Method for the synthesis of actinide chloride(s) from actinide oxide(s) present in a molten salt

Abstract

The present invention relates to a method for the synthesis of actinide chloride(s) from actinide oxide(s) present in a molten salt, the method using an aluminium(I) salt, a silicon(II) salt and / or a beryllium(III) salt, and optionally at least one chloride salt of an alkali and / or alkaline-earth metal. The present invention also relates to the use of an aluminium(I) salt, a silicon(II) salt and / or a beryllium(III) salt, for example aluminium chloride AlCl3, for the synthesis of actinide chloride(s) from actinide oxide(s) in a molten fuel salt for molten salt nuclear fission reactors (MSR).

Description

Title of the invention: Process for synthesizing actinide chloride(s) from actinide oxide(s) present in a molten salt

[0001] The present invention relates to a process for synthesizing actinide chloride(s) from actinide oxide(s) present in a molten salt, said process comprising the use of an aluminum chloride salt (I), a silicon chloride salt (II), and / or a beryllium chloride salt (III), and optionally at least one chloride salt of an alkali and / or alkaline earth metal distinct from salts (I), (II), and (III). The present invention also relates to the use of said salts (I), (II), and / or (III) for the synthesis of actinide chloride(s) from actinide oxide(s) in a molten salt fuel for molten salt nuclear fission reactors (MSF). This synthesis is carried out, for example, at a temperature between 100 and 850°C, between 120 and 500°C or between 150 and 300°C.

[0002] Molten salt reactors (MFRs) consist of a reactor core in which a molten salt fuel made from heavy fissile or fissile nuclei undergoes self-sustaining nuclear fission reactions, and a primary heat exchanger in which the hot fuel salt transfers heat to a coolant molten salt. In an MFR, the molten fuel salt flows from the core to a heat exchanger where it transfers its heat to the coolant molten salt before returning to the reactor vessel. The molten fuel salt enters the core at a temperature of approximately 500-550°C and exits at a higher temperature of approximately 700-800°C.The implementation of a molten fuel salt therefore involves two types of salts: on the one hand, molten fuel salt which includes a fuel based on heavy fissile or fissile nuclei and, on the other hand, a heat transfer molten salt, which does not include any fuels.

[0003] In a solid-state reactor (SSR), the molten salts comprise at least one salt, such as a chloride or a fluoride. The salts are solid (crystals) at room temperature and become liquid above their melting point. Unlike heat transfer molten salts, fuel molten salts contain nuclear material, notably in the form of actinide chlorides or fluorides. The actinide chlorides and fluorides must be synthesized before being introduced into the SSR. For example, the synthesis of actinide chlorides, including plutonium chloride (PuCl) and uranium chloride (UCL), is carried out from their corresponding oxides: plutonium oxide (P11O2) and uranium oxide (UsO3) in the case of PuCl and UCl3, respectively.

[0004] The use of molten salt reactors (MSRs) offers numerous advantages, including improved intrinsic safety and reduced waste. Molten salt reactors use liquid fuel that can be drained into a safety tank in the event of a failure, thus significantly reducing the risk of core meltdown. Furthermore, molten salts expand as the temperature rises, resulting in a The reduction of the fission reaction (negative feedback coefficients) provides inherent safety to this type of design. Furthermore, RSFs (Refuse-Derived Fuels) use fuel more efficiently and can burn existing nuclear waste, thus reducing the amount of long-term radioactive waste. However, the development of this technology relies on identifying innovative solutions to improve the process's profitability and facilitate its implementation.

[0005] The inventors have identified a way to lower the synthesis temperature and stabilize the chloride forms of actinides in salts, which contributes to an improvement in the profitability of the process, while facilitating its implementation.

[0006] Within the scope of the present invention: - the expression “between ... and …” (for example, a range of values) should be understood as including the limits (for example, the limit values ​​of this range of values); - any description relating to one embodiment is applicable and interchangeable with all other embodiments of the invention; and - when an element or component is included in and / or selected in a list of elements or components, it should be understood that that individual element or component may be selected and combined with other individual elements, or may be selected to form a subgroup of two or more explicitly listed elements or components; also, any element or component cited in a list of elements or components may be omitted from that list.

[0007] An object of the present invention relates to a process for the synthesis of actinide chloride(s) from actinide oxide(s) present in a molten salt, said synthesis process employing a) at least one aluminum salt (I), a silicon salt (II) and / or a beryllium salt (III), and b) optionally at least one chloride salt of an alkali and / or alkaline earth metal distinct from salts (I), (II) and / or (III), said process comprising the chlorination of the actinide oxide(s) to the corresponding actinide chloride(s) within said salt in the molten state.

[0008] More specifically, the process of the present invention uses at least one aluminum salt (I), one silicon salt (II) and / or one beryllium salt (III) (also referred to as "salt a" hereafter): MxlAlylXzl (I) M x2 If y2 X z2 (II) M x3 Be y3 X z3 (III) according to which: M is an alkali metal and / or an alkaline earth metal, preferably Na, K and / or Li. X is Cl, 0 < xl < 10, 1 < yl < 2, 1 < zl < 13, 0 < x2 < 10, 1 < y2 < 2, 4 < z2 < 14, 0 < x3 < 10, 1 < y3 < 2, and 2 < z3 < 12.

[0009] The molten salt may also optionally include at least one chloride salt of an alkali and / or alkaline earth metal distinct from salts (I), (II) and / or (III) (also referred to as "salt b" below).

[0010] Salts a) and b), when present, are used in combination during the process of the present invention.

[0011] The process of the present invention may further include the implementation of a reducing element selected from aluminium metal (Al), silicon metal (Si) and / or beryllium metal (Be), preferably aluminium metal (Al).

