Method for treating an acidic aqueous solution comprising fluoride ions and radionuclides

Abstract

The invention relates to a method for treating an acidic aqueous solution A comprising hydrofluoric acid, fluoride ions and radionuclides, which comprises at least the following steps: a) adjusting the pH of the aqueous solution A to a value greater than or equal to 10; b) reacting the fluoride ions of the aqueous solution A with calcium ions by mixing a source of calcium ions with the aqueous solution A in proportions such that the calcium ions are in excess relative to the fluoride ions, while maintaining, if necessary, the pH of the mixture at a value greater than or equal to 10; c) subjecting the mixture formed in step b) to a solid-liquid separation, whereby a precipitate comprising fluorine and an aqueous phase depleted in fluoride ions are obtained, the radionuclides being distributed between the precipitate and the aqueous phase according to their solubility in aqueous medium at the pH of the mixture formed in step b); and in which step b) is carried out simultaneously with step a) or after step a). Field of application: nuclear industry.

Description

DESCRIPTION TECHNICAL FIELD The invention relates to the field of the treatment of acidic and radioactive aqueous solutions. More specifically, it relates to a method for treating an acidic aqueous solution comprising both fluoride ions and radionuclides, with a view to optimising the treatment of this solution and the management of waste produced from this type of solution. The invention is applicable in the nuclear industry, in particular for the treatment of solutions obtained, directly or after optional dilution, from etching with hydrofluoric acid, alone or in a mixture with another inorganic acid, one or more radioactive solids produced during spent nuclear fuel operations and / or rinsing and / or decontamination operations of a nuclear facility in operation or being dismantled. PRIOR ART At the spent nuclear fuel treatment plant in La Hague (France), laboratories, tasked with characterising radioactive solids produced during this treatment or during rinsing or decontamination operations of nuclear facilities in operation or being dismantled, are required to solution-treat these solids by subjecting them to etching with concentrated mixtures of hydrofluoric acid and nitric acid, the operating procedures of which are described in the standard NF M60-323. The following are thus particularly produced: - solutions resulting from a solution treatment (also referred to as etching) of fission product (FP) precipitates with a mixture of 0.25 N hydrofluoric acid and 14 N nitric acid, followed by a dilution, particularly to 4:5 with 0.5 N nitric acid, and - solutions resulting from a solution treatment (also referred to as etching) of dissolution fines with a mixture of 11 N hydrofluoric acid and 7 N nitric acid, also followed by a dilution, particularly to 4:5 with 0.5 N nitric acid. These solutions of very high acidity are rich in fluoride ions, which result from a dissociation of hydrofluoric acid in aqueous medium, and in various radionuclides, essentially P / y emitters of which caesium 137 and caesium 134, or a emitters of which americium 241 and curium 244. Furthermore, they can comprise molybdenum, zirconium, palladium, iron, etc. type cations, according to the initial solution-treated solid (precipitate or fines). It happens that only a small fraction of these solutions is used for characterizations and the residues are capable of being transformed, without prior treatment, into solid waste by immobilising in a stable matrix. With such an immobilisation, on one hand, all the radiological activity of the residues would be found in the solid waste thus produced and, on the other hand, the volume of this solid waste would be relatively substantial. With a view to optimising nuclear waste management, it would therefore be desirable to have a method which makes it possible to treat residues from fluoronitric solution etching of radioactive solids and, in general, any acidic aqueous solution which comprises fluoride ions together with radionuclides, so as to reduce both the radiological activity and the volume of solid waste produced from this type of solution as much as possible. It would also be desirable for this method to be simple to implement and for its implementation not to require any equipment other than that conventionally equipped in shielded lines and glove boxes of laboratories of nuclear fuel cycle facilities. DISCLOSURE OF THE INVENTION The invention aims precisely to provide a method for treating an acidic aqueous solution A, comprising hydrofluoric acid, fluoride ions obtained from dissociating hydrofluoric acid and radionuclides, said method comprising at least the following steps: a) adjusting the pH of the aqueous solution A to a value greater than or equal to 10; b) reacting the fluoride ions