Table 1 The aforementioned are indicative of the greater the enthalpy associated with the primary isotope the greater the bond strength with oxygen of hydrated species down the series will be i.e.: O-H < O-D < O-T. The manifestation of these primary isotope effects on the isotopologues of hydrogen have long be used to as a means of their selective enrichment or isolation, see e.g. US20060016681A1 and US20050279129A1.

Given the known thermodynamic differences between hydrogen isotopologues, the inventors has found, without being bound by theory, that from the dissolution of an inorganic salt arranged for providing a stable hydrate, in a mixed solvent of HTO and H₂0, the triturated species will preferentially precipitate, and thus the preparation of any stable hydrate, can be utilized to immobilise tritium and also to selectively and preferentially reduce the tritium concentration within tritium contaminated aqueous solution.

Since the interspatial distance of the water of crystallisation in a hydrate typically is more compact than in the crystalline lattice of ice crystals made of ordinary water, there is an associated lattice energy in the form of heat which needs to be provided to release the water of crystallisation.

The inventor conjectures that as water of crystallisation is more strongly held in a deeper ^entropy well' due to this close packing in the crystalline lattice, hydrated species that exhibit the propensity to form retained water of crystallisation, when crystallised from waters containing mixed isotopes of hydrogen are more likely to discriminate in favour of the more thermodynamically stable hydrate and thus preferentially precipitate the species with the heavier isotope such as the tritiate rather than the deuterate, and the deuterate rather than the hydrate.

Even though such discrimination might be subtle, it is still sufficient to provide a system wherein the heavier isotopes may be enriched in the water of crystallisation of a hydrates species relative to the water in the aqueous solution from which it is isolated. Also, given the advantages offered by the higher lattice energy of water of crystalline relative to solid ice, the process herein will be more discerning than separation of isotopologues of water HTO, DHO and H₂0 by selective crystallisation through freezing alone.

Accordingly, the present invention utilizes the ability of certain chemical inorganic salts to form stable hydrates, wherein the T₂0 is retained as water of crystallisation. The at least one inorganic salt can in principal be any salt capable of forming a stable hydrate incorporating the tritium as water of crystallisation. It is however preferred that the salt is a borate, e.g. a an alkali-metal borate and/or an alkaline earth metal borate, since borates are readily available, providing stable hydrates at a low cost and at a high efficiency. The Alkali-metal borate is preferably a sodium borate, preferably anhydrous borax or sodium borate pentahydrate, and the alkaline earth metal borate is preferably selected from the group comprising calcium borate, calcium tetraborate and calcium metaborate.

That the borates are a preferred is also due to the fact that they can retain a high degree of their original mass as water of crystallisation. As an example can be mentioned that the borax pentahydrate (sodium borate pentahydrate) can hydrate to its decahydrate retaining about 30.9% of its original mass as water of crystallisation. Similarly, anhydrous borax (sodium borate) can retain 89.5% of its own weight as a stable solid.

Borax decahydrate is easily formed by exothermic hydration see (i) and (ii) and is generally described as Na₂B₄0₇ · 10H₂O .

However, it is better chemically described as ( Na, [B.CL (OH) J · 8H,0, since borax contains the [B₄(X (OH) J^2~ ion.

Na₂B₄0₇ - 5H₂0_[S0LID] + 5 H₂0_[LIQUID] ^ Na₂B₄0₇ · 10H₂O_[SOLID]

ΔΗ Hydration - 89.45 kJmol

(ii) Na₂B₄0_7[SOLID] + 10 H₂0_[LIQUID] ^ Na₂B₄O₇-10H₂O_[SOLID]

ΔΗ Hydration - 1, 403 kJmol^-1

(iii) Na₂B₄0_7[SOLID] + 10 H₂0_[LIQUID] ^ Na₂B₄0₅ (OH)₄.8H₂0_[SOLID]

Borax decahydrate further has the benefit that it is stable to 60.8°C, whereupon it can melt with loss of water and revert to its pentahydrate. However, in a closed system or environment, where there is no loss of water, on subsequent cooling it will revert back to its decahydrate.

