquid by distillation of light gases, and mainly nitrogen, from the liquefied mixture, a third stage of elimination of argon by distillation cryogenic of the separate mixture of argon, xenon and krypton, previously liquefied, and a fourth step of separation of xenon and krypton, by cryogenic distillation of the separate mixture of xenon and krypton, previously liquefied.
  • a first stage of elimination of possible impurities such as hydrocarbons, nitrogen oxides, carbon dioxide, water
  • the argon necessary for the second concentration step can be introduced into the gas mixture to be treated, either before the first step of removing the various impurities, or before the second concentration step.
  • a part of the krypton separated from the xenon and obtained during the fourth stage is taken, and said part is introduced into the mixture obtained at the end of the first stage, before proceeding to the second stage of concentration of xenon and krypton in solution in liquid argon.
  • the invention also extends to installations suitable for carrying out the method.
  • installations include in particular catalytic reactors and cryogenic distillation columns with all their ancillary equipment, in themselves known, arranged and connected by conduits for circulation of the various products, so as to allow the successive operations of the defined process to be carried out above.
  • the first step of removing any impurities contained in the starting gas mixture comprises a first step of removing hydrocarbons by catalytic oxidation (and also catalytic dissociation of nitrogen oxide N 2 0), which takes place in the unit represented in la; a second stage of elimination of oxygen and nitrogen oxides by catalytic reduction, which takes place in the unit shown in lb; and a third stage of removal of carbon dioxide and water vapor by passage over a molecular sieve and / or silica gel, which takes place in the unit shown in lc.
  • the gaseous mixture to be treated is first introduced at 5 into unit 1a and leaves this unit free of hydrocarbons. It is then introduced, at 6, into unit lb where a catalytic reduction takes place in the presence of palladium by the action of hydrogen supplied at 7. It comes out of this unit lb, freed from oxygen and the oxides of l 'nitrogen, and is introduced, in 8, in the unit lc where it is freed from carbon dioxide and water vapor by passage over a molecular sieve.
  • the mixture introduced, at 9, into column 2 is a mixture of nitrogen, xenon and krypton, to which argon is added before, at 10, before entering column 2.
  • column 2 is carried out the cryogenic distillation which makes it possible to obtain the elimination of nitrogen at 11, which makes it possible to recover, at 12, a mixture of argon, xenon and krypton.
  • This mixture of argon, xenon and krypton is then introduced at 13, in column 3, where the elimination of the argon, at 14, takes place by cryogenic distillation and the recovery, at 15, of a mixture of krypton and xenon.
  • This mixture of krypton and xenon is then introduced at 16, in column 4, where the elimination of krypton, at 17, takes place by cryogenic distillation and the recovery of pure xenon at 18.
  • part of the krypton eliminated in 17 is taken, and it is recycled in 19 to reintroduce it at the inlet of column 2, so as to be able to carry out the cryogenic distillation at lower pressure.
  • the pressure at which the cryogenic distillation is carried out in column 2 is at most 18 bars
  • the pressure at which the cryogenic distillation is carried out in column 4 is approximately 3 bars
  • the pressure at which performs the cryogenic distillation in column 3 is between the pressure of column 4 and the pressure of column 2.
  • FIG 2 there is shown in more detail the different elements and circuits connecting the units la, Ib, lc, in which the first step of removing impurities is carried out according to the method of the invention.
  • the gaseous mixture to be treated coming from the irradiated fuel reprocessing plant, is first introduced at 20 into a compressor 21, then is cooled by a circulation of water in a refrigerant 22 and, after passing through an exchanger 23, is introduced at 5 into unit 1a which contains a platinum or rhodium catalyst: in this unit 1a, the hydrocarbons are eliminated from the gas mixture by catalytic oxidation and there is also elimination of the nitrous oxide N 2 0 by dissociation catalytic of the latter.
  • An external heater ensures that a maximum temperature of 700 ° C is maintained in this unit la.
  • the gas mixture freed from hydrocarbons passes through the exchanger 23, then, after mixing with part of the gas mixture coming from the water separator 27, into an electric heating system 24 which carries it at a temperature of 100 ° C. and is introduced, at 6, into the unit lb: in this unit 1b, the oxygen and the nitrogen oxides are eliminated by catalytic reduction, the unit lb containing a palladium catalyst and optionally a catalyst with rhodium and hydrogen being introduced at 7, so as to maintain a slight excess of this gas at the outlet of the unit lb.
  • the gas mixture freed of oxygen and nitrogen oxides, is cooled in a water cooler 25, then passes through a fan 26.
  • a part of the gas mixture After passing through a water separator 27, is recycled at 28 to unit 1b and the other part is directed at 8, to unit lc.
  • the mixture introduced at 8 into unit lc is freed from water vapor and traces of C0 2 by passing over a molecular sieve and / or silica gel in one of the two absorbers 29 arranged in parallel; these two absorbers 29 periodically and alternately undergo regeneration by heating and circulation of nitrogen.
  • the distillation column 2 operates at a pressure of at most 18 bar.
  • the lower part of column 2 is maintained at the necessary temperature using an electric heating device 31.
  • reflux is provided by a condenser 32, cooled by liquid nitrogen supplied at 33.
  • a mixture is extracted from the upper part of column 2, at 11, containing mainly nitrogen and possibly a fraction of argon; this mixture can be recycled in the shear scanning circuit or discharged into the atmosphere; it is heated beforehand by passing through the exchanger 30, from which it exits at 34.
  • a liquid mixture of argon concentrated in krypton and xenon is extracted and it is introduced at 13 into the column distillation 3.
  • column 3 which operates at a pressure between the pressure of column 4 and the pressure of column 2, the argon at 14 is separated by cryogenic distillation and the mixture of krypton and xenon is collected at the bottom of the column.
  • column 3 Optionally, the argon can be recycled, leaving at 14 from column 3, at the inlet of column 2.
  • part of the krypton obtained in 17 and 19 is recycled to the inlet of column 2; this makes it possible to increase the relative content of krypton in the feed gas mixture and to carry out the first cryogenic distillation in column 2 at a pressure notably less than 18 bars; for example, with a krypton to xenon ratio of 1, obtained with a reflux of 10 from krypton, it is possible to lower the operating pressure of column 2 to a value of 10 bars.
  • the pure xenon obtained in 18 is marketable.
  • the gaseous mixture to be treated to which a determined amount of argon has been added has the following composition: 81% nitrogen, 11% oxygen, 8% argon, 150 ppm of krypton, and 1,500 ppm of xenon, hydrocarbons, oxides of nitrogen, water vapor and carbon dioxide; it is introduced in 5, at a flow rate of 21.8 m 3 per hour, into the unit la.
  • the mixture freed from hydrocarbons is introduced at 6 into unit 1b and hydrogen is introduced at 7 at a flow rate of 4.8 m per hour.
  • the mixture, freed from oxygen and nitrogen oxides is introduced at 8 into unit lc.
  • the gaseous mixture freed from water vapor and CO 2 is introduced at 9 into column 2: at this time, the mixture has the following composition: 88% nitrogen, 12 % argon, 150 ppm krypton and 1,500 ppm xenon; it is introduced in column 2. At the head of column 2, there is recovered in 11 a mixture of 91% nitrogen and 9% argon. At the bottom of column 2, a mixture of 90% argon, 0.5% krypton and 5% xenon is recovered. This mixture is introduced at 13 into column 3.
  • argon is recovered at 14 at a flow rate of 600 l / h and at the bottom of this column 3, a mixture of 10% of krypton and 90% xenon. This mixture is introduced at 16 into column 4.
  • krypton is recovered at 17 at a flow rate of 3 1 / h and at the bottom of column 4, xenon at a flow rate of 30 1 / h .
  • the values given above relate to the case where part of the krypton obtained in 17 at the entry of column 2 is not recycled.
  • the gas mixture introduced at 9 at the inlet of column 2 then has the following composition: 88% nitrogen, 12% argon, 1500 ppm krypton and 1,500 ppm xenon. This makes it possible to operate column 2 at a pressure of the order of 12 bars instead of 18 bars.

