Field of the Invention

[001] The present invention relates generally to a process and system for the selective removal of anionic radionuclides from nuclear reactor waste, such as ion exchange resins. In particular, the present invention relates to a process for the selective removal of radiocarbon from the ion exchange resin using a reagent, and then subsequent release of the radiocarbon from the reagent, which regenerates the reagent.

Background of the Invention

[002] Radioactive waste is a by-product of various nuclear technology processes. Management and disposal of radioactive waste is regulated by government agencies in order to protect human health and the environment. Radioactive waste has been divided into categories based on the intrinsic radioactivity level, which reflects the danger it can pose. These categories include low-level waste, intermediate-level waste, and high-level waste. The classification level of the waste dictates the precautions that must be taken during management and disposal.

[003] Low-level waste (LLW) is by far the most prevalent waste product produced, and includes materials generated from hospitals, research labs, etc. that typically have small amounts of short-lived radioactivity. Disposal may require shielding during handling and transport but most low-level waste is suitable for shallow land burial.

[004] Intermediate-level waste (ILW) contains higher amounts of radioactivity compared to low-level waste, and may include materials such as resins, chemical sludge and metal nuclear fuel cladding, as well as contaminated materials from reactor decommissioning. Disposal may require solidification in concrete or bitumen or mixing with silica sand and vitrification for disposal. [005] High-level waste (HLW) is produced by nuclear reactors. While the exact definition of high-level waste differs internationally, it would include, e.g., a nuclear fuel rod after it has served one fuel cycle and is removed from the core. While there is no clear consensus on the best way to dispose of high-level waste, the minimum is typically deep geological burial, either in a mine or a deep borehole.

[006] Shifting the volume of waste generation from HLW and ILW to LLW will decrease the burden associated with disposal, which will ultimately make nuclear power generation more cost-effective.

[007] Ion exchange resins are a prominent waste product created by nuclear reactors. Ion exchange resins can be in the form of beads or granules, and remove radioactive material from wastes through the exchange of ions between the liquid or gaseous phase and the solid ion exchange resin. In nuclear reactors, ion exchange resins can be used for Primary coolant (water) purification, the treatment of primary effluents, the treatment of fuel storage pond water, steam generator blow-down demineralization, liquid waste and drainage water treatments, boric acid purification for recycling, and condensate polishing, to name a few. In some reactor types, irradiated carbon (graphite) waste also contains ¹⁴ C, which may be processed by incineration or laser ablation techniques to produce radioactive carbon dioxide gas ¹⁴ CO2. This gas may be captured and purified by using ion exchange resins.

[008] Ion exchange resins are very effective at transferring the radioactive content of a large volume of liquid into a small volume of solid. The treatment and conditioning of radioactive spent ion exchange materials is a complex process encompassing a detailed consideration of the materials' characteristics and their compatibility with the various processing, storage and/or disposal options.

[009] These ion exchange resins used in nuclear reactor systems ultimately contain high levels of Carbon-14 ( ¹⁴ C) when they are removed from service. Because of the long half-life of this radioisotope, i.e. about 5730 years, waste ion exchange resins are typically classified as Intermediate Level Wastes (ILW). [0010] In addition to the desire to reduce the volume and associated cost of ILW disposal, there is a present need to mitigate ¹⁴ C emissions (in the form of radioactive carbon dioxide gas) from waste resins that are currently in interim storage throughout the world. Ideally, the contaminated ion exchange resin is purified to substantially remove the ¹⁴ C so that it would qualify for LLW classification.

[0011] There are mainly four existing technologies that attempt to address the management of spent radioactive ion exchange resins. These are (1) thermal processes, (2) acid stripping processes, (3) use of supercritical carbon dioxide to extract carbon and (4) non-selective salt exchange processes.

[0012] The thermal process consists of heating spent ion exchange resins under controlled temperature conditions, such that water (first) and then radiocarbon is removed. This process is energy-intensive, produces radioactive and malodorous byproducts in a gaseous form and needs complex gas scrubber systems to mitigate emissions to the environment.

[0013] The acid stripping process uses strong mineral acids to remove vitrually all of the radionuclides from spent resins. It separates ¹⁴ C since it is the only radionuclide that emanates as a gas. Its drawbacks are that it uses hazardous chemicals (corrosive and fume producing) and generates large volumes of radioactive mixed waste. Furthermore, the radioactive secondary wastes are produced in both liquid and gas forms.

