Cleaning of target material for radioisotope production

Abstract

FIELD: target materials.SUBSTANCE: method for purifying target material for producing radioisotopes which can be used for recycling the target material. Method which includes obtaining a solution of irradiated target material containing Ra-226, Ra-225 and Ac-225, and subsequently adding HNO3 acid. Then, selective removal of H2O from the solution is carried out by distillation, leaving the acid predominantly within the solution, allowing the precipitation of the target material, while the concentration of the acid in the solution is increased, reducing or preventing the co-precipitation of radioisotopes and impurities. After removing excessH2O, the temperature of the solution is reduced to maximize precipitation of the target material and reduce its solubility in the remaining liquid. The liquid containing the radioisotopes is then separated from the precipitated target material and the precipitated target material is prepared for reuse.EFFECT: ensuring the chemical purity of the target material irradiated in both solid and liquid form.15 cl, 1 dwg

Description

[0001] FIELD OF TECHNOLOGY

[0002] The present invention relates to the field of radioisotopes. More specifically, the present invention relates to methods and systems for purifying irradiated targets for reuse in the production of radioisotopes.

[0003] STATE OF THE ART

[0004] Solid targets are generally used to produce radioisotopes due to their high product yield in modern systems, and in the case of solid targets, high density of the initial nuclide from which radioisotopes are obtained can be easily achieved.

[0005] As for liquid targets, most of the parent nuclide compounds have limited solubility in water (usually used as a liquid solvent) at room temperature. For example, Ra-226 salts (T 1 / 2 : 1600 years), which can be used as base chemicals to provide the parent nuclide for the production of the radioisotope Ra-225 (T 1 / 2: 14.8 days), which can decay into the radioisotope Ac-225 (T 1 / 2 : 10 days), have limited solubility in water. As an illustration, radium nitrate salt Ra(NO3)2 has a solubility of 13.9 g per 100 g H2O at 20°C. However, interest in liquid targets has increased recently as ways have been found to overcome the problem of limited solubility.

[0006] Both solid targets and liquid targets require separation of radioisotopes from the target, which can usually be accomplished in separation columns using solid phase extraction methods.

[0007] Global reserves of target materials for some parent nuclides from which radioisotopes can be derived are limited. In these cases, particularly (but not limited to) Ra-226, reusing the target material is beneficial.

[0008] The recycling of target material is mentioned in the international patent application WO 2020 / 260210, which describes a method for producing actinium based on the photonuclear method of irradiating a liquid radium-226 target and irradiating, after separation of actinium, a liquid solution of the radium-226 target as such, using a closed-loop system.

[0009] The purification of actinium in the process of producing actinium radioisotopes was described in international patent application WO 2020 / 148316.

[0010] However, there is still a need for good cleaning methods and systems to enable reuse of target materials for further irradiation to produce radioisotopes.

[0011] DISCLOSURE OF THE INVENTION

[0012] The objective of the present invention is to provide methods and systems for cleaning irradiated targets for reuse in the production of radioisotopes.

[0013] An advantage of embodiments of the present invention is that these systems and methods provide an efficient way to reuse irradiated targets, such as for producing radioisotopes.

[0014] An advantage of embodiments of the present invention is that systems and methods are provided for recycling irradiated targets, regardless of whether these targets were in solid or liquid form at the time of irradiation.

[0015] The advantage of the embodiments of the present invention is that the target material can be reused in the production of radioisotopes, which makes it possible to increase the production of radioisotopes with a given amount of target material. In addition, it should be noted that, for example, the production of Ac-225 without the addition of a carrier (NCA) formed by the decay of Ra-225 is impossible in the first stage of radium / actinium separation, since small amounts of Ac-227 (T1 / 2 : 21.8 years) are also produced during the photonuclear production process by neutron capture of the parent nuclide Ra-226. Thus, in the radium / actinium-based production example, the use of a liquid radium target in a closed system is undesirable when Ac-225 NCA is the main goal of the production process. After the first highly efficient separation of radium isotopes (224+225+226) from actinium isotopes (225+227), radium must be stored to accumulate new Ac-225 from Ra-225 decay, which will ultimately lead to the formation of Ac-225 NCA after the second Ra / Ac separation step. Consequently, this increases the amount of parent nuclide Ra-226 required to produce Ac-225 and highlights the importance of a proper Ra-226 reprocessing strategy.

