Use of oxoacid reducing element in molten chloride salts for nuclear fission reactor (MSR)

Abstract

The present invention relates to the use of at least one oxoacid reducing element, and optionally a salt of the oxoacid reducing element, in a molten chloride fuel salt for a molten-salt nuclear fission reactor (MSR). The present invention also relates to a process of nuclear fission within a molten-salt nuclear fission reactor (MSR), said process being characterized in that it is carried out within the MSR reactor, placed in which is an oxoacid reducing element, and optionally a salt of the oxoacid reducing element. The present invention further relates to a molten-salt nuclear fission reactor (MSR) comprising a molten chloride fuel salt, and a mixture comprising the aluminum metal, and its oxidized form, as an oxoacid reducing element, and optionally a salt of the oxoacid reducing element.

Description

Title of the invention: Use of an oxoacid reducing element in molten chloride salts for a nuclear fission reactor (SFR)

[0001] The present invention relates to the use of at least one oxoacid reducing element, and optionally a salt of the oxoacid reducing element, in a molten chloride fuel salt for a molten salt nuclear fission reactor (MSNR). The present invention also relates to a nuclear fission process within a molten salt nuclear fission reactor (MSNR), said process being characterized in that it is carried out within the MSNR in which an oxoacid reducing element, and optionally a salt of the oxoacid reducing element, are placed / introduced. The oxoacid reducing element is, for example, selected from aluminum (metal), silicon (metal), and beryllium (metal), and can be used alone, in a mixture, or as an alloy.

[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-fuel reactor (SFR), 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 SFR. For example, the synthesis of actinide chlorides, including plutonium chloride (PuCl) and uranium chloride (UCL), is carried out from their corresponding oxides: plutonium oxide (PuCl) and uranium oxide (UsO₂) 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, fuel-cooled reactors (FCRs) 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 the availability of structural materials resistant to contact with molten salt, as molten fuel salt is highly corrosive.

[0005] In the 1950s-1970s, the Oak Ridge National Laboratory (ORNL) Molten Salt Reactor Experiment (MSRE) research program led to the development of the Hastelloy N alloy, a nickel-based alloy with alloying elements including molybdenum (15-17 wt. Mo), chromium (6-8 wt. Cr), iron (4-6 wt. Fe), carbon (0.04-0.08 wt. C), and alloying elements such as manganese, silicon, aluminum, and titanium. A number of other alloys have been developed, including GH3535 alloys, Nb-added alloys, Al-added alloys, and Ni-W-Cr series alloys. However, no material specifically resistant to molten chlorides / fluorides has yet been identified or optimized.

[0006] The main studies conducted in these environments have revealed the complexity of corrosion mechanisms, which involve the interaction between species dissolved in the salt and the immersed materials, as well as the interaction between the gaseous atmosphere and the molten salt. Reference can be made to the thesis of Alexandre Chmakoff, entitled "Understanding corrosion mechanisms in the environment of future reactors with molten salt fuel and coolant," Materials, Université Paris-Saclay, 2023.

[0007] The synthesis of actinide chloride salts (e.g., plutonium, uranium, and thorium) is generally initiated from the oxide forms, which are usually more stable (e.g., PuCU, UO2, UsOs, and ThCf). The metal oxide dissociates into potentially soluble metal ions and oxide ions according to the following reaction (eq. 1): M x O y -> xM +2x + yO 2 (eq.l) The O₂ oxide ion content 2-In salt, also called oxoacid, it plays an important role in the corrosion of materials. Purification of the fuel salt and the heat transfer salt from oxide ions is necessary, adding a step to the process. Furthermore, this purification prevents the precipitation of actinide oxides.

[0008] The use of toxic chlorinated gases such as CU(g) or HCl(g), as well as the synthesis of chlorine-enriched gaseous species, is described in the literature for purifying molten chloride salts. Notable examples include the articles by (1) Michelle, et al., "The Synthesis of Plutonium Trichloride by Chlorination of Plutonium Dioxide with Phosgene" (1996), (2) Snyder, C., et al., "The Chlorination of Plutonium Dioxide," United States: N.p., 1988 Web., (3) Toni Y. Karlsson, et al., "Synthesis and Thermophysical Property Determination of NaCl-PuCl3 Salts," Journal of Molecular Liquids, Volume 387. 2023 and (4) Anderson, A., Mishra, B. Investigation of the Carbochlorination Process for Conversion of Cerium and Neodymium Oxides into Their Chlorides. J. Sustain. Metall. 1, 189-198 (2015). Reference may also be made to patent application WO 83 / 01249 Al (ALUMINIUM PECHINEY).

[0009] As mentioned above, one of the recurring problems when using molten salt nuclear fission reactors (MSFRs) is the corrosion of the reactor's structural materials. Therefore, there is a real need to find ways to limit corrosion. Inventors have identified that corrosion can be limited by controlling the concentration of oxide ions in the molten salts (oxoacidity) and by maintaining a low potential (a potential lower than the oxidation potentials of the structural materials).

