IL32398A

IL32398A - Method and device for the purification of heavy water

Info

Publication number: IL32398A
Application number: IL32398A
Authority: IL
Original assignee: Commissariat Energie Atomique
Priority date: 1968-06-21
Filing date: 1969-06-15
Publication date: 1972-08-30
Also published as: BE734923A; CA919389A; DE1931414A1; LU58842A1; DE1931414B2; ES368667A1; IL32398A0; GB1247590A; SE353618B; NL6909562A; CH511767A; JPS495160B1; FR1580313A

Description

Method and device for the purification of heavy water COMMISSARIAT A L'EHERGIE ATOMIQUE C. 30699 The invention relates to a method of purification of heavy water during use in a nuclear reactor or pile for the purpose of freeing the heavy water from its hydrogen and tritium content. The invention is also concerned with a device for carrying out said method.

The method in accordance with the invention is characterized in that a continuous flow of heavy water is diverted from the nuclear reactor or pile and that the proportion of hydrogen and of tritium contained in the diverted fraction is lowered by means of an isotopic exchange reaction with deuterium gas, that the deuterium gas thus enriched in hydrogen and tritium is subjected to fractionation by chromatography, preferably on a solid having a base either of palladium or of a palladium alloy, and that the deuterium gas which is freed from hydrogen and tritium is recycled towards the isotopic exchange reaction.

Apart from this main arrangement, the invention comprises a number of other arrangements which are preferably employed at the same time and which will be described in greater detail hereinafter.

The complementary description which now follows and the accompanying drawings will in any case serve to gain a clear understanding of the invention and are given primarily by way of indication.

In these drawings, Figs. 1 to 5 show diagrammatically the main portions of the apparatus in accordance with the invention.

The heavy water of a nuclear reactor is progressively contaminated during its industrial utilization, on the one hand as result of introduction of light water and, on the under the action of neutrons on the deuterium atoms.

The introduction of light water has the effect of lowering the reactivity of the reactor and tritium build-up exposes reactor operating personnel to major health hazards when the permissible dose is exceeded. In order to gain a clear idea, it can be noted that the quantity of light water which leaks into a reactor containing between 50 and 100 tonnes of heavy water can exceed 50 kg and that, in a power reactor containing 80 tonnes of heavy water and having a neutron flux of 5 x n cm2/sec, the equivalent of approximately 10 to 20 milliliters of tritiated water can be formed per month.

It has already been proposed to remove light water from heavy water by fractional distillation. However, it is in that case necessary to resort to the use of a considerable number of theoretical plates by reason of the extremely low separation factor between heavy water and light water which is of the order of 1.04.

By reason of the fact that the separation factor is even lower, namely of the order of 1 .01 in the case of tritiated water, it is common practice to allow the tritiated water to build up until it reaches the saturation concentration at which the rate of disappearance by radioactive decay is equal to the rate of formation. However, the saturation concentration is several times higher than that which is compatible with safety conditions, thereby entailing the need to adopt costly protective measures.

In order to free the heavy water which is being use in a nuclear reactor or pile from the hydrogen and tritium contained therein, it is intended according to this invention reactor and to lower the proportion of hydrogen and of tritium contained in the diverted fraction by means of an isotopic exchange reaction with deuterium gas, whereupon the deuterium gas thus enriched in hydrogen and in tritium is subjected to fractionation by chromatography, preferably on a solid having a base either of palladium or of a palladium alloy, with the result that the deuterium gas is partially freed from hydrogen and from tritium and can advantageously be recycled towards the isotopic exchange reaction.

The isotopic exchange process can be represented by the following two principal reactions : (HDO) -;· (D2) * (D20) + (HD) (TDO) -;· (D2) ^ (D20) + (TD) It is known that the respective equilibrium constants of these two reactions, namely : D20] X HD] 1 " [HDO] X [D2] and are practically equal, within the range of concentrations under consideration, to the separation factors which are defined as follows : _ atomic concentration of H in deuterium 1 atomic concentration of H in heavy water - atomic concentration of T in deuterium 2 ~ atomic concentration of T in heavy water It is also known that the values and c&2 are different from 1 and are placed on each side of 1 , being always greater than 1 whereas a2 is always smaller than 1 ; this means that, at the time of equilibration of deuterium gas and of heavy water containing small quantities of concentration of hydrogen and a lower concentration of tritium than heavy water. Since it is also known that the separation factors usually come close to 1 when the temperature of isotopic exchange equilibrium increases, it can be concluded that action is produced on the two equilibria in opposite directions by means of an increase in temperature.