[0016] An advantage of the embodiments of the present invention is that, thanks to the proposed purification method, the problems caused by washing (e.g., dilution of the target) and the uncertainties associated with the pH of the irradiated solution can be overcome so that the target material can be reused.

[0017] An advantage of the embodiments of the present invention is that inorganic and organic contaminants can be removed from the target material.

[0018] An advantage of the embodiments of the present invention is that they provide the ability to obtain the minimum chemical purity required for the target material, such as Ra, for recycling and re-irradiation.

[0019] An advantage of the embodiments of the present invention is that the complexity caused by the cleaning process according to the embodiments of the present invention is limited.

[0020] The above object is achieved by the method and device according to the present invention.

[0021] The present invention relates in one aspect to a method for purifying target material for reuse in producing radioisotopes, the method comprising:

[0022] - obtaining a solution of irradiated target material, wherein the solution contains at least target material containing Ra-226 and, optionally, also radioisotopes Ra-225 and Ac-225 and, optionally, impurities,

[0023] then,

[0024] - adding an acid, which is HNO3, in a given quantity and concentration and providing conditions for quantitative dissolution of the target material and preventing co-precipitation of optionally present radioisotopes and / or impurities,

[0025] - selective removal of H2O from the solution by evaporation, leaving the acid preferentially within the solution, thereby allowing the precipitation of the target material as the concentration of acid in the solution increases, and thereby reducing or preventing the co-precipitation of optionally present radioisotopes of radioisotopes,

[0026] - reducing the temperature of the solution after removing excess H2O to maximize the precipitation of the target material and reduce the solubility of the target material in the remaining liquid,

[0027] - separating the liquid containing optionally present radioisotopes and / or impurities from the deposited target material, and

[0028] - preparation of deposited target material for reuse in obtaining radioisotopes.

[0029] The latter may be, for example, re-irradiation to produce radioisotopes or may include, for example, storage to accumulate new Ac-225.

[0030] Evaporation may refer to the selective removal of H2O by converting it into a vapor state. In some embodiments, evaporation may be distillation.

[0031] Temperature reduction may involve an active cooling step, but does not necessarily require an active cooling step. Temperature reduction refers to the fact that the temperature at which evaporation occurs is higher than the temperature at which liquid separation occurs.

[0032] An advantage of the embodiments of the present invention is that at least one concentration step is performed, which in the embodiments of the present invention is carried out using an evaporation process, such as a distillation process.

[0033] For example, when producing actinium-225 from radium-226 target material, Ac-225 is separated from the radium on average every two weeks. This facilitates a slower process than that achieved by evaporation, such as distillation, allowing for greater focus on minimizing Ra-226 loss and ensuring rapid recycling of Ac-225 after separation.

[0034] An acid, such as HNO3, can be added at a concentration of 1% to 100%, for example, in a range with an upper limit of, for example, 90%, for example, 80%, for example, 75%, for example, 70%, for example, 69%, and with a range having a lower limit of, for example, 10%, for example, 25%, for example, 40%. The acid can be HNO3, for example, in the case of producing Ac-225 isotopes using Ra-226 target material. It should be noted that the method can be used to recycle the target material, even if the separation of the target materials and the radioisotopes obtained during the previous irradiation is performed in a different way. For example, in the case of a target material that is Ra-226, the method can also be used when the amounts of Ra-225 and Ac-225 are small or completely absent, and the method is mainly carried out to obtain Ra-226 in a pure and concentrated form without the presence of inorganic or organic impurities or large amounts of HNO3.

[0035] It should be noted that the cleaning method can be applied to the target material that has been irradiated for the first time or to the target material that has been processed repeatedly.

[0036] Producing a solution containing irradiated target material may include producing an irradiated solution of the target material or producing a solution of irradiated target materials in which the irradiated target material was irradiated while in solid form. An advantage of embodiments of the present invention is that they provide purification methods that can be used for both solid irradiation targets and liquid irradiation targets.

[0037] Irradiation of the target material, whether in liquid or solid form, can be accomplished with photons, neutrons, or charged particles such as protons or deuterons. In preferred embodiments, the radium-226 target material is irradiated with photons or neutrons in liquid or solid form to produce actinium radioisotopes by producing radium-225.

