LU81226A1 - PROCESS FOR EXTRACTING XENON AND / OR KRYPTON FROM A CARRIER GAS - Google Patents

Abstract

1. Method for extracting xenon and/or krypton from a carrier gas, notably a carrier gas comprising essentially nitrogen or a mixture of nitrogen with oxygen and/or argon, by cryogenic distillation in a rectifying column (R) comprising at the bottom thereof a heated evaporator (A) and at the top thereof a condenser (C) which is fed with a refrigerating fluid, according to which one feeds a load (F) formed by xenon and/or krypton and a carrier gas in gaseous form and at a temperature higher than that temperature causing unsublimating of the one component thereof under the nominal partial pressure thereof, at a defined level of said column, inside which the pressure is retained at a substantially constant value higher than 0.4 MPa, and the calorie amount and cold calorie amount fed to the column are controlled, characterized in that said load (F) is fed, the krypton and xenon concentration of which in the carrier gas is lower than 1.10**-2 and 2.10**-3 mole/mole carrier gas, respectively, and in which the relative concentrations of xenon relative to krypton lie in the range from 0 to 50 mole/mole carrier gas, in column (R) at a substantially constant temperature which is at the most higher by 5 degrees K than that temperature causing unsublimating of the one component thereof at the nominal partial pressure thereof, and one controls inside said column, the level of the separation area for the most volatile element to be extracted, such as krypton, and the less volatile component of the carrier gas, by acting on the momentary ratio of the calorie amount and cold calorie amount fed to the column, in such a way as to retain said separation area on the one hand above a buffer area for the most volatile element to be extracted, such as krypton, and on the other hand below a balance area between the liquid and gaseous phases lying in turn below that column level where feeding said load occurs, the liquid flow down into the area lying below said level, the so-called enrichment area (E), comprising the balance (e), separation (s) and buffer (t) areas, being adjusted as a function of the column pressure, so as to prevent forming a solid phase in said enrichment area (E), the level of the load (F) being adjusted as a function of the column pressure in a way known per se, with a view to preventing the formation of a solid phase in said enrichment area.

Description

'- 2.4191 ow

Patent application jg May 4, 197 9 Designation of the Inventor

ADDITIVE

C) The undersigned ....... M..9 ..! LL! .E.ur ..... Charles ..... München., ..... council ..... jn jDre.v et s ...... ä ...... Luxem bourg lia, boulevard Prince-Henri * * acting as depositor - agent of the depositor - {') L 1 ëtab'l i ssement d 'public utility that ..... bel ge di tejJ'Çentre d.'. Study of ..... Nucl éaire ", ......" Ç. E ... N ... "......." Studiecentrum voor ..... Kernenergie11, "SCK '', ...... Avenue ..... Plasky .., ... ..1.44., ...... Schaerbeek, Belgium.

(3) of the invention relating to: ...... LErocédé ..... dlextraction ..... de ...... xénon ..... et / ou ..... de. ..... krypton of a gas pnrt.en r ".

designates as inventor (s):

a M,> Mister Jozef STEVENS

J. Surname and first names ............................................. .................................................. .................................................. .................................................. ...........................

Address ..................................... Greessebaan "...... 20, .. .... Balen-Hul sen. Belgium..................................

2. Surname and first names ............................................. .................................................. .................................................. .................................................. ................................

Address ................................................. .................................................. .................................................. .................................................. ..............................................

3. Surname and first names ............................................. .................................................. .................................................. .................................................. ...............................

' Address ................................................ .................................................. .................................................. .................................................. ..............................................

He affirms the sincerity of the aforementioned indications and declares to assume full responsibility for them.

Luxembourg on May 14, 19 79. jfa + QLa ..

(signature] A 68026_v _ (') Last name, first names, company, address.

fr DESCRIPTIVE MEMORY 'filed in support of an INVENTION PATENT application in the name of: "Center d'Etude de l'Energie Nucléaire", "C.E.N." "Studiecentrum voor Kernenergie", "S.C.K." for: "Process for extracting xenon and / or krypton from a carrier gas". Inventors: Guy, Eugène COLLARD - Petrus, Jacobus VAESEN.

The present invention relates to a process for extracting xenon and / or krypton from a carrier gas, in particular from a carrier gas essentially comprising nitrogen or a mixture of nitrogen with oxygen and / or of argon, by cryogenic distillation I in a rectification column comprising at its bottom a heated boiler and at its top a condenser supplied with a refrigerant.

