Preparation method for MOX fuel powder

Abstract

Provided in the embodiments of the present application is a preparation method for an MOX fuel powder. An MOX fuel powder comprises a plurality of actinide nuclide oxides. The method comprises the following steps: S1, mixing different actinide nuclide salts with urea to form a mixed actinide eutectic system, the actinide nuclide salts being one of hexavalent actinide nitrates, tetravalent actinide nitrates, hexavalent actinide oxalates and tetravalent actinide oxalates; S2, heating the mixed actinide eutectic system obtained in step S1 to a first preset temperature for performing deamination treatment on the mixed actinide eutectic system, so as to remove the urea therein; and S3, heating the product obtained after the deamination treatment in step S2 to a second preset temperature for performing denitrification and / or decarburization treatment on the product obtained in step S2, so as to obtain a plurality of actinide nuclide oxides. Provided in the embodiments of the present application is the preparation method for an MOX fuel powder, which is simple, does not produce a waste liquid, is more economical and environmentally friendly, and can obtain a completely uniform MOX fuel powder.

Description

Preparation method of MOX fuel powder Technical Field

[0001] The embodiments of this application relate to the field of nuclear fuel preparation technology, specifically to a method for preparing MOX fuel powder. Background Technology

[0002] Mixed oxide (MOX) fuel is one of the most studied nuclear fuel types both domestically and internationally in recent years, and it is a key component in achieving a closed nuclear fuel cycle and sustainable nuclear energy development. In the MOX fuel preparation process, the quality of the powder, especially the uniformity of its macroscopic and microscopic composition and isotopic structure, directly affects the performance of subsequent fuel pellets. Therefore, obtaining uniformly mixed MOX powder has always been a key focus of MOX fuel manufacturing research.

[0003] Currently, based on the different powder mixing methods, the processes for preparing MOX powder are mainly divided into two categories: mechanical mixing (commonly known as the dry method) and chemical co-precipitation (commonly known as the wet method). The dry method was first used for the production of fast reactor MOX fuel with high PuO2 content. Researchers in France and Belgium have adopted a two-step mixing method, namely the Micronized Master Blend (MIMAS) process, which can be used for the production of light water reactor (LWR) MOX fuel with low PuO2 content. The dry process is difficult to operate and has high requirements for equipment and process parameters. The wet method can obtain better product uniformity and form a solid solution powder. Wet processes include the Ammonium Uranyl Plutonyl Carbonate (AUPuC) co-precipitation process, etc. However, the wet process has a long flow and produces a lot of waste liquid. Summary of the Invention

[0004] A brief overview of this application is provided below to offer a basic understanding of certain aspects thereof. It should be understood that this overview is not an exhaustive summary of the application. It is not intended to identify key or essential parts of the application, nor is it intended to limit its scope. Its purpose is merely to present certain concepts in a simplified form as a prelude to the more detailed description that follows.

[0005] This application provides a method for preparing MOX fuel powder, which contains a variety of actinide nuclide oxides. The method includes the following steps: S1, mixing different actinide nuclide salts with urea to form a mixed actinide eutectic, wherein the actinide nuclide salt is one of hexavalent actinide nitrate, tetravalent actinide nitrate, hexavalent actinide oxalate, and tetravalent actinide oxalate; S2, heating the mixed actinide eutectic obtained in step S1 to a first preset temperature and performing a deammoniation treatment on the mixed actinide eutectic to remove urea; S3, heating the product obtained after the deammoniation treatment in step S2 to a second preset temperature and performing denitrification and / or decarbonization treatment on the product obtained in step S2 to obtain a variety of actinide nuclide oxides.

[0006] The embodiments of this application utilize tetravalent / hexavalent actinide nitrates and tetravalent / hexavalent actinide oxalates to form a mixed actinide eutectic with urea, and then subject the mixed actinide eutectic to deammoniation, denitrification, and decarbonization treatments to obtain various MOX fuel powders. The embodiments of this application provide a novel method for preparing MOX fuel powder, capable of achieving uniform mixing of elemental composition from the macroscopic to the microscopic (molecular level).

[0007] Furthermore, the method provided by this invention uses simple raw materials, directly employing tetravalent / hexavalent actinide nitrates and tetravalent / hexavalent actinide oxalates as raw materials. This greatly simplifies the preparation process of AnO2-type MOX fuel powder, reduces the use of process reagents, and generates no process waste liquid. Thus, it provides a simple, efficient, waste-free, more economical and environmentally friendly method for preparing completely uniform MOX fuel powder. Attached Figure Description

[0008] To further illustrate the above and other advantages and features of this application, the specific embodiments of this application will be described in more detail below with reference to the accompanying drawings. The drawings, together with the following detailed description, are included in and form a part of this specification.

[0009] Figure 1 is a comparison of the preparation method provided in the embodiments of this application with the dry and wet methods for preparing MOX fuel powder;

[0010] Figure 2 shows the relationship between the melting point of the mixture of uranyl nitrate hexahydrate and urea and the molar content of urea, as well as photographs of the mixtures formed by uranyl nitrate hexahydrate and urea at different molar ratios at room temperature.