[0038] The production of a solution of irradiated target material may further include the production of aqueous solutions or solids, such as wash materials used to wash the target capsule / container, wash materials used to wash the transfer pipeline, side process streams containing smaller amounts of target materials and radioisotopes or mixtures thereof in solid or liquid form, before, together with or after the transfer of the main target material.

[0039] In some embodiments, the method may be substantially carried out to obtain Ra-226 in a pure and concentrated form without the presence of impurities or large amounts of HNO3.

[0040] The irradiated target material may contain Ra-226 and, if necessary, Ra-225 and Ac-225, wherein the acid is HNO3, and wherein HNO3 is present at a concentration of 65% to 68% when the radium is deposited. An advantage of embodiments of the present invention is that by using a concentration of 65% to 68% for deposition, it is possible to avoid the need to remove an increased amount of H2O during subsequent evaporation, which is often the case when adding lower concentrations, or to avoid the increased presence of aggressive vapors (HNO3, NOX), which is often the case when adding higher concentrations.

[0041] One or more stages of the method can be performed at reduced pressure, i.e., a pressure below atmospheric pressure. Reduced pressure can be an operating pressure in the range of 50 mbar to 200 mbar. The latter can enable selective capture of volatile isotopes and / or reduce the spread of corrosive vapors. Reduced pressure can advantageously lower the boiling point of the solution.

[0042] Heating or cooling of the solution can be achieved by using circulating liquid in the double wall of the double wall reactor vessel (equipped with a jacket).

[0043] The method may include visual monitoring of the process using a transparent reactor vessel.

[0044] The heating / cooling solution can be mainly H2O.

[0045] The method may further include stirring the solution, for example, using magnetic stirring. An advantage of embodiments of the present invention is that stirring can improve the evaporation process or the boiling process during an evaporation process, such as distillation.

[0046] The method can be applied to a rotary evaporator system. An advantage of the embodiments of the present invention is that the evaporation surface area is actively increased, thereby improving the efficiency of the process.

[0047] The method can be applied in a closed loop heated and / or cooled via a heat exchanger. An advantage of the embodiments of the present invention is that, when using a closed loop, the target material can be extracted from the liquid in the event of a double-wall failure when using a double-wall reactor vessel.

[0048] After removing excess H2O, the temperature can be lowered below room temperature but above the freezing point of the liquid.

[0049] The solution can be filtered using an immersion filter connected to a filtrate collection tank, if necessary with a buffer tank and a vacuum pump.

[0050] Obtaining precipitated target material may involve washing the precipitate with concentrated acid after initial filtration and, if necessary, repeating the filtration process. By washing the precipitate with acid after initial filtration and, if necessary, repeating the filtration process, radioisotope recovery can be improved while minimizing target material dissolution.

[0051] After final filtration, the target material precipitate can be dried to remove residual acid, and thus the solubility of the target material in H2O can be further improved.

[0052] H2O can be added to extract the target material, which results in complete dissolution of the target material.

[0053] In some embodiments, the solution may be heated to clean the reactor vessel, wherein the process is carried out by condensing and dissolving residual solids of the target material.

[0054] The solution can be used for irrigation.

[0055] In one aspect, the present invention also relates to a target material cleaning system comprising:

[0056] reactor vessel,

[0057] inlet for irradiated target material solution,

[0058] inlet for adding acid,

[0059] a reactor vessel containing evaporation equipment, such as, for example, distillation equipment, for removing H2O from a solution of irradiated target material, leaving the acid predominantly within the solution, thereby allowing the precipitation of the target material as the concentration of the acid in the solution increases and thus reducing or preventing the co-precipitation of optionally present radioisotopes, and

[0060] wherein the system further comprises a filter means for separating the liquid containing optionally present radioisotopes from the deposited target material.

[0061] The irradiated target material may contain Ra-226 and, if necessary, Ra-225 and Ac-225. The acid inlet may be an HNO3 inlet.

[0062] The system may include a heating / cooling system for controlling the reactor vessel temperature by heating and / or cooling. The heating / cooling system may comprise a double-walled heating / cooling jacket. The heating / cooling system may connect the heating / cooling jacket to the primary fluid circuit and the fluid circulation system.

[0063] The system may include an air evacuation system to create a reduced pressure in the reactor vessel.

[0064] The system may include a pressure sensor for measuring the pressure in the reactor vessel.

[0065] Furthermore, the system may comprise a controller for controlling a system such as, for example, an air pump system, a heating / cooling system, and a system for controlling the amount of acid added, to perform the method as described above.