By producing action of the temperature of the isotopic exchange reaction, it is thus possible according to requirements to promote the transfer of one of the isotopes towards the deuterium at the expense of the transfer of the other isotope. In other words, the transfer of tritium is promoted by increasing the temperature and the transfer of hydrogen is promoted by lowering the temperature .

In order to start and accelerate the isotopic exchange reaction (which does not tend to start-up spontaneously), recourse can be had either to solid catalysts such as, for example, platinum or palladium on an inert support, ion oxide or nickel deposited on chromium oxide, or alternatively to a thermal activation process.

It is apparent that the choice, between these two solutions depends not only on economic considerations but also depends on the temperature zone' at which it is desired to operate in order to eliminate preferentially either one isotope or the other, taking the foregoing into account | the choice also depends on the respective rates of introduction of said isotopes into the heavy water of the reactor.

In order to give a clear idea, it is pointed out that, by means of the above-mentioned catalysts, the operation may be carried out at temperatures of the order of 80 to 400° C and that, by resorting solely to thermal activation, 1200"C. In the case last mentioned, the reaction may be assisted by increasing the area of contact of the gas with the walls, for example by means of inert packings.

In order to carry out this method, recourse can be had to the apparatus which is shown diagrammatically in Fig.l and which comprises an isotopic exchange reactor 1 of a type known per se (for example of the cocurrent type) towards which the heavy water which is continuously withdrawn from the reactor is directed via a pipe 2 after having been vaporized and freed from the gases contained therein in solution by means of known devices which are not illustrated.

Deuterium gas is admitted into said isotopic exchange reactor via a pipe and the heavy water which is in contact with said gas is partially freed 'from the hydrogen and tritium, contained therein.

At the outlet of the isotopic exchange reactor, the heavy water whose hydrogen and tritium content has been lowered is recycled to the nuclear reactor through a pipe after having been condensed and the deuterium whose hydrogen and tritium content has been increased is directed via a pipe 5, after drying and purification if necessary, by means of devices known per se which have not been illustrated, towards an installation within which the deuterium is subjected to the above-mentioned separation by chromatography on a solid having a palladium base.

This chromatographic process results in the establishment of an equilibrium of sorption on the palladium-base solid and can be carried out either in a mobile-bed column or in a fixed-bed column.

During this chromatographic process, the sorption according to the equilibrium whereby the equilibria 2 KD * H2 + D. 2 DT ^ D0 T, between the EL-,! DH and D≥ species as well as the D2> DT and T2 species are established at each moment, with the result that the isotopic mixture behaves as a ternary H-D-T mixture. Since the values of the separation factor are very high, namely of the order of 2 between H and D and 1.4 between D and T, the achievement of the isotopic equilibrium is rapid and the separation efficiency is high.

By reason of the fact that the affinities of the different isotopes of hydrogen for palladium are classified in the increasing order T - D - H, the tritium is concentrated at the top of the column whilst the hydrogen is concentrated at the bottom of the column.

In the case of the embodiment which is illustrated in Fig. 1, an installation of the mobile bed type is shown diagrammatically at 6. An installation of this type which is known per se comprises a column through which the gas to be fractionated is circulated upwards whilst a solid granulated mass such as porous alumina containing palladium is circulated downwards within the column. At the foot of the column, the solid is extracted, the gas which is trapped within said solid being desorbed by heating, for example, and being passed up the column whilst the regenerated solid is returned to the top of the column via a loop R. At the top of the column, said solid is again contacted with the upflowing gas, absorbs said gas and returns down the column. of two sections A and B but it remains apparent that use can be made of two separate columns.

A small quantity of deuterium highly enriched in tritium is continuously withdrawn from the top of section A and a small quantity of deuterium highly enriched in hydrogen is continuously withdrawn from the bottom of section B. The respective length of the sections A and B governs the concentration of the products which can be collected therein.

The greater part of the deuterium which is thus partially freed from its tritium and hydrogen content leaves the installation 6 through a pipe which is in fact the above-mentioned pipe 3 in the case of the present embodiment and is then returned to the isotopic exchange reactor 1, The pipe 5 for the admission of deuterium which is enriched in tritium and hydrogen is shown in Fig. 1 at the same level as the inlet pipe 3. However, it is possible to place the pipe 3 at another level which depends on the relative extraction rates which are desired for the tritium or for the hydrogen. It will be noted that, by placing the level of the pipe 3 above the level of the pipe 5» the extraction of hydrogen is assisted at the expense of that of tritium and conversely.

