Method for monitoring the actinide composition of a bath of molten chloride salts

Abstract

The present invention relates to a method for obtaining a bath of molten chloride salts comprising at least one actinide in which the oxidation state and / or degree of oxidation of said at least one actinide are predetermined according to the intended application, comprising the following steps: (a) establishing, for said at least one actinide, its potential-oxoacidity diagram at a given temperature T in a bath of molten chloride salts, (b) from the potential-oxoacidity diagram established in step (a), defining the potential-oxoacidity domain in which said at least one actinide is in the predetermined oxidation state and / or degree of oxidation, (c) selecting at least three different compounds which are different from said at least one actinide setting, at the temperature T, the potential and oxoacidity of the bath of molten chloride salts in the domain defined in step (b), it being possible for one of said at least three compounds to be the chloride ion contained in the bath of molten chloride salts, then (d) introducing, into a bath of molten chloride salts comprising said at least one actinide at the temperature T, said at least three compounds selected in step (c). The present invention relates to the use of various mixtures or compositions in the preparation of a nuclear fuel, during its operation or else during its reprocessing.

Description

[0001]METHOD FOR CONTROLLING THE ACTINIDE COMPOSITION OF A CHLORIDE MELTED SALT BATH DESCRIPTION TECHNICAL FIELD The present invention relates to the general field of molten salt baths and, more particularly, to molten salt nuclear reactors. More specifically, the present invention proposes a method for controlling the state and / or degree of oxidation of one or more actinides both during the synthesis of the chloride molten salt bath for use in a nuclear reactor and during the operation of this reactor or during the reprocessing of the spent chloride molten salt bath. This method involves bringing the bath into contact with a mixture of gaseous or non-gaseous compounds,judiciously selected. PRIOR TECHNOLOGY Molten salt reactors (MSRs) are a class of nuclear reactors that offer several advantages over traditional light water reactors (LWRs). LWRs typically use solid fuel with a long radioactive half-life and relatively inefficient fuel utilization, which can result in hazardous and long-lived waste. MSRs are a class of nuclear fission reactors in which the primary coolant, or even the fuel itself, is a mixture of molten salts. In other words, in MSRs, the coolant used to remove the thermal energy produced in the reactor is based on molten salts, typically chlorides or fluorides of alkali or alkaline earth metals.It also contains nuclear fuel in solution or suspension. In general, MSRs can provide energy more safely and at a lower cost than LWRs. The fuel elements dissolved in the salts vary but may include thorium, uranium, plutonium, or other actinides. In a certain configuration, the MSR can be designed to operate in a thorium fuel cycle, in which thorium absorbs neutrons and is transmuted into uranium-233, which becomes the primary fuel. In MSRs, specific salts are chosen for their excellent heat transfer capabilities, high chemical stability, and radiation-neutral behavior. Indeed, the selection of molten salts must take into account not only neutronics, but also their physicochemical properties, melting and operating temperatures, the solubility of uranium and plutonium, and their reprocessing.but also requirements in terms of power density and size. Based on this, the use of fluorinated salts combined with the Uranium-Plutonium fuel cycle does not appear to be the most appropriate, particularly due to the low solubility of plutonium in these salts and the risk of uranium and plutonium precipitation. Furthermore, operating temperatures with fluoride molten salts are generally higher than with chloride molten salts, which increases the corrosion kinetics of reactor materials and reduces their mechanical strength. For this reason, numerous molten salt reactor concepts using molten chloride salts are currently being developed worldwide. Due to the growing interest in chloride molten salt nuclear reactors, they are the subject of much research, on the one hand,at the level of the synthesis of nuclear fuel salts, i.e., actinide chlorides, the composition of which must be controlled throughout the reactor's lifetime, and, on the other hand, at the level of the reprocessing of spent fuel salts. The inventors therefore set themselves the goal of proposing a process that allows not only the control of the actinides used during the synthesis of nuclear fuel salts but also during their reprocessing in the case of spent fuel. DESCRIPTION OF THE INVENTION The present invention makes it possible to achieve the goal set by the inventors. Indeed, the inventors' work has shown that it is possible to control the state and degree of oxidation of the actinides contained in a bath of molten chloride salts by contacting this bath with at least three judiciously selected compounds,one of said at least three compounds, which may be the chloride ion contained in the molten chloride bath. This process is of interest both for the synthesis of a molten chloride bath and for the reprocessing of such a spent bath. More particularly, the process according to the invention can be implemented (i) during the preparation of a molten chloride bath, (ii) during its use, and in particular to maintain it within its stability range, or (iii) during certain reprocessing steps such as chlorination and precipitation. More particularly, the present invention relates to a process for obtaining a molten chloride bath comprising at least one actinide, in which the state and / or degree of oxidation of said at least one actinide are predetermined according to the intended application, comprising the following steps: a) establishing, for said at least one actinide, its potential-oxoacidity diagram at a given temperature T in a molten chloride bath,b) using the potential-oxoacidity diagram established in step a), define the potential-oxoacidity range in which said at least one actinide is in the predetermined state and / or oxidation state, c) select at least three different compounds, distinct from said at least one actinide, capable of fixing, or fixing at temperature T, the potential and oxoacidity of the chloride molten salt bath within the range defined in step b), one of said at least three compounds being the chloride ion contained in the chloride molten salt bath, and then d) introduce said at least three compounds selected in step c) into a chloride molten salt bath comprising said at least