[0066] In addition, the system may contain a radon removal device to remove radon.

[0067] Specific and preferred aspects of the invention are set forth in the appended independent and dependent claims. The features of the dependent claims may be combined with the features of the independent claims and with the features of other dependent claims, depending on the circumstances, and not only as expressly set forth in the claims.

[0068] While devices in this field are continually being improved, modified, and evolved, it is believed that the concepts presented represent significant new and innovative improvements, involving departures from prior practice, that result in more efficient, stable, and reliable devices of this kind.

[0069] The above and other characteristics, features, and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is presented by way of example only and does not limit the scope of the invention. The reference signs given below refer to the accompanying drawings.

[0070] BRIEF DESCRIPTION OF DRAWINGS

[0071] Fig. 1 shows a target material cleaning system according to an embodiment of the present invention.

[0072] In different figures, the same symbols refer to the same or similar elements.

[0073] IMPLEMENTATION OF THE INVENTION

[0074] The present invention will be described with respect to specific embodiments and with reference to specific drawings. However, the invention is not limited thereto, but is defined solely by the claims. The drawings described are merely diagrams and are not limiting. In the drawings, the size of some elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and relative sizes do not correspond to the actual reduced representations for the practical implementation of the invention.

[0075] Furthermore, the terms "first," "second," "third," and the like in the description and claims are used to distinguish similar elements and not necessarily to describe a sequence, whether temporal, spatial, rank-ordered, or otherwise. It should be understood that the terms so used are interchangeable under appropriate circumstances, and that the embodiments of the invention described herein may function in sequences different from those described or illustrated herein.

[0076] Furthermore, the terms "upper," "lower," "above," "below," and the like in the description and claims are used for descriptive purposes and not necessarily to describe relative positions. It is to be understood that the terms so used are interchangeable in appropriate circumstances, and that the embodiments of the invention described herein may operate in orientations different from those described herein.

[0077] It should be noted that the term "comprising" used in the claims should not be interpreted as limited to the means listed below; it does not exclude other elements or steps. Thus, it should be interpreted as indicating the presence of the specified features, entire objects, steps or components when referring to them, but does not exclude the presence or addition of one or more other features, entire objects, steps or components or groups thereof. Therefore, the term "comprising" covers a situation in which only the specified features are present, and a situation in which these features and one or more other features are present. Thus, the word "comprising" according to this invention also includes, as one of the embodiments of the invention, the absence of any additional components.Thus, the scope of the expression "a device comprising elements A and B" should not be interpreted as being limited to devices consisting only of components A and B. As applied to the present invention, it means that only A and B are significant components.

[0078] Similarly, it should be noted that the term "coupled" should not be interpreted as limited to direct connections. The terms "coupled" and "connected" may be used, along with their derivatives. It should be understood that these terms are not synonymous with each other. Thus, the scope of the expression "device A coupled to device B" should not be limited to devices or systems in which the output of device A is directly connected to the input of device B. This means that there is a path between the output of A and the input of B, which may be a path involving other devices or elements. The term "coupled" may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but still work together or interact with each other.

[0079] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout the specification do not necessarily refer to the same embodiment, but may refer to one. Furthermore, particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments, as will be apparent to one skilled in the art from this disclosure.

[0080] Similarly, it should be understood that in the description of exemplary embodiments of the present invention, various features of the present invention are in some cases grouped together in a single embodiment, figure, or description thereof for the purpose of organizing the description of the invention and facilitating an understanding of one or more different aspects of the present invention. However, this method, according to the invention, should not be interpreted as reflecting an intention that the claimed invention requires more features than are expressly set forth in each claim. Rather, as the following claims reflect, aspects of the invention are not contained in all features of the single embodiment disclosed above.Any claims following the detailed description are hereby expressly incorporated into the present detailed description, and each claim stands alone as a separate embodiment of the invention.

[0081] Furthermore, although some embodiments described herein include some, but not other, features included in other embodiments, combinations of features of different embodiments should be within the scope of the invention and form different embodiments, as will be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0082] Furthermore, some of the embodiments are described herein as a method or a combination of method elements that can be implemented using a computer system processor or other means for performing a given function. Thus, a processor with the necessary instructions for performing such a method or method element forms a means for performing the method or method element. Furthermore, an element of the embodiment of the device described herein represents an example of a means for performing the function performed by said element for the purpose of implementing the invention.