It is clearly understood that, in order to make up for the loss of deuterium which is caused by removal of the quantities extracted in the installation 6, provision must be made for a continuous supply of fresh deuterium, for example through a pipe 7. Said fresh deuterium can be formed by radiolysis within the nuclear reactor and subjected to a purification process prior to utilization.

The two fractions of deuterium which are respective-ly enriched in tritium and in hydrogen and respectively with bottom of said column via the pipe 9 can evidently be treated in turn by means of a known isotopic enrichment process for the purpose of recovering part of the heavy water in the second case and for the purpose of extracting part of the tritium in the first case . The tritium-enriched deuterium can also be retained, if necessary after conversion to heavy water, until partial disappearance of the tritium as a result of radioactive decay.

In the case of the apparatus which is shown dia-grammatically in Fig. 2, the isotopic exchange reactor 1 has been replaced by an assembly comprising three stages 10, 11 and 12 connected in series. The vaporized heavy water is admitted to stage 10 via a pipe 13, then passes through the stages 11 and 12, then returns to the nuclear reactor via a pipe 1 . On the other hand, the deuterium is admitted from the separation installation (which is not illustrated but is similar to the installation 6 of the equipment unit of Fig, l) via a pipe 15 (which is similar to the pipe 3 of the apparatus of Fig. 1) and enters into isotopic exchange reac-tion with the heavy water successively within the stages 12, 11 and 10 along the path shown in Fig. 2, then returns towards the chromatographic installation via a pipe 16. The countercurrent contacting which is thus achieved improves the efficiency of the exchange.

As in the case of the equipment unit which is illustrated in Fig. 1, the devices which are intended to condense the heavy water or to re-evaporate this latter at the inlet and at the outlet of the assembly of stages 10, 11 and 12 or between these latter have not been shown.

It would also be possible to contemplate other ■4 be so arranged that the deuterium is passed through the three stages 10 , 11 and 12 in series whilst the heavy water passes through in parallel or conversely.

Should it be desired to give special preference to the extraction of hydrogen rather than to the extraction of tritium, the equipment in accordance with the invention can be so arranged that the countereurrent isotopic exchange is carried out in a reaction vessel or column which is fitted alternately with bubble plates on which the "liquid heavy water / vaporized heavy water" exchange is carried out and with catalyst beds on which the "vaporized heavy water / gas" exchange operation is carried out. In fact, in this case, by reason of the presence of the liquid heavy water, the exchange process is limited to the zone of low temperatures of the order to 100 to 150°C.

It has already been mentioned earlier in the description of the apparatus of Fig. 1 that the extraction of hydrogen was improved by placing the pipe 3 above the pipe 5 but that the extraction of tritium was thereby lowered and conversely.

In order to overcome this disadvantage, the installation 6 of Fig. 1 can be replaced as shown in Fig. 3 by two separate columns 17 and 18 of the mobile bed type which is again constituted by a palladium-base granular solid.

Each column has an enrichment section and a depletion section as designated respectively by the references 19 and 20 in the case of the column 17 and the references 21 and 22 respectively in the case of the column 18. Furthermore, each column operates in the manner which was described earlier in connection with Fig. 1 and comprises a pipe for The return pipes of the columns 17 and 18 are designated respectively by the references R1 and R2„ Thus, the deuterium loaded with tritium and hydrogen which is derived from the isotopic exchange reactor (not shown in Fig. 3 ) is fed into the column 17 through a pipe 23 . At the head of the depletion section 20 of the column 17 , a small quantity of deuterium highly enriched in tritium is withdrawn via a pipe 24 and the greater part of the deuterium which is partially freed from tritium but still contains practically the entire quantity of hydrogen is withdrawn through a pipe 25 at the bottom of the enrichment section 19 of the column 17 . Said deuterium is fed into the column 18 as shown in Fig. 3 and a small quantity of deuterium highly enriched in hydrogen is withdrawn through a pipe 26 from the bottom of the depletion section 22 of said column 18 whereas the greater part of the deuterium which is partially freed from tritium and from hydrogen is withdrawn at the head of the enrichment section 21 of the column 18 through a pipe 27 which is in fact the pipe 3 of Fig. 1.in the case of the present embodiment, and this latte ^is . then recycled to the isotopic exchange reactor.

