A process for extracting plutonium-238 from an irradiated neptunium target and recovering neptunium-237

Abstract

This invention relates to a process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target, comprising the following steps: First, using a first fluorination gas, the oxides of neptunium in the irradiated neptunium target core are converted into neptunium hexafluoride and the oxides of plutonium are converted into plutonium tetrafluoride, thus achieving neptunium extraction; the first fluorination gas carrying neptunium hexafluoride is passed into a cold trap for collection and purification to obtain the neptunium product; then, using a second fluorination gas, plutonium tetrafluoride is further converted into plutonium hexafluoride gas, thus achieving plutonium extraction; the next step... Plutonium hexafluoride carried by difluoride gas is collected and purified in a cold trap to obtain plutonium products; finally, the fission products are processed and disposed of; the reaction characteristics of two different fluoride gases with neptunium and plutonium can be utilized to fundamentally change the existing process of extracting plutonium-238 and recovering neptunium-237 from irradiated neptunium targets through fluorination volatilization; it can simplify the process, reduce the scale of equipment, eliminate the use of organic reagents, reduce the amount of radioactive waste, solve the problem of severe radiolysis, and improve the separation effect of neptunium and plutonium.

Description

Technical Field

[0001] This invention belongs to the field of nuclear fuel reprocessing technology, specifically relating to a process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target. Background Technology

[0002] Heat sources and isotope batteries made from plutonium-238 possess advantages such as high power density, long half-life, low toxicity, few harmful impurities (no high-energy neutrons or high-energy gamma rays produced), simple protection, and lightweight shielding. Therefore, heat sources and isotope batteries made from plutonium have wide applications in many harsh environments, such as aerospace and extremely cold regions. However… 238 Pu does not exist in nature and can only be artificially produced through reactor irradiation. 238 Pu. A common method is to recover from spent fuel reprocessing. 237 Np, after recycling 237 After Np is used to make a neptunium-237 target (aluminum and magnesium matrix), it is irradiated in the reactor. The irradiated neptunium target undergoes a series of chemical processes to extract plutonium-238 and recover neptunium-237.

[0003] Existing processes for extracting plutonium-238 and recovering neptunium-237 are scarce, including Chinese patent CN111020244A, which discloses "a method for extracting and separating plutonium-238 and recovering neptunium-237 from an irradiated neptunium target." This method uses solvent extraction to separate neptunium from plutonium and extract plutonium-238 via an aqueous process. However, this process uses large amounts of organic solvents, resulting in large equipment scale, large volumes of waste liquid (especially organic waste liquid), and complex process flow. Furthermore, due to the strong alpha radioactivity of plutonium-238, it severely decomposes organic reagents under irradiation, reducing reagent lifespan and affecting the purification of neptunium-plutonium products. The inorganic treatment of the waste organic phase is also a challenge in post-processing. In addition, the aqueous process uses large amounts of salt-containing reagents, such as metavanadate, silver nitrate, and mercuric nitrate, significantly increasing the amount of radioactive waste.

[0004] Fluorination volatilization is one of the reprocessing methods for spent fuel, especially in molten salt reactors. As early as the 1960s, the United States completed the validation of fluorination volatilization separation for irradiated fuel. Russia established a fluorination volatilization process for spent fuel from the BOR-60 reactor. In recent years, the Czech Republic and Japan have developed fluorination volatilization separation technology, proposing the FLUOREX process, a combination of dry and wet methods. The fluorinating gases used in these processes are mainly F2 and HF. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target. This method fundamentally changes the existing process of extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target through fluorination volatilization. It simplifies the process, reduces equipment size, eliminates the use of organic reagents, and reduces the amount of radioactive waste, while simultaneously solving the problem of severe radiolysis during plutonium-238 extraction. Furthermore, it addresses a series of problems associated with organic reagent processing, reduces the use of salt-containing reagents, and thus lowers the amount of radioactive solid waste.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target, the method comprising the following steps:

[0007] S1. Extraction of Neptunium: The irradiated neptunium target core is placed in a reactor, and a first fluorination gas is introduced into the reactor. The irradiated neptunium target core is fluorinated at a first set temperature, converting the neptunium oxide in the irradiated neptunium target core into neptunium hexafluoride and the plutonium oxide into plutonium tetrafluoride. The first fluorination gas carries the neptunium hexafluoride into step S2 for neptunium product collection and purification. Plutonium remains in the reactor in the form of plutonium tetrafluoride, ready to be extracted in step S3.