present in the aqueous solution A with calcium ions by mixing, under stirring, a source of calcium ions with the aqueous solution A in proportions such that the calcium ions are in excess relative to the fluoride ions, while maintaining, if necessary, the pH of the mixture at a value greater than or equal to 10; c) subjecting the mixture formed in step b) to a solid-liquid separation, whereby a precipitate comprising fluorine and an aqueous phase depleted in fluorine ions are obtained, the radionuclides being distributed between the precipitate and the aqueous phase according to their solubility in aqueous medium at the pH of the mixture formed in step b); and wherein step b) is carried out simultaneously with step a) or after step a). Thus, according to the invention, the aqueous solution A is defluorinated by precipitating the fluoride ions present in this solution in the form of fluorine, CaF2, by reacting said fluoride ions with an excess of calcium ions, for example in the order of 5% to 10%, the reaction being expressed as: 2F + p2^CaF2. This reaction being carried out at a pH at least equal to 10, the radionuclides present in the aqueous solution A, which are insoluble or slightly soluble in aqueous medium at the pH of the mixture formed in step b), are wholly or partially immobilised in the precipitate (which will be, for example, the case of antimony 125, americium 241, europium 154 and cobalt 60 if, of course, these radionuclides are present in the aqueous solution A) whereas those which are soluble in aqueous medium at the pH of the mixture formed in step b) are found mainly, indeed even exclusively in the aqueous phase resulting from the solid-liquid separation (which will be, for example, the case of caesium 137 and caesium 134 if, of course, these radionuclides are present in the aqueous solution A). As a result, treating the aqueous solution A with the method according to the invention makes it possible to obtain: - on one hand, solid waste (namely the precipitate) wherein the fluoride ions are immobilised stably in the form of fluorine and the radiological activity and volume of which are reduced significantly compared to those of waste obtained by immobilising the entire solution in the form of a solid material, and - on the other hand, an aqueous phase which, because it has a low, indeed even very low, concentration of fluoride ions, can be directed to a unit for concentration (by evaporation), calcination and vitrification (i.e. immobilising the radionuclides in a glass matrix) or to an effluent treatment unit before discharge into the environment in compliance with administrative authorisations. In the above, the expression "while maintaining, if necessary, the pH of the mixture at a value greater than or equal to 10" means that in step b), the pH of the mixture is maintained at a value at least equal to 10 if it turns out that this pH tends to fall below 10 due to the reaction of the fluoride ions with the calcium ions. According to the invention, the aqueous solution A is, preferably, a solution which comprises hydrofluoric acid together with an inorganic acid other than hydrofluoric acid, for example nitric acid, phosphoric acid or sulphuric acid, preferably nitric acid. Furthermore, in step a), the pH of the aqueous solution A is advantageously adjusted to a value equal to or greater than 11, preferably equal to or greater than 12, and more preferably between 13 and 14. The source of calcium ions is preferably an inorganic calcium salt such as calcium hydroxide (or slaked lime), calcium nitrate, calcium carbonate, calcium sulphate or calcium phosphate, this salt optionally being in hydrated form. Among these, calcium hydroxide, calcium nitrate and calcium carbonate are preferred, given that, if the fluoride ion content of the aqueous solution A is greater than or equal to 30 g / L, then the use of calcium hydroxide is highly recommended. According to the invention, the source of calcium ions can be in the form of an aqueous suspension, which will particularly be the case if the source of calcium ions is calcium hydroxide. Indeed, it is preferred to use calcium hydroxide in the form of a milk of lime previously obtained by dissolving slaked lime in water, preferably by supersaturating the water with slaked lime (for example, up to 400 g of slaked lime per litre of water), and to which the aqueous solution A is added in portions and under stirring, raising the pH above 10 and, preferably, 11 by adding sodium hydroxide if necessary. In this regard, it is recalled that slaked lime is the product of the reaction of quicklime with water, the quicklime itself being the product of a thermal decomposition of limestone (for example, by calcination) and, as such, essentially consisting of calcium oxide, CaO. By reacting with water, the calcium oxide from the quicklime is converted into calcium hydroxide, Ca(OH)2, which is therefore the main constituent