From the above it is apparent that any borate compound or blend thereof, with hydration level of less than 1:10, e.g. Na₂B₄0₇ to water, whether utilized solely or utilized as a component within a mixture may act as a sequestering agent for contaminated water by adsorbing the contaminated water into its crystalline structure as it reverts to its decahydrate or indeed any other higher hydration level than its original hydration level.

It will be understood that the at least one salt can be one, two, or a mixture of several salts, the only requirement being that the salt is capable of forming stable hydrates, retaining tritium as water of crystallisation.

The same chemistry as above can be used to strip borates from solution by addition of calcium ions, e.g.: 2Na⁺ + [B₄0₅ (OH) J²-_[solu] + 2Ca²⁺ + 2Cr_[S0LU] + xsH₂0

Ca₂B₄0₇ - 6H₂0_[SOLID] + 2NaCl_[S0LU]

Similarly alkali-metal and/or an alkaline earth metal boron compounds, such as calcium borate, calcium tetraborate and calcium metaborate can react with water to form highly stable and insoluble hydrates:

Ca₃(B0₃)₂ + 6H₂0 -» Ca₃ (B0₃)₂· 6H₂0

Ca,B,0.. + 5HO -» Ca,B,0. -5H.0

CaB₃0₇ + 6H₂0 -> CaB₃0₇ - 6H₂0

Ca(B0₂)₂ + 2H₂0 -> Ca (Β0₂)₂·2Η₂0

NaCaB₅0₆ (OH)₆ + 5H₂0 -> NaCaB₅0₆ (OH)₆ · 5H₂0

Crystallization and precipitation of borates can be carried out quickly and are thus preferred over other types of inorganic salts. In this respect the low solubility of the alkali earth borate compounds slows the progress of the reaction and thus mitigates the need for cooling required by their alkali metal analogues, by a reduction in the amount and rate of release of the consequential heat of hydration.

Conventionally, Ordinary Portland Cement (OPC) has been used to embed radioactive waste, however even though the initial rate of hydration being fast the rate of hydration of OPC slows after the first few hours and days, and it takes circa 28 days to hydrate to 80% of its potential capacity, equating to immobilisation of only 20% of its original anhydrous mass. In comparison, anhydrous borax (sodium borate) can, as mentioned earlier, retain 89.5% of its own weight as a stable solid, thereby providing an efficient way of incorporating large amounts of among others, tritium, as water of crystallisation.

Anhydrous borax costs about $700-900 per tonne, whereas comparative OPC costs are $500-700 per tonne, but due to the higher water retention in the anhydrous borax, the use of the method according to the invention, also provides a less expensive alternative than OPC.

From the above it is evident that alkali metal, alkali earth metal and mixed alkali metal - alkali earth based borate compounds, such and without limitation, borates, tetraborates and metaborates and mixtures thereof can be utilised to immobilise water and its heavier hydrogen isotope analogues; D₂0, DHO, DTO, HTO and T₂0, and or concentrate the heavier hydrogen isotope analogues of water. Additionally, it is self evident that such boron compounds may be used in combination of sequence with other isolation and containment systems and reagents, synergists and adjuncts.

The water molecules being effectively locked into the hydrate crystal structure as water of crystallisation. Advantageously the process can be reversed by application of significant heat to liberate the water of crystallisation should this be so desired, e.g. after the radioisotopes have safely decayed. A similar effect can be obtained with other hydrated ions of other metal or amphoteric salts of copper, cobalt, chromium, vanadium, iron, manganese, and/or nickel.

For instance, anhydrous Copper II sulphate on dissolution in water can be crystallized as its stable pentahydrate and thus retain 56.4% of its own weight in water as a stabilised solid:

CuS0_4[SOLID] + 5 H₂0_[LIQUID] ^ CuS0₄-5H₂0_[SOLID] The contaminated water from the Fukushoma Daiichat site is in addition to tritium contaminated with caesium (¹³⁷Cs, 10⁴Bq/l), strontium (⁹°Sr, 10⁸Bq/l).