[0012] The process of the present invention comprises at least the chlorination of the actinide oxide(s) to the corresponding actinide chloride(s), this chlorination taking place within the molten salt. The process of the invention is indeed carried out within a molten salt. Depending on the various embodiments described below, the molten salt comprises the actinide oxide(s), and possibly salts a) and b). These latter salts can be used (or introduced) into the process in solid, liquid (or molten), or gaseous form.

[0013] The inventors realized that the presence of salt a) in the molten salts during the synthesis of actinide chlorides stabilized the chloride forms of the actinides in the salts. The advantages of using aluminum in molten salts are described in more detail below.

[0014] The process of the present invention is particularly suitable for the preparation of nuclear fuels for RSF reactors.

[0015] The use of aluminum, silicon, and / or beryllium in this synthesis allows, on the one hand, for a lower synthesis temperature, thus saving energy, and on the other hand, for the stabilization of the chloride forms of the actinides in the salts. Indeed, the synthesis temperature is preferably in the range of 20 °C to 300 °C, more preferably from 115 °C to 260 °C or from 20 °C to 60 °C. Furthermore, the use of aluminum, silicon, and / or beryllium reduces or eliminates the use of toxic chlorinated gases such as O₂(g) or HCl(g), as well as the synthesis of chlorine-enriched gaseous species, which are sometimes described in association with this type of reaction.

[0016] According to one embodiment, salt a) is an aluminium salt (I): Mxi Al y i Xzi (I) according to which: M is an alkali metal and / or an alkaline earth metal, preferably Na, K and / or Li. X is Cl, 0 < xl < 10, preferably xl = 0 or 1, 1 < yl < 2, preferably yl = 1, and 1 < zl < 13, preferably 2 < zl < 10 or 3 < zl < 8.

[0017] Examples of aluminium (I) salts include the following chlorides: AlCl, AlCl„, KaICl4, NaAlCu, and / or LiAlCu.

[0018] According to one embodiment of the present invention, aluminium is used in chloride form in combustible molten salts for the synthesis of actinide chloride(s) from actinide oxide(s) and consumes the solubilised oxide ions according to one of the following reactions (eq. 1, eq. 2):

[0019] According to another embodiment, salt a) is a silicon (II) salt: M x2 If y2 X z2 (II) according to which: M is an alkali metal and / or an alkaline earth metal, preferably Na, K and / or Li. X is Cl, 0 < x2 < 10, preferably x2 = 0 or 1, 1 < y2 < 2, preferably y2 = 1, and 4 < z2 < 14, preferably 4 < z2 < 10 or 4 < z2 < 8.

[0020] Examples of silicon (II) salts include SiCl, KSiCl, NaSiCl, and / or LiSiCl chlorides.

[0021] According to another embodiment, salt a) is a beryllium (III) salt: M x3 Be y3 X z3 (III) according to which: M is an alkali metal and / or an alkaline earth metal, preferably Na, K and / or Li. X is Cl, 0 < x3 < 10, preferably x3 = 0 or 1, 1 < y3 < 2, preferably y3 = 2, and 2 < z3 < 12, preferably 2 < z3 < 6.

[0022] Examples of beryllium (III) salts include BeCE, KBeCE, NaBeCls, and / or LiBeCE chlorides.

[0023] Preferably, the process of the present invention is a process for synthesizing plutonium chloride (PuCE) from plutonium oxide (PuCE). Preferably, salt a) is an aluminum (I) salt, such as A1CE, or a silicon (II) salt, such as SiCU, or a beryllium (III) salt, such as BeCE.

[0024] Alternatively, and preferably, the process of the present invention is a process for synthesizing uranium chloride from uranium oxide. Preferably, salt a) is an aluminum (I) salt, such as A1CE, or a silicon (II) salt, such as SiCU, or a beryllium (III) salt, such as BeCE.

[0025] The process of the present invention can be carried out according to different embodiments.

[0026] According to a first embodiment, the process comprises contacting the actinide oxide(s) with salt a), and optionally salt b), in a molten state. This contacting of the actinide oxide(s) with said salt a), and optionally salt b), in a molten state, can be carried out at a temperature of at least 100°C, for example, at least 115°C, or at least 120°C, or at least 150°C. This temperature can, in particular, be chosen to correspond at least to the melting point of the constituent salts of the molten salt. Thus, if the process of the present invention uses a silicon(II) salt as salt a), the synthesis temperature could even be lower than 100°C; for example, the synthesis temperature could be in the range of 20 to 60°C.

[0027] According to a second embodiment, the process comprises preparing an initial mixture including the actinide oxide(s), salt a), and optionally salt b), followed by heating the initial mixture. In this case, the heating can be carried out gradually up to a temperature of at least 100°C, for example, at least 115°C, or at least 120°C, or at least 150°C. This temperature can, in particular, be chosen to correspond at least to the melting point of the constituent salts of the molten salt.

[0028] The process of the present invention can be operated at a temperature between 20 and 850°C, for example between 20 and 60°C, between 120 and 500°C, between 150 and 300°C, or between 115 and 260°C. It has been demonstrated that, thanks to the process of the present invention, it is possible to lower the synthesis temperature. Preferably, the process of the present invention is operated at a temperature in the range of 20 to 600°C, more preferably in the range of 20 to 500°C, more preferably in the range from 115 to 300°C, more preferably in the range from 115 to 260°C, more preferably in the range from 150 to 260°C, more preferably in the range from 175°C to 260°C; or more preferably in the range from 20 to 60°C.

[0029] The process for synthesizing actinide chloride(s) of the present invention is carried out outside the RSF reactor. In particular, it can be performed in a crucible, which can be placed in a furnace providing the heat necessary to maintain the salt in a molten state. For example, the synthesis can be carried out under argon, in a glassy carbon crucible, an alumina crucible, or a metallic crucible (e.g., nickel-based).