[0014] The supercritical carbon dioxide process operates at temperatures above 31°C and pressures above 7.4 MPa, removing ¹⁴ C from spent ion exchange resins by isotopic exchange. Its main disadvantages are that it requires high- pressure equipment, and its waste processing rate is slow.

[0015] The salt exchange process uses a neutral salt (e.g. NaCI) solution to elute all radionuclides from the waste resin, with no simple separation of ¹⁴ C from the other radionuclides. Another disadvantage is that it generates large volumes of radioactive secondary waste that are costly to dispose. [0016] Areva, C-14 - Recovery from spent resin, 37th Annual Conference of the Canadian Nuclear Society and 41st Annual CNS/CNA Student Conference (2017) teaches the use of unnamed organic acids to remove C-14 from spent resins. In the absence of regeneration of the organic acids, the process can prove costly over time.

[0017] University of Michigan, Relative determination of ¹⁴ C on spent ionexchange resins by resin regeneration and sample combustion, Applied Radiation and Isotopes (1993), Volume 44, Number 4, pp. 701-705, briefly reviews two techniques for the recovery of C-14 from ionic exchange resins from nuclear power plants. The first method is combustion and oxidation. The second method is stripping with acids or bases.

[0018] The Ontario Hydro, Determination of carbon-14 in spent ion exchange resins, International Journal of Applied Radiation and Isotopes (1982), Volume 33, Number 7, pp. 584-585 teaches the use of acid regeneration to remove C-14 from spent resins.

[0019] US2017/148535 to Korea Atomic Energy teaches the use of heat to treat waste ion exchange resins. KR101624453 to Sunchon National University teaches the use of acids to treat ionic salt exchange to treat resins. US2016/247589 to Hitachi GE Nuclear Energy teaches the use of electrodeposition to decontaminate resins.

[0020] US2016/289790 to Kurion Inc. teaches the use of submersible filters for separating radioactive isotopes from radioactive waste materials. US2012/088949 to Electric Power Research Institute teaches the use fractionation of radioactive waste based on density. EP1786000 to Areva NP GmbH teaches conditioning ion exchange resins with hydroxy radicals.

[0021] EP1564188 to INER AEC teaches a method of treating ionic exchange resins through wet oxidation, using H2O2, barium hydroxide, and heat. JP2005181256 to Institute Nuclear Energy Research teaches the use of heat, acids and H2O2 to treat waste ion exchange resins. US6407143 to Sandia Corp teaches the removal of perchlorate from ion exchange resins.

[0022] US4687581 to Macedo teaches the use of ion exchange for decontaminating toxic waste streams such as radioactive waste streams. This methodology is based on porous silicate glass or a gel. US4628837 to Hitachi Ltd. teaches the use of pyrolysis for the removal of radioactive material from ion exchange resins. JP50121700 teaches the use of heat and either formic acid or ammonium acetate to treat radioactive waste.

[0023] US5286468 to Ontario Hydro teaches the use of liquid carbon dioxide to remove C-14. CA1250378 to Atomic Energy teaches the use of heat, carbon dioxide and calcium or barium for the removal of C-14 from ion exchange resins. US4122048 to Commissariat a I'Energie Atomique teaches the use of bases to block the active sites on cationic resins for conditioning contaminated ionic exchanges resins.

[0024] There is a need for a more efficient process for the selective removal of radiocarbon from reactor waste.

Summary of the Invention

[0025] According to an aspect of the present invention, there is provided a process for the removal of anionic radionuclides from spent ion exchange resin comprising: mixing at least one reagent with said resin in solution to form a first mixture, and removing the anionic radionuclides from the spent ion exchange resin to produce radionuclide-bound reagent, wherein the reagent has the following general formula:

(Ri )n H(4-n) X Y AGENT wherein

R.i is a linear or branched C1-C12 alkyl, a linear or branched C1-C12 alkenyl, cycloalkyl, phenyl, or a linear or branched C1-C12 alkyl or alkenyl substituted with cycloalkyl or phenyl; 1 < n > 4;

X is N, P, or As; and

Y is Cl, Br, I, bromate, bisulfite, benzenesulfonate, salicylate, citrate, and phenate.

[0026] Using an example in which Y is a halide, the agent binds to the carbon:

2 AGENT-halide + R2- ¹⁴ CO ₃ + 2 R-halide Eq. 1

[0027] Step 2 is the regeneration of the selective agent. The radiocarbon is separated from the non-radioactive components in the liquid by a liquid extraction stream. The reagent can be reused.

