Preparation method of pressurized water reactor MOX fuel powder

Abstract

The invention relates to a pressurized water reactor MOX fuel powder preparation method, which comprises: preparing a mixed actinide eutectic melt from a mixed actinide salt and a urea solid, and carrying out deamination, denitrification / decarbonization and reduction on the mixed actinide eutectic melt to directly obtain MOX fuel powder, the mixed actinide salt is hexavalent actinide nitrate and tetravalent actinide oxalate; when the mixed actinide salt is a uranyl nitrate hexahydrate solid and a thorium oxalate hexahydrate solid, the MOX fuel powder is (UxTh1-x) O2; when the mixed actinide salt is a uranyl nitrate hexahydrate solid and a plutonium oxalate hexahydrate solid, the MOX fuel powder is (UxPu1-x) O2. According to the method provided by the invention, the raw materials are simple, the preparation process flow of the MOX fuel powder composed of UO2 and PuO2 (or ThO2) can be greatly simplified, the use of process reagents is reduced, and no process waste liquid is generated, so that the MOX fuel powder preparation method which is simple, convenient, high in production efficiency, free of waste liquid and more economical and green is provided.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear fuel preparation, and in particular relates to a method for preparing MOX fuel powder for a pressurized water reactor. Background Art

[0002] MOX fuel is one of the most popular nuclear fuel types in recent years. It is one of the key links to achieve closed cycle of nuclear fuel and sustainable development of nuclear energy. In the MOX fuel preparation process, powder preparation is a key link. The quality of powder, including composition and uniformity (impurities, isotopes), powder performance (particle size, specific surface area, bulk density, etc.) directly affects the performance of subsequent pellets. Therefore, MOX powder manufacturing has always been the focus of MOX fuel manufacturing research at home and abroad.

[0003] In order to obtain uniformly mixed MOX fuel powder, a lot of research has been carried out at home and abroad, and multiple process flows have been developed. According to the different powder mixing methods, they are mainly divided into two categories: mechanical mixing method (commonly known as dry method) and chemical co-precipitation method (commonly known as wet method). The wet method can obtain better product uniformity and form solid solution powder. The wet method includes the German uranium tricarbonate plutonium ammonium co-precipitation process

[0004] (AUPuC), Japan formed by microwave denitrification of a 1:1 mixed solution of plutonium nitrate and uranyl nitrate (U 0.5 Pu 0.5 )O2 solid solution powder. The dry method was first used for the production of fast reactor MOX fuel with a high PuO2 content. The two-step mixing method developed by France and Belgium, namely the micronized main mixing (MIMAS) process, replaced the original French one-step mixing (COCA) process and can be used for the production of LWR (light water reactor) MOX fuel with a low PuO2 content. The binderless process (SBR) developed by the United Kingdom has a better distribution uniformity of Pu than the MIMAS process. Russia relies on the ABC-150 high-efficiency magnetic mixer to prepare uniform MOX powder. The above-mentioned wet process has a long process flow and a lot of waste liquid, and it is difficult to adapt to the requirements of products with different abundances and contents; the dry grinding process is difficult to operate, has high requirements on equipment and process parameters, and inevitably has the problem of plutonium-rich particles. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a pressurized water reactor MOX fuel powder, using a low eutectic formed by uranyl nitrate hexahydrate, plutonium oxalate hexahydrate (or thorium oxalate hexahydrate) and urea to prepare a microscopic (molecular level) uniformly mixed uranyl nitrate hexahydrate (U-2O ... x Pu 1-x )O2 or (U x Th 1-x)O2, and the obtained MOX fuel powder can be used to produce MOX fuel for irradiation in LWR, FNR and other reactor types.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing MOX fuel powder for a pressurized water reactor, the method comprising the following steps:

[0007] S1. preparing a mixed actinide eutectic: mixing a dry mixed actinide salt with urea solid in a certain proportion until the mixture becomes a completely clear liquid, thereby obtaining a mixed actinide eutectic; the mixed actinide salt is a hexavalent actinide nitrate and a tetravalent actinide oxalate;