[0010] Thus, the present invention relates to the use of at least one oxoacid reducing agent, and optionally a salt of the oxoacid reducing agent, in a molten chloride salt for a molten salt nuclear fission reactor (MSNR) to prevent an increase in the redox potential of said molten salt and to limit the oxoacidity of said molten salt in a molten salt for a molten salt nuclear fission reactor (MSNR). The oxoacid reducing agent, and optionally the salt of the oxoacid reducing agent, are therefore used to control the oxoacidity of the molten salt and its redox potential. Controlling the oxoacidity of the molten salts allows for the purification of the molten salts and prevents the precipitation of actinide oxides.Thus, by controlling the oxoacidity of the molten salts, the oxoacid reducing element, and possibly the salt of the oxoacid reducing element, makes it possible to maintain the actinides in chloride form solubilized in the molten salts, and thus allows their implementation in the nuclear fission process.

[0011] The concept of oxoacidity is defined by Lux and Flood (Lux, H. (1939), “Sâuren” und “Basen” im Schmelzfluss: Die Bestimmung der Sauerstoffionen-Konzentration. Zeitschrift fur Elektrochemie und angewandte physikalische Chemie, 45: 303-309. https: / / doi.org / 10.1002 / bbpc.19390450405 and FLOOD H, FORLAND T. The acidic and basic properties of oxides. Acta Chem Scand. According to this concept, an oxoacid is a species capable of capturing an oxide ion (O 2 ) and an oxobase is a species capable of releasing this ion (equation (1)). Oxoacidity (pO 2) is measured according to a logarithmic scale of the oxide ion activity (equation (2)) in the same way as the pH acid-base scale with the H ion + for aqueous solutions. Oxobase Oxoacid + O 2 ~ (1) pO 2 ~ = -log (u02-) (2)

[0012] It is possible to define the redox potential range of a molten salt. The anodic and cathodic limits of the electroactivity range of a molten salt correspond to oxidation and reduction. salt. It is necessary to identify the redox couples involving the constituent species of the combustible salt and to calculate their redox potential from the Nemst equation. This potential is calculated with respect to a redox system arbitrarily chosen as a reference, whose standard potential is set at 0 V. Generally, in chloride salts, this reference is the CL / Cl couple, whose Nemst equation is given below.

[0013] From these two definitions—oxoacidity and the redox potential range of a molten salt—it is possible to construct thermodynamic stability diagrams for molten salts, as presented by Delpech et al. in "Corrosion mitigation in molten salt environments." Figure 1 shows the thermodynamic stability diagram of the combustible salt NaCl-UCl-PuCl. This diagram demonstrates a narrow stability range for the NaCl-UCl-PuCl salt. Equivalent to Pourbaix diagrams, it is possible to construct stability diagrams for structural materials (e.g., Fe, Cr, and Ni) or the behavior of fission products in the combustible salt.

[0014] This type of diagram shows that it is necessary to maintain both a low potential close to -1.9 V vs CL / Cl and an extremely low oxide ion concentration (therefore, a high -log(aNa2O)) to: i) stabilize the combustible salt by preventing the precipitation of actinide oxides, ii) protect the structural materials, and iii) stabilize certain fission products in liquid or solid form to limit the amount of gaseous fission products to be treated. Within the scope of the present invention, it has been discovered that the use of an oxoacid reducing element, and possibly a salt of an oxoacid reducing element, makes it possible to overcome the corrosion problems encountered in the prior art.

[0015] DEFINITIONS

[0016] 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 this individual element or component can be selected and combined with other individual elements, or can 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.

[0017] In the context of the present invention, the term "oxoacid reducing agent" in the expression "oxoacid reducing element" means that the element is capable of both lowering the potential of the molten salt, into which it has been introduced, and of oxidizing to limit the oxoacidity of this molten salt.

[0018] Thus, in the context of the present invention, the term "oxoacid reducing element" indicates an element which: when in metallic form is capable of donating electrons (oxidation), transforming into a metallic ion and which, in the presence of oxide ions, is converted into a metallic oxide; when in ionic form or as a salt, is converted into a metallic oxide in the presence of oxide ions.

[0019] In the context of the present invention, the oxoacid reducing element preferably comprises a metal, such as Al, Be, or Si. This type of metal, once introduced into the combustible salt, prevents an increase in the redox potential of the combustible salt (and possibly even reduces it) and, once oxidized, limits the oxoacidity of the molten salt. Indeed, the metal, in its oxidized form, precipitates with the oxide ions present in the combustible salt, thus limiting the oxide ion concentration.

[0020] In the context of the present invention, the expression "a combustible molten chloride salt" refers to the presence of a molten salt or a mixture of molten salt.

[0021] In the context of the present invention, the term "in operation" means when the nuclear fission reactor in which the molten fuel salt is located is operating / running.