[0028] Step 3 is drying. The radiocarbon-free resin is dried to further reduce the volume of waste. This step is optional.

[0029] Additionally, the reagent can be citric acid, salicylic acid, benzenesulfonic acid, and the water-soluble salts thereof (such as the sodium or potassium, for example); and water-soluble nitrates, sulfates, and iodides. In embodiments, the reagent can be water-soluble salts or acids that contain the ions benzenesulfonate, salicylate, citrate, and phenate.

[0030] Sodium and potassium compounds may be preferred compounds.

[0031] In an embodiment, the process further comprises separating the resin from the radionuclide-bound reagent in the first mixture.

[0032] In an embodiment, the process further comprises drying the resin through the application of heat, vacuum, or both.

[0033] In an embodiment, the separating of the resin from the radionuclidebound reagent in the first mixture is by one or more of gravity, centrifugation, and filtration. [0034] In an embodiment, the reagent is at least one of an alkyl ammonium halide, an alkyl benzyl ammonium halide, an alkyl benzyl phosphonium halide, and substituted derivatives thereof. In an embodiment, the reagent is at least one of: an alkyl ammonium halide, an alkyl phenyl ammonium halide, an alkyl phosphonium halide, an alkyl phenyl phosphonium halide, alkyl arsonium halides, an aryl ammonium halide, an aryl phenyl ammonium halide, an aryl phosphonium halide, an aryl phenyl phosphonium halide, an aryl arsonium halide, a phenyl ammonium halide, a phenyl phosphonium halide, a phenyl arsonium halides, and substituted derivatives thereof.

[0035] In an embodiment, the process further comprises mixing the radionuclide-bound reagent with a precipitating agent to form a second mixture, and removing the anionic radionuclides from the radionuclide-bound reagent to produce radionuclide-bound reaction product and regenerated reagent, wherein the precipitating agent is at least one of calcium halide, barium halide calcium hydroxide and barium hydroxide.

[0036] In an embodiment, the precipitating agent is barium chloride.

[0037] In an embodiment, the radionuclide-bound reaction product of the radionuclide-bound reagent and the precipitating agent is precipitated out of the second mixture.

[0038] In an embodiment, the process further comprises separating the precipitated radionuclide-bound reaction product from the second mixture by one or more of gravity, centrifugation, and filtration.

[0039] In an embodiment, the regenerated reagent is recycled back into the process for reuse with new spent resin.

[0040] In an embodiment, the anionic radionuclide is ¹⁴ CO3 ² '. [0041] Brief Description of the Drawings

[0042] Figure 1 is a schematic drawing depicting the process for the selective removal of radiocarbon from spent ion exchange resins.

[0043] Figure 2 is a process flow diagram for the selective removal of radiocarbon from spent ion exchange resins.

Detailed Description of the Preferred Embodiments

[0044] Embodiments of the disclosure are discussed in detail below. In describing embodiments, specific terminology is employed for the sake of clarity. However, the disclosure is not intended to be limited to the specific terminology so selected. A person skilled in the relevant art will recognize that other equivalent parts can be employed and other methods developed without parting from the spirit and scope of the disclosure. All references cited herein are incorporated by reference as if each had been individually incorporated.

[0045] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0046] The present invention provides a process for the selective removal of radiocarbon, or other anionic radionuclides, from spent ion exchange resins.

[0047] Anionic radionuclides in addition to carbonate ¹⁴ CO3 ² ', such as pertechnetate ⁹⁹ TcO4 ² ', antimonate ¹²⁵ SbO3-, and molybdate ⁹⁹ MoO4 ² ', for example, may be bound to the ion exchange resin. Such anionic radionuclides can also be targeted and removed by the process as discussed below. While radiocarbon is primarily discussed in the present disclosure as an example, it is to be understood that the process may also result in the removal of further anionic radionuclides from the ion exchange resin other than ¹⁴ CO3 ² ', and can be carried out with the intention of targeting other anionic radionuclides other than ¹⁴ CO3 ² '. Accordingly, any mention of radiocarbon in the present disclosure should be interpreted as encompassing other anionic radionuclides. [0048] In one embodiment, a process for selectively regenerating a spent ion exchange resin by removing radiocarbon generally comprises mixing the spent resin with a reagent. The reagent is able to disengage the radiocarbon, which is typically in the form of ¹⁴ CO3, from the spent resin, and then binds the radiocarbon. The reagent is then separated from the resin. The treated resin may optionally undergo further processing to reduce its volume prior to storage and disposal. The radiocarbon-bound reagent undergoes further processing, and is mixed with a precipitating agent. The precipitating agent disengages the radiocarbon from the reagent, and then binds the radiocarbon. Preferably, once the precipitating agent binds the radiocarbon, this compound precipitates from solution, simplifying its separation from the reagent. The reagent, now being effectively regenerated, can be recycled back into the process to be used with further spent resin.

