Neptunium-uranium mixed target for irradiation production of plutonium-238 in heavy water reactors and method of making same

Abstract

The application provides a mixed target of neptunium uranium for irradiation production of plutonium-238 in a heavy water reactor, comprising at least one fuel rod; the fuel rod comprises at least one fuel rod; the fuel rod comprises a first core block, the first core block comprises neptunium-237 and enriched uranium, and satisfies R x m U1 = 0.72% x (m U1 +m Np ), wherein m U1 represents the mass of the enriched uranium in the first core block; m Np represents the mass of the neptunium-237 in the first core block; and R represents the content of uranium-235 in the enriched uranium.

Description

Technical Field

[0001] This invention belongs to the field of nuclear fuel technology, specifically relating to a neptunium-uranium hybrid target for the production of plutonium-238 isotopes by heavy water reactor irradiation and its preparation method. Background Technology

[0002] Plutonium-238 is an important radioactive isotope widely used in spacecraft power supplies, medical radioisotope batteries, and other fields. Plutonium-238 production typically involves four stages: extraction of neptunium feedstock at a spent fuel reprocessing plant, preparation of the neptunium target, reactor irradiation of the neptunium target, and extraction of plutonium-238. Currently, plutonium-238 is primarily produced by irradiating neptunium-237 targets in a reactor. Traditional methods typically use research reactors (such as the High Flux Isotope Reactor (HFIR)) to produce plutonium-238; however, the high operating costs and limited capacity of research reactors result in persistently high production costs for plutonium-238.

[0003] In recent years, the method of producing plutonium-238 by irradiating neptunium targets in nuclear power plant reactors (such as heavy water reactors) has gradually attracted attention. Compared with research reactors, nuclear power plant reactors have advantages such as low operating costs, large capacity, and continuous operation, and can produce plutonium-238 while generating electricity, thus significantly reducing production costs. However, when pure neptunium-237 targets are irradiated in heavy water reactors, their high thermal neutron absorption cross-section can lead to insufficient local reactivity in the reactor, affecting the safe and stable operation of the reactor. In addition, if low-enriched uranium is used as compensating material, the total amount of uranium introduced (uranium-235 + uranium-238) will be too large, resulting in a high content of isotopes other than plutonium-238, making it difficult to meet the requirement of plutonium-238 purity greater than 80%.

[0004] Therefore, improvements are still needed in the production of plutonium-238. Summary of the Invention

[0005] The purpose of this invention is to provide a neptunium-uranium hybrid target for plutonium-238 production via heavy water reactor irradiation and its preparation method, thereby solving the problem of insufficient local reactivity in heavy water reactors caused by pure neptunium targets and effectively reducing the content of isotopes other than plutonium-238 to meet the requirement of plutonium-238 purity greater than 80%. Furthermore, this invention utilizes a nuclear power plant's heavy water reactor to irradiate the neptunium target for plutonium-238 production, enabling simultaneous power generation and production of plutonium-238, thus offering a cost advantage.

[0006] To achieve the above objectives, the present invention provides a neptunium-uranium hybrid target for heavy water reactor irradiation production of plutonium-238, comprising at least one fuel rod; the fuel rod comprises a first core block, the first core block comprising neptunium-237 and enriched uranium, and satisfying R×m U1 =0.72% × (m U1 +m Np );

[0007] Where, m U1 This indicates the mass of enriched uranium in the first core; m Np R represents the mass of neptunium-237 in the first core block; R represents the uranium-235 content in the enriched uranium.

[0008] Therefore, the overall reactivity of the uranium-neptunium mixture fuel rod of the present invention is comparable to that of the original natural uranium fuel rod, thereby effectively compensating for the insufficient reactivity caused by the low reactivity of neptunium-237.

[0009] In some embodiments, the enriched uranium includes one or more of the following: low-enriched uranium with a uranium-235 content of 3%-20%, medium-enriched uranium with a uranium-235 content of 20%-80%, and highly enriched uranium with a uranium-235 content of greater than 80%.

[0010] In some embodiments, the density of the core block is 10.0 g / cm³. 3 Up to 11.0 g / cm 3 .

[0011] In some embodiments, the mass ratio of neptunium-237 to enriched uranium is from 1:4 to 99:1.

[0012] In some embodiments, the remaining materials in each fuel rod, excluding the pellet, are materials with a thermal neutron macroscopic absorption cross section of less than 10 Ω.

[0013] In some embodiments, the fuel rod includes a second pellet comprising natural uranium.