[0030] According to a preferred embodiment, the synthesis is carried out under anhydride conditions, in the presence of an inert gas, for example, argon, helium, krypton, xenon, nitrogen, or neon. More particularly, the synthesis of actinide chloride(s) according to the present invention is preferably carried out under argon, which has a purity > 99.999%.

[0031] According to one embodiment of the present invention, the synthesis is carried out under anhydrous conditions by bubbling the inert gas in the molten salt.

[0032] According to one embodiment of the present invention, salt a) is used in a mixture with salt b). Salt a) may comprise several distinct compounds, and salt b) may also comprise several distinct compounds. In particular, salt a), for example aluminum chloride AlCl, may be used in a mixture with one, two, or three chloride salts of an alkali and / or alkaline earth metal, thus constituting, respectively, a binary, ternary, or quaternary mixture of salts a) and b).

[0033] More specifically, the salt (a), for example aluminum chloride (AlCl), can be used in a mixture with sodium chloride (NaCl), calcium chloride (CaCl₂), magnesium chloride (MgCl₂), potassium chloride (KCl), lithium chloride (LiCl), beryllium chloride (BeCl), or a mixture of two or more of these chlorides. Thus, according to this embodiment of the synthesis process, the molten salt comprises (a) aluminum chloride (AlCl), and (b) sodium chloride (NaCl), calcium chloride (CaCl₂), magnesium chloride (MgCl), potassium chloride (KG), lithium chloride (LiCl), beryllium chloride (BcCl), or a mixture of two or more of these chlorides.

[0034] According to one embodiment of the synthesis process, the molten salt comprises from 1 to 80 mol% of salt a), relative to the total number of moles of salts a) and b). For example, the molten salt may comprise from 5 to 65 mol% of salt a), for example of AlCl, relative to the total number of moles of salts a) and b).

[0035] Alternatively, the process of the present invention is carried out in the presence of salt a) only. In other words, the process of the present invention does not use salt b). According to this embodiment, salt a) may, in particular, consist of NaAlCl chloride.

[0036] According to one embodiment, the process of the invention uses salt a) and salt b).

[0037] Preferably, the process of the present invention uses salt a) and salt b), where the molar ratio of salt a) to salt b) is in the range of 1:99 to 80:20, more preferably in the range of 5:95 to 65:35. More preferably, the process of the present invention uses salt a) and salt b), where the molar ratio of salt a) to salt b) is in the range of 30:70 to 70:30, more preferably in the range of 51:49 to 69:31, more preferably in the range of 55:45 to 65:35.

[0038] According to one embodiment, salt a) is in excess relative to salt b).

[0039] Preferably, the process of the present invention implements: 1) from 1 to 80 mol. % of salt a), for example 1 to 80 mol. % of AlCE, for example from 5 to 65 mol. % of salt a), for example from 5 to 65 mol. % of AlCE; 2) from 20 to 99 mol. % of alkali and / or alkaline earth metal chloride, for example from 35 to 95 mol. % of alkali and / or alkaline earth metal chloride, relative to the total number of moles of salts a) and b).

[0040] According to another embodiment, the melted salt comprises (or consists of): 1) from 1 to 80 mol. % AlCh, for example from 5 to 65 mol. % AlCh; 2) 20 to 99 mol% of at least one alkali and / or alkaline earth metal chloride(s) chosen from NaCl, CaCE, MgCE, KCl, LiCl, BeCE, for example 35 to 95 mol% of at least one of these alkali and / or alkaline earth metal chlorides, for example one, two or three chloride(s) and preferably at least NaCl, relative to the total number of moles of AICE and alkali and / or alkaline earth metal chloride in the molten salt.

[0041] According to another embodiment, the melted salt comprises (or consists of): 1) from 1 to 80 mol. % AICE, for example from 5 to 65 mol. % of AICE; 2) from 20 to 99 mol. % of NaCl, for example from 35 to 95 mol. % of NaCl, relative to the total number of moles of AICE and alkali and / or alkaline-earth metal chloride in the molten salt.

[0042] According to a preferred embodiment of the process of the present invention, the salt (a) is aluminum in the form of chloride (AlCl₂) and is used in a mixture with sodium chloride (NaCl). Thus, according to this embodiment, the process of the invention uses a molten salt consisting of a binary salt (NaCl-AlCl₂E). Furthermore, according to this embodiment, the molar ratio of NaClClE in the salts Binary NaCl-AlCh can vary between 20:80 and 99:1, for example between 5:95 and 95:5 or between 10:90 and 90:10.

[0043] According to one embodiment of the process of the invention, the process of the invention uses a molten salt comprising (or consisting of) 35-50 mol% NaCl and 50-65 mol% AlCh (for example, 40 mol% NaCl and 60 mol% AlCh). The mixture of the two salts at such a composition forms a eutectic that melts at a temperature lower than the individual melting points of the pure components. Such a mixture is therefore particularly advantageous. Indeed, the use of a mixture of salt a) and salt b) allows for a reduction in the synthesis temperature of actinide chlorides, which notably contributes to a reduction in production costs. The process of the present invention is therefore more cost-effective while maintaining good efficiency compared to prior art processes and allowing for the preservation of the materials used for the reactor.

[0044] Thus, the use of salt (a), optionally mixed with salt (b), i.e., at least one alkali and / or alkaline earth metal chloride(s), not only allows for the consumption of oxide ions solubilized during the synthesis of actinide chlorides, but also lowers the melting point of the molten salts based on the thermal properties of the mixtures, thereby limiting the energy expenditure required for the preparation of the actinide chlorides. Furthermore, it stabilizes the chloride forms of the actinides in the salts.

[0045] The molar quantity of actinide oxide(s) involved in the synthesis process of the present invention is typically at least 1 mol%, relative to the total number of moles of salts a) and b). In particular, the molar quantity of actinide oxide(s) involved in the synthesis process of the present invention is typically at least 5 mol% or at least 10 mol%. Preferably, between 50 and 100 mol% of actinide oxides are used in the synthesis process of the present invention.