The at least one salt used in the method according to the invention, can preferably also precipitate and immobilise radioactive compounds of periodic group I and II, e.g. strontium and caesium. If anhydrous borax is used, the following will take place, see (iv) and (v) : (iv) Na₂B₄0_7[SOLID] + Sr²⁺_[S0LUBLE] + nH₂0_[LIQUID] ^ SrB₄0₇ · nH₂0_[SOLID]

(n=4 to 6)

Thus, the chemistry of borax is fortuitous in that it can be utilised to immobilize the radio-nucleotides¹³⁷Cs,⁹°Sr and³H . Moreover, as boron has a comparatively high atomic cross- section it is an ideal material to act as a radiation shield, see Martin, James E (2008) . Physics for Radiation Protection: A Handbook, pp. 660-661. ISBN 978-3-527-61880-4. The molar ratio between the at least one salt and the aqueous solution depend on the used salt, and will be readily available for a person skilled in the art based on the simple chemical reaction. It is however preferred that the at least one salt is added in excess, or that an excess amount of the at least one salt is added after the stable hydrate is formed, in order to ensure that the radioactive isotopes are securely confined in the hydrate.

The specific heat of water is 4.186 J/gram°C and given the high heat of hydration it is preferred that the process is controlled to ensure that contamination is not mobilised in the form of water vapours or steam. The latent heat of fusion of water ice is 333.55 J/gram. Thus, the preferred embodiment of the invention is to convert the contaminated waters to ice snow prior to hydration. Ice snow can be provided by any conventional means, e.g. using liquid nitrogen, methods well known to a person skilled in the art.

Said ice snow can then be mixed with the at least one salt under additional cooling, in order to ensure that the heat generated during the hydration will not be excessive and liberate the tritiated water. If the at least one salt is an anhydrous borax, it is preferred that the temperature is held between 60°C and 80°C during the mixing, at this effectively will control the exothermic heat of hydration.

The mixing of the aqueous solution and the at least one salt, will initially provide a preliminary slurry, basically consisting of a combination of the desired stable hydrate, the at least one salt and the aqueous solution. The hydration process can in one embodiment be allowed to run to completion in the mixing container, but it is preferred that the preliminary slurry is transferred to a closed storage container, preferably a stainless steel drum wherein the process is allowed to run to completion to form a solid stable hydrated salt. In this way it is possible to handle large volumes of contaminated aqueous solutions, since the process does not have to be completed before being place in a storage facility. It will be understood that the mixing container and the storage container can be different containers or the same container, depending on the conditions promoting the formation of the stable hydrates.

In this way a method of ensuring that aqueous solutions comprising radioactive matter can be placed in a form that will neither react nor degrade for extended periods of time is provided .

In order to ensure that the stable hydrate predominantly contains the radioactive elements, e.g. tritium, the aqueous solution can in one embodiment be subjected to a concentration step, before the aqueous solution is mixed with the at least one salt. Such concentration steps are well known in the art and will depend on the radioisotope of interest. If the radioisotope is tritium, this concentration can e.g. be effectuated though a distillation step, the method disclosed in US2006016681 Al can be also used, or any other methods known for the person skilled in the art, which will concentrate the tritium in the aqueous solution, preferably leaving a solution (mother solution) with safe levels of the tritium. It is preferred that not all the treated aqueous solution will be formed into stable hydrates. For instance, radioactive contaminated water also contain large amounts of H₂0, some of which will also be incorporated into the stable hydrate as water of crystallisation. However, as described earlier, when hydrates are formed from waters containing mixed isotopes of hydrogen, the hydrates are more likely to incorporate the tritiate rather than the deuterate, and the deuterate rather than the hydrate in the hydrate. Accordingly it is possible to form stable hydrates predominantly incorporating the tritium, and at the same time selectively remove the tritiate from the aqueous solution, accordingly providing an aqueous solution free from the radioactive tritium.

Said method comprises

a. providing a stable hydrate incorporating tritium as water of crystallisation, by mixing the aqueous solution with the at least one salt,

b. separating said stable hydrate from the remaining aqueous solution, e.g. by filtration, decanting or distillation, and

c. repeating step a) and b) on the remaining aqueous solution until the tritium concentration reaches levels permissible for safe discharge of the aqueous solution to the environment.