[0011] Figure 3a is a secondary electron imaging (SEI) image of the surface of the MOX fuel powder sample prepared in Example 1 of the present invention;

[0012] Figure 3b is a surface scan distribution diagram of characteristic X-rays (Mα1 series) of U element in MOX fuel powder prepared in Example 1 of the present invention;

[0013] Figure 3c is a surface scan distribution diagram of characteristic X-rays (Mα1 series) of Th element in MOX fuel powder prepared in Example 1 of the present invention;

[0014] Figure 3d is a layered image of the energy-dispersive X-ray spectroscopy (EDS) of the MOX fuel powder prepared in Example 1 of the present invention, namely, the layered images of Figures 3a to 3c.

[0015] Figure 4a is an SEI image of the surface of the MOX fuel powder prepared in Example 2 of the present invention;

[0016] Figure 4b is a surface scan distribution diagram of the characteristic X-ray (Mα1 series) of U element in the MOX fuel powder prepared in Example 2 of the present invention;

[0017] Figure 4c is a surface scan distribution diagram of characteristic X-rays (Mα1 series) of Th element in MOX fuel powder prepared in Example 2 of the present invention;

[0018] Figure 4d is an EDS layered image of the MOX fuel powder prepared in Example 2 of the present invention, namely, the layered images of Figures 4a to 4c.

[0019] Figure 5a is an SEI image of the surface of the MOX fuel powder prepared in Example 3 of the present invention;

[0020] Figure 5b is a surface scan distribution diagram of the characteristic X-ray (Mα1 series) of U element in the MOX fuel powder prepared in Example 3 of the present invention;

[0021] Figure 5c is a surface scan distribution diagram of characteristic X-rays (Mα1 series) of Th element in MOX fuel powder prepared in Example 3 of the present invention;

[0022] Figure 5d is an EDS layered image of the MOX fuel powder prepared in Example 3 of the present invention, namely, the layered images of Figures 5a to 5c. Detailed Implementation

[0023] Exemplary embodiments of this application will be described below with reference to the accompanying drawings. For clarity and brevity, not all features of actual implementations are described in the specification. However, it should be understood that many implementation-specific decisions must be made in the development of any such actual embodiment to achieve the developer's specific goals, such as complying with constraints related to the system and business, and these constraints may vary depending on the implementation. Furthermore, it should be understood that while development work can be very complex and time-consuming, such development work is merely a routine task for those skilled in the art who benefit from the content of this application.

[0024] It should also be noted that, in order to avoid obscuring this application with unnecessary details, only the equipment structure and / or processing steps closely related to the solution according to this application are shown in the accompanying drawings, while other details that are not closely related to this application are omitted.

[0025] It should be noted that, unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning as understood by a person with ordinary skills in the field to which this application pertains.

[0026] In the description of the embodiments of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0027] The embodiments of this application provide a method for preparing MOX fuel powder, wherein the MOX fuel powder contains a variety of actinide nuclide oxides.

[0028] The preparation method of the embodiments of this application includes the following steps: steps S1 to S3.

[0029] S1. Mix different actinide nuclide salts with urea to form a mixed actinide eutectic, wherein the actinide nuclide salt is one of hexavalent actinide nitrate, tetravalent actinide nitrate, hexavalent actinide oxalate, or tetravalent actinide oxalate.

[0030] S2. Heat the mixed actinide eutectic obtained in step S1 to a first preset temperature and perform ammonia removal treatment on the mixed actinide eutectic to remove urea from it.

[0031] S3. The product obtained after the deammoniation treatment in step S2 is heated to a second preset temperature, and the product obtained in step S2 is subjected to denitrification and / or decarbonization treatment to obtain a variety of actinide nuclide oxides.

[0032] The embodiments of this application utilize tetravalent / hexavalent actinide nitrates and tetravalent / hexavalent actinide oxalates to form a mixed actinide eutectic with urea, and then subject the mixed actinide eutectic to deammoniation, denitrification, and decarbonization treatments to obtain various MOX fuel powders. The embodiments of this application provide a novel method for preparing MOX fuel powder, capable of achieving uniform mixing of elemental composition from the macroscopic to the microscopic (molecular level).

[0033] The method provided by this invention uses simple raw materials, directly employing tetravalent / hexavalent actinide nitrates and tetravalent / hexavalent actinide oxalates, which can greatly simplify the preparation process of AnO2 type MOX fuel powder.

[0034] In step S1, mixing different actinide nuclide salts with urea means mixing actinide nuclide salts of at least two different nuclides with urea to ensure that the resulting mixed actinide eutectic contains at least two actinide nuclides.

[0035] Figure 1 is a comparison of the preparation method provided in the embodiments of this application with the dry and wet processes for preparing MOX fuel powder. As can be seen from Figure 1, the method provided in the embodiments of this application reduces the number of process steps compared with the original wet and dry processes. It only adds urea to form a mixed actinide eutectic, without generating any process waste liquid. Therefore, this method is a simple and easy-to-operate process that can reduce the use of process reagents, simplify the operation process, and eliminate the need for additional equipment, thereby reducing production costs and improving production efficiency.

[0036] In some embodiments, in step S1, after different actinide nuclide salts are mixed with urea, the mixed actinide nuclide salts and urea are made into a completely clear liquid, i.e., a mixed actinide eutectic, by at least one of shaking, stirring, grinding, sonicating and heating.

