Patent Description:
For the production of radio-isotopes, generally, solid targets are being used for their high yield in state-of-the-art systems, as for solid targets, a large density of a parent nuclide, from which the radio-isotopes are produced, may be easily achieved.

For liquid targets, there is the limited solubility of most parent nuclide compounds in water (typically used as the liquid solvent) at room temperature. For example, salts of Ra-<NUM> (T<NUM>/<NUM>: <NUM> years), which may be used as basic chemicals for providing the parent nuclide for producing the radio-isotope Ra-<NUM> (T<NUM>/<NUM>: <NUM> days) that may decay to the radio-isotope Ac-<NUM> (T<NUM>/<NUM>: <NUM> days), have a limited solubility in water. By way of illustration, radium nitrate salt Ra(NO<NUM>)<NUM> has a solubility of <NUM> per <NUM> of H<NUM>O at <NUM>. Nevertheless, recently, interest in liquid targets has been increased since methods have been found to overcome the limited solubility issue.

Both in the case of solid targets and liquid targets, separating the radio-isotopes from the target is required, which typically may be done in separation columns by solid phase extraction methods.

The worldwide available stock of target materials of some parent nuclides from which the radio-isotopes can be produced is limited. Especially in these cases, such as for e.g. in the case of Ra-<NUM>, but not limited thereto, it is useful to re-use target material.

The re-use of target material has been referred to in international patent application <CIT>, where a method is described for the production of Actinium based on the photonuclear route of irradiating a Radium-<NUM> liquid target and irradiating - after separation of the Actinium - the Radium-<NUM> liquid target solution as such using a closed loop system.

Purification of actinium in the production process of actinium radio-isotopes has been described in international patent application <CIT>.

Further systems suitable for the purification of radioisotopes can be found in patent documents <CIT> and <CIT>.

Nevertheless, there is still a need for good purification methods and systems to be able to re-use target materials for further irradiations in the production of radio-isotopes.

It is an object of the present invention to provide methods and systems for purifying irradiated targets for re-use in the production of radio-isotopes.

It is an advantage of embodiments of the present invention that these systems and methods provide an efficient way of re-using irradiated targets for e.g. generation of radio-isotopes.

It is an advantage of embodiments of the present invention that systems and methods are provided for re-using irradiated targets, independent whether these targets at the moment of irradiating were in solid or in liquid form.

It is an advantage of embodiments of the present invention that in the production of radio-isotopes, the target material can be re-used, allowing an increased production of radio-isotopes with a given amount of target material. It furthermore is to be noted that, for example, production of non-carrier added (NCA) Ac-<NUM>, formed by the decay of Ra-<NUM>, is not possible by the first Radium / Actinium separation step, as small amounts of Ac-<NUM> (T<NUM>/<NUM>: <NUM> years) are also formed in the photonuclear production route by neutron capture of the parent nuclide Ra-<NUM>. Therefore, for the example of Radium / Actinium based production, operation of a liquid radium target in a closed loop system is not desired when NCA Ac-<NUM> is the main goal of the production process. After a first high-efficiency separation of Radium (<NUM>+<NUM>+<NUM>) isotopes from Actinium (<NUM>+<NUM>) isotopes, the radium must be stored for ingrowth of fresh Ac-<NUM> by decay of Ra-<NUM>, which will finally result into NCA Ac-<NUM> after the second Ra/Ac separation step. This consequently increases the amount of parent nuclide Ra-<NUM> needed to produce Ac-<NUM>, and emphasis the importance of a good recycling strategy for Ra-<NUM>.

It is an advantage of embodiments of the present invention that due to the purification process provided, problems induced due to rinsing (e.g. dilution of the target) and uncertainties related to pH of the irradiated solution can be overcome so that re-use of the target material can be performed.

It is an advantage of embodiments of the present invention that inorganic and organic contaminations can be removed from the target material.

It is an advantage of embodiments of the present invention that these allow to obtain the minimum chemical purity required for the target material, e.g. Ra, to be recycled and irradiated again.

It is an advantage of embodiments of the present invention that the complexity induced by the purification process according to embodiments of the present invention is limited.