of slaked lime. Alternatively, the source of calcium ions can also be in a particulate form, typically a powder, which will particularly be the case if the source of calcium ions is calcium nitrate, calcium carbonate, calcium phosphate or calcium sulphate. As previously stated, step b) can be carried out simultaneously with step a) or after step a). In fact, it all depends on the source of calcium ions used to bring, when mixed with the aqueous solution A, the pH of the latter to a value at least equal to 10. Thus, if the source of calcium ions is milk of lime, then mixing this milk of lime with the aqueous solution A can make it possible to carry out steps a) and b) simultaneously. Alternatively, if the source of calcium ions is calcium nitrate, calcium carbonate, calcium sulphate, or calcium phosphate, then it is preferable to carry out steps a) and b) one after the other. In which case, step a) comprises adjusting the pH of the aqueous solution A by mixing with an aqueous solution of a strong base, typically sodium hydroxide or potassium hydroxide, preferably in the form of a highly concentrated solution, for example 18 N or 20 N. According to the invention, the method can comprise, between steps b) and c), a step of allowing the mixture formed in step b) to rest (also referred to as maturation), in which case the sizes of the fluoride nuclei formed will increase until grains are obtained which can be separated more readily by solid-liquid separation during step c) while depleting the solution of fluoride ions. Step c) can be carried out with any technique making it possible to separate a precipitate from the aqueous medium wherein it is immersed, for example by filtration, particularly in a vacuum or under pressure, by settling, by centrifugation or by settling followed by centrifugation, the latter technique being preferably used in shielded lines or glove boxes of laboratories of nuclear fuel cycle facilities. Furthermore, step c) can be followed by one or more washings of the precipitate with water or with a weakly concentrated sodium hydroxide solution, for example 0.2 N, each washing being itself followed by a solid-liquid separation. According to the invention, the aqueous solution A can be any solution obtained, directly or after optional dilution, from etching with hydrofluoric acid, alone or in a mixture with another inorganic acid such as nitric acid, one or more radioactive solids produced during spent nuclear fuel treatment operations and / or rinsing and / or decontamination operations of a nuclear facility in operation or being dismantled. Thus, the aqueous solution A can particularly be: - a solution obtained from etching one or more precipitates produced during the treatment of a spent nuclear fuel and, in particular, a solution obtained from etching one or more FP precipitates with a mixture of hydrofluoric acid, for example 0.25 N, and nitric acid, for example 14 N, or - a solution obtained from etching dissolution fines with a mixture of hydrofluoric acid, for example 11 N, and nitric acid, for example 7 N, or - a mixture thereof. Alternatively, the aqueous solution A can also be a solution obtained from etching, particularly fluoronitric, etching of one or more radioactive solids resulting from rinsing and / or decontamination operations of a spent nuclear fuel treatment plant or a nuclear reactor in operation or being dismantled. FP precipitates mean residues based on zirconium molybdate and / or caesium phosphomolybdate, which are obtained by concentrating, typically by evaporation, aqueous solutions resulting from uranium and plutonium extraction, separation and purification operations typically implemented in spent nuclear fuel treatment. Dissolution fines means all the solids of small particle size remaining after dissolving the spent nuclear fuel in nitric acid and separated by clarification from the solution thus obtained by means of pendulum centrifuge decanters. Other features and advantages of the invention will appear from the following additional description. However, it goes without saying that this additional description is given solely as an illustration of the subject matter of the invention and should in no case be interpreted as a limitation of this subject matter. DETAILED DISCLOSURE OF PARTICULAR MODES OF IMPLEMENTATION Example I: Treatment with calcium nitrate of a mixture of HF and HNO3 FP precipitate etching solutions: The following example relates to a test carried out with 100 mL of a solution, hereinafter referred to as "solution SI", previously obtained by combining four residues, each of 25 mL, of solutions, all four resulting from etching fission product precipitates with 40 mLof a mixture of 0.25 N hydrofluoric acid and 14 N nitric acid, and of which the volume was adjusted to 50 mL by adding 0.5 N nitric acid. The solution SI comprises approximately 3.8 g / L of fluoride ions and, as seen in Table 1 hereinafter, caesium 137, caesium 134, antimony 125, europium 154, ruthenium 106, rhenium 106, cerium 144 and praseodymium 144, the caesium 137-related activity being predominant. The activity of each of these radionuclides in the solution SI, as measured by y spectrometry, is given in Table 1. For the treatment of the solution SI with the method according to the invention, the procedure is as follows: 1. a volume of 80 mL of 20 N sodium hydroxide is introduced into a canister; 2. a volume of 100 mL of the solution SI is gradually introduced under stirring into the canisterso that the pH of the mixture between the solution SI and NaOH is greater than a value of 13 (measured with pH paper); 3. 