[0049] An exemplary embodiment is illustrated generally in Figure 1. The process 100 generally begins with spent ion exchange resin 102. Spent ion exchange resin 102 generally refers to ion exchange resin that has a decreased exchange capacity, such as below a predetermined threshold, and has therefore been replaced within the nuclear facility. The process 100 can take place at, for example, a waste treatment area of the nuclear facility, an offsite waste treatment area, or the process can be performed in situ on waste resin that has already been disposed and is in, e.g. storage barrels.

[0050] Based on the precise nature of a given ion exchange resin, a number of different radionuclides and non-radioactive ions may be bound. For example, spent ion exchange resins may be loaded with radiocarbon ( ¹⁴ C), often in the form of carbonate or bicarbonate, especially when used to treat waste from heavy water reactors. The presence of this long lived radioisotope influences the strategy for the disposal of spent resins because most near surface disposal facilities have strict concentration limits for long lived radioisotopes. The removal of radiocarbon from spent ion exchange resin 102 is therefore a goal of the present process.

[0051] In one embodiment, the first step of the process 100 comprises mixing the spent ion exchange resin 102 with a reagent 106, to produce a spent ion exchange resin/reagent mixture 104. The preferred quantity of reagent 106 is a near stoichiometric equivalent to the calculated or anticipated ion exchange capacity of the anion fraction of the resin 102, although an excess of the reagent 106 can be used to ensure that a sufficient amount is present to maximize removal of radiocarbon.

[0052] The reagent 106 preferably has the general formula:

(Ri)n H(4-n) X Y AGENT where:

R.i is a linear or branched C1-C12 alkyl, a linear or branched C1-C12 alkenyl, cycloalkyl, phenyl, or a linear or branched C1-C12 alkyl or alkenyl substituted with cycloalkyl or phenyl;

1 < n > 4;

X is N, P, or As; and

Y is Cl, Br, bromate, bisulfite, benzenesulfonate, salicylate, citrate, and phenate.

[0053] The desired properties of the reagent are that it be soluble in water, and that the corresponding carbonate compound (where carbonate replaces the Y group) is also soluble in water. The reagent may be at least one of: an alkyl ammonium halide, an alkyl phenyl ammonium halide, an alkyl phosphonium halide, an alkyl phenyl phosphonium halide, alkyl arsonium halides, an aryl ammonium halide, an aryl phenyl ammonium halide, an aryl phosphonium halide, an aryl phenyl phosphonium halide, an aryl arsonium halide, a phenyl ammonium halide, a phenyl phosphonium halide, a phenyl arsonium halides, and substituted derivatives thereof. Preferably, the reagent is an alkyl ammonium halide, an alkyl benzyl ammonium halide, an aryl ammonium halide, an alkyl phosphonium halide, an alkyl benzyl phosphonium halide, or an aryl phosphonium halide. The reagent can be secondary, tertiary or quaternary substituted, but is preferably quaternary substituted.

[0054] The agent binds to the carbon:

2 AGENT-halide + R.2- ¹⁴ CO ₃ + 2 R.-halide Eq. 1 [0055] Step 2 is the regeneration of the selective agent. The radiocarbon is separated from the non-radioactive components in the liquid by a liquid extraction stream. The reagent can be reused.

[0056] Step 3 is drying. The radiocarbon-free resin is dried to further reduce the volume of waste. This step is optional.

[0057] As an example, the reagent 106 is shown in Figure 1 as tetrahexyl ammonium chloride (THA Chloride). The reagent 106 is able to target and exchange radiocarbon bound to the resin 102, resulting in the radiocarbon binding to the reagent 106. Preferably, the reagent 106 selectively targets carbon and radiocarbon, while minimizing or avoiding stripping away other radionuclides that may be bound to the resin.

[0058] Equation 1 shown below is an exemplary representation of the reaction occurring between the resin 102 and the reagent 106. In this equation, R. is the resin 102 bound to ¹⁴ C in the form of carbonate, and (THA)CI is tetrahexyl ammonium chloride as an example of the reagent 106.