Since the hydrate predominantly incorporate the radioactive³H₂0 instead of H₂0, the storage facilities for the stable hydrate will be reduced, significantly reducing the storage costs. Prior to application of either solidification procedure above, the aqueous solution may optionally be treated with a heavy metals precipitations agent to render any potential soluble and mobile heavy metal radio nucleotides of Periodic Table Group III and above, immobile. Suitable reagents are, without limitation, sulphides, polysulfide, organo-mercaptans , heavy metals chelating agents, phosphates and organophosphates or blends thereof, or proprietary treatment systems such as CyCurex® or CyFix® heavy metals sequestering reagents of Cylenchar limited, Huddersfield United Kingdom. The contaminated waters may then be further processed to remove radioactive elements of Periodic Table Group I and II as described below.

The invention will be explained in greater detail below, describing only exemplary embodiments of the method according to the invention with reference to the drawing, in which Fig. 1 describes a multi-stage method according to the present invention, Fig. 2 describes a single-stage method according to the present invention, and

Fig. 3 shows a schematic representation of a distillation system for use the method according to the invention.

The invention will be described below with the assumption that the aqueous solution is water contaminated at a nuclear site, e.g. at the Fukushoma Daiichat site. However, this assumption is not to be construed as limiting, and the aqueous solution could just as easily be other kind of solutions contain radio nucleotides .

Fig. 1 is a schematic representation of a multi-stage precipitation method according to the invention. The contaminated water 1, comprises 137cs, 90Sr, 3HOH, and *M^{X +}₍, wherein *Mx+ represents a number of radio-nucleot ide metals of the Periodic table Group III and above.

The contaminated water is initially treated with the heavy metals precipitations agent CyCurex®, which render any potential soluble and mobile heavy metal radio nucleotides of Periodic Table Group III and above immobile. Said immobilised heavy metal radio nucleotides are removed from the solution by known means, e.g. filtration. The remaining solution is then treated with liquid sodium tetraborate (Na₂B₄0₅ (OH)₄ thereby immobilising the radioactive caesium and strontium by precipitation as described earlier. Said precipitate can thereafter be removed from the remaining solution, leaving the tritium in the solution. Said tritium is then entrapped using the solid anhydrous borax, Na₂B₄0₇, entrapping the tritium as water of crystallisation. The resultant borate hydrate, concentrated in tritium, can be safely stored for disposal on decay of their radio chemical contaminants.

Figure 2, shows a schematic representation of a single stage precipitation method according to the invention, wherein all radioactive elements of the contaminated water, i.e. 137cs, 90sr, 3HOH, and * M^ + , are co-precipitated, solidified and/or crystallised in a single step, by mixing the contaminated water with both the heavy metals precipitations agent CyCurex® and the solid anhydrous borax, Na₂B₄0₇ simultaneously and storing the combined stabilised solid at an appropriate site.

Experiments have shown that for each 89 kg of contaminated water there will be approximately 189 kg waste to be placed in the storage site.

Said system comprises three vessels A, B, C. The vessels are interconnected via valves bl and cl respectively.

After contaminated water has been added to vessel A via valve al, the at least one salt, e.g. anhydrous borax can be added via a gated charging hatch allowing a stable hydrate, e.g. sodium borate decahydrate to be formed in vessel A. In this way at least part of the tritium in the contaminated water will be entrapped in said hydrate. During the mixing process in vessel A, valves bl and cl is closed effectively preventing any flow into vessel B and C. After the stable hydrate is formed, valve bl is opened allowing the remaining solution in vessel A, to be distilled off into vessel B, using conventional distillation techniques. Depending on the level of remaining tritium in vessel B, said solution can either be subjected to an additional cycle in vessel A, in order to entrap further tritium by mixing said solution with the at least one salt, or it can be disposed to the environment if the tritium level is sufficiently low.

The solid hydrate in vessel A is thereafter heated to such an extend that the tritium enriched water of crystallisation entrapped in the hydrate is released and said water can, by opening valves cl and closing valves bl, be driven off to vessel C.

The residues (borate) in vessel A are then cooled and can be reused by re-dissolving it with a fresh batch of contaminated water, and the process repeated.

If the process in vessel A is repeated using the solution from vessel C, this will ensure that higher concentrations of tritium is entrapped in the hydrate, freeing more and more uncontaminated water to vessel B. A similar situation happens if the process is repeated using the solution of vessel B, i.e. more and more tritium is removed from the solution, providing an aqueous solution with radioactive levels permissible for safe discharge of the aqueous solution to the environment.