One of the essential aims of the present invention is to present a process making it possible to extract, at economically justified conditions -, / • ✓, xenon, krypton or a mixture of the two, from a carrier gas in a very pure state .

In this regard, the invention presents a process for conducting the rectification column which makes it possible to avoid an accumulation in the boiler or boiler of products with a volatility greater than that of krypton and which may constitute a danger of explosion, such as than methane and oxygen. Especially oxygen is particularly dangerous in the presence of the isotope 85 of krypton whose irradiation field can cause the formation * of ozone.

To this end, according to the invention, a charge formed of xenon and / or krypton and a carrier gas is introduced, in gaseous form and at a slightly constant temperature | higher than the temperature causing the desublimation of a j of its components at its nominal partial pressure, at a ni- Î; determined calf from the above column, in which the pressure is maintained at · j I at a substantially constant value greater than

S

; less than 0.4 MPa and in that in this column is checked the level of the separation zone of the most volatile element to be extracted, such as krypton, and of the least volatile component of the carrier gas by acting on the momentary ratio ^ of the amount of calories and the amount of frigories

Introduced into the column so as to maintain this separation zone, on the one hand, above a buffer zone of the most volatile element to be extracted, such as krypton and, on the other hand, below d '' an equilibrium zone between the liquid and gaseous phase which is itself situated below the level of the column where the introduction of the above-mentioned charge takes place, the flow of liquid descending into the zone situated below this level, / called enrichment zone, being adjusted according to the * // · / - 3 - V; V "I pressure of the column so as to avoid the formation of a solid phase in this enrichment zone.

| Advantageously, action is taken on the momentary ratio of the quantity of calories and the quantity of frigories introduced £ ′ into the column by varying the cooling at the top t of the column.

’V. i

According to a particular embodiment, one acts on the cooling of the column by providing a current of | refrigerant ensuring the cooling of the top of the column, consisting of two parts, the flow of the first part "; having a set point which varies linearly with the flow! of the charge and mistletoe has a value slightly lower than that corresponding to the sum of the refrigeration losses and the heating power of the column boiler when the charge flow is zero, the flow of the second part being adjustable in depending on the level of the separation zone.

The invention also relates to a method for treating gaseous effluents from a reprocessing of fuel; nuclear ^ including the washing of nitrous vapors, the separation of iodine and semi-volatile products, the elimination of hydrocarbons, residual nitrogen compounds and oxygen, the adsorption of water, carbon and possibly traces of ammonia and nitrogen oxides by passing the effluent through i. .

I 1.

an adsorption unit while another adsorption unit is regenerated by a part of the effluent having undergone the adsorption treatment. fl // 1 "- 4 -

This particular process is characterized in that the part of the effluent that has been used for the above-mentioned regeneration is recycled upstream of the elimination of hydrocarbons, residual nitrogen compounds and oxygen after condensation of the water. contained therein.

'Other details and particularities of the invention come from the description given below, by way of nonlimiting example, with reference to the appended drawings, of some particular embodiments of a xenon extraction process and krypton of a carrier gas and a process for treating gaseous effluents from reprocessing of nuclear fuel.

Figure 1 is a schematic elevational view of a continuous rectification column for the implementation of the xenon and krypton extraction process from a carrier gas.

Figure 2 is a schematic representation of a regulation system of the rectification column shown in Figure 1

FIG. 3 represents a graph showing the sublimation temperature of xenon as a function of its partial pressure.

FIG. 4 represents a graphic plot of the number of theoretical plates in the enrichment zone of a mixture of nitrogen, argon and krypton and of a mixture of nitrogen and krypton with a reflux rate equal to 1 .

FIG. 5 represents a block diagram of a circuit for the purification of effluents from fuel / nuclear reprocessing plants. / / / // t * - 5 -

In the various figures, the same reference numerals designate analogous or identical elements.

According to the invention, the separation of the carrier gas and the krypton-xenon mixture is done in a continuous rectification column R (Figures 1 and 2) having at its bottom a boiler A

heated electrically or by a heat-transfer fluid whose melting point is higher than the boiling point of the krypton-xenon mixture, a tower T furnished with trays or lining allowing the adequate bubbling of rising vapors through descending liquids, a condenser C at the top of column R cooled so that it causes the condensation of a fraction of the carrier gas or of a device for distributing in liquid form a certain amount of the most volatile component = of the mixture constituting the carrier gas.