32 g of calcium nitrate tetra hydrate, Ca(NO3)2.4H2O, is gradually added to the solution SI at the adjusted pH; 4. the mixture obtained at point 2 is allowed to settle for at least 48 hours to obtain by maturation a precipitate of sufficient size for the solid / liquid separation of the next step; 5. the mixture obtained at the end of maturation is transferred in several passes into two centrifugation tubes, each transfer being followed by a centrifugation (3,200 or 3,600 rpm) followed by collection of the supernatant; 6. the precipitate obtained at point 4, separated by centrifugation in the two tubes at point 5, is subjected to two successive washings, each washing being carried out by introducing 10 mL of disilicated water into each centrifugation tube, subjecting each tube to a centrifugation (3,200 or 3,600 rpm) and collecting the supernatant. The supernatants obtained at points 5 and 6 above are combined in the same container to form a solution (volume: 180 mL) which, for the purposes of simplicity, will be considered hereinafter as the solution SI after treatment. A first sample of this solution undergoes a fluoride ion assay by ion chromatography whereas a second sample undergoes a y spectrometry analysis to measure the activity of the different radionuclides contained therein. The fluoride ion assay shows that their concentration in the solution SI after treatment is less than 10 mg / L, which makes it possible to envisage the option of directing this solution to a unit for concentration by evaporation, calcination and vitrification. The radionuclide activity is reported in Table 1 hereinafter. Table 1 Radionuclides Activity before treatment of the solution SI (Bq per 100 mL) Activity after treatment of the solution SI (Bq per 180 mL*) 137Cs 5.44.109 5.41.109 134Cs 4.92.108 4.92.108 125Sb 1.59.108 <2.107 154Eu 9.62.107 1.15.107 106Ru 4.81.107 8.88.107 106Rh 4.81.107 8.88.107 144Ce 4.44.107 < 2.03.107 144Pr 4.44.107 < 2.03.107 * Volume of supernatants obtained at points 5 and 6 and combined This table shows that more than 99% of the activity of caesium 137 and 134 in the solution SI before treatment is found in the solution SI after treatment. Therefore, significant immobilisation of caesium 137 and 134 in the precipitate formed during this treatment did not occur. In the knowledge that the activity of caesium 137 and 134 alone represented approximately 93% of the activity of the SI before treatment, most of the Py activity of the solution SI is therefore found in this solution after treatment. Table 1, on the other hand, shows a substantial decrease in the activity of antimony 125, europium 154, cerium 144 and praseodymium 144 in the solution SI after treatment compared to before treatment, which means that these radionuclides were partially or almost completely immobilised in the precipitate. In this example, it should be noted that the activity of ruthenium 106 and, hence, of rhenium 106 is higher in the solution SI after treatment than that in the solution SI before treatment, which is attributed to ambient pollution from the shielded line wherein the test was carried out. Example II: Treatment with milk of lime of a mixture of HF and HNO3 dissolution fine etching solutions: The following example relates to a test carried out with 80 mL of a solution, hereinafter referred to as "solution S2", corresponding to the mixture of different residues of solutions resulting from etching dissolution fines with a mixture of 11 N hydrofluoric acid and 7 N nitric acid. The solution S2 comprises 170 g / L of fluoride ions and has a P / y activity of 1.0.1010 Bq / L, mainly related to ruthenium 106 (45%), the other radionuclides being rhodium 106, antimony 125 and caesium 137. For the treatment of this solution S2 with milk of lime, the procedure is as follows: 1. 