[0008] S2, deamination: the mixed actinide eutectic is heated to a specified temperature according to a specified program and kept at the temperature for a specified time to obtain a deamination powder, wherein the deamination powder is a uniform mixture of hexavalent actinide nitrate and tetravalent actinide oxalate;

[0009] S3, denitrification / decarbonization: the deammoniation powder is heated to a set temperature according to a set program and kept at the temperature for a set time to obtain a denitrification / decarbonization powder;

[0010] S4, reduction: the denitrification / decarbonization powder is heated to a certain temperature according to a certain procedure under an argon atmosphere, and then switched to a hydrogen-argon mixed gas or hydrogen atmosphere and kept warm for a certain period of time to obtain MOX fuel powder.

[0011] Furthermore, the hexavalent actinide nitrate is a solid uranyl nitrate hexahydrate, and the tetravalent actinide oxalate is a solid thorium oxalate hexahydrate or a solid plutonium oxalate hexahydrate.

[0012] Furthermore, the molar ratio of the metal ions in the mixed actinide salt to the urea is 1:9.

[0013] Furthermore, the molar ratio of uranyl nitrate hexahydrate solid to thorium oxalate hexahydrate solid in the mixed actinide salt is ≥95:5, or the molar ratio of uranyl nitrate hexahydrate solid to plutonium oxalate hexahydrate solid in the mixed actinide salt is ≥95:5.

[0014] Furthermore, in the process of mixing the mixed actinide salt and urea solid in step S1, the mixed actinide salt and urea are uniformly mixed by one or more methods of shaking the mixture, stirring the mixture, and grinding the mixture.

[0015] Furthermore, in the process of mixing the mixed actinide salt and the urea solid in step S1, the mixed actinide salt and the urea are evenly mixed by ultrasonic vibration to obtain a completely clarified mixed actinide eutectic.

[0016] Further, step S2 includes the following specific steps: sucking the mixed actinide eutectic into a crucible by a pipette, and heating the crucible to 150-160° C. according to a specified program and keeping the temperature for more than 30 minutes to obtain the deaminated powder.

[0017] Further, in step S2, the deamination process is carried out under air or argon atmosphere;

[0018] The specified procedure refers to a specified heating rate, and the specified heating rate is 5-10°C / min.

[0019] Furthermore, when the mixed actinide salt is solid uranyl nitrate hexahydrate and solid thorium oxalate hexahydrate, the denitrification / decarbonization powder is U3O8 and ThO2 powder;

[0020] When the mixed actinide salt is solid uranyl nitrate hexahydrate and solid plutonium oxalate hexahydrate, the denitrification / decarbonization powder is U3O8 and PuO2 powder.

[0021] Furthermore, in step S3, the deaminated powder is heated to 650-800° C. according to a set program and kept at this temperature for more than 30 minutes to obtain a denitrified / decarbonized powder.

[0022] Further, in step S3, the denitrification / decarbonization process is carried out under air or argon atmosphere;

[0023] The setting procedure refers to the setting heating rate, and the setting heating rate is 5-10°C / min.

[0024] Further, in step S4, the denitrified / decarbonized powder is heated to 680-900° C. at a heating rate of 5-10° C. / min under an argon atmosphere, and then switched to a hydrogen-argon mixed gas or hydrogen atmosphere and kept warm for 10-30 minutes to obtain MOX fuel powder.

[0025] Further, when the mixed actinide salt is solid uranyl nitrate hexahydrate and solid thorium oxalate hexahydrate, the MOX fuel powder is (U x Th 1-x )O2; when the mixed actinide salt is solid uranyl nitrate hexahydrate and solid plutonium oxalate hexahydrate, the MOX fuel powder is (U x Pu 1-x )O2;

[0026] Among them, 0.95≤X<1.0.