[0037] In some embodiments, when the sample amount of the mixed actinide eutectic to be prepared is large (e.g., the total weight of the mixed actinide eutectic is several grams to tens of grams), it can be mixed by grinding in a mortar. The grinding operation usually involves grinding while rotating the mortar with a large amplitude, which can achieve a good stirring effect.

[0038] In some embodiments, during step S1, the mixture formed by the actinide nuclide salt and urea solid can be heated to make the actinide nuclide salt and urea mix evenly, so as to obtain a completely clear mixed actinide eutectic.

[0039] In some embodiments, in step S1, the heating method is as follows: heating the mixture formed by actinide nuclide salt and urea on a hot plate for about 5 to 10 minutes at 80 to 100°C.

[0040] In some embodiments, when insoluble matter remains after heating a mixture of actinide nuclide salts and urea, a completely clear mixed actinide eutectic can be obtained by adding a small amount of deionized water to the mixture and then sonicating or shaking it. The maximum amount of deionized water added is six times the molar amount of the metal ions, and it is volatile during deammoniation.

[0041] In some embodiments, in step S2, the first preset temperature is 150–160°C. At this temperature range, urea can be removed from the mixed actinide eutectic. When a small amount of deionized water is added in step S1 to obtain a completely clear mixed actinide eutectic, step S2 can also remove the added small amount of deionized water.

[0042] In some embodiments, in step S2, the mixed actinide eutectic is heated to 150–160°C according to a specified program and held at that temperature for at least 30 minutes to obtain a deaminated powder, which includes different actinide nuclide salts. When the actinide nuclide salt includes tetravalent actinide nitrates, the deaminated powder also includes a small portion of actinide oxides formed after the thermal decomposition of tetravalent / hexavalent actinide nitrates to remove nitrate ions.

[0043] Specifically, in step S2, the mixed actinide eutectic is drawn into a crucible using a pipette or dropper, and the crucible is heated to 150-160°C and held for at least 30 minutes according to a specified procedure to remove urea from the mixed actinide eutectic. The resulting deammoniated powder includes a uniformly mixed mixture of different actinide nuclides, as well as actinide oxides formed after thermal decomposition of some tetravalent / hexavalent actinide nitrates in the different actinide nuclides to remove nitrate.

[0044] In some embodiments, the deammoniation process is carried out under an air or argon atmosphere. In some embodiments, "according to a specified procedure" means according to a specified heating rate, which may be, for example, 5 to 10 °C / min.

[0045] In some embodiments, in step S3, the second preset temperature is above 500°C. In some embodiments, in step S3, the denitrification and / or decarbonization treatment is carried out under an air or argon atmosphere.

[0046] In step S3, the deammoniation powder is heated to a second preset temperature according to a set program and held at that temperature for at least 30 minutes. In some embodiments, in step S3, "according to a set program" means according to a set heating rate, which is 5 to 10 °C / min.

[0047] In some embodiments, the hexavalent actinide nitrate is uranyl nitrate hexahydrate solid. In some embodiments, the tetravalent actinide nitrate is thorium nitrate hexahydrate solid, plutonium nitrate pentahydrate solid, or U(NO3)4·3-4H2O solid. In some embodiments, the tetravalent actinide oxalate is thorium oxalate (IV) hexahydrate solid, plutonium oxalate (IV) hexahydrate solid, or U(IV) oxalate solid. In this document, (IV) indicates that the actinide nuclide in the corresponding actinide nitrate or actinide oxalate is tetravalent.

[0048] The method provided by this invention uses simple raw materials, directly employing plutonium nitrate / thorium nitrate / U(VI) nitrate / U(IV) nitrate and plutonium(IV) oxalate / thorium(IV) oxalate / U(IV) oxalate as raw materials, which can greatly simplify the preparation of AnO2 type ((Th x Pu 1-x O2、(U x Th 1-x O2 or (U x Pu 1-x The preparation process of MOX fuel powder (such as O2).

[0049] Deep eutectic solvents (DES) typically consist of two or three components, often obtained by mixing a metal salt with a hydrogen bond donor. The components are interconnected through hydrogen bonds and possess low lattice energy, resulting in a lower melting point for the eutectic mixture compared to any single component. The lower the melting point of the eutectic mixture, the more stable it is at room temperature, which is more advantageous for preparing homogeneous MOX fuel powders.

[0050] Referring to Figure 2, Figure 2 shows the relationship between the melting point of the mixture of uranyl nitrate hexahydrate and urea and the molar content of urea, as well as photographs of mixtures formed at room temperature at different molar ratios of uranyl nitrate hexahydrate and urea. The vertical axis of Figure 2 represents the melting point of the uranyl nitrate and urea mixture, and the horizontal axis represents the molar ratio of urea in the mixture.

[0051] As can be seen from Figure 2, when the molar ratio of metal ions to urea in the uranyl nitrate and urea mixture is 1:9 and 1:4, a eutectic with a melting point below room temperature can be formed.