275 mL of milk of lime with an initial pH equal to 13 is prepared in a jug; 2. a volume of 80 mL of the solution S2 is gradually introduced into the jug, 10 mL by 10 mL, with, after each addition, a check (on pH paper) that the pH of the mixture is greater than 11 and, if not, an adjustment of the pH to 13 by adding 20 M sodium hydroxide is carried out; 3. the mixture is allowed to settle for 24 hours, thereby obtaining a suspended precipitate and some clear liquid supernatant; 4. it is checked that the pH of the clear liquid supernatant is greater than 11 and, if not, this pH is readjusted to 13 by adding sodium hydroxide, then this liquid undergoes a centrifugation (2,200 rpm) with some of the suspension, after which the centrifugation supernatant (47 mL) is collected; 5. the suspension remaining in the jug at point 4 undergoes two successive washings with 0.2 N sodium hydroxide followed by settling and centrifugation of the liquid resulting from this settling with some suspension, followed by collection of the centrifugation supernatants (30 mL and 74 mL respectively for washings 1 and 2). The centrifugation supernatants obtained at points 4 and 5 above are combined in the same container to form a solution (volume: 151 mL) which, for the purposes of simplicity, will be considered hereinafter as the solution S2 after treatment. A first sample of this solution undergoes a fluoride ion assay by ion chromatography whereas a second sample undergoes a y spectrometry analysis to measure the activity of the different radionuclides contained therein. The fluoride ion assay shows that their concentration in the solution S2 after treatment is 10.6 mg / L, i.e. 99.99% of fluoride ions immobilised in the precipitates. The radionuclide activity is reported in Table 2 hereinafter. Table 2 Radionuclides Activity before treatment of the solution S2 (Bq per 80 mL) Activity after treatment of the solution S2 (Bq per 151 mL*) 106Ru 3.64.108 5.95.105 106Rh 3.64.108 5.95.105 125Sb 3.37.107 6.40.104 137Cs 2.82.107 8.31.106 134Cs 2.46.106 6.31.105 60Co 3.90.105 8.11.102 * Volume of supernatants obtained at points 4 and 5 and combined Example III: Treatment with different sources of calcium ions of a mixture of HF and HNO3 etching solutions: The following example relates to different tests carried out on volumes of 100 mL or 120 mL according to the tests, of a solution, hereinafter referred to as "solution S3", corresponding to a mixture of: - different residues of solutions (40 mL) resulting from etching precipitates or other solid samples from different locations of the La Hague spent nuclear fuel treatment plant with mixtures of 0.25 N hydrofluoric acid and 14 N nitric acid and the volumes of which were adjusted to 50 mL by adding 0.5 N nitric acid; and - different residues of solutions (40 mL) resulting from etching precipitates or other solid samples from different locations of the La Hague spent nuclear fuel treatment plant with mixtures of 11 N hydrofluoric acid and 7 N nitric acid and the volumes of which were also adjusted to 50 mL by adding 0.5 N nitric acid. The solution S3 comprises 18.7 g / L of fluoride ions. It has a P / y activity of of 2.085.107 Bq / L, mainly related to caesium 137 (98%) - the other p / y emitting radionuclides detected by y spectrometry being europium 154 and cobalt 60 - and also an a activity of 1.27.107 Bq / L related to americium 241. Tests are carried out with different sources of calcium ions, namely: milk of lime (test 1), calcium nitrate (test 2) and calcium carbonate (test 3). For the treatments with calcium nitrate and calcium carbonate, the procedure is as described in Example I above except that there is no washing of the precipitates obtained. For the treatment with milk of lime, the procedure is as described in Example II above except that there is also no washing operation. The characteristics of these tests are summarised in Table 3 below. Table 3 Test 1 - Milk of lime Test 2 - Ca(NOj)2 Test 3 - CaCO? Volume of solution S3 (mL) 100 100 120 Volume of milk of lime (mL) 200 — — Volume of 20 N NaOH (mL) 100 100 pH (checked with pH paper) 13 13 13 Mass of Ca added by CafNChhor CaCOs (g) 17 g 32.8 g + 6.8 g in the supernatant Maturation time > 24 h (several days) > 24 h (several days) Final concentration measured in F (mg / L) 30.6 41.7 4.4 The radionuclide activity is reported in Table 4 hereinafter. Table 4 Radionuclides Activity before treatment of the solution S3 (Bq per 100 mL) Activity after treatment of the solution S3 Test 1 - Milk of lime (Bq per 151 mL) Test 2 - Ca(NO3)2 (Bq per 93 mL) Test 3 - CaCO3 (Bq per 80 mL) 137Cs 2.04.106 7.36.105 7.87.105 3.87.105 154Eu 2.51.104 not detected not detected not detected “Co 1.61.104 not detected not detected not detected Americium 241, europium 154 and cobalt 60 were immobilised in the precipitate because they are not detected in the solution S3 after treatment, regardless of the source of calcium ions used. The example that has just been described can be used as a basis for other applications, where the residues of solutions referred to in this example can also result from etching precipitates and / or other solid samples taken from equipment in the operating phase, during rinsing or decontamination operations or during dismantling 5 phases, both of fuel cycle plants and nuclear facilities of the reactor or laboratory type.