[0027] The beneficial effects of the present invention are as follows: a method for preparing a pressurized water reactor MOX fuel powder provided by the present invention is adopted, and the following steps are performed: a mixed actinide eutectic is prepared from a mixed actinide salt and a urea solid, and the mixed actinide eutectic is subjected to deamination, denitrification / decarbonization, and reduction to directly obtain MOX fuel powder; the mixed actinide salt is a hexavalent actinide nitrate and a tetravalent actinide oxalate; when the mixed actinide salt is a hexahydrated uranyl nitrate solid and a hexahydrated thorium oxalate solid, the MOX fuel powder is (U x Th 1-x )O2; when the mixed actinide salt is solid uranyl nitrate hexahydrate and solid plutonium oxalate hexahydrate, the MOX fuel powder is (U x Pu 1-x )O2. The method provided by the present invention directly uses solid uranyl nitrate and plutonium oxalate / thorium oxalate as raw materials. The advantage of simple raw materials can greatly simplify the preparation process of MOX fuel powder composed of UO2 and PuO2 (or ThO2), reduce the use of process reagents, and no process waste liquid is generated, thereby providing a simple, high-efficiency, waste-free, more economical and green MOX fuel powder preparation method. The specific beneficial effects of the present invention are mainly reflected in:

[0028] (1) A mixed actinide eutectic obtained by directly mixing three solids, namely, uranyl nitrate hexahydrate, plutonium oxalate hexahydrate (or thorium oxalate hexahydrate) and urea in a certain proportion and being liquid at room temperature is used as the mother liquor for preparing MOX fuel powder. Compared with the wet method in which two actinides are first dissolved into solutions and then co-precipitated under certain conditions, the process is simple, with fewer steps, high efficiency and no waste liquid is generated; the mixed actinide eutectic can be decomposed at a certain temperature to obtain MOX fuel powder, and only a high-temperature sintering atmosphere furnace is required, which is an existing general equipment in conventional UO2 fuel production. No other special equipment is required. Compared with the dry method, it is simple to operate and does not require additional equipment. This method can greatly simplify the process flow, effectively reduce production costs, and has better economy and safety.

[0029] (2) The mixed actinide eutectic prepared by the present invention has very stable properties and requires only one additive, urea, which is easily available, low in cost, and can be completely removed by heating to around 160°C.

[0030] (3) The MOX fuel powder prepared by the present invention has good uniformity of chemical composition and is evenly mixed at the microscopic molecular level.

[0031] (4) The preparation method of MOX fuel powder provided by the present invention can prepare MOX powder particles of various sizes and shapes as needed. For example, by using vibration dispersion method, microfluidics method, two-phase dispersion method or aerosol spray method, monodisperse MOX microspheres with a controllable particle size range of 1 μm to 1 mm and a narrow particle size distribution range can be prepared, which can be applied to TRISO fuel and other purposes as a new, economical and green MOX microsphere preparation scheme. Moreover, the preparation scheme of MOX fuel powder can also be expanded to all hexavalent actinide nitrate and tetravalent actinide oxalate systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic flow chart of a method for preparing MOX fuel powder for a pressurized water reactor according to an embodiment of the present invention;

[0033] Figure 2 It is a process flow chart comparing the method provided by this embodiment of the present invention with the dry method and the wet method for preparing MOX fuel powder;

[0034] Figure 3 This is a diagram showing the elemental surface distribution analysis results of the MOX fuel powder prepared in Example 1 of the present invention using a scanning electron microscope-energy spectrum method. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention will be further clearly and completely described below in conjunction with the drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0036] Deep eutectic solvents (DES) are generally composed of two or three components, often a mixture of metal salts and hydrogen bond donors. The components are connected to each other by hydrogen bonds and have a small lattice energy, which results in the melting point of the deep eutectic mixture being lower than the melting point of any component alone. Macroscopically, most deep eutectic mixtures are liquid at room temperature. In the article "Structure and properties of 'Type IV' lanthanide nitrate hydrate: urea eutectic solvents" published by Hammond et al. in Sustainable Chemistry & Engineering of ACS in 2019, the performance and structure of the deep eutectic mixture formed by the mixture of trivalent lanthanide metals such as cerium, protactinium and neodymium with urea were studied, and the hydrogen bonding between water and urea was confirmed. In the article "Electrochemical and thermodynamic insights on actinide type (IV) deep eutectic solvent" published in Journal of Molecular Liquids in 2021, Ruma Gupta et al. found that when uranyl nitrate hexahydrate (UNH) and urea are mixed in a certain proportion, a low eutectic will also be formed. By adjusting the ratio of uranyl nitrate hexahydrate to urea (molar ratio of 1:4), the melting point can be reduced to below 0°C, and UO2 nanocrystals are prepared by electrochemical reduction of the low eutectic.