Contrary to the preceding embodiment, in order to carry out first the separation of the hydrogen and then the separation of the tritium, recourse may be had to the equipment unit which is shown diagrammatically in Fig. and which also replaces the installation 6 of Fig. 1 .

This equipment unit comprises two columns 28 and 29 having respectively an enrichment section and a depletion section (as designated by the reference numerals 30 and 31 in the case of the column 28 and 32 and 33 in the case of the for the return of the regenerated solid and the column 29 comprises a similar pipe R^.

The deuterium derived from the isotopic exchange reactor (not shown) is fed into the column 28 through a pipe 34, a small quantity of deuterium highly enriched in hydrogen-being collected through a pipe 35 at the top of the depletion section 31 of said column. The greater part of the deuterium which is partially freed from its hydrogen content but still contains practically the entire quantity of tritium is with-drawn from the top of the enrichment section 0 of said column by way of a pipe 36. Said deuterium is fed into the column 29 through the pipe 36 and a small quantity of deuterium highly enriched in tritium is withdrawn from the bottom of the depletion section 33 of said column through a pipe 37 whereas the greater part of the deuterium which is partially freed both from hydrogen and from tritium is with-drawn from the bottom of the enrichment section 32 by means of a pipe 38 which is in fact the pipe 3 of Fig. 1 in the present embodiment, this latter being then returned ...to -the isotopic exchange reactor.

In the foregoing, the chromato raphic installations employed were of the mobile bed type.

However, as has been mentioned earlier, the chromatographic process can also be carried on fixed-bed columns. An installation of this type is shown diagram-matically in Pig. 5» in which the reference 39 designates a column which is packed with an inert granular mass which retains a predetermined quantity of palladium. This column can either be heated or cooled by means of a device 40 which is so designed that action may be produced at will on only column 39.

At the outset, said column does not contain hydrogen and is cooled, for example, to room temperature. The gaseous mixture derived from the isotopic exchange reaction is introduced continuously through a pipe 41. The mixture is retained on the palladium of the packing and thus saturates this latter at successive points starting from the inlet whilst the gas which was initially present in the interstitial volume of the column passes' out through a pipe 42. When a predetermined fraction of the column which is a function of the desired enrichment factors is saturated (in which case a "band" of absorbed hydrogen is formed), the supply of gas through the pipe 41 is interrupted and the column is heated progressively to approximately 200°C from the top of the column downwards. This heating causes desorption of the hydrogen at the tail of the band ; this desorbed hydrogen passes through the column (downwards as shown in Pig. 5>) and is again absorbed by the palladium at the head of the band. This band therefore passes through the column.

When the band reaches the end of the column (namely at the bottom of Pig. 5), the hydrogen begins to leave the column progressively as the heated zone extends towards this end. By reason of the different affinities of the three isotopes of hydrogen for palladium, a fractionation occurs and consequently gives rise to the successive release of · - a head fraction which is enriched in tritium, - a central fraction constituted by deuterium which is depleted both in tritium and in hydrogen, - a tail fraction which is enriched in hydrogen, In order to carry out the separation of these with a timing system which is capable of directing these fractions respectively and successively to three pipes designated by the numerals 43, 44 and 45 after first directing the gas which was initially present to the pipe 42.

The device C can be controlled according to the indications supplied by a continuous effluent-gas analyzer based, for example, on the measurement of thermal conductivity of the gas and on its radioactivity (in the case of tritium).

The central fraction is recycled to the heavy water - deuterium isotopic exchange installation so as to be reloaded with hydrogen and tritium.

. The small quantity of hydrogen-enriched deuterium which remains on completion of the operation within the interstitial volume of the column 39 may be swept if necessary by an inert gas which is fed in through a pipe 46 and can be collected with the tail fraction. On completion of the operation, the column is cooled and ready for a further operation.

In an alternative embodiment, it is possible to split up the column 39 into a number of columns which may be heated or cooled separately.

Whichever embodiment is adopted, the methods and devices for the purification of heavy water which are thus made available and the characteristics and operation of which have become' sufficiently clear from the foregoing to call for no extended description provide many advantages over comparable methods and devices of the prior art, especially in regard to convenience of operation.

The advantages of the method in accordance with the invention in which the separation of hydrogen isotopes is f heights of column required for a same separation process are much smaller.

When the method of distillation of heavy water is employed, the elementary liquid-vapor separation factor between the trxtiated and deuterated species is of the order of 1 .01 ; this value is so small that it requires several hundred theoretical plates. Despite the existence of columns having high degrees of efficiency which permit heights of theoretical plate of only a few centimeters, the method is highly unfavorable from an economic standpoint.