Claims

1. A method for treating an acidic aqueous solution A, comprising hydrofluoric acid, fluoride ions obtained from dissociating hydrofluoric acid and radionuclides, said method comprising at least the following steps:a) adjusting the pH of the aqueous solution A to a value greater than or equal to 10;b) reacting the fluoride ions present in the aqueous solution A with calcium ions by mixing a source of calcium ions with the aqueous solution A in proportions such that the calcium ions are in excess relative to the fluoride ions, while maintaining, if necessary, the pH of the mixture at a value greater than or equal to 10;c) subjecting the mixture formed in step b) to a solid-liquid separation, whereby a precipitate comprising fluorine and an aqueous phase depleted in fluorine ions are obtained, the radionuclides being distributed between the precipitate and the aqueous phase according to their solubility in aqueous medium at the pH of the mixture formed in step b);and wherein step b) is carried out simultaneously with step a) or after step a).

2. The method according to claim 1, wherein the aqueous solution A is a solution which comprises hydrofluoric acid and an inorganic acid other than hydrofluoric acid, preferably nitric acid, phosphoric acid or sulphuric acid, and, more preferably, nitric acid.

3. The method according to claim 1 or claim 2, wherein the pH of the aqueous solution A is brought to a value equal to or greater than 11, preferably equal to or greater than 12, and, more preferably, between 13 and 14.

4. The method according to any one of claims 1 to 3, wherein the source of calcium ions is an inorganic calcium salt, preferably calcium hydroxide, calcium nitrate, calcium carbonate, calcium sulphate or calcium phosphate, where the salt can be in hydrated form.

5. The method according to claim 4, wherein the source of calcium ions is calcium hydroxide which is used in the form of a milk of lime previously obtained by dissolving a slaked lime in water and to which the aqueous solution A is added.

6. The method according to claim 4 or claim 5, wherein the source of calcium ions is a milk of lime and step b) is carried out simultaneously with step a).

7. The method according to claim 4, wherein the source of calcium ions is calcium nitrate, calcium carbonate, calcium sulphate or calcium phosphate, the pH of the aqueous solution A is adjusted in step a) by mixing said aqueous solution A with a strong base, preferably sodium or potassium hydroxide, and step b) is carried out after step a).