[0037] In the previous study, the inventors found that when the molar ratio of uranyl nitrate hexahydrate to urea was 1:9, a low eutectic could also be formed, and it was stable for several months at room temperature, and its stability was better than that of the 1:4 type uranium-containing low eutectic. The 1:9 type uranium-containing low eutectic, combined with the microfluidics method or the vibration dispersion method, can be used to prepare UO2 fuel core microspheres with tristructural isotropic (TRISO) coated fuel particles for high temperature gas-cooled reactor fuel.

[0038] In the embodiment of the present invention, the inventors have found through research that a low eutectic can also be formed when the ratio of mixed actinide salts (uranyl nitrate hexahydrate + thorium oxalate hexahydrate / plutonium oxalate hexahydrate) to urea is a molar ratio of 1:9. Based on this, a method for preparing MOX fuel powder for a pressurized water reactor is provided to solve the shortcomings of the mixed oxide fuel (MOX) fuel powder preparation process, namely, the long wet process flow and the large amount of waste liquid; the dry grinding process is difficult to operate and has high requirements for equipment and process parameters. The technical concept is: after adding a small amount of co-solvent to uranyl nitrate powder and thorium oxalate (or plutonium oxalate) powder, a uniform liquid-low eutectic (DES) is obtained, and after heating, the co-solvent is removed and the oxalate and nitrate are decomposed to obtain a mixed oxide powder containing U3O8 and PuO2 (or ThO2), and can be further reduced to obtain a microscopic (at the molecular level) element composition containing (U3O8) and a uniform mixture of PuO2 (or ThO2). x Pu 1-x )O2 or (U x Th 1-x )O2 MOX fuel powder. This method is an advanced anhydrous process with simple process and easy operation, which can reduce the use of process reagents, does not produce waste liquid, simplifies the operation process, and does not require additional equipment, thereby reducing production costs and improving production efficiency. The process flow of the method provided in this embodiment and the dry method and wet method for preparing MOX fuel powder are compared as shown in the figure. Figure 2 shown.

[0039] like Figures 1-2 As shown, this embodiment provides a method for preparing a pressurized water reactor MOX fuel powder, the method comprising the following steps:

[0040] S1. preparing a mixed actinide eutectic: mixing a dry mixed actinide salt with urea solid in a certain proportion until the mixture becomes a completely clear liquid to obtain a mixed actinide eutectic;

[0041] Optionally, the mixed actinide salt includes hexavalent actinide nitrate and tetravalent actinide oxalate.

[0042] Specifically, the hexavalent actinide nitrate is a solid uranyl nitrate hexahydrate (UNH), and the tetravalent actinide oxalate is a solid thorium oxalate hexahydrate or a solid plutonium oxalate hexahydrate; that is, the mixed actinide salt is a solid uranyl nitrate hexahydrate and a solid thorium oxalate hexahydrate, or the mixed actinide salt is a solid uranyl nitrate hexahydrate and a solid plutonium oxalate hexahydrate.

[0043] Specifically, the molar ratio of the metal ions in the mixed actinide salt to the urea is 1:9.

[0044] In a specific embodiment, the molar ratio of uranyl nitrate hexahydrate solid to thorium oxalate hexahydrate solid in the mixed actinide salt is ≥95:5, or the molar ratio of uranyl nitrate hexahydrate solid to plutonium oxalate hexahydrate solid in the mixed actinide salt is ≥95:5.