[0008] S2. Collection and purification of neptunium product: The neptunium hexafluoride carried by the first fluorinated gas is passed into a cold trap for collection and purification to obtain neptunium product;

[0009] S3. Extracting plutonium: A second fluorination gas is introduced into the reactor, and the irradiated neptunium target core is fluorinated at a second set temperature to further convert plutonium tetrafluoride into plutonium hexafluoride gas. The second fluorination gas carries plutonium hexafluoride into step S4 for plutonium product collection and purification.

[0010] S4: Collection and purification of plutonium products: Plutonium hexafluoride carried by the second fluorinated gas is passed into a cold trap for collection and purification to obtain plutonium products;

[0011] S5. Handling and disposing of fission products.

[0012] Furthermore, the first fluorinated gas is a mixture of nitrogen trifluoride and an inert gas, wherein the inert gas is selected from one or two of N2 and Ar.

[0013] Furthermore, the volume percentage of nitrogen trifluoride in the first fluorinated gas is not less than 5%.

[0014] Furthermore, the first set temperature is 450℃~700℃.

[0015] Furthermore, step S2 also includes the following step: transforming the neptunium product by using hot water hydrolysis reduction to convert the neptunium product into neptunium dioxide.

[0016] Furthermore, the second fluorinated gas is a mixture of a fluorinated functional gas and an inert gas;

[0017] The inert gas is selected from one or both of N2 and Ar;

[0018] The fluorinated functional gas includes one or more of F2, HF, O2F2, etc.

[0019] Furthermore, in the second fluorinated gas, the volume percentage content of the fluorinated functional gas is not less than 50%.

[0020] Furthermore, the second set temperature is above 300°C.

[0021] Furthermore, step S4 also includes the following step: transforming the plutonium product by using hot water hydrolysis reduction to convert the plutonium product into plutonium dioxide.

[0022] Furthermore, the temperature of the hot water hydrolysis reduction is higher than 600°C.

[0023] The beneficial effect of this invention lies in the following: the process method provided by this invention for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target includes the following steps: First, neptunium oxide in the irradiated neptunium target core is converted into neptunium hexafluoride and plutonium oxide is converted into plutonium tetrafluoride using a first fluorination gas, thus achieving neptunium extraction; the first fluorination gas carrying neptunium hexafluoride is passed into a cold trap for collection and purification to obtain the neptunium product; then, the tetrafluoride is purified using a second fluorination gas. Plutonium is further converted into plutonium hexafluoride gas, achieving plutonium extraction; the plutonium hexafluoride carried by the second fluorinated gas is passed into a cold trap for collection and purification, yielding the plutonium product; finally, the fission products are processed and disposed of. This method utilizes the reaction characteristics of two different fluorinated gases with neptunium-plutonium to fundamentally change the existing process for extracting plutonium-238 and recovering neptunium-237 from irradiated neptunium targets through fluorination volatilization, simplifying the process, reducing equipment size, and significantly improving the neptunium-plutonium separation efficiency. Furthermore, the method provided by this invention, employing a dry process, eliminates the need for organic reagents, reduces the amount of radioactive waste, and fundamentally solves the problem of severe α-radiolysis during plutonium-238 extraction; it also solves a series of problems arising from subsequent waste organic reagent treatment, reducing the use of salt-containing reagents and significantly decreasing the amount of radioactive solid waste. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target, provided by an embodiment of the present invention. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be further described clearly and completely below with reference to the accompanying drawings and examples. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] Plutonium-238 has important applications in national economic production and defense construction. It is particularly important to extract plutonium-238 and recover neptunium-237 safely, efficiently and with minimal radioactive waste generation from irradiated neptunium targets.

[0027] In this invention, the process of extracting plutonium-238 and recovering neptunium-237 from irradiated neptunium targets is fundamentally changed by the fluorination volatilization method. This method can simplify the process, reduce equipment size, eliminate the use of organic reagents, and reduce the amount of radioactive waste, while solving the problem of severe radiolysis during plutonium-238 extraction. Furthermore, it can solve a series of problems caused by organic reagent treatment, reduce the use of salt-containing reagents, and thus reduce the amount of radioactive solid waste.

[0028] like Figure 1 As shown, an embodiment of the present invention provides a process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target, the method comprising the following steps:

[0029] S1. Neptunium Extraction: The irradiated neptunium target core is placed in a reactor, and a first fluorination gas is introduced into the reactor. The irradiated neptunium target core is fluorinated at a first set temperature, converting the various metal oxides in the irradiated neptunium target core into fluorides. Among them, the oxide of neptunium is converted into neptunium hexafluoride, and the oxide of plutonium is converted into plutonium tetrafluoride. Since neptunium hexafluoride is a gas, it enters step S2 for neptunium product collection and purification under the carrying capacity of the first fluorination gas, thus achieving neptunium extraction. Plutonium, however, remains in the reactor in the form of plutonium tetrafluoride along with most of the fragmented elements, ready to enter step S3 for plutonium extraction, thus achieving neptunium-plutonium separation.