When making use of the heavy water - deuterium exchange process combined with a deuterium distillation process as described in French patent N° PV 1,526,867, the performances given hereinafter are commonly achieved. The extraction coefficient of tritium in the heavy water - deuterium exchange process is 0.8 in three catalysis stages ; in other words, of the tritium contained in the water which passes out of the reactor are transferred to the deuterium. The distillation of this deuterium in order to obtain a depletion of 100 , that is to say in order that the deuterium which is withdrawn from the top of the column and returned to the catalytic exchange should contain only 1/ 100 of the feed tritium, calls for 25 theoretical plates by reason of the value of the separation factor of approximately 1 .2 . In other words, the depletion section comprises one to two meters of column according to the efficiency of this latter. On the other hand, since the required enrichment factor is usually 1000 or may even be higher, the enrichment section must comprise approximately ten meters of column.

In the case of the process in accordance with the process is combined with a mobile-bed chromatography on palladium-containing masses for the fractionation of the deuterium, the performances are as follows : the extraction coefficient of the tritium in the catalytic exchange process being again 0.8 as in the previous case, the depletion of the withdrawn product in respect of a factor of 100 requires only 14 theoretical plates by reason of the higher value of the separation factor (approximately 1.4) ; since the column efficiency is higher, only a few decimeters of columns are required in order to attain this depletion factor of 100, For the same reason, the enrichment section only comprises two or three meters of column.

Moreover, the method in accordance with the present invention does not call for any liquefaction of deuterium, thereby making the method more reliable and resulting in higher economic performance .

As has in any case been brought out' by the foregoing, it must be clearly understood that the invention is not limited in any sense to those modes of application or forms of construction of its various parts which have been more especially indicated but extends on the contrary to all alternative forms and especially to the mode of execution in which the chromatographic process is carried out on a physical adsorbent at low temperature.

Claims

What we claim is :

1. , A method of purification of heavy water during use in a nuclear reactor for the purpose of freeing the heavy water from its hydrogen and tritium content, characterized in that a continuous flow of heavy water is diverted from said nuclear reactor, that the proportion of hydrogen and of tritium contained in the diverted fraction is lowered by means of an isotopic exchange reaction with deuterium gas, that the deuterium gas thus enriched in hydrogen and tritium is subjected to fractionation by chromatography and that the deuterium gas which is freed from hydrogen and tritium is recycled towards the isotopic exchange reaction.

2. , A method in accordance with claim 1, characterized in that the deuterium gas enriched in hydrogen and in tritium derived from the isotopic exchange reaction is introduced at an intermediate point of a column through which a granular solid is circulated, in that deuterium highly enriched in tritium is collected at the top of said column and a small quantity of deuterium highly enriched in hydrogen is collected at the bottom of said column, that the deuterium which is freed from tritium and from hydrogen is recycled to the isotopic exchange reactor by way of a pipe located at the same level as the pipe for the admission of deuterium to be purified into the column and that the granular solid is desorbed by heating prior to re-introduction at the top of the column.

3. , A method in accordance with claim 1, characterized in that the deuterium gas enriched in hydrogen and in tritium derived from the isotopic exchange reaction is introduced at an intermediate point of a first column comprising an enrichment section and a de letion section the introduction bein small quantity of deuterium highly enriched in tritium is withdrawn at the head of the depletion section and the greater part of the deuterium which is freed from tritium is withdrawn at the bottom of the enrichment section so that it 'CaiLJhej ibe passed into a second column comprising an enrichment section and a depletion section, the introduction being carried out at the head of the depletion zone, and that a small quantity of deuterium highly enriched in hydrogen is withdrawn from the bottom of the depletion section of the second column and the greater part of the deuterium which is freed from tritium and from hydrogen is withdrawn from the head of the enrichment section of the second column and recycled to the isotopic exchange reactor.,

4. A method in accordance with claim 1, characterized in that the deuterium gas which is enriched in hydrogen and in tritium derived from the isotopic exchange reaction is introduced at an intermediate point of a first column comprising an enrichment section and a depletion section, the introduction being carried out at the head of the depletion section, and that a small quantity of deuterium highly enriched in hydrogen is withdrawn from the bottom of the depletion section of the first column and the greater part of the deuterium which is partially freed from its hydrogen content is withdrawn from the top of the enrichment section of the first column and directed into a second column comprising an enrichment section and a depletion section, the introduction being carried out at the head of the enrichment zone, and that a small quantity of deuterium highly enriched in tritium is withdrawn at the top of the depletion section of the second column and the greater part of the deuterium which is freed from hydrogen and tritium is withdrawn from the bottom of the nr m t c o of o to the isotopic exchange reactor,,