[0022] DETAILED DESCRIPTION OF THE PRESENT INVENTION The present invention relates to the use of at least one oxoacid reducing element, and optionally a salt of the oxoacid reducing element, in a molten chloride fuel salt for a molten salt nuclear fission reactor (MSN) to prevent an increase in the redox potential of said molten salt and to limit the oxoacidity of said molten salt. It also relates to a nuclear fission process using, within the MSN, an oxoacid reducing element, and optionally a salt of the oxoacid reducing element. Finally, the present invention relates to a molten salt nuclear fission reactor (MSN) comprising a molten chloride fuel salt and a mixture comprising a metal, preferably aluminum, and its oxidized form as an oxoacid reducing element. and possibly a salt of the reducing oxoacid element, the salt preferably being one or more of AlCh, A12C16, KAICI4, NaAlCl, or LiAlCU.

[0023] The nuclear fission process described in the present invention involves reactions that generate oxide ions (O₂⁻) 2- in salt. Furthermore, the gaseous surface is maintained by a gas sweep that is never completely free of moisture. As previously indicated, the O₂ oxide ion content 2-The oxoacidity of salts contributes significantly to material corrosion, making purification of the molten salts typically necessary to maintain reaction efficiency and prevent premature equipment wear, as well as to inhibit the precipitation of actinide oxides. However, this purification process releases toxic chlorinated gases. The inventors have identified that using an oxoacid reducing agent during the nuclear fission process allows for the control of the oxoacidity of the molten salts, prevents the precipitation of actinide oxides, and, in particular, limits the corrosion of structural metals used in RSF equipment. All these technical benefits associated with the use of at least one oxoacid reducing agent contribute to improved reaction efficiency and nuclear reactor safety.

[0024] Examples of oxoacid reducing elements used in the context of the present invention include aluminum (Al), silicon (Si), and beryllium (Be), in their metallic form. Once introduced into the fuel salt, these elements are also present in ionic form or as salts (e.g., chlorides, fluorides, iodides, or bromides).

[0025] In the case of aluminum metal, aluminum loses electrons (either chemically or by electrolysis) to form aluminum ions (Al₂O₃). 3+ which react with the oxide ions present in the molten salt to form aluminium oxide (Al2O3). Al -> Al 3+ + 3rd

[0026] Within the framework of the present invention, the oxoacid reducing element is likely to be found in various forms as described below.

[0027] When the oxoacid reducing agent is aluminum, the salt of the oxoacid reducing agent is found in the form MxlAlylXzl (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.

[0028] Thus, the salt of the reducing element oxoacid can be, for example, A1CL, ALCL, KA1CU, NaAlCU, or LiAlCU.

[0029] When it is in salt form, particularly in chloride form, the salt of the reducing element aluminium oxoacid can be in liquid, solid or gaseous form.

[0030] According to one embodiment, the salt of the reducing element aluminium oxoacid is used in the form of gaseous chloride, for example NaAlClcg), NagAhChcg), AlCh(g) ou(AhClecg). Thus, according to this embodiment, the aluminum oxoacid reducing agent salt is injected in gaseous form into the molten salt, for example by bubbling. This differs from prior art methods that focus on bubbling with H2O, H2, and / or HF, particularly in hydroxide and fluoride salts. In the case of chloride salts, this type of gas does not allow for control of the oxoacidity.

[0031] When the oxoacid reducing element is silicon, the salt of the oxoacid reducing element is found in the form M x2 If y2 X Z 2 (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.

[0032] Thus, the salt of the oxoacid reducing element can be, for example, SiCl, KSiCl, NaSiCl, or LiSiCl.

[0033] When it is in salt form, particularly in chloride form, the salt of the reducing element silicon oxoacid can be in liquid, solid or gaseous form.

[0034] In one embodiment, the salt of the reducing element silicon oxoacid is used in gaseous chloride form, for example SiCF®. Thus, according to this embodiment, the silicon chloride salt is injected in gaseous form into the molten salt, for example by bubbling. This differs from prior art methods that focus on bubbling with FLO, FL, and / or HF, particularly in Hydroxide and fluoride salts. In the case of chloride salts, this type of gas does not allow for the control of oxoacidity.

[0035] When the oxoacid reducing element is beryllium, the salt of the oxoacid reducing element is found in the form 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.

[0036] Thus, the salt of the oxoacid reducing element can be BeCl, KBeCl3, NaBeCl3, or LiBeCl3.

[0037] When in salt form, particularly in chloride form, the salt of the reducing element beryllium oxoacid can be in liquid, solid or gaseous form.

[0038] In one embodiment, the salt of the reducing agent beryllium oxoacid is used in gaseous chloride form (e.g., BeChcg). Thus, according to this embodiment, the salt of the reducing agent is injected in gaseous form into the molten salt, for example, by bubbling. This differs from prior art methods that focus on bubbling with H3O, H2, and / or HF, particularly in hydroxide and fluoride salts. In the case of chloride salts, this type of gas does not allow for control of the oxoacidity.