[0046] The molar quantity of actinide chloride(s) in the molten salt at the end of the synthesis process is typically at least 1 mol%, relative to the total number of moles of salts a) and b). In particular, the molar quantity of actinide chloride(s) in the molten salt at the end of the synthesis process is typically at least 5 mol% or at least 10 mol%. Preferably, between 50 and 100 mol% of actinide chloride(s) are present in the molten salt at the end of the synthesis process.

[0047] According to one embodiment of the synthesis process of the present invention, the actinide is selected from the group consisting of uranium, plutonium, americium, and thorium, alone or in mixtures. The actinide is preferably uranium and / or plutonium. The actinide is even more preferably plutonium or uranium.

[0048] According to another preferred embodiment of the process of the present invention, aluminum in the form of chloride (AlCh) is used in combination with sodium chloride (NaCl) and magnesium chloride (MgCl). Thus, according to this embodiment, the molten salt consists of a ternary salt: NaCl-MgCb-AlCl₂. For this type of ternary salt, the synthesis temperature is preferably above 260 °C, and more preferably above 400 °C.

[0049] Alternatively, preferably salt b) is not used in the process according to the present invention. For example, according to this alternative, salt a) is preferably a silicon(II) salt, preferably silicon chloride (SiCu).

[0050] In the context of the present invention, according to one embodiment of the synthesis process, the actinide(s) comprises plutonium dioxide P11O2, uranium dioxide UO2, uranium sesquioxide UsO3, thorium oxide ThCl, americium oxide AmCl, or a mixture of two, three, four, or five of these oxides. The actinide(s) preferably comprises plutonium dioxide P11O2, or uranium dioxide UO2, or a mixture of plutonium oxide P11O2 and uranium oxide LhO3. More preferably, plutonium dioxide P11O2 or uranium dioxide UO2.

[0051] According to one embodiment of the synthesis process, the actinide(s) chloride comprises plutonium chloride (PuCl), uranium chloride (UClCl4), uranium chloride (UClCl3), thorium chloride (ThCl), americium chloride (AmCl), or a mixture of two, three, four, five, or six of these chlorides. The actinide(s) chloride preferably comprises a mixture of plutonium chloride (PlCl3), uranium chloride (UClCl4), and uranium chloride (UClCl3).

[0052] The synthesis of actinide chloride(s) from actinide oxide(s) present in a molten salt according to the present invention is typically carried out over a reaction time of between 30 minutes and 10 hours, for example between 1 hour and 6 hours or between 3 hours and 5 hours.

[0053] The process of the present invention preferably relates to the synthesis of at least two distinct actinide chlorides from their corresponding actinide oxides. Preferably, these are plutonium chloride (PuCl) and uranium chloride (UCi3 and UCl, UCl4 reduced to UCl3 by the addition of uranium metal or another reducing metal). The at least two actinide oxides can be added to the molten salt sequentially, simultaneously, or separately.

[0054] According to another embodiment of the process of the present invention, said process comprises: a) The synthesis of a first actinide chloride by contacting the corresponding actinide oxide (first actinide oxide) with said salt in the molten state, then b) The synthesis of a second actinide chloride by contacting the corresponding actinide oxide (second actinide oxide) with the molten salt obtained in step a).

[0055] According to this embodiment (sequential synthesis), the first actinide oxide is added to the molten salt, and then the second actinide oxide is added when the first actinide chloride is, at least partially or totally, synthesized. This embodiment may include a third substep involving the addition of a third actinide oxide.

[0056] According to another embodiment of the process of the present invention, said process comprises the simultaneous synthesis of a first actinide chloride and a second distinct actinide chloride, or even a third actinide chloride, by contacting the corresponding actinide oxides with said salt in the molten or unmolten state in a single common step.

[0057] According to another embodiment of the process of the present invention (separate synthesis), said process comprises: a) The synthesis of a first actinide chloride by contacting the corresponding actinide oxide with a first quantity of salt in the molten state, b) The synthesis of a second actinide chloride by contacting the corresponding actinide oxide with a second quantity of salt in the molten state, and c) The mixing of the molten salts obtained in steps a) and b).

[0058] When the synthesis process involves the preparation of two (or three) actinide chlorides, the first actinide oxide may be added to the molten salt in a molar amount of at least 0.5 mol%, at least 5 mol%, or at least 10 mol%, relative to the total number of moles of AlCl₂ and alkali and / or alkaline earth metal chloride in the molten salt. The second actinide oxide may be added to the molten salt in a molar amount of at least 0.5 mol%, at least 5 mol%, or at least 10 mol%, relative to the total number of moles of AlCl₂ and alkali and / or alkaline earth metal chloride in the molten salt.

[0059] In addition to chlorinating the actinide oxide(s) into the corresponding actinide chloride(s), the process of the invention may also include one or more other steps, before or after the chlorination step.

[0060] Salt (a) can be used in liquid, solid, or gaseous form in the process of the present invention. Salt (b), if used in the process of the invention, can also be used in liquid or solid form in the process of the present invention.

[0061] The process of the invention may in particular include the preparation of a powder of salts a) and b) before use in the synthesis process of the invention.

[0062] The process of the invention may alternatively include a step of melting salts a) and / or b) before use in the synthesis process of the invention. For example, the process of the invention may include a step of melting salts a) and b) as a mixture, and then introducing the actinide oxide(s) into said melted salt, in order to carry out the synthesis process of the invention.

[0063] According to one embodiment, the process of the invention comprises introducing salt a) into molten salt, the molten salt comprising the actinide oxide(s), salt a) being in solid or liquid form. According to this embodiment, salt a) is alone or mixed with salt b), the latter also being in solid or liquid form.