[0014] In some embodiments, the fuel rod has a length of 500 mm to 1000 mm and a diameter of 10 mm to 20 mm.

[0015] The present invention also provides a method for preparing a neptunium-uranium hybrid target for heavy water reactor irradiation to produce plutonium-238, wherein the neptunium-uranium hybrid target includes at least one fuel rod; the fuel rod includes a first core. The method includes:

[0016] Neptunium-237 oxide powder and enriched uranium oxide powder were ball-milled for 2 to 10 hours to obtain a mixed powder;

[0017] The mixed powder is extruded under a pressure of 100 MPa to 500 MPa to obtain a green body; and

[0018] The blank is sintered at 1600°C to 1800°C for 2 to 8 hours to obtain the first core block.

[0019] Therefore, the neptunium-uranium hybrid target preparation process provided by the present invention is simple and easy to industrialize. Attached Figure Description

[0020] Figure 1 A schematic diagram of the structure of a neptunium-uranium hybrid target provided in one embodiment of the present invention is shown.

[0021] Figure 2 An end view of a neptunium-uranium hybrid target provided according to an embodiment of the present invention is shown. Detailed Implementation

[0022] The following detailed description discusses exemplary embodiments. The specific embodiments included herein should not be construed as limiting the invention. Furthermore, while specific language may be used to describe features, actions, and / or structures in the embodiments described herein, the claims are not limited to the described features, actions, and / or structures. Those skilled in the art will understand that other embodiments, including improvements, are within the spirit and scope of the invention.

[0023] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] Heavy water reactors use natural uranium as fuel, offering advantages in neutron economy. However, due to the low uranium-235 content (0.72%) in natural uranium, the reactor's burnup depth is relatively low. Typical heavy water reactor fuel elements usually consist of natural uranium dioxide (UO2) fuel pellets and a zirconium alloy cladding. Taking the CANDU reactor as an example, its fuel rods are 500 mm long and 10 mm to 20 mm in diameter, with each fuel rod containing approximately 500 g to 1000 g of natural uranium. Fuel rods are typically bundled in groups of 37 or 28 to form fuel assemblies.

[0025] In this invention, a portion of natural uranium is replaced with a mixture of neptunium-237 and enriched uranium of a certain enrichment level. The uranium-235 content of the enriched uranium is comparable to that of the natural uranium, and the total amount of enriched uranium and neptunium is comparable to the total amount of natural uranium before the replacement. After this replacement, the overall reactivity of the uranium-neptunium mixture fuel rods is comparable to that of the original natural uranium fuel rods. This effectively compensates for the insufficient reactivity caused by the low reactivity of neptunium-237 and effectively reduces the content of isotopes other than plutonium-238, meeting the requirement that plutonium-238 purity is greater than 80%. Furthermore, this invention utilizes the heavy water reactor of a nuclear power plant to irradiate a neptunium target to produce plutonium-238, enabling the production of plutonium-238 simultaneously with power generation, thus offering a cost advantage.

[0026] Specifically, conventional heavy water reactor fuel rods include those containing natural uranium m u A pellet of grams, containing m grams of uranium-235. 235 =0.72% × m U The amount of uranium-238 is m 238 =99.28% × m U When replacing the chips from the cost application, the amount of enriched uranium contained therein is m. U1 The enrichment level of uranium-235 is R, and the amount of neptunium-237 is m. Np The following relationship must be satisfied:

[0027] m U =m U1 +m Np (Total mass remains unchanged)

[0028] R×m U1 =0.72% × m U (Uranium-235 reactive compensation).

[0029] It should be understood that in some embodiments, this application may involve substitution within the same fuel rod. For example, a fuel rod may include multiple pellets, some or all of which may be pellets of this application, while the remainder may still use natural uranium pellets.

[0030] In other embodiments, this application may involve substitution in different fuel rods. For example, in a bundle of 37 fuel rods, some or all of the fuel rods may contain pellets of this application, while the rest may still use natural uranium pellets.

[0031] The present invention will now be described in further detail with reference to the accompanying drawings.

[0032] Figure 1 and Figure 2 Schematic structural diagrams and end views of the neptunium-uranium hybrid target are shown respectively. See also Figure 1 and Figure 2 The neptunium-uranium hybrid target may include a bearing pad 1, a casing tube 2, an end plug 3, an end plate 4, a core block 5, a coating 6, a spacer block 7, and a pressure tube 8.