one actinide at temperature T). For the purposes of this invention, the term "state" of an actinide means an actinide in solution, an actinide in gaseous form, or an actinide in precipitate form. In other words,The process according to the invention allows for the dissolution, volatilization from a molten chloride bath, or precipitation of an actinide in a molten chloride bath. In the process according to the invention, the predetermined oxidation state of an actinide can be selected from among the various oxidation states that such an actinide may exhibit. For example, when the actinide in question is uranium, the predetermined oxidation state of this actinide can be selected from the group consisting of oxidation state +3, oxidation state +4, oxidation state +5, and oxidation state +6. The term "state and / or oxidation state of an actinide predetermined according to the intended application" means a state and / or oxidation state of an actinide previously selected or chosen depending on whether a molten chloride bath is to be prepared,to maintain the latter within its stability range or to reprocess it, in particular by subjecting the actinide(s) to chlorination or precipitation, or even by separating the actinides it contains. In a particular embodiment, the process according to the invention aims to obtain a molten chloride bath comprising at least two different actinides in which the state and / or oxidation state of said at least two actinides are predetermined. In other words, the molten chloride bath comprises at least two different actinides whose state and / or oxidation state are predetermined according to the intended application, and the process comprises the following steps: a) establishing, for each of said at least two actinides, its potential-oxoacidity diagram at a given temperature T in a molten chloride bath, b) from the potential-oxoacidity diagrams established in step (a),(c) define the potential-oxoacidity range in which said at least two actinides are in the predetermined state and / or oxidation state; (b) select at least three different compounds, distinct from said at least two actinides, capable of fixing, or fixing, at temperature T, the potential and oxoacidity of the molten chloride bath within the range defined in step b), one of said at least three compounds being the chloride ion contained in the molten chloride bath; and (d) bring into contact a molten chloride bath comprising said at least two actinides at temperature T and said at least three compounds selected in step c). In the process according to the invention, the temperature T is chosen from among the temperatures conventionally used in molten salt nuclear reactors. Typically,The temperature T is between 450°C and 1000°C. It should be noted that the reasoning related to the calculations presented in the experimental section below is applicable to such a temperature range. Within the framework of the process according to the invention, any type of chloride salt used in MSRs is usable. Advantageously, chloride salts capable of forming low-melting-point eutectics, on the order of 500°C, with good solubilities of the Uranium / Plutonium pair, will be chosen. Consequently, within the framework of the process according to the invention, the molten chloride salt bath comprises at least one salt chosen from the group consisting of sodium chloride (NaCl), magnesium dichloride (MgCl2), potassium chloride (KCl), lithium chloride (LiCl), calcium dichloride (CaCl2), and a mixture thereof. However, in addition to the commonly studied LiCl-KCl mixture,NaCl alone exhibits interesting characteristics: it can provide a eutectic with uranium and plutonium at temperatures close to 500°C. From a neutron perspective, sodium is the best element, followed at a considerable distance by calcium (10 times more absorption). In fact, in the process according to the invention, the molten chloride bath comprises at least sodium chloride (NaCl). For the actinide(s) for which a given state and / or oxidation state is desired in the molten chloride bath at temperature T, the potential-oxoacidity diagram(s) are constructed. A potential-oxoacidity diagram is also known as a "thermodynamic diagram." Such a diagram summarizes the thermodynamic properties of a system at a given temperature T. In the diagram(s) established in step a),The potential axis is referenced to the redox couple Cl2(1 atm) / Cl- (a=1) in a molten chloride bath, and particularly in a molten chloride bath containing NaCl. The chloride activity is fixed at 1 (see experimental section below), but a person skilled in the art will be able to determine without inventive effort whether this value needs to be adjusted during implementation of the process of the invention. The acidity axis depends on the chloride salt used. In molten salts, this is referred to as oxo-acidity because the acidity is carried by the O- anion. 2- The acidity or oxo-acidity axis is expressed by the logarithm of the O₂ anion 2- : p(aO 2- ) = -log(a(O 2-In other words, when the molten chloride used is NaCl, the acidity or oxo-acidity axis of the diagram(s) established in step a) is expressed by the logarithm pa(Na2O) (= -log a(Na2O)). When the molten chloride used is MgCl2, the acidity or oxo-acidity axis of the diagram(s) established in step a) is expressed by the logarithm pa(MgO) (= -log a(MgO)). When the molten chloride used is KCl, the acidity or oxo-acidity axis of the diagram(s) established in step a) is expressed by the logarithm pa(K2O) (= -log a(K2O)). When the molten chloride salt used is LiCl, the acidity or oxo-acidity axis of the diagram(s) established in step a), is expressed by the logarithm pa(Li2O) (= - log a(Li2O)).When the molten chloride salt used is CaCl2, the acidity or oxo-acidity axis of the diagram(s) established in step a) is expressed by the logarithm pa(CaO) (= -log a(CaO)). When the process according to the invention involves a single actinide, step b) is carried out by simply observing the potential-oxo-acidity diagram established in step a). This aspect is illustrated in the experimental section below for uranium and plutonium, respectively in Figures 1 and 2. When the process according to the invention involves at least two different actinides, step b) is carried out by juxtaposing the potential-oxo-acidity diagrams established in step a) for each of the actinides and selecting the range in which the different actinides considered are in the desired state and / or oxidation state. This aspect is illustrated in the experimental section below for uranium and plutonium, in Figure 3.The present invention applies to any actinide that may be present in a molten salt chloride nuclear reactor, regardless of the isotope of that actinide. In a particular embodiment of the