[0039] In one embodiment, the oxoacid reducing element is in metallic form, for example, as a metallic component positioned in the RSF reactor in contact with the salt. When the oxoacid reducing element is in metallic form, it may, for example, and without limitation, be in the form of a rod, bar, strand, powder, filament, granule, sheet, and / or plate.

[0040] In another embodiment, the salt of the oxoacid reducing element is in chloride form and is introduced into the reactor before or during the nuclear fission reaction. The salt of the oxoacid reducing element is, for example, introduced in solid, liquid (or molten), or gaseous form.

[0041] When the oxoacid reducing element is introduced into the reactor during the nuclear fission reaction, it can be introduced discontinuously in one go or in several steps in solid form.

[0042] When the salt of the oxoacid reducing agent is introduced into the reactor during the nuclear fission reaction, it can be introduced discontinuously, either all at once or in several stages, for example, in solid or liquid (molten) form. The salt of the oxoacid reducing agent can also be introduced continuously into the RSF reactor, for example, in gaseous form, such as by bubbling through the molten salt.

[0043] In one embodiment, the salt of the oxoacid reducing element is in chloride form and is mixed with the fuel salt (molten or unmolten) before the latter is introduced into the RSF reactor. For example, aluminum chloride (AlCl₃) is added in solid or gaseous form to the molten fuel salt just before it is introduced into the RSF reactor for the nuclear fission process. In another example, the salt of the oxoacid reducing element is mixed with the fuel salt (molten or unmolten) to purify it. In this example, the salt of the oxoacid reducing element can be removed before the fuel salt is introduced into the RSF reactor, or alternatively, it can be left in place.Purification may include introducing the oxoacid reducing element in saline form to the combustible salt, waiting for the purification reaction, waiting for the natural elimination of excess unreacted aluminum, silicon or beryllium chloride, and filtering the salt to separate the precipitated oxides.

[0044] In the context of the present invention, the combustible salt is broadly defined. It may, in particular, include actinide chlorides; for example, it may be a salt comprising ThCl, AmCl, PuCl, UCl4, and / or UCl3, or a combination of these three, four, or five chlorides. The combustible salt may also include NaCl and / or AlCl chlorides, used in the synthesis of actinide chlorides. In one embodiment, the combustible salt comprises a mixture of NaCl-AlCl-UCL, NaCl-AlCl-PuCl, or NaCl-AlCl-UCL-PuCl chlorides.

[0045] In one embodiment, the salt of the oxoacid reducing element is in chloride form and is mixed with a heat transfer salt (molten or not). For example, aluminum chloride (AlCl₃) is added in solid or gaseous form to the molten heat transfer salt just before it is introduced into the RSF reactor for the nuclear fission process. In another example, the salt of the oxoacid reducing element is mixed with the heat transfer salt (molten or not) to purify it. In this example, the salt of the oxoacid reducing element can be removed before the fuel salt is introduced into the RSF reactor, or alternatively, it can be left in place. The purification process may, in particular, consist of introducing the oxoacid element in saline form into the heat transfer salt, waiting for the purification reaction, wait for the natural elimination of excess unreacted aluminum chloride, silicon or beryllium chloride and filter the salt to separate the precipitated oxides.

[0046] Also, when the salt of the oxoacid reducing element is used in solid form, it may be found mixed with other salts. For example, when the salt of the solid oxoacid reducing element is Aids, it may be used in powder form as AlCh-NaCl, AlCh-NaCl-PuCf, AlCh-NaCl-PuCh-UCh, AlCh-NaCl-UCh, AlCl3-NaCl-ThCl4, AlCh-NaCl-ThCl-UCh.

[0047] As previously indicated, these embodiments can be combined with each other. For example, within the framework of the present invention, an oxoacid reducing element in metallic form, positioned in the RSF reactor, and a salt of the same or different oxoacid reducing element, in ionic form or as a salt, for example chloride, can be used and placed in the RSF reactor before or during the nuclear fission reaction.

[0048] The oxoacid reducing element is, for example, chosen from aluminium (metal), silicon (metal) and beryllium (metal), and can be used alone, in a mixture or in the form of an alloy.

[0049] Within the framework of the present invention, the oxoacid reducing agent can be used in combination with a reducing agent that differs from the oxoacid reducing agent. The use of a reducing agent in combination with an oxoacid reducing agent also reduces the electrochemical potential of the reaction and stabilizes the oxoacid reducing agent. For example, aluminum is most stable at moderately negative potentials, around -2V, compared to Cl2 / CF.

[0050] In a preferred embodiment, this reducing element differs from the oxoacid reducing element in that it is metallic uranium. When used in combination with the oxoacid reducing element, metallic uranium can, for example, be in the form of pellets, beads, powder, filament, wire, bars, or rods. It can also be used as an alloy with the oxoacid reducing element.

[0051] According to a preferred embodiment of the present invention, the oxoacid reducing element is aluminium (metal) and / or silicon (metal) and / or beryllium (metal) and is used in combination with uranium metal.