[0083] The description provided herein sets forth numerous specific details. However, it should be understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures, and techniques have not been shown in detail in order not to obscure the understanding of this description.

[0084] The invention will now be described in detail by describing several embodiments of the invention. Obviously, other embodiments of the invention can be configured in accordance with the knowledge of those skilled in the art without departing from the technical description of the invention, and the invention is limited only by the claims appended hereto.

[0085] According to a first aspect, the present invention relates to a method for purifying a target material for reuse in the production of radioisotopes. The method can also be used in the production of radioisotopes, and therefore, the present invention also relates to a method for producing radioisotopes using the purification of the target material and the reuse of the target material in the production of radioisotopes.

[0086] A method for purifying a target material includes obtaining a solution of irradiated target material, wherein the solution contains at least the target material and, optionally, also radioisotopes and, optionally, impurities. Obtaining a solution of irradiated target material may include obtaining a liquid target that has been irradiated, or obtaining a solution that is obtained by dissolving irradiated target material that has been irradiated in solid form. In some embodiments, the solution may be a solution of Ra-225 and Ra-226, which is stored before the Ac-225 purification process. Such a solution can be stored, for example, for two weeks. The method also includes subsequently adding an acid in a predetermined amount, and the concentration can be increased under predetermined temperature conditions to quantitatively dissolve the target material and prevent co-precipitation of optionally present radioisotopes.Thus, the temperature at which the acid is added, as well as the amount and concentration of the acid, can be selected such that coprecipitation of radioisotopes and impurities is either absent or substantially absent. Alternatively, conditions during or after the addition can be selected to quantitatively dissolve or redissolve the target material and avoid or prevent coprecipitation of optionally present radioisotopes. The method also includes selectively removing H2O from the solution by evaporation, such as distillation, leaving the acid predominantly within the solution, thereby allowing the target material to precipitate, while the acid concentration in the solution increases, thereby reducing or preventing coprecipitation of optionally present radioisotopes.The method also includes reducing the temperature after removing excess H2O from the solution to maximize target material precipitation and reduce the solubility of the target material in the remaining liquid. This provides a particular advantage, as the amount of Ra introduced during the actinium purification step is reduced, and less Ra must be recovered from this process sidestream. Temperature reduction may include an active cooling step, although such cooling is not required to be active.

[0087] Furthermore, the method includes separating a liquid containing optionally present radioisotopes and impurities from the deposited target material and preparing the deposited target material for reuse in producing radioisotopes. The method may include re-irradiation to produce radioisotopes and / or storage for new accumulation of Ac-225 from Ra-225.

[0088] As an illustration and not limitation of the embodiments of the present invention, additional standard and optional features will be illustrated below in exemplary methods and embodiments.

[0089] The first exemplary method describes a method for purifying radium target material after irradiation to produce actinium. The process begins with transferring a liquid target solution, having a pH of 1 to 3 and containing Ra-226, Ra-225, Ac-225, and impurities, to a precipitation vessel. Rinse solutions are subsequently transferred, and by maximizing the throughput of the rinse process, this ensures (nearly) quantitative transfer of Ra-226 to the precipitation vessel. The liquid target solution can be an irradiated liquid target or can be formed from a solid irradiated target dissolved in a solvent to produce a liquid target solution. The Ra solution is now diluted well below the maximum solubility point. Then an acid is added, such as, for example, concentrated HNO3, for example, 25 to 50 ml of concentrated HNO3 (68%), preferably in a molar amount, in which Ac is preferably separated by filtration.At this point, some precipitation of Ra is possible, since. After this addition, the HNO3 concentration can increase to 1-3 M HNO3. However, once evaporation, such as distillation, begins, all of the Ra is redissolved by increasing the temperature, thereby eliminating the possibility of co-precipitation of Ac-225 / Ac-227 and impurities upon the addition of concentrated HNO3. Alternatively, even excess H2O can be added to ensure that all of the Ra-226 dissolves after the addition of concentrated HNO3. In other words, conditions are ensured for quantitative dissolution of the target material and the prevention of co-precipitation of optionally present radioisotopes. H2O is then separated from the solution by evaporation, such as distillation at elevated temperature and reduced pressure, and collected in a distillate collection container. As the HNO3 concentration increases and the volume decreases during evaporation, such as distillation, more and more Ra(NO3)2 crystals are formed.However, due to this slow and controlled formation and growth of crystals during evaporation, such as distillation, temperature changes within the liquid, the inclusion of Ac by co-precipitation is effectively prevented.