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Abstract

Procédé de traitement d'effluents gazeux. Il se caractérise en ce qu'il comprend une étape de concentration des gaz rares en solution dans de l'argon liquide (2), par distillation cryogénique des gaz légers (3 et 4), et principalement de l'azote, à partir d'un mélange liquéfié. Application au traitement des combustibles irradiés.Process for the treatment of gaseous effluents. It is characterized in that it comprises a step of concentrating the rare gases in solution in liquid argon (2), by cryogenic distillation of the light gases (3 and 4), and mainly nitrogen, from 'a liquefied mixture. Application to the treatment of irradiated fuels.

Description

La présente invention, due aux travaux de Monsieur Alain LEUDET de la Société d'ETUDES CHIMIQUES et de Messieurs Jacques DUHAYON, Jean-Pierre GOUMONDY et Jean-Claude ROUSSEAU du COMMISSARIAT A L'ENERGIE ATOMIQUE, a pour objet un procédé de traitement d'un mélange d'air avec des gaz rares, notamment du xénon et du krypton, et plus particulièrement de traitement des effluents gazeux provenant du retraitement de combustibles nucléaires irradiés, un tel traitement ayant également pour but de récupérer le xénon que ces mélanges contiennent.The present invention, due to the work of Mr. Alain LEUDET of the Society of CHEMICAL STUDIES and of Messrs Jacques DUHAYON, Jean-Pierre GOUMONDY and Jean-Claude ROUSSEAU of the ATOMIC ENERGY COMMISSIONER, relates to a process for the treatment of a mixture of air with rare gases, in particular xenon and krypton, and more particularly for treatment of gaseous effluents originating from the reprocessing of irradiated nuclear fuels, such treatment also having the aim of recovering the xenon that these mixtures contain.

Les effluents gazeux provenant des usines de retraitement des combustibles irradiés sont essentiellement constitués d'air, dont la teneur en oxygène peut être inférieure à la teneur naturelle, de gaz rares tels que le xénon et le krypton, et contiennent généralement de la vapeur d'eau, du gaz carbonique, des traces d'hydrocarbures, et aussi des oxydes d'azote dont la présence est due à la dissolution des combustibles effectuée en milieu nitrique.Gaseous effluents from plants for the reprocessing of irradiated fuels consist essentially of air, the oxygen content of which can be lower than the natural content, of rare gases such as xenon and krypton, and generally contain vapor of water, carbon dioxide, traces of hydrocarbons, and also nitrogen oxides whose presence is due to the dissolution of fuels carried out in a nitric medium.

Il est connu de traiter ces effluents gazeux par des procédés qui comprennent essentiellement une étape d'épuration fournissant un mélange d'air et de gaz rares, exempt d'autres impuretés, puis une étape de préconcentration des gaz rares dans l'un des deux constituants de l'air, àasavoir l'oxygène ou l'azote.It is known to treat these gaseous effluents by processes which essentially comprise a purification step providing a mixture of air and rare gases, free of other impurities, then a step of preconcentrating the rare gases in one of the two constituents of air, to have oxygen or nitrogen.

Selon le procédé consistant à préconcentrer les gaz rares dans l'azote, cette étape de préconcentration s'effectue, après réduction catalytique de tout l'oxygène du mélange avec de l'hydrogène, par concentration des gaz rares dans une fraction de l'azote par distillation cryogénique. Puis le mélange de krypton et de xénon dans l'azote est alors soumis à une autre distillation cryogénique pour séparer le krypton et l'azote du xénon. Ce procédé présente l'inconvénient que, étant donné la faible solubilité du xénon dans l'azote liquide, il se produit des bouchages dans les colonnes de distillation qui sont dus à une cristallisation du xénon.According to the process consisting of preconcentrating the rare gases in nitrogen, this preconcentration step is carried out, after catalytic reduction of all the oxygen in the mixture with hydrogen, by concentration of the rare gases in a fraction of the nitrogen. by cryogenic distillation. Then the mixture of krypton and xenon in nitrogen is then subjected to another cryogenic distillation to separate the krypton and the nitrogen from the xenon. This process has the drawback that, given the low solubility of xenon in liquid nitrogen, blockages occur in the distillation columns which are due to crystallization of the xenon.