[0052] A eutectic with a metal ion to urea molar ratio of 1:9 can be simply referred to as a type 1-9 eutectic, and a eutectic with a metal ion to urea molar ratio of 1:4 can be simply referred to as a type 1-4 eutectic. As can be seen from Figure 2, both type 1-4 and type 1-9 eutectics are clear liquids at room temperature.

[0053] The eutectic points (temperatures) of type 1-4 and type 1-9 eutectic are above zero degrees Celsius, which makes it easy for the eutectic to be stored at room temperature.

[0054] During the implementation of this invention, the inventors discovered through research that a mixed actinide nuclide salt containing at least two different nuclides (the actinide nuclide salt can be tetravalent / hexavalent actinide nitrate or tetravalent / hexavalent actinide oxalate) and urea in a molar ratio of 1:4 or 1:9 can also form a eutectic with a melting point below room temperature.

[0055] Therefore, in some embodiments, in the mixed actinide eutectic, the molar ratio of metal ions to urea in all actinide nuclide salts is 1:4 or 1:9.

[0056] When the molar ratio of metal ions to urea in all actinide nuclide salts is 1:4 or 1:9, the mixed actinide eutectic prepared by this invention has very stable properties, requires only one additive, urea, which is readily available, low in cost, and can be completely removed by heating to around 160°C.

[0057] The inventors of this application further discovered that type 1-9 eutectic mixtures can remain stable at room temperature for several months, exhibiting superior stability compared to type 1-4 eutectic mixtures. In some embodiments, in the mixed actinide eutectic mixture, the molar ratio of metal ions to urea in all actinide nuclide salts is 1:9.

[0058] In some embodiments, in step S1, two actinide nuclides are reacted with urea to form a mixed actinide eutectic, wherein the first actinide nuclide is a tetravalent actinide nitrate and the second actinide nuclide is a tetravalent actinide oxalate. In such embodiments, the resulting mixed actinide eutectic can be referred to as a first mixed actinide eutectic.

[0059] In some embodiments, the first actinide nuclide forming the first mixed actinide eutectic is solid plutonium nitrate pentahydrate, solid thorium nitrate hexahydrate, or solid U(NO3)4·3-4H2O; the second actinide nuclide is solid thorium oxalate (IV) hexahydrate, solid plutonium oxalate (IV) hexahydrate, or solid U(IV) oxalate.

[0060] In some embodiments, the doping concentration of tetravalent actinide oxalate in the first mixed actinide eutectic formed is 9.0 At% (atomic percentage).

[0061] In step S3, denitrification and / or decarbonization are carried out in an air or argon atmosphere. The deammoniation powder is heated to 500-800℃ according to a set program and held for more than 30 minutes. The tetravalent actinide nitrates and tetravalent actinide oxalates in the deammoniation powder undergo thermal decomposition, and the resulting various actinide nuclide oxides are the corresponding AnO2 type MOX fuel powders.

[0062] In some embodiments, in the first mixed actinide eutectic formed, when the first actinide nuclide is solid plutonium nitrate pentahydrate and the second actinide nuclide is solid thorium oxalate (IV) hexahydrate, or when the first actinide nuclide is solid thorium nitrate hexahydrate and the second actinide nuclide is solid plutonium oxalate (IV) hexahydrate, the MOX fuel powder is (Th x Pu 1-x O2 type powder.

[0063] In the first mixed actinide eutectic formed, when the first actinide nuclide and the second actinide nuclide are solid plutonium nitrate pentahydrate and solid thorium oxalate (IV) hexahydrate, respectively, 0.0 < X ​​≤ 0.1; when the different actinide nuclides are solid thorium nitrate hexahydrate and solid plutonium oxalate (IV) hexahydrate, 0.9 ≤ X < 1.0.

[0064] In the first mixed actinide eutectic formed, when the first actinide nuclide is U(NO3)4·3-4H2O solid and the second actinide nuclide is thorium oxalate(IV) hexahydrate solid, or the first actinide nuclide is thorium nitrate hexahydrate solid and the second actinide nuclide is oxalate U(IV) solid, the MOX fuel powder is (U x Th 1-x O2 powder.

[0065] In the first mixed actinide eutectic formed, when the first actinide nuclide and the second actinide nuclide are solid U(NO3)4·3-4H2O and solid thorium oxalate(IV) hexahydrate, respectively, 0.9 ≤ X < 1.0; when the first actinide nuclide and the second actinide nuclide are solid thorium nitrate hexahydrate and solid U(IV) oxalate, respectively, 0.0 < X ​​≤ 0.1.

[0066] When the first mixed actinide eutectic is formed, and the first actinide nuclide is solid U(NO3)4·3-4H2O and the second actinide nuclide is solid plutonium oxalate(IV) hexahydrate, or the first actinide nuclide is solid plutonium nitrate pentahydrate and the second actinide nuclide is solid U(IV) oxalate, the MOX fuel powder is (U x Pu 1-x O2 powder.

[0067] In the first mixed actinide eutectic formed, when the first actinide nuclide and the second actinide nuclide are solid U(NO3)4·3-4H2O and solid plutonium oxalate (IV) hexahydrate, respectively, 0.9 ≤ X < 1.0; in the first mixed actinide eutectic formed, when the first actinide nuclide and the second actinide nuclide are solid plutonium nitrate pentahydrate and solid U(IV) oxalate, respectively, 0.0 < X ​​≤ 0.1.