The above objective is accomplished by a method and apparatus according to the present invention.

The present invention relates in one aspect to a method for purification of a target material for re-use in the production of radio-isotopes, the method comprising.

The latter may for example be by re-irradiation for the production of radio-isotopes or may for example involve storage for ingrowth of new Ac-<NUM>. Evaporation may refer to selectively removing H<NUM>O by bringing it in vapor phase. The evaporation may in some embodiments be distillation.

Lowering the temperature may comprise an active cooling step, but does not need to require an active cooling step. Lowering of the temperature refers to the fact that the temperature at which evaporation is performed is higher than the temperature at which the separating of the liquid is performed.

It is an advantage of embodiments of the present invention that at least one concentrating step is performed, in embodiments of the present invention being performed by an evaporation process, e.g. a distillation process.

For example in case of production of Actinium-<NUM> from a Radium-<NUM> target material, on average Ac-<NUM> is separated from Radium every two weeks. This facilitates a slow process as obtained with the evaporation, e.g. distillation, process, allowing to focus on minimizing Ra-<NUM> losses and allowing quick processing of Ac-<NUM> after separation.

The acid, e.g. HNOs, may be added in a concentration between <NUM>% and <NUM>%, e.g. in a range with as an upper limit for example <NUM>%, e.g. <NUM>%, e.g. <NUM>% e.g. <NUM>%, e.g. <NUM>% and with a range having as a lower limit for example <NUM>%, e.g. <NUM>%, e.g. <NUM>%. The acid may be HNOs, for example in the case of production of Ac-<NUM> isotopes using Ra-<NUM> target material. It is to be noted that the method may be used for recycling target material, even if separation between the target material and the radio-isotopes produced during the earlier irradiation is performed in a different manner. Although the target material is Ra-<NUM>, the method may also be used when Ra-<NUM> and Ac-<NUM> quantities are small or completely absent, and the process is mainly performed to obtain Ra-<NUM> is a pure and concentrated form without presence of inorganic or organic impurities or large quantities of HNO<NUM>.

It is to be noticed that the method of purification may be applied to target material that has been freshly irradiated or to target material that has been milked for a plurality of times.

Obtaining a solution comprising irradiated target material may comprise obtaining an irradiated solution of target material or obtaining a solution of irradiated target materials wherein the irradiated target material was irradiated when in solid form. It is an advantage of embodiments of the present invention that these provide purification methods that can be used both for solid irradiation targets as well as liquid irradiation targets.

Irradiation of the target material, either in liquid or solid form of the target material, may be by photons, neutrons, or charged particles, such as for example protons or deuterons. In advantageous embodiments, Radium-<NUM> target material is irradiated by photons or neutrons, in liquid or solid form, for production of Actinium radio-isotopes through production of Radium-<NUM>.

Obtaining a solution of irradiated target material, may further comprise obtaining aqueous solutions or solids, e.g. rinsing materials used for rinsing the target capsule/container, rinsing materials used for rinsing the transfer tubing, side process streams containing smaller quantities of target materials and radio-isotopes or a mixture of those, in solid or liquid form, before, together or after transfer of the main target material.

According to the embodiments, the method may be mainly performed to obtain Ra-<NUM> in a pure and concentrated form without presence of impurities or large quantities of HNOs.

The irradiated target material comprises Ra-<NUM> and optionally Ra-<NUM> and Ac-<NUM>, wherein the acid is HNOs and wherein the HNOs is present in a concentration between <NUM>% and <NUM>% when precipitation of Radium is performed. It is an advantage of embodiments of the present invention that by using a concentration between <NUM>% and <NUM>% for the precipitation, it can be avoided that an increased amount of H<NUM>O needs to be removed in the consecutive evaporation process, which often is the case when adding lower concentrations, or it can be avoided that there is an increased presence of corrosive vapours (HNOs, NOX), which often is the case when adding higher concentrations.

One or more of the method steps may be performed at reduced pressure, i.e. a pressure below atmospheric pressure. The reduced pressure may be an operational pressure in the range <NUM> mbar to <NUM> mbar. The latter may allow selectively capturing of volatile isotopes and/or reducing the spreading of corrosive fumes. Reducing the pressure may advantageously result in reducing the boiling point of the solution.