Selon l'autre procédé consistant à préconcentrer les gaz rares dans l'oxygène, on effectue cette préconcentration en éliminant tout l'azote du mélange et une partie de l'oxygène par distillation cryogénique. Le mélange de krypton et de xénon concentré dans l'oxygène alors obtenu est d'abord soumis à une étape de réduction catalytique de l'oxygène avec de l'hydrogène, puis à une étape de distillation cryogénique pour séparer le krypton du xénon. Ce procédé présente, par rapport au procédé de préconcentration dans l'azote, l'avantage que la solubilité du xénon est nettement plus grande dans l'oxygène liquide que dans l'azote liquide. Mais en raison de la radioactivité du milieu, il y a formation d'ozone dans le bouilleur de la colonne de distillation ; cette présence d'ozone engendre des risques d'explosion. Ces risques d'explosion pourraient éventuellement être évités par une destruction continue et "in situ" de l'ozone formé ; mais la mise au point d'un tel système d'élimination pose un certain nombre de problèmes et n'a encore jamais été réalisée.According to the other method of preconcentrating the rare gases in oxygen, this preconcentration is carried out by removing all of the nitrogen from the mixture and part of the oxygen by cryogenic distillation. The mixture of krypton and xenon concentrated in oxygen then obtained is first subjected to a step of catalytic reduction of oxygen with hydrogen, then to a cryogenic distillation step to separate the krypton from the xenon. This method has, compared to the preconcentration process in nitrogen, the advantage that the solubility of xenon is much higher in liquid oxygen than in liquid nitrogen. However, due to the radioactivity of the medium, ozone is formed in the boiler of the distillation column; this presence of ozone creates the risk of explosion. These explosion risks could possibly be avoided by continuous and "in situ" destruction of the ozone formed; but the development of such a disposal system poses a number of problems and has never been carried out.

La présente invention a justement pour objet un procédé de traitement, notamment d'effluents gazeux provenant du retraitement de combustibles irradiés, qui pallie les inconvénients rappelés ci-dessus ; en effet, lors de la mise en oeuvre du procédé considéré, il n'y a pas formation d'ozone, et donc pas risque d'explosion ; quant aux problèmes de cristallisation du xénon, ils peuvent aisément être évités.The subject of the present invention is precisely a process for the treatment, in particular of gaseous effluents originating from the reprocessing of irradiated fuels, which overcomes the drawbacks mentioned above; in fact, during the implementation of the process considered, there is no formation of ozone, and therefore no risk of explosion; as for the problems of crystallization of xenon, they can easily be avoided.

Le procédé conforme à l'invention se caractérise en ce qu'il comprend une étape de concentration des gaz rares en solution dans de l'argon liquide, par distillation cryogénique des gaz légers, et principalement de l'azote, à partir du mélange liquéfié.The process according to the invention is characterized in that it comprises a step of concentrating the rare gases in solution in liquid argon, by cryogenic distillation of the light gases, and mainly nitrogen, from the liquefied mixture .

De préférence, ce procédé comprend en outre, après ladite étape de concentration, une étape de récupération du xénon par distillation cryogénique du ou des autres gaz à partir du mélange concentré et liquéfié.Preferably, this method further comprises, after said concentration step, a step of recovering xenon by cryogenic distillation of the other gas or gases from the concentrated and liquefied mixture.

En effet, le demandeur a étudié le comportement du xénon du point de vue de la solubilité dans trois solvants cryogéniques, à savoir l'oxygène, l'azote et l'argon. Le demandeur a étudié quelle était la pression maximale telle que l'équilibre solide-liquide-vapeur xénon-solvant puisse exister. Il importait donc, pour éviter tout risque de cristallisation du xénon, d'opérer l'étape de préconcentration à une pression supérieure à cette pression remarquable citée plus haut. Le demandeur a recherché et découvert que pour un système oxygène-xénon, cette pression remarquable est de 17 bars absolus, que pour un système argon- xénon, cette pression remarquable est de 18,5 bars absolus, et que pour un système azote-xénon, cette pression remarquable serait notablement supérieure par exemple, de l'ordre de 35 bars absolus.Indeed, the applicant has studied the behavior of xenon from the point of view of solubility in three cryogenic solvents, namely oxygen, nitrogen and argon. The applicant studied what was the maximum pressure such that the solid-liquid-vapor xenon-solvent balance could exist. It was therefore important, to avoid any risk of crystallization of the xenon, to operate the preconcentration step at a pressure higher than this remarkable pressure mentioned above. The applicant has researched and discovered that for an oxygen-xenon system, this remarkable pressure is 17 bars absolute, that for an argon-xenon system, this remarkable pressure is 18.5 bars absolute, and that for a nitrogen-xenon system , this remarkable pressure would be notably higher, for example, of the order of 35 bar absolute.

C'est pourquoi le fait d'opérer une étape de préconcentration du xénon et du krypton dans de l'argon liquide selon le procédé conforme à l'invention, présente l'avantage, par rapport au procédé de préconcentration du xénon et du krypton dans l'azote, d'éviter la cristallisation du xénon tout en opérant la distillation cryogénique à une pression nettement plus faible et également l'avantage, par rapport au procédé de préconcentration du xénon et du krypton dans l'oxygène, d'éviter la formation d'ozone.This is why the fact of operating a step of preconcentration of xenon and krypton in liquid argon according to the process according to the invention has the advantage, compared to the process of preconcentration of xenon and krypton in nitrogen, to avoid crystallization of xenon while operating cryogenic distillation at a significantly lower pressure and also the advantage, compared to the process of preconcentration of xenon and krypton in oxygen, to avoid the formation ozone.