[0090] When the evaporation process, such as distillation, is complete, the vacuum is released, boiling immediately ceases, and the liquid should be cooled to a minimum. The heating mantle should be cooled from 70-80°C, for example, to 5°C. This will minimize the residual solubility of Ra in concentrated HNO3.

[0091] After complete cooling, a dip tube with a filter is inserted into the reactor, and the filter is directed into the bottom of the round-bottomed reactor vessel. The dip tube and filter are connected to a tank for collecting the actinium fraction, a small buffer tank, and a vacuum pump connected to the Rn capture system. Filtration then begins.

[0092] Add 25-50 ml of cold concentrated HNO3 (68%) to the reactor while the filter dip tube is still in place. This additional volume is then removed back toward the actinium collection vessel. This process is designed to remove all Ac from Ra while minimizing additional Ra dissolution. It can be repeated several times, keeping the volumes minimal. After quantitative transfer of Ac from Ra, the filter dip tube is removed and rinsed with H2O to remove all Ra.

[0093] These wash solutions can be, for example, recycled distillate (low in HNO3) or pure H2O. The primary focus is on minimizing additional Ra transfer to Ac in concentrated HNO3, as Ra-226 is more difficult to recover from this sidestream. The distillate can now be used to dilute concentrated HNO3 containing Ac to suitable conditions for Ra / Ac DGA separation, typically 2-4 M HNO3.

[0094] After removing the filter dip tube, the evaporation process is restarted to remove any residual traces of concentrated HNO3 from the reactor and H2O / HNO3 separator. By removing the last traces of HNO3, Ra solubility is maximized, and a minimum of acid is potentially transferred to the liquid target irradiation system.

[0095] Add 120-200 ml of pure H2O to the reactor vessel, and begin evaporation again, similar to distillation, by heating the vessel and applying reduced pressure. This process effectively cleans the walls of any remaining Ra-226 by irrigating the vessel with H2O. The process is then stopped and the liquid is removed using a dip tube. Pure H2O can be added to the reactor, and the process is repeated until the reactor is effectively cleaned of any residual Ra-226.

[0096] Depending on whether the Ra-226+Ra-225 is sent to a decay product storage tank for two weeks to accumulate Ac-225 or returned to the irradiation process, rinses are either added to the Ra solution or not. In the former case, the rinse solution can be added to the Ra batch that will be processed one last time before being sent back to irradiation. With this strategy, the Ra-226 cycle in this precipitation reactor is complete.

[0097] The volume of the radioactive waste tank is comparable to the volume of the liquid target + rinse. This ensures that there is no difference between the initially irradiated target and the one subsequently processed, further simplifying the process.

[0098] For the successful recycling of target materials, such as, for example, Ra, a minimum degree of chemical purity is required. Therefore, the processes used in methods for producing isotopes from target material by recycling the target material should avoid or minimize the introduction of organic substances or leachable extractants. The purification methods according to embodiments of the present invention advantageously contribute to the reduction of the amount of impurities. Such impurities include, for example, fission products, such as products of the photofission process, products obtained from target materials (such as, for example, in the case of radium, the presence of stable and / or radioactive Pb and Po-210), leaching products, such as products obtained from encapsulating materials such as Ti, Fe, Ni, Cr, Zr, Nb or Si, Al, Na, B obtained from quartz or borosilicate, etc., activation products, etc.

[0099] In some exemplary embodiments, the reactor vessel operates under reduced pressure. The reduced pressure may, for example, be in the range of 50 mbar to 200 mbar, such as in the range of 100 mbar to 200 mbar. In this way, leakage of acid vapors and radon (Rn-220, Rn-222) from the vessel into the sealed shell of the hot cell can be prevented. Radon can be filtered and captured at a low flow rate. Leakage of acid vapors and radon can alternatively or additionally be reduced by using dehumidifier columns, Ag-ETS10 columns, or by using a radioactive waste holding tank. According to one embodiment, the radioactive waste holding tank can, for example, have a volume of 100 liters and be pressurized at, for example, a maximum of 10 bar. When the reactor vessel operates at a pressure of 100 mbar to 200 mbar, the boiling temperature of the liquid decreases to a temperature in the range of 50°C to 70°C.In some embodiments, a pressure sensor is installed between the condenser and the distillate collection vessel. A similar setup, such as that known from a rotary evaporator system, can be used. An advantage of the present invention is that the equipment used is radiation-hardened and, therefore, adds little to the system's complexity. Another advantage of the present invention is that pressure and pressure drops can be easily measured within the system, such as in a hot cell.