[0052] According to a preferred embodiment of the present invention, the oxoacid reducing element is aluminium (metal) and / or silicon (metal) and / or beryllium (metal) and is used in combination with uranium metal in alloy form.

[0053] For example, an alloy of the oxoacid reducing element (e.g., metallic aluminum) and the distinct reducing element (e.g., uranium) is used. The alloy may comprise several of each of these species. The mass percentage of the distinct reducing element (for example uranium) (or of the mixture of these elements where applicable) can vary from 5 to 95% by weight, relative to the total weight of the alloy.

[0054] According to a preferred embodiment of the present invention, a binary alloy of aluminum and uranium is used. This alloy preferably comprises (or consists of): 1 to 99%, for example, 5 to 95% mol of uranium metal, and 1 to 99%, for example, 5 to 95% mol of aluminum metal, relative to the total weight of the alloy. Such a U-Al alloy has the advantage of exhibiting a melting point higher than that of aluminum metal alone and therefore better resistance to the operating temperatures of the nuclear fission process. Examples include the following alloys: ALU, ALU, and AUU.

[0055] The present invention also relates to a nuclear fission process within a molten salt nuclear fission reactor (MSFR), comprising the steps of: a) placing a molten chloride salt fuel based on fissile or fissile heavy nuclei in the core of the MSFR; b) carrying out self-sustaining nuclear fission reactions; c) circulating the hot fuel chloride salt in a primary heat exchanger so that it transfers heat to a molten salt heat transfer fluid; said process being characterized in that it is carried out within the MSFR in which an oxoacid reducing element, and optionally a salt of the oxoacid reducing element, is placed (or introduced).

[0056] The nuclear fission process of the present invention can have various objectives. These include, but are not limited to, the production of heat, the production of electricity and the transmutation of nuclear waste (including americium and plutonium in certain cases).

[0057] As described previously in the context of using an oxoacid reducing agent, and possibly a salt of the oxoacid reducing agent, to reduce the oxoacidity of the molten salt, examples of oxoacid reducing agents placed within the RSF reactor during nuclear fission are aluminum (Al), silicon (Si), and beryllium (Be). These elements are in their metallic form and may be combined with a salt of these elements, as described previously. For example, it could be aluminum in the form of Al (which will yield its ionic form Al₂O₅). 3+ ) in combination with Aids salt.

[0058] The oxoacid reducing agent can, for example, be placed (or introduced) into the RSF reactor in the fuel molten salt and / or in the coolant molten salt. It can also be placed (or introduced) into the fuel molten salt just before it is introduced into the RSF reactor for nuclear fission.

[0059] In one embodiment, the oxoacid reducing element is in metallic form, for example as a metallic part positioned in the RSF reactor, in contact with the salt. When the oxoacid reducing element is in metallic form, it may, for example, be in the form of a rod, bar, strand, powder, filament, granule, sheet, and / or plate.

[0060] According to one embodiment, the salt of the oxoacid reducing element is in the form of chloride, and is introduced into the reactor before or during the nuclear fission reaction.

[0061] According to one embodiment, the salt of the oxoacid reducing element is in the form of chloride, and is mixed with the molten fuel salt before the latter is introduced into the RSF reactor.

[0062] According to one embodiment, the salt of the oxoacid reducing element is in the form of chloride, and is mixed with the molten heat transfer salt.

[0063] The oxoacid reducing element can, for example, be chosen from aluminium (metal), silicon (metal) and beryllium (metal), and can be used alone, in mixtures or as an alloy.

[0064] The reducing element for oxoacids is preferably aluminium (metal).

[0065] The salt of the oxoacid reducing agent can be introduced into the RSF reactor or into the molten salts in solid, liquid, or gaseous form. When the salt of the oxoacid reducing agent is introduced into the process in liquid form, it is preheated to a temperature at least equal to its melting point. For example, when the salt of the oxoacid reducing agent is aluminum chloride and it is introduced into the process of the invention in liquid form, the process includes a preheating step to a temperature of at least 120°C or at least 150°C.

[0066] As described previously, the oxoacid reducing element can be used in combination with a reducing element different from the oxoacid reducing element.

[0067] In a preferred embodiment, this reducing element differs from the oxoacid reducing element in that it is metallic uranium. When used in combination with the oxoacid reducing element, metallic uranium can, for example, be in the form of pellets, beads, powder, filament, wire, bars, or rods. It can also be used as an alloy with the oxoacid reducing element.

[0068] In the process of the present invention, an alloy of the oxoacid reducing element (e.g., aluminum) and the distinct reducing element (e.g., uranium) is preferably used, which offers the advantages described above. The technical characteristics of this alloy are the same as those mentioned previously.