L'invention a également pour objet un procédé de traitement de gaz effluents provenant du retraitement de combustibles nucléaires irradiés, constitués d'un mélange contenant au moins du xénon et du krypton radioactif dans l'air, caractérisé en ce qu'il comprend essentiellement et successivement une première étape d'élimination d'impuretés éventuelles telles que les hydrocarbures, les oxydes de l'azote, le gaz carbonique, la vapeur d'eau, une seconde étape de concentration du xénon et du krypton en solution dans de l'argon liquide par distillation des gaz légers, et principalement de l'azote, à partir du mélange liquéfié, une troisième étape d'élimination de l'argon par distillation cryogénique du mélange séparé d'argon, de xénon et de krypton, préalablement liquéfié, et une quatrième étape de séparation du xénon et du krypton, par distillation cryogénique du mélange séparé de xénon et de krypton, préalablement liquéfié.The subject of the invention is also a process for treating effluent gases originating from the reprocessing of irradiated nuclear fuels, consisting of a mixture containing at least xenon and radioactive krypton in the air, characterized in that it essentially comprises and successively a first stage of elimination of possible impurities such as hydrocarbons, nitrogen oxides, carbon dioxide, water vapor, a second stage of concentration of xenon and krypton in solution in argon liquid by distillation of light gases, and mainly nitrogen, from the liquefied mixture, a third stage of elimination of argon by distillation cryogenic of the separate mixture of argon, xenon and krypton, previously liquefied, and a fourth step of separation of xenon and krypton, by cryogenic distillation of the separate mixture of xenon and krypton, previously liquefied.

Selon le procédé considéré, l'argon nécessaire pour la seconde étape de concentration peut être introduit dans le mélange gazeux à traiter, soit avant la première étape d'élimination des diverses impuretés, soit avant la deuxième étape de concentration.According to the process considered, the argon necessary for the second concentration step can be introduced into the gas mixture to be treated, either before the first step of removing the various impurities, or before the second concentration step.

Selon une caractéristique avantageuse du procédé de l'invention, on prend une partie du krypton séparé du xénon et obtenu lors de la quatrième étape, et on introduit ladite partie dans le mélange obtenu à la fin de la première étape, avant de procéder à la deuxième étape de concentration du xénon et du krypton en solution dans de l'argon liquide. Cette réintroduction d'une certaine quantité du krypton obtenu en fin de procédé permet d'abaisser la pression à laquelle s'effectue la deuxième étape de concentration du xénon et du krypton dans de l'argon liquide.According to an advantageous characteristic of the process of the invention, a part of the krypton separated from the xenon and obtained during the fourth stage is taken, and said part is introduced into the mixture obtained at the end of the first stage, before proceeding to the second stage of concentration of xenon and krypton in solution in liquid argon. This reintroduction of a certain amount of krypton obtained at the end of the process makes it possible to lower the pressure at which the second stage of concentration of xenon and krypton is carried out in liquid argon.

Naturellement, l'invention s'étend également aux installations appropriées pour la mise en oeuvre du procédé. De telles installations comprennent notamment des réacteurs catalytiques et des colonnes de distillation cryogénique avec tous leurs équipements annexes, en eux-mêmes connus, disposés et reliés par des conduits de circulation des différents produits, de manière à permettre la réalisation des opérations successives du procédé défini ci-dessus.Naturally, the invention also extends to installations suitable for carrying out the method. Such installations include in particular catalytic reactors and cryogenic distillation columns with all their ancillary equipment, in themselves known, arranged and connected by conduits for circulation of the various products, so as to allow the successive operations of the defined process to be carried out above.

Les caractéristiques d'une telle installation ainsi que celles du procédé apparaîtront plus clairement à la lecture de la description ci-après, qui concerne un exemple de mise en oeuvre de l'invention. Bien entendu, cette description n'a aucun caractère limitatif vis-à-vis de l'invention.The characteristics of such an installation as well as those of the method will appear more clearly on reading the description below, which relates to an example of implementation of the invention. Of course, this description has no limiting character with respect to the invention.

La description qui suit est faite en référence aux figures jointes dans lesquelles :

  • - la figure 1 illustre schématiquement le déroulement global du procédé décrit et l'installation utilisée ;
  • - les figures 2 et 3 représentent, de manière schématique mais plus en détail, des parties de l'installation utilisée et la circulation des produits entre les différentes étapes.
The following description is made with reference to the attached figures in which:
  • - Figure 1 schematically illustrates the overall progress of the process described and the installation used;
  • - Figures 2 and 3 show, schematically but in more detail, parts of the installation used and the movement of products between the different stages.

Sur la figure 1, on a symbolisé les différentes unités de traitement permettant d'effectuer successivement les étapes du procédé de l'invention, dans cet ordre :

  • - en 1 : l'unité dans laquelle s'effectue la première étape d'élimination des impuretés du mélange gazeux provenant de l'usine de retraitement de combustibles nucléaires, première étape d'épuration qui permet d'obtenir un mélange constitué d'air ne contenant pratiquement plus que du xénon et du krypton ; cette première étape s'effectue en trois stades successifs, respectivement dans trois unités symbolisées en la, 1b et lc ;
  • - en 2 : une colonne dans laquelle s'effectue la deuxième étape de concentration du xénon et du krypton dans de l'argon liquide, permettant d'éliminer principalement l'azote du mélange et de recueillir un mélange concentré de xénon et de krypton dans de l'argon ;
  • - en 3 : la colonne dans laquelle s'effectue.la troisième étape d'élimination de l'argon par distillation cryogénique du mélange d'argon, de xénon et de krypton ;
  • - en 4 : la colonne dans laquelle s'effectue la séparation du xénon et du krypton par distillation cryogénique de façon à éliminer le krypton et à recueillir du xénon pur.
In FIG. 1, the various processing units have been symbolized making it possible to successively carry out the steps of the method of the invention, in this order:
  • - in 1: the unit in which the first step of removing impurities from the gas mixture from the nuclear fuel reprocessing plant takes place, the first purification step which makes it possible to obtain a mixture consisting of air containing practically nothing but xenon and krypton; this first stage is carried out in three successive stages, respectively in three units symbolized in la, 1b and lc;
  • - in 2: a column in which is carried out the second stage of concentration of xenon and krypton in liquid argon, making it possible mainly to remove the nitrogen from the mixture and to collect a concentrated mixture of xenon and krypton in argon;
  • - in 3: the column in which the third step of removing argon is carried out by cryogenic distillation of the mixture of argon, xenon and krypton;
  • - in 4: the column in which the separation of xenon and krypton is carried out by cryogenic distillation so as to eliminate the krypton and to collect pure xenon.