Heating or cooling of the solution may be performed using a circulating liquid in a double wall of a double walled (jacketed) reactor vessel.

The method may comprise visually following-up the process using a transparent reactor vessel.

The solution for heating/cooling may be predominantly H<NUM>O.

The method may furthermore comprise stirring the solution, e.g. using magnetic stirring. It is an advantage of embodiments of the present invention that stirring may improve the evaporation or boiling process during the evaporation process, e.g. the distilling.

The method may be applied in a rotary evaporator system. It is an advantage of embodiments of the present invention that the surface for evaporation is actively increased, thus improving the efficiency of the process.

The method may be applied in a closed circuit that is heated and/or cooled through a heat-exchanger. It is an advantage of embodiments of the present that by using a closed circuit, target material can be recovered from the liquid in case of breaking of a double wall when the double wall reactor vessel is used.

After removal of the excess H<NUM>O, the temperature may be lowered below room temperature but above the freezing temperature of the liquid.

The solution may be filtered using an immersion filter connected to a filtrate collection vessel, optionally a buffer vessel, and a vacuum pump.

Preparing the precipitated target material may comprise washing the precipitate with a concentrated acid after initial filtration, and optionally repeating the filtration process. By washing the precipitate with an acid after initial filtration and optionally repeating the filtration process, the recovery of radio-isotopes may be improved while minimising dissolution of the target material.

After the final filtration, the target material precipitate may be dried to remove residual acid and the solubility of the target material in H<NUM>O may thus be further improved.

H<NUM>O may be added for recovering the target material, thereby fully dissolving the target material.

In some embodiments, the solution may be heated to clean the reactor vessel in which the process is performed by condensation and dissolution of residual target material solids.

In one aspect, the present invention also relates to a system for the purification of a target material, the system comprising.

The irradiated target material comprises Ra-<NUM> and optionally Ra-<NUM> and Ac-<NUM>. The inlet for acid is an inlet for HNOs.

The system may 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 wall heating/cooling jacket. The heating/cooling system may connect a heating/cooling jacket with a primary fluid circuit with a liquid circulation pumping system.

The system may comprise an air pumping system for inducing a reduced pressure in the reactor vessel.

The system may comprise a pressure sensor for measuring a pressure in the reactor vessel.

The system furthermore may comprise a controller for controlling the system, such as for example the air pumping system, the heating/cooling system and a system for controlling the amount of acid added, for performing a method as described above.

The system furthermore may comprise a Radon removal apparatus for removing Radon.

<FIG> illustrates a system for purification of a target material, according to an embodiment of the present invention.

The drawings described are only schematic and are nonlimiting.

The word "comprising" according to the invention therefore also includes as one embodiment that no further components are present.

Similarly, it is to be noticed that the term "coupled" should not be interpreted as being restricted to direct connections only. The terms "coupled" and "connected", along with their derivatives, may be used. Thus, the scope of the expression "a device A coupled to a device B" should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. "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 yet still co-operate or interact with each other.

In a first aspect, the present invention relates to a method for purification of a target material for re-use in the production of radio-isotopes. The method further may be applied in the framework of the production of radio-isotopes, and consequently, the present invention also relates to a method for producing radio-isotopes, making use of purification of the target material and re-using the target material in the production of radio-isotopes.