process according to the invention, the actinide(s) involved in the process according to the invention include uranium and transuranic elements (TRUs). TRUs are elements found in spent fuel. They consist of plutonium and so-called "minor" actinides, as they are produced in small quantities. These minor actinides currently represent the largest part of the waste resulting from the operation of a molten salt nuclear reactor, and in particular a molten salt chloride reactors. It is envisaged that these minor actinides, and in particular americium, could be used for transmutation, that is, for conversion into other radionuclides with shorter half-lives in advanced fast neutron reactors, known as "fourth-generation" reactors.The process according to the invention thus finds a particular application in this respect. Indeed, via the process according to the invention, minor actinides can be separated, i.e., precipitated, during the reprocessing of spent fuel for loading into advanced fast neutron reactors, known as "fourth-generation" reactors. In a more particular embodiment of the process according to the invention, said at least one actinide or at least two actinides is / are selected from the group consisting of thorium (Th), uranium (U), plutonium (Pu), neptunium (Np), americium (Am), and curium (Cm). In a further particular embodiment of the process according to the invention, said at least one actinide or at least two actinides comprises / comprise uranium (U) and / or plutonium (Pu).As previously explained, the process according to the invention is based on the selection of at least three different compounds, distinct from the actinide(s) contained in the molten chloride bath, which allow the molten chloride bath to be maintained at temperature T within the range in which the actinide(s) considered are in the desired state and / or degree of oxidation. In the preceding and following text, the expressions "at least three different compounds" and "at least three different compounds, distinct from at least one actinide or at least two actinides contained in the molten chloride bath" are equivalent and may be used interchangeably.Furthermore, it is clear that these at least three compounds, with the exception of the chloride ion, are introduced into the molten chloride bath following a deliberate selection (step c) of the process and a conscious and reasoned choice by a person skilled in the art. This means that these at least three compounds are not byproducts, i.e., products obtained during the reactions occurring in the molten chloride bath. For example, when one of these three compounds is carbon monoxide (CO) or carbon dioxide (CO2), it is not the carbon monoxide or carbon dioxide produced during a reaction occurring in the molten chloride bath, such as chlorination. On the contrary, the carbon monoxide (CO) or carbon dioxide (CO2) are introduced into, brought into contact with, the molten chloride bath from outside the system, i.e., from the molten chloride bath.During this introduction, this contacting, the carbon monoxide (CO), carbon dioxide (CO2), or any other compound used in the invention is carried out, in a defined and controlled manner, by the direct intervention of a person skilled in the art or by any other technical means of implementation. Thus, within the scope of the invention, the aforementioned at least three different compounds, with the exception of the chloride ion contained in the molten chloride bath when the latter is one of said at least three different compounds, are not products or by-products of one or more reactions occurring in the molten chloride bath. Advantageously, the different compounds used in the process according to the invention are selected from among gaseous compounds, the chloride ion from the molten chloride bath, and carbon.Furthermore, for the reasons discussed in the experimental section below, the various compounds used in the process according to the invention include two compounds forming a redox couple, two compounds forming an acid-base couple, and at least one chlorinated gas. In step c) of the process according to the invention, the selection of the at least three different compounds used to determine, at temperature T, the potential and oxo-acidity of the molten chloride salt bath within the range defined in step b) is performed by calculation based on the redox and acid-base reactions occurring between said at least three different compounds and the associated relationships of the Nernst equation and equilibrium constant type. When the mixture of at least three compounds includes gases, the potential and oxo-acidity of this mixture are calculated by varying the partial pressure of the different gases between 0.5 and 10. -6atm. Thus, by fixing, at temperature T, the potential and oxoacidity of the molten chloride salt bath within the range defined in step b), the actinide(s) concerned are found within such a range and therefore present in the desired, i.e., predetermined, state and / or degree of oxidation. Points III.1 to III.4 in the experimental section below illustrate this aspect of the invention for mixtures comprising three or four different compounds. Those skilled in the art will be able to extrapolate it to any mixture of at least three different compounds.More specifically, the various compounds used in the process according to the invention are chosen from the group consisting of water (H2O), dihydrogen (H2), hydrochloric acid (HCl), dichlorine (Cl2), chloride ion (Cl-), carbon (C), carbon monoxide (CO), carbon dioxide (CO2), carbon tetrachloride (or terachloromethane, CCl4), carbonyl dichloride (or phosgene, COCl2), thionyl chloride (SOCl2), sulfur dichloride (S2Cl2), and sulfur dioxide (SOCl2). Some of these compounds may be in gaseous form. This is the case for water (H2O(g)), dihydrogen (H2(g)), hydrochloric acid (HCl(g)), dichlorine (Cl2(g)), carbon monoxide (CO(g)), carbon dioxide (CO2(g)), carbon tetrachloride (or terachloromethane, CCl4(g)), carbonyl dichloride (or phosgene, COCl2(g)), thionyl chloride (SOCl2(g)), disulfur dichloride (S2Cl2(g)) and sulfur dioxide (SOCl2(g)).Carbon (C), on the other hand, is in solid form (C(s)). It can be introduced, in particular, by means of a graphite rod that carries the other gaseous compound(s) associated with the carbon into the molten chloride bath during contact in step d) of the process according to the invention. C(s) can also be introduced in the form of graphite powder dispersed in the molten salt bath. In the calculations on which the process according to the invention is based, the activity of carbon is set at 1. The chloride ion (Cl-) is in solubilized form and is already present in the molten chloride bath. In the calculations on which the process according to the invention