[0069] The present invention further relates to a molten salt nuclear fission reactor (MSFR) comprising a molten chloride fuel salt and a mixture comprising aluminum metal, and its oxidized form, as an oxoacid reducing agent, and optionally a salt of the oxoacid reducing agent, the salt of the oxoacid reducing agent preferably being selected from AlCl₂, AlCl₂, Ka₂Cl₂, NaAlCl₂, or LiAlCl₂. Preferably, the metal is aluminum, and the salt of the oxoacid reducing agent is selected from AlCl₂, AlCl₂, Ka₂Cl₂, NaAlCl₂, and LiAlCl₂.

[0070] Preferably, the RSF reactor of the present invention comprises the molten chloride fuel salt, and said mixture comprising Al (metal), Al-U (as an alloy), Al 3+ , AICI3, NaAlCk

[0071] The present invention relates to the use of at least one oxoacid reducing element, and optionally a salt of the oxoacid reducing element, in a molten chloride fuel salt for a molten salt nuclear fission reactor (MSF), whereby the oxoacid reducing element, and the optional salt of the oxoacid reducing element, stabilize the fuel salt in its chloride form during operation and prevent the precipitation of actinides in their oxide form. The oxoacid reducing element, the salt of the oxoacid reducing element, and the fuel salt are as described herein.

[0072] The present invention relates to the use of at least one oxoacid reducing element, and optionally a salt of the oxoacid reducing element, in a molten chloride fuel salt for a molten salt nuclear fission reactor (MSF). This allows for the stabilization, during operation, of the metallic shape of structural materials (such as stainless steel, Inconel®, or ceramics) and limits their corrosion. The oxoacid reducing element, the salt of the oxoacid reducing element, and the fuel salt are as described herein.

[0073] The present invention relates to the use of at least one oxoacid reducing element, and optionally also a salt of the oxoacid reducing element, in a molten chloride fuel salt for a molten salt nuclear fission reactor (MSF), enabling the stabilization, during operation, of certain fission products in their liquid or solid form and thus limiting the amount of gaseous fission products to be treated. This is illustrated in particular in FIG. 2. The oxoacid reducing element, the salt of the oxoacid reducing element, and the combustible salt are as described here.

[0074] BRIEF DESCRIPTION OF THE FIGURES

[0075] FIG. 1 is the thermodynamic stability diagram of the combustible salt NaCl-UCU-PuCl3(64 - 5 - 31% mol) at 700 °C and the thermodynamic stability diagrams of Fe, Cr, Ni in this combustible salt at 700 °C.

[0076] Figure 2 shows the thermodynamic stability diagram of iodine superimposed on the stability diagram of the NaCl-UCls-PuCE salt (represented by the shaded area) at 700°C. This diagram illustrates that by controlling the redox potential and the oxo-acidity of the molten chloride fuel salt, the iodine is found in the form of Na₂Al, soluble in the fuel salt. This limits the formation of gaseous fission products such as E(g).