The method for purification of a target material comprises obtaining a solution of irradiated target material, the solution thus comprising at least target material and optionally also radio-isotopes and optionally impurities. Obtaining a solution of irradiated target material may comprise obtaining a liquid target that has been irradiated or obtaining a solution that is obtained by dissolving irradiated target material that was irradiated in solid form. In some embodiments, the solution may be a Ra-<NUM> and Ra-<NUM> solution that is stored before an Ac-<NUM> purification process. Such a solution may be stored for e.g. two weeks first. The method also comprises, subsequently, adding an acid in a predetermined quantity and concentration may be adding under predetermined temperature conditions for quantitatively dissolving the target material and avoiding co-precipitation of the optionally present radio-isotopes. The temperature at which the acid is added as well as the quantity and concentration of the acid may thus be selected so that no or substantially no co-precipitation of radio-isotopes and impurities occurs. Alternatively, during or after adding, conditions may be selected so as to quantitatively dissolve or re-dissolve the target material and avoid or remove co-precipitation of the optionally present radio-isotopes. The method also comprises selectively removing H<NUM>O from the solution by evaporation such as for example distillation, leaving the acid predominantly inside the solution thereby allowing the target material to precipitate while the acid concentration in the solution increases and thereby reducing or avoiding co-precipitation of the optionally present radio-isotopes. The method also comprises, after removal of the excess H<NUM>O, lowering the temperature of the solution to maximise the precipitation of the target material and reduce the solubility of the target material in the remaining liquid. This has the particular advantage that amount of Ra material introduced into the Actinium Purification step is reduced, and less Ra needs to be recovered from this process side stream. Lowering the temperature may include an active cooling step, although it is not required that such cooling is active.

The method furthermore comprises separating the liquid containing the optionally present radio-isotopes and impurities from the precipitated target material, and preparing the precipitated target material for re-use in the production of radio-isotopes. The method may comprise re-irradiation for the production of radio-isotopes and/or storing for new ingrowth of Ac-<NUM> from Ra-<NUM>.

By way of illustration, embodiments of the present invention not being limited thereto, further standard and optional features will be illustrated below in exemplary methods and embodiments.

In a first exemplary method, a method for purifying a Radium target material after irradiation for the production of Actinium is described. The process is started by transferring a liquid target solution having a pH between <NUM> and <NUM> and containing Ra-<NUM>, Ra-<NUM>, Ac-<NUM> and impurities into a precipitation vessel. The rinsing solutions are transferred afterwards, and by maximizing the performance of the rinsing process, it guarantees a (near) quantitative transfer of Ra-<NUM> towards the precipitation vessel. The liquid target solution may be an irradiated liquid target or may stem from a solid irradiated target dissolved in a solvent to obtain a liquid target solution. The Ra solution is now diluted well below the maximum solubility point. Next, acid such as for example concentrated HNOs, e.g. between <NUM>-<NUM> concentrated HNOs (<NUM>%) is added, preferably in the molar quantity in which Ac is preferably separated in the filtration process. At this point, some Ra precipitation is likely to occur, as HNOs concentration can be increased to <NUM> - <NUM> HNOs after this addition. However, upon starting the evaporation, e.g. distillation process, all Ra is again dissolved by increase of temperature, therefore excluding the chance of co-precipitation of Ac-<NUM>/Ac-<NUM> and impurities upon the addition of the concentrated HNO<NUM>. Alternatively, even excess H<NUM>O can still be added to come to the point that all Ra-<NUM> is dissolved after addition of the concentrated HNO<NUM>. In other words, conditions are provided for quantitatively dissolving the target material and avoid co-precipitation of the optionally present radio-isotopes. Next, H<NUM>O is being stripped from the solution by evaporation, e.g. distillation at elevated temperature and reduced pressure, and collected in the distillate collection flask. When during evaporation, e.g. distillation, the HNOs concentration rises, and the volume is reducing, more and more Ra(NO<NUM>)<NUM> crystals are formed. However by this slow and controlled formation and growth of crystals during evaporation e.g. distillation, temperature variations inside the liquid, the inclusion of Ac by co-precipitation is effectively avoided.

When the evaporation process, e.g. distillation process, is completed, the reduced pressure is removed, the boiling process stops immediately, and the liquid should now be cooled down to a minimum. The heating jacked should be cooled from <NUM>-<NUM> to e.g. <NUM>. This will minimize the residual solubility of Ra in the concentrated HNOs.

After full cool-down, a filter dip tube is inserted in the reactor, and the filter is directed to the bottom of the round bottom reactor vessel. The filter dip tube is connected to a collection vessel for the Actinium fraction, a small buffer vessel, and a vacuum pump connected to the Rn trapping system. The filtration process is performed.