is based, the activity of the chloride ion is set at 1.When the at least three compounds include the chloride ion (Cl-), it is more accurate to speak of a combination, since these elements cannot be used as a mixture, the chloride ion being already present in the molten chloride bath. Thus, the at least three compounds selected in step c) can be in the form of (i) an exclusively gaseous mixture, (ii) a mixture comprising one or more gases and a solid (i.e., carbon), (iii) a combination comprising one or more gases and an ion (i.e., the chloride ion), or (iv) a combination comprising one or more gases, a solid (i.e., carbon), and an ion (i.e., the chloride ion). The contacting in step d) of the process according to the invention consists of introducing the three or more compounds into the molten chloride bath. The compounds can be introduced sequentially, in groups, or all simultaneously. This last option is advantageously chosen.It is evident that, when the chloride ion is found among the at least three compounds selected in step c), the contacting in step d) of the process according to the invention essentially consists of bringing the molten chloride bath into contact with the other compounds of this mixture selected in step c), since the chloride ion is already present in the molten chloride bath. In a first embodiment, the molten chloride bath used in step d) is a molten chloride bath in the process of being prepared. In this case, the actinide in question is typically an actinide oxide from which an actinide chloride, and in particular uranium trichloride, is to be prepared. Consequently, in this first embodiment, the contacting in step d) typically takes place in the critical heat production zone of molten salt reactors.In a second embodiment, the molten chloride bath used in step d) is a molten chloride bath currently in use, the composition of which must be kept stable. Therefore, in this second embodiment, the contact in step d) also occurs within the critical heat generation zone of molten salt reactors. In a third embodiment, the molten chloride bath used in step d) is a spent molten chloride bath from which certain actinides, particularly minor actinides as previously defined, must be recovered by precipitation. This third embodiment can also be used to recover fuel salt containing plutonium, which, once recovered, can be reinjected into the fuel circuit.Therefore, in this third embodiment, the contact in step d) typically takes place in a reprocessing unit such as a molten salt reactor. This third embodiment can also be implemented continuously or in batches. Those skilled in the art will be able to determine, without inventive effort, the duration for which the contact in step d) of the process according to the invention must be maintained, depending on the desired outcome, i.e., bringing the actinide(s) to the predetermined state and / or degree of oxidation. Typically, the duration of step d) of the process according to the invention is between 30 minutes and 72 hours, and in particular, between 1 and 48 hours.In a particular embodiment, the at least three different compounds are chosen from the group consisting of HCl / H2O / H2, Cl2 / O2 / Cl- ion, Cl2 / CO / C / Cl- ion, Cl2 / CO2 / C / Cl- ion, Cl2 / CO2 / CO / Cl- ion, CCl4 / CO2 / C, CCl4 / CO2 / CO, SOCl2 / SO2 / S2Cl2, COCl2 / CO2 / C, COCl2 / CO2 / CO, CCl4 / CO2 / HCl / H2 and CCl4 / CO / HCl / H2. Thus, when said at least three different compounds comprise chlorine (Cl2), chloride ion (Cl-) and carbon (C), said at least three compounds further comprise carbon monoxide (CO) or carbon dioxide (CO2). The properties in terms of potential and oxo-acidity of the gas mixture HCl / H2O / H2, of the combination Cl2(g) / CO2(g) / C(s) / Cl- ion, of the gas mixture SOCl2 / SO2 / S2Cl2 and of the gas mixture CCl4 / CO / HCl / H2 are illustrated respectively in points III.1 to III.4 of the experimental part below.Similarly, the redox reactions and acid-base equilibrium involved for the combinations Cl2(g) / O2(g) / Cl- ion, Cl2(g) / CO(g) / C(s) / Cl- ion, Cl2(g) / CO2(g) / CO(g) / Cl- ion, CCl4(g) / CO2(g) / C(s), CCl4 / CO2 / CO gas mixture, COCl2 / CO2 / C gas mixture, COCl2 / CO2 / CO gas mixture, and CCl4 / CO2 / HCl / H2 gas mixture are given in section III.5 of the experimental part below. Based on the work illustrated in the experimental part below, it is possible to select compositions or mixtures of at least three different compounds for specific applications. Thus, the present invention relates to: - the use of the CCl4 / CO2 / HCl / H2 mixture or the CCl4 / CO / HCl / H2 mixture to synthesize uranium trichloride (UCl3) in a bath of molten chloride salts, in particular based on NaCl, and containing at least uranium or to control the redox of the fuel salt in such a bath.- the use of the combination Cl2 / CO / C / Cl-, the combination Cl2 / CO2 / C / Cl-, the combination Cl2 / CO2 / CO / Cl-, the mixture CCl4 / CO2 / C, the mixture CCl4 / CO2 / CO, the mixture SOCl2 / SO2 / S2Cl2, the mixture COCl2 / CO2 / C, the mixture COCl2 / CO2 / CO, the mixture CCl4 / CO2 / HCl / H2 or the mixture CCl4 / CO / HCl / H2 to synthesize plutonium trichloride (PuCl3) in a bath of molten chloride salts, in particular based on NaCl, and containing at least plutonium. - the use of the HCl / H2O / H2 mixture or the Cl2 / O2 / Cl- combination to precipitate uranium and plutonium oxides in a bath of molten chloride salts, in particular based on NaCl containing at least uranium and at least plutonium.- the use of the combination Cl2 / CO / C / Cl-, the combination Cl2 / CO2 / C / Cl-, Cl2 / CO2 / CO / Cl-, the mixture CCl4 / CO2 / C, the mixture CCl4 / CO2 / CO, the mixture SOCl2 / SO2 / S2Cl2, the mixture COCl2 / CO2 / C, or the mixture COCl2 / CO2 / CO for the chlorination of fuel salt and the separation of uranium and plutonium in a molten chloride bath, particularly one based on NaCl containing at least uranium and at least plutonium. As previously explained, in the uses described above, the compounds of the aforementioned combinations and mixtures, with the exception of the chloride ion contained in the molten chloride bath, are not products or by-products of one or more reactions occurring in the molten chloride bath. Other features and advantages of the present invention will become apparent to the person skilled in the art upon reading the examples below, given by way of illustration and not limitation, with reference to the attached figures.BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the thermodynamic diagram of plutonium calculated in a chloride medium at 700°C (x(PuCl3)=0.31). Figure 2 shows the thermodynamic diagram of uranium calculated in a chloride medium at 700°C (x(UCl3)=0.05). Figure 3 shows the thermodynamic