The reference F indicates the place where the fresh charge is introduced, consisting of the krypton-xenon mixture and the carrier gas, * in gaseous form.

The zone between the level of introduction of the charge * and the boiler or boiler A constitutes the enrichment zone and has been indicated by the reference E.

Under the column regime, the enrichment zone E comprises a separation zone s of the most volatile element to be extracted, which is krypton in the case of the mixture of xenon and krypton, and the least volatile component of the carrier gas extending over a space equivalent to a theoretical plateau height. A certain height of the enrichment zone E, consisting of aipy / -. 6 - I 1 a determined number of equivalent theoretical plates is used below this separation zone to form a buffer zone t of the most volatile element to be extracted, such as. krypton, between xenon and the carrier mixture.

Finally, a certain height of this same enrichment zone _ is used between the separation zone s and the level where the introduction of the charge F takes place in the column to form an equilibrium zone e between the liquid and gas phases.

The zone situated above the level of introduction of the charge F comprises a certain number of equivalent theoretical plates depending on the desired degree of decontamination of the carrier gas.

According to the invention, the charge is introduced, in gaseous form and at a substantially constant temperature slightly above the temperature causing the desublimation of one of these components at its nominal partial pressure, at a determined level of the above column while maintaining in the latter. a substantially constant pressure greater than 0.4 MPa, in particular 0.5 to 1 MPa and preferably of the order of 0.8 MPa, and the level of the separation zone s is checked in this column by acting on the momentary ratio of the quantity of calories and the quantity of frigories introduced into the column respectively into the boiler or boiler A and the condenser C, so as to maintain in permaiEnœ a buffer zone below the separation zone s and a zone equilibrium d,, above this separation zone s and below the level / column where the introduction of charge F takes place. In addition, the flow of liquid descending into the enrichment zone E is adjusted as a function of the pressure in column> so as to avoid the formation of a solid phase in this enrichment zone E.

The temperature of the load F is at most 5 ° K higher than the temperature causing the desublimation of one of these components at its nominal temperature.

To reach this temperature of the charge, the latter is precooled, for example by the refrigerant of the condenser C and / or the purified carrier gas D leaving the column. R, in a heat exchanger, not shown in the figures and designed so that excessive desublimation of one or more of the components of the charge F does not occur there and that the temperature of the latter at the column entry is kept constant.

Advantageously, this can for example be obtained either by an appropriate design of the exchanger with the possibility of short-circuiting part of the cooling or cooled gases, or by slightly heating the cold gases, the power of this heating being controlled by the temperature of the load at the entry of the column.

The temperature will be maintained at a value depending on the nominal concentration of the least volatile product.

In this regard, Figure 3 gives for example the sublimation temperature of xenon as a function of its partial pressure (Ref. Freeman & Halsey - The solid solution Kr-Xe from 90 ° K to, 120 ° K - The vapor pressure of A , Kr and Xe - J. Phys. Chem. 60, - / I · - 8 -

It should also be noted that the charge cooling system is designed so that it does not have a cold spot at a temperature below the above desublimation temperature.

The heating of the boiler or of the boiler A can be of a constant power making it possible to obtain, in the enrichment zone E, a gas flow compensated by a liquid flow such as the concentrations of these various components, particularly from xenon to near the level of introduction of the charge F, do not exceed their point of solubility in the liquid phase.

—6 —1

For example, for a load F of 1 kmole / h (278; 10 s ""} —3 -3 containing 2 10 kmole / kmole in xenon and 0.1.10 kmole / hmole in krypton in nitrogen, the flow rate must be at least greater than 3 to 6.6.10 kmole / hour to avoid the formation of a soli-nitrogen-krypton-xenon mixture under a pressure of 0.8 MPa.

This value does not take into account the technical imperfections of the column and is to be considered as an absolute minimum that is difficult to access.

Advantageously, the control of the separation zone s, which in fact constitutes the basis of the thermal regulation of the rectification column, takes place by detecting the temperature at a determined location in the enrichment zone E.

This regulation is based on the fact that the different krypton / nitrogen, krypton-oxygen or krypton-argon separations can be done on a limited number of equivalent theoretical plates. For example, one passes from a liquid argon-krypton mixture at 95% in argon to a mixture at 25% in argon representing a temperature variation close to 35 ° K in the space of two equivalent theoretical plates.