[0045] Optionally, during the mixing of the mixed actinide salt and urea in step S1, the mixed actinide salt and urea are mixed uniformly by shaking and / or stirring the mixture.

[0046] In a specific embodiment, in step S1, the mixed actinide salt and urea are evenly mixed by shaking and ultrasonic vibration, so that the solid powder softens and gradually liquefies, thereby obtaining a completely clarified mixed actinide eutectic.

[0047] In another specific embodiment, when the sample amount of the mixed actinide eutectic to be prepared is large, the mixed actinide salt and urea can be uniformly mixed by grinding in a mortar accompanied by stirring.

[0048] Optionally, in step S1, the mixture formed by the mixed actinide salt and urea is heated to uniformly mix the mixed actinide salt and urea to obtain a completely clarified mixed actinide eutectic.

[0049] S2, deamination: the mixed actinide eutectic is heated to a specified temperature according to a specified program and kept at that temperature for a specified time to obtain a deamination powder;

[0050] Specifically, in step S2, the mixed actinide eutectic is sucked into a crucible by a pipette, and the crucible is heated to 150-160° C. according to a specified program and kept warm for more than 30 minutes to remove urea from the mixed actinide eutectic. The obtained deaminated powder is a uniform mixture of hexavalent actinide nitrates and tetravalent actinide oxalates.

[0051] Optionally, in step S2, the deamination process is carried out in air or argon atmosphere, and the specified procedure refers to a specified heating rate, and the specified heating rate is 5-10°C / min.

[0052] S3, denitrification / decarbonization: the deammoniation powder is heated to a set temperature according to a set program and kept at the temperature for a set time to obtain a denitrification / decarbonization powder;

[0053] Specifically, when the mixed actinide salt is a hexahydrated uranyl nitrate solid and a hexahydrated thorium oxalate solid, the denitrification / decarbonization powder is U3O8 and ThO2 powder; when the mixed actinide salt is a hexahydrated uranyl nitrate solid and a hexahydrated plutonium oxalate solid, the denitrification / decarbonization powder is U3O8 and PuO2 powder.

[0054] Specifically, in step S3, the denitrification / decarbonization process is carried out in air or argon atmosphere, the deaminated powder is heated to 650-800°C according to a set program and kept warm for more than 30 minutes, the hexavalent actinide nitrate and tetravalent actinide oxalate uniformly mixed in the deaminated powder undergo thermal decomposition, and the obtained denitrification / decarbonization powder is the corresponding actinide metal oxide U3O8 and ThO2 powder, or U3O8 and PuO2 powder.

[0055] Optionally, in step S3, following a set program refers to following a set heating rate, and the set heating rate is 5-10° C. / min.

[0056] S4, reduction: the denitrification / decarbonization powder is heated to a certain temperature according to a certain procedure under an argon atmosphere, and then switched to a hydrogen-argon mixed gas or hydrogen atmosphere and kept warm for a certain period of time to obtain MOX fuel powder.

[0057] Specifically, in step S4, the denitrification / decarbonization powder is heated to 680-900° C. at a heating rate of 5-10° C. / min under an argon atmosphere, and then switched to a hydrogen-argon mixed gas or hydrogen atmosphere and kept warm for 10-30 minutes to obtain MOX fuel powder.

[0058] Specifically, when the mixed actinide salt is solid uranyl nitrate hexahydrate and solid thorium oxalate hexahydrate, the MOX fuel powder is (U x Th 1-x )O2; when the mixed actinide salt is solid uranyl nitrate hexahydrate and solid plutonium oxalate hexahydrate, the MOX fuel powder is (U x Pu 1-x )O2; wherein, 0.95≤X<1.0.

[0059] The specific implementation modes of the present invention are further described below through examples.