[0100] In some exemplary embodiments of the invention, the temperature for controlling evaporation, i.e., distillation, can be controlled using a liquid-based heating / cooling system. An advantage of embodiments of the present invention is that electrical heating equipment in direct contact with the reactor vessel is not required. The liquid-based heating / cooling system can be, for example, a double-walled heating / cooling system, such as a double-walled heating / cooling jacket. Such a double-walled heating / cooling system can be, for example, water-based.Since a double-wall system can operate at, for example, 80°C, the system can be advantageously used when the reactor vessel is operated at reduced pressure. Since the boiling point of the liquid typically decreases to a temperature in the range of 50°C to 70°C, temperature control using water is quite feasible. Since a heating / cooling jacket with water can operate at, for example, 80°C, the above conditions can advantageously provide a significant temperature difference, allowing the evaporation process to be controlled and / or accelerated.

[0101] A double-wall heating / cooling system can be connected via a primary liquid circuit to a circulation pump. An advantage of the present invention is that, when using water and in the event of a malfunction of the double-wall heating system, the radium will be diluted in the water, but this allows for easier recovery (e.g., compared to heating / cooling with silicone oil).

[0102] An advantage of some embodiments is that an electric heating mantle and thermocouples are not required to control evaporation, such as distillation for precipitation. Since the use of an electric heating mantle, as well as thermocouples, adds complexity to the isotope production system and / or target material purification system, the ability to eliminate electric heating mantles and / or thermocouples makes such systems easier to control and use.

[0103] An advantage of embodiments of the present invention is that they can use forced cooling, such as before filtration, to reduce the concentration of residual target material (e.g. Ra-226) and / or to accelerate the cooling process after evaporation, such as distillation.

[0104] An advantage of embodiments of the present invention is that subsequent precipitation of Ra-226 can be avoided by filtering the liquid containing Ac-225 at a temperature below room temperature.

[0105] In embodiments according to the present invention, a stirring device can be used to perform stirring in the reactor vessel, for example, in the lower portion of the reactor vessel. In one embodiment, such a stirring device can be a magnetic stirrer. In one embodiment, the magnetic stirrer can be an oval-type stirrer, for example, coated with borosilicate instead of polytetrafluoroethylene (PTFE). The stirrer can be advantageously used in a reactor vessel with a round bottom, although embodiments are not limited to this. Using a stirring device can reduce the size of bubbles during boiling, which can be intense at lower pressures, and centralize gas formation in the middle of the reactor.

[0106] According to embodiments of the present invention, evaporation parameters, such as distillation, are adjusted such that HNO3 remains almost entirely in solution, and the evaporation process slows significantly upon reaching an azeotropic mixture of concentrated HNO3. This improves safety and reduces the likelihood of unwanted complete evaporation of the liquid. In some embodiments, a Vigreux-type column between the reactor vessel and the distillation bridge is effective in separating HNO3 from H2O, and a maximum practical concentration of 68% HNO3 can be achieved relatively easily. Above this azeotropic point, brown nitrous oxide (NOX) vapors are typically observed in the solution, which should be avoided. The distillate remains relatively free of HNO3 unless the pressure is greatly reduced.

[0107] In a second aspect, the present invention relates to a target material purification system. The system comprises a reactor vessel, an inlet for a solution of irradiated target material, and an inlet for adding an acid. The reactor vessel comprises evaporation equipment, such as distillation equipment, for removing H2O from the solution of irradiated target material, leaving an acid, such as HNO3, predominantly in the solution, thereby enabling the precipitation of the target material with increasing acid concentration in the solution and thereby reducing or preventing the co-precipitation of optionally present radioisotopes and impurities. Furthermore, it comprises a filter means for separating a liquid containing optionally present radioisotopes from the precipitated target material. The system may also comprise an inlet for adding a solvent, such as H2O.The system may also comprise a heating / cooling system for controlling the temperature of the reactor vessel by heating and / or cooling. The heating / cooling system may be a double-walled heating / cooling jacket. The system may also comprise a pumping system for creating a reduced pressure in the reactor vessel. The system may further comprise a pressure sensor for measuring the pressure in the reactor vessel. According to some embodiments, the system may also comprise a controller for controlling the system to perform the method described in the first aspect. The system may also comprise a radon removal device for removing radon. Additional features and components may be provided that implement the functionality described in the first aspect of the present invention. By way of illustration, which does not limit the embodiments of the present invention, the various components may be as shown in Fig. 1.