stability diagram of the NaCl-PuCl3-UCl3 (64-31-5 mol%) fuel salt at 700°C. Figure 4 shows the limits of the oxo-acidity zone that the HCl / H2O gas mixture takes on (partial pressures between 10. -3 and 10 -1 atm). Figure 5 shows the limits of the potential range of the HCl / H2 gas mixture (partial pressures between 10 -3 and 10 -1 atm). Figure 6 shows the thermodynamic stability domains of the HCl / H2O / H2 gas mixture (filled polygon) of combustible salt at 700°C (empty polygon). The partial pressures of the gases vary from 0.5 to 10 -6Figure 7 shows the superposition of the thermodynamic diagrams of uranium and plutonium with the stability domain of the HCl / H2O / H2 gas mixture. Figure 8 shows the superposition of the stability diagram of the NaCl-PuCl3-UCl3 salt with the stability domain of the Cl2 / CO2 / C / chloride ion combination. Figure 9 shows the superposition of the thermodynamic diagrams of uranium and plutonium with the stability domain of the Cl2 / CO2 / C / chloride ion combination. Figure 10 shows the superposition of the stability diagram of the NaCl-PuCl3-UCl3 salt with the stability domain of the SOCl2 / SO2 / S2Cl2 gas mixture. Figure 11 shows the superposition of the thermodynamic diagrams of uranium and plutonium with the stability domain of the SOCl2 / SO2 / S2Cl2 gas mixture. Figure 12 shows the superposition of the stability diagram of the NaCl-PuCl3-UCl3 salt with the stability domain of the CCl4 / CO / HCl / H2 gas mixture.Figure 13 shows the superposition of the thermodynamic diagrams of uranium and plutonium with the stability domain of the CCl4 / CO / HCl / H2 gas mixture. DETAILED DESCRIPTION OF SPECIFIC IMPLEMENTATION METHODS I. Calculation of the thermodynamic diagrams of the molten salt NaCl-PuCl3-UCl3 at 700°C. The potential-acidity or potential-oxoacidity thermodynamic diagrams are used in molten salt mixtures in a manner analogous to Pourbaix diagrams in aqueous solution. The potential axis is referenced to the redox couple Cl2(1 atm) / Cl- (a=1) in a chloride salt mixture. The acidity axis is represented by pa(Na2O) ( = -log a(Na2O)) in a NaCl-based salt. In molten salts, we will speak of oxoacidity because the acidity is carried by the O2 anion. 2-Oxo-acidic salts or gaseous mixtures are poor in oxide ions and are found on the right side of the potential-acidity diagram, while oxo-basic salts or mixtures are located on the left side. The stability ranges of the different forms an element can take in a molten salt can be calculated from a database of pure substances. The diagrams for plutonium and uranium are shown in Figures 1 and 2. They were calculated for the fuel salt composition of XAMRs, corresponding to the NaCl-PuCl3-UCl3 mixture (64-31-5 mol%) at 700°C, using the HSC Chemistry 6.0 database. Regarding thermodynamic calculations, there is generally little difference with temperature; the extent of the stability ranges is essentially the same. The reasoning related to the calculations presented in the experimental part can be applied to a temperature range between 450°C and 1000°C.The stability range of the NaCl-PuCl3-UCl3 salt (64-31-5 mol%) at 700°C is deduced from Figures 1 and 2 as the range in which NaCl, PuCl3, and UCl3 are all stable. It is shown in Figure 3. II. Preliminary work: use of gas mixtures. Gas mixtures can be used to fix a potential or an oxo-acidity of interest in a mixture of molten salts. The principle consists of fixing a potential using a redox system and an oxo-acidity using an acid-base pair. If a redox pair is considered alone, the oxo-acidity will not be controlled, and similarly, an acid-base pair will not fix the potential. II.1. Example of a gaseous mixture controlling oxo-acidity Consider the acid-base couple H2O / HCl, the thermodynamic equilibrium to consider is the following: The equilibrium constant is given by the relation: We deduce that: pa(Na O) ^ logK ^ 2P(HCl) 2 2HCl / H2O loga(NaCl) ^ log P(H (3) 2O) In these relationships, a(M) and P(M) represent the activity and partial pressure of element M, respectively. In the ternary mixture considered, the activity of NaCl is considered equal to its mole fraction. Therefore, a(NaCl) = 0.64. It is observed that the value of p(Na₂O) depends on the ratio P(HCl). 2 / P(H2O). If we consider gaseous mixtures with partial gas pressures between 10 -3 and 10 -1 atm, the ratio a(HCl) 2 / a(H2O) varies from 10 -5 at 10. We thus calculate two values ​​of pa(Na2O) which delimit the oxo-acidity zone fixed by the gas mixture. The limits depend on the composition of the mixture (Figure 4). Note that nothing fixes the potential in Figure 4. II.2. Example of a gas mixture controlling the potential. Let us now consider the redox couple HCl / H2; the associated redox reaction is: The associated Nernst equation is given by: In this relationship, E is the equilibrium potential, E° the standard potential of the redox system, R is the ideal gas constant (=8.314 J / K / mol), T is the temperature (K), and F is the Faraday constant (=96500 C / mol). In a salt such as NaCl-PuCl3-UCl 3, The activity of chlorides is probably less than 1. However, since the value has not yet been determined experimentally, as a first approximation, a(Cl-) = 1 is taken for the numerical applications presented in the works of this description. It is observed in relation (5) that the value of the potential depends on the ratio P(HCl) 2 / P(H2). We consider gaseous mixtures whose partial gas pressures vary between 10 -3 and 10 -1 atm. In this case, the ratio P(HCl) 2 / P(H2) varies by 10 -5at 10. Two potential values ​​EHCl / H2 are thus calculated, which delimit the potential range fixed by the gas mixture (Figure 5). Figure 5 shows that the oxo-acidity is not fixed by the HCl / H2 mixture. III. Use of mixtures according to the invention. III.1. HCl / H2O / H2 gas mixture. The reactions and mathematical relationships established for this gas mixture are presented in Table 1. Table 1. Reactions involved in the HCl / H2O / H2 gas mixture and associated relationships. Redox reaction. Nernst equation. E°(V) / Cl2 / Cl- 2 2 2HCl(g) + 2e^(-H2(g)E ... ) 2 2 H2O(g) + 2NaCl + 2e⁻ ^ E ^ ^2.3RT log P(H 2 O)a(NaCl) 2 ^ H2(g) + Na2O +H2O / H2 H2O / H2 -2.88 (7)2Cl-2F P(H 2 )a(Na 2 O)a(Cl^ ) 2 Acid-base reaction: Equilibrium constant Log K 2 2HCl(g) + Na₂O P(H O)a(NaCl) ^2 2 ^K18.995 (8) HCl / H2O 2 P(HCl) a(Na O)H2O(g) + 2NaCl 2 The calculation of the potential and oxo-acidity was carried out by varying the pressures - 6Partial concentrations of HCl, H2O, and H2 are between 0.5 and 10 atm. The stability range of this gas mixture is shown in Figure 6. A small common zone is observed between the gas mixture and the fuel salt. Superimposing the stability range of the gas mixture with the diagrams for uranium and plutonium