De façon plus précise, la première étape d'élimination des impuretés éventuelles contenues dans le mélange gazeux de départ comporte un premier stade d'élimination des hydrocarbures par oxydation catalytique (et également de dissociation catalytique de l'oxyde d'azote N20), qui s'effectue dans l'unité représentée en la ; un deuxième stade d'élimination de l'oxygène et des oxydes de l'azote par réduction catalytique, qui s'effectue dans l'unité représentée en lb ; et un troisième stade d'élimination du gaz carbonique et de la vapeur d'eau par passage sur tamis moléculaire et/ou gel de silice, qui s'effectue dans l'unité représentée en lc.More specifically, the first step of removing any impurities contained in the starting gas mixture comprises a first step of removing hydrocarbons by catalytic oxidation (and also catalytic dissociation of nitrogen oxide N 2 0), which takes place in the unit represented in la; a second stage of elimination of oxygen and nitrogen oxides by catalytic reduction, which takes place in the unit shown in lb; and a third stage of removal of carbon dioxide and water vapor by passage over a molecular sieve and / or silica gel, which takes place in the unit shown in lc.

Ainsi, le mélange gazeux à traiter est tout d'abord introduit en 5 dans l'unité la et sort de cette unité débarrassé des hydrocarbures. Il est alors introduit, en 6, dans l'unité lb où s'effectue une réduction catalytique en présence de palladium par action d'hydrogène amené en 7. Il ressort de cette unité lb, débarrassé de l'oxygène et des oxydes de l'azote, et est introduit, en 8, dans l'unité lc où il est débarrassé du gaz carbonique et de la vapeur d'eau par passage sur tamis moléculaire. Ainsi, le mélange introduit, en 9, dans la colonne 2 est un mélange d'azote, de xénon et de krypton, auquel on additionne préalablement de l'argon, en 10, avant l'entrée dans la colonne 2. Dans la colonne 2 s'effectue la distillation cryogénique qui permet d'obtenir l'élimination de l'azote en 11, ce qui permet de récupérer, en 12, un mélange d'argon, de xénon et de krypton. Ce mélange d'argon, de xénon et de krypton est alors introduit en 13, dans la colonne 3, où s'effectue l'élimination de l'argon, en 14, par distillation cryogénique et la récupération, en 15, d'un mélange de krypton et de xénon. Ce mélange de krypton et de xénon est alors introduit en 16, dans la colonne 4, où s'effectue l'élimination du krypton, en 17, par distillation cryogénique et la récupération de xénon pur en 18.Thus, the gaseous mixture to be treated is first introduced at 5 into unit 1a and leaves this unit free of hydrocarbons. It is then introduced, at 6, into unit lb where a catalytic reduction takes place in the presence of palladium by the action of hydrogen supplied at 7. It comes out of this unit lb, freed from oxygen and the oxides of l 'nitrogen, and is introduced, in 8, in the unit lc where it is freed from carbon dioxide and water vapor by passage over a molecular sieve. Thus, the mixture introduced, at 9, into column 2 is a mixture of nitrogen, xenon and krypton, to which argon is added before, at 10, before entering column 2. In column 2 is carried out the cryogenic distillation which makes it possible to obtain the elimination of nitrogen at 11, which makes it possible to recover, at 12, a mixture of argon, xenon and krypton. This mixture of argon, xenon and krypton is then introduced at 13, in column 3, where the elimination of the argon, at 14, takes place by cryogenic distillation and the recovery, at 15, of a mixture of krypton and xenon. This mixture of krypton and xenon is then introduced at 16, in column 4, where the elimination of krypton, at 17, takes place by cryogenic distillation and the recovery of pure xenon at 18.

Eventuellement, selon un mode préféré de l'in- vention, on prend une partie du krypton éliminé en 17, et on le recycle en 19 pour le réintroduire à l'entrée de la colonne 2, de façon à pouvoir effectuer la distillation cryogénique à une pression plus faible.Optionally, according to a preferred embodiment of the invention , part of the krypton eliminated in 17 is taken, and it is recycled in 19 to reintroduce it at the inlet of column 2, so as to be able to carry out the cryogenic distillation at lower pressure.

Selon l'invention, la pression à laquelle on effectue la distillation cryogénique dans la colonne 2 est au plus de 18 bars, la pression à laquelle on effectue la distillation cryogénique dans la colonne 4 est d'environ 3 bars et la pression à laquelle on effectue la distillation cryogénique dans la colonne 3 est comprise entre la pression de la colonne 4 et la pression de la colonne 2.According to the invention, the pressure at which the cryogenic distillation is carried out in column 2 is at most 18 bars, the pressure at which the cryogenic distillation is carried out in column 4 is approximately 3 bars and the pressure at which performs the cryogenic distillation in column 3 is between the pressure of column 4 and the pressure of column 2.