[0060] Example 1: Eutectic Process (U x Th 1-x Preparation Example of O2 type (i.e., UO2 and ThO2 mixed type, where X = 0.95) MOX fuel powder

[0061] S11, preparing a mixed actinide eutectic: firstly, taking 0.0256 g (0.05 mmol) of dry thorium oxalate 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 shaking the glass bottle with the aid of ultrasonic vibration to fully mix the sample, during the mixing process, the solid powder softens and gradually liquefies, and after about 5 to 10 minutes, the mixture becomes a completely clear liquid, that is, a U (VI) / Th (IV) type mixed actinide eutectic containing 5 At% (atomic percentage) of Th (IV) is obtained;

[0062] Optionally, when the sample amount of the mixed actinide eutectic to be prepared is large, the mixture may be ground in a mortar and mixed with stirring.

[0063] S12, deamination: use a pipette to draw 20 μl of 5At% U / Th type mixed actinide eutectic into a crucible, heat the liquid to 150-160°C at a heating rate of 5-10°C / min in an air / argon atmosphere for 30 min to remove urea therein, and obtain a deamination powder of uniformly mixed hexavalent actinide nitrate and tetravalent actinide oxalate;

[0064] S13, denitrification / decarbonization: the deamination powder is heated to 650-800°C at a heating rate of 5-10°C / min in an air / argon atmosphere and kept at this temperature for more than 30 minutes, so that the hexavalent actinide nitrate and tetravalent actinide oxalate mixed evenly in the deamination powder are fully decomposed, and the denitrification / decarbonization powder obtained is U3O8 and ThO2 powder;

[0065] S14, reduction: the U3O8 and ThO2 powders are further heated to 680-900°C at a heating rate of 5-10°C / min under an argon atmosphere, and then switched to a 4% hydrogen-argon (V / V) mixed (or pure hydrogen) atmosphere for reduction for 10-15 minutes, and the obtained MOX fuel powder is a uniformly mixed UO2 and ThO2 powder.

[0066] The elemental distribution analysis results of the MOX fuel powder obtained in Example 1 by scanning electron microscope-energy spectrum method are shown in the figure below: Figure 3 shown. Figure 3 The analysis results show that UO2 and ThO2 powders are evenly distributed in the MOX fuel powder prepared in Example 1, which indicates that the chemical composition of the MOX fuel powder obtained in Example 1 is uniform and is evenly mixed at the microscopic molecular level.

[0067] The preparation method of MOX fuel powder provided in this embodiment can prepare MOX powder particles of various sizes and shapes as needed. For example, by using vibration dispersion method, microfluidics method, two-phase dispersion method or aerosol spray method, monodisperse MOX microspheres with a controllable particle size range of 1μm to 1mm and a narrow particle size distribution range can be prepared, which can be used in TRISO fuel and other purposes as a new, economical and green MOX microsphere preparation scheme. The preparation scheme of MOX fuel powder can also be expanded to all hexavalent actinide nitrate and tetravalent actinide oxalate systems.

[0068] The method described in the present invention is not limited to the specific embodiments described. The above embodiments are only examples of the present invention. The present invention can also be implemented in other specific ways or other specific forms without departing from the gist or essential features of the present invention. Therefore, the described embodiments should be regarded as illustrative rather than restrictive in any respect. The scope of the present invention should be described by the attached claims, and any changes equivalent to the intent and scope of the claims should also be included in the scope of the present invention.

Claims

1. A method for preparing MOX fuel powder for a pressurized water reactor, characterized in that: The method comprises the following steps: S1. preparing a mixed actinide eutectic: mixing a dry mixed actinide salt with urea solid in a certain proportion until the mixture becomes a completely clear liquid, thereby obtaining a mixed actinide eutectic; the mixed actinide salt is a hexavalent actinide nitrate and a tetravalent actinide oxalate; S2, deamination: the mixed actinide eutectic is heated to a specified temperature according to a specified program and kept at the temperature for a specified time to obtain a deamination powder, wherein the deamination powder is a uniform mixture of hexavalent actinide nitrate and tetravalent actinide oxalate; S3, denitrification / decarbonization: the deammoniation powder is heated to a set temperature according to a set program and kept at the temperature for a set time to obtain a denitrification / decarbonization powder; S4, reduction: the denitrification / decarbonization powder is heated to a certain temperature according to a certain procedure under an argon atmosphere, and then switched to a hydrogen-argon mixed gas or hydrogen atmosphere and kept warm for a certain period of time to obtain MOX fuel powder.