The above process can be so configured that multiple distillation units are arranged and operated in series as a closed system, such that tritium/deuterium enriched waters pass up the series and depleted pass down until the desired level of enriched or depletion is attained. Examples

Solidification procedure 1

In one embodiment of the invention, 89 litres of contaminated water are frozen using liquid nitrogen to form a water ice snow. The snow is a then blended with lOOKg anhydrous borax in portions and with additional cooling at a temperature between around 80°C.

Na₂B₄0_{7 [S0LID]} + 10 H₂0/T₂0_[SOLID] ^ Na₂B₄O₇-10H₂O/T₂O_[SOLID]

The resultant slurry is transferred to a 210 litre stainless steel drum in a cold room (temperature between 10-20°C) to allow the process to run to completion to form a solid fused mass at a temperature below 60°C.

Solidification Procedure 2

In an alternative embodiment, lOOKg anhydrous borax may be added in portions to 89 litres of contaminated water such that the temperature of the resultant mixture is raised above 60°C but preferably does not exceed 80°C, the heat of the hydration reaction being controlled by external cooling of the drum.

On completion of the borax addition and abatement of the hydration exothermic heating, the mixture is allowed to cool to room temperature, whereupon it solidifies below 60°C as sodium borate decahydrate/tritiate (Na₂B₈0₁₄ · 10H₂O/T₂O) .

Optionally, a further 2Kg anhydrous borax may added on the top of the crystalline mass to ensure full conversion of the contaminated water to the sodium borate decahydrate/tritiate . On attaining thermal equilibrium, the drum is sealed and weight checked and sent for disposal at a suitable site. Solidification Procedure 3

In an alternative embodiment of the invention, anhydrous calcium chloride (14Kg) is dissolved in tritium contaminated water (45 litres) and the solution chilled to <5°C then blended with lOOKg sodium borate pentahydrate with additional cooling.

2Na₂B₄0_{7 [S0LID]} + CaCl_2[S0LID] + 10H₂O/T₂O_[LIQUID] ^ CaNa₂B₈0₁₄ · 10H₂O/T₂O_[

2NaCl. The resultant slurry is transferred to a 210 L stainless steel drum in a cold room, (temperature between 10-20°C) to allow the process to run to completion to form a solid fused mass of (CaNa₂B₈0₁₄- 10H₂O/T₂O-2NaCl) at a temperature below 60°C.

Solidification Procedure 4

In an alternative embodiment of the invention, anhydrous calcium chloride (28Kg) is dissolved in tritium contaminated water (45 litres) and the solution chilled to <5°C then blended with lOOKg sodium borate pentahydrate with additional cooling at a temperature of 80°C to prevent evaporation of contaminated water .

Na₂B₄0_{7 [S0LID]} + CaCl_2[S0LID] + 6H₂0/T₂0_[LIQUID] ^ CaB₄0₇ · 6H₂0/T₂0_[SOLID] + 2NaCl_2[SOLID] The resultant slurry is transferred to a 210 stainless steel drum in a cold room to allow the process to run to completion to form a solid fused mass of (Ca₂B₈0₁₄ · 10H₂O/T₂O · 2NaCl) at a temperature below 60°C. Solidification Procedure 5

In an alternative embodiment of the invention, contaminated water (46 litres) is chilled to <5°C then blended with 150Kg sodium borate penthydrate with additional cooling.

Na₂B₄0₇ - 5H₂0_[S0LID] + 5 H₂0/T₂0_[LIQUID] ^ Na₂B₄0₇ · 10H₂O/T₂O The resultant slurry is transferred to a 210 stainless steel drum in a cold room to allow the process to run to completion to form a solid fused mass at a temperature below 60°C. Solidification Procedure 6

In an alternative embodiment of the invention, 35.2 litres of contaminated water are frozen using liquid nitrogen to form a water ice snow. The snow is a then blended with lOOKg anhydrous calcium borate in portions. CaB₄0_{7 [S0LID]} + 6H₂0/T₂0_[LIQUID] ^ CaB₄0₇ - 6H₂0/T₂0_[SOLID]

The resultant mixture is transferred to a 210 stainless steel drum in a cold room to allow the process to run to completion to form a solid fused mass at a temperature below 60°C.