Sur la figure 2, on a représenté plus en détail les différents éléments et circuits reliant les unités la, Ib, lc, dans lesquelles on effectue la première étape d'élimination des impuretés selon le procédé de l'invention. Le mélange gazeux à traiter provenant de l'usine de retraitement de combustibles irradiés, est d'abord introduit en 20 dans un compresseur 21, puis est refroidi par une circulation d'eau dans un réfrigérant 22 et, après passage dans un échangeur 23, est introduit en 5 dans l'unité la qui contient un catalyseur au platine ou au rhodium : dans cette unité la, les hydrocarbures sont éliminés du mélange gazeux par oxydation catalytique et il y a également élimination du protoxyde d'azote N20 par dissociation catalytique de ce dernier. Un dispositif de chauffage externe assure le maintien d'une température maximale de 700°C dans cette unité la. A la sortie de l'unité la, le mélange gazeux débarrassé des hydrocarbures passe dans l'échangeur 23, puis, après mélange avec une partie du mélange gazeux provenant du séparateur d'eau 27, dans un système de réchauffage électrique 24 qui le porte à une température de 100°C et est introduit, en 6, dans l'unité lb : dans cette unité 1b, l'oxygène et les oxydes de l'azote sont éliminés par réduction catalytique, l'unité lb contenant un catalyseur au palladium et éventuellement un catalyseur au rhodium et de l'hydrogène étant introduit en 7, de façon à maintenir un léger excès de ce gaz en sortie de l'unité lb. A la sortie de l'unité lb, le mélange gazeux débarrassé de l'oxygène et des oxydes d'azote est refroidi dans un réfrigérant à eau 25, puis passe dans un ventilateur 26. A la sortie du ventilateur 26 une partie du mélange gazeux, après passage dans un séparateur d'eau 27, est recyclée en 28 vers l'unité 1b et l'autre partie est dirigée en 8, vers l'unité lc.In Figure 2, there is shown in more detail the different elements and circuits connecting the units la, Ib, lc, in which the first step of removing impurities is carried out according to the method of the invention. The gaseous mixture to be treated, coming from the irradiated fuel reprocessing plant, is first introduced at 20 into a compressor 21, then is cooled by a circulation of water in a refrigerant 22 and, after passing through an exchanger 23, is introduced at 5 into unit 1a which contains a platinum or rhodium catalyst: in this unit 1a, the hydrocarbons are eliminated from the gas mixture by catalytic oxidation and there is also elimination of the nitrous oxide N 2 0 by dissociation catalytic of the latter. An external heater ensures that a maximum temperature of 700 ° C is maintained in this unit la. At the outlet of the unit la, the gas mixture freed from hydrocarbons passes through the exchanger 23, then, after mixing with part of the gas mixture coming from the water separator 27, into an electric heating system 24 which carries it at a temperature of 100 ° C. and is introduced, at 6, into the unit lb: in this unit 1b, the oxygen and the nitrogen oxides are eliminated by catalytic reduction, the unit lb containing a palladium catalyst and optionally a catalyst with rhodium and hydrogen being introduced at 7, so as to maintain a slight excess of this gas at the outlet of the unit lb. At the outlet of the unit 1b, the gas mixture, freed of oxygen and nitrogen oxides, is cooled in a water cooler 25, then passes through a fan 26. At the outlet of the ven screen 26 a part of the gas mixture, after passing through a water separator 27, is recycled at 28 to unit 1b and the other part is directed at 8, to unit lc.

Le mélange introduit en 8 dans l'unité lc est débarrassé de la vapeur d'eau et des traces de C02 Par passage sur un tamis moléculaire et/ou un gel de silice dans l'un des deux absorbeurs 29 disposés en parallèle ; ces deux absorbeurs 29 subissent périodiquement et alternativement une régénération par chauffage et circulation d'azote.The mixture introduced at 8 into unit lc is freed from water vapor and traces of C0 2 by passing over a molecular sieve and / or silica gel in one of the two absorbers 29 arranged in parallel; these two absorbers 29 periodically and alternately undergo regeneration by heating and circulation of nitrogen.

Sur la figure 3, on reconnaît les colonnes 2, 3 et 4 servant respectivement à la mise en oeuvre des deuxième, troisième et quatrième étapes du procédé de l'invention. Le mélange gazeux contenant de l'azote, de l'argon, du krypton et du xénon provenant de l'unité 1 est d'abord refroidi dans un échangeur de chaleur 30, puis est introduit en 9, dans la colonne 2.In Figure 3, we recognize the columns 2, 3 and 4 respectively used for the implementation of the second, third and fourth steps of the method of the invention. The gas mixture containing nitrogen, argon, krypton and xenon coming from unit 1 is first cooled in a heat exchanger 30, then is introduced into 9, in column 2.

La colonne de distillation 2 fonctionne à une pression au plus de 18 bars. La partie inférieure de la colonne 2 est maintenue à la température nécessaire à l'aide d'un dispositif de chauffage électrique 31. En tête de la colonne 2, un reflux est assuré par un condenseur 32, refroidi par de l'azote liquide amené en 33. On extrait de la partie supérieure de la colonne 2, en 11, un mélange contenant principalement de l'azote et éventuellement une fraction d'argon ; ce mélange peut être recyclé dans le circuit de balayage de la cisaille ou rejeté dans l'atmosphère ; on le réchauffe préalablement par passage dans l'échangeur 30, d'où il sort en 34. Du bas de la colonne 2, on extrait un mélange liquide d'argon concentré en krypton et xénon et on l'introduit en 13 dans la colonne de distillation 3.The distillation column 2 operates at a pressure of at most 18 bar. The lower part of column 2 is maintained at the necessary temperature using an electric heating device 31. At the top of column 2, reflux is provided by a condenser 32, cooled by liquid nitrogen supplied at 33. A mixture is extracted from the upper part of column 2, at 11, containing mainly nitrogen and possibly a fraction of argon; this mixture can be recycled in the shear scanning circuit or discharged into the atmosphere; it is heated beforehand by passing through the exchanger 30, from which it exits at 34. From the bottom of column 2, a liquid mixture of argon concentrated in krypton and xenon is extracted and it is introduced at 13 into the column distillation 3.

Dans la colonne 3, qui fonctionne à une pression comprise entre la pression de la colonne 4 et la pression de la colonne 2, on sépare par distillation cryogénique l'argon en 14 et on recueille le mélange de krypton et de xénon en bas de la colonne 3. Eventuellement, on peut recycler l'argon, sortant en 14 de la colonne 3, à l'entrée de la colonne 2.In column 3, which operates at a pressure between the pressure of column 4 and the pressure of column 2, the argon at 14 is separated by cryogenic distillation and the mixture of krypton and xenon is collected at the bottom of the column. column 3. Optionally, the argon can be recycled, leaving at 14 from column 3, at the inlet of column 2.