<NUM>-<NUM> cold concentrated HNOs (<NUM>%) is added into the reactor with the filter dip tube still in position, and this additional volume is again removed towards the Actinium collection vessel. This process is focused on removing all Ac from the Ra, while minimizing the additional dissolution of Ra, and can be repeated several times while keeping volumes to a minimum. After a quantitative transfer of Ac from the Ra, the filter dip tube is removed, and washed with H<NUM>O to remove all present Ra from it.

These washing solutions can be for example the recycled distillate (low in HNOs) or fresh H<NUM>O. The main focus is to minimize the additional transfer of Ra towards the Ac in concentrated HNOs, as Ra-<NUM> is more difficult to recover from this side-stream. The distillate can now be used to dilute the concentrated HNOs containing the Ac to the proper conditions for DGA Ra/Ac separation, which is typically <NUM> - <NUM> HNO<NUM>.

After removal of the filter dip tube, the evaporation process is again started to remove any residual traces of concentrated HNOs in the reactor, and the H<NUM>O/HNO<NUM> separator. By removal of the last quantities of HNOs, the Ra solubility is maximized, and a minimum of acid is potentially transferred to the irradiation liquid target system.

Fresh H<NUM>O, <NUM>-<NUM> is added to the reactor vessel, and the evaporation, e.g. distillation process is again started by heating of the jacket, and applying of reduced pressure. This process effectively cleans the walls from any residual Ra-<NUM> by the refluxing of H<NUM>O. Next, the process is stopped and the liquid is removed using a dip tube. Fresh H<NUM>O can be added to the reactor, the process repeated, until the reactor is effectively purified from any residual Ra-<NUM>. Depending if the Ra-<NUM>+Ra-<NUM> is being sent to a decay storage vessel for two weeks of ingrowth of Ac-<NUM>, or back towards the irradiation process, the rinsings are being added to the main Ra solution or not. In the first case, the rinse solution can be added to the Ra batch that will be milked for a final time before sending back towards irradiation. This strategy closes the loop for Ra-<NUM> in this precipitation reactor.

The volume in the decay tank is comparable to the volume of the liquid target + rinsing. By doing this, the process will not discriminate between a freshly irradiated target, and a consecutive milking, further simplifying the process.

In order to successfully re-use target materials, such as for example Ra, a minimum amount of chemical purity is required. Therefore, the processes used in methods for producing isotopes from target material by re-using target material should avoid or minimise the introduction of organics or leached extractants. Methods for purifying according to embodiments of the present invention, advantageously assist in reducing impurities. Such impurities include for example fission products such as for example photo-fission process products, products stemming from the target materials (such as for example in the case of Radium the occurrence of stable and/or radio-active Pb, and Po-<NUM>), leaching products, such as products stemming from encapsulation materials like Ti, Fe, Ni, Cr, Zr, Nb, or Si, Al, Na, B stemming from quartz or borosilicate, etc., activation products, etc..

In some exemplary embodiments, the reactor vessel is operated in reduced pressure. The reduced pressure may for example be in the range <NUM> mbar to <NUM> mbar, for example in the range <NUM> mbar to <NUM> mbar. In this way, leaks of acid fumes and radon (Rn-<NUM>, Rn-<NUM>), from the vessel into the hot cell containment can be avoided. Radon can be filtered and captured on a low flow rate. Leakage of acid fumes and Radon can alternatively or additionally be reduced using moisture trap columns, Ag-ETS10 columns, or by using a decay tank. In one embodiment, the decay tank may for example have a volume of <NUM> liter, pressurized to e.g. maximum <NUM> bar. Operating the reactor vessel at a pressure of <NUM> mbar to <NUM> mbar, lowers the boiling point of the liquid to a temperature in a range of <NUM> to <NUM>. In some embodiments, a pressure sensor is installed between the condenser and the distillate collection vessel. A similar setup as for example known from a rotary evaporator system may be used. It is an advantage of embodiments of the present invention that the equipment used is radiation resistant and therefore adds little to no complexity to the system. It is an advantage of embodiments of the present invention that pressure and pressure differences can be easily measured in the system, e.g. hot cell.