2. The method for preparing a pressurized water reactor MOX fuel powder according to claim 1, characterized in that: The hexavalent actinide nitrate is solid uranyl nitrate hexahydrate, and the tetravalent actinide oxalate is solid thorium oxalate hexahydrate or solid plutonium oxalate hexahydrate.

3. The method for preparing a pressurized water reactor MOX fuel powder according to claim 2, characterized in that: The molar ratio of the metal ions in the mixed actinide salt to the urea is 1:

9.

4. The method for preparing a pressurized water reactor MOX fuel powder according to claim 2, characterized in that: The molar ratio of uranyl nitrate hexahydrate solid to thorium oxalate hexahydrate solid in the mixed actinide salt is ≥95:5, or the molar ratio of uranyl nitrate hexahydrate solid to plutonium oxalate hexahydrate solid in the mixed actinide salt is ≥95:

5.

5. The method for preparing a pressurized water reactor MOX fuel powder according to claim 1, characterized in that: In step S1, during the mixing process of the mixed actinide salt and the urea solid, the mixed actinide salt and the urea are uniformly mixed by one or more methods of shaking the mixture, stirring the mixture, and grinding the mixture.

6. The method for preparing MOX fuel powder for a pressurized water reactor according to claim 5, characterized in that: In the process of mixing the mixed actinide salt and the urea solid in step S1, the mixed actinide salt and the urea are evenly mixed by ultrasonic vibration to obtain a completely clarified mixed actinide eutectic.

7. The method for preparing MOX fuel powder for a pressurized water reactor according to claim 1, characterized in that: Step S2 includes the following specific steps: sucking the mixed actinide eutectic into a crucible by a pipette, and heating the crucible to 150-160° C. according to a specified program and keeping the temperature for more than 30 minutes to obtain the deaminated powder.

8. The method for preparing MOX fuel powder for a pressurized water reactor according to claim 1, characterized in that: In step S2, the deamination process is carried out under air or argon atmosphere; The specified procedure refers to a specified heating rate, and the specified heating rate is 5-10°C / min.

9. The method for preparing MOX fuel powder for a pressurized water reactor according to claim 2, characterized in that: When the mixed actinide salt is a hexahydrated uranyl nitrate solid and a hexahydrated thorium oxalate solid, the denitrification / decarbonization powder is U3O8 and ThO2 powder; when the mixed actinide salt is a hexahydrated uranyl nitrate solid and a hexahydrated plutonium oxalate solid, the denitrification / decarbonization powder is U3O8 and PuO2 powder.

10. The method for preparing MOX fuel powder for a pressurized water reactor according to claim 1, characterized in that: In step S3, the deammoniation powder is heated to 650-800° C. according to a set program and kept at this temperature for more than 30 minutes to obtain a denitrification / decarbonization powder.

11. The method for preparing MOX fuel powder for a pressurized water reactor according to claim 1, characterized in that: In step S3, the denitrification / decarbonization process is carried out under air or argon atmosphere; The setting procedure refers to the setting heating rate, and the setting heating rate is 5-10°C / min.

12. The method for preparing MOX fuel powder for a pressurized water reactor according to claim 1, characterized in that: In step S4, the denitrified / decarbonized powder is heated to 680-900° C. at a heating rate of 5-10° C. / min under an argon atmosphere, and then switched to a hydrogen-argon mixed gas or hydrogen atmosphere and kept warm for 10-30 minutes to obtain MOX fuel powder.

13. The method for preparing MOX fuel powder for a pressurized water reactor according to claim 2, characterized in that: When the mixed actinide salt is solid uranyl nitrate hexahydrate and solid thorium oxalate hexahydrate, the MOX fuel powder is (U x Th 1-x )O2; when the mixed actinide salt is solid uranyl nitrate hexahydrate and solid plutonium oxalate hexahydrate, the MOX fuel powder is (U x Pu 1-x )O2; Among them, 0.95≤X<1.0.

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