Le mélange de krypton et de xénon sortant du bas de la colonne 3 est introduit en 16 dans la colonne 4, où l'on effectue la séparation du krypton et du xénon par distillation cryogénique : le krypton est obtenu en 17, en tête de la colonne 4, et le xénon en 18, en bas de la colonne 4.The mixture of krypton and xenon leaving the bottom of column 3 is introduced at 16 into column 4, where the separation of krypton and xenon is carried out by cryogenic distillation: krypton is obtained at 17, at the head of the column 4, and xenon in 18, at the bottom of column 4.

Eventuellement, on recycle une partie du krypton obtenu en 17, en 19, à l'entrée de la colonne 2 ; ceci permet d'augmenter la teneur relative de krypton dans le mélange gazeux d'alimentation et d'effectuer la première distillation cryogénique dans la colonne 2 à une pression notablement inférieure à 18 bars ; par exemple, avec un rapport krypton sur xénon de 1, obtenu avec un reflux de 10 de krypton, on peut abaisser la pression de fonctionnement de la colonne 2 à une valeur de 10 bars.Optionally, part of the krypton obtained in 17 and 19 is recycled to the inlet of column 2; this makes it possible to increase the relative content of krypton in the feed gas mixture and to carry out the first cryogenic distillation in column 2 at a pressure notably less than 18 bars; for example, with a krypton to xenon ratio of 1, obtained with a reflux of 10 from krypton, it is possible to lower the operating pressure of column 2 to a value of 10 bars.

Le xénon pur obtenu en 18 est commercialisable.The pure xenon obtained in 18 is marketable.

A titre indicatif, on donne ci-dessous un exemple de circulation des produits en précisant les concentrations des mélanges et les différents débits. Pour plus de simplicité, on se réfère à la figure 1.As an indication, an example of product circulation is given below, specifying the concentrations of the mixtures and the different flow rates. For simplicity, we refer to Figure 1.

Le mélange gazeux à traiter auquel il a été ajouté une quantité déterminée d'argon présente la composition suivante : 81% d'azote, 11% d'oxygène, 8% d'argon, 150ppm de krypton, et 1.500 ppm de xénon, des hydrocarbures, des oxydes de l'azote, de la vapeur d'eau et du gaz carbonique ; il est introduit en 5, à un débit de 21,8 m3 par heure, dans l'unité la. A la sortie de l'unité la, le mélange débarrassé des hydrocarbures est introduit en 6 dans l'unité 1b et de l'hydrogène est introduit en 7 à un débit de 4,8 m par heure. A la sortie de l'unité 1b, le mélange débarrassé de l'oxygène et des oxydes de l'azote est introduit en 8 dans l'unité lc. A la sortie de cette unité lc, le mélange gazeux débarrassé de la vapeur d'eau et du CO2 est introduit en 9 dans la colonne 2 : à ce moment là, le mélange a la composition suivante : 88% d'azote, 12% d'argon, 150 ppm de krypton et 1.500 ppm de xénon ; il est introduit dans la colonne 2. En tête de la colonne 2, on récupère en 11 un mélange de 91% d'azote et de 9% d'argon. En bas de la colonne 2, on récupère un mélange de 90% d'argon, de 0,5% de krypton et de 5% de xénon. Ce mélange est introduit en 13 dans la colonne 3. En tête de cette colonne 3 , on récupère en 14 de l'argon à un débit de 600 1/h et en bas de cette colonne 3, on récupère un mélange de 10% de krypton et de 90% de xénon. On introduit ce mélange en 16 dans la colonne 4. En tête de la colonne 4, on récupère en 17 du krypton à un débit de 3 1/h et en bas de la colonne 4, du xénon à un débit de 30 1/h. Les valeurs données ci-dessus concernent le cas où l'on n'effectue pas le recyclage d'une partie du krypton obtenu en 17 à l'entrée de la colonne 2.The gaseous mixture to be treated to which a determined amount of argon has been added has the following composition: 81% nitrogen, 11% oxygen, 8% argon, 150 ppm of krypton, and 1,500 ppm of xenon, hydrocarbons, oxides of nitrogen, water vapor and carbon dioxide; it is introduced in 5, at a flow rate of 21.8 m 3 per hour, into the unit la. At the outlet of unit 1a, the mixture freed from hydrocarbons is introduced at 6 into unit 1b and hydrogen is introduced at 7 at a flow rate of 4.8 m per hour. On leaving unit 1b, the mixture, freed from oxygen and nitrogen oxides, is introduced at 8 into unit lc. At the outlet of this unit lc, the gaseous mixture freed from water vapor and CO 2 is introduced at 9 into column 2: at this time, the mixture has the following composition: 88% nitrogen, 12 % argon, 150 ppm krypton and 1,500 ppm xenon; it is introduced in column 2. At the head of column 2, there is recovered in 11 a mixture of 91% nitrogen and 9% argon. At the bottom of column 2, a mixture of 90% argon, 0.5% krypton and 5% xenon is recovered. This mixture is introduced at 13 into column 3. At the top of this column 3, argon is recovered at 14 at a flow rate of 600 l / h and at the bottom of this column 3, a mixture of 10% of krypton and 90% xenon. This mixture is introduced at 16 into column 4. At the head of column 4, krypton is recovered at 17 at a flow rate of 3 1 / h and at the bottom of column 4, xenon at a flow rate of 30 1 / h . The values given above relate to the case where part of the krypton obtained in 17 at the entry of column 2 is not recycled.

Si l'on effectue ce recyclage, en 19, d'une partie du krypton obtenu en fin de procédé, par exemple à un débit de 27 1/h, le mélange gazeux introduit en 9 à l'entrée de la colonne 2 a alors la composition suivante : 88% d'azote, 12% d'argon, 1500 ppm de krypton et 1.500 ppm de xénon. Ceci permet de pouvoir faire fonctionner la colonne 2 à une pression de l'ordre de 12 bars au lieu de 18 bars.If this recycling is carried out in 19 of a portion of the krypton obtained at the end of the process, for example at a flow rate of 27 l / h, the gas mixture introduced at 9 at the inlet of column 2 then has the following composition: 88% nitrogen, 12% argon, 1500 ppm krypton and 1,500 ppm xenon. This makes it possible to operate column 2 at a pressure of the order of 12 bars instead of 18 bars.