Optional Pre-solidification Procedure

The contaminated waters can initially be treated with a heavy metals precipitations agent to render any potential soluble and mobile heavy metal radio nucleotides of Periodic Table Group III and above immobile, e.g. using CyCurex® or CyFix® heavy metals sequestering reagents of Cylenchar limited, Huddersfield United Kingdom. The contaminated waters may then be solidified as described above or further processed to remove radioactive elements of Periodic Table Group I and II as described below.

Optionally the contaminated waters can be treated with hydrated sodium borate to a concentration of <=40 grams per litre (at 20°C) . Alkaline earth radio-nucleotides of Periodic Table Group II may be precipitated and if desired recovered by conventional filtration, with or without the use of flocculants to assist solid deposition. The contaminated waters may then be solidified as described above.

Optional Post Solidification Procedure

Optionally, a further 2Kg anhydrous borax is added on the top of the crystalline mass to ensure full conversion of the contaminated water to the calcium/sodium hydrate/tritiate . On attaining thermal equilibrium, the drum is sealed and weight checked and sent for disposal at a suitable.

Selective Crystallisation Procedure for the Concentration of Titrated Water.

In one embodiment of the invention, 50 mis of tritium contaminated (and/or deuterium rich water) are charged into a stainless water jacketed reaction vessel. lOg anhydrous borax is added in portions and the mixture is allowed to rise above 60°C with vessel cooling but preferably not above 80°C, with excess exothermic heat of hydration being controlled by external cooling.

The solution is slowly permitted to cool to below 20°C with slow stirring. Approximately 16.5g of sodium borate decahydrate/deuterate/tritiate is deposited as a crystalline solid, which may be isolated on an enclosed filtration unit or by decanting off the supernatant solution. The residual solution comprising 1.17g of borax as its anhydrous equivalent and 42.3mls water.

The molar concentration of tritium (or deuterium) in the residual solution is measurably lower that its original concentration, the degree of de-tritiation/de-deuteriation being a function of the rate of cooling.

The above process on a solution of approximately 1.0-2.0 ml 99.9 mol % deuterium oxide (D₂0) in water (H₂0) wherein the deuterium content relative to the hydrogen content by GC Mass spectroscopy as evident form ions masses at 18, 19 and 20 atomic mass units, the molar ratio was found to be 1.801-1.840 D: 100 H. After a single crystallisation performed as above, the deuterium content in the residual solution was reduced by 0.675-0.344%. By inference, the deuterium concentration in the in the isolated borate decahydrate/deuterate had been concentrated by a factor of 1.78 to 3.71%. The aforementioned procedure may be employed on tritium contaminated waters, repeating the crystallisation cycle on the mother liquors until the tritium concentration reaches levels permissible for safe discharge of the mother liquors to the environment. Prior to discharge the mother liquors are treated with calcium chloride solution to precipitate residual borates and filtered, such that the residual solution contain only water and trace levels of calcium chloride. Such de-tritiated solution, post removal of residual borates may be safely disposed off at minimal risk to the environment.

Furthermore, the isolated borate decahydrate/deuterate/ tritiate can be dehydrated at temperatures between 60 and 130°C, and preferably heated to above 130°C to release all water of crystallisation.

This water can be condensed and further treated with anhydrous borate as above to further increase the deuterium or tritium concentration in the retained materials. Borate hydrates concentrated in tritium can be safely stored for disposal on decay of their radio chemical contaminants.

Removal of tritiated water from the contaminated water.

In a further embodiment of the invention, tritium contaminated water (and/or deuterium enriched water) are subjected to a separation process using the distillation system shown in fig. 3, and reference is therefore made to said figure in the following example.

24 litres of tritium contaminated (or alternativly deuterium rich water) are charged into a stainless jacketed reaction vessel A via valve al . The reaction vessel being fitted with: twin limpet coils, one for cooling and another for heating, and double Dean Stark distillation heads. lOKg anhydrous borax is added in portions via the gated charging hatch which is sealed post addition and the mixture allowed to rise above 60°C with vessel cooling but preferably not above 80°C, with excess exothermic heat of hydration being controlled by external cooling. The solution is slowly permitted to cool to below 20°C. Sodium borate decahydrate enriched in tritiate is deposited as a crystalline solid in the vessel . After the formation of sodium borate decahydrate is completed, valves bl is opened (valves cl remains closed) and the vessel is subjected to high vacuum allowing the tritium depleted solutions to be distilled off and collected into vessel B. Said vessel is chilled with coolant to < minus 40°C via circulation of calcium chloride eutectic solution or similar.