[0059] R ₂ - ¹⁴ CO ₃ + 2(THA)CI - 2 R-CI + (THA) ₂ ¹⁴ CO ₃ Eq. 3

[0060] The reagent 106 is preferably in solution to facilitate forming a mixture 104 with the resin 102. The mixing of the reagent with the resin 102 may take place in a batch process, such as in a vessel. Preferably, the process 100 operates under ambient temperature and pressure conditions, such as 10°C to 30°C and at or near atmospheric pressure. This avoids the cost of heating and the safety issues associated with pressurized systems.

[0061] Contact time does not have to be extensive. Two hours is sufficient and high throughput is achievable. [0062] After mixing the reagent 106 with the ion exchange resin 102, the resin 102 is preferably separated from the reagent solution 104. Separation of the resin 102 from the reagent solution 104 can be done by various known procedures, such as gravity, centrifugation, filtration, etc. This precipitation step is more or less instantaneous, thus the limiting factor will usually be the rate at which the precipitate can be either centrifuged or filtered from the liquid. After separation, the radiocarbon depleted ion exchange resin 108 can be classified and disposed of as a LLW.

[0063] After separation, the radiocarbon depleted resin 108 will still contain some amount of water, which impacts its volume and therefore the costs associated with storage and disposal. Optionally, at this stage the resin 108 can be dried, such as through the application of heat 110, vacuum 112, or both. This optional drying stage further reduces the volume of the processed resin 114, which will reduce waste disposal costs.

[0064] Following the removal of radiocarbon from the resin 102 and the subsequent separation of the resin 102 and the reagent 106, the radiocarbonbound reagent 106, can be subject to further processing. The further processing can occur in the initial vessel, or the reagent solution may be transferred to a secondary vessel 118. Further processing comprises adding a precipitating agent 116 to the radiocarbon-bound reagent. The precipitating agent 116 separate the radiocarbon from the reagent 106 to form a radiocarbon-bound reaction product, and effectively a regenerated reagent. The radiocarbon-bound reaction product then precipitates from solution, leaving the regenerated reagent 106 behind. The precipitating agent may be added already in solution, or alternatively, if the radiocarbon-bound reagent is in solution, the precipitating agent can be added in solid form.

[0065] In one embodiment, the precipitating agent is a calcium or barium halide, such as BaCh. In this embodiment, the precipitating agent exchanges the halide for the radiocarbon, creating calcium or barium-bound radiocarbon and a regenerated reagent. In other embodiments, a water-soluble salt (preferably a halide) of any transition metal could also be used. Preferred embodiments could be nickel (II) chloride, copper (II) chloride, or manganese (II) chloride.

[0066] The precipitating agent preferably is initially soluble, but once it substitutes its halide for the ¹⁴ CO3 bound to the reagent, it is preferred that this newly formed compound is substantially insoluble and precipitates from solution.

[0067] Preferably, the precipitating agent is added at or near stoichiometric equivalence with the amount of anticipated or calculated radiocarbon bound to the reagent. If too little precipitating agent is added, not all of the radiocarbon will be emancipated from the reagent; too much precipitating agent will result in not all of it being exhausted, and the excess precipitating agent will be left to contaminate the recycled reagent, which will impact subsequent treatment cycles of new spent resin.

[0068] Equation 2 shown below is an exemplary representation of the reaction occurring between the precipitating agent 116 and the radiocarbon-bound reagent 106, in which BaCI ₂ is shown as an example of the precipitating agent.

[0069] (THA) ₂ ¹⁴ CO ₃ + BaCI ₂ - Ba ¹⁴ CO ₃ + 2 (THA)CI Eq. 4

[0070] As can be seen in the equation, after the ¹⁴ CO ₃ bound reagent is mixed with the precipitating agent (BaCI ₂ in this example), the ¹⁴ CO ₃ is exchanged with chloride. The result is Ba ¹⁴ CO ₃ , and a regenerated reagent ((THA)CI in this example). The Ba ¹⁴ CO ₃ is poorly soluble in solution, and forms a precipitate 120. The precipitate can be separated out of solution by various known means, such as through gravity, centrifugation, filtration, etc. As shown in Figure 1, the remaining solution, which contains the regenerated reagent 106, can be recycled back into the process 100 for subsequent mixing with additional spent ion exchange resin 102. The precipitated Ba ¹⁴ CO ₃ , which has a much smaller volume than the treated resin 108, can now be disposed as ILW. Optionally, the Ba ¹⁴ CO ₃ can undergo drying, such as with heat or vacuum, to further reduce the volume of the precipitate 120 prior to storage and disposal. [0071] The skilled worker will understand that the process of the present invention can be carried out in a number of ways. An exemplary system 200 for carrying out the process is illustrated in Figure 2.