FIG. 4 illustrates this phenomenon for a reflux rate = 1 in the enrichment part E of the column working with a mixture of nitrogen, argon and krypton and with a mixture * of nitrogen and krypton.

The equation of the equilibrium curves in the liquid-vapor equilibrium diagram in Figure 4 can be written as follows: yx i- y "αι-χ“ N, / Ar 2 · 2> NPT âa Jfc,? ** at 1 (? / Ar 2 '2 = 11 for ^ / Ar aAr / Kr + 12 - * NJ? T de yAr = î9 * at ^' '= 3 for Ar / Kr The location of the separation zone s is determined by a temperature probe TC (see Figure 2) which is chosen so that the enrichment of the liquid in the lower zone of the column meets the required requirements for purity of xenon and krypton collected at n and that the area above the separation area s and indicated by the reference e is large enough to allow the column to balance with the load despite the fluctuations due to regulation.

Thus, it has been found, according to the invention, that the part of the enrichment zone E located below the probe re- -12 -10-.

tration in carrier gas less than 10 moles / moles in the liquid of the boiler A and a number of five equivalent theoretical plates between this probe TC and the place of the introduction of the load F allows a regular and stable control of the column rectification.

One acts on the momentary ratio of the quantity of calories and the quantity of frigories introduced into the column by varying the cooling at the top of the column by the condenser C. This cooling depends on the temperature and the physical state of the load F, heating of the boiler, thermal losses from the installation and accumulation of krypton and xenon in boiler A.

The regulation of the column cooling has been illustrated in FIG. 2 and is done by providing a stream of * refrigerant fluid L; supplying the condenser C, consisting of two parts L 'and L ". The flow rate of the first part L' has a set point LC varying linearly with the gas flow rate of the feed F and having a value slightly lower than that corresponding to the sum of the refrigeration losses and the heating power of the boiler when the feed flow rate is zero.

We therefore have L '= A.F. + B, since the heat balance is written: P, Te, Vap Pp'Te

L [& H 1 = F Uh_] * + W + V

Xi Γ P ^ Te.Liq Ρ ^ ,, Τ ^ ΔΗ = enthalpy variations: Joules / kilo moles -1 / L = Coolant flow: kilo moles s / /? / I * - 11 - W = Power of boiler heating Watts V = Refrigeration losses Watts P = pressure Pa

T = temperature ° K

indices L = coolant / e = boiling F = charge.

The second part L "has a flow rate adjustable as a function of the level of the separation zone s. Thus, thanks to this second part L", it is possible to carry out an additional injection of refrigerant fluid into the condenser C when, by insufficient flow of the part L1 / the krypton t buffer zone rises in the column above the TC probe.

In practice, the coolant stream is split into these two parts L 'and L "which add up before entering the condenser C.

Fractionation of the refrigerant can take place before entering or after condenser C. as shown in figure 2.

In any case, these two parts L and L "must pass through the condenser C, ie add up before entering the latter.

The thermal regulation, according to the invention, makes it possible to carry out the control. massigue by simply maintaining constant pressure in the column and equal to a predetermined set point at the outlet of the column without there being a risk of undesired accumulation or release, a / "> - 12 -

In the extraction process according to the invention, methane and oxygen accumulate above the buffer zone of "krypton T and are periodically removed by temporarily raising this buffer zone in the enrichment zone E until 'a short distance from the level where the introduction of the load F takes place. Thus these gases are entrained in the upper part of the column and evacuated at the top thereof.

This procedure keeps the quantity of methane and oxygen in the column at a low value independent of the quantity of noble gas concentrated in the boiler. This amount of oxygen and methane can also be reduced by choosing a type of column with low liquid retention.

The krypton or a mixture of krypton and xenon collected -12 in the boiler A can contain up to less than 10 moles / moles of the carrier gas, the nominal concentrations of krypton and xenon in the carrier gas, ie d. in charge F, is located —2 —3 respectively below 1..10 and 2.10 moles / moles and the ratio of the relative xenon concentrations relative to krypton covering the range from 0 to 50 moles / moles , while the concentrations of krypton and xenon in the gas D leaving the top of the column can be respectively lower than -7 -9 10 and 10 moles / moles, and this without prior enrichment in krypton of the load F.

The extraction process according to the invention advantageously applies to the separation of krypton, xenon or rare gases followed by a subsequent separation of these rare gases.