After the tritium depleted solution has been allocated to vessel B, valves bl are closed preventing any backflow into vessel A. Vessel A is then allowed to pressurise to atmosphere after which valve cl is opened. The solid borate in the reaction vessel A is then heated to >160°C to drive off approx 8 litres of the tritium enriched water which is condensed into vessel C. The borate residues are then cooled and re-dissolved with a further 24 litre portion of tritium contaminated water and the process repeated until the desired result has been reached, either by recycling the solutions from vessel B or C, or by adding additional contaminated water to vessel A.

The present invention is useful industrially by virtue of the action of the processes described herein and the method for application, which efficiently, conveniently and in a sustainable manner renders safe or less harmful, toxic radio- chemical pollutants, such that they me be safely contained or disposed of. Moreover, the processes described herein are advantageously cost effective when compared to water immobilisation by cement materials such as OPC.

Advantageously, the present invention can be used to concentrate the heavier hydrogen isotopes, deuterium and tritium, and the person skilled in the art will understand that the invention also is suitable for the concentration, entrapment and separation of deuterium, in deuterium enriched aqueous solutions.

The invention has been described in terms of various exemplary and preferred embodiments, but is not limited thereto. Various modifications can be made without departing from the invention, the scope of which is limited only by the appended claims and their equivalents. Throughout the claims, use of "an" and other singular articles is not intended to proscribe the use of plural components.

Claims

A method for concentrating and/or entrapping radioisotopes from an aqueous solution comprising tritium, said method comprises mixing the aqueous solution with at least one inorganic salt under conditions in which said salt forms at least one stable hydrate, incorporating the tritium as water of crystallisation.

The method according to claim 1, wherein the at least one salt is a borate, such as tetraborate and/or metaborate.

The method according to claim 2, wherein the borate is an alkali-metal borate, such as sodium borate, preferably anhydrous borax or sodium borate pentahydrate; or an alkaline earth metal borate, such as calcium borate, calcium tetraborate and calcium metaborate.

The method according any of the preceding claims, wherein the at least one salt is a metal or amphoteric salt selected from the group comprising salts of copper, cobalt, chromium, vanadium, iron, manganese, and nickel.

The method according any of the preceding claims, wherein said aqueous solution further comprises radioisotopes from group I and II of the Periodic System of Elements, such as¹³⁷Cecium and/or⁹°Strontium, and wherein said radioisotopes are immobilised in the stable hydrate.

The method according any of the preceding claims, wherein the aqueous solution is frozen to an ice snow before being mixed with the at least one inorganic salt. The method according claim 6, wherein the ice snow is mixed with the one or more salts under cooling, preferably at a temperature between 60°C and 80°C.

The method according any of the preceding claims, wherein the mixing of the aqueous solution and the at lest one salt will provide a preliminary slurry comprising a combination of the aqueous solution, the at least one salt and the stable hydrate, said preliminary slurry is transferred to a storage container, and wherein the hydration process is allowed to run to completion to form a solid stable hydrated salt in said storage container.

The method according any of the preceding claims, wherein the aqueous solution is treated with a heavy metals precipitations agent prior to mixing with the at least one salt, said precipitations agent is arranged for immobilising soluble and mobile heavy metal radio nucleotides from Group III and above of the Periodic System of Elements.

The method according any of the preceding claims, wherein the method further comprises providing a higher concentration of the tritium in the aqueous solution prior to mixing with the at least one salt.

The method according any of the preceding claims for proving an aqueous solution with a reduced concentration of tritium, said method comprises

a. providing a stable hydrate incorporating tritium as water of crystallisation

b. separating said stable hydrate from the remaining aqueous solution, and

c. repeating step a) and b) on the remaining aqueous solution until the tritium concentration reaches radioactive levels permissible for safe discharge of the aqueous solution to the environment.