[0068] In some embodiments, the specific steps for preparing the first mixed actinide eutectic are as follows: First, take 0.6180 g (0.990 mmol) of dry thorium nitrate hexahydrate solid, 0.0492 g (0.096 mmol) of thorium oxalate (IV) hexahydrate solid, and 0.6218 g (10.353 mmol) of urea solid in a transparent glass bottle. During the mixing process, the solid powder softens and gradually liquefies. Gently shake the glass bottle to ensure the sample is thoroughly mixed. Heat the mixture on a hot plate at 80–100 °C for about 5–10 minutes. The mixture still contains a small amount of insoluble particles. 60 μL of deionized water is added and the mixture is sonicated for 5 min. The mixture becomes a completely clear liquid, thus obtaining an An(IV) type nitrate-oxalate mixed actinide eutectic with an incorporation amount of 8.84 At%. For MOX fuels that need to be prepared (e.g., MOX fuels with ThO2 mixed with a small amount of PuO2), the method provided in this embodiment is applicable to the preparation of eutectic precipitates from mixed actinide salt raw materials containing a small amount of tetravalent actinide oxalate (10% or less) in all tetravalent actinide nitrates.

[0069] The embodiments of this application use a first mixed actinide eutectic, which is liquid at room temperature, obtained by directly mixing three solids—plutonium nitrate pentahydrate (or thorium nitrate hexahydrate), thorium oxalate (IV) hexahydrate (or plutonium oxalate (IV)) and urea—in a certain proportion as the mother liquor for preparing MOX fuel powder. Compared to the wet process, which involves dissolving the two actinide salts separately into solutions and then co-precipitating them under certain conditions, this method is simpler, has fewer steps, is more efficient, and does not generate any waste liquid. MOX fuel powder can be obtained by decomposing the first mixed actinide eutectic at a certain temperature, requiring only a high-temperature sintering atmosphere furnace and no additional specialized equipment. Compared to the dry method, this method is simpler to operate and does not require additional equipment. This method greatly simplifies the process flow, effectively reduces production costs, and has better economic efficiency and safety.

[0070] In some embodiments, when the various actinide nuclides obtained in step S3 include hexavalent actinide nuclides, the preparation method further includes: S4, heating the various actinide nuclides obtained in step S3 to a third preset temperature, and performing a reduction treatment on the various actinide nuclides to reduce the hexavalent actinide nuclides to tetravalent actinide nuclides.

[0071] In some embodiments, the reduction process can be carried out in a pure hydrogen atmosphere or in a mixed atmosphere of hydrogen and inert gas. The third preset temperature for the reduction process can be above 680°C. In some embodiments, the third preset temperature is between 680°C and 900°C.

[0072] In some embodiments, during the reduction process, the various actinide nuclides obtained in step S3 are heated to 680–900°C under an argon atmosphere according to a certain program, and then switched to a hydrogen-argon mixture or a hydrogen atmosphere and held at that temperature for 10–30 min to obtain MOX fuel powder.

[0073] In step S4, "following the set program" means following the set heating rate, which is 5-10℃ / min.

[0074] In some embodiments, two actinide nuclides are reacted with urea to form a mixed actinide eutectic, wherein the first actinide nuclide is a hexavalent actinide nitrate and the second actinide nuclide is a tetravalent actinide nitrate. In such embodiments, the resulting mixed actinide eutectic can be referred to as a second mixed actinide eutectic.

[0075] In some embodiments, the first actinide nuclide forming the second mixed actinide eutectic is uranyl nitrate hexahydrate solid; the second actinide nuclide is thorium nitrate hexahydrate solid or plutonium nitrate pentahydrate solid.

[0076] In some embodiments, the molar ratio of uranyl nitrate hexahydrate solid to thorium nitrate hexahydrate solid in the formed second mixed actinide eutectic is arbitrary. In some embodiments, the molar ratio of uranyl nitrate hexahydrate solid to plutonium nitrate pentahydrate solid in the formed second mixed actinide eutectic is arbitrary.

[0077] In one specific embodiment, the molar ratio of uranyl nitrate hexahydrate solid to thorium nitrate hexahydrate solid in the formed second mixed actinide eutectic is 1:1. In another specific embodiment, the molar ratio of uranyl nitrate hexahydrate solid to plutonium nitrate pentahydrate solid in the formed second mixed actinide eutectic is 1:1.

[0078] In the second mixed actinide eutectic formed, when the first actinide nuclide and the second actinide nuclide are uranyl nitrate hexahydrate solid and thorium nitrate hexahydrate solid, respectively, the denitrification powder is U3O8 and ThO2 powder; when the first actinide nuclide and the second actinide nuclide are uranyl nitrate hexahydrate solid and plutonium nitrate pentahydrate solid, respectively, the denitrification powder is U3O8 and PuO2 powder.

[0079] In some embodiments, in step S3, the denitrification process is carried out in an air or argon atmosphere. The denitrification powder is heated to 500-800°C according to a set program and held at that temperature for more than 30 minutes. The mixed actinide nitrates in the denitrification powder undergo thermal decomposition, and the resulting denitrification powder is the corresponding actinide metal oxide U3O8 and ThO2 powder, or U3O8 and PuO2 powder.