In some exemplary embodiments, temperature for controlling evaporation, i.e. distillation, can be controlled using a liquid based heating/cooling system. It is an advantage of embodiments of the present invention that no electric heating equipment is required in direct contact with the reactor vessel. The liquid based heating/cooling system may for example be a double wall heating/cooling system, e.g. a double wall heating/cooling jacket. Such a double wall heating/cooling system may for example be based on water. Since a double wall heating system can be operated at e.g. <NUM>, the system advantageously can be used when operating the reactor vessel in reduced pressure, since the boiling temperature of the liquid typically is reduced to a temperature in the range <NUM> to <NUM> and thus temperature control with water is perfectly possible. Since a double wall heating/cooling jacket with water can be for example operated at <NUM>, the above conditions advantageously may provide a significant temperature difference, such that the evaporation process may be controlled and/or speeded up.

The double wall heating/cooling system may be connected with a primary liquid circuit with a circulation pump. It is an advantage of embodiments of the present invention that in the case of use of water and in the case of a failing double wall heating system, Radium will dilute in water but this would allow easier recuperation (e.g. compared to heating/cooling with silicon oil).

It is an advantage of some embodiments that no electrical heating jacket and thermocouples are required for controlling evaporation e.g. distillation for precipitation. Since using an electrical heating jacket as well as using thermocouples adds complexity to the isotope production system and/or target material purification system, the possibility of avoiding electrical heating jackets and/or thermocouples makes such systems more easy to control/use.

It is an advantage of embodiments of the present invention that they can make use of forced cooling, e.g. before filtration, to lower the residual Ra-<NUM> target material concentration, and/or to speed up the process of cool-down after evaporation e.g. distillation.

It is an advantage of embodiments of the present invention that post-precipitation of Ra-<NUM> can be avoided by filtering the liquid containing Ac-<NUM> at a temperature lower than room temperature.

In embodiments according to the present invention, a stirring device may be used to perform a stirring action in the reactor vessel, e.g. at the bottom of the reactor vessel. In one embodiment, such a stirring device may be a magnetic stirrer. The magnetic stirrer may in one embodiment be an oval type stirrer, e.g. coated in borosilicate instead of PTFE. The stirrer can advantageously be used in a round bottom reactor vessel, although embodiments are not limited thereto. By using a stirring device, the bubble size of the boiling process - which can be violent at lower pressure - can be reduced and the formation of gas can be centralized in the middle of the reactor.

According to embodiments of the present invention, the parameters of the evaporation, e.g. distillation, are tuned to a point that HNOs remains almost entirely in the solution, and the evaporation process slows down a lot when an azeotrope of concentrated HNOs is reached. This increases safety and reduces the chance to unwantedly evaporate the liquid to dryness. In some embodiments, a Vigreux type column between reactor vessel and distillation bridge is efficient at separation of HNOs from H<NUM>O, and the maximum practical concentration of <NUM>% HNOs can be relatively easy reached. Above this azeotrope point, brown NOX fumes are typically observed in the solution, which is to be avoided. The distillate remains relatively free from HNOs unless pressure is strongly reduced.

Claim 1:
- A method for purification of a target material for re-use in the production of radio-isotopes, the method comprising
- obtaining a solution of irradiated target material, the solution thus comprising at least target material and optionally also radio-isotopes and optionally impurities,
subsequently,
- adding an acid in a predetermined quantity and concentration and providing conditions for quantitatively dissolving the target material and avoiding co-precipitation of the optionally present radio-isotopes,
- selectively removing H<NUM>O from the solution by evaporation, leaving the acid predominantly inside the solution thereby allowing the target material to precipitate while the acid concentration in the solution increases and thereby reducing or avoiding co-precipitation of the optionally present radio-isotopes,
- after removal of the excess H<NUM>O, lowering the temperature of the solution to maximise the precipitation of the target material and reduce the solubility of the target material in the remaining liquid,
- separating the liquid containing the optionally present radio-isotopes from the precipitated target material, and
- preparing the precipitated target material for re-use in the production of radio-isotopes,
characterised in that the irradiated target material comprises Ra-<NUM> and optionally Ra-<NUM> and Ac-<NUM> and that the acid is HNOs.