[0030] Specifically, in step S1, neptunium is extracted using a fluorination volatilization method.

[0031] Specifically, in step S1, the first fluorinated gas is a mixture of nitrogen trifluoride (NF3) and an inert gas, wherein the inert gas is selected from one or two of N2, Ar, etc., but is not limited thereto.

[0032] In one specific embodiment, the volume percentage content of nitrogen trifluoride (NF3) in the first fluorinated gas is not less than 5%, and the volume percentage content of the inert gas is 0-50%.

[0033] Optionally, the selectable temperature range for the first set temperature is 450℃~700℃.

[0034] Optionally, in step S1, the duration of the first fluorinated gas venting is not less than 1.5 hours, which is the duration of neptunium extraction using the fluorination volatilization method in step S1, during which neptunium fluorination volatilization is completed.

[0035] S2. Collection and purification of neptunium product: The neptunium hexafluoride carried by the first fluorinated gas is passed into a cold trap for collection and purification to obtain neptunium product;

[0036] Specifically, the main component of the neptunium product is neptunium tetrafluoride.

[0037] Specifically, step S2 further includes the following steps: transforming the neptunium product by using hot water hydrolysis reduction to convert the neptunium product into neptunium dioxide.

[0038] Specifically, the temperature of the hot water hydrolysis reduction should be higher than 600℃.

[0039] In one specific embodiment, the conversion of the neptunium product into neptunium dioxide using hot water hydrolysis reduction includes the following specific steps: The neptunium product is placed in a reaction vessel, which is maintained at approximately 900°C. A mixture of water vapor and hydrogen (H2 volume content 2%) is introduced for 2 hours, after which the gas introduction is stopped. The conversion rate of neptunium dioxide was found to be higher than 99%.

[0040] S3. Plutonium Extraction: After stopping the first fluorination gas, a second fluorination gas is introduced into the reactor. The irradiated neptunium target core is then fluorinated at a second set temperature. The plutonium that has been converted into plutonium tetrafluoride is further converted into plutonium hexafluoride gas. Under the carrying capacity of the second fluorination gas, the plutonium product is collected and purified in step S4 to achieve plutonium extraction.

[0041] Specifically, in step S3, plutonium is extracted using the fluorination volatilization method.

[0042] Specifically, in step S3, the second fluorinated gas is a mixture of a fluorinated functional gas and an inert gas. The inert gas is selected from one or two of N2, Ar, etc., but is not limited thereto; the fluorinated functional gas includes one or more of F2, HF, O2F2, etc., but is not limited thereto.

[0043] In one specific embodiment, the volume percentage of the fluorinated functional gas in the second fluorinated gas is not less than 50%.

[0044] Optionally, the second set temperature is above 300°C.

[0045] Optionally, in step S1, the duration of the second fluorinated gas is 2 to 6 hours, which is the duration of plutonium extraction using the fluorination volatilization method in step S3, during which plutonium fluorination volatilization is completed.

[0046] S4: Collection and purification of plutonium products: Plutonium hexafluoride carried by the second fluorinated gas is passed into a cold trap for collection and purification to obtain plutonium products;

[0047] Specifically, the main component of the plutonium product is plutonium tetrafluoride.

[0048] Specifically, step S4 further includes the following steps: transforming the plutonium product by using hot water hydrolysis reduction to convert the plutonium product into plutonium dioxide.

[0049] Specifically, the temperature of the hot water hydrolysis reduction should be higher than 600℃.

[0050] In one specific embodiment, the conversion of plutonium product to plutonium dioxide using hot water hydrolysis reduction includes the following steps: The plutonium product is placed in a reactor, which is maintained at approximately 900°C. A mixture of water vapor and hydrogen (H2 volume content 2%) is introduced for 2 hours, after which the gas flow is stopped. The plutonium dioxide conversion rate was found to be higher than 99%.

[0051] S5. Treatment and disposal of fission products: This refers to the treatment and disposal of the fission products of the remaining irradiated neptunium target core in the reactor.

[0052] Example 1

[0053] In this Example 1, the process method provided in this embodiment for extracting plutonium-238 from an irradiated neptunium target and recovering neptunium-237 is used to separate and recover plutonium from a mixture of neptunium dioxide and plutonium dioxide (2g neptunium dioxide, 0.2g plutonium dioxide), including the following steps:

[0054] S11. Extraction of neptunium: Place a mixture of neptunium dioxide and plutonium dioxide in a reaction dish, and place the reaction dish in a reaction vessel; keep the reaction vessel at about 500°C, and introduce a mixture of NF3 and Ar (where the volume percentage of NF3 is 10%) for 1.5 hours, during which the neptunium will escape in the form of NpF6.