[0033] The bearing pad 1 is an important support component used to reduce friction between moving parts or surfaces, which helps to reduce energy loss and extend the service life of the components, as well as absorb shock and vibration, protect the structural integrity of the fuel target, and evenly distribute the load to prevent local overload, ensuring the stability and safety of the fuel target.

[0034] In this application, there are no special requirements for the material and size of the bearing pads; those commonly used in the art, such as zirconium alloy bearing pads, can be used.

[0035] The cladding tube 2 can be composed of an outer cladding tube and an inner cladding tube, which serves to protect and contain the fuel. The fuel pellet 5 is loaded between the inner and outer cladding tubes, and the two cladding tubes are sealed into a whole by end plugs 3 at both ends.

[0036] In this application, there are no special requirements for the material and size of the cladding tube; any of those conventionally used in the art can be used, such as any of the following nuclear-grade materials: zirconium alloy, niobium alloy, molybdenum alloy, stainless steel, aluminum alloy, nickel-based alloy, and silicon carbide. In one embodiment, the cladding tube is a zirconium alloy cladding tube.

[0037] End plugs 3 are fixed (e.g., welded) to both ends of the casing tube 2 to seal the casing tube and ensure the sealing and structural integrity of the fuel element.

[0038] End plate 4 is mainly used to fix and support fuel elements, ensuring the overall structural stability and operational safety of the fuel target.

[0039] See Figure 2 The spacer block 7 secures and supports the fuel elements, ensuring that the fuel elements maintain the correct geometric position and spacing during reactor operation. The pressure pipe 8 is used to contain and protect the fuel elements while withstanding the internal pressure generated during operation.

[0040] The neptunium-uranium hybrid target provided by this invention has a fuel rod length of 500mm to 1000mm, a diameter of 10mm to 20mm, and a total mass of uranium and neptunium in a single fuel rod of 500g to 1000g.

[0041] The size of the core block 5 of the present invention is not particularly required and can adopt the size conventionally used in the art, such as φ12.15×17.7mm, but is not limited thereto.

[0042] Neptunium-237 and enriched uranium mixture fuel pellets are prepared by the following steps:

[0043] Neptunium-237 oxide powder and enriched uranium oxide powder were mixed at a mass ratio and ball-milled for 4 hours.

[0044] The mixed powder is extruded and molded under pressure of 100MPa to 500MPa.

[0045] The shaped green body is sintered at 1600℃ to 1800℃ for 2 to 8 hours to obtain a density of 10.0 g / cm³. 3 Up to 11.0 g / cm 3 Fuel pellets.

[0046] The prepared Neptunium-237 and enriched uranium mixture fuel pellets replace some of the natural uranium pellets in the heavy water reactor fuel rods, making the overall reactivity of the replaced fuel rods comparable to that of the original natural uranium fuel rods.

[0047] In this application, a uranium-naphthium mixture fuel was prepared and irradiated in a heavy water reactor for 70 to 100 days. After irradiation, the fuel rods were removed, plutonium-238 was extracted, and the purity of plutonium-238 was subsequently determined.

[0048] The present invention will be described in more detail below through embodiments. It should be understood that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially. The raw materials used in the embodiments are nuclear-grade raw materials.

[0049] Example 1:

[0050] 14.4 kg of low-enriched uranium with a uranium-235 content of 5% was mixed with 85.6 kg of neptunium-237 and ball-milled for 4 hours.

[0051] The mixed powder is then extruded and molded under a pressure of 300 MPa.

[0052] The shaped green body was sintered at 1700℃ for 4 hours to obtain a density of 10.5 g / cm³. 3 Fuel pellets.

[0053] The obtained fuel pellets were loaded into a heavy water reactor and irradiated for 70 days. After irradiation, the fuel rods were removed, and plutonium-238 was extracted. Testing showed that the purity of plutonium-238 was greater than 80%.

[0054] Example 2

[0055] 4 kg of low-enriched uranium with a uranium-235 content of 18% was mixed with 96 kg of neptunium-237 and ball-milled for 4 hours.

[0056] The mixed powder is then extruded and molded under a pressure of 300 MPa.

[0057] The shaped green body was sintered at 1700℃ for 4 hours to obtain a density of 10.5 g / cm³. 3 Fuel pellets.

[0058] The obtained fuel pellets were loaded into a heavy water reactor and irradiated for 71 days. After irradiation, the fuel rods were removed, and plutonium-238 was extracted. Testing showed that the purity of plutonium-238 was greater than 80%.