[0080] In the second mixed actinide eutectic formed, when the first actinide nuclide and the second actinide nuclide are uranyl nitrate hexahydrate solid and thorium nitrate hexahydrate solid, respectively, the MOX fuel powder is (U x T h1-x O2; When different actinide nuclides are uranyl nitrate hexahydrate solid and plutonium nitrate pentahydrate solid, the MOX fuel powder is (U x Pu 1-x O2; where 0.0 < X ​​< 1.0.

[0081] In some embodiments, two actinide nuclides are reacted with urea to form a mixed actinide eutectic, wherein the first actinide nuclide is a hexavalent actinide nitrate and the second actinide nuclide is a tetravalent actinide oxalate. In such embodiments, the resulting mixed actinide eutectic can be referred to as a third mixed actinide eutectic.

[0082] In some embodiments, the first actinide nuclide forming the third mixed actinide eutectic is uranyl nitrate hexahydrate solid; the second actinide nuclide is thorium oxalate (IV) hexahydrate solid or plutonium oxalate (IV) hexahydrate solid.

[0083] In some embodiments, in the third mixed actinide eutectic formed, the molar ratio of the first actinide nuclide to the second actinide nuclide is ≥95:5.

[0084] In one specific embodiment, the molar ratio of uranyl nitrate hexahydrate solid to thorium oxalate (IV) hexahydrate solid in the formed third mixed actinide eutectic is ≥95:5.

[0085] In the third mixed actinide eutectic formed, when the first actinide nuclide and the second actinide nuclide are uranyl nitrate hexahydrate solid and thorium oxalate (IV) hexahydrate solid, respectively, the denitrification / decarburization powder is U3O8 and ThO2 powder; when the first actinide nuclide and the second actinide nuclide are uranyl nitrate hexahydrate solid and plutonium oxalate (IV) hexahydrate solid, respectively, the denitrification / decarburization powder is U3O8 and PuO2 powder.

[0086] In some embodiments, in step S3, the denitrification / decarbonization process is carried out in an air or argon atmosphere. The deammoniation powder is heated to 650-800°C according to a set program and held at that temperature for more than 30 minutes. The hexavalent actinide nitrate and tetravalent actinide oxalate mixed evenly in the deammoniation powder undergo thermal decomposition, and the resulting denitrification / decarbonization powder is the corresponding actinide metal oxide U3O8 and ThO2 powder, or U3O8 and PuO2 powder.

[0087] In the third mixed actinide eutectic formed, when the first actinide nuclide and the second actinide nuclide are uranyl nitrate hexahydrate solid and thorium oxalate (IV) hexahydrate solid, respectively, the MOX fuel powder is (U x T h1-x O2; When different actinide nuclides are uranyl nitrate hexahydrate solid and plutonium oxalate (IV) hexahydrate solid, the MOX fuel powder is (U x Pu 1-x O2; where 0.95≤X<1.0.

[0088] The MOX fuel powder preparation method provided in this embodiment can prepare MOX powder particles of various sizes and shapes as needed. For example, by combining methods such as vibration dispersion, microfluidic dispersion, two-phase dispersion, or aerosol spraying, monodisperse MOX microspheres with a controllable particle size range of 1 μm to 1 mm and a narrow particle size distribution can be prepared. These microspheres can be used in TRISO fuel and other applications, serving as a novel, economical, and green MOX microsphere preparation method. This MOX fuel powder preparation method can also be extended to all hexavalent / tetravalent actinide nitrate and tetravalent actinide oxalate systems.

[0089] The preparation method of the present invention will be further described below through specific embodiments.

[0090] Example 1

[0091] S1. Preparation of the first mixed actinide eutectic: In an oxygen-free glove box, first take 0.5009 g (0.90-0.93 mmol) of dry U(NO3)4·3-4H2O solid, 0.0526 g (0.10 mmol) of thorium oxalate (IV) hexahydrate solid and 0.5587 g (9.30 mmol) of urea solid into a transparent glass bottle. During the mixing process, the solid powder softens and gradually liquefies. Gently shake the glass bottle to mix the sample thoroughly. After heating at 80-100°C on a hot plate for about 5-10 minutes, the mixture becomes a completely clear liquid, thus obtaining a nitrate-oxalate mixed actinide eutectic with an incorporation amount of 9.97-10.3 At%.

[0092] S2. Deamination: Using a pipette, 20 μL of the nitrate-oxalate mixed actinide eutectic is placed in a crucible. The nitrate-oxalate mixed actinide eutectic is heated to 150-160°C at a heating rate of 5-10°C / min under an argon atmosphere and held for 30 min to remove urea. Part of the nitrate in the actinide nitrate is also removed. The resulting deamination powder is a powder of different actinide nuclide salts and some actinide oxides.

[0093] S3. Denitrification / Decarbonization: The above-mentioned deamination powder is heated to 500-800℃ under an argon atmosphere at a heating rate of 5-10℃ / min and held at this temperature for at least 30 minutes to fully decompose the actinide nitrates and actinide oxalates in the different actinide nuclide salts in the deamination powder. The resulting denitrification / decarbonization powder is (U 0.9 Th 0.1 O2 type powder.