[0108] In a further aspect, the present invention also relates to the use of the purification method according to the first aspect for producing a target material that can be reused for irradiation to produce radioisotopes.

Claims

1. A method for purifying target material for producing radioisotopes for reuse, the method comprising: - obtaining a solution of irradiated target material, wherein the solution contains at least the target material and also radioisotopes and impurities, then - adding acid in a given quantity and concentration and providing conditions for quantitative dissolution of the target material and preventing co-precipitation of radioisotopes, - selective removal of H2O from the solution by evaporation, leaving the acid predominantly within the solution, thereby allowing the precipitation of the target material, while the concentration of the acid in the solution increases, and thereby reducing or preventing the co-precipitation of radioisotopes, - reducing the temperature of the solution after removing excess H2O to maximize the precipitation of the target material and reduce the solubility of the target material in the remaining liquid, - separation of the liquid containing radioisotopes from the deposited target material, and - preparation of deposited target material for reuse in the production of radioisotopes, characterized in that the irradiated target material contains Ra-226 and the acid is HNO3.

2. The method of claim 1, wherein obtaining a solution containing irradiated target material comprises obtaining an irradiated solution of target material or obtaining a solution of irradiated target materials, wherein the irradiated target material was irradiated while in solid form.

3. The method according to any of the preceding claims, wherein producing a solution of irradiated target material further comprises producing aqueous solutions or solids, such as wash materials used to wash the target capsule / container, wash materials used to wash the transfer pipeline, side process streams containing smaller amounts of target materials and radioisotopes or mixtures thereof in solid or liquid form, before, together with or after the transfer of the main target material.

4. The method according to any one of the preceding claims, wherein the concentration of HNO3 when added to the reactor vessel is from 65% to 68%.

5. The method according to any of the preceding claims, wherein one or more steps of the method are performed at a pressure below atmospheric pressure.

6. The method according to any of the preceding paragraphs, wherein the heating or cooling of the solution is carried out using a circulating liquid in a double wall of a double wall reactor vessel, and / or the method is used in a closed loop which is heated and / or cooled through a heat exchanger.

7. The method according to any of the preceding paragraphs, comprising visually monitoring the process using a transparent reactor vessel.

8. The method according to any of the preceding claims, further comprising stirring the solution, for example using magnetic stirring.

9. The method according to any of the preceding paragraphs, wherein the method is used in a system with a rotary evaporator.

10. The method according to any of the preceding claims, wherein after removing excess H2O, the temperature is lowered below room temperature but above the freezing point of the liquid.

11. A method according to any one of the preceding claims, wherein the solution is filtered using a submersible filter connected to a filtrate collection vessel and a vacuum pump or buffer vessel.

12. The method of any one of the preceding claims, wherein obtaining the precipitated target material comprises washing the precipitate with acid after initial filtration and repeating the filtration process.

13. A system for cleaning target material, comprising: reactor vessel, an inlet for the solution of irradiated target material containing Ra-226, an inlet for adding at least HNO3 acid, wherein the reactor vessel comprises evaporative equipment for removing H2O from the solution of the irradiated target material, leaving the acid predominantly in the solution, thereby allowing the precipitation of the target material, while the concentration of the acid in the solution increases, and thereby reducing or preventing the co-precipitation of the radioisotopes, and a filtering means for separating liquid containing radioisotopes from deposited target material.

14. The system of claim 13, comprising one or more of the following: a heating / cooling system for controlling the temperature of the reactor vessel by heating and / or cooling and / or a pumping system for creating a pressure below atmospheric pressure in the reactor vessel, a pressure sensor for measuring the pressure in the reactor vessel and / or Radon removal device for radon removal.

15. The system according to any one of paragraphs 13, 14, further comprising a controller for controlling the system for performing the method according to any one of paragraphs 1-12.

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