[0064] According to one embodiment, the process of the invention comprises the introduction of the actinide oxide(s) into the salt a) in the molten state, the salt a) being alone or mixed with the salt b), the latter also being in solid or liquid form.

[0065] According to one embodiment, the process of the invention comprises the introduction of the salt a), in gaseous form into the molten salt, said molten salt comprising the actinide oxide(s).

[0066] According to one embodiment, the process of the invention comprises the introduction of the salt a) in gaseous form into the molten salt, said molten salt comprising the actinide oxide(s) and the salt b).

[0067] The process of the present invention may include the following operations: a substep of mixing, in solid state (powder), the constituent compounds of the molten salt; and a substep of heating said mixture obtained to a suitable temperature to obtain the melting of this mixture, which may be carried out in several substeps whose temperature, atmosphere (use of inert gas or not, type of inert gas used) and duration conditions are adjusted to achieve the complete melting of the salts present.

[0068] According to a second variant, the aforementioned preparation step may include the following operations: a substep of mixing, in solid state (powder), the constituent compounds of the molten salt and at least one actinide oxide; and a substep of heating said mixture obtained to a suitable temperature to achieve the melting of this mixture, which may be carried out in several substeps whose temperature, atmosphere (use of inert gas or not, type of inert gas used) and duration conditions are adjusted to achieve the complete melting of the salts present.

[0069] According to another embodiment of the process of the present invention, said process further comprises a step of purifying the actinide chloride(s). The purification of the actinide chloride(s) may, for example, include the evaporation of the residual salt a), for example residual AlCh, and the filtration of the corresponding salt oxide a), for example aluminium oxide Al2O3.

[0070] The filtration stage can be carried out using equipment typically used for filtering the species concerned.

[0071] The evaporation step may include increasing the temperature of the salt to a temperature above 600°C (for example 700 or 750°C) and maintaining this temperature for a period of at least 10 hours (for example 12 hours or 15 hours) under an inert gas (for example Argon), for example by bubbling in the molten salt.

[0072] Preferably, the process does not use tetrachloromethane (ClC4) to purify the salt. Indeed, it is not necessary to use it to prevent the formation of oxides since the salt a) will have efficiently captured the oxide ions present in the molten salt during the synthesis (example of AlCl in eq. 2).

[0073] The present invention further relates to the use of an aluminum (I) salt, a silicon (II) salt, and / or a beryllium (III) salt for the synthesis of actinide chloride(s) from actinide oxide(s) in a molten salt fuel for molten salt nuclear fission reactors (MSFRs). The salt can be used, in particular, to avoid the use of toxic gases commonly used in this type of synthesis. It can be used to lower the synthesis temperature. The synthesis temperature is preferably in the range of 20 to 300 °C, more preferably in the range of 115 to 250 °C. Finally, it can be used to stabilize the chloride forms of the actinides in the salts. The aluminum (I) salt, silicon (II) salt, and / or beryllium (III) salt are as defined above.In particular, it is preferably at least one salt chosen from aluminium chloride AIC3, aluminium chloride ALCle, aluminium chloride KAICL, aluminium chloride NaAlC'L, aluminium chloride LiAlCL, beryllium chloride BcCL, beryllium chloride KBcCL, beryllium chloride NaBeCL, beryllium chloride LiBeCL, silicon chloride SiCl, or a mixture of two or more of these chlorides.