yields Figure 7. The stability range of the gas mixture lies primarily within the stability ranges of uranium dioxide (UO2) and plutonium dioxide (PuO2). If precipitating these elements is desired during reprocessing, the use of this gas mixture would be suitable. III.2. Cl2 / CO2 / C / Cl- ion combination. The reactions and mathematical relationships established for this mixture are presented in Table 2. - Table 2. Reactions involved in the Cl2 / CO2 / C / Cl- ion gas mixture and associated relationships. E°(V) / Redox reaction: Cl2 / Cl- Nernst equation: Cl2(g) + 2e^(-E) P(Cl-) Cl2^(-E) log2 C l 0 (9)2 ^ 2 - 2F a(Cl )2Cl CO2(g) + 42.3RT P(CO2) α(NaCl) - 4NaCl + 4e 2E ^ E ^ ^ log(10)CO2 / C CO2 / C 2 4^4F α(NaO) α(C)α(Cl) 2.896 ^ C + 2Na2O + 2 - 4Cl 14F ^ ^ From (9) and (10) α(NaO)^ E ^ E ^ ^ 4logα(NaCl) ^ logP(CO2) )(11)^ ^2 Cl2 CO2 / C 2^ ^ 2 2.3RT^ ^ In this case, the potential is determined by the partial pressure of Cl (g) and the oxo-acidity2 by relation (11) established by the combination of relations (9) and (10). The carbon activity (α(C)) is set to 1 in the calculations. Figures 8 and 9 show the calculated thermodynamic diagrams – with the Cl2 / CO2 / C / Cl ion mixture. This gaseous mixture is useful for preparing PuCl3 from its oxide and for oxidizing UCl3 to UCl5(g). III.3. SOCl2 / SO2 / S2Cl2 Gaseous Mixture. Oxo-acidity is determined by the SOCl2 / SO2 acid-base pair, and redox by the SOCl2 / S2Cl2 and SO2 / S2Cl2 pairs. The reactions and relationships considered are given in Table 3. Table 3.Reactions involved in the gaseous mixture SOCl2 / SO2 / S2Cl2and associated relationships E°(V) Redox reaction Nernst relationship / Cl2 / Cl- 2SOCl2(g) + 4NaCl + 6e2E 2.3RT P(SOCl2) a(SOCl2) 4SOCl2 / S2Cl2 ^ E ^ SOCl2 / S2Cl2 ^ log^ S2Cl2(g) + 2Na2O6F P(S 2 Cl 2 )a(Na 2 O) 2 a(Cl^) 6 -1.714 (12)+ 6Cl- 2SO (g) + 8Na2Cl2(g)+2. a(NaCl)6e 2E ^ E ^ ^ log -3.449 (13) SO2 / S2Cl2 SO2 / S2Cl2 4 6^6F P(S Cl )a(Na O) a(Cl )^ S Cl (g) + 4Na O2 2 2. 2 2 2 - + 6Cl Acid equilibrium- Equilibrium constant log K basic 2P(SO )a(NaCl)SOCl2(g) + Na2O 2 ^ K 26.961 (14) SOCl2 / SO2P(SOCl )a(Na O)^ SO (g) + 2NaCl2 2 2The calculated thermodynamic diagrams are shown in Figures 10 and 11. These diagrams demonstrate a very high oxidizing power. However, they are less oxo-acidic than those containing CO(g) or CO2(g). These gas mixtures are not of particular interest due to the difficulty of handling them. III.4. CCl4 / CO / HCl / H2 Gas Mixture None of the gas mixtures considered previously allows for the stabilization or synthesis of UCl3. It has been shown that the HCl / H2 redox system allows for reaching sufficiently low potentials to be within the stability range of UCl3. However, in the presence of H2O, the oxo-acidity is too low to stabilize uranium chloride. The other gas mixtures are too oxidizing and lead to the preferential stability of UCl5(g). We therefore propose to examine a gas mixture consisting of a strongly oxo-acidic acid-base pair and a redox pair with a strong reducing power.The choice fell on the gaseous mixture CCl / CO / HCl / H .4 2 The reactions and relationships used are gathered in Table 4. Table 4. Reactions involved in the gaseous mixture CCl / CO / HCl / H and associated relationships4 2 E°(V) / Redox reaction Nernst relation - Cl2 / Cl 2HCl(g) + 2eE 2.3RT P(HCl)2 HCl / H2 ^ E ^ HCl ^ log -(15) ^ H2(g) + 2Cl- / H2 2F P(H )a(Cl^. ) 2 2 1.043 CCl4(g) + Na2O + 2e ^ CO(g) + 2NaCl +EC / CO ^ E ^ CCl4 / CO ^2.3RTlog P(CCl 4 )a(Na 2 O)Cl4 2F P(CO)a(NaCl) 2 a(Cl^ 2 3.097 (16)2Cl- ) From (15) and (16): pa(Na2 O) ^2F E ^ ^ E ^ 2loga(N(17) 2.3RT^ CCl4 / CO HCl / H2 ^ aCl) ^ logP(CCl4) ^ logP(CO) The thermodynamic diagrams are given in Figure 12 and Figure 13. It can be seen that this gas mixture allows extremely high oxo-acidity. This gas mixture is therefore very interesting for producing UCl3 from UO, for example. Furthermore, it allows the fuel salt to be maintained within its stability range and can be a solution to compensate for changes in the fuel salt composition inherent to reactor operation. III.5. Reactions and relationships considered for the other mixtures studied - i) Cl(g) / O(g) / Cl2 ion combination Table 5 presents the reactions and relationships considered for this combination. - Table 5. Reactions involved in the Cl2(g) / O2(g) / Cl ion combination and associated relationships - Redox reaction Nernst equation E°(V) / Cl / Cl2 P (Cl )2.3RT 2-E ^ E ^ ^ log 0 (18)Cl2(g) + 2e ^ 2ClCl2 Cl2 ^ 22F P(Cl )42.3RT P(O )a(NaCl)O (g) + 4NaCl+ 4e2 2E ^ E ^ ^ log -1.87 (1.87) O-F22(42) O-NaCl. a(Cl )^ 2Na O + 4Cl2 2 Acid-base equilibrium Equilibrium constant log K 4P(O )a(NaCl)2Cl2(g) + 2Na2O ^ O2(g) + 2 ^ K38.758 (20 Cl2 / O2 2 2 P(Cl ) a(Na O)4NaCl 2 2 - ii) Combination Cl2(g) / CO(g) / C(s) / Cl ion Table 6 presents the reactions and relations considered for this combination introduced, for its gaseous part, with a graphite rod. Table 6. Reactions involved in the Cl2(g) / CO(g) / C(s) / Cl- ion combination and associated relationships Redox reaction Nernst relationship E°(V) / Cl2 / Cl- Cl2(g) + 2nd ^E ^ E ^ ^2.3RT log P(Cl 2 ) 02Cl-Cl2 Cl2 2F a(Cl^ ) 2 (21)CO(g) + 2NaCl+ 2eE ^ E ^ ^ 2.3RT P(CO)a(NaCl)2 ^ C + NaCO / C CO / log -2.896 (22)2O +C 2F a(Cl)a(Cl)a(a)^ ) 22 2Cl- From (21) and (22) pa(Na O) ^2FE ^ E ^ ^ 2loga(NaCl) ^ logP(CO) (23) ^ ^2 Cl2 CO / C2.3RT In this case, the potential is determined by the partial pressure of Cl2 and the oxo-acidity by relation (23) established by the combination of relations (21) and (22). The activity of carbon (a(C)) is set to 1 in the calculations. - iii) Combination Cl2(g) / CO2(g) / CO(g) / Cl ion By introducing CO2 and CO in the same combination, we can omit the carbon C. The Cl2 / Cl redox couple determines the potential as in the previous case, and the CO2 / CO couple, which is both redox and oxo-acid, determines the oxo-acidity. The reactions and relationships used to study this combination are presented in Table 7. - Table 7. Reactions involved in the Cl2(g) / CO2(g) / CO(g) / Cl ion mixture and associated relationships E°(V) / Redox reaction Nernst equation - Cl2 / Cl P (Cl )2.3RT2-E ^ E ^ ^ log 0 (24) Cl2 Cl2Cl (g) + 2e ^ 2Cl2^ 22F a(Cl )CO (g) + 2NaCl+ 2e2 22.3RT P(CO )a(NaCl) -2E ^ E ^ ^ log(25) ^CO(g) + Na O +CO2 / CO CO2 / CO22^2F a(Na O)P(CO)a(Cl )2.8962- 2Cl 2FDe (24) and (25) (26): pa(Na O) ^ E ^ ^ 2loga(NaCl) ^ logP(CO ) ^ logP(CO) ^ ^2 Cl2 CO2 / CO 22.3RT iv) CCl4(g) / CO2(g) / C(s) mixture The acid-base pair is determined by the partial pressures of the gases CCl4 and CO2 and the associated redox couples are CCl4 / C and CO2 / C. The reactions and relationships considered are given in Table 8. Table 8. Reactions involved in the CCl4(g) / CO2(g) / C(s) mixture. Redox reaction. Nernst equation. E°(V) / Cl2 / Cl-. CCl4(g) + 