[0094] The elemental surface distribution of the MOX fuel powder obtained in Example 1 was analyzed using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and the results are shown in Figures 3a to 3d. Figures 3a to 3d show that the UO2 and ThO2 powder particles in the AnO2-type MOX fuel powder prepared in Example 1 are uniformly distributed. This indicates that the AnO2-type MOX fuel powder obtained in Example 1 has good chemical composition uniformity and is uniformly mixed at the microscopic molecular level.

[0095] Example 2

[0096] S1. Preparation of the second mixed actinide eutectic: First, take 0.312 g (0.5 mmol) of dry thorium nitrate hexahydrate solid, 0.251 g (0.5 mmol) of uranyl nitrate hexahydrate solid and 0.5405 g (9 mmol) of urea solid in a transparent glass bottle. During the mixing process, the solid powder softens and gradually liquefies. Gently shake the glass bottle to mix the sample thoroughly. After heating at 80-100°C on a hot plate for about 5-10 minutes, the mixture becomes a completely clear liquid, thus obtaining a U(VI) / Th(IV) type mixed actinide eutectic with a Th(IV) content of 50 At%.

[0097] S2. Deamination: Use a pipette to take 20 μL of U / Th type mixed actinide eutectic into a crucible. Heat the U / Th type mixed actinide eutectic to 150-160℃ at a heating rate of 10℃ / min under an air / argon atmosphere and hold for 30 min to remove urea. Part of the actinide nitrates are also deamination. The deamination powder obtained is a powder of different actinide nuclide salts and some actinide oxides.

[0098] S3. Denitrification / Decarbonization: The above deammoniation powder is heated to 500-800℃ at a heating rate of 10℃ / min under an air / argon atmosphere and held for more than 30min to fully decompose the nitrate ions of different actinide nuclide salts in the deammoniation powder. The resulting denitrification powder is U3O8 and ThO2 powder.

[0099] S4. Reduction: Under an argon atmosphere, the U3O8 and ThO2 powders are heated to 680–900°C at a rate of 10°C / min. Then, the temperature is switched to a 4% hydrogen-argon (V / V) mixed atmosphere (or pure hydrogen) for reduction for 10–15 min. The resulting MOX fuel powder is (U 0.5 Th 0.5 O2 type powder.

[0100] The elemental distribution of the MOX fuel powder obtained in Example 2 was analyzed using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and the results are shown in Figures 4a to 4d. Figures 4a to 4d show that UO2 and ThO2 powders are uniformly distributed in the MOX fuel powder prepared in Example 2, indicating that the MOX fuel powder obtained in Example 2 has good chemical composition uniformity and is uniformly mixed at the microscopic molecular level.

[0101] Example 3

[0102] S1. Preparation of the third mixed actinide eutectic: First, take 0.0256 g (0.05 mmol) of dry thorium oxalate (IV) hexahydrate solid, 0.477 g (0.95 mmol) of uranyl nitrate hexahydrate solid and 0.5405 g (9 mmol) of urea solid in a transparent glass bottle. Gently shake the glass bottle and use ultrasonic vibration to mix the sample thoroughly. During the mixing process, the solid powder softens and gradually liquefies. After about 5 to 10 minutes, the mixture becomes a completely clear liquid, thus obtaining a U(VI) / Th(IV) type mixed actinide eutectic with a Th(IV) content of 5 At%.

[0103] S2. Deamination: Use a pipette to take 20 μL of U / Th type mixed actinide eutectic into a crucible. Heat the U / Th type mixed actinide eutectic to 150-160°C at a heating rate of 5-10°C / min under an air / argon atmosphere and hold for 30 min to remove urea. The deamination powder obtained is a uniformly mixed hexavalent actinide nitrate and tetravalent actinide oxalate.

[0104] S3. Denitrification / Decarbonization: The above-mentioned deamination powder is heated to 650-800℃ under an air / argon atmosphere at a heating rate of 5-10℃ / min and held for more than 30 minutes to fully decompose the hexavalent actinide nitrate and tetravalent actinide oxalate mixed evenly in the deamination powder. The resulting denitrification / decarbonization powder is U3O8 and ThO2 powder.

[0105] S4. Reduction: Under an argon atmosphere, the U3O8 and ThO2 powders are heated to 680–900°C at a rate of 5–10°C / min. Then, the temperature is switched to a 4% hydrogen-argon (V / V) mixed atmosphere (or pure hydrogen) for reduction for 10–15 min. The resulting MOX fuel powder is (U…0.95 Th 0.05 O2 type powder.

[0106] The elemental distribution of the MOX fuel powder obtained in Example 3 was analyzed using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and the results are shown in Figures 5a to 5d. Figures 5a to 5d show that UO2 and ThO2 powders are uniformly distributed in the MOX fuel powder prepared in Example 3, indicating that the MOX fuel powder obtained in Example 3 has good chemical composition uniformity and is uniformly mixed at the microscopic molecular level.