[0074] ASPECTS OF THE PRESENT INVENTION

[0075] The present invention relates in particular to the following aspects: Aspect 1. Process for the synthesis of actinide chloride(s) from actinide oxide(s) present in a molten salt, said process comprising the use of: a) at least one aluminum salt (I), one silicon salt (II) and / or one beryllium salt (III): MxlAlylXzl (I) M x2 If y2 X z2 (II) M x3 Be y3 Xz3 (III) according to which: M is an alkali metal and / or an alkaline earth metal, preferably Na, K and / or Li. X is Cl, 0 < xl < 10, 1 < yl < 2, 1 < zl < 13, 0 < x3 < 10, 1 < y3 < 2, 2 < z3 < 12, 0 < x2 < 10, 1 < y2 < 2, and 4 < z2 < 14, and b) optionally at least one chloride salt of an alkali and / or alkaline earth metal distinct from salts (I), (II) and / or (III), said process comprising the chlorination of the actinide oxide(s) to the corresponding actinide chloride(s) within said salt in the molten state. Aspect 2. A process according to aspect 1, wherein the salt a) is used in solid (powder) or liquid form, alone or mixed with salt b), the latter also being in solid (powder) or liquid form. Aspect 3. A process according to aspect 1, wherein the salt a) is used in gaseous form within the molten salt. Aspect 4. A process according to aspect 1, comprising the introduction of the salt a) in gaseous form into the molten salt, said molten salt comprising the actinide oxide(s) and the salt b). Aspect 5. A process according to any one of the preceding aspects, wherein the molten salt comprises from 1 to 80 mol. % of salt a), relative to the total number of moles of salts a) and b). Aspect 6. A process according to any one of the preceding aspects, wherein the actinide is selected from uranium, plutonium, americium and thorium, alone or in mixture, preferably from uranium and plutonium, alone or in mixture. Aspect 7. A process according to any one of the preceding aspects, wherein the salt a) is selected from aluminium chloride A1C13, aluminium chloride Al2Cle, aluminium chloride KA1CU, aluminium chloride NaAlCU, aluminium chloride LiAlCU, beryllium chloride BeCl2, beryllium chloride KBeCl3, beryllium chloride NaBeCl3, beryllium chloride LiBeCl3, silicon chloride SiCU, or a mixture of two or more of these chlorides. Aspect 8. Process according to aspect 7, wherein the salt a) is aluminium chloride AlC13, the actinide is plutonium or uranium and wherein the synthesis is carried out at a temperature in the range of 115 to 250 °C. Aspect 9. A process according to any one of aspects 1 to 7, wherein the salt a) is a beryllium (III) salt. Aspect 10. A process according to claim 9, wherein the beryllium (III) salt is beryllium chloride BcC'h and the actinide is plutonium or uranium. Aspect 11. A method according to any one of claims 1 to 7, wherein the salt a) is a silicon (II) salt. Aspect 12. A process according to claim 11, wherein the silicon (II) salt is silicon chloride SiCl and the actinide is plutonium or uranium, wherein the synthesis is preferably carried out at a temperature in the range of 20 to 60°C. Aspect 13. A method according to any one of claims 1 to 11, wherein M in salt a) is Na or Li. Aspect 14. A process according to any one of the preceding aspects, wherein the salt b) is selected from sodium chloride NaCl, calcium chloride CaC'h, magnesium chloride MgCE, potassium chloride KG, lithium chloride LiCl, beryllium chloride BeCk, or a mixture of two or more of these chlorides. Aspect 15. A process according to claim 14, wherein a mixture of salt a) and salt b) NaG-AIGs is used for the synthesis of actinide chloride(s). Aspect 16. A process according to any one of the preceding claims, wherein the process of the present invention employs salt a) and salt b), wherein the molar ratio of salt a) to salt b) is in the range of 30:70 to 70:30, more preferably in the range of 51:49 to 69:31, more preferably in the range of 55:45 to 65:35. Aspect 17. A method according to any one of claims 1 to 12, wherein salt b) is not used. Aspect 18. A process according to any one of the preceding aspects, wherein the actinide oxide(s) is / are selected from plutonium oxide P11O2, uranium oxide UO2, uranium oxide UsOs, thorium oxide Ti1O2, americium oxide AmCk, alone or in mixtures, for example a mixture of two or three of these oxides, preferably from plutonium oxide PuC>2 and uranium oxide UO2. Aspect 19. A process according to any one of the preceding aspects, wherein the actinide chloride(s) is / are selected from plutonium chloride P11Cl3, uranium chloride UCU, uranium chloride UCl3, thorium chloride ThCU, americium chloride AmCh, alone or in a mixture, for example a mixture of two or three of these chlorides, preferably from plutonium chloride P11Cl3 and uranium chloride UCU. Aspect 20. A process according to any one of the preceding aspects, characterized in that the synthesis is carried out at a temperature above the melting point of salt a), or of the mixture of salts a) and b), if b) present, preferably the synthesis temperature is in the range of 20 to 850°C, more preferably in the range of 115 to 300°C, or more preferably in the range of 450 to 650°C, or more preferably in the range of 20 to 60°C. Aspect 21. Process according to aspect 20, wherein the synthesis temperature is in the range of 115 to 250 °C. Aspect 22. A process according to any one of the preceding aspects, further comprising a step of purification of the actinide chloride(s), said purification preferably comprising evaporation of salt a) and / or filtration of the oxide corresponding to salt a). Aspect 23. A process according to any one of the preceding aspects, comprising a step of purification of the actinide chloride(s), said purification preferably comprising evaporation of residual AlCh and / or filtration of aluminium oxide Al2O3. Aspect 24. Use of an aluminium (I) salt, a silicon (II) salt and / or a beryllium (III) salt: MxlAlylXzl (I) M x2 If y2 X z2 (II) M x3 Be y3 X z3 (III) according to which: M is an alkali metal and / or an alkaline earth metal, preferably Na, K and / or Li. X is Cl, 0 < xl < 10, 1 < yl < 2, 1 < zl < 13, 0 < x2 < 10, 1 < y2 < 2, 4 < z2 < 14, 0 < x3 < 10, 1 < y3 < 2, and 2 < z3 < 12, for the synthesis of actinide chloride(s) from actinide oxide(s) in a fuel molten salt for molten salt nuclear fission reactors (MSRs). Aspect 25. Use according to aspect 14, wherein salt (I), (II) and / or (III) is selected from aluminium chloride A1C13, aluminium chloride AUCle, aluminium chloride KA1CU, aluminium chloride NaAlCU, aluminium chloride UiAlCU, beryllium chloride BeCl2, beryllium chloride KBeCL, beryllium chloride NaBeCL, beryllium chloride LiBeCh, silicon chloride SiCU, or a mixture of two or more of these chlorides. Aspect 26. Use according to aspect 24 or 25, according to which the synthesis temperature is in the range of 115 to 250 °C, preferably according to which, for the use of aluminium salt (I), the synthesis temperature is in the range of 115 to 250 °C or in the range of 20 to 60 °C, if salt (II) is used. Aspect 27. In use according to any one of aspects 24 to 26, aluminium (I) salt is used for the synthesis of actinide chloride(s) from actinide oxide(s) in a molten salt fuel for molten salt nuclear fission reactors (MSRs). Aspect 28. In use according to any one of aspects 24 to 26, silicon(II) salt is used for the synthesis of actinide chloride(s) from actinide oxide(s) in a molten salt fuel for molten salt nuclear fission reactors (MSRs). Aspect 29. The use according to aspect 24 or 25, beryllium (III) salt is used for the synthesis of actinide chloride(s) from actinide oxide(s) in a molten salt fuel for molten salt nuclear fission reactors (MSRs). Aspect 30. Use of aluminium chloride AlCL for the synthesis of actinide chloride(s) from actinide oxide(s) in a fuel molten salt for molten salt nuclear fission reactors (MSRs). Aspect 31. Use according to any one of aspects 24 to 30, characterized in that the synthesis is carried out in the presence of at least one chloride salt of an alkali and / or alkaline earth metal distinct from salts (I), (II) and / or (III), for example sodium chloride NaCl, calcium chloride CaCl, magnesium chloride MgCl, potassium chloride KG, lithium chloride LiCl, beryllium chloride BeCl, or a mixture of two or more of these chlorides.