Another advantageous application is that of the separation of the krypton-xenon mixture of gaseous effluents from nuclear fuel reprocessing plants or nuclear reactors in order to isolate the radioactive isotope 85 of krypton from these effluents, optionally followed by krypton-xenon separation allowing the reduction of the volume of radioactive gases to be stored and possibly the production of xenon starting from a carrier gas in which its concentration is around 10,000 times the natural concentration in air.

As an essential advantage of the extraction process based on the thermal control according to the invention of the distillation column, mention may be made of the reduction in the cooling power of the condenser C and safety in the conduct of the rectification column.

In fact, by the fact that the regulation maintains the buffer zone or the krypton front in the enrichment zone E of the column, no component of the volatility charge greater than that of krypton accumulates in the boiler.

There is therefore no need for frigories used to condense part of the charge in the boiler without making column control more difficult.

From the safety point of view, it should be noted that the conduct of the distillation column, according to the invention, makes it possible to avoid an accumulation in the boiler A of products such as methane and oxygen, higher volatility '-14-.

ί * * to that of krypton and which may present explosion hazards.

As already mentioned above, especially oxygen is particularly dangerous in the krypton isotope 85.

As already indicated above, this process for extracting xenon and krypton from a carrier gas can advantageously be integrated into a process for the purification of effluents from nuclear reactors or nuclear reprocessing plants, with subsequent separation of the active krypton and xenon to store the former as waste or to market it as | radioactive product and market the second as a non-active product.

FIG. 5 represents a block diagram of such a circuit for purifying effluents from reprocessing plants.

Fuel is dissolved in a dissolver 1, releasing nitrogen oxides, iodine compounds, xenon, krypton, semi-volatile products, such as ruthenium tetra-oxide, etc., all entrained by a carrier gas, mainly air.

In the proposed scheme, part of the nitrous vapors are washed with water or diluted nitric acid in a washing column 2, in order to recover part of the nitric acid.

Part of the iodine is retained in a 3P device which is either a second washing column using an acid solution of mercuric nitrate or concentrated hot nitric acid, or an adsorption column comprising a bed of / 4 - 15 - sorbent such as a molecular sieve exchanged with silver or a catalytic support impregnated with a silver salt. The decontamination factor 3 at this level is 11 orders of 10.

The semi-volatile particles are stopped by physical or chemical adsorption on a fixed bed 4 constituted for example,. silica-gel or a mixture of silica-gel and earthy oxide.

The residual iodine is then stopped by chemical adsorption on a silver bed 5 producing a complementary decontamination factor 3 4 I of the order of 10 to 10.

After optional compression of the effluents, hydrocarbons, residual nitrogen compounds and oxygen are removed on a succession of catalytic beds or on a bed formed of successive layers of different catalysts or else formed of a mixture of catalysts. For example, hydrocarbons are transformed into water and carbon dioxide. Nitrogen oxides form nitrogen and water; by reaction with hydrogen or ammonia, and oxygen forms water by reaction with hydrogen.

At the outlet of this device 6, the residual contents of hydrocarbon, nitrogen oxide, oxygen and possibly of ammonia -6 are of the order of or less than 10 moles / moles of gas leaving.

The effluents are then compressed to a pressure of the order of 1 MPa and pass through an adsorption or drying unit 7 where the water, carbon dioxide and the pupnhipl traces 1ps fl'ammnniar and oxvde d are adaorbps on / d Λ -16.-

Part of the effluent having passed through a unit 8 of the adsorption device 7 then passes through the other unit 9 to regenerate it, as indicated by the arrow 10.

According to the invention, the part of the effluent having served * for this regeneration is recycled upstream of the device 6 used for the elimination of hydrocarbons and nitrogenous products, as indicated by arrow 11, after having passed through a cooler 12, intended to condense most of the water it contains, and in a device for removing carbon dioxide 13 and a device for removing ammonia or residual nitrogen oxides 14 L the effluent is dried in the device 7 to a dew point below 190 ° K, while the regeneration takes place at a temperature of the order of 200 ° C and at a pressure below the adsorption pressure.

This procedure has the great advantage of avoiding any risk of releasing into the atmosphere of krypton possibly coadsorbed with the water vapor in ùs. device 7 without requiring a complex system using the chromatographic nature of the adsorption on the molecular sieve.

The carbon dioxide stop device 13 is for example constituted by a washing column with calcium or sodium hydroxide, since, by the repeated recycling of carbon dioxide, a high decontamination is not necessary.