4e^(-C) + E^(-C) + E^(-C) + 2.3RT log P(CCl 4 ) 4Cl-CCl4 / C CCl4 / C 4F a(C)a(Cl^ ) 4 0.100 (27)2.3RT P(CO )a(NaCl4 CO2(g) + 4NaCl+ 4e E ^ E ^ ^ 2 ) CO2 / C CO2 / log^ C + 2Na2O + 4Cl-C 4F a(Na O) 2 a(C)a(Cl^) 4 -2.896 (28)2 Acid-base equilibrium Equilibrium constant log K 4 CCl4(g) + 2Na2O ^ K 4 ^ P(CO 2 )a(NaCl) CO (g) + 4NaClCCl / CO2 2 P(CCl )a(Na O) 2 62.093 (29) 4 2 v) CCl4 / CO2 / CO gaseous mixture. Carbon is replaced by gaseous CO. The redox couples are CCl4 / CO and CO2 / CO. The reactions and relationships considered are given in Table 9. Table 9. Reactions involved in the CCl4 / CO2 / CO gaseous mixture - Redox reaction Nernst equation E°(V) / Cl2 / Cl CCl4(g) + Na2O + 2e2.3RT P(CCl)a(Na2O)^ CO(g) + 2NaCl + E4 / CO^ E^ CCl4 / CO^ log 4 2 CCl -2F P(CO)a(NaCl) 2 a(Cl^ ) 2 3.097 (30)2Cl CO2(g) + 2NaCl+ 2e 2 E ^ E ^ 2.3RT P(CO 2 )a(NaCl) ^ CO(g) + Na2O +CO2 / CO CO2 / CO ^ log2Cl- 2F a(Na ^ 2O)P(CO)a(Cl ) 2 -2.896 (31)Acid equilibrium-Basic log K equilibrium constant 4P(CO)a(NaCl)CCl (g) + 2Na O4 2 2 ^ K62.093 (32) CCl4 / CO2 2 P(CCl )a(Na O)^ CO2(g) + 4NaCl 4 2vi) COCl2 / CO2 / C Gas Mixture In this gas mixture, the oxo-acidity is determined by the COCl2 / CO2 couple and the redox potential by the COCl2 / C and CO2 / C couples. The reactions and relationships used are summarized in Table 10. Table 10. Reactions involved in the COCl2 / CO2 / CE°(V) gas mixture Redox reactions Nernst equation / Cl2 / Cl- COCl2(g) + 2NaCl + 4eE 2.3RT P(COCl2 )a(NaCl) 2 -COCl2 / C ^ E ^ COCl2 / C ^ log^ C + Na2O + 4Cl4F a(C)a(Na2 O)a(Cl ^) 4 -1.387 (33)CO2(g) + 4NaC 2.3RT P(CO )a(NaCl) 4l+ 4e 2E ^ E ^ ^ log -2.896 (34) CO2 / C CO2 / C 2 4^-4F a(C)a(Na O) a(Cl )^ C + 2NaO + 4Cl2 2 Acid equilibrium- Basic log K equilibrium constant 2P(CO )a(NaCl)COCl2(g) + Na2O 2 ^ K 31,258 (35) COCl2 / CO2P(COCl )a(Na O)^ CO(g) + 2NaCl2 2 2vii) COCl / CO / CO2 Gaseous Mixture In this gaseous mixture, the oxo-acidity is always determined by the COCl / CO2 couple and the redox potential by the COCl / CO and CO / CO couples. The reactions and relationships used are summarized in Table 11. Table 11. Reactions involved in the COCl / CO / CO2 gaseous mixture E°(V) Redox reactions Nernst equation - / Cl2 / Cl P (COCl )2.3RT COCl(g) + 2e2 2E ^ E ^ ^ log 0.121 (36) COCl2 / CO COCl2 / CO ^ 2-2F P(CO)a(Cl )^ CO(g) + 2Cl CO(g) + 2NaCl+ 2e2 22.3RT P(CO )a(NaCl)2E ^ E ^ ^ log -2.896 (37) CO2 / CO CO2 / CO^ CO(g) + NaO +22^2F P(CO)a(Na O)a(Cl )2- 2Cl Acid-equilibrium Base log K equilibrium constant 2P(CO)a(NaCl)COCl2(g) + Na2O 2 ^ K 31,258 (38) COCl2 / CO2P(COCl )a(Na O)^ CO(g) + 2NaCl2 2 2viii) CCl / CO / HCl / H4 Gas Mixture The CCl / CO / HCl / H4 gas mixture also constitutes a gas mixture consisting of a strongly oxo-acidic acid-base pair and a redox pair with a strong reducing power. The reactions and relationships used are summarized in Table 12. Table 12. Reactions involved in the CCl / CO / HCl / H4 gas mixture E°(V) Redox reactions Nernst equation P(HCl)2HCl(g) + 2eE E E E E E E log -1.043 (39) HCl / H2 HCl / H2 2^-2F P(H)a(Cl) H(g) + 2Cl2 2 Acid-base equilibrium Equilibrium log K 4 CCl4(g) + 2Na2O K ^ P(CO 2 )a(NaCl) ^ CO2(g) + 4NaClCCl4 / CO2 P(CCl)a(Na O) 2 62.093 (40) 4 2 III.6. Conclusion Table 13 summarizes the different mixtures considered by the inventors and recalls the potential and oxo-acidity ranges that these mixtures can reach depending on their composition (between 10 -6and 0.5 atm). Table 13. Potential and oxo-acidity ranges of different mixtures for partial pressures between 10 -6and 0.5 atm Mixture Emin (V) / Cl2 Emax (V) / Cl2 pa(Na2O) min pa(Na2O) max HCl-H2O-H2 -2.17 -0.52 7.7 24.8 Cl2-O2-ion Cl- -0.58 -0.03 13.9 22.5 Cl2-CO-C-ion Cl- -0.58 -0.03 24.7 36.1 Cl2-CO2-C-ion Cl- -0.58 -0.03 24.6 33.1 Cl2-CO2-CO-ion Cl- -0.58 -0.03 18.7 35.8 CCl4-CO2-C -0.19 0.085 28.6 34.3 CCl4-CO2-CO -0.45 0.65 28.6 34.3 SOCl2-SO2-S2Cl2-0.72 0.56 21.7 33 COCl2-CO2-C -0.44 0.38 25.9 37.3 COCl2-CO2-CO -0.44 0.67 25.9 37.3 CCl4-CO2-HCl-H2-2.17 -0.52 28.6 34.3 CCl4-CO-HCl-H2-2.17 -0.52 32.3 60.7 The lowest potentials are obtained with mixtures containing H2 and the highest oxidizing potentials with mixtures containing CCl4(g) or COCl2(g). The highest oxoacidity is obtained with mixtures containing CO(g) and CO2(g). The most reducing gas considered here is therefore H2 and the most oxoacid is CO(g).These different mixtures can also be classified according to the following 5 potential applications: - Synthesis of PuCl3 (from PuO2) - Synthesis of UCl3 (from UO2 or U3O8) - Redox control of the fuel salt during operation - Precipitation of uranium and plutonium oxides - Chlorination of the fuel salt, U / Pu separation (UCl5(g), PuCl3 in the salt). Table 14 presents a summary of the use of the mixtures according to these potential applications. Table 14. Use of mixtures according to potential application HCl Cl2 Cl2 Cl2 Cl2 CCl4 CCl4 SOCl2 COCl2 COCl2 CCl4 CCl4 H2O O2 CO CO2 CO2 CO2 CO2 SO2 CO2 CO2 CO2 CO H2 Cl- CC CO C CO S2Cl2 C CO HCl HCl Cl- Cl- Cl- H2H2U Synthesis Cl3 XX Synthesis of P uCl3 xxx XX x XXX XX Redox control of fuel salt xx Precipitation of U and Pu oxides xx Chlorination of fuel salt, XX x XXXX x U / Pu separation

Claims

CLAIMS 1) A method for obtaining a chloride molten salt bath comprising at least one actinide in which the state and / or oxidation state of said at least one actinide are predetermined according to the intended application, comprising the following steps: a) establishing, for said at least one actinide, its potential-oxoacidity diagram at a given temperature T in a chloride molten salt bath, b) from the potential-oxoacidity diagram established in step a), defining the potential-oxoacidity range in which said at least one actinide is in the predetermined state and / or oxidation state, c) selecting at least three different compounds, distinct from said at least one actinide, which fix, at temperature T, the potential and oxoacidity of the chloride molten salt bath in the range defined in step b), one of said at least three compounds being the chloride ion contained in the chloride molten salt bath,then d) introduce into a molten chloride bath comprising said at least one actinide at temperature T said at least three compounds selected in step c), said at least three different compounds different from said at least one actinide, with the exception of the chloride ion contained in the molten chloride bath when the latter is one of said at least three different compounds, not being products or by-products of one or more reaction(s) occurring in the molten chloride bath, and provided that, when said at least three different compounds different from said at least one actinide comprise chlorine (Cl2), the chloride ion (Cl-) and carbon (C), said at least three compounds further comprise carbon monoxide (CO) or carbon dioxide (CO2). 