[0059] Example 3:

[0060] 1.4 kg of moderately enriched uranium with a uranium-235 content of 50% was mixed with 98.6 kg of neptunium-237 and ball-milled for 4 hours.

[0061] The mixed powder is then extruded and molded under a pressure of 300 MPa.

[0062] The shaped green body was sintered at 1700℃ for 4 hours to obtain a density of 10.5 g / cm³. 3 Fuel pellets.

[0063] The obtained fuel pellets were loaded into a heavy water reactor and irradiated for 75 days. After irradiation, the fuel rods were removed, and plutonium-238 was extracted. Testing showed that the purity of plutonium-238 was greater than 80%.

[0064] Example 4:

[0065] 0.9 kg of highly enriched uranium with a uranium-235 content of 80% was mixed with 99.1 kg of neptunium-237 and ball-milled for 4 hours.

[0066] The mixed powder is then extruded and molded under a pressure of 300 MPa.

[0067] The shaped green body was sintered at 1700℃ for 4 hours to obtain a density of 10.5 g / cm³. 3 Fuel pellets.

[0068] The obtained fuel pellets were loaded into a heavy water reactor and irradiated for 71 days. After irradiation, the fuel rods were removed, and plutonium-238 was extracted. Testing showed that the purity of plutonium-238 was greater than 80%.

[0069] The neptunium-uranium hybrid target provided by this invention can effectively solve the problem of insufficient local reactivity in heavy water reactors caused by pure neptunium targets, improving reactor safety and stability. It also offers a high plutonium-238 yield, meeting the production requirements for plutonium-238. Furthermore, this invention uses enriched uranium as a compensating material, effectively reducing the content of isotopes other than plutonium-238, meeting the requirement of plutonium-238 purity greater than 80%. Simultaneously, this invention utilizes the irradiation of the neptunium target in a nuclear power plant's heavy water reactor to produce plutonium-238, enabling simultaneous power generation and production of plutonium-238, offering a cost advantage.

[0070] Although this disclosure has been described with reference to specific exemplary embodiments thereof, many different variations, modifications, etc. will become apparent to those skilled in the art.

[0071] By studying the accompanying drawings, the disclosure, and the appended claims, those skilled in the art can understand and implement variations of the disclosed embodiments in the practice of this disclosure.

Claims

1. A neptunium-uranium hybrid target for heavy water reactor irradiation production of plutonium-238, comprising at least one fuel rod; said fuel rod comprising a first core block, the first core block comprising neptunium-237 and enriched uranium, and satisfying the following conditions: R ×m U1 =0.72%×(m U1 +m Np ), in, m U1 This indicates the mass of enriched uranium in the first core; m Np This indicates the mass of the neptunium-237 in the first core block; R This indicates the content of uranium-235 in the enriched uranium; The enriched uranium includes one or more of the following: low-enriched uranium with a uranium-235 content of 3%-20%, medium-enriched uranium with a uranium-235 content of 20%-80%, and highly enriched uranium with a uranium-235 content of more than 80%.

2. The neptunium-uranium hybrid target according to claim 1, wherein, The density of the core block is from 10.0 g / cm³ to 11.0 g / cm³.

3. The neptunium-uranium hybrid target according to claim 1 or 2, wherein, The mass ratio of neptunium-237 to enriched uranium is from 1:4 to 99:

1.

4. The neptunium-uranium hybrid target according to claim 1 or 2, wherein, The remaining materials in each of the fuel rods, excluding the fuel pellet, are materials with a thermal neutron macroscopic absorption cross section of less than 10 Ω.

5. The neptunium-uranium hybrid target according to claim 1 or 2, wherein, The fuel rod includes a second core block, which contains natural uranium.

6. The neptunium-uranium hybrid target according to claim 1 or 2, wherein, The fuel rods are 500 mm to 1000 mm in length and 10 mm to 20 mm in diameter.

7. A method for preparing a neptunium-uranium hybrid target for heavy water reactor irradiation production of plutonium-238 according to claim 1, wherein the neptunium-uranium hybrid target comprises at least one fuel rod; the fuel rod comprises a first core; the method comprising: Neptunium-237 oxide powder and enriched uranium oxide powder were ball-milled for 2 to 10 hours to obtain a mixed powder; The mixed powder is extruded under a pressure of 100 MPa to 500 MPa to obtain a green body; The blank is sintered at 1600°C to 1800°C for 2 to 8 hours to obtain the first core block.

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