[0077] ASPECTS OF THE PRESENT INVENTION

[0078] The present invention relates in particular to the following aspects: Aspect 1. Use of at least one oxoacid reducing element, and possibly in addition a fuel salt of the oxoacid reducing element, in a molten chloride fuel salt for a molten salt nuclear fission reactor (MSR) to prevent the increase in the redox potential of said molten salt and to limit the oxoacidity of said molten salt. Aspect 2. Use of at least one oxoacid reducing element, and possibly in addition a salt of the oxoacid reducing element, in a molten chloride fuel salt for a molten salt nuclear fission reactor (MSR) to prevent the precipitation of actinide chlorides to actinide oxide during the nuclear fission reaction. Aspect 3. Use of at least one oxoacid reducing element, and possibly a salt of the oxoacid reducing element, in a molten chloride fuel salt for a molten salt nuclear fission reactor (MSF) to purify the fuel salt or the heat transfer salt, for example to purify the fuel salt upstream of its introduction into the MSF reactor. Aspect 4. Use according to any one of aspects 1-3, wherein the oxoacid reducing element is in the form of a metallic part positioned in the RSF reactor, in contact with said molten chloride salt. Aspect 5. Use according to aspect 1 or 4, according to which the oxoacid reducing element, and the possible salt of the oxoacid reducing element, make it possible to stabilize, in operation, the combustible salt in chloride form and prevent the precipitation of actinides in oxide form. Aspect 6. Use according to aspect 1 or 4, in which the oxoacid reducing element e, and the possible salt of the oxoacid reducing element, allow the metallic form to be stabilized during operation structural materials (such as stainless steel, Inconel® or ceramic) and helps to limit their corrosion. Aspect 7. Use according to aspect 1 or 4, according to which the oxoacid reducing element, and the possible salt of the oxoacid reducing element, make it possible to stabilize, in operation, certain fission products in their liquid or solid form and thus to limit the quantity of gaseous fission products to be treated. Aspect 8. Use according to any one of aspects 1-7, whereby the salt of the oxoacid reducing element is a chloride salt, and is introduced into the reactor before or during the nuclear fission reaction (e.g. in solid, liquid or gaseous form). Aspect 9. Use according to any one of aspects 1-7, whereby the salt of the oxoacid reducing element is a chloride salt, and is mixed with the fuel salt (molten or not) before the latter is introduced into the RSF reactor (e.g. in solid, liquid or gaseous form). Aspect 10. Use according to any one of aspects 1-7, whereby the salt of the oxoacid reducing element is a chloride salt, and is mixed with a heat transfer salt (molten or not) (for example in solid, liquid or gaseous form). Aspect 11. Use according to any one of aspects 1-10, wherein the oxoacid reducing element is selected from aluminium metal (Al), silicon metal (Si), beryllium metal (Be), and a mixture or alloy of one or more of these, preferably the oxoacid reducing element is aluminium metal (Al). Aspect 12. Use according to aspect 11, whereby the oxoacid reducing element is aluminum metal (Al) and the salt of the oxoacid reducing element is an aluminum chloride salt. Aspect 13. Use according to any one of the preceding aspects, whereby the oxoacid reducing element is aluminum metal (Al) and the aluminum salt is a salt (I): M X Al y lX Z l (I) according to which: M is an alkali metal and / or an alkaline earth metal, preferably Na, K and / or Ui, 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. Aspect 14. Use according to any one of the preceding aspects, wherein the reducing oxoacid element is aluminium in the form of Al (aluminium metal), and the aluminium salt is AlCh, Al2Cl6, Ka1Cu, NaAlCu, or LiAlCu. Aspect 15. Use according to any one of aspects 1-10, in which the oxoacid reducing element is beryllium metal (Be) and the beryllium salt is a salt (III): 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 Ui, 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. Aspect 16. Use according to aspect 15, whereby the reducing oxoacid element is beryllium, in the form of Be, and the beryllium salt is BeCl2, KBeCh, NaBeCh, or UiBeCh. Aspect 17. Use according to any one of aspects 1-10, in which the oxoacid reducing element is silicon metal (Si) and the silicon salt is a salt (II): 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 Ui, 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. Aspect 18. Use according to any one of the preceding aspects, in which the salt of the oxoacid reducing element is added to the combustible chloride salt in liquid, solid or gaseous form. Aspect 19. Use according to any of the preceding aspects, according to which the oxoacid reducing element is used in combination with a reducing element different from the oxoacid reducing element. Aspect 20. Use according to the previous aspect, according to which the reducing element differs from the reducing element oxoacid is uranium metal. Aspect 21. Use according to aspect 19 or 20, according to which the oxoacid reducing element is aluminium metal (Al) and / or silicon metal (Si) and / or beryllium metal (Be) and is used in combination with uranium metal. Aspect 22. Use according to any one of aspects 19-21, wherein the oxoacid reducing element is aluminum metal and / or silicon metal and / or beryllium metal and is used in combination with uranium metal in alloy form. Aspect 23. A nuclear fission process within a molten salt nuclear fission reactor (MSFR), comprising the steps of: a) placing a molten chloride salt fuel based on heavy fissile nuclei in the core of the MSFR; b) carrying out self-sustaining nuclear fission reactions; c) circulating the hot fuel chloride salt in a primary heat exchanger so that it transfers heat to a molten salt heat transfer fluid; said process being characterized in that it is carried out within the MSFR in which an oxo-acid reducing element, and optionally a salt of the oxo-acid reducing element, is placed. Aspect 24. A process according to aspect 23, in which the oxoacid reducing element is in the form of a metallic part positioned in the RSF reactor, in contact with the salt. Aspect 25. A process according to aspect 23 or 24, in which the oxoacid reducing element is selected from aluminum metal, silicon metal, beryllium metal, and a mixture or alloy thereof. Aspect 26. A process according to any one of aspects 23-25, wherein the oxoacid reducing element is used in combination with a separate reducing element, preferably the oxoacid reducing element is aluminium metal (Al) and / or silicon metal (Si) and / or beryllium metal (Be). Aspect 27. A process according to aspect 26, wherein the separate reducing element is uranium metal. Aspect 28. A process according to aspect 27, wherein the oxoacid reducing element is aluminum metal and the separate reducing element is uranium metal. Aspect 29. A process according to any one of aspects 23-28, wherein the oxoacid reducing element is aluminum metal and / or silicon metal and / or beryllium metal and is used in combination with uranium metal in alloy form. Aspect 30. A process according to any one of aspects 23-29, wherein the oxoacid reducing element is in the form of an alloy with a separate reducing element, preferably an aluminium-uranium alloy. Aspect 31. A molten salt nuclear fission reactor (MSR) comprising a molten chloride fuel salt, and a mixture comprising aluminum metal, and its oxidized form, as an oxoacid reducing element, and optionally a salt of the oxoacid reducing element, the salt of the oxoacid reducing element being preferably selected from AlCl₂AlCl₂, NaAlCl₂, or LiAlCl₂. Aspect 32. The reactor according to aspect 31, in which the metal is aluminum, and the salt of the oxoacid reducing element is chosen from AlCl, AlCl₂, KaCl, NaAlCl, and LiAlCl₂. Aspect 33. The reactor according to aspect 31 or 32, comprising the molten chloride fuel salt, and said mixture comprising Al (metal), Al-U (as an alloy), Al 3+ , AICL, NaAlCL. .