8. The method according to any one of claims 1 to 7, which further comprises, between steps b) and c), a step of allowing the mixture formed in step b) to rest.

9. The method according to any one of claims 1 to 8, wherein the aqueous solution A is a solution obtained, directly or after optional dilution, from etching with hydrofluoric acid, alone or in a mixture with another inorganic acid, one or more radioactive solids produced during spent nuclear fuel treatment operations and / or rinsing and / or decontamination operations of a nuclear facility in operation or being dismantled.

10. The method according to claim 9, wherein the aqueous solution A is a solution obtained from etching one or more precipitates produced during spent nuclear fuel treatment.

11. The method according to claim 9, wherein the aqueous solution A is a solution obtained from etching one or more fission product precipitates with a mixture of hydrofluoric acid and nitric acid, a solution obtained from etching dissolution fines with a mixture of hydrofluoric acid and nitric acid, or a mixture thereof.

12. The method according to claim 9, wherein the aqueous solution A is a solution obtained from etching one or more radioactive solids resulting from rinsing and / or decontamination operations of a spent nuclear fuel treatment plant or a nuclear reactor in operation or being dismantled.INTERNATIONAL SEARCH REPORT International application No. PCT / FR2023 / 052041 A. CLASSIFICATION OF SUBJECT MATTER G21F9 / 10(2006.01)1 According to International Patent Classification (IPC) or to both national classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) G21F Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched Electronic data base consulted during the international search (name of data base and, where practicable, search terms used) EPO-Intemal, WPI Data C. DOCUMENTS CONSIDERED TO BE RELEVANT Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. Y A FR 2112428 Al (REDERIAKTIE NORDSTERNAN) 16 June 1972 (1972-06-16) page 1, line 12 - page 11, line 37; claims 1-9 1-8,10-12 9 Y A EP 3244418 Al (RWE POWER AG [DE]) 15 November 2017 (2017-11-15) paragraphs [0010], [0026] - [0043]; claims 1-17 1-8,10-12 9 | | Further documents are listed in the continuation of Box C. | | See patent family annex. * Special categories of cited documents: “T” later document published after the international filing date or priority “A" document defining the general state of the art which is not considered date and not in conflict with the application but cited to understand the to be of particular relevance principle or theory underlying the invention ■SE” earlier application or patent but published on or after the international “X” document of particular relevance; the claimed invention cannot be filing date considered novel or cannot be considered to involve an inventive step •SL” document which may throw doubts on priority claim(s) or which is when the document is taken alone cited to establish die publication date of another citation or other “y” document of particular relevance; the claimed invention cannot be special reason (as specified) considered to involve an inventive step when the document is “O” document referring to an oral disclosure, use, exhibition or other combined with one or more other such documents, such combination means being obvious to a person skilled in the art “P” document published prior to the international filing date but later than document member of the same patent family the priority date claimed Date of the actual completion of the international search 07 March 2024 Date of mailing of the international search report 19 March 2024 Name and mailing address of the ISA / EP European Patent Office p.b. 5818, Patentlaan 2,2280 HV Rijswijk Netherlands Telephone No. (+31-70)340-2040 Facsimile No. (+31-70)340-3016 Authorized officer Lohberger, Severin Telephone No.INTERNATIONAL SEARCH REPORT International application No.Information on patent family members ,FC 1 / B KZ0Z3 / vbZ041Patent document cited in search report Publication date (day / month / year) Patent family member(s) Publication date (day / month / year) FR 2112428 Al 16 June 1972 CA 957156 A 05 November 1974 DE 2154462 Al 10 May 1972 FR 2112428 Al 16 June 1972 GB 1356835 A 19 June 1974 IT 942770 B 02 April 1973 SE 351444 B 27 November 1972 US 3800024 A 26 March 1974 EP 3244418 Al 15 November 2017 DE 102016208202 Al 16 November 2017 EP 3244418 Al 15 November 2017 ES 2906428 T3 18 April 2022