One could also provide a fixed bed of calcium hydroxide or any other suitable product. A / Λ * - 17 -

The device for removing ammonia and nitrogen oxides may for example comprise a bed of mordenite in hydrogenated form allowing the complete elimination of this ammonia or nitrogen oxides desorbed either by adding a fraction of the effluents still containing oxygen.

The main flow leaving the adsorption device 7 then enters, as indicated by arrow 15, in the rectification column R described above and already shown in Figures 1 and 2. This flow therefore forms the load F of the latter.

The carrier gas freed from krypton and xenon constitutes the distillate D. The mixture of xenon and krypton, collected in the boiler A, constitutes the heavy fraction n which is sent to a discontinuous distillation column 16 working at a pressure lower than column R.

In this regard, a pressure of 0.25 MPa is sufficient to avoid a solid phase of the krypton-xenon mixture. Thus, the transfer from column R to column 16 can be done by vacuum.

The purity of the krypton collected in the condenser 17 of the column 16 does not necessarily have to be very high, unless it is intended for particular applications such as medical applications.

On the other hand, the xenon harvested in the boiler 18 of column 16, can only contain minute traces of radioactive krypton. /> 'Λ * - 18 -

The relative volatility of krypton compared to xenon being close to 12 under a pressure of 0.2 MPa, we find, using the Mc method. Cabe and Thiele to a discontinuous rectification column, gu * liquid xenon can be obtained in the boiler of column 16 within _3. 10 moles krypton / moles xenon and gaseous krypton at the top of _3 this column 16 to 1.10 mole of xenon / mole of krypton with an ef column of 7 equivalent theoretical plates under a reflux rate of 100.

—8

Similarly, we obtain liquid xenon 1.10 mole of krypton / mole xenon in the boiler of the column - 8 16 and krypton at 1.10 mole of xenon / mole of krypton in the condenser thereof in 9 equivalent theoretical plates under a 3 reflux rate of 10.

It is understood that the invention is not limited to the embodiments described above and that many variants can be envisaged without departing from the scope of this patent.

Thus, the control or the detection of the separation zone s or of the buffer zone of krypton t can be done by any other means, such as a gamma ray detector.

Furthermore, the carrier gas can be of any kind allowing the application of the thermal regulation according to the invention.

In some cases, to act on the momentary ratio of the quantity of calories introduced into the column, it is possible, for example, to reduce the heating in boiler A. / 1 /

Claims (20)