Claims

DEMANDS 1. Use of at least one oxoacid reducing element, and possibly in addition of a salt of the oxoacid reducing element, in a molten chloride fuel salt for a molten salt nuclear fission reactor (MSR) to prevent the increase of the oxy-reduction potential of said molten salt and to limit the oxoacidity of said molten salt.

2. Use according to claim 1, wherein the oxoacid reducing element is in the form of a metallic piece positioned in the RSF in contact with said molten chloride salt.

3. Use according to claim 1 or 2, wherein the salt of the oxoacid reducing element is added to the combustible salt in liquid, solid or gaseous form.

4. Use according to any one of claims 1 to 3, wherein the salt of the oxoacid reducing element is a chloride salt, and is introduced into the reactor before or during the nuclear fission reaction.

5. Use according to any one of claims 1 to 3, wherein the salt of the oxoacid reducing element is a chloride salt, and is mixed with the fuel salt before the latter is introduced into the RSF reactor.

6. Use according to any one of claims 1 to 3, wherein the salt of the oxoacid reducing element is a chloride salt, and is mixed with a heat transfer salt.

7. Use according to any one of claims 1 to 6, wherein the oxoacid reducing element is selected from aluminium metal, silicon metal, beryllium metal, and a mixture or alloy thereof.

8. Use according to any one of claims 1 to 7, wherein the oxoacid reducing agent is aluminum in the form of Al (aluminum metal), and the salt of the oxoacid reducing agent is an aluminum salt selected from Aids, AFCl, KA1CU, NaAlCU, and UiAlCU 9. Use according to any one of claims 1 to 8, wherein the oxoacid reducing element is used in combination with a reducing element different from the oxoacid reducing element.

10. Use according to claim 7, wherein the oxoacid reducing element is aluminium metal (Al) and / or silicon metal (Si) and / or beryllium metal (Be) and the reducing element other than the oxoacid reducing element is uranium metal.

11. Use of at least one oxoacid reducing element, and possibly also a salt of the oxoacid reducing element, in a molten chloride fuel salt for a fission reactor molten salt nuclear reactor (MSR), according to which the oxoacid reducing element, and the optional salt of the oxoacid reducing element, make it possible to stabilize, in operation, the fuel salt in chloride form and prevent the precipitation of actinides in oxide form, preferably according to which at least one oxoacid reducing element and / or the salt of the oxoacid reducing element are as described in any one of claims 2 to 10.

12. The use of at least one oxoacid reducing element, and optionally also a salt of the oxoacid reducing element, in a molten chloride fuel salt for a molten salt nuclear fission reactor (MSF) allows the metallic shape of the structural materials to be stabilized during operation and limits their corrosion, preferably whereby the at least one oxoacid reducing element and / or the salt of the oxoacid reducing element are as described in any one of claims 2 to 10.

13. The use of at least one oxoacid reducing element, and optionally also a salt of the oxoacid reducing element, in a molten chloride fuel salt for a molten salt nuclear fission reactor (MSF), makes it possible to stabilize, during operation, certain fission products in their liquid or solid form and thus to limit the amount of gaseous fission product to be treated, preferably according to which the at least one oxoacid reducing element and / or the salt of the oxoacid reducing element are as described in any one of claims 2 to 10.

14. A nuclear fission process within a molten salt nuclear fission reactor (MSFR), comprising the steps of: a) placing a molten chloride salt fuel based on fissile heavy nuclei in the core of the MSFR; b) carrying out self-sustaining nuclear fission reactions; c) circulating the hot fuel chloride salt in a primary heat exchanger so that it transfers heat to a molten salt heat transfer fluid; said process being characterized in that it is carried out within the MSFR, into which an oxo-acid reducing element, and optionally a salt of the oxo-acid reducing element, are introduced.

15. Method according to claim 14, wherein the oxoacid reducing element is in the form of a metallic part positioned in the RSF reactor, in contact with the fuel salt, and is in the form of an alloy with a reducing element distinct from the oxoacid reducing element, preferably an aluminum-uranium alloy.

16. A molten salt nuclear fission reactor (MSF) comprising a molten chloride fuel salt, and a mixture comprising aluminum metal, and its oxidized form, as an oxoacid reducing element, and optionally a salt of the oxoacid reducing element.

17. The reactor according to claim 16, wherein the metal is aluminium, and the salt of the reducing element oxoacid is selected from AlCl AlCl, KA1Cl, NaAlC'U and Li AlCl.

18. The reactor according to claim 16 or 17, comprising the molten chloride fuel salt, and said mixture comprising Al (metal), Al-U (as an alloy), Al3+ , AICL, NaAlCL.

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