[0055] S12. Collection and purification of neptunium product: NpF6 carried by NF3 is collected and purified by passing it through a cold trap to obtain neptunium product; the neptunium yield is higher than 99%, and the neptunium / plutonium ratio in the neptunium product is higher than 3 × 10⁻⁶. 6 .

[0056] S13. Extraction of plutonium: After stopping the flow of NF3, keep the reactor at a temperature of about 360°C, and introduce pure F2 for 4 hours. The plutonium will escape in the form of PuF6.

[0057] S14: Collection and purification of plutonium products: PuF6 carried by F2 is collected and purified by passing it through a cold trap to obtain plutonium product PuF4; the plutonium yield is higher than 98%, and the plutonium / neptunium ratio in the plutonium product is higher than 1×10⁻⁶. 6 .

[0058] Example 2

[0059] In this second embodiment, the plutonium product obtained in the first embodiment is transformed into plutonium dioxide using a hot water hydrolysis reduction method, including the following steps:

[0060] S21. Take 0.1g of the plutonium product PuF4 obtained in step S14 and place it in a corundum reaction dish. Place the corundum reaction dish in the reaction vessel.

[0061] S22. The plutonium product is then converted: The reactor is kept at approximately 900°C, and a mixture of steam and hydrogen (H2 volume content 2%) is introduced at a flow rate of 25 ml / min for 2 hours, after which the gas flow is stopped. Testing shows that the plutonium dioxide conversion rate is higher than 99%.

[0062] The methods described in this invention are not limited to the specific embodiments described above. The embodiments are merely illustrative examples of this invention, and this invention can also be implemented in other specific ways or forms without departing from the spirit or essential characteristics of this invention. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of this invention should be defined by the appended claims, and any variations equivalent to the intent and scope of the claims should also be included within the scope of this invention.

Claims

1. A process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target, characterized in that, The method includes the following steps: S1. Extraction of Neptunium: The irradiated neptunium target core is placed in a reactor, and a first fluorination gas is introduced into the reactor. The irradiated neptunium target core is fluorinated at a first set temperature, converting the neptunium oxide in the irradiated neptunium target core into neptunium hexafluoride and the plutonium oxide into plutonium tetrafluoride. The first fluorination gas carries the neptunium hexafluoride into step S2 for neptunium product collection and purification. Plutonium remains in the reactor in the form of plutonium tetrafluoride, ready to be extracted in step S3. S2. Collection and purification of neptunium product: The neptunium hexafluoride carried by the first fluorinated gas is passed into a cold trap for collection and purification to obtain neptunium product; S3. Extracting plutonium: A second fluorination gas is introduced into the reactor, and the irradiated neptunium target core is fluorinated at a second set temperature to further convert plutonium tetrafluoride into plutonium hexafluoride gas. The second fluorination gas carries plutonium hexafluoride into step S4 for plutonium product collection and purification. S4: Collection and purification of plutonium products: Plutonium hexafluoride carried by the second fluorinated gas is passed into a cold trap for collection and purification to obtain plutonium products; S5. Handling and disposing of fission products.

2. The process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target according to claim 1, characterized in that, The first fluorinated gas is a mixture of nitrogen trifluoride and an inert gas, wherein the inert gas is selected from one or two of N2 and Ar.

3. The process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target according to claim 2, characterized in that, In the first fluorinated gas, the volume percentage of nitrogen trifluoride is not less than 5%.

4. The process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target according to claim 1, characterized in that, The first set temperature is 450℃~700℃.

5. The process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target according to claim 1, characterized in that, Step S2 further includes the following step: transforming the neptunium product by using hot water hydrolysis reduction to convert the neptunium product into neptunium dioxide.

6. The process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target according to claim 1, characterized in that, The second fluorinated gas is a mixture of fluorinated functional gas and inert gas; The inert gas is selected from one or both of N2 and Ar; The fluorinated functional gas includes one or more of F2, HF, and O2F2.

7. The process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target according to claim 6, characterized in that, In the second fluorinated gas, the volume percentage content of the fluorinated functional gas is not less than 50%.

8. The process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target according to claim 5, characterized in that, The second set temperature is above 300°C.

9. The process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target according to claim 1, characterized in that, Step S4 further includes the following step: transforming the plutonium product by using hot water hydrolysis reduction to convert the plutonium product into plutonium dioxide.

10. A process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target according to claim 5 or 9, characterized in that: The temperature of the hot water hydrolysis reduction is higher than 600℃.

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