1, - Method for extracting xenon and / or krypton from a carrier gas, in particular from a carrier gas comprising essentially ·: · also nitrogen or a mixture of nitrogen with oxygen and / or argon, by cryogenic distillation in a rectification column comprising at its bottom a heated boiler and at its top a condenser supplied with a cooling fluid, characterized in that a charge is introduced, formed of xenon and / or krypton and a carrier gas, in gaseous form and at a substantially constant temperature slightly higher than the temperature causing the desublimation of one of its components at its nominal partial pressure, at a determined level of the above column, in which the pressure is maintained at a substantially constant value greater than 0.4 MPa and in that in this column the level of the separation zone of the most volatile element to be extracted, such as krypton, and of the component is controlled the least volatile carrier gas by acting on the momentary ratio of the quantity of calories and the quantity of frigories introduced into the column; so as to maintain this separation zone, on the one hand, above a buffer zone of the most volatile element at extract, such as krypton, and, on the other hand, below an equilibrium zone between the liquid and gaseous phase itself located below the level of the column where the introduction of the above charge takes place , the flow of liquid descending into the zone below this level, called the enrichment zone, being adjusted as a function of the pressure of the column so as to avoid the formation of a solid phase in this enrichment area. 2. Method according to claim 1, characterized in that the pressure in the column is maintained at a value between 0.5 and 1 MPa, and preferably of the order of. 0.8 MPa. 3. Method according to either of claims 1 and 2, characterized in that the charge is maintained, during its introduction into the column, at a temperature of at most 5 ° K higher than the temperature causing the desublimation of one of its components at its nominal pressure. 4. Method according to any one of claims 1 to 3, characterized in that the charge is cooled to the above temperature slightly above the temperature causing the desublimation of one of its components at its partial pressure, by coolant formed by purified carrier gas collected at the top of the rectification column and / or the fluid used to condense part of the purified carrier gas at the top thereof. 5. Method according to any one of claims 1 to 4, characterized in that the liquid collected at the bottom of the column is heated so as to allow obtaining, in the aforementioned enrichment zone, a gas flow compensated by a liquid flow such as the concentrations of different components of the gas phase, particularly xenon in the vicinity of the place of introduction of the 4. • rf - 21 - 6. Method according to any one of claims 1 to 5 / characterized in that the above-mentioned separation zone is controlled by detecting the temperature at a determined location in the enrichment zone. 7, - Method according to any one of claims 1 to 6, characterized in that one acts on the momentary ratio _ of the amount of calories and the amount of frigories introduced into the column by varying the cooling at the top of the column. 8. Method according to claim 7, characterized in that it acts on the cooling of the column by providing a stream of refrigerant, ensuring cooling at the top of the column, consisting of two parts, the flow rate of the first part having a setpoint which varies linearly with the flow rate of the charge and which has a value slightly lower than that corresponding to the sum of the refrigeration losses and the heating power at the boilers of the column when the charge flow rate is zero , the flow ! of the second part being adjustable as a function of the level of the separation zone or of the abovementioned buffer zone. 9, - Process according to any one of Claims 1 to 8, characterized in that a rectification column is used in which the above-mentioned separation zone is located at a distance from the level where the introduction of the charge representing takes place on the order of three to six equivalent theoretical plates, and at a distance from the boiler on the order of six y / y? / to twelve equivalent theoretical platforms. // - 22 - t «* 10. A method according to claim 9, characterized in that the separation zone is located at a distance from the level where the introduction of the charge representing the order of cim equivalent equivalent plates takes place and at a distance from the boiler. the order of ten equivalent theoretical platforms. 11. Method according to any one of the claims? there ΙΟ, characterized in that the momentary ratio of the quantity of calories and the quantity of frigories introduced from the column is periodically adjusted so as to temporarily elevate the above buffer zone near the level where the charge is introduced into the column. 12. Method according to any one of claims 1 to 11, characterized in that a charge is used whose concentration of krypton and xenon in the carrier gas is -2 -3 less than 1.10 and 2.10 mole / mole of carrier gas. 13. Method according to any one of claims 1 to 12, characterized in that a charge is used in which the relative concentrations of xenon with respect to krypton are in the range from 0 to 50 moles / moles. 14. Method according to any one of claims 1 to 13, characterized in that the concentrations of krypton and xenon in the carrier gas leaving the top of the -7 -9 column are reduced below respectively 10 and 10 moles / moles of the carrier gas. 15. A method according to any one of claims 1 to 14, characterized in that krypton or a me- 23 -, "" is extracted. 15.- A method according to any one of claims 1 to 15 / characterized in that a gaseous effluent from a reprocessing of nuclear fuel or nuclear reactors is used as the feed in order to separate the radioactive isotope 85 from krypton of the effluent and in that this separation is optionally followed by a separation. krypton-xenon. 17. Method for extracting xenon and / or krypton from a carrier gas by cryogenic distillation as described above or resulting from the attached drawings. 18. Rectification column used for the implementation of the method described above. 19. Krypton and / or Xenon obtained by the implementation of the process described above. 20. A process for the treatment of gaseous effluents from the reprocessing of nuclear fuel, comprising washing of nitrous vapors, separation of iodine and semi-volatile products, elimination of hydrocarbons, residual nitrogen compounds and oxygen, the adsorption of water, carbon dioxide and possibly traces of ammonia and nitrogen oxides by passing the effluent through an ad-sDrption unit while another unit adsorption is regenerated by part of the effluent having undergone the adsorption treatment, characterized in that the part of the effluent having been used for the above-mentioned regeneration is recycled upstream of the elimination of hydrocarbons, of residual nitrogen and oxygen compounds, after condensation of the water contained therein. / * '”......' ί I”. »* * F - 24 - t 21. The method of claim 20, characterized in that gu1on dries the effluents during the above-mentioned adsorption treatment to a dew point below 190 ° K, after having been compressed at a pressure of the order of 1 MPa, and in that the regeneration is carried out at a temperature of the order of 200 ° C. and at a pressure lower than the pressure y of adsorption. 22. Process for the treatment of gaseous effluents from reprocessing of nuclear fuel as described above or shown in the accompanying drawings. I Drawings: ·· £ ............ n'anohes ....... ccni: ίκ: r S »- - -, * - i j- y j c a *. - I ................ c.1 ·· 7. "-I ® I llVf -î-r. ·" ·· - H rnvcuù I L.Û * / d / f