Claims (8)

1. Procédé de traitement d'un mélange d'air avec des gaz rares, notamment du xénon et du krypton, au moins partiellement radioactifs, notamment d'effluents gazeux provenant du retraitement de combustibles irradiés, caractérisé en ce qu'il comprend une étape de concentration des gaz rares en solution dans de l'argon liquide, par distillation cryogénique des gaz légers, et principalement de l'azote, à partir du mélange liquéfié.1. Process for treating a mixture of air with rare gases, in particular xenon and krypton, at least partially radioactive, in particular gaseous effluents originating from the reprocessing of irradiated fuels, characterized in that it comprises a step concentration of rare gases in solution in liquid argon, by cryogenic distillation of light gases, and mainly nitrogen, from the liquefied mixture. 2. Procédé selon la revendication 1, caractérisé en ce qu'il comprend une étape de récupération du xénon par distillation cryogénique du ou des autres gaz à partir du mélange concentré et liquéfié.2. Method according to claim 1, characterized in that it comprises a step of recovery of the xenon by cryogenic distillation of the other gas or gases from the concentrated and liquefied mixture. 3. Procédé selon l'une quelconque des revendications 1 ou 2, caractérisé en ce que l'étape de concentration des gaz rares s'effectue à une pression d'au plus 18 bars.3. Method according to any one of claims 1 or 2, characterized in that the step of concentrating the rare gases is carried out at a pressure of at most 18 bars. 4. Procédé de traitement de gaz effluents provenant du retraitement de combustibles nucléaires irradiés, constitués d'un mélange contenant au moins du krypton radioactif et du xénon dans l'air, caractérisé en ce qu'il comprend essentiellement et successivement une première étape d'élimination d'impuretés éventuelles telles que les hydrocarbures, les oxydes de l'azote, le gaz carbonique, la vapeur d'eau, une seconde étape de concentration du xénon et du krypton en solution dans de l'argon liquide par distillation des gaz légers, et principalement de l'azote, à partir du mélange liquéfié, une troisième étape d'élimination de l'argon par distillation cryogénique du mélange séparé d'argon, de xénon et de krypton, préalablement liquéfié, et une quatrième étape de séparation du xénon et du krypton par distillation cryogénique du mélange séparé de xénon et krypton, préalablement liquéfié.4. Process for the treatment of effluent gases from the reprocessing of irradiated nuclear fuels, consisting of a mixture containing at least radioactive krypton and xenon in the air, characterized in that it essentially and successively comprises a first step of elimination of possible impurities such as hydrocarbons, nitrogen oxides, carbon dioxide, water vapor, a second stage of concentration of xenon and krypton in solution in liquid argon by distillation of light gases , and mainly nitrogen, from the liquefied mixture, a third step of removing argon by cryogenic distillation of the separated mixture of argon, xenon and krypton, previously liquefied, and a fourth step of separating the xenon and krypton by cryogenic distillation of the separate mixture of xenon and krypton, previously liquefied. 5. Procédé selon la revendication 4, caractérisé en ce que l'on prend une partie du krypton, séparé du xénon et obtenu lors de la quatrième étape, et on introduit ladite partie dans le mélange obtenu à la fin de la première étape, avant de procéder à la deuxième étape de concentration du xénon et du krypton en solution dans de l'argon liquide.5. Method according to claim 4, characterized in that one takes a part of the krypton, separated from the xenon and obtained during the fourth step, and the said part is introduced into the mixture obtained at the end of the first step, before proceeding to the second stage of concentration of xenon and krypton in solution in liquid argon. 6. Procédé selon l'une quelconque des revendications 4 ou 5, caractérisé en ce que la première étape d'élimination des impuretés éventuelles comporte un premier stade d'élimination des hydrocarbures par oxydation catalytique, un deuxième stade d'élimination de l'oxygène et des oxydes de l'azote par réduction catalytique, et un troisième stade d'élimination du gaz carbonique et de la vapeur d'eau par passage sur tamis moléculaire et/ou gel de silice.6. Method according to any one of claims 4 or 5, characterized in that the first stage of elimination of any impurities comprises a first stage of elimination of hydrocarbons by catalytic oxidation, a second stage of elimination of oxygen and nitrogen oxides by catalytic reduction, and a third stage of elimination of carbon dioxide and water vapor by passage over a molecular sieve and / or silica gel. 7. Procédé selon l'une quelconque des revendications 4 à 6, caractérisé en ce que la quatrième étape de séparation du xénon et du krypton s'effectue à une pression d'environ 3 bars.7. Method according to any one of claims 4 to 6, characterized in that the fourth step of separation of xenon and krypton is carried out at a pressure of about 3 bars. 8. Procédé selon l'une quelconque des revendications 4 à 7, caractérisé en ce que la troisième étape d'élimination de l'argon du mélange d'argon, de xénon et de krypton obtenu s'effectue à une pression comprise entre la pression à laquelle s'effectue la quatrième étape et la pression à laquelle s'effectue la deuxième étape.8. Method according to any one of claims 4 to 7, characterized in that the third step of removing argon from the mixture of argon, xenon and krypton obtained is carried out at a pressure between the pressure at which the fourth step takes place and the pressure at which the second step takes place.
EP79400556A 1978-08-11 1979-08-06 A process for treating effluent gases arising from the reprocessing of irradiated nuclear fuels Expired EP0008273B2 (en)

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FR7823735 1978-08-11
FR7823735A FR2433229A1 (en) 1978-08-11 1978-08-11 PROCESS FOR TREATING AN AIR MIXTURE WITH RARE GASES

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JPS5547499A (en) 1980-04-03
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EP0008273B1 (en) 1982-03-24
JPS5853320B2 (en) 1983-11-28
EP0008273B2 (en) 1988-01-27
FR2433229B1 (en) 1981-01-30

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