[0076] EXAMPLES

[0077] The invention will now be described in more detail with reference to the following examples, the purpose of which is merely illustrative and not intended to limit the scope of the invention.

[0078] Examples 1 and 2 of this application relate to the synthesis of CcCl and NaCl-CcCls. CeCl was used in the examples to illustrate the feasibility of this process for the synthesis of actinide chloride(s), such as plutonium chloride. It is known to those skilled in the art that CcCl reacts / acts similarly to P11O2 or UO2; therefore, CeCl is a simulant of these actinide oxides (see "Applicability of CeCl as a surrogate for PuC in a MOX fuel development", Hann Soo Kim, et al., Journal of Nuclear Materials 378 (2008) 98-104, en particulier voir passages “Cerium oxide was found to be a useful surrogate to simulate the Pu behavior in the MOX fuel fabrication”,, « Measurements of the liquidus surface and solidus transitions of the NaCl-UC and NaCl-UC -CeC phase diagrams », E.S. Sooby et al., Journal of Nuclear Materials 466 (2015) 280-285, voir passages “For this reason Ce is chosen as the appropriate surrogate for Pu due to their common (III) and (IV) valence states”, et « Enhancing cerium and plutonium solubility by reduction in borosilicate glass », J.-N. Cachia, et al., voir passages “Cerium, with two stable trivalent and tetravalent oxidation states in the glass depending on the melting conditions, was used in this study as a surrogate for plutonium”).Thus it was considered that the proof of operation of the synthesis of cerium chloride according to the present invention would allow the conclusion that this same synthesis would be successful starting from actinide oxide(s) such as P11O2.

[0079] Example 1: Synthesis of CeCl from CeCh in the molten NaCl-AlCl mixture (40-60 mol.%) at 150°C

[0080] Equation 3 below represents the chlorination reaction: 6CeO2+ 8Al2O3+ 6CeCl3+ 4Al2O3+ 3Cl2^ with aG° = -183.721 kJ.mol' 1 at 150°C (eq. 2) For your information, the equation for plutonium would be as follows:

[0081] The preparation of 100 g of NaCl-AlCl salt (40-60 mol%) was carried out in a glove box to avoid any contact with ambient humidity. In the presence of water, the salt undergoes partial hydrolysis, producing hydrogen chloride. The fusion protocol is presented in Table 1. Table 1: NaCl -Aids fusion steps (40-60 mol.%)

[0082] In this experiment, 1.557 g of CeCl, corresponding to 1 mol.%, was added to molten NaCl-AlCl salt at 150°C. For a period of 2 hours, at a flow rate of 60 mL / min, argon was injected directly into the salt through a Pyrex tube, acting as a stirrer to accelerate the chlorination process. After this step, the salt was placed under an argon flow at a rate of 3 mL / min to allow the settling of solid precipitates.

[0083] A sample was then taken for ICP analysis to determine the amount of dissolved Ce, using a nickel bar (the salt crystallizes on the cold nickel bar when introduced into the salt).

[0084] The results of the ICP analyses presented in Table 2 reveal that the concentration of dissolved Ce measured by ICP is consistent with the predicted theoretical value. Table 2: ICP results of samples taken after the addition of CcCl to NaCl-AICl salt

[0085] Thus, the conversion rate from CeCL to CeCL is 83%.

[0086] Example 2: Synthesis of 50g of NaCl-CeCU mixture (73-27 mol%) from CeCh in the molten NaCl-AlCl mixture at 300°C

[0087] In this test, 50g of NaCl-AICl salt with a composition of 57.1 mol. % NaCl-42.9 mol. % A1Cl was used to carry out the synthesis (Table 3). Table 3: Composition of the NaCl-AICl mixture used for the synthesis

[0088] A quantity of CeCl equal to 30.537 ga was added to react completely with 0.237 mol of AlCl. The objective of this experiment was to evaluate the conversion rate using the minimum amount of AlCl, so that at the end of the experiment, only AlCl remained to be removed.

[0089] Once CcCl was added, the temperature was gradually increased to 600 °C for 4 hours, then maintained at 600 °C for 15 hours. The salt was then crystallized under argon.

[0090] Once crystallized, three salt samples were taken for ICP analysis. The ICP results showed an average Ce concentration of 2.51 ppm, compared to the theoretical 3.84 ppm expected with complete conversion. This corresponds to a conversion rate of 65%. The NaCl-CeCl composition was recalculated based on this result, assuming that the AlCl₂ had completely evaporated. Table 4: Composition of the final mixture calculated from the ICP analysis results

[0091] Example 3: Synthesis of UCE from UCh in NaCl-CaCh salt at 600°C

[0092] In a research context, corrosion tests were carried out in the NaCl-CaCl-UCi3 salt (46.75 - 52.75 - 0.5 mol%). Table 5 presents the synthesis protocol for UCI3 from UO2, aluminum chloride, and a reducing agent (metallic aluminum). The reducing agent (metallic aluminum or uranium metal, for example) allows the production of uranium trichloride (UCi3) by reducing uranium tetrachloride (UCi4). Table 5: Synthesis steps of UCL from UO2 and aluminium chloride. In this test, an amount corresponding to 0.5 mol.% of UO2 was added to the molten NaCl-CaCl salt at 600°C with an excess of AIC3.

[0094] Two samples were then taken for ICP analysis to determine the amount of dissolved U (as uranium chloride), using a nickel bar (the salt crystallizes on the cold nickel bar when introduced into the salt).