[0072] Spent ion exchange resins can be temporarily stored in various types of storage vessels 202. In this embodiment, the spent ion exchange resin can be transported as a slurry via a slurry pump 204 to an extraction/drying vessel 206. In this part of the process, a reagent as defined above is added to the resin the extraction/drying vessel via a chemical pump 208. The reagent is able to selectively remove ¹⁴ C from the spent resin. The reagent is pumped into the extraction/drying vessel 206 from a reagent tank 210, and can be from a fresh source, or can be recycled reagent that has been regenerated according to the present process.

[0073] Preferably, the extraction/drying vessel has the capability of having its contents mixed using a mixer 212, such as paddle mixer, to ensure a homogenous mixure. During the mixing of the spent resin with the reagent, ¹⁴ CO3 ² ' anions are removed from the resin and become bound to the reagent in the solution inside the vessel 206.

[0074] The solution in the vessel 206 comprising the radiocarbon-bound reagent is preferably separated from the treated resin, such as with a centrifuge or by filtration 220, and is pumped to a precipitation vessel 216 via a transfer pump 216. The treated resin can be tested to detect remaining levels of ¹⁴ C. If levels of ¹⁴ C above a certain threshold remain, the resin can undergo the treatment step with new reagent. Otherwise, if the ¹⁴ C levels are below a certain threshold, the resin can be disposed of as LLW. The resin can be subject to further processing, such as drying through heat treatment and/or vacuum to reduce the size of the resin.

[0075] At this point of the process, a pump 224 adds a precipitating agent from a storage tank 226 (e.g., a solution of soluble BaCh) to the solution in the precipitation vessel 216. Preferably, the precipitation vessel 216 also has mixing capabilities, such as by a mixer 222, e.g. a paddle mixer, to ensure homogeneity of the mixture. The precipitating agent causes dissociation of the ¹⁴ CO3 from the reagent, and subsequently binds the ¹⁴ CO3. The newly formed carbonate is poorly soluble, and precipitates out of solution within the precipitation vessel 216.

[0076] The precipitated ¹⁴ CO3 can be recovered by a variety of means, such as centrifugation 228 shown or by filtration etc., leaving the regenerated reagent in solution. The precipitate can optionally be dried via e.g. a dryer 230 to further decrease volume for storage and disposal. A pump 232 then transfers the regenerated reagent back to the reagent tank 210, where it is ready to be reintroduced back into the process.

[0077] After being mixed with the reagent in the extraction/drying vessel 206, the treated resin can optionally be further processed with e.g. a dryer (not shown) and/or vacuum 214 to further minimize volume prior to storage and disposal.

Examples

[0078] Carbonate was removed from ion exchange resin using various reagents as described above.

[0079] The percentage of carbonate removed from the resin was calculated as follows. In the case of inactive resins, the amount of carbonate residing on the untreated resin was determined by measuring the amount of carbonate in a carbonate-containing solution that was brought into contact with a fresh resin sample, then subtracting the amount of carbonate remaining in solution following the contact. The difference between the values represents the quantity of carbonate that was loaded onto the resin, by mass balance. In the case of active waste resins, the radiocarbon content was directly measured using, first, an alkaline extraction step, then second, liquid scintillation counting of the a I ka line-extracted radiocarbon.

[0080] Determination of the fraction of carbonate removed from the ion exchange resin, using the claimed process was made by measuring the amount extracted and dividing by the total amount present on the resin prior to the treatment. This value is expressed in Table 1 as a percentage.

[0081] Representation of the fraction of other radionuclides or stable chemicals was done in the same manner. The extracted amount was ratioed against the amount known to be present on the resins before the process treatment was applied.

Table 1

A B C D

[0082] In Table 1, A represents citric acid as the reagent (0.1 mol/L), B represents citric acid as the reagent (0.01 mol/L), C represents citric acid as the reagent (0.001 mol/L), and D represents benzenesulfonic acid as the reagent (0.01 mol/L).

[0083] It is to be understood that what has been described are the preferred embodiments of the invention. The scope of the claims should not be limited by the preferred embodiments set forth above, but should be given the broadest interpretation consistent with the description as a whole.