2) A process for obtaining according to claim 1, characterized in that said molten chloride bath comprises at least two different actinides whose state and / or the,The oxidation state of said at least two actinides is predetermined according to the intended application, and the process comprises the following steps: a) establishing, for each of said at least two actinides, its potential-oxoacidity diagram at a given temperature T in a bath of molten chloride salts, b) from the potential-oxoacidity diagrams established in step (a), defining the potential-oxoacidity range in which said at least two actinides are in the predetermined state and / or oxidation state, c) selecting at least three different compounds, distinct from said at least two actinides, that fix, at temperature T, the potential and oxoacidity of the bath of molten chloride salts within the range defined in step b), one of said at least three compounds being the chloride ion contained in the bath of molten chloride salts, and then d) bringing into contact,a molten chloride bath comprising said at least two actinides at temperature T and said at least three compounds selected in step c), said at least three compounds being different from said at least two actinides, with the exception of the chloride ion contained in the molten chloride bath when the latter is one of said at least three different compounds, not being products or by-products of one or more reaction(s) occurring in the molten chloride bath, and provided that, when said at least three different compounds being different from said at least two actinides comprise chlorine (Cl2), the chloride ion (Cl-) and carbon (C), said at least three compounds further comprise carbon monoxide (CO) or carbon dioxide (CO2). 3) Process for obtaining according to claim 1 or 2,characterized in that said temperature T is between 450°C and 1000°C. 4) A method for obtaining according to any one of claims 1 to 3, characterized in that said molten chloride bath comprises at least one salt selected from the group consisting of sodium chloride (NaCl), magnesium dichloride, (MgCl2), potassium chloride (KCl), lithium chloride (LiCl), calcium dichloride (CaCl2) and a mixture thereof. 5) A process for obtaining according to any one of claims 1 to 4, characterized in that said molten chloride bath comprises at least sodium chloride (NaCl). 6) A process for obtaining according to claim 5, characterized in that, in the diagram(s) established in step a), the potential axis is referenced with respect to the redox couple Cl2(1 atm) / Cl- (a=1) and the oxo-acidity axis is expressed by the logarithm pa(Na2O) (= - log a(Na2O)). 7) A method for obtaining according to any one of claims 1 to 6, characterized in that said at least one actinide or said at least two actinides is / are selected from the group consisting of thorium (Th), uranium (U), plutonium (Pu), neptunium (Np), americium (Am) and curium (Cm).8) A process for obtaining according to any one of claims 1 to 7, characterized in that said at least one actinide or at least two actinides comprise / comprise uranium (U) and / or plutonium (Pu). 9) A process for obtaining according to any one of claims 1 to 8, characterized in that said at least three different compounds are selected from gaseous compounds, the chloride ion from the molten chloride salt bath, and carbon. 10) A process for obtaining according to any one of claims 1 to 9, characterized in that said at least three different compounds comprise two compounds forming a redox couple, two compounds forming an acid-base couple, and at least one chlorinated gas. 11) A method for obtaining according to any one of claims 1 to 10, characterized in that, during step c), the selection of said at least three different compounds is done by calculation on the basis of the redox and acid-base reactions involved between said at least three different compounds and the associated relationships of the type Nernst relation and equilibrium constant. 12) A process for obtaining according to any one of claims 1 to 11, characterized in that said at least three different compounds are chosen from the group consisting of water (H2O), dihydrogen (H2), hydrochloric acid (HCl), dichlorine (Cl2), chloride ion (Cl-), carbon (C), carbon oxide (CO), carbon dioxide (CO2), carbon tetrachloride (or terachloromethane, CCl4), carbonyl dichloride (or phosgene, COCl2), thionyl chloride (SOCl2), disulfide dichloride (S2Cl2) and sulfur dioxide (SOCl2).13) A process for obtaining according to any one of claims 1 to 12, characterized in that said at least three different compounds are chosen from the group consisting of the mixture HCl / H2O / H2, the combination Cl2 / O2 / Cl- ion, the combination Cl2 / CO / C / Cl- ion, the combination Cl2 / CO2 / C / Cl- ion, the combination Cl2 / CO2 / CO / Cl- ion, the mixture CCl4 / CO2 / C, the mixture CCl4 / CO2 / CO, the mixture SOCl2 / SO2 / S2Cl2, the mixture COCl2 / CO2 / C, the mixture COCl2 / CO2 / CO, the mixture CCl4 / CO2 / HCl / H2 and the mixture CCl4 / CO / HCl / H2. 14) Use of the CCl4 / CO2 / HCl / H2 mixture or the CCl4 / CO / HCl / H2 mixture to synthesize uranium trichloride (UCl3) in a bath of molten chloride salts, in particular based on NaCl, and containing at least uranium or - to control the redox of the fuel salt in such a bath.15) Use of the combination Cl2 / CO / C / Cl-, the combination Cl2 / CO2 / C / Cl-, the combination Cl2 / CO2 / CO / Cl-, the mixture CCl4 / CO2 / C, the mixture CCl4 / CO2 / CO, the mixture SOCl2 / SO2 / S2Cl2, the mixture COCl2 / CO2 / C, the mixture COCl2 / CO2 / CO. 16) Use of the mixture CCl4 / CO2 / HCl / H2 or of the mixture CCl4 / CO / HCl / H2 for synthesizing plutonium trichloride (PuCl3) in a bath of molten chloride salts, in particular based on NaCl, and containing at least plutonium, the compounds of said combinations and mixtures, with the exception of the chloride ion contained in the bath of molten chloride salts, not being products or by-products of one or more reaction(s) occurring in the bath of molten chloride salts. Use of the mixture HCl / H2O / H2 or of the combination Cl2 / O2 / Cl- for precipitating uranium and plutonium oxides in a bath of molten chloride salts, in particular based on NaCl, containing at least uranium and at least plutonium.17) Use of the combination Cl2 / CO / C / Cl-, the combination Cl2 / CO2 / C / Cl-, the combination Cl2 / CO2 / CO / Cl-, the mixture CCl4 / CO2 / C, the mixture CCl4 / CO2 / CO, the mixture SOCl2 / SO2 / S2Cl2, the mixture COCl2 / CO2 / C or the mixture COCl2 / CO2 / CO for the chlorination of fuel salt and the separation of uranium and plutonium in a bath of molten chloride salts, in particular based on NaCl containing at least uranium and at least plutonium.

Images