[0095] The results of the ICP analyses presented in Table 6 reveal that the concentration of dissolved U measured by ICP is consistent with the predicted theoretical value. Table 6: ICP results of samples taken after the addition of UO2 to NaCl-CaCh salt in the presence of AICI3 and a reducing species (metallic aluminium)

Claims

DEMANDS 1. Process for the synthesis of actinide chloride(s) from actinide oxide(s) present in a molten salt, said process employing: a) at least one aluminum salt (I), one silicon salt (II) and / or one beryllium salt (III): MxlAlylXzl (I) M x2 If y2 X z2 (II) M x3 Be y3 X z3 (III) according to which: M is an alkali metal and / or an alkaline earth metal, preferably Na, K and / or Li. X is Cl, 0 < xl < 10, 1 < yl < 2, 1 < zl < 13, 0 < x2 < 10, 1 < y2 < 2, and 4 < z2 < 14, 0 < x3 < 10, 1 < y3 < 2, and 2 < z3 < 12, b) optionally at least one chloride salt of an alkali and / or alkaline earth metal distinct from salts (I), (II) and / or (III), said process comprising the chlorination of the actinide oxide(s) to the corresponding actinide chloride(s) within said salt in the molten state.

2. A process according to claim 1, wherein the salt a) is used in solid form or in liquid (molten) form, alone or in a mixture with the salt b), the latter also being in solid form or in liquid (molten) form.

3. A process according to claim 1, wherein the salt a) is used in gaseous form within the molten salt.

4. A process according to any one of the preceding claims, wherein the molten salt comprises from 1 to 80 mol. % of salt a), relative to the total number of moles of salts a) and b).

5. A process according to any one of the preceding claims, wherein the actinide is selected from uranium, plutonium, americium and thorium, alone or in mixture, preferably from uranium and plutonium, alone or in mixture.

6. A method according to any one of the preceding claims, wherein the salt a) is selected from aluminum chloride A1C13, aluminum chloride Al2Cl, aluminum chloride KA1CU, aluminum chloride NaAlCU, aluminum chloride LiAlCU, beryllium chloride BeCl2, beryllium chloride KBeCl3, beryllium chloride NaBeCl3, chloride of beryllium LiBeCh, silicon chloride SiCU, or a mixture of two or more of these chlorides.

7. A process according to claim 6, wherein the salt a) is aluminium chloride AlCh, the actinide is plutonium or uranium and wherein the synthesis is carried out at a temperature in the range of 115 to 250 °C.

8. A method according to any one of claims 1 to 6, wherein the salt a) is a beryllium (III) salt.

9. A process according to claim 8, wherein the beryllium (III) salt is beryllium chloride BcCb and the actinide is plutonium or uranium.

10. A method according to any one of claims 1 to 6, wherein the salt a) is a silicon (II) salt.

11. A process according to claim 10, wherein the silicon (II) salt is silicon chloride SiCh and the actinide is plutonium or uranium, wherein the synthesis is preferably carried out at a temperature in the range of 20 to 850°C.

12. A method according to any one of claims 1 to 11, wherein M in salt a) is Na or Li.

13. A method according to any one of the preceding claims, wherein the salt b) is selected from sodium chloride NaCl, calcium chloride CaC'h, magnesium chloride MgCE, potassium chloride KG, lithium chloride LiCl, beryllium chloride BeCk, or a mixture of two or more of these chlorides.

14. A process according to claim 13, wherein a mixture of salt a) and salt b) is the NaQ-AlCl3 binary used for the synthesis of actinide chloride(s).

15. A process according to any one of the preceding claims, wherein the process of the present invention employs salt a) and salt b), wherein the molar ratio of salt a) to salt b) is in the range of 30:70 to 70:30, more preferably in the range of 51:49 to 69:31, more preferably in the range of 55:45 to 65:

35.

16. A method according to any one of claims 1 to 12, wherein salt b) is not used.

17. A process according to any one of the preceding claims, characterized in that the synthesis is carried out at a temperature above the melting point of salt a), or of the mixture of salts a) and b), if b) present, preferably the synthesis temperature is in the range of 20 to 850°C, more preferably in the range of 115 to 300°C, or more preferably in the range of 450 to 650°C, or more preferably in the range of 20 to 60°C.

18. A process according to claim 17, wherein the synthesis temperature is in the range of 115 to 250 °C.

19. A process according to any one of the preceding claims, further comprising a step of purifying the actinide chloride(s), said purification preferably comprising evaporation of salt a) and / or filtration of the oxide corresponding to salt a).

20. Use of an aluminium (I) salt, a silicon (II) salt and / or a beryllium (III) salt: MxlAlylXzl (I) M x2 If y2 X z2 (II) M x3 Be y3 X z3 (III) according to which: M is an alkali metal and / or an alkaline earth metal, preferably Na, K and / or Li. X is Cl, 0 < xl < 10, 1 < yl < 2, 1 < zl < 13, 0 < x2 < 10, 1 < y2 < 2, 4 < z2 < 14, 0 < x3 < 10, 1 < y3 < 2, and 2 < z3 < 12, for the synthesis of actinide chloride(s) from actinide oxide(s) in a fuel molten salt for molten salt nuclear fission reactors (MSRs).

21. The use according to claim 20, wherein the synthesis temperature is in the range of 20 to 850°C, preferably in the range of 115 to 250°C or in the range of 20 to 60°C.

22. In the use according to claim 20 or 21, aluminium (I) salt is used for the synthesis of actinide chloride(s) from actinide oxide(s) in a molten salt fuel for molten salt nuclear fission reactors (MSR).

23. In the use according to claim 20 or 21, silicon(II) salt is used for the synthesis of actinide chloride(s) from actinide oxide(s) in a molten salt fuel for molten salt nuclear fission reactors (MSRs).

24. In the use according to claim 20 or 21, the beryllium (III) salt is used for the synthesis of actinide chloride(s) from actinide oxide(s) in a molten salt fuel for molten salt nuclear fission reactors (MSRs).

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