[0107] Therefore, the embodiments of this application utilize tetravalent / hexavalent actinide nitrates and tetravalent / hexavalent actinide oxalates to form a mixed actinide eutectic with urea. The mixed actinide eutectic is then subjected to deammoniation, denitrification, and decarbonization treatments to obtain a uniformly mixed MOX fuel powder with a microscopic (molecular level) elemental composition. Furthermore, the method provided by this invention uses simple raw materials, directly employing plutonium nitrate / thorium nitrate / U(VI) nitrate / U(IV) nitrate and plutonium(IV) oxalate / thorium(IV) oxalate / U(IV) oxalate, which greatly simplifies the preparation of AnO2((Th x Pu 1-x O2、(U x Th 1-x O2 or (U x Pu 1-x This paper describes a process flow for preparing MOX fuel powder of the O2 type, which reduces the use of process reagents and generates no process waste liquid. This provides a simple, efficient, waste-free, more economical and green method for preparing completely uniform MOX fuel powder.

[0108] Regarding the embodiments of this application, it should also be noted that, without conflict, the embodiments of this application and the features in the embodiments can be combined with each other to obtain new embodiments.

[0109] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. The scope of protection of this application shall be determined by the scope of the claims.

Claims

1. A method for preparing MOX fuel powder, wherein the MOX fuel powder comprises a variety of actinide nuclide oxides, characterized in that, The method includes the following steps: S1. Mix different actinide nuclide salts with urea to form a mixed actinide eutectic, wherein the actinide nuclide salt is one of hexavalent actinide nitrate, tetravalent actinide nitrate, hexavalent actinide oxalate, and tetravalent actinide oxalate; S2. The mixed actinide eutectic obtained in step S1 is heated to a first preset temperature, and the mixed actinide eutectic is subjected to ammonia removal treatment to remove urea therein. S3. The product obtained after the deammoniation treatment in step S2 is heated to a second preset temperature, and the product obtained in step S2 is subjected to denitrification and / or decarbonization treatment to obtain a variety of actinide nuclide oxides.

2. The preparation method according to claim 1, characterized in that, When the various actinide oxides obtained in step S3 include hexavalent actinide oxides, the preparation method further includes: S4. The various actinide nuclides obtained in step S3 are heated to a third preset temperature to reduce the various actinide nuclides to reduce the hexavalent actinide nuclides to tetravalent actinide nuclides.

3. The preparation method according to claim 1, characterized in that, The hexavalent actinide nitrate is uranyl nitrate hexahydrate solid; The tetravalent actinide nitrate is thorium nitrate hexahydrate solid, plutonium nitrate pentahydrate solid, or U(NO3)4·3-4H2O solid; The tetravalent actinide oxalate is thorium oxalate hexahydrate (IV) solid, plutonium oxalate hexahydrate (IV) solid, or oxalate U (IV) solid.

4. The preparation method according to claim 1, characterized in that, In the mixed actinide eutectic, the molar ratio of metal ions in all actinide nuclide salts to urea is 1:4 or 1:

9.

5. The preparation method according to claim 1, characterized in that, In step S1, different actinide nuclide salts are mixed with urea, and then the mixed actinide nuclide salts and urea are mixed by at least one of the following methods: shaking, stirring, grinding, sonication, and heating, so that the mixed actinide nuclide salts and urea form a completely clear liquid.

6. The preparation method according to claim 1, characterized in that, In step S2, the first preset temperature is 150-160°C.

7. The preparation method according to claim 1, characterized in that, In step S3, the second preset temperature is above 500°C.

8. The preparation method according to claim 1, characterized in that, In step S1, two actinide nuclides are reacted with urea to form the mixed actinide eutectic, wherein the first actinide nuclide is a hexavalent actinide nitrate and the second actinide nuclide is a tetravalent actinide oxalate.

9. The preparation method according to claim 8, characterized in that, The first actinide nuclide is uranyl nitrate hexahydrate solid; the second actinide nuclide is thorium oxalate (IV) hexahydrate solid or plutonium oxalate (IV) hexahydrate solid.

10. The preparation method according to claim 9, characterized in that, The molar ratio of the first actinide nuclide to the second actinide nuclide is ≥95:

5.

11. The preparation method according to claim 1, characterized in that, In step S1, two actinide nuclides are reacted with urea to form the mixed actinide eutectic, wherein the first actinide nuclide is a hexavalent actinide nitrate and the second actinide nuclide is a tetravalent actinide nitrate.

12. The preparation method according to claim 11, characterized in that, The first actinide nuclide is uranyl nitrate hexahydrate solid; the second actinide nuclide is thorium nitrate hexahydrate solid or plutonium nitrate pentahydrate solid.

13. The preparation method according to claim 1, characterized in that, In step S1, two actinide nuclides are reacted with urea to form the mixed actinide eutectic, wherein the first actinide nuclide is a tetravalent actinide nitrate and the second actinide nuclide is a tetravalent actinide oxalate.

14. The preparation method according to claim 13, characterized in that, The first actinide nuclide is solid plutonium nitrate pentahydrate, solid thorium nitrate hexahydrate, or solid U(NO3)4·3-4H2O; the second actinide nuclide is solid thorium oxalate (IV) hexahydrate, solid plutonium oxalate (IV) hexahydrate, or solid U(IV) oxalate.

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