5. A method in accordance with claim 1, characterized in that the deuterium gas which is enriched in hydrogen and in tritium derived from the isotopic exchange reaction is introduced at the top of a column containing a fixed granular solid, that said column is heated progressively to a temperature of the order of 200 °C starting from the top of said column and that there is collected at the foot of the column successively a tritium-enriched head fraction, a central fraction constituted by deuterium depleted in tritium and in hydrogen and a tail fraction enriched in hydrogen.

6. A method in accordance with claims 1 to 5, characterized in that the tritium-enriched deuterium fraction is subjected to an isotopic enrichment process which is known per se for the purpose of extracting part of the tritium.

7. A method in accordance with claims 1 to 5, characterized in that the fraction of deuterium which is enriched in hydrogen is subjected to a method of isotopic enrichment which is known per se for recovering part of the heavy water.

8. A method in accordance with claim 1, characterized in that the granular solid is a solid having a base of palladium or a palladium alloy.

9. A method in accordance with claim 8, characterized in that the granular solid is constituted by porous alumina containing palladium.

10. A device for the practical application of the method in accordance with claims .1 to 9, characterized in that it comprises an isotopic exchange reactor for withdrawing by means of a stream of deuterium gas the hydrogen and the tritium from the heavy water which is continuously conveyed thereto, and an installation for fractionation by chromato deuterium gas.

11. A device in accordance with claim 10, characterized in that the installation for fractionation by chromatography is constituted by a column filled with a granular solid and comprising pipes located substantially at the same level for the introduction of deuterium enriched in tritium and in hydrogen derived from the isotopic exchange reactor and for the discharge of deuterium freed from tritium and hydrogen to the isotopic exchange reactor, a pipe located at the top of 0 said column for the extraction of deuterium which is very ■ .. highly enriched in tritium, a pipe located at the bottom of said column for the extraction of deuterium which is very highly enriched in hydrogen and a pipe for recycling the solid to the top of the column.

12. , A device for the practical application of the method in accordance with claim 10, characterized in that the installation for fractionation by chromatography is constituted by a first column through which a granular solid is circulated and comprises a pipe for the admission of deuterium 0 enriched in tritium and in hydrogen, a pipe located at the top of said column for the extraction of deuterium which is very highly enriched in tritium, a pipe located at the bottom of said column for the discharge of deuterium which is partially freed from tritium and a pipe for the re-introduction of the solid at the top of the column, by a second column comprising a pipe for the admission of deuterium which is partially freed from tritium, a pipe located at the bottom of said column for the extraction of deuterium which is very highly enriched in hydrogen, a pipe located at the top of Q said column for the discharge of deuterium which is freed from tritium and from hydrogen and a pipe for the re- *

13. A device in accordance with claim 10, characterized in that the installation for fractionation by chromatography is constituted by a first column through which a granular solid is circulated, comprising a pipe for the admission of deuterium which is enriched in hydrogen and in tritium, a pipe located at the bottom of said column for the extraction of deuterium which is very highly enriched in hydrogen, . a." pipe located at the top of said column for the extraction of deuterium which is partially freed from hydrogen, and a pipe for the re-introduction of the solid at the top of the column, by a second column comprising a pipe for the admission of deuterium which is freed from hydrogen, a pipe located at the top of said column for the extraction of deuterium which is very highly enriched in tritium, a pipe located at the bottom of said column for the extraction of deuterium which is freed from hydrogen and from tritium and a pipe for the re-introduction of the solid at the top of said column.

14. A device in accordance with claim 10, characterized in that the installation for fractionation by chromatography is constituted by a column containing a fixed granular solid and provided with means for heating or cooling said column on one or a number of portions of its length, said column being provided at one extremity with a pipe for the admission of deuterium enriched in hydrogen and tritium and at the other extremity with pipes for collecting the tritium-enriched head fraction, the central fraction constituted by deuterium which is depleted in tritium and in hydrogen, the tail fraction which is enriched in hydrogen and the gas which was initially present in the column.

15. A method of purification of heavy water in accordance with claim 1, substantially as hereinbefore ,-ί,

16. A device for carrying out the method of purification of heavy water in accordance with claim 1, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings „ For the Applicants B. 3229-3